A QUADRATIC YIELD FUNCTION FOR FIBER-REINFORCED COMPOSITES

A simple, 3-D yield function that is quadratic in stresses was propose d to describe the plastic behavior of fiber composites. It relaxes the two usually used assumptions that hydrostatic stress does not influen ce plastic deformation and that the total plastic dilatation is incomp ressible. It is also general in nature to allow for composites with va rious fiber volume fractions and different fiber arrays. The applicabi lity of this quadratic yield function to fiber composites was examined , and the accuracy of the elasto-plasticity model was verified by usin g the macro stress-strain data generated by a 3-D nonlinear micromecha nics model. Because this anisotropic plasticity model is simple and is in the general form of those widely used in existing numerical plasti city codes, it can easily be incorporated into the existing codes with little effort.