Failure Prediction for Polymer Products with Short Fiber

Polymers have been often used as structural materials under mechanically severe conditions instead of metals. We usually use FEM simulation when we design polymer products. The failure prediction of impact is especially important because its effect for reduction of development duration and number of trial products cannot be disregarded. The failure prediction has been investigated for a long time [1][2]. We generally start impact simulations using elasto-plastic material such as MAT_024 by giving stress-strain curves with strain rate dependency. We often add our own research achievement about material model by the user defined material models which LS-DYNA offers us to improve prediction accuracy. We developed the isotropic material model based on damage of polymers and introduced it into LS-DYNA by using user subroutine “*MAT_041-050”. We found many good coincidences between experimental impact test and numerical results with our material model. After that, we found the reason why we got good coincidence by simulation with isotropic material model was that glass fibers in the structural specimen of these experimental tests align well at the impact area. Therefore, we decided to start simulations for structural specimens with various fiber distributions. Differences between the isotropic simulation results and anisotropic results are recognized. The importance for taking fiber orientation into account in impact simulations is known [3]. Then, we conducted the experimental impact tests using structural specimen made of Polyamide 66 with 35 weight% short fiber (ASAHI-KASEI LeonaTM 14G35). We set different fiber distribution by giving two gate types in injection molding. In this paper, the effect of introducing fiber distribution is discussed.