Deformation design for short‐fiber‐reinforced thermoplastics

Stiffness matrices are predicted, using the Halpin‐Tsai laminate analogy, at different locations in 4 short glass‐fiber‐reinforced thermoplastic moldings, and the resulting anisotropy and inhomogeneity discussed, relative to quasi‐isotropic values. The predictions are based on actual material structure as obtained from contact microradiographs. Considerable anisotropy and inhomogeneity are noted. The response of the materials to tensile, flexure, and shear loads is calculated and it is shown that this deviates to a lesser degree from a quasiisotropic response. Finally the load deformation behavior in plate bending and twisting are predicted using both a quasiisotropic model and the stiffness properties based on actual structure and compared with previously available experimental data. It is concluded that, in the absence of a predictive approach to fiber orientation in short‐glass‐fiber‐reinforced thermoplastic moldings, the use of quasi‐isotropic stiffness data provides an acceptable means of performing deformation design analysis. Based on the analysis of the moldings considered, the quasi‐isotropic assumption could be expected to introduce errors of less than 20 percent in deformation predictions for planar moldings.