Testing and modelling of creep crack growth in compact tension specimens from a P91 weld at 650 °C

Creep crack growth tests were performed, at 650 °C, on compact tension (CT) specimens machined from the parent material and from the weld region of a P91 weldment. Parent material tests were performed on a number of different CT specimen designs in order to investigate the effects of side grooves on the shape of the crack front. Tests of CT specimens machined from the weld region were performed with the initial cracks located within the heat-affected zone (HAZ) along the interface with the parent material (i.e. the type IV position). All of the specimens were prepared with initial cracks created by wire spark erosion. Good correlations between creep crack growth rates and C∗ were obtained for both the parent and type IV test results. The results indicate that the crack growth rates in the weld specimens are about four times higher than those of the parent material specimens, at the same C∗. Microstructural investigations of the fracture surfaces using SEM and hardness measurements have shown that the exact location of the initial crack within the weldment has a large effect on the crack growth rate, at various loading levels. The results of Finite Element (FE) analyses of the parent material specimen tests, using a creep continuum damage material model, compared favourably with those obtained from the experiments.