Numerical Evaluation of Stress Intensity Factors (Ki) J-Integral Approach

摘要

The purpose of this Coastal and Hydraulics Engineering Technical Note (CHETN) is to describe the numerical evaluation of the stress intensity factors using the J-integral approach (Rice 1968a, 1968b). The stress intensity factors have been calculated for a semi-infinite plate with an edge crack. This case has a known closed-form solution, and only a 1.25 percent difference between the numerical and closed-form solution was obtained. This CHETN also presents the methodology to perform a detailed three-dimensional (3-D) meshing of any complicated geometry. The meshing approach was used to generate a 3-D mesh of a hydraulic steel structure with multiple cracks. Stress intensity factors for the 3-D problem with multiple cracks are also discussed. This approach is being developed to be used in fracture mechanics analysis of U.S. Army Corps of Engineers structures. Steel hydraulic structures maintained by the U.S. Army Corps of Engineers have experienced numerous cases of fatigue cracking. This CHETN describes the combination of the fracture mechanics approach with the 3-D finite element analysis to calculate the stress intensity factors on cracked hydraulic steel structures. The stress intensity factors are calculated using the J-integral approach to determine the remaining capacity of the cracked sections. BACKGROUND: Steel hydraulic structures maintained by the Corps consist primarily of lock and spillway gates, bulkheads, and other closure structures. In recent history there has been ample evidence of unsatisfactory performance of these structures. This evidence has included numerous cases of fatigue cracking caused by welded connections with low fatigue resistance, poor weld quality, unanticipated structural behavior, or unexpected loading. In the most severe cases there has been at least one catastrophic failure of a bulkhead system, and complete replacement of lock gates has been required in at least two other cases.