Experimental Study of Helical Gear Failure in Off-Road 4 × 4 Gearboxes

The helical gear in a off-road 4 × 4 gearbox was found to have failed on the surface. Therefore, this study aims to determine the factors causing this failure through the application of visual observation, hardness test, chemical composition test, microstructure observation, Scanning Electron Microscope (SEM) observation, and stress analysis. The chemical composition test showed that the gear material is classified as high carbon steel with AISI 1080 standard, the average hardness value was recorded to be 95.49 HRB which is slightly lower than AISI 1080, and the microstructure is pearlite and cementite. Moreover, the observation of the fracture surface showed some initial defects propagated to a brittle fracture, while the shear stress value was found to be 286.13 MPa which exceeds the allowable shear stress limit of 253.47 MPa. It was concluded that the helical gear failed due to the initial defects in the form of fine cracks and the fact that the shear stress value exceeds the allowable limit.