A quadratic yield function for fiber-reinforced composites

A simple, 3-D yield function that is quadratic in stresses was proposed to describe the plastic behavior of fiber composites. It relaxes the two usually used assumptions that hydrostatic stress does not influence plastic deformation and that the total plastic dilatation is incompressible. It is also general in nature to allow for composites with various fiber volume fractions and different fiber arrays. The applicability of this quadratic yield function to fiber composites was examined, and the accuracy of the elasto-plasticity model was verified by using the macro stress-strain data generated by a 3-D nonlinear micromechanics model. Because this anisotropic plasticity model is simple and is in the general form of those widely used in existing numerical plasticity codes, it can easily be incorporated into the existing codes with little effort.