NDE Characterization of Surface Defects on Piston Rods in Shock Absorbers Using Rayleigh Waves

In general, shock absorbers are components that can absorb shock and vibration energy caused by wheel behavior, and they provide handling stability. As a piston rod is an important component in shock absorbers, multiple processes are performed in order to guarantee its quality during manufacturing. Micro-defects can be generated on the surfaces of piston rods after processing. Because these defects can degrade the function of shock absorbers, proper non-destructive techniques are necessary to monitor the surfaces of piston rods. In this study, micro-defects were artificially machined on the surfaces of piston rods. In particular, a Rayleigh wave technique was adopted to detect defects on the surfaces of the piston rods, and Rayleigh wave behaviors were analyzed to establish beam profiles. In terms of the experimental method, defects were fabricated on the piston rods, and the optimal Rayleigh angle was determined using the pulse-echo method with ultrasonic transducers in a water tank. This was performed to evaluate the characteristics of the Rayleigh waves. In testing, regardless of the types of micro-defects on the surfaces of the pistons, it was found that the optimal inspection condition could be in the range of 5–10 mm, where ultrasonic signals were received with a high resolution. Moreover, the behaviors of the transmitted Rayleigh waves were simulated, and reflection, transmission, and scattering occurred due to defects at the interface between the water and steel. Thus, the propagation of Rayleigh waves and the optimal test conditions were implemented through FEM simulation to generate effective Rayleigh waves.