Issue 33

J.M. Ayllon et alii, Frattura ed Integrità Strutturale, 33 (2015) 415-426; DOI: 10.3221/IGF-ESIS.33.46 425 the material have to be known for SIF calculation. Finally, the uniaxial fatigue curve of the material is needed to obtain the initiation curves. All of these material properties can be obtained in the laboratory by testing simple geometry specimens, or found easily in the literature for the most commonly used materials. In the case of the TCD model, tests are needed to obtain the material fatigue curves under traction and torsion conditions and in the presence of a notch. These are not complicated tests, but the curves are not so easily found in the literature. Regarding the calculations, the VIL model requires a longer time, first to obtain the initiation curves, but majorly to characterise the stress intensity factor. A CKNOWLEDGEMENTS he authors wish to thank the Spanish Ministry of Science and Innovation for research funding through project DPI2011-23377 and the company Galimplant ® for providing their implants and test specimens. N OMENCLATURE a = crack length, minor semiaxis of the crack a f = crack length at failure a 0 = El Haddad constant b = major semiaxis of the crack f = parameter in a approximation to Kitagawa-Takahashi diagram d = distance from the surface to the first microstructural barrier L = critical distance n = exponent in Paris law da/dN = crack growth rate C = coefficient in Paris law E = Young modulus F = force applied to the implant j Sf N = number of cycles to failure in a plain fatigue test with stress S j i j aS N = number of cycles to generate a crack of length a i in a plain fatigue test with stress S j R a = surface rougness  K = stress intensity factor range  K D = stress intensity factor range at the deepest point of the crack  K S = stress intensity factor range at the surface  K th∞ = fatigue crack growth threshold for long cracks σ FL = fatigue limit σ y = yield strength σ u = tensile strength R EFERENCES [1] Wetzel, R.M., Fatigue under complex loading: analysis and experiments, Society of Automotive Engineers, (1977). [2] Navarro, C., Muñoz, S., Domínguez, J., Propagation in fretting fatigue from a surface defect, Trib. Int. 39 (2006) 1149–1157. [3] Lankford, J., The growth of a small fatigue cracks in 7076-t6 aluminium, Engng. Fract. Mech., 5 (1982) 232–248. [4] Navarro, A., de los Rios, E.R., Fatigue crack growth by successive blocking of dislocations, Proceedings: Mathematical and Physical Sci., 437 (1992) 375–390. T