PSI - Issue 14

L. Chikmath et al. / Procedia Structural Integrity 14 (2019) 922–929 Author name / Structural Integrity Procedia 00 (2018) 000–000

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The fatigue crack initiation life is estimated on the critical location in both cold worked joint and non cold worked joint as shown in Fig.11. Since the cold working is done up to a point where the yielding of the material just begins, the fatigue life is estimated using S-N approach assuming (neglecting) smaller plastic deformation. The fatigue crack initiation life is computed using modified Basquin's relation with Morrow's mean stress effect and the damage caused due to applied fatigue load cycle is determined using Miner's rule given in Eqns 2&3 respectively (section 2.2). The extent of fatigue life enhancement due to cold work of hole is shown in Fig.11. The below figure gives an estimate of the remaining life for crack initiation at any given load cycle of P max and when the number of operations at a particular time interval are known.

Fig 11: Fatigue crack initiation life

4. Conclusions Lug joints with fasteners are salient components in aircrafts whose failure may lead to adverse effects. Hence their health is a major concern from design point of view. It is well known that introducing a interference fit fastener pin in these types of joints assists in improving fatigue life. The benefits of the interference fit are marginally offset due to increase in mean stress levels at the local critical points of maximum tensile stresses. This can be improved further with cold working of holes. This is achieved and shown in this paper through numerical analysis using FE method. Inverse formulation from the literature is adopted in estimating the separation/contact regions in interference fits, since they lead to moving boundary value problem. Fatigue crack initiation life is estimated using modified Basquin's equation at the discovered critical location from stress analysis for constant amplitude load ratio of R p =0. Remaining fatigue crack initiation life estimation is presented that will assist in implementing damage tolerance design concept at preliminary stages of design of lug joint which help in health monitoring aspects. 5. References Budiansky, B. A. (1959),"Reassessment of deformation theories of plasticity", Journal of Applied Mechanics, vol. 81, pp. 259–264 Chakherlou, T.N. and Vogwell, J. (2003), "The effect of cold expansion on improving the fatigue life of fastener holes", Journal of engineering failure analysis, vol. 10, pp.13-24. Champoux, R.L. (1986), "An overview of hole cold expansion methods", Proc. Conference on fatigue prevention and design, Amsterdam, Netherlands, Published by Engineering materials advisory services, London, pp. 35-52. Chikmath, L.and Dattaguru, B. (2017),"Prognostic analysis of fastener joints in straight attachment lugs", International journal of structural integrity, vol. 8 (3), pp. 404-422 De Matos, P.F.P., Moreira, P.M.G.P., Camanho, P.P. and De Castro, P.M.S.T. (2005),"Numerical simulation of cold working of rivet holes", Finite element in analysis and design, vol. 41, pp. 989-1007. Duprat,D., Campassens, D., Balzano, M. and Boudet, R. (1996), "Fatigue life prediction of interference fits and cold worked holes", International journal of fatigue, vol. 18 (8), pp. 515-521 Ball, D.L. and Lowry, D.R. (1998), "Experimental investigation on the effects of cold expansion of fastener holes", Fatigue and fracture of Engineering materials and structures, vol. 21 (1), pp. 17-34