12Aug 2009 Use menu "View - Header & Footer" for Presentation title - Siglum - Reference...

Use menu "View - Header & Footer" for Presentation title - Siglum - Reference

12Aug 2009

Presentation on IsoTrussGeneral Applications

Event / Business Area (optional)

Presented by

John Cole

Weights Engineer

Month 200X Use menu "View - Header & Footer" for Presentation title - Siglum - Reference © A

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Note from the Presenter

• None of this material is meant to imply that this particular approach will be used by Airbus.

• Many new ideas are investigated on an ongoing basis and assessed on their individual merit for further development.


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IsoTruss® Efficiency

Concrete Block12,000 lb. (5440 kg)


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Introductory Comment on IsoTruss

"David Jensen and his colleagues recognized for a long time that the most efficient use of composite materials was to keep the fiber straight," explains Stanford professor Stephen W. Tsai, who worked on a similar concept called the IsoGrid (a NASA and McDonald Douglas–designed forerunner to the IsoTruss). "While their recognition of this fact was not unique, building a structure that could utilize it was indeed most outstanding."


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HISTORIC GRID STRUCTURES

Wellington Bomber Fuselage (World War II)


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HISTORIC GRID STRUCTURES

NASA & McDonnell Douglas Engineers

Invented 2-D IsoGrid Structure In

1960’s


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Extract from Green Design & Manufacturing

One of the structures in which NASA has made an investment is the IsoTruss grid structure, an extension of a two-dimensional “isogrid” concept originally developed at McDonnell Douglas Astronautics Company, under contract to NASA’s Marshall Space Flight Center in the early 1970s. IsoTruss is a lightweight and efficient alternative to monocoque composite structures, and can be produced in a manner that involves fairly simple techniques…………….


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IsoTruss® Pictures – Image of a Strut with Bonded Fork End Fittings

04/21/23 8Confidential


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TECHNOLOGY: DESIGN PARAMETERS

Number of Nodes

Truss Length

Outer Diameter

Bay Length

Member Diameter

Material Type

Truss Length

Bay Length

Outer Diameter

Longitudinal Members

Helical Members

6-Node IsoTruss® 8-Node IsoTruss® 10-Node IsoTruss® 12-Node IsoTruss®


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TECHNOLOGY

IsoTruss® Technology:

3-Dimensional Composite Grid Structure

Made From Continuous Unidirectional fibers

Typically Advance Composite Materials


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The IsoTruss® is a 3-dimensional, symmetric grid:• Longitudinal Members• Helical Members

Variations of the IsoTruss®:• Single-grid • Double-grid• Hybrid• IsoPanel • IsoBeam

Bay LengthHelical MembersLongitudinal Members

BackgroundBackground


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2 CFRP Wing Box Rib Concepts


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Drive Shaft


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• Overall Dimensions

• Member Diameters

• Curvature

• Configuration

IsoTruss® Panel Design Flexibility


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Typical Compression Failure Chart


Ultimate Load


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Mass and Static RF Summary of a long Strut – Buckling driven. Not including Bonded Fork Fittings

Mass 8.1352 kg

Design Load -337Kn

Connection 3

Consolidation Method 3

Number of Nodes N

Length L 222.20 cm 87.4803 in

Outer Diameter d 11 cm 4.33071 in

Bay Length b 12.000 cm 4.72441 in

Axial Load P 390.00 kN 87.68 kip

Torque T 150.00 kN*cm 13.28 kip*in

Moment M 250.00 kN*cm 22.13 kip*in

Geometry Input

Simultaneous Loading

10

Pinned-Pinned

Braiding

Axial Capacity PN 673.9500569 kN 151.51 kip

Torsional Capacity TN 4476.12 kN*cm 396.17 kip*in

Bending Capacity MN 2159.37 kN*cm 191.12 kip*in

Capacity (Uncombined Loading)

Modulus of Elasticity E1 202507.2954 MPa 29371.20 ksi

Global Buckling F.S.

Longi Local Buckling F.S.

Longi Material Strength F.S.

Longi Side Crushing F.S.

Heli Local Buckling F.S.

Heli Material Strength F.S.

Heli Side Crushing F.S.

Analysis Summary

7.46

1.72

25.48

2.06

113.38

71.26

24.95

Fiber 4

Resin 6

Fibers/Tow 8 9

Carbon M30

TCR UF3325

12k

Compressive Strength 1c 697.06 MPa 101.10 ksi

Aluminium equivalent approx 23kg

Longitudinal Tows NL

Fiber Volume Fraction Vf

224

0.68

Helical Tows NH

Fiber Volume Fraction Vf

56

0.68

In this instance the Strut is buckling Driven and will not approach max stress level

before failure

+ Fork Ends & bushes approx 1.2 kg


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Comparison with CFRP Conventional Rods

• The detail results are not shown, but comparison with conventional CFRP struts showed a weight saving of between 30% and 50% depending on which Material was selected. Very High Modulus material would probably be too brittle. 30% seems achievable even with a Low Modulus material of approx 157GPa. 40% saving using approx 200GPa material which is still a reasonably modest specification.

• The Design Load is the Ultimate Load ( Limit x 1.5). Current CFRP structural Rods use an additional factor of 1.25 as a Qualification load. Due to the inherent redundancy in IsoTruss an additional margin factor of 1.15 over Ultimate is assumed to be sufficient. Margin Policy to be agreed for this type of structure.

• All analysis has been carried by a Weights Engineer using a BYU developed process and is therefore not verified by the Structures department.


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Future Developments

• Analysis Methods – Non Linear Analysis development is needed for many applications.

• Manufacturing developments – Continuous high consistency structures.

• Pursuing the most optimised structures – Hybrid Isotruss with outer Longitudinal members. IsoBeam and IsoPanel configurations also have potential applications.


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Hybrid vs. Single-gridHybrid vs. Single-gridSecondary BendingSecondary Bending

Hybrid Members are 10% Smaller than Single-grid

Hybrid 20% Lighter than Single-grid

Hybrid is More Damage Tolerant than Single-grid


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Carbon/Epoxy HybridCarbon/Epoxy HybridBending ResultsBending Results

8-NodePrimary Bending

8-NodeSecondary

Bending

Note Hybrid Structures are more difficult to manufacture


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Physical Testing

• Advanced Composite Solutions have been recently carrying out impact testing and are acquiring knowledge of how the structure reacts from these tests.

• Various Static and Fatigue tests have been carried out over the last 15 years

• Among the various Thesis studies already done is one on Residual Strength after damage. This gives a good indication of the damage tolerance characteristics.


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Materials Selection

• The IsoTruss concept is unique because of its Geometry and the fact that it utilizes Composites in a way that allows the Fibre to remain straight.

• By this means very good performance is obtained from Standard Composite materials. The ideal material for a given application may vary. High Modulus materials give the best performance in terms of stiffness, but tend to be more brittle, so an environment where impact damage is likely is best suited to a stronger but less stiff material.


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Other Properties to address

• Thermal / Dissimilar Materials

• Corrosion / Aggressive Fluids

Damage Tolerance

• Fatigue

• Impact

• Testing



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Critical Composite Characteristics

• *Composite Modulus:T700/TCR UF3325: 157 GPaM50/TCR UF3325: 334 GPa

• Toughness:Typical Carbon Fiber issuesTruss geometry gives structural support even if one

element is gone/failed

*Modulus is function of fiber and resin properties



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Axial Stress

• P: Force

• A: Area of the longitudinals



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Local Buckling

• k: Boundary condition factor

• E: Young’s Modulus (material)

• I: Local moment of Inertia

• L: Local element length



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Global Buckling

• E: Young's Modulus (Materials)

• I: IsoTruss® moment of inertia

• L: Global length


Note: Smaller diameter may require more weight if failure mode is global buckling.


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Bending Stress

• M: Bending moment

• y: Distance from neutral axis

• I: IsoTruss® moment of inertia



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IsoTruss Analysis Tools

Mechanics of Materials• Put a simple load on a structure

• Define the load path

• Analyze and test results

Finite Element• Model & mesh

• Boundary conditions & loads

• Analysis



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12Aug 2009 Use menu "View - Header & Footer" for Presentation title - Siglum - Reference...

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