Analysis of crankshafts vibrations to compare the dynamic behavior of steel and cast iron crankshafts

Due to the requirements of advanced industries to use lighter materials at high speed, static analysis of stress and strain can not be applied as a complete and powerful method, the dynamic behavior of the system should also be considered, however, the results should be confirmed by experiment. In this research, first, in order to investigate the effects of flywheel on natural frequency of crankshaft, the crankshaft, by using ANSYS software, was modeled in two cases; with flywheel and without flywheel at free-free condition. In the second phase, experimental modal analysis; the way that gives particularization of system responses, was applied to measure Frequency Response Function FRF). To do the experiments, the crankshaft was hanged in the laboratory and impact testing was applied to obtain FRF by a two channels FFT analyzer. Since the FRF is independent from input forces and actually it shows the inherent characteristics of the structure at the measuring points, FRF was measured just at drive points for each crankshaft. Finally, based on theoretical and experimental results, it is concluded that the cast-iron crankshaft is better to be used in NISSAN-2400 engines than steel crankshafts. © 2006 Asian Network for Scientific Information.