Seyyedvahid Mortazavian

Notch Effects on Fatigue Behavior of Thermoplastics

An experimental study was conducted to evaluate notch effects on fatigue behavior of a neat polymer (PP impact co-polymer) and a composite made of 30 wt% short glass fibers in polybutylene terephthalate (PBT). A plate-type specimen geometry with a central circular hole was used. The experiments were conducted at room temperature in uniaxial tension-tension (R = 0.1) and tension-compression (R = -1) loading conditions. Some analytical methods including Neubers rule and the method of critical distances were used in addition to FEA to predict fatigue life of notched specimens. Neubers rule commonly used for metallic materials proved to be an accurate method for predicting the notched fatigue life of the thermoplastics considered.

Tensile behavior and modeling of short fiber-reinforced polymer composites including temperature and strain rate effects:

An experimental study was conducted to investigate the effects of temperature and strain rate on tensile behavior of polybutylene terephthalate and polyamide-6 reinforced with short glass fibers. Tension tests were performed in several mold flow directions, at a range of temperatures between −40°C and 125°C, and a range of strain rates between 5 × 10−5 s−1 and 5 × 10−1 s−1. Mathematical relationships were developed to represent the stress–strain response, as well as tensile strength and elastic modulus in terms of strain rate and temperature. Time–temperature superposition principle was also employed to superimpose the effect of temperature and strain rate on tensile strength. A temperature-dependent shift factor of Arrhenius type is suggested, which is independent of the mold flow direction. Mechanisms of tensile failure were also identified from fractured surface of specimens.