PSI - Issue 17

Mihaela Iordachescu et al. / Procedia Structural Integrity 17 (2019) 434–439 M. Iordachescu et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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their corresponding wire-actuators, in order to respectively capture the micromechanisms concerning the fracture process and the large plastic deformation occurred under the contact area.

Fig. 2 . a) Tensile bearing load capacity of ES and LDS wires vs. the applied transverse load; b) Contact area dependency on transverse load magnitude in ES and LDS wires; Circular contact area in the interrupted T-QL tests of: c) LDS wire for Q = 11 kN; d) ES wire for Q= 20 kN.

3. Results and discussion

3.1. Effect of transverse load on tensile resistant capacity of wires

Fig. 2a brings together all the results obtained in the T-QL tests of the ES and LSD wires. As an attempt to unify their failure criterion the graph illustrates the dependency of the maximum recorded tensile loads P m on the transverse loads Q in non-dimensional terms, by using the tensile load in simple tension P 0 of each wire class as load unit. Viewed in this manner, the results gather together and yield the same negative slope line, whose equation expresses the common empirical criterion that predicts the failure for both ES and LDS wires by tensile loading in the presence of a locally concentrated, transverse load: P m P 0 = 1 − 0,56 Q P 0 (1) Nevertheless, other factors largely influencing the failure do not unify in the same way, as shown by the differences between ES and LDS wires given in Fig. 2b, where the size of the contact area was plotted against the applied transverse load Q, in non-dimensional terms. In this case, the wires cross-section A 0 was used to adimensionalize the contact area A h . These areas were obtained from optical measurements on the actuator-end wire-sample, but also on the T-QL tested wires in some tests interrupted before rupture, beyond maximum load. The data in Fig. 2b indicate that the LDS wires are more deformable against the transverse load than the ES wires, although the difference is difficult to appreciate for transverse loads lower than 0.3P 0 . Given that the indentation process is controlled to a large extent by the strain hardening capacity of the wire steel, this behavior is consistent with the considerable lower yield strength of LDS when compared with that of ES in conjunction with their practically equal tensile strength. On the contrary, the unification of the empirical criterion illustrated in Fig. 2a reflects that tensile plastic collapse under transversal loading is mainly influenced by the tensile strength of the steel wire. Figs. 2c and 2d show the circular contact areas, obtained in two interrupted T-QL tests of LDS and ES specimens just beyond the maximum tensile load, under transverse loads of 11 kN and 20 kN, respectively.