Finite element modeling of ultrasonic nonlinearity for creep damage of P91 steel

A theoretical method is proposed to evaluate the creep damage in a 91 steel by using ultrasonic nonlinear technique. A 2-dimensional finite element model is developed to simulate the creep damage of steel P91 and the ultrasonic wave propagation through the degraded material. The micro-structural changes in the degraded material cause the distortion in the ultrasonic wave, and this material's nonlinearity leads to the generation of the second-harmonic wave component. Both the experimental and theoretical results show that the material nonlinearity increases with the increase of thermal treatment temperature. The results show the feasibility of the model to evaluate the early stage of the degradation of materials by using ultrasonic nonlinearity.