The Three-Dimensional Finite-Element Analyses for Stress Intensity Factors of Semi-Elliptical Cracks at Fillet Weld Toes

• Main Authors: Yu-JungLu, 盧宥融
• Other Authors: Hsin-Yang Chung
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/86554371902699530157

碩士 === 國立成功大學 === 土木工程學系碩博士班 === 100 === This thesis mainly employed a three-dimensional finite-element program to compute and analyze the stress intensity factors (SIFs) of semi-elliptical cracks at fillet weld toes in two types of joints. The first type of joint was the cruciform joint which was used to connect steel plates by fillet welds. The second type of joint was the T-shaped joint which was created to simulate the joint connecting a steel box-column and a steel plate by all-around fillet weld. A semi-elliptical crack was simulated in the fillet weld toe of each joint. This thesis developed three-dimensional finite-element models for two types joints, and, in each type of joint, a number of finite-element joint models were created by varying the key geometric parameters to investigate the influences of the key geometric parameters to the SIFs of semi-elliptical cracks at fillet weld toes. In addition to acquiring the SIFs directly from the three-dimensional finite-element program, this thesis also utilized the crack opening displacements (CODs) of the deepest point in the semi-elliptical crack that were simulated from the three-dimensional finite-element program, and then computed the SIFs of the deepest point by least-squares method. The simulation results showed that semi-elliptical cracks in the two types of joints were affected by tensile/opening mode (mode I) significantly. The SIFs at crack front decreased from the surface point to the deepest point. The SIFs of crack front at surface point were all greater than those at the deepest point. When the attachment plate of the T-shaped joint was applied with the tensile force, the weld toe semi-elliptical crack occurred only in the main plate yielded greater SIFs than the weld toe semi-elliptical crack occurred only in the attachment plate. When the attachment plate of the T-shaped joint was applied with the shear force of the same magnitude, the weld toe semi-elliptical crack occurred only in the attachment plate yielded greater SIFs than the weld toe semi-elliptical crack occurred only in the main plate.