High speed crack propagation in bi-phase materials: an experimental study

We have studied experimentally the high speed propagation of a crack perpendicular to an interface between materials with different mechanical properties. The tests presented in this paper were restricted to the case of a two-dimensional model, without debonding of the interfacial region. Cracks started at a notch machined in the first low modulus phase of the bi-phase single edge notch samples. Our investigations were focussed on the relation between the crack velocity in each phase and the mechanical state of the specimen. The results demonstrate a direct dependence of the crack velocity on the elastic energy stored in the specimen at the moment of crack initiation. For a given experimental situation, we show that the velocity of the crack in each phase and the occurrence of crack arrest can be predicted knowing the relative positions of the two curves crack speed vs. elastic energy for the two constituents of the "bimaterial". For example, this permits the determination of the critical level of stored elastic energy which is necessary to obtain an acceleration of the crack at the interface, without arrest.