Comparison of Damage Distribution and Ultrasonic Nonlinear Responses of Two Typical Plate Structures

Abstract: In engineering, it is important to evaluate the structures' health on early time. Due to the excellent sensitivity to micro defects, ultrasonic nonlinear technique has become one of the best choices to monitor the early damages in alloys. It’s worth studying whether the detection method obtained from regular specimens is universal. In power equipment, plate with constant thickness (PWCT) and plate with varying thickness (PWVT) are two common structures on which it is necessary to implement early damage detection. Axial tensions on the two AA6060-T6 structures are simulated and the results show that the plastic deformation is equal everywhere along the axis in PWCT while that presents a linear change in PWVT. The nonlinear ultrasound experiments are made in simulation. The results show that A₂/A₁2 goes up linearly in PWCT but in PWVT it presents a quadratic growth. With constant propagation distance, A₂/A₁2 shows a linear relation to the plastic deformation in each structure. The wave equations of ultrasonic stress waves propagating in PWCT and PWVT are constructed and solved. According to the solution, the quantitative characterization methods of plastic deformation in PWCT and PWVT are proposed respectively. This research shows that the shape of the structure can affect the damage distribution, however, the quantitative early damage detection can still be conducted by ultrasonic nonlinearity through reasonable analysis.