PSI - Issue 3

Jilali Nattaj et al. / Procedia Structural Integrity 3 (2017) 579–587 Jilali NATTAJ/ Structural Integrity Procedia 00 (2017) 000–000

587

9

Conclusion In this paper we have shown that the strength of a material is constant. It’s an intrinsic characteristic parameter of it. Then, we noticed that the resistance and the endurance limit of the material decrease when it is subjected to a number of applied cycles under a given loading level. The A36 steel subjected to fatigue phenomena breaks after a number of cycles N f which represents a fraction of the total number of cycles N f0  10 6 cycles at rupture corresponding to a cyclic loading level of an amplitude equal to its endurance. Moreover, we have shown through the figures 4 and 5 that the two approaches of the unified theory damage and the rate of reduction of the cycle’s number of breaking damage are very close and shows good concordance which validate the newly developed model. Indeed, the endurance of material subjected to fatigue depends on the applied loading level as an external parameter and the "K" parameter as an intrinsic one. Finally, the model we developed in this paper, is principally based on three parameters which are the life fraction, the rate of reduction of the cycle’s number at break and the intrinsic parameter of the material "k" for symmetric experimental conditions. References Dubuc, J., Bui-Quoc, T., Bazergui, A., Biron, A., 1969. Unified Theory of cumulative Damage in metal fatigue. Rapport soumis à PVRC, I et II, Ecole polytechnique. Valluri, S.R., 1961. A unified engineering theory of high stress level fatigue, Aerospace Engineering, 20, 18-19. Gatts, R., 1961. Application of a cumulative damage concept to fatigue, Trans ASME, JL of Bas.Eng. 83, 529-540. Miner, M., 1945. Cumulative damage in fatigue. Trans ASME, JL of Appl. Mech, 67, A159-A164. Shanley F. R. (1952), A theory of fatigue based on unbonding during reversed slip, Report P-350, The Rand Corporation, Santa Monica. Rabbe, P., Amzallag, C., Fatigue of Materials and Structures, Figure 3.2 page N°73, by C. Bathias & J. P. Bailon, University of Compiegne. Peterson, R.E., 1974. Stress concentration factor. John Wiley & Sons, New York.