Laser Ultrasonic Determination Method of Metal Third-Order Elastic Constant

Abstract

The invention discloses a method for utilizing a laser ultrasonic wave to precisely measure a third order elastic constant of metal. The method comprises the following steps: respectively measuring wave velocities of a longitudinal wave, a transverse wave and a surface wave excited by a laser under stress-free state and stress state; utilizing the wave velocities of the longitudinal wave, the transverse wave and the surface wave measured under stress-free state to calculate a second order elastic constant and a density of metal according to a sonic elasticity theory and a Rayleigh equation; utilizing the ultrasonic wave velocities of the longitudinal wave, the transverse wave and the surface wave measured under stress state to introduce an equivalent second order elastic constant and an independently measured linear coefficient of thermal expansion; and lastly, calculating the third order elastic constant according to the sonic elasticity theory. According to the method, a pulse laser source is utilized to excite a sound surface wave, non-contact exciting is performed under a thermal elastic system and an overheated phenomenon of materials is avoided, so as to realize nondestructive measurement. A large amount of sound surface wave data spread for different distances is collected and a correlation function is utilized to calculate a wave velocity of the sound surface wave and a spread distance of sound wave, thereby greatly reducing error of arriving time value of the sound surface wave and promoting the measuring precision of a sound wave velocity.

Description

technical field [0001] The invention relates to a method for accurately measuring the third-order elastic constant of metal, in particular to a method for accurately measuring the third-order elastic constant of metal by using laser ultrasonic waves. Background technique [0002] The acoustoelastic effect means that the ultrasonic wave velocity in a solid will change with the deformation or stress applied to the solid. This effect is widely used in static non-destructive testing and residual stress testing. In these applications, it is generally believed that the wave velocity and strain have a linear relationship. The existing method can measure the wave velocity of various ultrasonic modes with an accuracy of up to 10 -4 Even higher, see our previous research results - such as literature 1 [SPIE, Vol.7544, 754451 (2010) "Measurement of velocity distribution of laser-generated Rayleigh wave on welded structure"]. The main difficulty is to obtain the relationship parameter ...

AI Technical Summary

Problems solved by technology

However, this method excites and receives ultrasonic waves on both sides of the sample, so the judgment of the arrival time of the sound wave (especially for samples with small thickness) is prone to misjudgment, thus causing errors in the calculation of the wave velocity and the calculation of the final elastic constant; Under the state of axial stress, the density and axial length of the solid have certain changes, and the material density and acoustic wave propagation distance values ​​​​at the time of no stress are still used, which also brings large errors to the calculation of elastic constants.

Images