Anisotropy in sheet molding compounds during compression molding

Abstract This paper deals with an improved mathematical description of the anisotropic behavior of chopped fiber reinforced polymer composites, SMC (sheet molding compound). The material possesses isotropy in its planar direction and anisotropy normal to its plane. Axisymmetric compression and plane strain compression moldings are simulated via uniaxial compression testing and biaxial compression testing, respectively. Flow stresses and anisotropic parameters are obtained by solving nonlinear algebraic equations which are derived from a modified anisotropic flow rule and the constrained condition of the anisotropic parameters, together with two sets of experimental data curves. The solutions were obtained via nonlinear iteration. The results show that the SMC possesses anisotropic behavior, and the anisotropic parameters vary during compression processing. It is also shown that the effective strain‐rate plays an important role in the flow stress. Numerical simulation of short‐fiber composite compression molding is easily implemented by use of our derived relationships of flow stress and anisotropic parameters as functions of strain‐rate and strain.