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A new apparatus for investigating friction and metal-to-metal contact in fretting joints is described. This apparatus is used with a standard, flat-plate, reciprocating-bending fatigue machine to induce fretting at the surface of the critical section of a fatigue specimen. A practical range is possible for both the normal contact force and the cyclic amplitude of the relative sliding motion between the fatigue specimen and the second fretting surface, a cylindrically shaped fretting shoe. The most important part of the apparatus is a special force transducer which permits the friction between the two surfaces to be continuously observed. This force transducer and an electronic circuit for estimating contact between the surfaces are described. Data showing friction-force and metal-contact characteristics in the range from zero to 106 fretting cycles are presented for tests conducted with 7075-T6 aluminum alloy and Ti-6Al-4V titanium alloy. The friction data indicate an increase in friction during the first 104 to 105cycles followed by a relatively high, but stable, friction force for the remaining fretting cycles. Metal-contact data indicate good contact early in each test and poor contact later in each test.
testing, fatigue, fretting, friction, joint, aluminum alloys, titanium alloys
Assistant Professor, The University of Wisconsin, Madison, Wis.