Nondestructive evaluation for tensile properties of metallic materials using laser ultrasonics

Abstract

Nondestructive testing (NDT) using ultrasonic waves enables one to check not only the defects or voids inside a material but also the mechanical properties of the material. However, most ultrasonic NDT uses a contact-type transducer, which has disadvantages such as couplant application or testing at a curved surface. Laser ultrasonic waves can generate and receive with non-contact status to avoid the disadvantages of contact-type transducers. In this study, it is intended to verify the possibilities of evaluating the tensile properties of materials with laser ultrasonic techniques. First, the longitudinal velocity and attenuation coefficient, in which waves are generated at the Ti-6Al-4V/Yttria-Stabilized Zirconia (YSZ) composite in ablation mode, were compared with the mechanical properties of the composites, which obtained by tensile test. It was verified that the longitudinal velocity increased, and the attenuation coefficient decreased as the YSZ content increased; thus, there was a significant correlation with the yield stress. Therefore, the possibilities of NDT using laser-generated longitudinal waves in the Ti64-YSZ composite was demonstrated. Second, the laser-generated Rayleigh wave signals and tensile curve data, which were obtained at aluminum alloys, are learned by Long Short-Term Memory (LSTM) model based on Recurrent Neural Network (RNN) to predict the tensile curve. As a result, the relative error in the elastic region shows 17.79% but 3.23% in the plastic region, which means that the model performance is better in the plastic region than elastic region. Also, the ground-truth and estimated values of yield stress, ultimate tensile stress, and failure point at tensile curve have been compared to verify the relative error and it is showed as 4.54%, 2.53%, and 8.38%, respectively. These results verified the possibilities of estimating the tensile properties of metallic materials using laser-generated longitudinal and Rayleigh waves.