PSI - Issue 34

T. Silva et al. / Procedia Structural Integrity 34 (2021) 45–50

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Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 4. Plastic and damage laws identified towards numerical modelling of the 18Ni300 AMed material: (a) inversely identified quasi-static hard ening law, using tensile, compression and double notched bar specimens; (b) comparison between the modelled strain rate behaviour (JC) and the experimental (EXP) dynamic compression tests; (c) determination of a damage onset law based on both double-notched and tensile (smooth and notched) specimens; (d) comparison of numerical and experimental load-displacement results of the multiaxial double notched specimens using the considered plastic and damage laws, adapted from (Silva, 2021; Silva et al., 2021a,b)). in figure 4a). The procedure is comprehensively described in Silva et al. (2021b), where is further shown that the presented model is capable of portraying the plastic behaviour of the AMed maraging steel under varied triaxial conditions. Moreover, digital image correlation is employed in the validation of the identified plastic law (Silva et al., 2021a) and on damage onset identification of the double notched specimens. Together with the smooth and notched tensile specimens the double notched specimens allowed for the determination of a damage initiation law (refer to figure 4c) modelled through the first term of the equation proposed by Johnson and Cook (1985). As thoroughly described in Silva et al. (2021a), the procedure consisted in the numerical simulation of both specimen types and through the comparison of both experimental and numerical load-displacement curves the strain at fracture could be determined for the displacement at which the (fully) plastic prediction and experimental curve diverge. The strain rate e ff ect on damage initiation was based on literature values of identical maraging steel Fu et al. (2020); Madhusudhan et al. (2018). Damage evolution was defined through the critical energy dissipation model presented by Hillerborg et al. (1976), through inverse estimation. Figure 4d shows the comparison between the numerical and experimental load-displacement curves of the double notched specimens using both plastic and damage (initiation and evolution) considerations. Despite being performed in both perpendicular- and parallel-to-build directions, very slight di ff erences ( < 5%) were noticed in the compression stress-strain behaviour due to AM material anisotropy. On the other hand, the AMed maraging presents a significantly higher mechanical strength than the CMed counterpart (refer to figure 4a). Due to being performed in distinct speed conditions, the compression tests enabled, as well, the modelling of strain rate e ff ect (refer to figure 4b) which was performed using the second term of the Johnson and Cook (1983) equation, namely the C parameter. The strain-rate sensitivity term was then coupled to the previously determined Swift-Voce plastic law, making the whole model sensitive to dynamic applications.

4. Conclusions

This paper reports a set of input data towards material modelling of the 18Ni300 maraging steel in FEM software. The conducted characterization revealed significant di ff erences in the mechanical behaviour of CMed and AMed 18Ni300. Table 2 summarizes the identified material properties of the latter.