Investigation Of Crankshafts Fatigue Damage For Characterization Based On Micro-Electrical Resistance Measurement Technology

In 2008 about 10 million vehicles were produced and sold in China. China has become the country whose number of vehicles produced and sold was the second after USA. At the same time, the annual number of End-of-Life Vehicles (ELV) covers 6 percent of existing ones. Remanufacturing is one of the best methods of solving the difficulty. But the residual life of the components of ELV is the key factor affecting the reliability of remanufactured components. Therefore studying the fatigue damage law of typical components is the urgent task to guide the assessment of the residual life.This paper studied the typical crankshafts of auto engines. Based on micro-electrical resistance measurement technology, the fatigue damage course was investigated by using micro-electrical resistance as a parameter to discover the fatigue damage law of micro-electrical resistance of crankshafts.Firstly, do the experiment of investigation of micro-electrical resistance to the rolling-bend standard 48MnV specimen. Compared with the theoretical model of metal fatigue damage, the measuring result indicates that the measuring data has the agreement with the theoretical model, and the data fit well with the model during from the beginning to the moment of crack emergency. At the moment of crack emergency the data differ from the theoretical model. After that they have the same trend and get to infinite maximum. Meanwhile this experiment proved that the parameter of micro-electrical resistance describing the procress of fatigue damage of crankshafts is feasible. Secondly, in order to do the experiment of fatigue damage of crankshafts, the bend fatigue damage measuring system of crankshafts was developed based on virtual instrument technology. The system has the functions as follow: output of analogue sine wave signal, data acquisitions, scanning resonance frequency automatically, adjusting constant load, automatic diagnosing the failure of crankshafts, display and saving of real sigal, micro-electrical resistance measureing and so on.Finally, the experiment of parameter characterization for fatigue damage of crankshafts using micro-electrical resistance was made. The experiment drew the conclusions as follow: during the whole fatigue life the micro-electrical resistance is becoming bigger and bigger with the increase of cycle numbers, and the bigger the load is, the more speed the micro-electrical resistance increases. Under the load level of 2500NM for crankshafts, the micro-electrical resistance is increasing slowly at the stage from the beginning to macro crack emergency which covers 70~80 percent of whole life, and the micro-electrical resistance varied badly at the moment of macro crack emergency. After that the micro-electrical resistance increased quicklly until the failure of crankshafts. The whole increased amplitude of micro-electrical resistance allows of 20~30 percent of original one. Otherwise the theoretical model of fatigue damage was explored and the functional formular was expressed.This paper attained the law and model of micro-electrical resistance for fatigue damage of crankshafts through the experiment, explored the new method describing the fatigue damage of crankshafts, and gave guidance to asses the residual fatigue lfie of ELV crankshafts.