Reasons for the fracture of the pin shaft of the truck mounted crane

The pin shaft at the connection between the mechanical arm and the hydraulic rod of a truck mounted crane suddenly broke during operation. The causes of pin fracture were analyzed using methods such as macroscopic observation, chemical composition analysis, metallographic examination, hardness testing, scanning electron microscopy and energy spectrum analysis. The results show that during operation, cracks initiated at the stress concentration point on the outer surface of the pin shaft, and the cracks rapidly propagated along the circumferential direction of the hardened layer to both sides, eventually converged to form cracks around the surface. Under alternating loads, circumferential cracks propagated along the direction of the applied force, formed dual source fatigue cracking. When the remaining effective strength of the pin shaft was insufficient, the pin shaft experienced a one-time rapid fracture.