Elucidating nature of elastomeric fracture by local characterization

This work studies the effect of sample thickness on fracture behavior of polybutadiene rubber (BR). Single edge notch (SEN) test pieces with three varying thicknesses, 0.6 mm, 1.3 mm, and 5.2 mm and involving four cut sizes from 0.8 to 8.3 mm. By making in situ spatially resolved photoelasticity (e.g., birefringence), we show how strain field builds up around crack tip all the way to the onset of fracture. We confirm a previous study1 that upon approach cut tip stress ceases to build up and reveal a stress plateau zone (SSZ) of a size independent of load. With increasing thickness, fracture toughness (Gc or K­­c) remains the same, corresponding to the critical tip stress at fracture sigma_tip(F) (equal to the inherent strength) decreasing and SSZ size increasing as thickness increases.

1. Smith, T.; Gupta, C.; Fan, Z.; Brust, G. J.; Vogelsong, R.; Carr, C.; Wang, S.-Q. Toughness arising from inherent strength of polymers. Extreme Mechanics Letters 2022, 101819.