Hoop stresses in the con-rod small end

Having in mind con-rods for motorbike and car engines, and spurred by the disagreements evidenced in the pertinent literature, the maximum circumferential stresses within the small end are investigated analytically, photoelastically, and numerically. The analytical models are based upon a plane assumption, and they adopt both beam and theory of elasticity idealizations. The plane photoelastic study concentrates on small ends with outer to inner radii ratios ranging from 1.2 to 1.5. A plane numerical model aimed at thoroughly mimicking the pin ovalization is developed, and a design chart of the peak hoop stress within the small end is provided for a wide spectrum of small end and pin geometries, for zero initial clearance. Such diagrams allow a prompt preliminary dimensioning of the small end to be carried out, which may be refined by effecting a three-dimensional finite element study of the specific conrod geometry. The consequences of an initial clearance between small end bore and gudgeon pin are examined for selected geometries, and three-dimensional aspects are explored for specific con-rod shapes.