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# Simulation Mechanical and Multiphysics

#### Materials Library Models

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06/09/2017 4:27 PM

Hi, I am very new to Simulation Mechanical and was wondering what some of the material models in the 2017 program are used for. I just need someone to give a brief summary on each material model and maybe what it's used for. If that's not possible, any information would be much appreciated. Thanks,

Jim Gibson

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#### Re: Materials Library Models

06/09/2017 7:51 PM

Hi Jim. Welcome to Simulation Mechanical forum.

There are 28 material models in nonlinear/MES, and maybe a few other in the other analysis types. I doubt that you are interested in all of those, so let me describe the ones that are used most often. Then it is probably better if you ask "what material model do I use to simulate XYZ".

For everyone's benefit, a "material model" is simply the mathematics used to describe how a material responds to the load. You can think of it as the "stress-strain" behavior of the material. Does it have a linear stress-strain slope all the way to infinity? Does it yield before infinite strain? Is the material elastic (returns to the same shape when the load is removed) but the stress-strain curve is not linear?

In some cases, what is important is how the part will be deformed in the analysis, not how the part behaves in real life. A rubber material has a nonlinear but elastic stress-strain curve if you apply enough load. But if the analysis only takes it to X% strain, and if the stress-strain curve is practically linear in that range, then an isotropic material may be acceptable.

Also, it is necessary sometimes a use a more "complicated" material model in order to get some feature that you need for the analysis. For examples, you need to include thermal expansion in the analysis. Some analysis types only include thermal effects with a temperature dependent material model. Sometimes, you just need to poke around Help.)

So here are the common material models:

1. Isotropic - the material has the same linear stress-strain diagram in tension and compression all the way to infinity. It is elastic, so it returns to 0 displacement when the loads are removed. The strength is the same in all directions. Metals are a common example of an isotropic material as long as the stress is below the yield strength.
2. Orthotropic - the material has the same linear stress-strain curve in tension and compression all the way to infinity. It is elastic, so it returns to 0 displacement when the loads are removed. The strength is different in 3 perpendicular directions. Wood is a good example of an orthotropic material: the strength is strongest in the direction of the grain, and weaker is the two directions perpendicular to the grain. Some composite materials are orthotropic for the same reason (strong in the direction of the fibers, weak perpendicular to the fibers.)
3. Von Mises - the material has a linear stress-strain curve in tension and compression (same magnitude) up to the yield strength, followed by plastic deformation following a linear line or a series of linear lines (Von Mises Curve material model). If the yield strength is exceeded, there will be permanent deformation. This material model is only available in a nonlinear/MES analysis. Ductile metals follow the Von Mises material model.
4. Anisotropic - the material has a linear stress-strain curve in tension and compression all the way to infinity. It is elastic, so it returns to 0 displacement when the loads are removed. The strength is different in 3 directions that are not perpendicular to each other. Crystalline materials typically use an anisotropic material model.
5. Mooney-Rivlin, Arruda-Boyce, Blatz-Ko and Yeoh - material models for hyperelastic materials such as rubber. The stress-strain diagram is a curve. The material is elastic, so it returns to the same shape when the load is removed.
6. Composite - used for composite materials where each lamina (is that the right terminology?) has orthotropic material properties.

So, what would you like to analyze today?

John Holtz, P.E.
Technical Support Specialist
Customer Service & Support
Autodesk, Inc.

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