Applications of microscopy to the deformation and fracture of rubber-toughened polymers

The principal mechanisms of inelastic deformation in rubber-toughened plastics, and in other similar multiphase polymers, are shear yielding and multiple crazing in the rigid matrix phase, and cavitation in the soft disperse phase. Microscopy has played a very important part in the identification and study of these mechanisms. However, no one technique has been predominant. Polarized-light microscopy is useful for observing crazing, and has proved to be the most effective method for studying shear yielding, whereas transmission electron microscopy has provided valuable insights into the cavitation behaviour of complex rubber particles. Scanning electron microscopy has made significant contributions in the study of all three micromechanisms. In some microscopy investigations, thin sections have been strained in situ on the microscope stage. In others, specimens have been deformed in the bulk state before being polished and etched, or stained and microtomed, or coated with a thin layer of metal, in preparation for examination in the microscope. The importance of combining microscopy with other, complementary methods for studying deformation micromechanics is emphasized, and two novel methods for detecting cavitation in multiphase polymers are discussed briefly.