Abstract:
This research is to study the cause of failure of the crank shaft in a pickup car with a
power output of 120 Hp that has been in use for 15 years under proper maintenance. The
crank shaft is made from JIS-S55C hardened low-alloyed steel. It has been determined in many
ways on the failure analysis of this crank shaft i.e. 1) Composition (wt%) analysis with a
spectrometer, 2) Vickers test, 3) Microstructural analysis with optical microscope, which the
crack of surface layer using a scanning electron microscope. The summary result of fracture
surface of this crank shaft was cause by fatigue, where the initial crack occurs from the
weakened region causing high stresses to cause cracking and extending the inward crack area of
the crank shaft until a final fracture occurred consistent with the detection of beach marks,
ratchet marks, river marks and fatigue striations which these results indicate that the fracture
mode of the outer surface is brittle fracture. The microstructure of the outer surface region is
tempered martensite and the central region is an upper bainite. The maximum hardness of
approximately 40 HRC occurred near the surface and the minimum hardness is 18 HRC near
the center of the crank shaft. The results of the study will be able to identify the damage
mechanisms that occur and provide information for ways to prevent future shaft fracture