Studying the effect of the electrolyte-plasma modification on the fatigue strength of the KamAZ-740 crankshaft after overhaul using finite element modeling

During the crankshaft overhaul, a hardened material layer is removed from the journal's surface. The resource and mechanical properties of such an engine have been shown to be considerably reduced when compared to the new one. The study proposes a method of electrolyte-plasma modification of the surface of the repaired journals of the KamAZ-740 crankshaft made of chromium-molybdenum-vanadium steel 42CrMoVA TU 14-1-5083-91 (analog AISI 4140) to restore and improve fatigue strength. The crankshaft was destroyed after overhaul and had a fatigue crack on the surface of the crankpin journal, which was examined. The microstructure revealed the formation of a phase of high-carbon martensite on the surface of the modified sample, as well as inclusions of carbides of alloying elements (Cr, Mo, V), and cementite (Fe3C). Microhardness analysis of the samples using the Vickers method showed an increase in surface hardness from 356...380 HV (initial structure) to 592...624 HV (after modification). The behavior of the KamAZ-740 crankshaft when exposed to cyclic operating loads was modeled using the finite element method in the ANSYS Mechanical analysis software. The analysis showed that the greatest stresses of 91.673 MPa occur in the bearing fillets of the crankpin journal, and the maximum values of deformation of the neck body reach 11.829 microns. It was found that the ground crankshaft, without surface hardening, has a reduced number of operating cycles up to 163070, but after surface electrolyte-plasma modification, it can operate for an unlimited number of cycles. The method of electrolyte-plasma modification of the surface of the crankshaft journals makes it possible to increase the safety margin by 18... 38%. The results of this study are of practical importance for improving the quality of overhaul of steel crankshafts of diesel and gasoline engines and extending their service life.