A. Strozzi

A Mass-Conserving Complementarity Formulation to Study Lubricant Films in the Presence of Cavitation

A new mass-conserving formulation of the Reynolds equation is developed using the concept of complementarity. This new method overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. Validation against a number of analytical and semi-analytical formulations, for a variety of problems including textured bearings and squeeze film dampers, is performed. The current formulation is shown to be in very good agreement with existing analytical and numerical mass-conserving solutions.

Axisymmetric Mechanical Analysis of Ceramic Heads for Total Hip Replacement

An axisymmetric, mechanical analysis of conical press-fit ceramic heads is performed. The head strength and its fracture modes are assessed experimentally. The stress field is examined by finite element, strain gauge and photoelastic methods. An alternative head design, characterized by a cylindrical engagement with the stem, is analysed with the same techniques and its merits are explored.

Static Stresses in an Unpressurized, Rounded, Rectangular, Elastomeric Seal

The Static Stress field in and unpressurized, rounded, rectangular, elastomeric seal is examined using both experimental and numerical techniques. A particular stress separation method is successfully employed in the photoelastic study. The salient features of the stress field and their relevance to the seal performances are outlined. An approximate theoretical model is proposed which permits the determination of the contact pressure profile.

Theoretical analysis of an unpressurized elastomeric O-ring seal inserted into a rectangular groove

Abstract Based on linear elasticity, a theoretical model is developed which is able to describe the mechanical behaviour of an unpressurized, elastomeric O-ring seal inserted into a rectangular groove. First, the analytical tools employed to handle the unilateral contact problem and to improve the pressure profile regularity are discussed in detail. Next, an assessment of the model is performed for a laterally free seal, for which a variety of studies exist in the literature. Finally, the model is applied to the analysis of a seal installed into several grooves of different width, and the results retrieved are compared with the few data available. The model response to a perturbation of Poisson ratio of the elastomer is also critically examined.

Formulation of three lubrication problems in terms of complementarity

Abstract It is shown that the cavitation, the mixed lubrication and the tangential velocity slip problems can be rigorously described in terms of the complementarity formulation. The salient aspects of this formulation are discussed. A numerical example dealing with the tangential velocity slip problem in a lubricated rigid slider is presented.

Normalization of the stress concentrations at the rounded edges of a shaft–hub interference fit

The elastic stress concentrations developed from the keyless frictionless static press-fit of a shaft into a hub are addressed. Two configurations are examined, namely (a) an infinitely long solid shaft press-fitted into a hollow hub with bore rounded edges, and (b) a shaft with filleted extremity, partially inserted into a hub. Derived from an analytical approach, a normalizing parameter is proposed that accounts for the combined effects on the stress concentrations of the fillet radius, the shaft radius, the interference, and Young’s modulus. With the aid of finite elements, various design charts are compiled that report the elastic stress concentrations within the hub versus the proposed normalizing parameter. Each curve is valid for a fixed ratio of inner to outer hub radii.

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.

Maximum Equivalent Stress in a Pin-Loaded Lug Subject to Inclined Loading

The elastic maximum equivalent stress in a pin-loaded, straight- or taper-shanked, round-ended lug subject to inclined loading is investigated using the finite element and the boundary element methods, and, partly, photoelasticity. The influence of the load direction, of the ratio between the bore diameter and lug width, and of the shank taper angle are particularly addressed. In addition, the effects of the axial length of the lug trunk and, partially, of the initial clearance between the lug bore and pin are numerically examined in the presence of a loading variously inclined to the lug axis. An interpolating expression for the maximum equivalent stress as a function of the ratio between the bore diameter and lug width, taper angle, and load inclination angle is proposed.

Hoop stresses in the con-rod small end

Abstract 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 con-rod 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.

Mechanical analysis of an annular plate subject to a transverse concentrated load

Abstract The periphery deflection in an annular plate clamped along its inner edge and loaded at its outer boundary by a transverse concentrated force are studied via a series solution. The corrected expressions for the series coefficients are presented. The series convergence is accelerated via a simple technique. Approximate methods are proposed to account for the compliant clamp and shear strain effects on the plate deflections, and they are validated against simplified theoretical models.