Detailed design of fretting fatigue apparatus and tests on 7050-T7451 Al alloy

The aim of this work was to design a fretting apparatus and to carry out a series of tests to evaluate the effect of a mean bulk load on the fretting fatigue life of an aeronautical Al 7050-T7451 alloy. The device was mounted on a servohydralic test system. The configuration chosen to carry out the experimental program was of cylindrical pads pressed against flat tensile specimens. A model was proposed to compute the apparatus equivalent stiffness, which controls the magnitude of the fretting load. The tests were designed so that all relevant parameters, apart from the mean bulk load (always applied before the contact loads), were kept constant. This essentially means that the equivalent shear stress amplitude computed at a material point, as defined in many multiaxial stress based high cycle fatigue models, was identical from test to test although the registered fretting lives varied greatly. These results pose a great challenge to a number of fretting lifing methodologies available in the literature.