Evaluation of material damage using non-specular reflection of a bounded ultrasonic beam at a liquid-solid interface

Abstract

This paper proposes an effective method for evaluating the level of material damage using the non-specular reflection of a bounded ultrasonic beam at a liquid-solid interface. Non-specular reflection occurs when a bounded ultrasonic beam is obliquely incident from a liquid onto a solid surface. This paper formally formulates the acoustic field of the non-specular reflection of a bounded ultrasonic beam and analyzes the influences of some factors such as the incident angle and the level of material damage (characterized by a decrease in Young's modulus) on the non-specular reflection field. To characterize the effect of the non-specular reflection of a bounded ultrasonic beam, this paper defines a specific parameter called the specular reflection coefficient (SRC) of a bounded ultrasonic beam. A finite-element (FE) model is established to quantitatively observe the response of the defined SRC to the incident angle and the level of material damage. The FE simulations are conducted for the bounded ultrasonic beam obliquely incident at longitudinal, transverse, and Rayleigh critical angles, respectively. The simulations demonstrate that the change rate of SRC at the Rayleigh critical angle exhibits a monotonically sensitive response to the level of material damage, providing an effective means for accurately evaluating it. To validate this method, we conducted an experiment with oblique incidence testing of the bounded ultrasonic beam at the Rayleigh critical angle of the water-aluminum interface. The experimental results are consistent with the FE simulations, and show that the change rate of SRC at the Rayleigh critical angle has a monotonous and sensitive response to the level of material damage. The consistency of theoretical predictions, FE simulations, and experimental results confirms the feasibility of using the non-specular reflection of a bounded ultrasonic beam incident at the Rayleigh critical angle as an effective method for evaluating the level of material damage.