Contact between a centrally loaded plate and a rigid or elastic base, with application to pivoted pad bearings

Abstract

Coker and Filon first introduced the idea that the contact area between a pad and a support may decrease under the application of a load, the process subsequently called a ‘receding contact’ by Keer et al. Filon analysed the contact between two matching slabs under a line load, and showed that, for the two to remain in contact, the mid-plane contact stresses must change from compression to tension beyond a distance from the line load of approximately 1.35 times the slab thickness. Filon argued that, since the tensile stresses are small, in a real contact the two slabs will separate at approximately these locations. A photoelastic study by Frocht of the stress pattern when a line load acts through a pad resting on an elastic base supported Filon's prediction. It is shown by a three-dimensional finite element (FE) solution for the axisymmetric load problem that the radius of separation on a rigid base is significantly smaller than that calculated using the Filon assumption. When the pad is supported on an elastic base of the same material, the same is true, though both radii are significantly larger than with the rigid base. The results are applicable to several practical problems. For a rigid base, examples are two slabs pressed together by circular dies, and the initial geometry in resistance spot welding. The case of an elastic base is of wide application in civil engineering, when a pillar is supported on a bearing plate on an elastic base. In tribology it may explain the start-up under load of a centrally pivoted thrust pad bearing, which otherwise must rely on surface tension to retain a residual oil film.