Iosipescu shear deformation and fracture in model thermoplastic polyolefins

Shear deformation and fracture behaviors in polypropylene (PP)-based model thermoplastic polyolefins (TPOs) were investigated with the Iosipescu shear test. The shear deformation process was monitored in situ via video camera to obtain experimental shear stress-strain curves of model TPOs. Shear fra cture mechanisms were studied with optical microscopy and scanning electron microscopy. Macroscopically, the cracks in neat PP propagated along the ma ximum shear plane, which indicated that mode-II shear failure existed in ne at PP. Microscopically, it was shown that shear fracture initiated in the f orm of partial, discontinuous inclined microcracks that later coalesced and formed the final continuous crack. The incorporation of rubber in PP could transform the shear fracture process into a stretching process in the shea r damage zone. (C) 2001 John Wiley & Sons, Inc.