Dissertation
Dissertation > Mathematical sciences and chemical > Mechanics > Solid Mechanics > Strength theory > Fracture theory

The Simulation of Fatigue Crack Growth Based on Boundary Element Methods

Author FengJiaZuo
Tutor ShiDeXin
School Harbin Engineering University
Course Design and manufacture of ships and marine structures
Keywords boundary element method crack propagation numerical simulation stress intensity factor
CLC O346.1
Type Master's thesis
Year 2013
Downloads 64
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Fracture caused by fatigue is one of the main forms of structural failure, resulting in alot of major accidents in the actual engineering structures. In order to prevent accidents andreduce losses, fatigue crack propagation should be researched. Experimental methods andnumerical analysis method are currently two main important ways for crack propagation.However, the experimental method is time-consuming and relatively low efficiency, andnumerical analysis method is very convenient and efficient. Based on the boundary elementtheory, two-dimensional and three-dimensional crack growth trajectory are numericalsimulated in this paper. The content completed in this paper are as follows:(1) Based on the boundary element method, the domain is divides by using the sub-domain method along the crack surface, and the domain boundary is discrete by using a linearunit and the secondary unit respectively. Based on the maximum stress criterion to determinethe direction of crack propagation, using the Fortran language program to simulate the crackgrowth trajectory of two-dimensional plane;(2) Due to the different area boundary unit type (linear unit, secondary unit),different types of crack tip unit (quarter-node unit, secondary unit), the density of the crack tipmesh and other factors having certain impact to the calculations, selecting the hole edge crackplate under uniaxial tension verify the impact of the above factors for the accuracy of results.The results showed that the secondary unit is more accurate than the linear unit, and thequarter singularity unit at the crack tip is more accurate for simulating the crack tip stress fieldmeanwhile the larger the mesh density to calculate the results is better;(3) Select inclined crack under uniform uniaxial tension plate as the object of study,and study the accuracy of calculation of the crack tip stress intensity factor and the crackplane expansion trajectory under different initial crack length, meanwhile study the variationof I the stress intensity factor and II stress intensity factor of the crack propagation process;(4) Study the application of the boundary element method for three-dimensionalcrack model by using boundary element fracture analysis software FRANC3D. Selectsemi-elliptical surface cracks and unilateral tension oblique crack model to verify FRANC3Dcalculation accuracy, and the results show that FRANC3D can accurately calculatethree-dimensional crack stress intensity factor; (5) The crack growth trajectory of the saddle point of the T-tube node is numericalsimulated by using FRANC3D software, and the variation of the stress intensity factor and theexpansion process are presented. The results show that the crack propagation is non-planeexpansion, and type I crack in the expansion process plays a major role.

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