Papers by Keyword: Crack Interaction

Abstract: In this paper, the evaluation of the SIFof a macrocrack in interaction with one or several microcracks in a material containing a geometrical defect was investigated. Several configurations were considered in order to apprehend the mechanisms induced by the interaction effect and in particular the effects of reduction and/or amplification of the stress field between macro and single or multiple microcracks. The obtained results show that, macro–microcrack spacing is an important parameter if the microscopic crack is relatively close to the macrocrack-tip. The macrocrack has the tendency to accelerate as it propagates towards the microcrack. When the relative distance characterizing this spacing is higher than 0.3, the interaction effect can be neglected and the SIF remains unchanged for both defect types. When this ratio is lower than 0.3, the interaction between the two defects becomes significant and the stress intensity factor at the macrocrack tip strongly increases.

Abstract: Numerical accuracy in assessing the strong shielding interaction that promotes cracking process based on continuum mechanics is presented in this paper. Crack interaction limit (CIL) and crack unification limit (CUL) are investigated based on strain energy release rate approach. The case of two interacting edge crack in finite body is simulated using finite element analysis and J-integral. As a result, the trend of CIL and CUL is presented to prove the limit and unification of energy release can be numerically shown at higher and lower crack-to-width ratio at two crack interval ratio b = 1 and b = 0. It can be concluded that the CIL and CUL is geometrically dependent.

Abstract: Stress shielding interaction effect of two parallel edge cracks in finite body under uniaxial loading is analysed using developed finite element (FE) analysis program. In present study, the stress shielding interaction is formulated as a mathematical model called stress shielding damage (SSD) model. SSD model used to define the combination and re-characterization of crack interaction from multiple cracks to single crack. Focus is given to weak crack interaction state as the crack interval exceed the length of cracks (b > a). The crack interaction factors are evaluated based on Griffith strain energy release rate and mode I SIF using J-integral analysis. For validation, the stress shielding factor parameters are compared to single edge crack SIF as a state of zero interaction in a form of crack unification limit (CUL) and crack interaction limit (CIL).

Abstract: Due to the use of mathematical cover system and physical cover system, the numerical manifold method (NMM) is very suitable for discontinuity problems, especially for multiple crack problems. In the NMM, the mathematical cover system is independent of the physical boundary, and in this case, fully regular mathematical elements can be used. In the present paper, the NMM, combined with the rectangular mathematical elements, is applied to solve crack interaction problems in the linear elastic fracture mechanics (LEFM). To verify the present method, a typical numerical example is investigated and the results agree well with the reference solutions.

Abstract: This paper presents the extensions of newly developed finite element (FE) formulation to evaluate fracture behavior of parallel edge cracks problems. The numerical formulation used Barsoum singular finite elements to compute fracture parameters in two dimensional finite element models subjected to different crack-width ratio and cracks interval ratio. Mixed mode stress intensity factors (SIFs) of parallel edge cracks are computed in extending of FE formulation for pure Mode I formulation proposed by authors. In 2D linear elastic problem under mixed mode condition, the variation of SIF value near crack tips are discussed comprehensively. The newly finite element formulations are resulted with remarkable agreement with energy release rate based method compared to analytical solution available in the literatures.

Abstract: The simplification of two dimensional approaches in singular finite elements has promoted the method to be used in the formulation of stress intensity factor (SIF) of multiple cracks in finite body. The effect of shielding and amplification are considered in defining the SIF. As been observed, the current available analytical approximations are more restricted to several assumptions. The more accurate and less restricted method has motivated this study. This paper presents the investigation of singular finite elements applied in two dimensional finite element models subjected to different crack-width ratio and cracks interval ratio. The newly finite element formulations are resulted with good agreement with theoretical statement compared to analytical solution. The weak points of presented analytical solution are discussed regards to the influence of crack width ratio and cracks interval ratio.

Abstract: This paper investigates crack interaction of multiple edge cracks in elastic solid finite body under pure Mode I loading. The cracks are located in parallel to another in 2D plate model. The stress intensity factors (SIFs) are determined based on strain energy release rate. The J-integral path independent is employed to study the interaction between cracks in regards to the effect of crack shielding and amplification of various cracks arrangement. The aim of present work is to test several numerical techniques reported in literature. J-integral approach are applied in 2D ANSYS finite element models subjected to different crack-width ratio (a/w) and cracks interval ratio (a/b). For validation, the results are compared to singular finite element approach and related analytical formulation. The results obtained by these methods are found in good agreement with singular finite element. Some discrepancies between analytical solutions are discussed. Nevertheless, since strain energy release is concern to characterize the near crack tip field, the J-integral method seems to be more applicable and accurate for interacting cracks analysis.

Abstract: It has been demonstrated, through theory and experiments, that compressive layers arrest large surface and internal cracks to produce a stress below which the material will not fail. This enables the materials to have a Threshold Strength. The stress intensity function, K, was derived for a crack sandwiched between two compressive layers. This function suggests that the threshold strength is proportional to the magnitude of the residual, compressive stress, the thickness of the compressive region, and inversely proportional to the distance between the compressive regions. All of these factors have been experimentally examined for laminar composites containing thin, compressive layers. Cracks that propagate straight though the layer obey the K function used to model this behavior. Crack bifurcation, which occurs at high compressive stresses, produces a larger threshold strength than predicted. Crack bifurcation is not fully understood. During the initial studies, differential thermal contraction during cooling from the densification temperature was used to develop the compressive stresses. A molar volume change to induce the compressive stress was also used to develop the compressive stresses. In one case, it was shown that the compressive stresses could arise when the compressive layer contained a material that underwent a structural phase transformation during cooling. In another, ion exchanged glass plates that are subsequently bonded together also produce a threshold strength. Factors that affect the threshold strength are reviewed.