Finite element simulation of ultrasonic reflection characteristics in layer-dropping composite structures

In order to study the ultrasonic propagation characteristics in the layer-dropping structure, this paper obtained the elastic matrix parameters of carbon fiber reinforced composite lay-up at any ply angle by introducing the concept of elastic matrix rotation transformation on the basis of analyzing the characteristics of the layer-dropping structure. The finite element method was used to perform numerical simulation and visualize the ultrasonic propagation process. With the non-reflective boundary condition set, the ultrasonic propagation characteristics of different upper and lower surface angles and heights in the layer-dropping structure are simulated. The simulation results show that when the angle is greater than 60° with the depth of the layer-dropping structure area is 12mm, the ultrasonic signal incident perpendicular to the upper surface cannot be reflected back to the upper surface through the lower surface. In this case, defects close to the bottom surface cannot be detected using ultrasonic reflection method.