PSI - Issue 13

Moritz Zistl et al. / Procedia Structural Integrity 13 (2018) 57–62

61

M. Zistl et al. / Structural Integrity Procedia 00 (2018) 000–000

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NP 1/0s+1

NP 1/-1s+1

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Figure 6. Principal strains in the upper notched part of the X0-specimen for the final load ratio F 1 = F 2 = 1 / + 1

NP 1/-1s+1

NP 1/0s+1

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1

1

1

1

1

1

1

1

1

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Figure 7. Fracture modes for the final load ratio F 1 = F 2 = 1 / + 1

with maxima now in a tilted band of strain with values about 15%. In the case of the alternative non-proportional loading ( 1 / − 1 s + 1 ) the principal strains are more localized (the band is smaller) and only maximum values of about 10% have been reached in the experiments. For the second principal strains the localized bands are again widely spread with about -5% for proportional path. For the non-proportional ( 1 / 0 s + 1 ) paths greater absolute values can be seen, again superimposed with a tilted band and maximum values of around -8%. For the non-proportional case ( 1 / − 1 s + 1 ) only smaller and more localized strains developed with minima of about -5%. The localized bands of principal strains illustrated in Fig. 6 di ff er slightly from the fracture lines shown in Fig. 7. In all cases nearly orthogonal orientated fracture lines can be observed forming a relief-like plane and therefore no remarkable influence of the loading paths on these results can be noted. Ultimately, detailed analysis of the fracture surfaces by scanning electron microscopy (SEM) was carried out, see Fig. 8. In the case of the proportional loading path tension loading occurred in the critical notched parts of the X0-specimen causing near hydrostatic tension stress states with the corresponding high positive triaxiality. On the microscale this leads to the growth of voids with very big voids. During the non-proportional loading path ( 1 / 0 s + 1 ) the critical notched parts of the X0-specimen are firstly loaded by tension-shear and after the change in the loading path (see Fig. 4) by superimposed tension. This leads in the first loading stage to simultaneous growth of voids and formation of micro-shear-cracks. During the final proportional part of the loading history (see Fig. 4) the growth of voids continues. The fracture mode for the non-proportional loading path ( 1 / 0 s + 1 ) is characterized by voids and slightly smeared-out dimples. Compared to the proportional loading history, slightly smaller and more voids are visualized by the SEM analysis. Furthermore, during the non-proportional loading path ( 1 / − 1 s + 1 ) the notched region of the X0-