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

Abstract

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, P max, and, also, on the time for the load to drop from P max to 1/2 · P max 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–Δ a curves ( R curves) of the X-750 material, in air and RLT environment, respectively. In this paper, a detailed analysis methodology is presented.