Failure analysis of the piston used in a pneumatic down the hole impactor

In this study, the piston's failure mechanism in the pneumatic down the hole(DTH) impactor has been investigated. Failed piston microstructure and hardness have been analysed using the SEM, nanoindentation and the Vickers hardness tester. The stress state of the piston during the impact process was studied using ABAQUS finite element software. The results show that the carburized layer transits from the acicular martensite phase to plate martensite from the surface towards the inside. According to finite element simulation results, the maximum Mises stress occurs when the piston strikes the bit at an angle of 0.22°, causing the carbide phase to crack. In addition, the stress at the piston's impact point propagates to generate tensile stress of 560 MPa on the piston's outer edge, causing the crack in carbide to grow along the radial and axial direction of the piston.