Closed Cracks Characterization in a Steel Sample Applying a Pump Probe Waves Ultrasonic Method

Abstract

Ultrasonic measurements are commonly used for crack sizing in the industrial context, but due to potential partial crack closure, the crack depth can be underestimated. It could be of importance regarding the prediction of remaining service life and maintenance scheduling of industrial components. In the literature, nonlinear ultrasonic methods have proven efficient for this issue. Among them, a pump probe waves method is investigated here for possible use in an industrial context. In this article, an industrial steel component with several partially closed fatigue cracks is studied. First, a three-point bending test associated with digital image correlation is performed with ultrasonic measurements to obtain reliable indications about the crack’s closure state. A three-dimensional laser vibrometry experiment shows the possibility of opening the crack using a pump wave. The pump probe waves method is conducted using a standard 45 deg shear wave transducer in echo mode as a probe. The results allow to discuss physical mechanisms in play. It also shows the possibility to detect the closed nature of all of the cracks even if the full opening state is not reached. Moreover, a coherent crack profile is found compared to the mechanical test. The results are validated on a notched sample for which the nonlinear response is negligible. Industrial application as well as possible improvement are discussed.