Issue 38

S. Tsutsumi et alii, Frattura ed Integrità Strutturale, 38 (2016) 244-250; DOI: 10.3221/IGF-ESIS.38.33 248 R ESULTS AND DISCUSSION Material simulation with single-quadrature point code e obtained preliminary results with single-quadrature point code where the input data for stress and strain are introduced directly to give perfect uniaxial loading conditions. Fig. 6 shows the S-N curves obtained for the three constant ratio tests by reporting the number of cycles necessary for the H d variable to reach a value equal to 1 or 10 under different stress ranges. The R = -1 case (fully reversible load) showed good agreement with previous experimental data for SM490B steel [8] when H d = 1 was assumed as a criterion for evaluating the fatigue life, whereas the number of cycles was overestimated slightly when H d = 10. Therefore, two additional tests were conducted with H d = 1 for R = 0 and 0.5. Both of the curves showed that fewer cycles were required to fulfil the condition H d = 1, although the number of cycles was lower for R = 0.5. Further simulations were performed with fully reversible loading ( R = -1), but varying the stress amplitude every 100 cycles. Figs. 7 and 8 show S-N curves obtained for two loading paths, mat.UpDown and mat.DownUp. Both of the tests stopped when H d reached unity. The first path had a shorter fatigue life compared with the constant stress analysis (black line in Fig. 6.), whereas the second path had a longer fatigue life. Figure 6 : S-N curves at H d = 1. Figure 7 : S-N curves in mat.UpDown ( σ max = 303 → 340 → 303 → 268 → 303). Figure 8 : S-N curves in mat.DownUp ( σ max = 303 → 268 → 303 → 340 → 303). W