Failure Time and Microcrack Nucleation

The failure time of samples of heterogeneous materials (wood, fiberglass) is studied as a function of the applied stress. It is shown that in these materials the failure time is predicted with a good accuracy by a model of microcrack nucleation proposed by Pomeau. It is also shown that the crack growth process presents critical features when the failure time is approached. It is very well known that different materials subjected to a constant load may break after a certain time, which is a function of the applied load [1-5]. Many models have been proposed to predict this failure time, but the physical mechanisms remain often unclear [4, 5]. Very recently Pomeau proposed a model [6], which explains quite well the failure time of microcrystals [7] and gels [8] submitted to a constant stress. This model is based on the interesting idea that a nucleation process of microcracks has to take place inside the materials, in order to form the macroscopic crack. This nucleation process is controlled by an activation law, as the coalescence of a phase into another in a liquid-solid transition. Based on this prediction [6], L. Pauchard et al.