Experimental assessment of ductile damage in P91 steel at high temperature

In this paper, we provide a comparison between two indirect experimental methodologies to assess ductile damage in P91 steel tested at 1100C: the micro-tomography and the ultrasonic wave propagation techniques. To understand the effect of the strain rate on damage or porosity evolution, two series of tensile tests were carried out: a first (quasi-static) one featuring a velocity of the testing machine track of 0.06 mm/s and a second (high strain rate) one featuring a track velocity of 50 mm/s. Each set consisted of tests conducted up to increasing values of the maximum track displacement, so as to provide pictures of damage distribution at increasing severity. A simplified micromechanical analysis is developed for data elaboration of the ultrasonic measurements. We show that the estimates of overall damage, provided by the two experimental techniques for the necked region of the specimens, agree fairly well in most of the cases.