Can You Perform a Static Study on Plastic Materials?

Let’s review of one of the rules when performing a linear static analysis.  Taken from the Solidworks 2019 Help

So the material has to be linear.  We see that when selecting the material for our study the material type is linear, elastic and isotropic.

For a linear material model we enter one value for the Elastic modulus so it must remain constant for Solidworks to be able to calculate accurate results.  The Elastic modulus is the gradient of the stress V’s strain graph for the material so the graph must be straight.

Material like steel behave linearly up to the yield point so we know as long as we are under the yield stress the elastic modulus is constant.  Plastics however do not perform linearly like steel.

Here we can see that the linear proportion of the purple plastic curve is much shorter than for green steel.  Steel is generally linear up to the yield point but most plastics have a significant nonlinear elastic response before yield is reached which may require a nonlinear analysis.  You need to identify the point at which the material becomes nonlinear and only use results up to this point.

Not only do the properties for a given polymer vary from manufacturer to manufacturer, they vary due changes in temperature, strain rate, orientation and a host of other things. This applies to the input properties as well as the failure quantities.

The moral of the story is know your material.  Don’t blindly use the ones from the Solidworks material library.  Research the Stress-Strain curve for your material so you can understand when a static study with linear material is valid.

Bianca Roberts
Applications Engineer
Central Innovation, Melbourne

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