The External Peripheral Instrument for Deformation Measurement (EPIDM) system is composed of a sensing device and an analysis process which determines the complete geometric description of the periphery of a cross-section of a body as it deforms or is deformed in time. The sensing device is a band attached to the surface of the deformable body along the external peripheral path of the desired geometrical cross-section. The analysis process utilizes the output from strategically located sensors along the length of the band to calculate and develop the contour of the body to which it is attached.

The advantages of the EPIDM arc that it:​ (a) obtains all necessary information for the determination of the body's geometrical cross-section from the peripheral sensing band thus eliminating the need for invasive or penetrating deflection sensing devices, (b) determines the complete cross-sectional geometry of the body under observation as a function of time rather than discrete pairs of deflection data, and (c) generates an output that is directly relatable to the fundamental physical parameters associated with failure of structures.

The details of the operational theory and construction of the EPIDM system are discussed as are the experimental results documenting the system's accuracy and dynamic response characteristics. Procedures for developing explicit relationships between the output of the EPIDM system and classical material state variables defining a structural failure are discussed. These relationships are then used to illustrate how the EPIDM measurement system has the capability of developing universal, thoracic trauma indices capable of evaluating the safety potential for the variety of loading conditions that the thorax can experience in today's automotive crash environment.