Structural integrity analysis of the main bearing cap screws of the turbo-diesel engine crank shaft

This article presents a study about the structural integrity of screws used in the fixation of the main bearing cap of the crank shaft of a turbo-diesel engine. Such a component was chosen for such an analysis for being an element of essential importance in the structural integrity of the engine. In this context, the main failure mode was fatigue. Functions of capacity and demand were determined. Two demand functions were built, one based on Goodman's diagram and the other one on Gerber's diagram. The parameters that characterize such functions were obtained by means of tension tests, hardness tests, and finite element analysis. For the characterization of the stress loading history applied in the screw, extensometer techniques were used. Based on those results, safety factor, reliability index and reliability of the screw were considered. The reliability index and the reliability were estimated according to Monte-Carlo, FOSM and ASM techniques. As result it was verified that those values are order 1.66% and 99.9%, respectively, to the safety factor and the reliability.