Plastic Failure Analysis

Plastics failure expert performs a root cause failure analysis on a plastic automobile door handle. The handle is from a van's sliding side door. The product failure occured when the user was trying to close the van's sliding door. This is a products liability issue because the handle failed in a brittle manner and a personal injury occured. The lower photograph is of the handle assembly after it was removed from the vehicle. The two arrows point to the two fracture surfaces on the broken handle. The upper photograph is of the fracture surface on the handle piece that came free. The failure started as a fatigue crack (see arrow). It initiated at a molding defect similar to the one indicated by the second arrow on the left of the photograph. Molding defects are manufacturing defects caused by improper molding conditions. The molding defect created a stress riser allowing crack initiation. The crack progressed due to fatigue. The final failure mode was overload, and it was mostly a brittle failure.