From a dipole lattice model, we derive a Boussinesq-type equation that governs the propagation
of a longitudinal strain wave in a uniform pre-strained bar with constant cross section. We then describe an
experiment based on high-speed, single-point photoelasticity to measure strain waves in a
Polymethylmethacrylate (PMMA) bar generated when it breaks whilst undergoing a tensile test. The
experimental results are finally compared to the model predictions, showing a good correspondence in terms
of wave propagation, strain rate at the leading edge and amplitude and frequency of the following ripple
