## Materials

#### FRP plasticity

• Venugopalb
Subscriber

Hello all,

I have used "multilinear isotropic hardening" as material nonlinearity for my steel structure. Now I want to add a material nonlinearity for my FRP composite structure....

I want to know whether material nonlinearity exists in FRP composite structures. If exists, which available material nonlinearity model in Ansys is suitable for FRP composite structures.

What are orthotopic stress and strain limits? why we need to include these properties in the structural analysis of FRP composite structures.

For isotropic material, the stress-strain curve is considered material non-linearity. Here, there are no direction-dependent properties. So, we can directly use multilinear isotropic hardening. But, in the case of orthotropic material, in each direction, we have different properties as well as stress-strain curves. Which directions curve we have used as material non-linearity.

Finally, what is the significance of material nonlinearity in isotropic and composite materials?

• Sheldon Imaoka
Ansys Employee

For your question on nonlinear behavior of FRP composites, while there are such effects present, but what you should consider is whether or not such nonlinear effects are important to your analysis objectives. For example, if you don't want your FRP composite structures to undergo nonlinear response, you can use failure criteria with orthotropic linear elastic material definition, for example, to determine the appropriate factors of safety for your design.
Composite failure can be quite complex, but there are damage models available in Ansys Mechanical to account for damage and anisotropic behavior. It may be useful to review texts on composites if you are not familiar with orthotropic stress/strain limits, but the idea is that you have different strengths in different directions (e.g., aligned with fiber orientation, for example). There may be different modes of failure (e.g., fiber failure, matrix failure, separation), and this can be accounted for by different failure criteria, where max strain or max stress criteria are simple ones, but one should have an understanding of possible modes of failure and how to account for that first, as that will help you determine which material models and/or failure criteria are suitable for your analysis purposes.
Regards Sheldon

• Venugopalb
Subscriber
Thank you very much