Issue 37

V. Anes et alii, Frattura ed Integrità Strutturale, 37 (2016) 124-130; DOI: 10.3221/IGF-ESIS.37.17 129 Thus, the FRI loading path (a variable amplitude loading) can be replaced by a constant amplitude loading using the SSF equivalent shear stress, and the virtual cycle counting method. This is particularly useful when one have loadings made of different loading blocks, which is may be the case of random loadings. Random loadings can be discretized into loading blocks [1] and treated as a damage accumulation case, however multiaxial criteria used in damage accumulation procedures must be able to capture fatigue damage of variable amplitude loadings. Fig. 3 depicts the fatigue life correlation for the two materials considered in this study. These results show that the 42CrMo4 damage map is suitable for high strength steels, which confirms previous studies performed by the present authors [9]. These results are reinforced by the 1050QT correlation pattern where the correlation slope is parallel to the boundary lines - please see Fig. 3. On the other hand, the correlation slope of the 304L steel is quite different from the slope of the boundary lines, i.e. the correlation trend line of the 304L fatigue data crosses the lower boundary lines. This indicates that the damage map of the 42CrMo4 high strength steel do not capture in full the 304L fatigue pattern, which is a result expected by the present authors. Stainless steels are extremely sensitive to non-proportionality and show strong variation of their mechanical properties under cyclic loadings. Thus their cyclic behavior is quite different from the one that is usually found in high strength steels. Figure 3: SSF fatigue life correlation for the 1050QT and 304L steels. C ONCLUSIONS he present study evaluates the performance of the SSF criterion under variable amplitude loading for two different materials, i.e. the 1050QT steel and the 304L stainless steel. The idea was to inspect the validity of the 42CrMo4 SSF damage map for other materials under variable amplitude loading conditions. The present authors have been using the 42CrMo4 SSF damage map in fatigue life predictions of high strength steels with success; examples are the Ck45 and C40 steels. The main focus of the SSF criterion has been on the idea that the damage scale of normal and shear stresses of a given multiaxial loading is not constant. This damage scale is strongly dependent on the stress level and stress amplitude ratio and can be evaluated with the so-called SSF damage map. In this paper, results confirm the validity of the 42CrMo4 SSF damage map for high strength steels, as seen in the obtained results for the 1050QT steel. This steel has mechanical properties very close to the 42CrMo4 properties, in some of them the 1050QT has higher values, thus it can be considered that both materials belong to the same steel family. Based on the results found here and based on previous results computed for the Ck45, and C40 high strength steels, it can be considered that a SSF damage map can be defined for each material family. To reinforce this, the results for the 304L stainless steel where not so good, which indicates the necessity to obtain the SSF damage map for this steel family. T