1 Basic-Piston Ring.pdf

Piston Ring

Problem:A cast-iron piston ring has a mean diameter of 81 mm, a radial height of h = 6 mm, anda thickness b = 4 mm. The ring is assembled using an expansion tool which separates thesplit ends a distance delta by applying a force F shown. Determine the deflection, delta,as a function of the force, F. Use E = 131 GPa.

Joseph Shigley and Charles Mischke. Mechanical Engineering Design5thed. New York: McGraw Hill, May 2002.

Piston RingOverview

Outcomes1) Learn how to start Ansys 8.0 2) Gain familiarity with the graphical user interface (GUI)3) Learn how to create and mesh a simple geometry4) Learn how to apply boundary constraints and solve problems

Tutorial OverviewThis tutorial is divided into six parts:

1) Tutorial Basics2) Starting Ansys3) Preprocessing4) Solution5) Post-Processing6) Hand Calculations

Anticipated time to complete this tutorial: 1 hour

AudienceThis tutorial assumes minimal knowledge of ANSYS 8.0; therefore, it goes into moderatedetail to explain each step. More advanced ANSYS 8.0 users should be able to completethis tutorial fairly quickly.

Prerequisites1) ANSYS 8.0 in house “Structural Tutorial”

Objectives1) Learn how to define keypoints, lines, and elements 2) Learn how to apply structural constraints and loads 3) Learn how to find and interpret nodal solutions4) Use parameters in the modeling process.

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Piston RingTutorial Basics

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In this tutorial:Instructions appear on the left.

Visual aids corresponding to the textappear on the right.

All commands on the toolbars arelabeled. However, only operationsapplicable to the tutorial are explained.

The instructions should be used as follows:

Bold > Text in bold are buttons, options, or selections that the user needs to click on

Example: Preprocessor > Element Type > Add/Edit/DeleteFile would mean to follow the options as shown to the right to get you to the Element Types window

Italics Text in italics are hints and notes

MB1 Click on the left mouse buttonMB2 Click on the middle mouse

buttonMB3 Click on the right mouse

button

Some Basic ANSYS functions are:

To rotate the models use Ctrl and MB3.

To zoom use Ctrl and MB2 and move themouse up and down.

To translate the models use Ctrl and MB1.

Piston RingStarting Ansys

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For this tutorial the windows version ofANSYS 8.0 will be demonstrated. The pathbelow is one example of how to accessANSYS; however, this path will not be thesame on all computers.

For Windows XP start ANSYS by eitherusing:

> Start > All Programs > ANSYS 8.0> ANSYSor the desktop icon (right) if present.

Note: The path to start ANSYS 8.0 may be different foreach computer. Check with your local network manager tofind out how to start ANSYS 8.0.


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Once ANSYS 8.0 is loaded, two separatewindows appear: the main ANSYSAdvanced Utility window and the ANSYSOutput window.

The ANSYS Advanced Utility window,also known as the Graphical User Interface(GUI), is the location where all the userinterface takes place.

The Output Window documents all actionstaken, displays errors, and solver status.

Graphical User Interface

Output Window


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The main utility window can be broken upinto three areas. A short explanation of eachwill be given.

First is the Utility Toolbar:

From this toolbar you can use the commandline approach to ANSYS and access multiplemenus that you can’t get to from the mainmenu.

Note: It would be beneficial to take some time and explorethese pull down menus and familiarize yourself with them.

Second, is the ANSYS Main Menu, asshown to the right. This menu is designedto use a top down approach and contains allthe steps and options necessary to properlypreprocess, solve, and postprocess a model.

Third is the Graphical Interface windowwhere all geometry, boundary conditions,and results are displayed.

The tool bar located on the right hand sidehas all the visual orientation tools that areneeded to manipulate your model.


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With ANSYS 8.0 open select> File > Change Jobname

and enter a new job name in the blank fieldof the change jobname window.

Enter the problem title for this tutorial.> OK

In order to know where all the output filesfrom ANSYS will be placed, the workingdirectory must be set, in order to avoidusing the default folder C:\Documents andSettings.

> File > Change Directory > then select the location that you wantall of the ANSYS files to be saved.

Be sure to change the working directory atthe beginning of every problem.

With the jobname and directory set, theANSYS database (.db) file can be given atitle. Following the same steps as you didto change the jobname and the directory,give the model a title.

Piston RingPreprocessing

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To begin the analysis, a preference needs tobe set. Preferences allow you to apply filter-ing to the menu choices; Ansys will removeor gray out functions that are not needed. Astructural analysis, for example, will notneed all the options available for a thermal,electromagnetic, or fluid dynamic analysis.

> Main Menu > Preferences

Place a check mark next to the Structuralbox.

> OK

Look at the ANSYS Main Menu. Click onceon the “+” sign next to Preprocessor.

> Main Menu > Preprocessor

The Preprocessor options currently avail-able are displayed in the expansion of theMain Menu tree as shown to the right. Themost important preprocessing functions aredefining the element type, defining real con-straints and material properties, and model-ing and meshing the geometry.


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The ANSYS Main Menu is designed in sucha way that you should start at the beginningand work towards the bottom of the menuin preparing, solving, and analyzing yourmodel.

Note: This procedure will be shown throughout the tuto-rial.

Select the “+” next to Element Type or clickon Element Type. The extension of themenu is shown to the right.

> Element Type

Select Add/Edit/Delete and the ElementType window appears. Select add and theLibrary of Element Types window appears.

> Add/Edit/Delete > Add

In this window, select the types of elementsto be defined and used for the problem. Fora pictorial description of what each elementcan be used for, click on the Help button.

For this model 3D Elastic Beam elementswill be used.

> Beam > 3D Elastic 4> OK

In the Element Types window Type 1Beam4 should be visible signaling that theelement type has been chosen.

Close the Element Types window.> Close


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The properties for the Beam4 element needto be chosen. This is done by adding RealConstants.

> Preprocessor > Real Constants > Add/Edit/Delete

The Real Constants window should appear.Select add to create a new set.

> Add

The Element Type for Real Constants win-dow should appear. From this window,select Beam 4 as the element type.

> Type 1 Beam4 > OK

The Real Constant Set for Beam4 windowwill appear. From this window you caninteractively customize the elementtype.

From the problem statement thecross-sectional area is 24, the Areamoment of inertia IZZ is 72 and theArea moment of inertia IYY is 32.The thickness along the z and y axisalso need to be specified.

Enter the values into the table asshown at the right.

> OK

Close the Real Constants window.> Close


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The material properties for the Beam4 ele-ment need to be defined.

> Preprocessor > Material Props > Material Models

The Define Material Models Behavior win-dow should now be open.

We will use isotropic, linearly, elastic, struc-tural properties.

Select the following from the MaterialModels Available window:

> Structural > Linear > Elastic > Isotropic

The window titled Linear IsotropicProperties for Material Number 1 nowappears.

Enter 131e3 for EX (Young's Modulus) and0.211 for PRXY (Poission’s Ratio).

> OK

Close the Define Material Model Behaviorwindow.

> Material > Exit


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The next step is to create an arc of 180degrees.

> Preprocessor > Modeling> Create > Lines > Arcs> By Cent & Radius

The Arc by Center & Radius windowshould appear. You will enter two WP loca-tion.

In the white box below Global Cartesian,enter 0 and press enter on the keyboard.Then enter 40.5 and press enter on the key-board.

Enter 180 into the Arc length in degreesfield.

> OK

The arc should appear similar as shownbelow.


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Now that the model has been created, itneeds to be meshed. Models must bemeshed before they can be solved. Modelsare meshed with elements.

First, the element size needs to be specified.> Preprocessing > Meshing > Size Cntrls > Manual Size > Lines > All Lines

The Element Sizes on All SelectedLines window should appear. Fromthis window, the number of divisionsper element can be defined and also theelement edge length.

Enter 50 into the Number of elementdivisions field.

> OK

Note: you could change the number of element divisionafter completing the tutorial to a different value and rerunthe solution to see how it affects the results.

With the mesh parameters complete, thelines representing the beam can now bemeshed. Select:

> Preprocessing > Meshing > Mesh > Lines

From the Mesh Lines window select PickAll.

> Pick all

Selecting Pick all will mesh all ofthe line segments that have beencreated.

The meshed line should appearsimilar to the one shown below.This completes the preprocessingphase.

Piston RingSolution

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We will now move into the solution phase.

Before applying the loads and constraints tothe beam, we will select to start a new analy-sis:

> Solution > Analysis Type > New Analysis

For type of analysis select static and selectOK.

The constraints and forces will now beadded. It will be easier to do so if the key-point numbers are turned on.

To turn on keypoint numbers, from themain menu select:

> PlotCtrls > Numbering > Check the box to turn the keypointnumbers on > OK

However, the current view probably showsjust the elements and not the keypoints. Youcan see both the elements and the keypointson the screen by selecting:

> Plot > Multiplots

To see just the keypoints;> Plot > Keypoints > Keypoints

Use the plot menu to viewyour model in the waythat will make it easier tocomplete each step intutorial.

Piston RingSolution

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For this problem, the left end of the beam isconstrained from moving in the X and Ydirections and from rotating about the Zaxis. There is an additional constraintrestricting motion in the Y direction at key-point 3.

To apply constraints select:> Solution > Define Loads > Apply> Structural > Displacement> On Keypoints

The Apply U, ROT on KP’s window nowappears.

With the Apply U, ROT on KP’s windowopen select KP 3 from the ANSYS graphicswindow.

> Apply

The Apply U, ROT on KP’s large windowshould appear. From this window thedegrees of freedom can be specified. To theright of DOFs to be constrained select AllDOF.

> OK.

The constraints now appear at the locationof keypoint 3.

Piston RingSolution

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The load will now be applied to the ring.> Solutions > Define Loads > Apply> Structural > Force/Moment> On Keypoints

The Apply F/M on KP’s window shouldappear.

Select KP 1 (far right) in the graphics win-dow.

> Apply

The expanded Apply F/M on KP’s windowshould appear. From this window the direc-tion of the force and its magnitude can bespecified.

Pick FY for the direction of the force. Enter1 in the Force/moment value field whichwill apply a 1 lb force upward.

Verify that all the fields match those ofthe figure shown to the right.

> OK

The fully loaded and constrainedmodel should appear similar to thepicture shown below.

Piston RingSolution

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If you wish to view a 3D picture of yourmodel select:

> Plot Controls > Style > Size and Shape

The Size and Shape window opens. Clickthe check box next to Display of element toturn on the 3D image.

Now when you rotate your model usingCTRL + MB3 , the model should appear tobe 3D. You should see something similar tothe image below.

You are now ready to solve the model.

Piston RingSolution

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The next step is to solve the current loadstep that has been created. Select:

Solution > Solve > Current LS

The Solve Current Load Step window willappear. To begin the analysis select OK.

If a Verify window appearstelling that the load data pro-duced 1 warning, just selectYes to proceed with the solu-tion.

The analysis should begin and whencomplete a Note window should appearthat states the analysis is done.

Close both the Note window and /STA-TUS Command window.

If your model is still in the 3-D view use theview icons on the right of the screen to bringthe model to a front view again.

Piston RingPost Processing

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From the ANSYS Main Menu select:> General Postproc> Results Viewer

The maximum displacement where theforce is applied will be estimated as request-ed in the problem statement. To obtain thevertical displacement, select Nodal solution,DOF Solution and Displacement vectorsum.

> Nodal solution > DOF Solution> Displacement vector sum

Select the contour from the drop menu andthen select the plot results button to plot thecontours.

If you did not do it already, turn on the ele-ments shapes.

> PlotCtrls > Style > Size and Shape

Select the Display of element box On> On


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The contour results should appear as shownbelow.

Select the Query result icon (right by theplot results button) and select the inner edgeof the far bottom right element.

The answer will appear near the pointselected.

In this case, .034.


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To finish the problem we need to interpretthe result.

If there were two open ends (for this tutori-al), the displacement of the two open endswould be approximately 0.034 and 0.034.

Sum both displacements and then divide bythe applied force of 1 N using kN.

0.0668/0.001 = 66.8mm.

Compare this to the answer to the handcalculations shown on the next page.

Therefore for every 1 kN of force applied tothe ring the ends will displace about 66.8mm.

Piston RingHand Calculations

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mmkNF

FmmF

mmR

mmbhI

EIFR

dFREI

dFMMR

EIFU

RFM

FRMhRU

EIRdMU

4.661

4.66)72(131)5.40(3

5.40281

7212

)6(412

3

)cos1(22

)cos1(

)cos1(10/

22

3

433

30

23

0

0

2

==

==

==

===

=

−=∂∂=

∂∂=

−=∂∂

−=>→

=

∫∫

∫

δ

πδ

πδ

θθθδ

θ

θ

θ

ππ

π

1 Basic-Piston Ring.pdf

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