Crack analysis using extended finite element method with virtual crack closure technique
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Date
2016-03-01
Authors
Wong Ee Fun
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Abstract
Fracture and failure are general problems in engineering structures where a small crack can potentially compromise the structural integrity. Although there are significant theories and findings in fracture mechanics field, the study of crack propagation analysis is still actively pursued. Stress Intensity Factor (SIF) and Strain Energy Release Rate (SERR) are the important fracture parameters used to estimate the structures behavior containing crack and surrounding of crack-tip.
In this study, XFEM in conjunction with VCCT was utilized to calculate the parameters of SERR and SIF. In the combination, the VCCT was specified as the fracture criterion to calculate the SERR at the crack tip. As case studies, non-crack propagation analysis was presented in edge-crack plate and inclined-crack plate. For crack propagation analysis, the double cantilever beam (DCB) problem was used as case study. The simulation results were compared to the theoretical results as the reference point. In the convergence analysis, the structured mesh analysis using XFEM-VCCT was proven to be stable for analysis when the crack lied on the face of element and also on the edge of element. In the edge-crack analysis, the average error obtained by XFEM-VCCT was approximately 0.5% whereas the average error computed by conventional FEM in conjunction with J-integral was more than 1% compared to theoretical results. Furthermore, in the different inclined-crack angle analysis, the average error produced by XFEM-VCCT was 1.06% and 1.45% for KI and KII, respectively. Besides, the average error for different crack length analysis was 2.58% in KI and 1.62% KII. For crack propagation analysis, XFEM-VCCT showed the maximum load achieved was 1246 N with 1.11% error compared to 1260
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N determined theoretically and the maximum crack length was 840mm, while the theoretical result was 880m. From the results, the number of elements used by XFEM-VCCT applied to all the models was significantly lower than the conventional FEM. On the whole, the proposed method showed good agreement through the results comparison. It greatly reduced the computational time and enhanced solution to fracture analysis in the engineering industry.