焊接桥梁钢疲劳裂纹扩展行为分析-analysis of fatigue crack growth behavior of welded bridge steel.docx

proposed crack closure correction model.(4)A modified zigzag approach is proposed to approximate moving crack front with arbitrary shape based on the virtual crack closure-integral technique. An approximated zigzag line are used to represent the complex crack front which has the same general shape for the given crack front. Based on this zigzag approximate crack front, the approaches to determine the required virtually closed area, displacement openings are proposed. The differences of approaches between present study and extraction approaches are discussed indetails. The comparison results indicate that the present approach provided a more detailed consideration to determine the virtually closed area, there is no blank space between the virtually closed areas for the consecutive crack tip nodes. Also, the present approach can be used to calculate G when the finite elements across the crack front have different sizes.Following the proposed modified zigzag approach, two kinds of mesh patterns, exact mesh pattern and zigzag mesh pattern, can be used. With exact mesh pattern, the nodes lie precisely along the crack front, and the FEM results agree well with the analytical solutions. With zigzag mesh pattern, the nodes cross the curved crack front in a zigzag pattern. The advantages of this mesh pattern are that (i) a simple stationary finite element mesh can be used for crack front with arbitrary shape and (ii) adaptive re-meshing technique is avoided in studying crack growth. The disadvantage of this mesh pattern is that, the G results oscillate around the analytical solutions. With zigzag mesh pattern, the G results evaluated by proposed approach are compared with these obtained from other approaches. The comparisons results indicated that the present approach provide much more accurate strain energy release rate G results than the extraction approaches.The crack growth simulations using the proposed modified zigzag approach are presented for cracks with complex init