Failure analysis on a safety clip
Today's Knowledge Share: I completed a failure analysis on a safety clip, which had failed an impact test at -30 °C. The parts are specified to be able to withstand the cold temperature impact test, and the failures were of serious concern due to potential safety issues. The parts were injection molded from an unfilled, impact modified nylon 6/6 resin. The fractographic examination indicated that the cracking was initiated through a brittle fracture mechanism, characterized by a relatively high crack propagation rate, and a significant amount of driving energy. In particular, this was characterized by the presence of stepwise-cracking associated with crack bifurcation, as well as secondary cracking. Additionally, the fracture surface within the origin zone showed a very smooth morphology, without micro ductility. The observed features were indicative of a high level of energy within the fracture as it propagated from the origin. The fracture surface characteristics were cons...