Abstract

In this contribution the mechanical behavior of a short glass fiber reinforced thermoplastic under creep loading is modeled. To do this, an elastic-plastic-viscoplastic model is taken and its parameter are adapted on quasistatic as well as creep experiments. As starting constitutive model, an isotropic one is chosen. It consists of a linear elastic model and a rate-independent plastic model with piecewise linear isotropic hardening. In order to account for the creep flow, the elastic-plastic model is supplemented by a vicoplastic (creep) model with power law stress dependency of the flow and isotropic strain hardening. In the next step, the isotropic model is enhanced by anisotropy. This is done to account for the characteristic anisotropic behavior of short fiber reinforced thermoplastics that comes from the orientation of the fibers developing during the injection molding process. In order to adapt the parameter of the constitutive model, uniaxial tensile quasistatic and creep experiments on dog bone shaped specimen are performed. The specimen are cut out of 120 mm x 80 mm x 2 mm injection molded plates: on the one hand aligned with the main flow direction (0°) and on the other hand transversal to the main flow direction (90°). First, 0°- and 90°-specimen are tested under quasistatic loading showing the typical higher stiffness and strength in the stress-strain response of the 0°-samples compared to the 90°-ones. Second, both types of specimen are tested under creep loading where the prescribed force is applied within seconds and then kept constant over many hours. This is done for several different load levels where the typical stress dependency of the creep flow is observed. As expected, creep flow appears at lower load levels for the 90°-samples. Finally, the capability of the model with the adapted parameter is tested on creep experiments of a semi-complex bottle-type demonstrator part at different load levels.