Structural-thermal finite element simulation of vibrothermography applied to cracked steel plates

One of the major drawbacks of ultrasound excited thermography applied to metal components manifests in the pronounced frequency dependence of crack detectability. This leads to an uncertainty in the application of the method. In order to investigate the crack face interaction by which it is constituted whether a certain crack can be detected or not a structural-thermal Finite Element simulation of a massive steel plate is conducted. The roughness of the crack faces is taken into account by generating a random asperity distribution. With this type of modelling the achieved numerical results are in a good agreement with experimental data of a performed ultrasonic sweep thermography (UST). Further investigation of the crack face morphology after repeated ultrasound excitation reveals that the true contact area is very small compared to the apparent contact area. The FE simulation approach allows for a realistic hot-spot size from which frictional heat is generated.