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Cases of corrosion of metal coated on its inner surface with insulating materials are frequently encountered, particularly where the insulation has become damp. Since this problem first arose acutely, shortly after the introduction in this country of the first all‐steel railway carriages some 24 years ago, many attempts have been made to overcome the trouble. For a long time the mechanism of this kind of corrosion was in doubt. Some thought that the materials used, especially asbestos, were the prime cause. Various attempts were made to use non‐absorbent insulants or to waterproof the visible face of the insulation with a film of bitumen or the like.

Building societies, as we illustrated in the Preface, occupy an important position in the British financial system. There are at present over four hundred societies although this industry is highly concentrated, with the ten largest societies (with well developed branch networks) in 1978 accounting for 66 per cent of the total assets.

This paper aims to propose a normal and tangential contact stiffness model to investigate the contact characteristics between rough surfaces of machined joints based on fractal geometry and contact mechanics theory considering surface asperities interaction.

The fractal geometry theory describes surface topography and Hertz contact theory derives the asperities elastic, elastic-plastic and plastic contact deformation. The joint normal and tangential contact stiffness are obtained. The experiment method for normal and tangential contact stiffness are introduced.

The relationship between dimensionless normal contact load and dimensionless normal and tangential contact stiffness are analyzed in different plasticity index. The results show that they are nonlinear relationships. The normal and tangential contact stiffness are obtained based on theoretical and experimental methods for milling and grinding machined specimens. The results indicate that the present model for the normal and tangential contact stiffness are consistent with experimental data, respectively.

The normal and tangential contact stiffness models are constructed by using the fractal geometry and the contact mechanics theory considering surface asperities interaction, which includes fully elastic, elastic-plastic and fully plastic contacts deformation. The present method can generate a more reliable calculation result as compared with the contact model no-considering asperities interaction.