A numerical approach to simulate ductile failure with mesh adaptivity within the finite strain framework

International audiencePredictive numerical simulation of ductile failure is a necessary step in the design of industrial structures for which full-scale experimental approaches are not conceivable (e.g. ductile tearing of an aircraft fuselage). The failure process of ductile materials involves extensive plastic strains together with the nucleation and growth of voids in a localized area whose size is not negligible in comparison with the size of the structure. Physically-based models can be used to describe the failure of the underlying microstructure, which is done in an average sense by means of a damage variable. There are many constitutive models aiming at representing the failure process, but standard local damage models all share the following limitations: (i) solving finite element problems involving material softening leads to mesh dependence; (ii) a continuous description is valid up to the onset of fracture but cannot properly describe the actual surface creation process nor the kinematics associated with crack opening. In this work, a regularized continuous-discontinuous approach is used in order to solve those issues for any type of damage model. To achieve mesh objectivity, damage evolution is described thanks to continuous non local models. The quality of the finite element results is ensured thanks to an implicit resolution scheme, preferred to an explicit one. During computation, a mesh adaptivity procedure is used to control accuracy and to keep the elements well shaped, which is necessary in the presence of large strains. To minimize error accumulation during transfer, a local remeshing strategy is preferred to a global one. An error indicator is used to determine where mesh refinement is needed and, only in these areas are the fields at the integration points smoothed for transfer. The rest of the mesh is kept unchanged and the the fields are thus transferred exactly. To simulate crack initiation and propagation, this mesh adaptivity procedure is combined with a new orientation criterion. This criterion relies on the projected gradient of a smoothed field to determine the orientation of the next crack increment. The strategy offers the possibility to use any unbounded field which is representative of the material degradation for the determination of the crack orientation (e.g. damage, effective plastic strain,...). This approach allows to simulate crack initiation inside the structure which would be impossible with a criterion using an averaged direction toward the most damaged points. Up to this point, the strategy had only been applied to mode I-II 2D and 3D cases within the small strain framework. This contribution deals with the extension of the methodology to the finite strains framework and the underlying challenges

A two characteristic length nonlocal GTN model: Application to cup–cone and slant fracture

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The second Sandia Fracture Challenge: predictions of ductile failure under quasi-static and moderate-rate dynamic loading

© 2016, The Author(s). 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 (Formula presented.) 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 real-world 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

The second Sandia Fracture Challenge: predictions of ductile failure under quasi-static and moderate-rate dynamic loading

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 real-world 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.National Science Foundation (U.S.

The second Sandia Fracture Challenge : predictions of ductile failure under quasi-static and moderate-rate dynamic loading

International audienceDuctile 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 real-world 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