Investigation of the effects of platelet morphology and flow conditions on the elastic behavior of discontinuous fiber composites

Abstract

In this work, the effects of platelet morphology and manufacturing flow conditions on the elastic behavior of discontinuous fiber composites are investigated. Two different platelet morphologies are explored: a narrow platelet and a square platelet with identical fiber lengths are used to manufacture specimens using two different processes to produce a quasi-isotropic low-flow condition, and a partially aligned high-flow condition. Three different specimen thicknesses are explored. Investigation of the elastic properties are carried out by means of tensile tests on unnotched specimens. This information is used to conduct a virtual study of the fiber orientation space by simulation with explicit modelling of the mesostructure and use of finite element analysis to determine the elastic properties. From the tensile testing it is observed that the thickness has negligible or slight impact on the longitudinal elastic moduli. However, the flow condition has a significant effect on the longitudinal elastic modulus, with low-flow specimens falling 9.2% to 22.5% below a quasi-isotropic reference, and high-flow specimens outperforming the quasi-isotropic reference from 0.8% to 3.7%. Platelet morphology is similarly tied to elastic modulus, with square platelet specimens consistently underperforming from 2.9% to 14.8% compared to narrow platelet specimens. An exploration of fiber orientation state is undertaken using microcomputed tomography. It is shown that flow condition has a significant effect on the orientation states in-plane and out-of-plane, with high-flow processes inducing significant longitudinal alignment. Simulations were undertaken which showed agreement within 2% for the elastic modulus seen in the experimental results, but significantly, with scatter much lower than that observed experimentally.