Fracture mechanics studies of crack healing and welding of polymers

Compact tension tests have been performed on re-healed and welded glassy polymers (PMMA-PMMA, SAN-SAN and PMMA-SAN). At temperatures above the glass transition temperature,Tg, it was observed that the facture toughness,KIi, in the interface increased with contact time,t, asKIi ?t1/4 as predicted by a diffusion model. The self-diffusion constantD(Tg + 15 K) of chains of molecular weight 1.2×105 can be estimated as 1×10-21sec-1 with an activation energy of 274 kJ mol-1. For full material resistance, the depth of interdiffusion, x2>1/2, was calculated to be between 2 and 3 nm. Vacuum drying of the specimens, as well as polishing the interfaces, decreases the speed of interdiffusion.