| Rear axle shaft is part of the tronton truck which transfers force from the differential to each rear wheels, and is an important part of the system, because failure at this component will render the truck useless and possess greater risk. This study is based on the facts from CV. XYZ’s rear wheel shaft failure. The shaft which failed was a two months old shaft, which could be classified as new, but failed in such a short usage time. Based on these facts, metallurgy study is chosen to analyze the failure of the rear wheel shaft. The first step is collecting data such as truck specification, shaft type and history of truck until it experiences failure. Then, visual observation is done on the fail shaft by pointing the position and shape of the fracture. Observation towards the fracture surface shows signs of fatigue fracture with short beach mark, that concludes the shaft is brittle. After visual observation is done, the shaft is then undergoes OES (Optical Emissions Spectrometry) to identify the chemical composition of the material. It also undergoes a metallography method to observe the micro-structure on the area around the fracture area. Then, hardness testing by using Rockwell B method is done to see whether there are changes on the value of the rear wheel shaft’s hardness or not, also to define the depth of the hardening. From the result of the observation and testing, it is found that there are neither changes in the micro-structures nor the hardness value of the rear wheel shaft. However, from the measurement of the depth of the hardening, it is obtained that a 5 mm value is the upper limit of the permitted hardening standard. From the chemical composition test, the shaft material was supposed to be AISI 5140 steel, but actually it is AISI 6150 steel. From the calculation of working force, it is obtained that the maximum shear stress is 346,46087 MPa. From the data collected, it can be concluded that the rear wheel shaft failed because : mistake in choosing material, which caused the rear wheel shaft to become more brittle; based on the shape of the fracture and the working load, the shaft failed because of excessive torsion load (torsional fatigue). |