Experimental and numerical investigations on fatigue behavior of 42CrMo4 high-strength steel single lap double-bolted joints

Cold extrusion forming is a manufacturing technology that effectively extends the fatigue life of mechanical structures and has been widely used in the processing of ship components. The fatigue behavior of 42CrMo4 high-strength single lap double bolted joints is investigated based on fatigue experiment and numerical simulation. The stress-strain distribution of joint plates under cold extrusion, bolted tightening and longitudinal external loads are evaluated based on the nonlinear finite element software ABAQUS. The fractographic of fatigue specimens is detected by scanning electron microscopy (SEM) to research the initiation location and propagation type of fatigue cracks, and a prediction method for the stiffness of joint plate bolt connections is further proposed. The results indicate that fatigue cracks propagated tortuously and exhibits a more complex distribution state. The combination of cold extrusion forming and bolt preload can effectively improve the fatigue life of high-locked bolted joints. Smooth surface, beneficial residual stress field and cold extrusion hardening phenomenon are considered the main reasons for improving fatigue life.