EFFECT OF EXTERNAL LOADING ON WEAR MAPS OF ALUMINUM-ALLOYS

Fretting fatigue tests differ from fretting wear tests in that an axia l (or body) load is added to the contact load. In most fretting device s, the contact amplitude, which has been shown to be a governing param eter in crack initiation, depends on the elongation of the test specim en which itself varies with the axial load. This difficulty can lead t o erroneous conclusions when transported to industrial components. In this paper, we present a new device and a new methodology which give t he test conditions leading to crack initiation. In this system, the '' body'' and ''contact'' loads and amplitude are controlled separately. The test is called ''fretting-static fatigue'' owing to the constant b ody stress (R = sigma(min)/sigma(max) = 1). Two fretting wear maps are discussed: in running condition fretting maps, zones of stick, partia l slip and gross sliding are identified; in material response fretting maps which plot equivalent stress vs. amplitude, the three zones of n o degradation, cracking, and particle detachment are identified. The s kin tension sigma(xx) is used to plot material response fretting maps. sigma(xx) appears a good criterion as it can be compared with the fat igue limit of the material and can take into account the original resi dual stresses in the crack domain. In addition, sigma(xx) can be used by designers to predict the life of industrial components. This method ology is applied to the fretting fatigue characterization of three ind ustrial aluminium alloys (2024, 2091 and 7075) widely used in aeronaut ics. Their fretting behaviour is discussed with respect to material pr operties such as fatigue limit and crack propagation resistance.