DOUBLE-SIDED ULTRASONIC TESTING AND IMAGING OF MULTILAYER COMPOSITES WITH OUT-OF-PLANE FIBER WRINKLING

For fiber reinforced polymers (FRPs), ply stacking errors and fiber waviness during manufacturing will have a great influence on the mechanical properties of composites, which requires non-destructive testing and evaluation (NDT&E) for potential structure defects. Herein, this study analyzes the ultrasonic echo signals in pulse-echo (PE) mode to assess the layered structure and sub-structure of laminates, analytically and numerically. Based on recursive stiffness matrix method and analytic-signal technology, analytical modeling is performed to investigate the propagation of ultrasound and detect the layered structure in flat laminates. In addition, a numerical finite element model is built to further study the propagation of ultrasound in wavy composites. Based on the circular variances of ply angles extracted by structure tensor analysis, the double-sided ultrasonic testing and B-scan imaging method is proposed to correct the imaging artifact areas of wavy composites. After statistical validation, this weighted sum method can indeed reduce the influence of ultrasonic beam deviation caused by out-of-plane fiber wrinkling, thereby improving the imaging effect in wavy composites.