A CRITERION FOR CRACK INITIATION IN GLASSY-POLYMERS SUBJECTED TO A COMPOSITE-LIKE STRESS STATE

Three epoxy systems of interest as composite matrix materials are exam ined for their yielding and failure behavior under uniaxial, biaxial a nd triaxial stress states. Yield criteria applicable to glassy polymer s, i.e. accounting for the hydrostatic stress effect on the deviatoric stress to yielding, are assessed. It is found that under stress state s resembling those in matrix constrained between fibers, e.g. equibiax ial and equitriaxial tension, yielding is suppressed while brittle fai lure, presumably caused by crack growth from cavitation, occurs. A cri terion for this mode of failure is proposed as the critical dilatation al strain energy density. Experimental data are found to support this criterion. (C) 1996 Elsevier Science Limited