Evaluation of Polymer Fatigue Strength and Durability

This technical report evaluates the fatigue strength and durability of NORYL 731 polymer samples subjected to cyclic loading and examines the effects of manufacturing artifacts, particularly knit lines. The study highlights the critical need for fatigue testing in material selection, as polymers typically exhibit lower fatigue strength compared to their tensile strength. The report details the experimental setup, including the injection molding of samples using single and dual gate designs, and outlines the methods employed for tensile and fatigue testing. Results indicate that while the modulus of the samples remained largely unchanged, the dual gate samples demonstrated a significant reduction in elongation at break and fatigue life compared to single gate samples. Specifically, single gate samples achieved 30,000 cycles at 50% of their ultimate tensile strength, whereas dual gate samples only reached 6,000 cycles. The findings underscore the importance of considering fatigue performance during the early stages of product development to prevent costly failures later in the design cycle.