Issue 37

N. Zuhair Faruq, Frattura ed Integrità Strutturale, 37 (2016) 382-394; DOI: 10.3221/IGF-ESIS.37.49 385 In the present paper, typical notched samples were considered from a pre-investigated literature [6] as shown in Fig. 3a. The samples were tested under fully reversed nominal tension-compression CA cyclic force F(t) , resulting in a fatigue failure at N f number of cycles to failure. In the meantime, by post processing the elastoplastic FE model, a stabilized stress/distance and strain/distance curve were plotted along the notch bisector as illustrated in Fig. 3d. Furthermore, it is worth mentioning here that the stress/strain states at the vicinity of notch tip are experiencing a triaxial history even if the external applied load is uniaxial. The behaviour of these multiaxial stress/strain states are varying proportionally. Under these particular circumstances, the level of multiaxiality of the local stress/strain and effect of nonzero mean stress are considered to modify Manson-Coffin curve. Then, by using the experimental number of cycles to failure, average value of a critical distance was computed for specimens subjected to different values of nominal loads. To sum up, according to the theory of critical distance, for a given material, the hypothesis is formed that such a distance is always the same in the same material regardless of notch geometry and notch sharpness. Figure 3 : Summary of a methodology proposed to determine the critical distance – Point Method L PM [6]. O RIENTATION OF THE CRITICAL PLANE AND MAXIMUM VARIANCE METHOD redicting fatigue lifetime of a component mainly depends on the accuracy in determining the orientation of the critical plane as well as the stress/strain components relative to that plane. The hypothesis is formed that the critical plane, which is defined as the plane experiencing maximum shear strain amplitude [1], coincides with the crack initiation plane. Recently, Susmel [15] has formalised a numerical algorithm to explore the orientation of the critical plane been applied along with the stress based approach. The algorithm is then reformulated in terms of cyclic strain that summarised in P