NDE of low-velocity impact damages in composite laminates using ESPI, digital shearography and ultrasound C-scan techniques

In this paper, the low-velocity impact damage in composite laminates was investigated by three NDE (Non-destructive Evaluation) techniques, Electronic Speckle Pattern Interferometry (ESPI), digital shearography and ultrasound C-scan. The objective of this study is to evaluate the detection performance of each NDE technique against low-velocity impact damage in fiber glass composite laminates when the specimen was inspected from front surface (impact side) which may be available in depot level. Unidirection and crossply fiber glass composite laminates were impact damaged with four energy levels (5, 10, 15, 18 J) by drop weight impact machine. The results showed that ESPI and digital shearography techniques were able to identify the barely visible low-velocity impact damage. However, some limitations for detection depth were found in ESPI and digital shearography because the impact damage on reverse side was rarely detected by them. Nonetheless, ESPI and digital shearography techniques were estimated as one of useful NDE methods embedded with improved post processings including image process and optimal calibration method for different excitations.