Issue 38

S. Tsutsumi et alii, Frattura ed Integrità Strutturale, 38 (2016) 244-250; DOI: 10.3221/IGF-ESIS.38.33 249 FE simulation of fatigue test on the non-load carrying fillet joint Next, the model was used in FE simulations to study the fatigue life of a non-load carrying fillet joint. Only the R = 0 case was considered to compare the results against experimental data provided by the JSSC. Loading procedures of a constant stress range and combinations of varying amplitude loads during cycles were investigated (Tab. 2). Only the paths W.UpDown1 and W.DownUp1 are discussed here. Fig. 9 shows the stress-strain curves obtained for element A in an enlargement of Fig. 5. The plastic contribution generated in the W.UpDown1 case was bigger than that induced with a constant stress range or in the W.DownUp1 path. This result is particularly relevant for the expected fatigue life of the components, as shown in Fig. 10 and the last two columns of Tab. 2. Fatigue life was estimated by using Eq. 2 based on the cumulative damage rule ( D in Fig. 10) and an equation based on the total strain ( H d in Fig. 10). . ,     f const n n D N N D (2) Here, n is the number of cycles in each range of amplitude, N const is the crack initiation life under constant loading estimated from the strain ranges [9], and N f is the fatigue life proposed in this paper. In both scenarios, the W.UpDown1 path has a shorter fatigue life than the W.DownUp1 path, whereas the estimated fatigue life is longer for a constant loading. Comparing the two fatigue life estimation methods shows that the method that uses H d produces shorter fatigue lives than the method using the cumulative damage criteria. Figure 9 : Stress-strain curves at element A (constant amplitude loading/variable loading). Figure 10 : S-N curves at element A (constant amplitude loading/variable loading). C ONCLUSIONS e investigated the fatigue life of metal structures with an unconventional plasticity model combined with a damage variable that includes the plastic work. We drew the following conclusions from the results. Material simulation tests (a) The R = -1 under constant loading case agreed well with previous experimental data [5] when H d = 1 is assumed as the fatigue life criterion. (b) The number of cycles necessary for fulfilling the condition H d = 1 was sensitive to the stress ratio used, and the number of cycles decreased as the ratio increased from R = -1 to 0 and 0.5. (c) Varying the load amplitude of a loading path for a number of cycles is also a key factor in the fatigue life. The mat.UpDown case had a shorter fatigue life compared with the constant stress analysis, whereas the loading path mat.DownUp had a longer fatigue life. W