Wong , Ee Fun (2016) Crack Analysis Using Extended Finite Element Method With Virtual Crack Closure Technique. Masters thesis, Universiti Sains Malaysia.
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Abstract
Kegagalan retakan adalah masalah umum dalam struktur kejuruteraan di mana retak kecil berpotensi untuk menjejaskan keseluruhan struktur. Walaupun terdapat teori yang sedia ada dan penemuan secara berterusan dalam bidang mekanik patah, kajian analisis perambatan retakan masih dalam penyelidikan. Faktor Kamatan tegasan (SIF) dan Kadar Tenaga Keterikan (SERR) adalah parameter retakan penting yang digunakan untuk menganggar kelakuan struktur yang mengandungi retakan dan sekitar hujung retakan. Dalam kajian ini, XFEM bersempena dengan VCCT diperkenalkan untuk mengira parameter SERR dan SIF. Dalam kombinasi tersebut, VCCT dinyatakan sebagai kriteria kegagalan untuk mengira SERR di hujung retakan. Selain itu, analisis tiada perambatan retakan dibentangkan di plat retakan pinggir dan plat retakan condong. Sementara itu, analisis perambatan retakan ditunjukkan oleh rasuk dua julur (DCB). Keputusan simulasi dibandingkan dengan keputusan teori di mana ia sebagai rujukan. Dalam analisis penumpuan, analisis jejaring berstruktur menggunakan XFEM-VCCT telah terbukti secara stabil dalam analisis apabila retakan terletak di muka elemen dan juga di pinggir elemen. Dalam analisis retakan pinggir, purata perbezaan diperolehi oleh XFEM-VCCT adalah kira-kira 0.5% manakala ralat purata dikira dengan FEM konvensional adalah lebih daripada 1% berbanding dengan penyelesaian teori. Selain itu, dalam analisis retakan condong yang berbeza sudut, purata perbezaan yang diperolehi XFEM-VCCT adalah 1.06% dan 1.45% bagi KI dan KII. Di samping itu, purata perbezaan dalam analisis perubahan panjang retakan adalah 2.58% bagi KI dan 1.62% bagi KII. Untuk analisis perambatan retakan, XFEM-VCCT menunjukkan beban maksimum yang dicapai adalah 1246 N dengan ralat 1.11% berbanding dengan 1260 N yang dikira secara teori dan panjang retakan maksimum ialah 840mm, manakala pengiraan teori adalah 880m. Daripada keputusan yang diperolehi, bilangan elemen yang digunakan oleh XFEM-VCCT dalam semua model adalah jauh kurang daripada FEM konvensional. Secara keseluruhannya, kaedah yang kini dicadang telah menunjukkan keputusan yang baik melalui perbandingan. Ia banyak mengurangkan masa pengiraan komputer dan meningkatkan penyelesaian dalam analisis retakan untuk industri kejuruteraan. ________________________________________________________________________________________________________________________ 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 1260N 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.
| Item Type: | Thesis (Masters) |
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| Additional Information: | Full text is available at http://irplus.eng.usm.my:8080/ir_plus/institutionalPublicationPublicView.action?institutionalItemId=3100 |
| Subjects: | T Technology T Technology > TJ Mechanical engineering and machinery > TJ1-1570 Mechanical engineering and machinery |
| Divisions: | Kampus Kejuruteraan (Engineering Campus) > Pusat Pengajian Kejuruteraan Mekanikal (School of Mechanical Engineering) > Thesis |
| Depositing User: | Mr Mohd Jasnizam Mohd Salleh |
| Date Deposited: | 30 Aug 2018 08:40 |
| Last Modified: | 30 Aug 2018 08:40 |
| URI: | http://eprints.usm.my/id/eprint/41610 |
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