Forensic engineering

Forensic engineering is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The field also deals with retracing processes and procedures leading to accidents in operation of vehicles or machinery. The subject is applied most commonly in civil law cases, although it 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. It can also involve investigation of intellectual property claims, especially patents. History: As the field of engineering has evolved over time, so has the field of forensic engineering. Early examples include investigation of bridge failures such as the Tay rail bridge disaster of 1879 and the Dee bridge disaster of 1847. Many early rail accidents prompted the invention of tensile testing of samples and fractography of failed components. Investigation: Vital to the field of forensic engineering is the process of investigating and collecting data related to the materials, products, structures or components that failed. This involves inspections, collecting evidence, measurements, developing models, obtaining exemplar products, and performing experiments. Often testing and measurements are conducted in an Independent testing laboratory or other reputable unbiased laboratory. Analysis: Failure mode and effects analysis (FMEA) and fault tree analysis methods also examine product or process failure in a structured and systematic way, in the general context of safety engineering. However, all such techniques rely on accurate reporting of failure rates, and precise identification, of the failure modes involved. There is some common ground between forensic science and forensic engineering, such as scene of crime and scene of accident analysis, integrity of the evidence and court appearances. Both disciplines make extensive use of optical and scanning electron microscopes, for example. They also share common use of spectroscopy (infrared, ultraviolet, and nuclear magnetic resonance) to examine critical evidence. Radiography using X-rays (such as X-ray computed tomography), or neutrons is also very useful in examining thick products for their internal defects before destructive examination is attempted. Often, however, a simple hand lens may reveal the cause of a particular problem. Trace evidence is sometimes an important factor in reconstructing the sequence of events in an accident. For example, tire burn marks on a road surface can enable vehicle speeds to be estimated, when the brakes were applied and so on. Ladder feet often leave a trace of movement of the ladder during a slipaway, and may show how the accident occurred. When a product fails for no obvious reason, SEM and Energy-dispersive X‑ray spectroscopy (EDX) performed in the microscope can reveal the presence of aggressive chemicals that have left traces on the fracture or adjacent surfaces. Thus an acetal resin water pipe joint suddenly failed and caused substantial damages to a building in which it was situated. Analysis of the joint showed traces of chlorine, indicating a stress corrosion cracking failure mode. The failed fuel pipe junction mentioned above showed traces of sulfur on the fracture surface from the sulfuric acid, which had initiated the crack. Extracting physical evidence from digital photography is a major technique used in forensic accident reconstruction. Camera matching, photogrammetry, and photo rectification techniques are used to create three-dimensional and top-down views from the two-dimensional photos typically taken at an accident scene. Overlooked or undocumented evidence for accident reconstruction can be retrieved and quantified as long as photographs of such evidence are available. By using photographs of the accident scene including the vehicle, "lost" evidence can be recovered and accurately determined. Forensic materials engineering involves methods applied to specific materials, such as metals, glasses, ceramics, composites and polymers.