Estimation of Fatigue Crack Propagation of Subsurface Cracks by “SCAN”

The authors have proposed an influence function method to calculate stress intensity factor, K, of the surface cracks. This method makes the calculating task easier for arbitrarily distributed surface stresses. They have developed the database of influence coefficients, Kij, for various types of surface cracks through a series of finite element analyses.[1] They also have developed a software system “SCAN” (Surface Crack Analysis), from the database. The K values of surface cracks can be evaluated immediately, and further, fatigue crack propagation can be simulated easily with a personal computer. A fatigue crack often initiates from a defect located at the subsurface of a structural member. In this case, it is important to account for the fatigue life from the initiation of a subsurface crack to its propagation into a surface crack. However, since it is difficult to simulate this process precisely, the authors have proposed a simple model about the transition from a subsurface crack into a surface crack based upon ASME CODE SECTION XI [2] and WES 2805 STANDARD. [3] They have developed a SCAN system – Subsurface Crack Version-. They calculated the fatigue life for some models of subsurface cracks and compared the quantitative differences between two standards.