Measurement of Elastic Constants of Additive Manufactured Ti-6Al-4V by Non-contact Multi-mode Laser Ultrasonic System

Titanium alloys have gained widespread attention in the aerospace industry due to their superior properties. Metal additive manufacturing (AM) is now popular to form various components including titanium alloy parts. Young's modulus and Poisson's ratio are important elastic constant parameters to verify the forming quality of additive manufactured parts. In a destructive testing approach, they are usually measured by a universal testing machine. However, an alternative non-destructive method based on the ultrasonic wave propagation velocities can also be used for this purpose. In order to obtain the additive manufactured Ti-6Al-4V wave velocities, a laser ultrasonic testing (LUT) system is built in this work, in which an interferometer is used to receive multi-mode ultrasound signals. This method realizes the simultaneous acquisition of longitudinal wave, shear wave, and surface wave in a non-contact way. The accuracy of the proposed method is verified by the tensile testing, and the results show that the relative errors of Young's modulus and Poisson's ratio measured by the LUT system are 0.7 and 2.8%, respectively. It is demonstrated that LUT is a promising method for quickly measuring Young's modulus and Poisson's ratio, which can be used for online monitoring of product quality in the AM process.