Failure of components and products by ‘engineered-in’ defects: Case studies

Manufacturing necessitates the transformation of raw materials from their initial form into finished, functional products. This change is achieved by a variety of processes, each of which is designed to perform a specific function in the transformation process. Implicit within the design and operation of such processes is a required understanding of the properties of engineering materials and their specific response to such manufacturing methods. The design or process engineer will endeavour to positively utilise these properties during different stages of the manufacturing process. However, various defects can be ‘in-built’ during the transformation cycle, dependent on factors such as materials, part design, and processing techniques. It must be said that manufacturers do not intentionally set out to make faulty or dangerous products and almost always operate rigorous quality control and ‘burn-in’ procedures at the production line. It is therefore unusual for faulty products to enter service. However, on occasion faulty products do manage to slip through the most rigorous of checks and enter service. While some inherent defects affect only the appearance of parts, others can have major adverse influence on structural integrity and/or service lifetime of the component or product in question. At this point, the forensic (or failure) engineer may well be instructed to determine the cause or causes of such product demise. With potential litigation ever present, the focus of such investigation may well centre on foreseeability of the event, requiring sound findings and a conclusion that clearly describes what happened and why. To this end, a review of the major routes in the production of engineered components will be presented, highlighting the possibilities of introducing defects at each stage. Typical defects are freely illustrated by appropriate inputs taken from the author’s forensic casebook.