Statistical properties of microcracking in polyurethane foams under tensile test, influence of temperature and density

摘要

We report tensile failure experiments on polyurethane (PU) foams. Experimentshave been performed by imposing a constant strain rate. We work onheterogeneous materials for whom the failure does not occur suddenly and candevelop as a multistep process through a succession of microcracks that end atpores. The acoustic energy and the waiting times between acoustic events followpower-law distributions. This remains true while the foam density is varied.However, experiments at low temperatures (PU foams more brittle) have notyielded power-laws for the waiting times. The cumulative acoustic energy has nopower law divergence at the proximity of the failure point which isqualitatively in agreement with other experiments done at imposed strain. Wenotice a plateau in cumulative acoustic energy that seems to occur when asingle crack starts to propagate.