Crazing and fatigue of poly(methyl methacrylate) due to case II diffusion of methanol

Abstract

Static torsion and dynamic fatigue tests were performed on poly(methyl methacrylate) in methanol at room temperature using solid cylindrical specimens which had previously been soaked in methanol for various periods. Presoaking for times in the range 8–96 h brought about dramatic increases in both the critical torsional moment for crazing and the fatigue lifetime. The latter, for instance, attained a value 10 4 times that of the specimen without presoaking. Presoaking for longer times, however, allowed shear flow to occur prior to crazing, and contributed less to the increase in fatigue life. These results are explained in terms of both the softening of matter and the generation of internal compressive stress in the swollen surface layer following the case II diffusion of methanol.