Modeling of the propagation of cracks in a welded structure

Abstract

Evolution of crack depends on several intrinsic parameters of material, such as geometries and mechanical properties of structure, or extrinsic properties like the extent of the crack or applied load. All these parameters must be taken into account in the digital simulation, in order to study the quasi-static crack propagation. It is impossible to use the stress intensity factor (SIF) or the rate of refund of energy to study the non-prefissured part. In this case, two easy methods of detecting the crack initiation place – the critical stress and the critical damage – are proposed. In a digital simulation, the constraints are calculated with each step of time (or increment of load) and in each point of integration. By studying the maximum constraints, the crack initiation position can be located. For that, we evaluate with each step of time, and in the ignition area, the value of the maximum constraint in each point of integration close to the border. We compare then the values obtained with a constraint characteristic of material; when this breaking value is exceeded, a crack is started perpendicular to the maximum constraint in this point of integration. Once started, the crack can continue to be propagated. When the geometry or the loading is not symmetrical, the crack is not propagated in a rectilinear way, and it is necessary to determine the directions of propagation. Many criteria were proposed to determine the angle of junction of a crack [1]. Once this angle is determined, one propagates the crack in the grid at a certain distance Δ a. The smaller this distance is, the more one approaches the exact solution. However, from a numerical point of view, it is necessary to determine this distance from propagation.