Engine Crank Shaft Fracture Analysis
Engine crankshafts are the main components that convert reciprocating linear motion of pistons into rotational motion. Generally, it consists of a crank pin, journal, crank web, bearing bevels, fillet radii and oil passages that play a significant role in the functioning of a combustion engine. Crankshafts can fail due to a number of factors such as fatigue, torsional vibration, thermal shock and corrosion.
Crank shaft fracture is one of the most common failure types observed in internal combustion engines. When a crankshaft breaks, the most common cause is fracture due to fatigue or torsional vibration. In this failure mechanism, cracks propagate from the surface along stress concentrations and reach a critical size before the fatigue limit is reached and final fracture occurs. In this paper, we will analyze the causes of crankshaft failure and discuss the factors that contribute to it.
In the automotive industry, fatigue is the predominant cause of crankshaft fracture. This phenomenon is characterized by the progressive accumulation of microscopic cracks caused by the repeated cyclic loading on a material. The fatigue behaviour of metals is typically inversely related to their hardness and tensile strength. As the hardness increases, the fatigue limit decreases and then fatigue cracking occurs at a faster rate. Fatigue damage is usually seen in the inner-most race of the crankpin bearing due to the presence of minute surface and subsurface cracks. In addition, it is also known that the amount of stress in strained regions of crankshafts influences the fatigue damage rate and lifetime.
Torsional vibration can also lead to crankshaft fracture. This is a phenomenon in which an oscillatory motion is imparted to the crankshaft, resulting in cyclic variations in both angular velocity and angular acceleration of the crankshaft. The magnitude of the torsional vibration is dependent on the engine’s speed and the crankshaft’s length and stiffness. As the crankshaft endures cyclic forces and moments, higher levels of stress occur at certain points, which can lead to fatigue and finally result in fracture.
Thermal shock can also contribute to crankshaft fracture. Thermal shock occurs when a material is subjected to a sudden change in temperature, often due to changing engine operating conditions. In engines, crankshafts are exposed to extreme temperature variations which can lead to uneven stress distributions, a decrease in tensile strength and finally, failure.
Corrosion is another aspect that needs to be considered when analyzing crankshaft failure. As the crankshaft is exposed to different environmental conditions, it can suffer from rust and wear, resulting in cracks and failure.
In order to prevent crankshaft fracture, it is important to take proper corrective measures.Materials used in the manufacture of crankshafts should be chosen carefully depending on the expected operating conditions. Applying adequate HRC values to these materials and implementing suitable heat treatment processes can increase their durability and decrease the probability of crankshaft failure. Additionally, regular maintenance practices such as lubrication, cleaning and inspection of crankshafts are also important.
In conclusion, crankshaft fracture is a common problem in internal combustion engines due to fatigue, torsional vibration, thermal shock and corrosion. Therefore, taking appropriate steps to address these causes and ensuring proper maintenance is crucial in preventing crankshaft fracture.
