Development of Evaluation Method of Stress Intensity Factor and Fatigue Crack Growth Behavior of Surface Crack under Arbitrarily Stress Distribution by Using Influence Function Method

We present an evaluation method of the crack growth rate and behavior for a semi-elliptical surface crack in a plate subjected to arbitrarily stress distribution. To calculate stress intensity factors, the influence coefficients were developed on the basis of the influence function method with the finite element method. Although the arbitrarily stress distribution such as weld residual stress on the crack surface are difficult to approximate by using a polynomial formula, the stress intensity factor could be calculated by direct mapping of arbitrary stress field obtained from doing finite element analysis of the crack surface. To determine whether the evaluation method based on the influence function method was valid, fatigue crack growth tests were conducted for flat plates with a semi-elliptical surface crack. Flat plate specimens had a distributed residual stress by the non-filler welding before the fatigue crack growth tests. The results of a comparison of estimations and the tests show that both the growth rate and behavior agreed well. From the calculated stress intensity factors based on the influence function method, the asymmetrical crack growth rates and behaviors can be calculated quickly.