Understanding fast macroscale fracture from microcrack post mortem patterns.
Dynamic crack propagation drives catastrophic solid failures. In many amorphous brittle materials, sufficiently fast crack growth involves small-scale, high-frequency microcracking damage localized near the crack tip. The ultrafast dynamics of microcrack nucleation, growth, and coalescence is inaccessible experimentally and fast crack propagation was therefore studied only as a macroscale average. Here, we overcome this limitation in polymethylmethacrylate, the archetype of brittle amorphous materials: We reconstruct the complete spatiotemporal microcracking dynamics, with micrometer/nanosecond resolution, through post mortem analysis of the fracture surfaces. We find that all individual microcracks propagate at the same low, load-independent velocity. Collectively, the main effect of microcracks is not to slow down fracture by increasing the energy required for crack propagation, as commonly believed, but on the contrary to boost the macroscale velocity through an acceleration factor selected on geometric grounds. Our results emphasize the key role of damage-related internal variables in the selection of macroscale fracture dynamics.
Commissariat à l'Energie Atomique, Saclay Institute of Matter and Radiation, Service de Physique et Chimie des Surfaces et Interfaces, Group Complex Systems and Fracture, F-91191 Gif sur Yvette, France.
Claudia
C
Guerra
Julien
J
Scheibert
Daniel
D
Bonamy
Davy
D
Dalmas
D003198:Computer Simulation; D020342:Finite Element Analysis; D008422:Materials Testing / Q000379:methods*; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D013314:Stress, Mechanical
D019904:Polymethyl Methacrylate