Toughening mechanisms of rubber toughened PMMA

Toughening mechanisms of three types of rubber toughened poly (methyl metha crylate) (RT-PMMA) were investigated under mode I loading condition by opti cal and electron microscopies in conjunction with the quantitative evaluati on of mode I fracture toughness. Polarizing optical microscopy clearly exhi bited damage zone development ahead of a crack-tip in the RT-PMMA's. The th ree RT-PMMA's revealed different shapes of the damage zone. Transmission el ectron microscopy exhibited microcrazes generated in the equator of rubber particles within the damage zones. Extensive deformation of rubber particle s corresponding to localized shear yielding of the PMMA matrix was also fou nd in a region close to a propagating crack-tip. In addition, cavitation of rubber particles was observed in the vicinity of the crack. It is therefor e understood that the toughening of the RT-PMMA's is due to energy dissipat ion caused by the microdamage formations such as microcrazing, matrix shear deformation and rubber particle cavitation ahead of the crack-tip.