Crack propagation behavior of a perforated plate of normalized and tempered 2 1/4Cr-1Mo steel modeling ligament regions of boiler headers was examined under out-of-phase thermal fatigue at a maximum temperature of 600°C in the air. Inelastic analysis of the perforated plate under the thermal fatigue was carried out, and the nonlinear fracture mechanics parameters such as the J and C* integral were obtained by the line integral method for observed crack distributions. A prediction method for these parameters was proposed, which is applicable to the displacement-controlled condition such as thermal fatigue. In this method, the change of the macroscopic stress-strain relation of the perforated plate with propagating cracks was combined with the reference stress concept under the displacement-controlled condition. The predicted fracture mechanics parameters from this method coincided well with those from the inelastic analysis. The prediction of the crack propagation life on the basis of the proposed method provided a good correspondence with the test results of the perforated plate under thermal fatigue.
