Subsurface imaging of glass fibres in a polycarbonate composite by acoustic microscopy

Using reflection acoustic microscopy at 800 MHz, we have imaged 10 m diameter glass fibres embedded in an optically opaque Makrolon (polycarbonate) matrix. Maximum depth of acoustic waves contributing to image formation was 105 m, with imaging resolution of several microns at shallower depths. The areal fibre distribution, lengths, and orientations were readily determined non-destructively from the acoustic images. Additionally, marked differences were observed between known normally bonded samples with high strengths, and poorly bonded samples from parts which exhibited fracturing and premature failures. In addition to acoustic microscopy, bulk sound velocity measurements were made and used to compute focus aberration for subsurface imaging. Results were correlated with destructive SEM techniques.