Wikepedia, although not our usual reference source, does provide a useful definition of Forensic Engineering:

Forensic engineering is the investigation of materials, products, structures or components that fail or do not operate/function as intended, causing personal injury for example. The consequences of failure are dealt by the law of product liability. The subject is applied most commonly in civil law cases, although may be of use in criminal law cases. Generally the purpose of a forensic engineering investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident...