Impact of Strain-Induced Crystallization on Fast Crack Growth in Stretched cis-1,4-Polyisoprene Rubber

cis-1,4-Polyisoprene (IR) elastomers harden via strain-induced crystallization (SIC) when the imposed stretch (lambda) exceeds the onset value of SIC (lambda*). We investigate the Mode-I fast crack growth in the IR sheets as a function of lambda in a pure shear geometry. The steady-state crack velocity (V) increases with increasing lambda, and V exceeds the shear wave speed of sound at lambda > lambda(s). Further stretch beyond lambda* (>lambda(s)) causes SIC-driven hardening, resulting in a pronounced increase in V. The characteristics of the crack-tip strain field are also significantly influenced by the SIC-driven hardening: The crack-tip opening displacement increases with increasing lambda at lambda < lambda* but exhibits an abrupt reduction beyond lambda*. The crack-tip singularity and the area of strain increment caused by the crack growth change discontinuously around lambda*. The abrupt variations in these crack-tip characteristics result from the considerable differences in the mechanical properties prior to the crack growth between the entirely amorphous state at lambda < lambda* and the partially crystallized state at lambda > lambda*.