1. Preamble

The study of the behavior of materials and structures subjected to dynamic stress, or the analysis of the deformations of machines in operation (e.g. automobile engines), is usually carried out using sensors that provide highly sensitive point contact measurements (accelerometers, strain gauges, etc.). Validation of calculation codes using this type of sensor can sometimes prove to be erroneous. Figure 1 shows a holographic strain map of a thin composite plate impacted at its center by a steel ball. The very marked asymmetry of the deformation (right-hand side in the photograph) is due to an accelerometer placed on the plate to ensure synchronization of the double ruby laser pulse with the dynamic displacement induced by the impact. We can imagine what...