nOpen the ANSYS Help system, go to Mechanical APDL, Material Reference, Nonlinear Material Properties, 4.4 Rate-Independent Plasticity. There you can read more about these material models.nUsing a plasticity material model allows the simulation to compute the response of the structure to loads that take the material past the yield point. nBilinear means there are two straight lines, one is the elastic line, which is defined by Isotropic Elasticity, the other is the plastic line. You are correct that entering 0 for the Tangent modulus creates an Elastic-Perfectly Plastic material. This is often used because it is a conservative assumption.nMultilinear means there is more than one plastic line. It works much like the Bilinear model, but has the ability to follow a more complicated stress-strain curve. One item that makes using this a bit more difficult than Bilinear is that the Engineering Stress-Strain curve that is recorded when a material is tested in a Tensile Testing Machine is that the data has to be transformed to True Stress-True Strain before entering numbers in the Multilinear Plasticity material model.nIf you want to provide details about the material, geometry, supports and loads applied, we can look at the ANSYS model and the experimental data to help you validate your model.n