Fatigue performance of an injection-molded short E-glass fiber-reinforced polyamide 6,6. I. Effects of orientation, holes, and weld line

This article presents the experimental results of stress-controlled 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.