In this study, a 0.4–1.6 mm deep semicircular crack was machined in DNV F690 offshore structural steel with an aspect ratio (As) of 1.0. After needle peening (NP), four-point bending fatigue tests were conducted. The fatigue limit estimated using the equation proposed by Ando et al. decreased with increasing crack size, but agreed with that obtained in the four-point bending fatigue test. The compressive residual stress increased the fatigue limit of the NP smooth and crack specimens. The fatigue limit of the NP crack specimen with a crack depth a = 0.8 mm was over 95 % of that of the smooth specimen. Semicircular cracks with crack depths up to a = 0.8 mm could be rendered harmless by NP, however, this was not the case for the NP crack specimen having a = 1.2 mm. It was estimated that the harmless crack depth of the NP crack specimen was a = 1.14 mm.

在本研究中，在纵横比 ( As ) 为 1.0 的DNV F690 海上结构钢上加工了 0.4-1.6 毫米深的半圆形裂纹。针刺（NP）后，进行四点弯曲疲劳试验。使用 Ando 等人提出的方程估计的疲劳极限。随裂纹尺寸的增加而降低，但与四点弯曲疲劳试验中获得的结果一致。压缩残余应力增加了NP光滑和裂纹试样的疲劳极限。裂纹深度a = 0.8 mm的NP裂纹试样的疲劳极限是光滑试样的 95% 以上。裂纹深度达a 的半圆形裂纹=0.8毫米可以通过以下方式变得无害NP，然而，这不是对的情况下NP具有裂纹标本一个= 1.2毫米。据估计，NP裂纹试样的无害裂纹深度为a = 1.14 mm。