Estimation of the stress distribution in metal using nonlinear acoustoelasticity

Abstract

A new nondestructive method to estimate the stress distribution in a metal is proposed. It is based on the use of nonlinear dependence of ultrasound velocity on stress in metals. First, the dependence of ultrasound velocity on stress in an aluminum alloy is observed, and it is confirmed that the relation is nonlinear and that its derivative changes monotonically in the stress range of interest. Hence, if a certain stress perturbation is given to the observing region in a metal and the change of ultrasound velocity due to the perturbation is measured, the stress in that region can be estimated. This is the basic idea of the measurement of stress in a metal. Now, the field to give the stress perturbation is scanned along the probing ultrasonic beam and a set of data of phase change due to the velocity change is acquired. Then a matrix inversion technique is applied to them by taking account of the spatial distribution of the stress perturbation to obtain a precise stress distribution along the probing beam. The applicability of the proposed method is confirmed by computer simulations. Then a measuring system is constructed which consists of an electromagnetic transducer as the stress perturbation generator which gives approximately 0.4 MPa of perturbation, and a 50-MHz ultrasonic probing wave transmitter/receiver to detect the phase change. Finally, the stress distribution along a line in a specific aluminum alloy block is estimated by using the constructed system. The estimated stress distribution showed good agreement with the expected one. ¸

Nondestructive characterization of materials with variable properties

“…The development of the measurement technique [48] encourages us to propose the wave profile nonlinear distortion data as the source of information in the nondestructive evaluation of inhomogeneous materials. Nonlinear effects of wave propagation are not widely used in NDT, yet [49].…”

Propagation of ultrasonic waves in materials under bending forces

“…The ultrasonic velocity in stressed materials can be determined by estimating the phase change of the propagating wave. Kato [5,6] determined the phase change resulting from the accumulation of the stresses through a small propagation path. More precise acoustoelastic measurements have been realised by Landa [7] to determine mechanical and elastic properties in compression stressed material.…”

Study of Shear Ultrasonic Waves Propagating in Materials under Static Uniaxial Loadings

“…To detect inside metals the stress conditions such as the limiting stress value of elastic deformation, Kato et al. [15] proposed an original method for calculating the change in the ultrasound velocity in stressed materials. This change in velocity is obtained from the measurement of the change in the phase difference between the reference wave and the wave propagated through the metal sample.…”