MEEG401 – Phase 4 - Mechanical Engineering at the ... · MEEG401 – Phase 4 Performance ......
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UDCCM – RAC
MEEG401 – Phase 4 Performance Validation
Team 7: Vincent Borsello, Michael Brill, Daniel Gempesaw, and Travis Mease
12/7/2007
The fourth Phase of the Senior Design project consists of empirical design validation of the prototype specified in Phase Three. This document provides a summary of the work done to with the inclusion of Phase Four, and discusses a path forward to be used at the end of the semester.
Table of Contents Introduction .................................................................................................................................................. 4
Performance Goals ........................................................................................................................................ 4
Design Process .............................................................................................................................................. 5
Phase One ................................................................................................................................................. 5
Phase Two ................................................................................................................................................. 5
Phase Three ............................................................................................................................................... 6
Analysis ................................................................................................................................................. 7
Phase Four ................................................................................................................................................. 8
Design Discrepancies ............................................................................................................................ 9
Tests: Summary, Results, & Analysis ............................................................................................................. 9
Weight ....................................................................................................................................................... 9
G‐Force Threshold ................................................................................................................................... 10
Fore/Aft Test ....................................................................................................................................... 10
Lateral Test of Base ............................................................................................................................. 11
Product Life ............................................................................................................................................. 12
Lateral Test of Arm & Base ................................................................................................................. 12
Footprint ................................................................................................................................................. 12
Path Forward: Conclusion ........................................................................................................................... 12
Conclusion ............................................................................................................................................... 13
Appendices .................................................................................................................................................. 14
A: UDesign – Customers Page & Scope ................................................................................................... 14
B: UDesign – Benchmarking & Metrics ................................................................................................... 15
C: UDesign – Metrics (continued) ........................................................................................................... 17
D: Force Analysis ..................................................................................................................................... 18
E: Stress & Deflection Analysis ‐ Arm ...................................................................................................... 21
E: Stress & Deflection Analysis – Base .................................................................................................... 24
F: Bolt Analysis ........................................................................................................................................ 27
G: Clevis Analysis ..................................................................................................................................... 31
H: Pivot Pin Analysis ................................................................................................................................ 34
I: Seat Attachment Analysis .................................................................................................................... 39
J: Gantt Chart .......................................................................................................................................... 41
K: Manufacturing .................................................................................................................................... 42
L: Fore/Aft Test Details ........................................................................................................................... 43
Fore/Aft Test Images ........................................................................................................................... 44
M: Lateral Test Details (No Arm) ............................................................................................................ 45
Lateral Base Test Images ..................................................................................................................... 46
N: Lateral Test Details (w/Arm)............................................................................................................... 47
Lateral Arm Test Images ..................................................................................................................... 48
O: Test Plans ............................................................................................................................................ 49
Base Fore/Aft Static Load .................................................................................................................... 49
Base Lateral Load ................................................................................................................................ 49
Base Arm Load .................................................................................................................................... 50
Data Analysis ....................................................................................................................................... 50
P: Cost Analysis ....................................................................................................................................... 51
Introduction Due to the extreme impacts experienced while
boating at high speeds in inclement weather, shock‐mitigating marine seats are a necessity for passengers and drivers on boats. In weight critical applications, the available solutions are incapable of satisfying customer wants, creating the need for a lightweight shock seat. The scope of this project is to design the support structure and manufacturing process for a shock mitigating seat, excluding the damping mechanism and the actual seat itself. To be clear, the term “shock mitigating marine seat” refers to an object comprised of four main parts: the seat, the attachment between the seat and the fixed base, the damping mechanism, and the fixed base or frame which includes the attachment to the boat. These parts can be seen in the figure shown above.
The main priority of Phase Four is empirical validation of the performance requirements. The performance requirements are based on the critical aspects of the application and correlate directly with the most important customer wants. Empirical validation consists of designing, conducting, and analyzing tests and test data in order to conclude affirmatively or negatively about the success of the design efforts made in the previous Phases.
Performance Goals The critical performance goals for the proposed proof‐of‐concept prototype are the weight of
the structure, its G‐Force threshold, the work life, and the footprint on the ship. Table 1 summarizes the current goals and status of the concept. Details about the derivation and ranking of these metrics can be found in Appendices A‐C.
Metric Goal Prototype Score Weight (lbs) 70.0 lbs 48.2 lbs G‐Force Threshold 20g Vertical, 4g Fore/Aft & Lateral Design: 22g vert, 6g fore/aft & lateral Product Life (hrs) 1400 hrs (150 cycles of worst load) Requires fatigue testing Footprint (in x in) < 28in x 40in 22in x 23in Table 1 ‐ Performance Goals and Prototype Scores
The general wall thickness was 0.1in and to provide reinforcement for localized stresses, certain areas were built up to a thickness of 0.25in. The tooling consisted of four support plates for the pivot rod, two clevis pin plates, and a steel rod to simulate the ActiveShock. Using a pre‐impregnated carbon‐aramid fiber composite fabric and 304SS for the tooling and including a car‐racing seat, the structure weighs 33.2 pounds. With the conservative assumption that substituting the real shock absorber for the steel rod and adding all of the necessary fasteners would increase the weight by fifteen pounds, giving a total of 48.2 pounds. The wall‐thicknesses, geometry, and material properties of the structure were
What is a shock mitigating seat?
engineered to withstand a vertical acceleration of 22g’s and an acceleration of 6g’s in the other directions: “lateral” and “fore and aft”. Due to the unavailability of the designed‐for composite, a substitute composite was used in the prototype – the implications of the change are discussed later. The analysis was performed to satisfy the worst case tri‐axial load, and since a the majority of the loadings are much weaker, its fatigue performance should be satisfactory. Long‐term testing of the validity of the prototype in fatigue conditions is outside of the scope of a one‐semester project, but it is the next clear step for the path forward. Finally, the footprint is 22in (width) by 23in (depth) – for comparison, the STIDD 800V53 footprint is 40in (depth) by 28in (width) (STIDD, 2007).
Design Process
Phase One The first phase of the design process began in early September and consisted of two main parts:
benchmarking and problem definition. Inherent in problem definition was the wants and constraints and the need to identify customers and their wants for the design. UDesign was employed as a method to sensibly rank and organize the customers’ wants in order to derive an aggregate set of wants that would be the main goals for the project. The specific scope of the project was clearly defined as the design of the frame and attachment mechanism portions of a shock mitigating seat, excluding the design of the damping mechanism or the seat.
The benchmarking efforts were primarily focused on the options that the Navy presently employed and the current market‐leading companies: “ShockwaveSeats” and “STIDD”. These seat designs featured a seat “sliding” on a vertical track while supported by a shock to provide damping. Researching other existing solutions led to a family of seats offered by Ullman Dynamics featuring a completely different design from the other benchmarks. Instead of a sliding mechanism, the seat was mounted on a “cantilever” beam or arm free to rotate in the vertical plane and its motion was damped by a shock attached to the seat.
Phase Two The next phase of the project was selecting a concept that would best satisfy all of the wants
defined in the previous stage. The results of the ranking the metrics based on their correlation with wants reflected the overall goal of the project: weight and G‐force capability were the highest metrics, followed by the number of parts, the size of the structure. A more detailed glimpse of the UDesign analysis is included in Appendices A – C.
It is important to note that the scope of the project did not dictate a full scale redesign or necessitate the generation of a new design that was a complete departure from the existing solutions. Instead, the scope was geared towards adapting an existing solution to use carbon fabric as the structural material instead of steel or aluminum alloys.
The cantilever concept was our design of choice because in benchmarking, the cantilever solutions were significantly lighter than the slider products. (See Appendix B for additional benchmarking information.) The importance of weight as the highest metric for success drove the selection of the cantilever concept, but it also held advantages in the other metrics. The cantilever benchmarks maintained a smaller footprint than the slider benchmarks and they also incorporated less large parts than the latter. In addition, the slider concept presented the problem of creating a bearing surface for the sliding parts of the mechanism, a problem that was relatively easy in metals but more complicated for composites.
Using the Solid Works modeling software, a virtual model of the prototype based on the cantilever concept was created – isometric views of two of the early stages of the design are shown in the figure at the top of the page, with the prevailing favorite at the end of Phase 2 on the right. The major subsystems are labeled: the arm would rotate around the pivot rod where it is attached to the base and its motion is damped by the shock. The design called for the seat, not shown in the picture, to be attached at the end of the arm at the flat planes.
Phase Three At the end of Phase 2, the team presented their progress to the CEO of RAC, Jonathan
Sadowsky, and other sponsor contacts for feedback and discussion. A number of modifications to the design were discussed during the presentation and over the extent of this phase with emphasis on concurrent design, or design for manufacturing. The first major change was to remove at least one of the faces of both the arm and the base to facilitate laying up the composite fabric in female molds. Next, the pivot rod interface was reworked: initially, two tabs stuck out above the top of the base and the arm sat inside of the tabs as seen in the image on the left at the top of the page, but the tabs would be weak in torsion and very susceptible to tear‐out failure. To solve the torsion and tear‐out problems, the top
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attachment point. As a rule of good practices, holes in any material require a higher factor of safety (usually a magnitude of 3) due to increased stress concentrations. At the adhesive joints, failure was an issue because the joint’s ability to resist failure was based solely on the shear strength of the adhesive which was roughly 3,500 psi.
To ensure the structure would not fail at these attachment points, a detailed failure analysis was undertaken for each one. Most of the joints had the capacity to fail through six different modes; tear‐out, pull‐out, compression, interlaminate shearing, bending, and deflection. The bolt connection joints were fairly simple to fix. A larger washer would inhibit compressive failure and a greater distance from the edge would safely keep the bolt from tearing out. The composite ply thickness possessed the ability to be increased to a certain extent, but this did not satisfy all of the failure modes. The mechanical failure of the bolt was not a huge concern, as the material properties of stainless steel ensure that failure in the composite would be induced first. The sizes and hole distances were all quantitatively found and the appropriate calculations can be found in Appendix F.
Failure problems related to the adhesive arose while determining the method for connecting the arm to the base. To ensure that failure would not occur at the pivot point, a metal support plate was adhesively attached to the inner wall of the base. The objective of the plate was to prevent the connector bar from tearing through the wall of the composite. At the pivot point, the lateral force of 4 G’s induces a large torque which the composite was incapable of handling. A metal support plate, 3.5 x 3.5 inches, distributes the load over a larger surface area and therefore reduces the stress concentrations. Although the failure of the composite has been avoided, another problem arises when attempting to transfer the load from the plate into the base. For the prototype, an effective industrial adhesive was applied between the two. The plate size was dimensioned through a shearing analysis of the adhesive found in Appendix H. The composite base also had a slightly larger diameter hole then the diameter of the connection rod to ensure that the entire load was transferred from the plate into the adhesive and then finally into the base.
Phase Four Although Phase Four nominally began at the beginning of November, the team spent the
majority of November continuing the analysis that was part of Phase Three. The manufacturing process was designed during the fourth phase and is outlined in great detail in the Appendices. In particular, the major modifications to be made related to manufacturing were in the mold design. Due to carbon fiber prepreg’s material characteristics there were a few slight modifications that had to be made to the design in order for it to be manufacturable. First, the mold design had a slight draft angle of two degrees, allowing for the actual part to be removed once the mold was cured. Another important manufacturing aspect of carbon fiber prepreg was that it was very challenging to lay up the material around sharp corners. For this reason, the design incorporated a minimum of a 1 inch radius around all corner to avoid bridging. The final thing considered as far as differences between the part and the mold was that the mold was oversized in comparison to the part, creating a bagging surface that does not interfere with the actual parts.
Design Discrepancies During prototype construction, a number of changes from the final version were implemented
for various reasons. The most obvious deviation from the final version was the material used – the analysis was performed assuming the material properties of a low temperature cure, carbon fiber epoxy pre‐impregnated composite, but due to lead times and cost, an alternative material with carbon‐aramid fibers was used. The prototype material did not have well defined material properties and had unexpected resistance to shear, complicating the manufacturing process and reducing the strength of the entire structure. In addition, a steel rod was substituted for the ActiveShock damping mechanism since efforts to obtain a sample shock for use in the prototype were unsuccessful. Without the motion allowed by the damping mechanism, the arm and the seat were fixed in one position.
The actual seat itself is another discrepancy between the prototype and the final version. As previously mentioned, RAC was planning to custom‐design a seat – the plastic seat currently used on the prototype was for demonstration purposes only. During RAC’s seat design, a number of features would need to be considered, including head, neck, and lateral support, arm rests, foot rests, harness configuration, and integration of boat controls. For the purposes of having a working prototype, a metal support bracket was designed to compensate for the height difference. Ultimately, a wood wedge was used instead of the metal support bracket because the bracket was not properly sized to interface between the seat and the arm. In addition, one of the support plates was machined out of aluminium instead of stainless steel because machining it out of aluminium saved time and was not as harsh on the tools used.
Tests: Summary, Results, & Analysis Each of the major performance goals correlates to a test or group of tests that would provide
sufficient validation from a statistical engineering standpoint.
Weight The tests corresponding to the most important metric, weight, are fortunately relatively simple.
There were two methods considered to weigh of the entire structure using a scale: piecewise, before assembly, and aggregate, after assembly. During the manufacturing and assembly phase of the project, each piece was weighed before the assembly was constructed – the results are shown in Table 2. The total weight, as seen, is estimated to be 48 pounds, and this is a sixty seven percent reduction from the
Part(s) Weight (lbs) Base 7.68 Arm 3.86 Seat 12.60 Tooling (support plates, pivot rod, extra rod, clevis ) 9.10 “Fake Shock” Steel Rod ‐ 4.00 ActiveShock Weight ( conservative estimate) 14.00 Fasteners (conservative estimate) 5.00 Total {Goal} 48.24 {Less than 72}
Table 2 ‐ Weight by Part
benchmark weight of 144 pounds. There was little statistical analysis to be performed for these tests because the scale was accurate (it repeatedly gave the exactly the same amount) and a large amount of error is unpreventable in the estimates for the weight of the ActiveShock and the fasteners, which were not available for direct weighing. The total weight will also be affected by the added weight of RAC’s seat of choice – since little to no information is available about the final seat, it could not be taken into consideration.
GForce Threshold Because a working damping mechanism was not included in the prototype, loading the structure
vertically would not be indicative of its true performance. As a result, the pertinent potential tests to perform were in the Fore/Aft and Lateral directions. Three tests in total were conducted: in the first two, the applied force and deflection were only applied to the base. In the third test, the arm was re‐attached and the combination structure of the arm and base was considered. Specific test plans and raw data are available in Appendices L – N.
Load Direction Maximum (lbf) 50% Of Max (lbf) Maximum (psi) 50% of Max (psi) Fore/Aft on Base 3700 1850 4700 2350 Lateral on Base 1350 675 1700 850 Lateral on Arm 1350 675 1700 850 Table 3 ‐ Conversion Table for Test Forces & Pressures
A Simplex hydraulic hand pump applied pressure over a face with a circular cross sectional area of .785in2. Due to the discrepancy between the design materials and the prototype materials, half of the applied load was considered as sufficient validation. Converting the forces from the Force Analysis to pressures and considering half of the applied force, the pressure values in the rightmost column represent the appropriate forces.
Fore/Aft Test The objective of the fore/aft test was to obtain fore/aft deflection at the pivot mechanism of the base as a function of the applied load to target a critical design feature. Static deflection was measured using a gauge with a maximum measurable deflection of one inch and the force was applied with the same vector for each of the six runs. The maximum applied pressure was 2250 psi, which corresponds to 1760 lbf, which is half of the calculated fore/aft load from the Force Analysis. At this load, there were no auditory or visual signs of failure at any the pivot or anywhere in the base.
Considering the disparity between the design material and the prototype material combined with the questionable properties of the prototype material, withstanding half of the applied load is a significant validation of design. The average deflection at 2250 psi was 0.463 inches, leading to an estimate of the tensile modulus of the material of 225 ksi instead of the 8000 ksi that was used during design. However, during testing, the base was not adequately clamped down – the flanges were rising off of the table and were contributing to the overall deflection that was measured at the very top of the base. Using photographs seen in Appendix L of the loaded state of the base, the contribution of the flanges to the overall deflection was estimated to be as much as .3in. The repercussions of the base
support clamps being insufficient are that the bolt pattern and washer sizes for the base flanges may become a crucial design issue that could warrant additional attention.
The chart at the top of the page is of the recorded deflection data as measured in the setup depicted in Appendix L. Of note is that the deflections are repeatedly close to each other, with a standard deviations for the first few points of .01in, indicating that, assuming a normal distribution, over 95% of loadings would result in a deflection that is at most +/‐ .03inches away from the average shown. In addition, the later runs did show slightly increased deflections, and fatigue testing will be necessary to investigate this trend further. The raw data and additional notes are presented in Appendix L.
Lateral Test of Base The lateral base test involved the pressure being applied directly to the pivot rod and
deflections of the side walls of the base was measured. Three runs were performed with the square rod
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seen in Appendix M and the final run was performed with the pivot pin and locking pin mechanism.
The first three runs seen in the Lateral Load graph are encouraging and present a linear relationship between load and deflection. As seen in Table 3, half of the expected pressure is 850psi but because the first three runs did not indicate any signs of failure, the load was increased to as much as 1600psi without any indication of imminent failure. The base structure far exceeds failure expectations in the lateral loading case, although the recorded deflection of .7in may later be deemed outside of the range of acceptable deflections. The fourth run was conducted with the pivot pin and loud cracks were heard at 700 psi – upon relieving and reapplying the load, the noises increased in magnitude and frequency so the test was concluded.
Product Life Long term fatigue testing was outside of the scope of the project because of the time constraints that prohibited its feasibility. Low cycle fatigue tests were performed and are discussed here.
Lateral Test of Arm & Base The arm was reaffixed to the base and a load was applied to the end of the arm at the seat attachment point. Table 3 shows a recommendation of 850psi for the pressure, but at a pressure of 600psi, the deflection exceeded an inch and so additional measurements past that were impossible. An applied pressure of 500 psi was cycled for 50 instances and the deflection was measured almost every time. There was a distinct increase in deflection of approximately a tenth of an inch, from ~.82in at the beginning to .90in at the end. The large deflection of the arm affirmed previous suspicions that a “cap” would be necessary to counter‐act the weakness of the current shape in bending, and closing off the back end of the arm will be strongly recommended in the next design iteration. Additional information is provided in Appendix N.
Footprint Using a measuring tape, the size of the base was taken to be 22in wide by 23in deep, a significant reduction from the benchmark of 28in by 40in. The reduction in footprint is a significant achievement and allows RAC more flexibility for seat placement, storage space, and deck design in the new boat.
Path Forward: Conclusion The prototype was built to satisfy form, fit, and function requirements due to the short amount
of time in which it was constructed. In order to integrate the prototype into RAC’s newest boat, additional testing on the prototype must be completed. The time constraints of the project prohibited the feasibility of subjecting the prototype to a full life fatigue test. It is very likely that the prototype will be redesigned during this testing phase, as unforeseen failure modes present themselves. After the design is sufficiently validated through fatigue testing, additional prototypes can be manufactured and a test boat will be outfitted with the prototype to provide for realistic testing conditions. Another phase of redesign may take place at this point, but assuming that design eventually meets all the requirements, it will be included in RAC’s newest boat which is being designed contemporaneously.
The actual transition plan of the project specifics to RAC was discussed with the sponsor contact, Stephen Andersen. The potential for an extended independent research project exists, and a portion or all of the Team may choose to continue working on the project. Because the CEO of RAC, Jonathan Sadowsky, was unable to travel to Delaware before the end of the semester, a final presentation will be made to Mr. Sadowsky in the Spring Semester. In the short term, the project details will need to be finalized and brought to a state appropriate for transition. The relevant SolidWorks files as well as the spreadsheets that were records of the analysis performed will be passed on electronically. Additionally, the final report, final presentation, and pictures will also be submitted to Mr. Andersen for final review.
Conclusion The early stages of the design process for a lightweight shock mitigating seat have been completed. The team designed a support structure based on sound engineering principles and backed by numerical analysis validating the design features. Moreover, the manufacturing process was accomplished as part of the project: the team played a very important role in designing the process and implementing it, starting out with ply layouts and finishing with the post‐cure trimming and machining. Validation of the design through well‐designed tests confirmed the analytical results achieved earlier in the project stages. The next step is to continue testing and to redesign as necessary based on the empirical results of the tests and the principles that were the foundation of the design process.
Appendices
A: UDesign – Customers Page & Scope
The Customers page of the UDesign process is shown here. A combination of role playing and direct discussion was used to order the wants for each of the customers to the best of our knowledge. Relative customer rankings were decided by the team as influenced by meetings with Revenge Advanced Composites and Dr. Glancey. The results of this spreadsheet reflect the ultimate goals of the project: weight reduction is the first priority, followed by shock absorbing capability.
B: UDesign – Benchmarking & Metrics Before the metrics and target values are determined, it is essential to know what specific shock mitigating seats are currently on the market. A company called STIDD offers one of the widely used seats on the market. All of the combat ready seats offered by STIDD are very bulky and extremely heavy. However, the STIDD seat is the seat of choice for some special warfare boats. The Advanced shock mitigating seat 800V53 is proven in 6 foot seas traveling at 50 knots (57mph) and has a shock system capable of a seven inch stroke. It offers single deck‐mounted, double deck‐mounted and single bulk head mounted configurations, weighing 144 pounds when fully assembled. The heavy weight of the seat inhibits it from being installed onto more marine crafts, but the
seat does provide sufficient protection against the vertical forces produced by ocean travel. 1
The second STIDD seat is the 870V53. This model has been proven in sea state 4 at fifty knots and the seat alone weighs 59 pounds without the deck mounting system. The performance features include a 4 inch shock mitigating range of motion and fully passive suspension that increases product longevity. The chair is also equipped with a pressure response valve system that prevents “bottoming out”. External adjustable coil spring provides are also available to compensate for various users’ weight. Another attribute is the Go‐No‐Go gauge instant visualization of
the suspension system readiness. These added features improve crew performance and significantly reduce the risk of spinal, orthopedic and ligament repetitive stress injuries.
The next company that provides shock mitigating technology is Ride Softly. This company provides a pedestal that a seat would be mounted on. The standard pedestal is an aluminum anodized post that provides 5 inches of stroke, standing 22 inches high with a coil over suspension. This technology is not very practical for high speed boating and is not applicable to military craft, as it provides little protection from the shock impact of unpredictable waves. 2 Unfortunately, this type of impact is very common in the environment in which the seat is used.
Shockwave Seats provides shock mitigating seats to both law enforcement and military boats. The Shockwave Seat has 8 inches of controlled vertical travel with an advanced suspension system capable of sensing and automatically compensating for rapid and high magnitude force
loadings. A urethane bumper assists the coil spring from “bottoming out”, a crucial feature in protecting the occupant’s spine and joints from sudden jolts. All the parts are marine grade and are covered in a Nyalic coating, giving superior corrosion protection. The combat seat has fold away features that would allow for more boat room when not in use, but the weight of
the chair is 155 pounds. Due to its larger size, the Shockwave design would cut down on the amount of supplies and personnel capable of fitting on the boat and its weight is undesirable. It does however provide enough protection to the user, performing very well adverse environments.3
1 http://www.stidd.com/products/800V53.htm 2 http://www.ridesoftly.com/RSInfo/PedestalDetails.htm 3 http://www.shockwaveseats.com
The Zodiac Company also has its own version of a shock mitigating seat. It is a removable seat that can be linked to other seats. This results in a continuous line of seats that can drastically lower the seating system’s footprint on the boat. Each seat is height adjustable and in order for this style of seat to be affective, it is crucial that the height is adjusted to each individual’s size. 4 The importance of unique features, like Zodiac’s seat linking aspect, must be properly assessed during the concept selection process.
Ullman Dynamics, a Swedish based company, offer a seat that is superior to all of the other benchmarks. It is lightweight and has advanced shock absorbing capabilities and better ergonomics than the STIDD seats. This technology is the best competition found and will serve as a great benchmark for ideas. Ullman Dynamics have approached the need for a shock mitigating seat from a bio‐mechanical point of view, so the seats take full advantage of the human body’s inherent shock mitigating system. The shape of the seat stabilizes the entire body, allowing for the occupant to use leg and arm muscles to lessen the shock while the chair keeps the shape of the spine in the optimal position to withstand impact. The nature of the chair also allows the spine to gradually flex sideways at lateral impact. The jockey seats are produced with high‐grade stainless steel and multi‐composite components. High‐comfort padding and heavy‐duty long‐life weather resistant upholstery are incorporated into the design. The seat weighs 36 pounds without the necessary fiber‐reinforced polymer pod and 48 pounds with the aforementioned pod, with a footprint of 10”x19”. These seats have been tested and proven at high speeds and rough seas. They are very lightweight and provide excellent protection against shock loadings.5
The top half of the Metrics worksheet in the UDesign spreadsheet is shown above. This section of the worksheet describes the current state of the art solutions and compares their performance to our Top Ten Customer Wants, as shown above in the previous screenshot. The Ullman seat is the best performer according to current information, as it is the lightest by far and performs as well as the other seats. Since weight was the main driver of the project, the Ullman’s advantage in weight led us to choose it as the design to modify and adapt for use with composites.
4 http://www.zodiacmilpro.com/news/index.html 5 http://www.ullmandynamics.com/
C: UDesign – Metrics (continued)
The process used in order to rank the metrics is shown here in the above screenshot. The UDesign methodology of comparing the metrics to the most important customer wants is used in order to arrive at a ranking of metrics that most directly echoes what the main customers are demanding. During Phase 4 of the project, we were able to re‐assess our metrics and re‐evaluate them based on the emphasis that we were applying to the various metrics that we considered. The finalized list is shown in the table below, a copy of what was shown in the beginning of the paper.
Metric Goal Prototype Score Weight (lbs) 70.0 lbs 48.2 lbs G‐Force Threshold 20g Vertical, 4g Fore/Aft & Lateral Design: 22g vert, 6g fore/aft & lateral Product Life (hrs) 1400 hrs (150 cycles of worst load) Requires fatigue testing Footprint (in x in) < 28in x 40in 22in x 24in
The most significant adjustment from Phase 3 was replacing the “Number of Parts” metric with the “Product Life” metric. Through correspondence with contacts at Special Naval Warfare Group FOUR, a goal for product life was determined by multiplying the years in service of each boat (5 years) by hours of service per year (280 hours per year). Additional details regarding the frequency of the loadings were derived by dividing the number of hours of service (1400 hours) by the time between the worst case loads (8‐10 hrs). The other three metrics were all sufficiently aligned with the sponsor’s wants and did not require adjustment during the fourth phase – direct discussions with Jonathan Sadowski, the CEO of RAC, led to the conclusions seen about the ranking of the metrics.
As previously stated in earlier Phase reports, the most important metric is weight, and the quantitative goals were clearly delineated at the beginning of the semester. In comparison to the Shockwave Seat, which had a weight of 144 pounds, a twenty‐five percent weight reduction (108 pounds) was the minimum for success and the goal was a fifty percent weight reduction (72 pounds). During the problem definition phases, the worst case required loadings were also specified as twenty g’s in the vertical direction and four g’s in fore/aft & lateral directions. In order to obtain a goal value for the footprint, benchmarks were compared and the STIDD seat’s size, referenced above in the table, was decided as the “size to beat” due to the ease of accessing the information on the STIDD website.
D: Force Analysis
In the FBD to the right, the cantilever beam is the length L2 and the shock is attached at length L1 from the pivots at the left vertex. L3 is the length of the shock, and L4 is the length between the pivots (left vertex) and the point where the shock is attached to the base. The applied force is denoted as Pz, Px and Mp, describing the vertical and fore/aft forces as well as a moment around the y‐axis. The reaction forces are Rx,Rz, Sx, and Sz ‐ the R forces are the reactions at the pivot that the bearings will hold, while the S forces are the shock reactions.
The spreadsheet shown at the beginning of this section is the result of the work that is described here. The formulas that were derived for the forces were input in the Microsoft Excel so that the analysis could be repeated for a wide range of values to allow for proper engineering conclusions to be made. Having performed an analysis of the resultant forces due to the vertical and fore/aft force, the only remaining force to be accounted for is the lateral force. The relevant analysis begins on the next page.
E: Stress & Deflection Analysis Arm The stress analysis for the arm, clevis, and the bolt layout for the clevis was done using simplified shapes and equations. The arm was simplified down to a C‐shape for our analysis. In order to design these parts and dimensions correctly, we had to account for six modes of failure. We also, along with the failure modes, had to account for deflection in the arm. We had to account for this because we do not want the Navy Seal to move around a lot in the seat. The least amount of movement was a priority for our project. The force analysis on the arm yielded what the thicknesses needed to be in order for the part not to fail and have the least amount of deflection. We found that the arm except for where the clevis and pivot attached it could be at a minimum of 5 mils. The thickness where the clevis attached had to be at a minimum of 0.25 inches thick with a minimum distance of 2” from the edge for it not to fail. The thickness around the pivot could be at a minimum of 0.25 inches with a minimum distance from the front edge of 3” and a minimum distance from the bottom edge of 3”. This is the maximum thickness the fiber can be due to the manufacturing process any thicker would be impractical. These thicknesses stated above will withstand all six modes of failure. We found the vertical deflection is 0.125” which is acceptable. The lateral deflection is 0.3” & this is an acceptable deflection. The fore and aft deflections were less than the above stated deflections.
What follows is a copy of the spreadsheet cells that were involved in the derivation discussed above. Due formatting issues, it is not as organized as it is in the spreadsheets. The first three rows involve parameters and simple calculations. The moments of inertia and area are necessary for the final round of calculations for the deflection and stresses, shown at the end. The final table is of the material properties used and notes on the spreadsheet. Lastly, the images that correspond to the symbols referenced in the tables have also been included here.
Width Length d Thickness 1 Inches 15 6 0.253 0.054 Meters 0.381 0.1524 0.00643 0.0013716
Thickness 2 Thickness 3 C(Lateral) C(Bottom) Inches 0.153 0.054 7.5 3.844095104 Meters 0.0038862 0.0013716 0.1905 0.097640016
C (Top) Neutral Axis(Vertical) Neutral Axis(Lateral) Inches 2.155904896 3.844095104 7.5 Meters 0.054759984 0.097640016 0.1905
CG(Distance)(in) CG(Distance)(m) Vertical
Moment(N*m) Lateral
Moment(N*m) Torsion(N*m) Fore and Aft Moment(N*m)
18 0.4572 1867.39784 3395.2688 2777.9472 3393.217406
Moment of Inertia(Vertical) (m^4)
Moment of Inertia(Lateral)(m^4)
Polar Moment of Inertia
Cross Sectional Area(m^2)
4.43562E‐06 4.78458E‐05 0.00003682 0.675302028
Deflection in the Vertical(in)
Deflection in the Lateral(in)
Deflection in theFore and Aft(in)
Angle of Twist(degrees)
‐0.246457813 ‐0.00415423 0.483113561
Vertical Lateral Fore and Aft Bending Stress Top Bottom Top Bottom
Pascals 23053991.13 ‐41106513.82 13518414.46 41891021.98 74693959.26 Psi 3343.704765 ‐5962.006552 1960.683796 6075.790047 10833.46246
Factor of Safety 24.72456924 13.86641549 42.16470814 13.60673416 7.631139193
Properties for Carbon/Epoxy Composite Sheet Youngs Modulus (Longitudal/Transverse)(Pa) Psi
70000000000 10152660 Compressive Strength(Longitudal/Transverse)(Pa)
570000000 82671.66 Tensile Strength(Longitudal/Transverse)(Pa)
600000000 87022.8 Shear Strength(In Plane)(Pa)
35000000 5076.33 Shear Modulus in Plane(Pa)
5000000000 725190 http://www.goodfellow.com/csp/active/static/A/Carbon‐Epoxy_Composite.HTML
Thickness1 is the thickness on top of the beam Thickness2 is the sidewall thickness Thickness3 is the flange thickness
The images that define the symbols and variables in the tables above are on the following page.
E: StAnalydeteshou
DeAnathicEstiEsti
Mat
ForeLoa
y_maFL^3/
LateLoa
y_maFL^3/
VerLoa
δ = F
tress & Deysis of the strmine a geneld yield a fact
eflectioalysis performckness of: mated Densitmated Weigh
terial Propert
e/Aft ding
ax = /(3EI_xx)
eral ding
ax = /(3EI_yy)
rtical ding
L/AE
eflection Aress and defleral thicknesstor of safety t
on in Bamed with a co
ty ht of Rider
ties from:
G Force
6
G Force
6
Le
Analysis – lections in ths for the basthat is greate
ase Inpnstant
httpEpo
Length (in)
20
Length (in)
20
ength (in) 20
F
Base he base were se with the cer than unity.
puts in Or
p://www.goooxy_Composit
Young's(M
8
Young's (M
8
Young's Mod(Msi) 8.4
F
very similar onstraint tha
range, Ou
00.05
3odfellow.com/te.HTML
s Modulus Msi)
8.4
Modulus Msi)
8.4
dulus F(3
to that of that deflections
utput In G
0.05 inches570 lb/in^3300 lbs /csp/active/s
Force (lbf)
1800
Force (lbf)
1800
Force (lbf)
C
3372
he arm. The gs should be s
Grey
static/A/Carbo
Moment o(in^
23
Moment o(in^
64.
Cross Section(in^2)2.14
goal of the ansmall (<.05in)
on‐
of Inertia ^4)
.9
of Inertia ^4)
.7
nal Area )
nalysis was to) and stresse
y_max (in)
0.02395
y_max (in)
0.00883
y_max (in)
0.00375
F
o s
Stresses In Base Inputs in Orange, Output In Grey Estimated Weight of Rider 300Material Properties from: http://www.goodfellow.com/csp/active/static/A/Carbon‐Epoxy_Composite.HTML
Fore/Aft Loading
G Force
Length (in)
σ_allow (psi)
Outer Distance ‐ c (in)
Moment of Inertia (in^4)
σ_y (psi)
FactorOfSafety
σ_y = Mc/I = (Fl)c/I 6 20 87022 7.62 23.86
11497.52 7.57
Lateral Loading
G Force Length (in)
σ_allow (psi)
Outer Distance ‐ c
(in) Moment of Inertia
(in^4) σ_y (psi) FactorOfSafety
σ_y = Mc/I = (Fl)c/I 6 20 87022 7.00 64.71 3894.54 22.34
Force Length Of
Cantilever (in) τ_allow (psi)
Outer Distance ‐ r
(in) Polar Moment of Inertia (in^4)
τ_yz (psi)
FactorOfSafety
τ_yz = Tr/J = (Fa)r/J 6 22 5000 7.00 88.56
3129.919282 1.60
Vertical Loading
G Force
Length (in)
σ_allow (psi)
Cross Sectional Area (in) σ_y (psi)
FactorOfSafety
σ_y = F/A 22 20 87022 2.14 3080.29061
6 28.25
The spreadsheet used to calculate the moments of inertia for the base section is shown here.
Section_Channel.xls To determine section properties By Alex Slocum, 12/28/03, last modified 02/09/06 by Alex Slocum Enters numbers in BOLD, Results in RED Schematic
Section dimensions Values Values
(in) Length of flange, a (mm) 279.4 11 Thickness of flange, b (mm) 1.27 0.05 Length of web, cc (mm) 355.6 14 Thickness of web, d (mm) 1.27 0.05 Corner fillet, rr (mm) 22.86 0.9 Corner inscribed circle, DD (mm) 9.332 Section properties Area (mm) 1382 2.143 yNA (neglect corner radii) (mm) 85.856 3.380 Ibending (mm^4) 9930694 23.859 Ibending (mm^4) 26932669 64.706 Itorsion (mm^4) 36863363 88.565
Approx. max torsional stress/Torque
(N/m^2) 2.53E-07
Derivation of DD:
( )( )( ) ( )
( )
2 22 2 2 2
34 43 4
44
22 2 212 2 12 22 2 2
1 12 0.21 1 0.105 13 12 2 3 1922 2
bendingNA NA NA
torsion
b c ba d a da dab d c by y yIab d c b
b c d db ba b dbI Dca ba b c b
⎡ ⎤ ⎡ ⎤+ − ⎛ ⎞ ⎛ ⎞= = + − + − + −⎢ ⎥ ⎢ ⎥⎜ ⎟ ⎜ ⎟+ − ⎝ ⎠ ⎝ ⎠⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦
⎡ ⎤⎛ ⎞⎡ ⎤ ⎢ ⎥⎛ ⎞ ⎜ ⎟⎛ ⎞= − − + − − − +⎢ ⎥⎜ ⎟ ⎢ ⎥⎜ ⎟ ⎜ ⎟
⎝ ⎠ −⎝ ⎠⎣ ⎦ ⎢ ⎥−⎜ ⎟⎝ ⎠⎣ ⎦
0.07 0.076 rb
⎧ ⎫⎪ ⎪⎛ ⎞⎪ ⎪+⎨ ⎬⎜ ⎟
⎝ ⎠⎪ ⎪⎪ ⎪⎩ ⎭
( ) ( ) ( )( ) ( )( )
2 2 2
2 22 2
let 22 2 26 2 2 2 0
DD D D Rd r b r r
R r d b r b db dR r
+ = =+ − + − +
+ − − − + + + + + =
b
d
r
Ø D
d+r-D/2
b+r-D/2
D/2+rD/2
F: BThe bstandthrouques
ForanForceat pivFp
33
Lat
ForceFL
1365
VeForcepivotFv (Lb
The astrenboltscalcuwill o
Bolt Analysbolt analysis dpoint, we ough tear‐out tion if the bo
re d Aft e Applied vot
369.211629
teral
e Lateral
RFBF
5.939138 3
rtical e Applied at t bs)
3372.134above calculangth bolt avais is strictly thulated for eaconly reduce th
sis was perform
only needed instead of th
olt pullout fail
Reaction Forat Bolts Fr
3644.738
Reaction orce at Bolts r 3644.73835
2
ReactiBolts Fr (lbs
4145 ations used a lable found whe minimumch of the 3 typhe number of
med primarilyone bolt at he bolt actuaure is conside
rce Proof Strenghσ
352 330
Proof Strengh σ
33000
on Force at
)
3644.738.25 diameter
within Machin number to pes of forces f bolts. The d
y with the baeach cornerlly failing. Asered.
h Area A
000 0.1104
661
Area A 0.110446
617
Proof Strengσ (psi)
8352r bolt, with gne Design an handle the (fore and aft
diagrams belo
se flanges in. The drivings seen here, l
Moment (Fp to B)h
4417
Moment Arm(Fp to B) h
h AreA (i
330000.1
iven proof stIntegrated Apworst case st, lateral and ow correspon
mind. As exg failure modless than one
Arm Mom(Fr tL
15
m Mome(Fr to Cw
15
ea Db
n^2) D11044661
7rength of 33 pproach p. 83scenario (comvertical). Incd to the analy
xpected, we fde was the ce bolt is need
ment Arm to B)
21
ent Arm C)
19.5
Diameter of bolt D (in)
0.3kpsi. This wa34 Table 14‐6mponents of creasing the Dysis shown ab
found that frcomposite mded to handle
Diameter of bolt D
0.375
Diameter of bolt D
0.375
NuBoNb
375 as the smalle6. Note that ta 20 g app
Diameter or Pbove.
om the bolt’material failinge the loads in
Number ofBolts Nb 0.6602887
51
Number of Bolts Nb 0.28828473
1
umber of olts b
0.925206097est and lowesthe number olied force) aProof Strength
s g n
f
71
31
7st of s h
Accoanalythrouimagapplithus direc
CeW
rding to bolt ysis with onlyugh the centginary verticalied further inmaking a w
ction is not ap
entroid CaW1
22
shear failurey 4 bolts at lotroid therefol line connectn closer to theorst case scepplicable.
alculationWC
4 11
, similar resuocations A, B, re removing ting the far rige points B anenario. Also
L
1 22
lts are obtainC and D. Asany momenght of the strnd D, pushingo note that s
L1 L3
ned. To demosume that thnts. The forcucture (not sg it out beyonsince we are
L2 L36
onstrate the ihe forces fromces in the lahown in diagnd these poinonly looking
Area14
mpact of a shm the fore anateral directioram). In realnts will only pg at shear, th
a 1 Area 2132
hear force wend aft directioon will be apity this lateraproduce a grehe force from
2 Area 3 64 64
e will begin anon are movingpplied on theal force will beeater momenm the vertica
Lc 4 8.415385
n g e e t al
MArm
Now compthat the S
Howethe f
Assu
Moment Armm
13.58462
examine eaponents. Assuthe Force FoShear Yield St
ever, if the foollowing resu
me interlami
m Forcin FL 13
ch of the foume the Forcre and Aft is rength is 50 k
Point A
Point B
Point C
Point D
ocus is placedults.
nar shear str
ce Lateral lbf
365.939
orces occurince Lateral is aacting in the kpsi (for low‐c
Fy ‐1863.5
Fy 1707.424
Fy ‐1863.5
Fy 1707.424
d on the failu
ess allowed i
Force ForeFF&A
3369.2
g at each ofacting upwarnegative X dcarbon steel)
Fx 2529.19
Fx 2529.19
Fx ‐844.584
Fx ‐844.584
ure modes of
s 5 ksi. Assuboltsbe caapplitop oSheahave somevariadista
and Aft lbf
212
f the 4 boltsd in positive direction or to.
|F| 3141.56
3051.57
2045.95
1904.89
the composi
me that loca shown abovarried by mored are the woof the seat). r (5000 psi) iseen on th
ething with ables that cannces.
NuNB
s. The forcY or upwardo the left with
Shear
τ 63 12566
73 12206
57 8183.8
93 7619.5
te, which wil
lly the loads ave. This is core than the morst case scenAnother imps a low estimhe market it a critical loadn be modified
mber of Bolts
4
es will be b with respecth respect to t
Stress Fact
Ns 6.25 3
6.29 4
826 6
574 6
l definitely fa
are carried byonservative sminimum numnario (a 20 g portant thing mation. Basedappears as
d of upwardd are the thic
s
Momentfrom Lateral Force
ML 18555.7
roken down t to the diagrthe diagram.
tor Safety
3.978911
4.096248
6.109612
6.562047
ail before the
y the minimuince in realitymber of boltsload applied to note is thd upon otherthough wes of 13 ksi. kness and th
t
lb*in
6
into x and yram. Assume Assume tha
e bolt, we find
um number oy the load wils. The forcefrom the veryat the Criticar materials wecould obtain The primarye appropriate
y e t
d
of ll s y al e n y e
Tear out
Lateral Force Area Thickness Distance
Number of Bolts Shear
Factor of Safety
PL (lbf) A (in^2) t (in) d1 (in) NB τxy (lbf) FS 2048.90
9 0.875 0.25 1.75 2 2341.61 2.135283034
Fore and Aft Force Area
Thickness Distance
Number of Bolts Shear
Factor of Safety
PF&A (lbf) A (in^2) t (in) d1 (in) NB τxy (lbf) FS 3369.21
2 1.25 0.25 2.5 3 2695.36
9 1.855033369
Vertical Force Area Thickness
Circumference of washer
Number of Bolts Shear
Factor of Safety
PV (lbf) A (in^2) t (in) Cw (in) NB τxy (lbf) FS 1686.06
7 0.58904
9 0.25 2.35619449 2 2862.35
6 1.746812544
As seen here, the factors of safety are much more concerning than in the prior analyses. The conclusion to make here is that the base flange thickness must be 0.25inches to make the factor of safety an acceptable value.
G: CThe cclevisfailuror shforceclevispivotWe pdistainch.
was holdithe pattacneedwherand 1minimsheathe c
Paramresul
InchMete
Clevis Analclevis posed s needed to re from the chearing throue. Our analyss to be at leat, the clevis hperformed shnce from the Now that th
The clevisthe only logiing the shockpin needed tchment pieceded that the pre the pin wo1.25 inches hmum distancer analysis of clevis has to b
Again, themeters comets of the ana
Diamethes ers 0.
lysis a few problebe on the arclevis itself. Tgh the compsis allowed usst .25 inches had to be a cehear analysise side edges hhe arm is com
s had to withsical way to ak to the clevisto be. The se for the shocpin could withould go throuhigh. The foue from the frthe compositbe is .25 inche
e relevant spre first, followelysis: the geo
S_9
ter of Plate 3 0762
ems with therm. We had The major proosite. This ws to make thethick. This aertain distanc on the armhas to be 1.7
mpleted we ha
stand all the fattach the shs. The pin dimshock attachmck was made hstand the fogh the clevis.urth step wasont, back, ante. The minies. The thickn
readsheet celed by relevanmetric param
_x (N) 961
Diameter of 0.5
0.0127
ShePasP
Factor o
ShPasP
Factor o
e thickness anto consider oblem of thewas due to thee minimum thanalysis holdsce away from given our m75 inches. Thad to analyze
forces the shhock given thmension was ment was .5 out of stainlerces if it were. The two kns to make sud top edges imum diametness of was a
lls have beennt failure mometers of the
Pin L1 0.25
0.0063
Shear of thar Stress in thscals Psi of Safety
hear Stress inscals Psi of Safety
nd the positia couple mo clevis was pe very large vhickness arous true for whem the edges somechanical pre minimum dthe clevis itse
ock is going te geometry dependent oinches in diaess steel so we made out ofobs have to bre the pin wois .5 inches. Tter the clevis function of t
copied in thdes. Finally, aclevis.
L2 0.5
5 0.0127
he Pin Failurehe Fore and A
n the Vertical
on the odes of pushing vertical und the ere the cleviso the bolts wroperties. Thdistance fromelf.
to take and thof the shockon the shock sameter so thwe knew if thef the same mbe at a minimould not sheaThe diameterneeds to be
the compress
e following pa pertinent b
S_z (N) 21115
Length C0.250
0.00635
e Mode Aft Direction
l Direction
s attaches to would not shehe analysis ym the back ed
hen some. Fik itself. Secoso we did nothat is how bie shock was daterial. The tmum of .25 inar through thr of the clevisis 3.5 inchesive strength o
ages to displabird’s eye view
Stress C
Cross Section
15179650.32201.6261212.2532466
111121866.16116.89321.67383797
the base. Saar through thyielded that tdge of the arm
rst the designond, we lookt have a choicig we made designed to third step wasnches thick, .5he knobs thes was determs. The minimof stainless st
ay the analysw is shown a
Concentratio3
nal Area of Cl0.196349541
33 25 68
.4 25 77
ame as for thehe compositethe minimumm has to be 1
n of the clevied at the pince on how bigthe pin. Thetake the loads to design fo5 inches widemselves. Theined from the
mum thicknesteel 304.
sis performedlong with the
n Factor
evis Pin(m^21
e e. m 1
s n g e s r e, e e s
d. e
2)
Pullout failure Mode in the Attachment Vertical Fore and Aft
Shear/Compressive Forces(w/concentration factor) 63344.56587 2884.365882
Shear Stress Upwards(w/3g upward force) Vertical Fore and Aft
Pascals 56506913.01 0 Psi 8195.64965 0
Factor of Safety 3.291632653 0
Shear Stress Fore and Aft Vertical Fore and Aft
Pascals 0 17883104.24 Psi 0 2593.729672
Factor of Safety 0 10.40087882
Bearing Failure Mode in the Knob Compressive Stress Downwards
Vertical Fore and Aft Pascals 261824729.3 0 Psi 37974.53508 0
Factor of Safety 1.565933062 0
Compression on the Plate Compressive Stresss
Vertical Pascals 84459 Psi 12.24982553
Factor of Safety 4854.402201
Shear of One Knob Bearing Failure of Pin from the
shock Shear Stress Vertical Bearing Stress
Pascals 5961034.745 Pascals 261824729 Psi 864.5765574 Psi 37974.53508
Factor of Safety 31.20263645 Factor of Safety 1.565933062
inm
inm
nches meters
Bolt nches meters
VolumEstim
Bird's ELength 0.250
0.00635
Hole Diamet0.375
0.009525
Po
me of Clevis(Imated Weight
Eye View of tWidth
1 0.0254
er
Density of unds Per Cub
Inches Cubedt of One Clevi
he Knobs on Height
1 0.0254
304 Stainlesbic Inch
d) is (Pounds)
the Clevis Plat T
4
s Steel
ate Thickness of
0.25 0.00635
0.285
2.05852440.58667947
Plate
5
48 77
H: P whersusceto bemoreexchastrenof tharea balan
by th
ForcP_ve
MatSheaCom
MatShea
Inpu
Inpu
Pivot Pin AOne of th
re all the loadeptible to teae less critical te than half ananged for bongth propertiee plate becauresulted in a nce between
The initiahe relevant eq
ce Data (sprtical (y) (lbsf
2972.9
terial Propr Strength (Inpressive Stre
terial Propr Strength
ut Data t_a 0.25
ut Data Y
Analysis e critical aread is transferrearing out of ththan tear‐outn inch – due tonding a metaes as comparuse it determstronger bonthe two extre
l pivot point quations and
plit betweef)
p for Carbon plane) ngth
perties for
Y_a 2
as of the desiged. The drivinhe composite t. Through ano the impractl plate onto ted to a compined how mund but increasemes based o
analysis showthe numerica
en 2 pivot
on Fiber(Ps
302 Steel
t_b 0.25
gn was the pig failure modto the nearealysis, the coticality of sucthe area and aposite, to withuch adhesive wsed the weighon the expect
wn here beginal evaluations
s) P_latera
2
si)
R_r0.68
X_b 2
ivot point – thde here was fost edge. Comnclusion wash a design, stallowing the hstand the fowould be useht and size ofted loads deri
ns with relevs of the equat
al (z) (lbsf) 2049.8
rod 875
he connectioound to be te
mpression failu that the thictrengthening metal, with grce with easeed to bond thef the plate, soived in the Fo
ant parametetions.
R_bea
1.00
Y_b 2
n between thear‐out: the pure was also cckness of comthe area by igreatly increase. The crucial e plate to theo an optimal sorce Analysis.
er and mater
P_fore/aft
556
ring 9 025
he arm and thpivot pin wouconsidered bu
mposite necesncreasing thicsed inter‐lamfactor was noe arm/base. Msolution was f
rial property d
(x) (lbsf) 61.8
X
OverHang of 1.3
he base ld be ut was foundsary was ckness was
minar shear ow the area More surface found at the
data followed
500082667.1
26977
X_a 2
f metal Rod 3
d
01
7
Safte
SafteFacto
As sethe eadhethen
ey Factors (N)F(ATS
ey ors (N)
een above, wiedge, the safeesive proved ifailure mode
) Figure 2 Arm) Tear out tress (x)
5562
0.90
ith thicknesseety factors wets design supe analysis is sh
Figure 1
FigurShea
Tear Out Stress (y)
2973
1.68
es everywherere still less thperiority. The hown.
re 1 (Bolt Shear in Arm (y)
CompStress
re around thehan unity. As plate analysi
ear)
8648 3.12
ressive (z) 2193
37.70
e pivot pin of 0a result, the s at the pivot
Fig
Figure 3 (Base) Tear Out Stress (x)
5562
0.90
0.25 inches afollowing anat follows here
Figure 2
gure 3
Shear In Bas
Tear OuStress (y
297
1.6
nd a distancealysis for a mee: parameters
2
se (y) 8648 3.12
ut y)
ComStre
73
68
e of at least 2etal plate bons, material pro
mpressive ess (z)
580
142.52
inches from nded on withoperties, and
Thickness Length Width Area of Rectangle
Area of bearing Area of Plate
T (in) L (in) W (in) AR (in^2) AB (in^2) AP (in^2)
0.125 3 3 9 3.157320252 5.842679748
Failure Mode along Adhesive Shear Strength of Adhesive
τA (Psi) 2000
Fore/Aft VerticalShear Strength 302.943 168.2447Factor of Safety 6.6019 11.88745
Failure Mode of Adhesive in Tension (Lateral Force) Tensile Strength of Adhesive
σA (Psi) 1500
Lateral Force Tensile Strength 653.125 Factor of Safety 2.29665
Failure Mode along Metal Plate
Shear Strength of Plate (Steel) Compressive Strength of Plate
(Steel) Shear Area
Shear Area (Lateral)
τP (Psi) (Psi) Ashear (in^2) AshearLat (in^2) 30000 60000 0.375 0.250625
Fore/Aft Vertical Lateral Force Shear Stress 14160 7864 22838.9 Factor of Safety 2.11864 3.814852 1.313548 The factors of safety are all greater than unity in the case with a metal plate bonded on to the arm/base, using conservative values for the shear strength of the adhesive. In order to size the plate, the following analysis was used: the various loads were examined separately and the plate was sized appropriately. The conclusion was that the pivot point should be able to withstand all three combined loads with a factor of safety of 1.36, as seen below:
Stress Concentration Adhesive Allowable Shear (psi) Adhesive Allowable Tensile Stress (psi) 3 1500 1500
Safety Factor ILSS (psi) Thickness
1.5 5000 0.05
Calculation of Area of Plate
Composite Failure
Vertical Load (lbf) % of Vertical Load Area (in^2) Length (in) FoS
491.5 100 0.74 1.97 2.01 # Pivots Handling Load
2
Lateral Load (lbf) % of Vertical Load Area (in^2) Length (in) FoS
1908 100 5.72 2.98 3.03 # Pivots Handling Load
1
Fore/Aft Load (lbf) % of Vertical Load Area (in^2) Length (in) FoS
885 100 1.33 2.12 2.15 # Pivots Handling Load
2
Combined Worst Load (lbf) % of Max Load Factor of Safety 4202 5 27.24
Chosen Area 10 13.62 5.72 15 9.08
Total Area (Hole Area Added) 20 6.81 8.88 25 5.45
Plate Length/Width 30 4.54 3.0 35 3.89
40 3.41 To obtain 4202 for combined worst 45 3.03
load, apply 4 lat, 22 vert, 4 fore/aft and 50 2.72 take the resultant of the columns 55 2.48
marked Radial Load X and Radial Load Z 60 2.27 65 2.10 70 1.95 75 1.82 80 1.70
85 1.60 90 1.51 95 1.43 100 1.36
0.001.002.003.004.005.006.007.008.009.0010.0011.0012.0013.0014.0015.0016.0017.0018.00
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Factor Of Safety
% of Combined Load
Factor of Safety vs % of Combined Load (Adhesive)
Factor of …
I: Seat Attachment Analysis The seat attachment mechanism was developed in a short period of time and was hastily thrown together to interface with the seat that was available to us. The following analysis verified that the introducing the holes into the top of the arm would not induce premature failure.
Material Properties For Carbon Fiber (Psi) Shear Strength (In Plane) 5000 Compressive Strength 82667.1
Force Data Forces (Newtons) Vertical Lateral Fore/Aft
33418 6076 6076
Force(Lbsf) Input Data
Vertical (y) Lateral (z) Fore/Aft (x)
Fixed By Bolt Layout
7516 1367 1367 Fixed By Mold Design
Dimensions (Inches) Hole Diameter X1 X2 X3 Z1
0.25 3.5 3.5 8 1.65
Dimensions (Inches) W1 D1 W2 D2 L1 L2
11.3 7 7.75 10.5 3 1
Dimensions (Inches) Composite Thickness Length of Support (Z)
0.096 10
FS
actor Of aftey
FailureFigure 1Hole1/3
Tear Out
Factor
e Modes 1
t (X1)
FC
r of Saftey
Tear O1525
3.28
Figure 2 Compressive
Out (X2)
Failure (L1) 222373
Figure 1
Figure 2
Tea(Z1
1525
3.28
Compressi
ar Out )
3235
1.55
ve Failure (L27511
HoTea(X3
2) 52 10
le 2/4 ar Out 3)
667
7
J: Gantt Chart
The completed Gantt Chart is shown above as a record of the steps taken to complete the project. The main changes in this version since Phase 3 are the exact dates on the items in Phase 4, including the expedited manufacturing process. It took five straight days to go from two molds to a completely assembled, stationary prototype, but it should be noted that allotting more time to the manufacturing process is highly recommended based on the team’s experience.
K: Manufacturing The manufacturing process can be broken down into a series of phases. The first phase or the pre‐mold phase
consisted of all of the components that needed to be done in preparation for the molds arrival. In order to make the laying up of the carbon fiber plies easier and manage time efficiently, an organized set of ply patterns and shapes was created which could fit like puzzle pieces into the molds. Appropriate core pieces were cut out as well.
The next phase to the manufacturing process was the actual mold preparation. The molds that were used for this project were particle board with an epoxy coating for where the part would be applied. Even though there was a 2 degree draft angle on these molds it was still crucial to make the surface as smooth as possible in order to have proper removal of the part from the mold. To do this multiple layers of wax coating were applied to the surface and then buffed off in order to fill in any minor discontinuities on the surface. Before any wax or other surface preparation was applied, a boundary layer of tape is attached to the borders of the mold. This tape would be removed further in the process in order to have a non‐waxed surface to attach the vacuum bag tack.
The third and longest phase of the manufacturing process was actually “laying up” the plies to form the part. First the pieces of prepreg that were previously cut were placed in their appropriate position on the mold and lined up as flush as possible with the adjacent pieces. From there a thin sheet of plastic was placed on top of the prepreg followed by a thin layer of fabric. Next, a line of tack was placed where the tape originally was on the edge of the mold with multiple pleats to allow for excess vacuum bag material to be attached. This excess is crucial so that when the air is removed the bag can evenly decompress down to the surface. The bag and the seal needed to be checked for leaks so that a constant vacuum was maintained; if there were leaks during the curing process it could have resulted in an entirely faulty part. After the first layer was de‐bulked, the vacuum bag was removed and another ply was added. This process will continue with adding plies and de‐bulking, except there will be more than 1 ply added each time before de‐bulking occurs. Normally there will be at least 3 to 4 maximum plies per each cycle. The special exception to this is when placing the core in between plies. For this project the core was cut out and then placed in between an even number of plies. The core was adhered to the prepreg using a special material specifically designed for the core/prepreg interface. Once the core was placed appropriately onto the adhesive another layer of adhesive is placed on top followed by another ply of prepreg.
At this point it was important to de‐bulk in order to prevent bridging between core pieces which is more likely to occur with more layers. Bridging would result in pockets of air in the material and also could promote propagation similar to that of a crack. It would greatly weaken the integrity of the part and should be avoided as much as possible. Since all of the core pieces were placed during the same ply, a special de‐bulking cycle only needed to occur once for both parts. Once the final ply was placed, the mold was prepped one final time for one more vacuum cycle. The mold is placed under vacuum into an oven where the temperature was ramped up to around 185 degrees and then held constant for around 5 hours. Left out to cool after the curing process, the mold should have easily popped out of the mold if the appropriate layers of wax had been applied in the mold prepping phase. In the case of this project, a few wedges and mallets had to be used to force the base part out of the mold. The arm was released from the mold with ease and was faster to lay up due to its being relatively less complex.
The final phase of manufacturing was the actual machining of the parts and assembly. This consisted of trimming of the parts down to their appropriate sizes and drilling the holes needed for attachment. Drilling through carbon fiber was a challenging process because the fibers wanted to pull out of the material and separate instead of being cleanly cut.
L: Fore/Aft Test Details Deflection(in) Deflection Deflection Deflection Deflection Deflection Deflection DeflectionPressure (psi) Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Average Std Dev
250 0.014 0.004 0.014 0.015 0.023 0.020 0.015 0.007 500 0.038 0.026 0.040 0.042 0.045 0.046 0.040 0.007 750 0.067 0.063 0.072 0.080 0.085 0.087 0.076 0.010
1000 0.099 0.096 0.115 0.118 0.118 0.124 0.112 0.011 1250 0.130 0.121 0.145 0.150 0.150 0.156 0.142 0.014 1500 0.166 0.158 0.190 0.199 0.198 0.209 0.187 0.020 1750 0.211 0.212 0.265 0.271 0.266 0.284 0.252 0.032 2000 0.298 0.297 0.410 0.382 0.385 0.398 0.362 0.051 2250 0.401 0.402 0.664 0.435 0.433 0.441 0.463 0.100 2500 0.526
Notes: Runs 2, 3, and 4 were on the same day. Runs 5, 6, and 7 were on the next day. No noticeably audible cracking occurred. The first run was invalidated because the strongback was not securely clamped down and it was moving away from the base. Because the deflection gauge was mounted on the strongback, the test was useless and so it was ignored.
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0 500 1000 1500 2000 2500
Deflection (in
)
Applied Pressure (psi)
Deflection vs Pressure ‐ Fore/Aft on Base w/ Square Rod
Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Average
Fore/Aft Test Images
The images above are of the fore/aft testing configuration. The triangular structure on the right was a “strongback” that was designed to help apply the load. The yellow cylinder was the actuator and it had a .785in2 surface area – reading the pressure from a gauge allowed for the determination of the force applied. The base and strongback were clamped down to prevent movement and the pressure was applied to the pivot bar. In the top right, the silver circular gauge that can be seen above the actuator was the deflection gauge. The pin, seen against the flat metal plate, would move to the right and allowed for the deflection to be measured.
The two pictures shown above are images of the flanges of the base rising up when pressure was applied, as mentioned in the paper. This definitely contributed to the deflection and will require further investigation in the path forward.
M: Lateral Test Details (No Arm)
Run 1 Run 2 Run 3 Run 4 Average Std Dev 100 0.044 0.036 0.04 0.016 0.04 0.004 200 0.087 0.072 0.075 0.05 0.078 0.007937 300 0.116 0.107 0.125 0.097 0.116 0.009 400 0.158 0.147 0.145 0.138 0.15 0.007 500 0.197 0.176 0.183 0.18 0.185333 0.010693 600 0.24 0.218 0.22 0.22 0.226 0.012166 700 0.274 0.252 0.259 0.261667 0.01124 800 0.323 0.29 0.3 0.304333 0.016921 900 0.376 0.327 0.334 0.345667 0.026502
1000 0.447 0.376 0.376 0.399667 0.040992 1100 0.505 0.424 0.419 0.449333 0.048274 1200 0.575 0.482 0.477 0.511333 0.055194 1300 0.547 0.541 0.544 0.004243 1400 0.621 0.609 0.615 0.008485 1500 0.67 1600 0.72
Notes: Run4 shown here was with the square rod replaced with the pivot pin & single locking pin mechanism. The square rod had supports at both sides and was able to reach approximately twice the loading as the pivot pin & single locking pin mechanism, which only had support on one side. At 700 psi, there was a loud crack but no visible failure. We released the pressure and re‐applied it. At 600 the second time, there were multiple loud cracks but no visible failure. We stopped the test due to the noises.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 200 400 600 800 1000 1200 1400 1600 1800
Deflection (in
)
Pressure (psi)
Deflection vs Pressure ‐ Lateral On Base w/Square Rod
Run 1 Run 2 Run 3 Run 4 Average
Lateral Base Test Images
On the left, the lateral load configuration is shown with the square rod mentioned throughout the paper. The square rod provided lateral support at both the left and right pivot, so deformation of the base occurred at both the left and right sidewalls. The image shown above is with a load already applied, which explains the slant of the sidewall. On the right is the second configuration used for the lateral test – the square rod has been replaced with the prototype pivot rod and its lateral motion is prevented by the pin on the right support plate.
In the images above, progressive deflection of the left sidewall can be seen. The pressure is increased by 100 psi from each image to the next and the change in deflection can clearly be seen. Note that the right sidewall does not experience noticeable deflection in comparison with the first image in this section. During this loading sequence, there were loud cracks at 700 psi and in the loading sequence with the square rods, there were not audible cracks until 1600psi – the relationship is approximately half the strength. We believe this correlates to the fact that the square rod configuration allows for both sides of the base to support the load but with the pivot rod, only the left wall supports the load so there is half the amount of strength, based on the geometry of the fastener setup.
N: Lateral Test Details (w/Arm) # deflection # deflection # deflection # deflection # deflection
1 11 0.837 21 0.838 31 0.873 41 0.849 2 0.88 12 0.827 22 0.836 32 0.868 42 0.886 3 0.862 13 0.828 23 0.842 33 0.888 43 0.889 Average4 14 0.832 24 0.83 34 0.885 44 0.881 0.8612 5 15 0.843 25 0.86 35 0.887 45 0.893 STD Dev6 0.828 16 0.819 26 0.84 36 0.887 46 0.891 .0275 7 0.828 17 0.845 27 0.853 37 0.894 47 0.899 8 18 0.837 28 0.852 38 0.911 48 0.893 9 0.817 19 0.833 29 0.87 39 0.893 49 0.886
10 0.836 20 0.828 30 0.878 40 0.874 50 0.91
The arm & base combination structure was cycled at 500 psi for fifty cycles. Half of the applied load corresponds to 900 psi, but the deflection gauge could not measure deflection greater than at 500 psi. There is a definite trend towards greater deflection as the cycles proceed.
0.8
0.82
0.84
0.86
0.88
0.9
0.92
0 10 20 30 40 50 60
Deflection (in
)
Cycle Count
Deflection vs Cycle ‐ Lateral Loading w/Arm
Lateral Arm Test Images
The lateral arm & base test configuration is shown above. The arm was reaffixed to the base and the fake shock was attached to provide it vertical support. The actuator is poised to act on a wooden block clamped to the top of the arm because that was more representative of the force the structure would actually see, as opposed to applying the forces to one of the flanges of the arm. On the right, the wooden table was brought near the setup to give the deflection gauge a stable surface to measure the deflection from.
Images of the arm & base under a 500 psi loading are seen above. The back view, shown on the left, displays excessive deformation and indicates that a cap is necessary on the back end of the arm to prevent such deflections.
O: Test Plans For all tests, sources of error should be minimized. First, human error in reading the pressure gauge and the
deflection gauge must be considered, as well as the error caused by the accuracy of the pressure gauge and deflection gauge. Next, it is possible that the clamping configurations for the base and the strongback would be insufficient to withstand the force created by the actuator. If the base or strongback moves away from its original position, the deflection gauge data reads off incorrect data.
Load Direction Maximum (lbf) 50% Of Max (lbf) Maximum (psi) 50% of Max (psi) Fore/Aft on Base 3700 1850 4700 2350 Lateral on Base 1350 675 1700 850 Lateral on Arm 1350 675 1700 850
The conversion table above is used to relate the expected loads, shown in the second and third columns, to the applied pressures that the pressure gauge will read in each of the following test plans. The deflection as measured by a one inch deflection gauge is the output variable. The only factor in the experiments is the magnitude of the load – all other variables will be held constant. The hydraulic actuator has a surface area of .785in2 and the pressure that the actuator is applying is read out to a gauge. Dividing the expected force by the area gives the appropriate pressure to apply.
In all tests, the goal is to achieve the 50% of Max pressure value shown in the table above. However, the load should not be applied instantaneously – instead, the pressure should be ramped up by 10% of the final pressure each time. For example, in the Fore/Aft on Base test, an acceptable interval is 250psi. Thus, the test data would consist of deflection at 250psi, 500psi, …, 2000psi, and 2250psi. This also applies to the Lateral on Base load and the Lateral on Arm load ‐ the appropriate pressure interval for these tests is 100psi.
Also, in all tests, the actuator should be perpendicular to a flat face on which it will push in order to apply an orthogonal load to the structure. In addition, the deflection gauge must also be perpendicular to a flat face and must not be attached to any moving parts of the test like the strongback. Otherwise, the deflection readings will be affected by motion of the part it is attached to.
Base Fore/Aft Static Load The objective of this test is to analyze the deformation of the base when subjected to the expected fore/aft
loads. The base will be clamped down and a Simplex hand pump with hydraulic actuator will apply a pressure to a square rod replacing the pivot pin to create a flat face.
In order to prepare the base, it must be clamped down on all sides. The most important clamps will be the ones closest to the actuator as that portion of the base will “want” to lift up off of the table. Also, the actuator needs a flat face on which to apply pressure, so the pivot rod which allows the arm to rotate must be replaced by a square rod with the necessary flat face. In order for the actuator to push on the base without moving, it needs an equal and opposite force applied to it – this comes from the strongback which will hold the actuator in place. The actuator must be secured in its bed and the strongback must be adequately clamped down.
Base Lateral Load The objective is to analyze deformation of the base when subjected to the expected lateral loads. There are two configurations for this test: a square rod that bolts into the base can be used to simulate lateral support on both sidewalls of the base, and the pivot pin that allows rotation of the arm can be used to simulate lateral support only on one sidewall of the base. The necessary clamping configurations for the base and strongback still apply, but now the actuator should be aligned with the bolt in the hole or the pivot pin, depending on the selected test variation.
Base Arm Load The objective of the test is to analyze the deflection of the arm when attached to the base using the pivot pin. The setup involves a wooden block clamped at the far end of the arm with which the actuator is aligned. The actuator applies the force to the block because this configuration best simulates the load created by a rider experiencing a lateral force and transferring it to the arm through the seat.
Data Analysis The deflection data will be read off of the deflection gauge and recorded to a laptop to allow for instantaneous
visualization of the deflection as a function of applied pressure. Data analysis includes determining the type of curve that is produced – linear, exponential, parabolic, or any of the many potential relationships that could connect deflection and applied pressure. Also, the since the material properties of the prototype composite are not fully defined, the deflection data can be used with estimates of the moments of inertia to determine approximate values for the material’s tensile modulus. Finally, the data should be compared to the analytical predictions for deflection that the team calculated early in the design process.
P: Cost Analysis (Bill of Materials) The only item missing from the cost analysis shown here is the approximate cost of the ActiveShock, because the data was not available.
Cost Analysis (For Prototype) Item Cost ($) Per Unit Quantity Sub Total Materials Pro High Back Race Seats $ 34.99 Per Unit 1 $ 34.99 ActiveShock N/A Per Unit 1 N/A Bolts $ 2.64 Per Unit 16 $ 42.24 304 Steel Cylinder $ 79.92 Per Unit 2 $ 159.84 Support Plate w/ cylindrical extension $ 60.89 Per Unit 1 $ 60.89 Support plate $ 27.46 Per Unit 1 $ 27.46 Washer $ 3.25 Per Pack of 10 2 $ 6.50 Clevis Pins $ 4.77 Per Unit 2 $ 9.54 Pivot Pins $ 3.13 Per Unit 2 $ 6.26 Adhesive Bottle $ 13.09 Per Unit 2 $ 26.18 Adhesive Gun $ 40.80 Per Unit 1 $ 40.80 Adhesive Nozzle $ 13.76 Per Unit 1 $ 13.76 Pivot Rod $ 79.88 Per Unit 1 $ 79.88 Bushing $ 1.46 Per Unit 2 $ 2.92 Roll of Prepreg $ 3,000.00 Per Unit 1 $ 3,000.00 Arm Plug and Mold $ 9,000.00 Per Unit 1 $ 9,000.00 Base Plug and Mold $ 9,500.00 Per Unit 1 $ 9,500.00 Sub Total $ 22,011.26 Machining Machine shop $10.00 Per Hour 30 $300.00 Composite Labor $30.00 Per Hour 50 $1,500.00 Sub Total $1,800.00Testing Technician $50.00 Per Hour 60 $3,000.00 Cyclic Loading Machine $20.00 Per Hour 200 $4,000.00 Sub Total $7,000.00 Notes Total $30,811.26
Cost Analysis (Per Seat) Item Cost ($) Per Unit Quantity Sub Total Materials Pro High Back Race Seats $ 34.99 Per Unit 1 $ 34.99 ActiveShock N/A Per Unit 1 N/A Bolts $ 2.64 Per Unit 16 $ 42.24 304 Steel Cylinder $ 79.92 Per Unit 2 $ 159.84
Support Plate w/ cylindrical extension $ 60.89 Per Unit 1 $ 60.89
Support plate $ 27.46 Per Unit 1 $ 27.46 Washer $ 3.25 Per Pack of 10 2 $ 6.50 Pivot Pins $ 3.13 Per Unit 2 $ 6.26 Adhesive Bottle $ 13.09 Per Unit 2 $ 26.18 Adhesive Gun $ 40.80 Per Unit 1 $ 40.80 Adhesive Nozzle $ 13.76 Per Unit 1 $ 13.76 Pivot Rod $ 79.88 Per Unit 1 $ 79.88 Bushing $ 1.46 Per Unit 2 $ 2.92 Base Plug and Mold $ 9,500.00 Per Unit 1 $ 9,500.00 Clevis Pins $ 4.77 Per Unit 2 $ 9.54 Sub Total $10,011.26Machining Machine shop $50.00 Per Hour 20 $1,000.00 Composite Labor $30.00 Per Hour 50 $1,500.00 Sub Total $2,500.00 Total $12,511.26