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.

Beer Bottle Impact Failure Analysis

Glass failure expert analyzed a failed beer bottle to determine if there was a product defect. It was stated that the bottle exploded when it was put into a cooler filled with ice. The failure analysis revealed that the bottle had been hit with a sharp object. The photograph on the left is the bottle after re-assembly. The photograph in the center is a closeup of the failure origin from the outside of the bottle, The photo on the right is the failure origin from the inside of the bottle. The hertzian cone from the impact is readily visible. It is obvious that this bottle broke after it was hit on the side. Thus there are no product liability issues or manufacturing defects associated with this failure.

Manufacturing Engineer and Product Liability

Product Liability, Design Defects and Manufacturing Defects are obvious arenas for an experienced manufacturing engineer or process engineer. He has the insight to best evaluate manufacturing defects in product liability cases. Naturally, he must first perform a complete root cause failure analysis to determine if there was product misuse, a manufacturing defect or a design defect. Naturally it is a benifit if the chosen engineer has experience with similar products, materials and processes in question. This is an asset because he can relate the defect back to a specific process step. In addition, he will be familiar with what is necessary for correct product development. An example is a case where a product failed after a short time in service. He is best qualified to determine if the product or process development procedures were thorough and proper. For example, he can determine if the proper accelerated life tests were performed to determine the product performance over its expected lifetime. Product development and process development usually occur in four stages: concept, bread board, pilot production and full production. An important aspect of this cycle is to determine if there are potential circumstances during normal use that might cause product failure and/or personnel injury. Documented tests must be performed to prove that the hypothetical degradation mechanisms do not cause premature product failure. If this is not done, an unreliable or dangerous product (i.e. poor product safety) may be put on the market. An experienced manufacturing engineer is the best prepared to determine if the product was properly developed to allow for proper product quality. This insight can only be gained from direct hands on manufacturing experience.