Crack Shape Evolution of Three-Dimensional Fatigue Cracks

• Main Authors: Yang-Hui Chang, 張揚揮
• Other Authors: Chien-Yuan Hou
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/21726238203286417130

碩士 === 國立暨南國際大學 === 土木工程學系 === 103 === Fatigue is the main reason that causing heavy casualties in steel structures. In many cases of steel structure which have been fatigue failure, most of the fatigue crack initiate at the toe of weld. Because the irregular geometry of weld toe, small cracks will start from weld toe after the force loading of the members. The rate of crack growth will be faster after various cracks combined, also the crack shape will change drastically. This study use finite element method with the previous theory and establish a set of automated computer program to simulate the foregoing growth process. The result showed that whether the initial crack shape is semicircular or very shallow, the value of aspect ratio is between 0.6 and 0.8 in the last stage of growth. And the maximum length of crack growth, , model width, b and height, h, are insignificant on crack shape growth simulation. This study also discuss the crack shape evolution of two symmetrical coplanar semi-elliptical after crack combined. The simulation results show that the greater distance between the center of the semi-elliptical and plane of symmetry, the required distance of the leading edge of two cracks grows into a single smooth curve is also larger.