R. Rosi

Influence of the initial clearance on the peak stress in connecting-rod small ends

Abstract The stress increase that is caused by the presence of an initial clearance within the small end of connecting rods for motorbike and car engines is investigated. Plane analytical and numerical modellings of the dry contact between the small-end and piston pin are adopted. Based upon a recent analytical result, a normalizing parameter is introduced, which allows the stress concentration factor at the small-end bore sides to be expressed as a function of a proper combination of the initial clearance between the small end and gudgeon pin, the applied load, and Youngs modulus, for prescribed aspect ratios of the small end and hollow pin. Design diagrams summarizing the consequences of an initial clearance between the small-end bore and gudgeon pin on the eye peak stress are reported, which cover a wide range of geometries, clearances, and loadings. Selected comparisons between two-dimensional and three-dimensional models are carried out.

Influence of different temperature distributions on the fatigue life of a motorcycle piston

In this paper, finite element analyses are performed to evaluate the stresses and the strains in a motorcycle piston. Non-linear finite element models are employed to mimic the piston behaviour when subjected to different loading conditions. In particular, the gas forces, the inertial forces and the piston-to-cylinder contact forces are considered. Appropriate temperature distributions are applied to the model to include the thermal stresses and strains in the analyses. Two different thermal configurations are considered: the first has a standard design of the oil jet hitting the underside zone of the piston crown, while the second presents modified parameters able to increase the heat transfer coefficient appreciably. The different operating temperature distributions related to the two thermal configurations considered strongly influence the piston’s thermomechanical behaviour. This paper aims to perform high-cycle fatigue analyses to show how the fatigue life and fatigue-critical points of the component change when moving from the standard configuration to the modified configuration.

On the Applicability of the Loading Parameter Φ in Pinned Connections with Relevant Initial Clearance

In pinned connections, the presence of an initial clearance increases the lug stress concentration with respect to a neat fit configuration. By employing a recently proposed loading parameter Φ valid for plane models, the applied load and initial clearance effects on the stress concentration are normalised for a straight-shanked, round-ended, longitudinally loaded pin-lug connection of fixed outer to inner radius ratio. Results are obtained with a Mitchell-type, Fourier series solution and with commercial Finite Elements. The applicability of the loading parameter Φ to pinned connections with small to relevant initial clearances is explored. Two preliminary design charts are presented, which quantify the lug stress concentration factor versus the loading parameter Φ for two lug geometries defined by inner to outer radii ratios of 0.376 and 0.77.