Issue 37

J. Vázquez et alii, Frattura ed Integrità Strutturale, 37 (2016) 38-45; DOI: 10.3221/IGF-ESIS.37.06 44 C ONCLUSIONS he experimental analysis shows several things about the initiation of cracks in fretting fatigue with cylindrical contact. One of them is that cracks, after a few microns of growing almost perpendicular to the surface, tend to grow at an inclined angle towards the inside of the contact. This angle, around 25º to the perpendicular of the contact plane, has been measured in one test. The cracks are semi-elliptical similar to the ones found in fretting fatigue with spherical contact. Not many cracks are initiated at the same time, three in this case, although this may be because of the high roughness of the surface. More tests with a lower roughness should be performed in order analyse this effect. From a theoretical point of view, “growing” the crack using the critical plane at each point is not correct, although in the case of SWT it predicts a crack path very similar to the third procedure and similar to the experiments. Searching for the direction with lower gradient of the fatigue parameter or the direction of higher mean value over a certain distance is more suitable. From the multiaxial fatigue parameters used in this paper, it seems that SWT gives better results. Figure 10 : Mean value of FS and SWT vs. θ . A CKNOWLEDGMENTS he authors wish to thank the Spanish Ministry of Science and Innovation for research funding through Project DPI2011-23377. R EFERENCES [1] Waterhouse, R.B., Fretting fatigue, London: Applied Science, Publisher (1981). [2] Nishioka, K., Hirakawa K., Fundamental investigation on fretting fatigue: Part 4, the effect of mean stress, Bull. Jpn. Soc. Mech. Eng., 163 (1969) 408–414. [3] Dobromirski, J.M., Variables of fretting process: are there 50 of them?, in: ASTM STP, vol. 1159, Standardization of fretting fatigue test methods and equipment, (1992) 60–6. [4] Vázquez, J., Navarro, C., Domínguez, J., Experimental results in fretting fatigue with shot and laser peened Al 7075- T651 specimens, Int. J. of Fatigue, 40 (2012) 143–153. [5] Hattori, T., Nakamura, M., Ishizuka, T., Fretting fatigue analysis of strength improvement models with grooving or knurling on a contact surface, in: ASTM STP, vol. 1159, Standardization of fretting fatigue test methods and equipment, (1992) 101-114. T T