Numerical Investigation Helical Gear in 4 × 4 Off-Road Gear Mechanism

The helical gear used in the 4 × 4 off-road gearbox is designed with materials capable of enduring substantial torque loads and accommodating high engine speeds. However, a disconcerting issue has arisen, after a mere 2 years of operation, the gear’s surface has fractured, a circumstance occurring prior to the projected economic lifespan of the component. Thus, the purpose of this research was to determine the causal factors of 4 × 4 off-road helical gear failure by numerical simulation. Two types of CAD modeling were used, namely models without crack and with initial crack. Numerical simulation with the finite element method was also intended to obtain stress distribution values in both gear modeling types. Simulation findings in the absence of cracks indicated that the mean stress intensity factor (KI) was 14.01 MPa·m1/2. Meanwhile, the simulation with modeling with initial crack showed that the mean stress intensity factor was 54.65 MPa·m1/2. The mean stress intensity factor in the presence of a crack exceeded the material’s fracture toughness (KIC) value of AISI 1080 steel, which was 45.5 MPa·m1/2. The results of the stress intensity factor analysis suggest that the helical gear failure was caused by the initial crack that propagated and therefore caused a fracture.