No abstract

International audienceTracking algorithms are used to predict crack paths in structures modeled with the finite element method, in such a way that the paths do not depend on the selected mesh. For regularized media, the simplest methods rely on scalar variables, somehow related to material degradation. Despite their simplicity, they suffer from a major limitation: they allow the crack to initiate and propagate in only one direction. Consequently, such approaches usually fail in case of crack branching or crack initiation inside the structure. To overcome this difficulty, we propose a new crack path tracking algorithm. It is designed to simultaneously detect several local maxima of a degradation-related variable by following the associated ridge lines. That is why the algorithm proposed in this paper could be referred to as a marching ridges algorithm. The performance of the proposed approach is illustrated by three numerical examples within different frameworks. The first ones show that the algorithm can be used to insert crack increments during a ductile failure computation with a quasi-static implicit resolution procedure, in 2D and 3D. The last example proves that the algorithm can be used as a post-processing tool to capture dynamic crack branching from a damage distribution image only

Ductile failure of structural metals is relevant to a wide range of engineering scenarios. Computational methods are employed to anticipate the critical conditions of failure, yet they sometimes provide inaccurate and misleading predictions. Challenge scenarios, such as the one presented in the current work, provide an opportunity to assess the blind, quantitative predictive ability of simulation methods against a previously unseen failure problem. Rather than evaluate the predictions of a single simulation approach, the Sandia Fracture Challenge relies on numerous volunteer teams with expertise in computational mechanics to apply a broad range of computational methods, numerical algorithms, and constitutive models to the challenge. This exercise is intended to evaluate the state of health of technologies available for failure prediction. In the first Sandia Fracture Challenge, a wide range of issues were raised in ductile failure modeling, including a lack of consistency in failure models, the importance of shear calibration data, and difficulties in quantifying the uncertainty of prediction [see Boyce et al. (Int J Fract 186:5-68, 2014) for details of these observations]. This second Sandia Fracture Challenge investigated the ductile rupture of a Ti-6Al-4V sheet under both quasi-static and modest-rate dynamic loading (failure in ∼0.1 s). Like the previous challenge, the sheet had an unusual arrangement of notches and holes that added geometric complexity and fostered a competition between tensile-and shear-dominated failure modes. The teams were asked to predict the fracture path and quantitative far-field failure metrics such as the peak force and displacement to cause crack initiation. Fourteen teams contributed blind predictions, and the experimental outcomes were quantified in three independent test labs. Additional shortcomings were revealed in this second challenge such as inconsistency in the application of appropriate boundary conditions, need for a thermomechanical treatment of the heat generation in the dynamic loading condition, and further difficulties in model calibration based on limited realworld engineering data. As with the prior challenge, this work not only documents the 'state-of-the-art' in computational failure prediction of ductile tearing scenarios, but also provides a detailed dataset for non-blind assessment of alternative methods.