Abstract: Impact damage is a harmful defect, which is easily induced in composite structures during manufacturing and in-service. Impulse ultrasonic wave reflections in carbon fiber-reinforced composites (CFRC) are analyzed. Ultrasonic surface dead-zone (USDZ) and lateral resolution (LR) can be improved markedly when time-width of probe pulse (TWOPP) is decreased reasonably and its property is polished appropriately. The datum about depth and size of impact damages in CFRC body can be extracted from ultrasonic reflected signals at damages and their time-of-flight (TOF). B-scan and C-scan in depth (or T-scan) imaging techniques based on the investigated high-resolution ultrasonic method are employed to explore the details and to carry out visualized inspection and quantitative evaluation of impact damages induced in CFRC laminated specimens. Experimental results have shown that time-resolved reflections resulted from defects nearby CFRC specimen surface can be obtained distinctly when their TOFs are close to the half of TWOPP and probe pulse has a single duration in time domain. In this case, the USDZ and LR can be approximately reached to the thickness of a single pre-preg ply of CFRC laminate, i.e., 0.13 mm. The distribution and development as well as depth of impact damages in cross-section of the CFRC laminated specimens can be seen well by using serials of B-scan imaging technique. The quantitative information about impact damage zone and size along layup direction of CFRC laminated specimens can be excavated and determined exactly by using ultrasonic T-scan imaging method. The combination of the two kinds of imaging methods provides a powerful imaging and quantitative approaches for evaluation of impact damage as well as visual exploring 3D behavior of impact damage in CFRC laminates.

Key words: Composites, Damage behavior, Impact damage, Non-destructive testing, Ultrasonic imaging