Scanning acoustic microscopy investigation of weld lines in injection-molded parts manufactured from industrial thermoplastic polymer

Scanning acoustic microscopy (SAM) and Terahertz imaging analysis of weld lines in thermoplastic polymer (ABS) manufactured by injection-molding. [Display omitted] •Two techniques to investigate plastic welds, Ultrasonic Microscopy and Terahertz Imaging•Weld lines, inevitable draw backs of melds, of unpredictable locations and of weaker mechanical properties•Micro-elastic visualization of weld lines by Scanning acoustic microscopy•Micro-elastic heterogeneity and acoustic anisotropy•Birefringence at weld lines Scanning acoustic microscopy (SAM) is used to characterize welds in a thermoplastic polymer (ABS) manufactured by injection-molding, particularly at the locations of weld-lines known to form as unavoidable significant defects. Acoustic micrographs obtained at 420 MHz clearly resolve the weld lines with morphological deformations and microelastic heterogenity. This is also where terahertz (THz) measurements, carried out in support of the SAM study, reveal enhanced birefringence corresponding to the location of these lines enabling verification of the SAM results. Rayleigh surface acoustic waves (RSAW), quantified by V(z) curves (with defocusing distance of 85 μm), are found to propagate slower in regions close to the weld lines than in regions distant from these lines. The discrepancy of about 100 m/s in the velocity of RSAW indicates a large variation in the micro-elastic properties between areas close to and distant from the weld lines. The spatial variations in velocity (VR) of RSAWs indicate anisotropic propagation of the differently polarized ultrasonic waves.