Fracture mechanic analysis of multiple edge cracks in a finite plate using kerf to emulate crack interaction
Ahmad Faizal, Annuar
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Multiple cracks with different or similar geometries that coexist on the same plane will affect its neighbouring counterpart’s Stress Intensity Factor (SIF) value due to interaction effect. The interaction effect is much related to the change of stress distribution profile that produced by neighbouring crack. The study had been proven true over the past years through various Finite Element Analysis FEA software packages and formulation, but an actual experiment and raw data acquisition is rather scarce in literature. This could well mean that the process to prepare multiple cracks study is hard to emulate physically as oppose to single crack study. The main intention of this study attempts to simulate and find a possibility to replace subsequent crack interaction to primary crack with kerf, incise in Electric Discharge Machining (WEDM) wire cut, by evaluating the longitudinal stress distribution component. Current regional technology of WEDM permits kerf gap machining at 0.050mm. This research, focuses on emulating two parallel edge cracks’ interaction as initial attempt to prove that kerf provides similar interaction on primary crack’s SIF. Through simulation using ABAQUS Computer Aided Engineering (CAE), values of non-uniform stress distributions produced by kerf within the potential primary crack region was analysed and compared to non-uniform stress distributions that produced by a crack as validation. Absolute error tabulation of stress distribution that produced by kerf suggests that it is fit to replace subsequent crack for further study of interaction in multiple cracks. A nonconventional method to determine Normalised SIF of crack, 𝑌𝑎 , using Multiple Reference State (MRS) Weight Function was chosen given its capability in complex computation of crack geometries that includes non-uniform stress distribution values in finite bodies. The 𝑌𝑎 values from FEA models of double edge cracks which were used as reference points exhibits decent agreement with data trend line from those conceived by MRS Weight Function Method. Experiments are carried out with three (3) specimens, made from Aluminium Alloy 6063 T6, which contains a crack, a, at varying length and 10mm kerf, b, each at similar edge surface at similar separation of 10mm to observe further growth of crack under presence of kerf. The three conditions of the specimens are designed as followed; i) a≈b, ii) a=1.5b, and iii) a=2b. This is to highlight the existence of interaction between crack and kerf under circumstance where primary crack at different conditions attempts to grow under loading. This research contributes the knowledge of kerf’s non-uniform stress distribution trend under tension loading and its influence to primary crack’s growth in which the results are comparable to those produced by subsequent crack. The study of kerf in this research is significant as it disclose characteristic of kerf and crack interaction and allows anticipation in the events structural failure for engineers and research in order to avoid potential disasters.