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A study of inner crack testing with the laser phased array method

As the optical penetration depth and thermal diffusion effect are small, shear waves and longitudinal waves generated by a laser pulse in thermoelastic regime are generally weak in metallic materials. The method of laser ultrasonic is rarely applied to inspect the inner cracks. In this paper, phased array laser ultrasonic is developed to focus and steer shear waves and longitudinal waves, and obtain inner crack characteristics. Firstly, a two-dimensional laser phased array finite element model is established. Secondly, based on this model, a study on numerical simulation of interaction between shear waves and cracks is conducted by adjusting time delay of laser phased array. It is found by analysis that the position of cracks can be determined by monitoring changes of polarity of shear-tip-shear (STS) diffraction received on the surface of metallic materials and the depth of cracks can be determined by the time of flight of STS diffraction and shear-tip-longitudinal (STL) diffraction. Last of all, a study on numerical simulation of interaction between longitudinal waves and cracks is also conducted. This study provides a possible method for the detection of inner cracks in metallic materials.