Metals and Alloys Residual Stresses Evaluation

Laser-ultrasound measurement of residual stresses is based on the acoustoelastic effect - the dependence of the propagation velocity of ultrasonic waves on the stresses in the investigated medium. Residual stresses distribution can be calculated with measuring the variation of the velocity of longitudinal and surface ultrasonic waves in the case of one-sided access to an object under testing by using transducer with pitch-catch configuration (PLU-6N-02). The short duration and high quality of laser excited ultrasonic pulses make it possible to measure the velocity of ultrasonic waves with precision accuracy on a small basis (the statistical spread of measurements exceeds 5x10-4 with a path length more than 2 mm.
 

The small dimensions of the laser-ultrasonic beam (2 mm) allow the local measurement of the velocity of the longitudinal and shear waves simultaneously. According to the velocity and density of the material, a complete set of material elastic modules (Young's modulus, shear modulus, Poisson's ratio) is calculated locally. Relative accuracy is better than 2%. The distribution of the longitudinal wave velocity CLZ and the velocity of the Rayleigh wave CRX along the sample are presented below. Measurements of ultrasound velocities unambiguously detect the localization region of internal stresses. These data are necessary for calculating the residual life of a part and determining its "weak" places.
 


Measurements of the local elastic properties of the chaped-charge element are presented below. The laser-ultrasonic measurement of the Young's modulus distribution of the chaped-charge element material (ZVP01) showed its variation at 8% over the surface of the element, which leads to an unstable formation of the cumulative jet.