The mechanical shear strength of dry and lubricated interfaces is evaluated by measuring the frictional force during sliding of a hemispherical pin in contact with a flat slide. The solids investigated include bare glass and aluminum-coated glass and interfaces are generated from pairings of these materials. Lubrication is obtained by depositing a stearic acid Langmuir-Blodgett layer on the slide. Shear strength is measured at contact stresses ranging from ~ 0.05 to 0.8 GPa and at a sliding speed of 60 μm s−1. The shear strength of dry interfaces is found to increase with contact stress, and increases slightly with aluminum film thickness. Because stearic acid adheres to glass and aluminum, the shear strength of lubricated interfaces originates from the interaction of two stearic acid layers generated from molecular redistribution over the surfaces during sliding. For lubricated interfaces, the shear strength increases nearly linearly with contact stress, in agreement with the results of earlier work. The shear strength of stearic acid is found to depend slightly on the combination of sliding materials. Lubricant durability is found to be largest in glass/glass sliding interfaces.

Bendability is an important forming parameter in many applications, but particularly in automotive parts where the formed parts in structures can be quite complex, and where outer skins are joined to inner panels through the hemming process. In this paper the bend performance of two aluminium based automotive alloys, the heat treatable skin alloy, AA 6111 and the non-heat treatable structural alloy AA 5754, are assessed by the cantilever bend test. This test enables the load ± bend angle relationship to be monitored, and provides a bend surface that can be examined for different bend angles, since the bending pin does not contact the specimen surface in the local region of the bend. The results demonstrate that the cantilever bend test can differentiate between different bend performance, and the differences relate to the damage process involved in bending. In the heat treatable AA 6111 the bendability is dependent on the alloy temper, which controls the bend angle at which large surface cracks appear on the surface. This fracture process is a result of differences in the development of surface topography and surface damage with bending strain. The AA 5754 alloy has similar behaviour, but the performance is superior to the best of the AA 6111 tempers, and re¯ects a lower rate of surface topography development, and an absence of signi® cant surface cracking over the bend angle range investigated.MST/5130

This paper reports measurements of the shear strength of dry and lubricated Au/Au, Al/Au and glass/Au couples from measurements of the frictional force during sliding of a hemispherical pin in contact with a flat side. The Au and Al surfaces are generated by vacuum deposition of thin metal films on glass. Shear strength is measured at a sliding speed of 60 μm s−1 and at contact stresses ranging from ~ 0.05 to 0.8 GPa. Lubrication is achieved by depositing a stearic acid on the slide. The shear strength of dry glass/Au sliding interfaces is found to increase linearly with contact stress but decreases slightly with increasing thickness of the gold film. The shear strength of dry Au/Au interfaces is larger than that of dry glass/Au. Stearic acid does not protect gold from mechanical wear during sliding because the acid is expelled from the gold/gold interface, even at the lowest compressive stresses used. These observations are interpreted in terms of the weak adhesion of stearic acid to gold. In contrast, stearic acid sustains mechanical shear in interfaces consisting of gold sliding on either bare glass or aluminum, to which the acid adheres. These observations suggest that a boundary lubricant film protects against mechanical wear if it adheres only to one of the contacting surfaces.

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