In-line monitoring of 3D printed parts is vital if quality is to be maintained with this new manufacturing modality. Specifically, the reliable detection of pores in printed parts is vital if the finished products are to have the desired strength characteristics. In this work, we utilize COMSOL(Burlington, MA) to numerically compare a new detection method where the interferometer and laser-generated ultrasound are focused at the same spatial location. The changes in the surface response to defects in the near-field of the induced ultrasound wave are then assessed as a function of defect size and depth. Our numerical results demonstrated that the impact of defects was easier to visualize when quantifying the surface velocity as opposed to surface displacement. The amplitude of the difference is comparable to that observed when utilizing scattering of the Rayleigh wave in the detection. However, the new approach does not require a 1 mm separation between the laser-generating ultrasound spot and the interferometer improving the spatial resolution of the detection.

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