PSI - Issue 37

R. Fernandes et al. / Procedia Structural Integrity 37 (2022) 462–468 R. Fernandes et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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of the as-built test, there is an initial cyclic strain-hardening behaviour, as already referred to above, but the shape of the hysteresis loops is almost the same throughout the entire lifetime. The most relevant changes occur in a final stage when the total failure is approaching. If we compare this case with that obtained for the stress-relief treatment, the differences in terms of hysteresis loop shapes are notorious. At a first sight, we see that either the linear portion of the hysteresis loops or the degree of strain-hardening is much smaller. This change is, in general, associated with the dislocation density and cell size (Plumtree, 2001). On the other hand, we can also distinguish strong changes in the shapes of the hysteresis loops during the test. This means that the area of the hysteresis loops decreases continuously and, therefore, the total strain energy density per cycle reduces considerably during the test. Regarding the T6 condition, the degree of strain-hardening slightly increases when compared to the stress-relief case. However, the tensile and compressive tips of the hysteresis loops are closer to the x-axis, i.e. in absolute values, these two stresses are smaller than those of the stress-relief case. It is also clear that the hysteresis loops maintained their shape during the entire test which leads to an almost constant value of the total strain energy density per cycle. The transient stress-strain response under strain-controlled conditions is usually analysed using dependent parameters, e.g. the stress amplitude (  a ). Figure 3 plots the variation of  a against the number of cycles at two different strain amplitudes (  a = 1.25% and  a = 0.50%) for the different manufacturing routes. As inferred from the previous figure, the differences are clear. We can see that the T6 condition exhibits a strain-hardening behaviour for higher and lower strain amplitudes. On the contrary, the other two states present a mixed transient behaviour, i.e.

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Fig. 3. Stress amplitude versus number of cycles of the AlSi10Mg aluminium alloy manufactured by laser-beam powder bed fusion for the different manufacturing routes: (a)  a = 1.25%; and (b)  a = 0.5%.