Structure-modulus relationships for injection-molded long fiber-reinforced polyphthalamides

The structural information needed for modulus evaluation of long fiber-reinforced composites includes the fiber volume fraction, the modulus and the Poisson's ratio of the constituents, the fiber orientation and the fiber length distribution. In this work, the fiber orientation distribution is expressed in terms of three parameters which may vary with spatial location on the part: the average orientation angle on the surface, the average orientation angle on the mid-plane and the thickness of shell-core layers. With the independent evaluation of the fiber length distribution, composite models are used to evaluate mechanical property distribution such as modulus and Poisson's ratio as a function of spatial location on the part. The approach used in this work combines the Halpin-Tsai equations and a stiffness modeling scheme which follows a combination of iso-stress and iso-strain averaging techniques to determine the anisotropic material behavior of these composites. The predictions are compared with experimental data from injection-molded plaques fabricated at different processing conditions. Modulus variation with location is measured by fabricating dog-bone tensile samples from the plaques at four in-flow and four crossflow positions. Modulus variability is shown to be high with location and the model captures this non-uniformity over the whole range of tested samples. (C) 1998 Elsevier Science Limited. All rights reserved.