Obtaining the J–Δa curves of an X-750 alloy from rising load test results and iso-a curves obtained by means of finite elements model

The rising load test (RLT) allows the susceptibility of the X-750 alloy to intergranular stress corrosion cracking (IGSCC) to be assessed. It consists of a three-point bending test of notched and precracked small specimens, in which the response in air and in an aggressive environment (water at 93 °C), under displacement control, is compared. The test classifies each material depending on the value of the stress intensity factor for the maximum load, Pmax, and, also, on the time for the load to drop from Pmax to 1/2 · Pmax during propagation. It is, in summary, a measurement of toughness at initiation together with a measurement of crack growth rate. In this paper, the response to IGSCC of an X-750 alloy under different heat treatments by means of the RLT is presented. In addition, a finite element model has been developed to obtain the iso-a curves (without propagation) for different crack lengths. By combining the experimental curves with the results of the numerical model it is possible to obtain the J–Δa curves (R curves) of the X-750 material, in air and RLT environment, respectively. In this paper, a detailed analysis methodology is presented.