Résumé
The fracture of materials can take place below the critical failure condition via the slow accumulation ofinternal damage followed by fast crack propagation. While failure due to subcritical fracture accounts formost of the structural failures in use, it is theoretically challenging to bridge the gap between moleculardamage and fracture mechanics, not to mention predicting the occurrence of sudden fracture, due to thelack of current nondestructive detection methods with suitable resolution. Here, we investigate the fractureof elastomers by using simultaneously space- and time-resolved multispeckle diffusing wave spectroscopy(MSDWS) and molecular damage mapping by mechanophore. We identify a fracture precursor thataccelerates the strain-rate field over a large area (cm2 scale), at considerably long times (up to thousands ofseconds) before macroscopic fracture occurs. By combining deformation or damage mapping and finiteelementsimulations of the crack-tip strain field, we unambiguously attribute the macroscopic responsein elastic deformation to highly localized molecular damage that occurs over a sample area of about0.01 mm2. By unveiling this mechanism of interaction between the microscopic molecular damage and theminute but long-ranged elastic deformation field, we are able to develop MSDWS as a flexible, wellcontrolledtool to characterize and predict microscopic damage well before it becomes critical. Tested usingordinary imaging and simple image processing, MSDWS predictions are proven applicable for unlabeledand even opaque samples under different fracture conditions.