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This article presents the experimental results of stresscontrolled fatigue tests of an injection-molded 33 wt% short E-glass fiber-reinforced polyamide 6,6. The effects of specimen orientation with respect to the flow direction, hole stress concentration, and weld line on the fatigue life have been considered. In addition, the effect of cyclic frequency has been examined. In addition to the modulus and tensile strength, the fatigue strength of the material was significantly higher in the flow direction than normal to the flow direction, indicating inherent anisotropy of the material caused by flow-induced orientation of fibers. The presence of weld line reduced the modulus, tensile strength, failure strain, and fatigue strength. The fatigue strength of specimens with a hole was lower than that of un-notched specimens, but was insensitive to the hole diameter. At cyclic frequencies ≤ 2 Hz, failure was due to fatigue, and fatigue life increased with frequency. However, at cyclic frequencies > 2 Hz, the failure mode was a mixture of fatigue and thermal failures, and fatigue life decreased with increasing frequency. POLYM. COMPOS., 27:230 -237, 2006.

Tensile behavior of extruded short E-glass fiber reinforced polyamide-6 composite sheet has been determined at different temperatures (21.5"C, 50°C 75°C 100°C) and Merent strain rates (O.O5/min, 0.5/min, 5/min). Experimental results show that this composite is a strain rate and temperature dependent material. Both elastic modulus and tensile strength of the composite increased with strain rate and decreased with temperature. Experimental results also show that strain rate sensitivity and temperature sensitivity of this composite change at a temperature between 25°C and 50°C as a result of the glass transition of the polyamide-6 matrix. Based on the experimental stress-strain curves, a two-parameter strain rate and temperature dependent constitutive model has been established to describe the tensile behavior of short fiber reinforced polyamide-6 composite. The parameters in this model are a stress exponent n and a stress coefficient u*. It is shown that the stress exponent n, which controls the strain rate strengthening effect and the strain hardening effect of the composite, is not only strain rate independent but also temperature independent. The stress exponent u*, on the other hand, varies with both strain rate and temperature.

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