Materials can be divided into linear and nonlinear material.
Linear Material models are suitable for any analysis in which small strains are considered and deformation remains in the elastic region.
Nonlinear Material models (Elasto-plastic, Hyper-elastic) provide more complex material models for analysis in which model is submitted to plastic deformation.
For isotropic material, properties are identical in all directions. This is the most commonly used model. Isotropic Material can be chosen as linear, elasto-plastic, hyperelastic materials or temperature-dependant.
For anisotropic material, properties are directionally dependant, as opposed to isotropic material.
Orthotropic material is a specific case of anisotropic material which has two or three mutually orthogonal twofold axes of rotation symmetry so that its mechanical properties are different along each axis. (ex: wood, crystal)
For CFD analysis, special CFD materials for fluid or solid have to be used.
Rigid material is a special type of material which is used to simulate parts with a very high stiffness (almost rigid). Rigid material can save calculation time during the analysis. When using rigid materials, boundary conditions must be assign to only one node of the part.