PSI - Issue 42

Denny Knabner et al. / Procedia Structural Integrity 42 (2022) 561–569 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 2: Results of the fretting-fatigue experiments on the connecting-rod ─ bushing assembly; x:failure, o:run out, F: fictitious attempt , (MPa) , (MPa) Stress ratio = 0.03 ; Test frequency = 18 Hz 49.15 46.28 x F 43.01 40.50 x x o 37.43 35.25 o o Test 1 2 3 4 5 6 Number of cylces 1,094,076 3,349,097 10,000,000 3,074,350 10,000,000 10,000,000 Failure location 65° 64° 66° The failure location for each fractured specimen was quantified using the symmetry plane of the connecting rods as shown in Figure 2 a. Once the failure location was roughly known after a few tests, the slip of some connecting rods was measured on this point using a capacitive displacement measuring system. This resulted in a slip amplitude of 7 to 8 µm at this location. The variations within the tests and between the test series were marginal. a) b)

Figure 2: a) – Components of the connecting-rod assembly and definition of the failure location; b) – Capacitive slip measurement

3.2. Flat-pad experiments

The flat-pad tests are performed with the specimen geometries and test bench already presented in [31]. The test structure consists of a tensile specimen with a rectangular cross section and two flat fretting pads attached to its flanks. The flat pads can be braced against the tensile specimen with a mechanical tensioning device. The tensile force is measured by means of load cells. The nominal contact pressure can be determined using the known contact area. Since the flat pads are mounted on movable holders, a relative movement of the flat pads collinearly with the tensile direction of the specimen can be achieved. This relative movement is driven by piezoelectric actuators. This makes it possible to achieve a micrometre-precise displacement, which is set as slip amplitude in the contact. The slip amplitude is measured during the test using laser extensometers, and the piezo actuators are controlled accordingly to keep the slip amplitude constant. The idea behind this test setup is specifically to investigate the tribological and stress-mechanical conditions prevailing at an arbitrary location in a real-life contact, as shown in Figure 3.