A thermomechanical theory of impact trauma

Abstract

A review of injuries in impact trauma reveals a plethora of ‘injury criteria’, many of which are enshrined in legislation. It is assumed here that injuries can be modelled as mechanical dissipative processes, and the formalism of continuum damage mechanics based on irreversible thermodynamics is applied to impact trauma. It is shown that peak virtual power (PVP) predicts the severity of injury, measured on the abbreviated injury scale, in around 90 per cent of cases for all types of injury to all body regions (brain, skull, thorax, spine, upper and lower extremities) for car occupants from the CCIS and NASS-CDC databases. Consideration of injury to body regions shows that PVP predicts the form of acceleration-based criteria, the head injury criterion and the viscous criterion. It is shown that in general the lower bound of severity of injury is proportional to δV³ or (ETS)³, where ETS is equivalent test speed, for restrained vehicle occupants, and the upper bound proportional to δV² or (ETS)² for unrestrained occupants. It is concluded that PVP is a suitable candidate for an objective universal injury criterion which can be correlated to real-world injury experience.