threshold, and whether or not stress states rather than surface conditions play a major role in the observed behavior. The parameters which govern the initiation and subsequent propagation of fretting fatigue cracks is still not well established. Thus the objectives of this investigation are to find several different fretting fatigue conditions analogous to the fatigue limit stress under uniaxial fatigue loading corresponding to a chosen high cycle fatigue (HCF) life. From these, both stress fields and stress intensity factors for specific cases can be obtained in order to find some commonality which may lead to development of parameters having broad application to fretting fatigue. EXPERIMENTS Tests were conducted using a high frequency test system to simulate the fretting fatigue loading conditions that occur in turbine engine blade attachments [1,2,3]. The apparatus uses flat fretting pads, with a radius at the edge of contact, against a flat specimen. Normal and shear loads are applied to the specimen as shown in Figure 1. A previous study has shown that the bending moment present in the apparatus is negligible relative to other parameters, and may be disregarded when designing the tests [4]. x y P P T M M T/2 T/2 Figure 1: Test geometry and loading schematic. The test geometry differs from conventional fretting fatigue tests [5,6] in two fundamental ways. First, the axial stress is transferred entirely to the fixture through shear. Resulting stresses in the specimen are zero on one end of the pad, thus the shear force into the pad is determined from the load applied to the specimen. Second, symmetry of the apparatus provides a specimen which breaks on one end, leaving the other end with a fretting scar and damage obtained under nominally identical conditions. As with a conventional fretting fatigue apparatus, the clamping force is constant and only the axial and shear loads are oscillatory. All tests were conducted at 300 Hz under ambient lab conditions. Specimens and pads were taken from forged Ti-6Al-4V plates used in a series of investigations under a U.S. Air Force sponsored high cycle fatigue program. The processing and microstructure are reviewed in previous work [7,8]. Each specimen was subjected to uniaxial fatigue using a step-loading procedure [9] to determine a fatigue limit stress corresponding to 107 cycle fatigue life. Tests were conducted by incrementing the maximum axial stress by five percent of the initial value for various combinations of specimen thickness, pad length, and clamping force. The step loading technique was validated in earlier fretting fatigue studies using the same apparatus [3,10], and is outlined in reference [11]. ANALYSIS Finite element analysis (FEA) results from a prior investigation [1] and additional computation provided stress fields through the specimen thickness and along the length of the specimen in the vicinity of the edge of contact. Load conditions were selected to cover a range of combinations of pad and specimen geometry, which produce average shear stresses typical of those tested in the experimental portion of the study. Conditions used in the numerical analysis are summarized in Table 1 along with some of the results for comparison. Axial stresses applied to the specimens in the model were taken from experimental
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