Theoretical and Experimental Study of the Stress Concentration Factor in Diesel Engine Crankshafts

The paper deals with the bending stress concentration evaluation of a marine diesel engine crankshaft. Experimental strain gauge tests were conducted on a full scale single crank to measure the stress concentration near the crank fillet. A three-dimensional finite element schematization of the crankshaft and the linear elastic calculations conducted show the stress field along the most overstressed zone and how it is influenced by different load conditions. It is now possible to calculate accurately the stress concentration factor K_t. However, a mesh of a mechanical element with a complex geometry like crankshaft is very expensive and difficult. Therefore a bidimensional model of the crankshaft has been also considered: experimental tests and numerical analyses under different load conditions were also carried out in this case. The agreement between the results obtained from these different kinds of analyses is good. The values of the stress concentration factors obtained from bidimensional and three-dimensional analysis with the same boundary and load conditions are similar. A plane model of crankshaft can be utilized to determine the theoretical stress concentration factor K_t with considerable saving of calculation time.