Volume change and light scattering during mechanical damage in polymethylmethacrylate toughened with core-shell rubber particles

Mechanical damage was investigated in polymethyl methacrylate toughened with core-shell (hard core) rubber particles. During a tensile experiment, volume changes, light absorption, right scattering and a small strain elastic modulus were recorded. Light scattering was quantitatively related to the number of damaged particles and a fast partial unloading technique allowed determination of the non-elastic part of these changes in material properties. Experiments performed between 10(-5) and 10(-1) s(-1) and between 20 and 70 degrees C showed time-temperature transitions. These appeared to be different for each property, and measurement of the activation energy for each parameter enabled microscopic damage mechanisms to be inferred. Three types of microstructural damage were observed: pure matrix plasticity at very low strain rates or high temperatures, rubber cavitation at correlated locations at medium strain rates and temperatures, and disordered cavitation, rubber tearing and matrix plasticity at high strain rates or low temperatures. The experimental mean stress triggering rubber cavitation was compared with the predicted value.