The numerical evaluation of multi-piece crankshafts

Abstract

This work develops a methodology for the FEM simulation of a multi-piece crankshaft. Various simulation models that include press-fit joint contact conditions and complex meshing schemes are examined in order to accurately capture details of the stress fields present at the stress concentration area (labeled as the SCA) on the edge of the press-fit. The maximum stress components are demonstrated to be of limited values (non-singular) and Hertzian in nature. To obtain the stress convergence sufficiently small elements, which can be determined using a 2-D axisymmetric model, are required at the vicinity of the SCA. The same level of mesh refinement is then used for large 3-D FEM models of the crankshaft geometry, to study the resulting behavior of the press-fit joint for the dynamic operating loads. However, it may not always be possible or practical, as some limits on the mesh refinement have to be imposed to obtain a reasonable computational time to run such models. Less complex 'equivalent' symmetrical FEM models are investigated to determine if these models can provide a sufficient level of accuracy at an acceptable computational effort. Such models may be useful as practical design tools, producing data to speed up the decision making process. The simulation results are compared to some test data for the stress state monitored in real crankshafts under operating conditions. 'Intuitive' design sensitivities to various crankshaft parameters are examined as well. The numerical tools and engineering rules developed in the thesis may be applied to systematically improve the design by extending the joint's life and/or load carrying capability.