Symposium 15: Advanced Computational Methods in Fracture

To precisely model crack growth, accurate calculations of crack front loading and crack deflection angles are essential. These calculations require solutions of the underlying boundary value problems (BVPs), which are typically obtained by applying numerical methods, e.g., the finite element method (FEM). However, since accuracy and computational cost of the analyses are in general competing aspects, compromises often have to be made in order to generate satisfactory results in acceptable times. In contrast, the use of more efficient methods, both for the solution of the BVP as well as for the subsequent crack tip loading analyses, can substantially lower the computational effort while maintaining desired accuracies. The virtual element method (VEM) is a fairly new discretization scheme for the numerical solution of BVPs, and can be interpreted as a generalization of the FEM. Since the VEM can handle arbitrary polytopal meshes in a straightforward manner, it provides a higher degree of flexibility in the discretization process than the FEM, which turns out to be profitable in terms of both computing times and accuracy. This holds in particular for the simulation of crack growth in 2D and 3D, sparing adaptive re-meshing or the construction of discontinuous element shape functions.
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Thermal expansion of the material usually causes existing cracks to close, resulting in the requirement to consider contact problems. The latter are complicated since one should consider the contact of crack faces accounting for sliding, friction, and unknown contact area. This study tries to solve this task by development of the 3D boundary element approach with iterative solver, which can determine the contact zone, sliding of crack faces and account for friction between them. Moreover, multifield materials and various thermal, mechanical, electric and magnetic boundary and contact conditions can be considered.
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This paper presents a modification of the domain integral method for cyclic loading and crack closure to compute the cyclic effective J-Integral as a near-field loading parameter. The path-dependency of the solution is discussed for different reference states of the field quantities in a cycle. It turns out that refering to the crack opening time point the cyclic effective J-Integral is path-independent for a domain outside the active plastic zone. The validity of this procedure is discussed by comparison with a global energy approach and theoretical field solutions for the J-controlled zone.
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The objective of this paper is to develop numerical models to predict and optimize the ratio (D/W) of hole diameter D over plate width W of a square plate with a center hole. The plate is made from tungsten carbide. The geometry of the model was a square plate with a circular hole in the center. FEM simulation was performed for hole diameter to plate width ratio from 0 to 0.71 in terms of fracture strength (Sut or Suc) under uniaxial compression, or uniaxial displacement. SCF values in the simulations showed good fit with analytical values.It is shown that maximum normal tensile stress develops at the upper point along the free edge of vertical hole,and maximum compressive stresses at left and right horizontal points along the free edge of the hole.. The numerical solution of the normal tensile stress distrbution on the "future fracture plane in Mode I" guarantees a certain degree of stability in the crack propagation in heterogeneous brittle materials.This stability, caused the compliance of the plate to remain independent of crack length, and hence
the fracture toughness can be measured by the critical load itself. The results are relevant to the design of inserts cutting tools.
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Friction widely exists in our daily life and nature, and the onset of sliding friction plays an important role. However, the underlying physical mechanism of this dynamic process is still unclear. This paper will further explore the physical nature of crack like defects. We reduce the experimental configuration to a slider-substrate model, where the slider can be described using thin long beams and the substrate is considered as an elastic half-space. In this way, the relevant displacement and stress field solutions can be obtained by solving Cauchy singular integral equations. The numerical results can well describe the experimental results. By introducing a critical criterion for static dislocation nucleation, the calculated critical forces are in good agreement with those of the sliding precursor. Based on the model, the dynamics of the sliding precursor is further considered. It is found that the strain field caused by the moving dislocation is in good agreement with the strain field caused by the defect in the experiment, and the transient emission process of the interface edge dislocation is similar to the spatio-temporal dynamic behavior observed in the experiment. These works may contribute to further understanding of the mechanism related to sliding friction processes.
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The objective of this work is to critically assess two commonly used localization limiters, viz. the crack band model (CBM) and rate dependent damage (RDD) for continuum scale dynamic fracture predictions. For this purpose, dynamic mode I fracture for an isotropic brittle material is considered under various loading rates and mesh sizes. A scalar damage model is employed, in conjunction with both localization limiters. The analyses reveal that neither of the localization limiters can successfully regularize the solution across all loading rates. Thus, with local damage models, mesh objective prediction of dynamic fracture can be completely ensured only if the mesh size is kept fixed.Role Of Localization Limiters And Lengthscales In Mesh Objective Dynamic Fracture Modeling
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