Model-based measurement of internal geometry of solid parts with sub-PSF accuracy using laser-ultrasonic imaging

Abstract

The problem of workpiece tolerance verification is of high interest in the field of nondestructive testing and evaluation. In this paper, reflection mode immersion 2D laser-ultrasound tomography is proposed for control of dimensions of solid objects with piecewise linear surface profiles. Pulsed laser radiation is used for generation of short ultrasonic probe pulse providing high spatial resolution. Wideband array of piezofilm sensors is used for detection of the waves reflected by the external and internal surfaces of the object. The image reconstruction algorithm accounts for refraction of acoustic waves at the liquid-solid interface. The contrast-enhanced reconstructed image is processed using the virtual model of the inspected part and the least-squares method to measure its actual dimensions. The accuracy obtained in the experiments with PMMA and duralumin samples is better than 100 μm in axial direction and is better than the size of the point-spread function in the material of the inspected part.