ORAL REFERENCE: ICF100833OR DYNAMICS OF INTER-FACIAL CRACK FRONT PROPAGATION Knut J rgen M al y 1 , Jean Schmittbuhl 2 , Arnaud Delaplace 3 , and Jose Javier Ramasco 1;4 1 Fysisk Institutt, Universitetet i Oslo, P. O. Boks 1048 Blindern, N-0316 Oslo 3, Norway 2 Laboratoire de G eologie, UMR 8538 E cole Normale Sup erieure, 24 rue Lhomond, 75231 Paris Cedex 05, France. 3 Laboratoire de M ecanique, et Technologie, E cole Normale Sup erieure de Cachan, 61 Avenue du Pr esident Wilson, F-94235 Cachan Cedex, France 4 Instituto de Fisica de Cantabria (CSIC-UC) Facultad de Ciencias, Av de los Castros s=n 39005 Santander, Cantabria, Spain Abstract. Here we report on in situ observations with a high speed CCD camera of an in-plane crack propagatingthroughatransparentheterogeneousPlexiglasblock. Thetoughnessiscontrolledarti - ciallyand uctuatesspatiallylikearandomnoise.AstablecrackinmodeIwasmonitoredbyloading the system by an imposed displacement. We show that the movement of the fracture front is controlled by local instabilities triggered by the depinning of asperities even for very slow loading. Development of crack roughness is described in terms of a Family-Vicsek scaling with a roughness exponent =0:60 and a dynamical exponent =1:2. Keywords: Inter facial fracture, roughness, depinning, local dynamics Introduction In this experiment we studied the dynamics of a slow inter-facial crack front line during its propagation through a transparent heterogeneous Plexiglas block. We found that the slip in the front line along the fracture interface is strongly correlated over scales much larger than the width of the fracture front and that the front moves in irregular bursts [1]. In contrast to the experiment presented here, most experiments are performed with unstable fractures which exhibit fast propagation of the order of the speed of sound. The fast propagation makes it very diÆcult to study dynamics. Direct observation of the crack front is usually impossible and an inverse description of the crack front obtained for instance from acoustic emissions is generally observed with a low spatial resolution. Most studies on fractures have focused on homogeneous materials. The role of heterogeneities has been addressed more recently. Fracture surfaces have been found to exhibit self-aÆne long range correlations [2, 3, 4, 5, 6, 7, 8, 9]. However, the physical origin of it is still not fully understood. Static elasticity leads to long range interactions [8, 10] but in addition elastic waves specially recently observed crack front waves [11, 12, 13, 14, 15] may play an important role. In most modeling of fracture dynamics in heterogeneous materials the latter are ignored since a quasi static assumption is used. A recent quasistatic simulation presented by Hansen et. al [16] (see this proceeding) shows results consistent with our experiments. Experimental method and results In this work we present an experimental study of a stable slow fracture propagating along an annealed interface between two Plexiglas blocks [17, 18, 19, 1]. Crack fronts are directly observable because of the 1
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