Quantitative imaging of surface cracks in polymer bonded explosives by surface wave tomographic approach

One of the effective ways to quantitatively inspect or monitor an industrial structure is to obtain images via either scanning or tomography. A combination of ultrasonic guided wave approach and tomographic technique by employing a reconstruction algorithm for the probabilistic inspection of damage (RAPID) can be used to inspect effectively the damage area via visual images. In this paper, surface cracks in polymer bonded explosives (PBXs) were quantitatively evaluated by a Rayleigh surface wave tomographic approach. Considering the relative low wave velocity in the material tested, special surface wave transducers with silicone wedge were designed and produced. The measured signals of Rayleigh surface wave propagation in the specimen with and without cracks were used in a tomographic algorithm to reconstruct images of defects. Results indicate that the setup of the array of transducers has significant influence on the appearance of images. Optimal transducer array setups were also proposed to measure the ultrasonic wave signals for irregular shaped defects to quantitatively image irregular surface cracks in PBXs. It was shown that the image generated by the proposed approach with the optimal transducer array and shape factor calculation method has good agreement with the real defect shape. The present approach provides an alternative tool that can be applied to detecting, locating and imaging the surface defects in PBXs.