PSI - Issue 13

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

60

4

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

NP 1/0s+1

F 2

2 1

F 1.1

F 2.1

u 2.1

F 1

u 1.1

NP 1/-1s+1

F 1

u 2.2

u 1.2

F 1.2

F 2.2

F 2

Figure 3. Definition of displacements and loading conditions of the X0-specimen

F [kN]

F [kN] 2

8.00

-8.00 -6.00 -4.00 -2.00 0.00 2.00 4.00 6.00 8.00

6.00

4.00

2.00

axis1 1/+1 axis2 1/+1

0.00

axis1 1/0s+1 axis2 1/0s+1 axis1 1/-1s+1 axis2 1/-1s+1

-2.00

1/+1 1/0s+1 1/-1s+1

F [kN] 1

-4.00

0.50 Δ u [mm] ref

0.00 2.00 4.00 6.00 8.00

-0.50

-0.25

0.00

0.25

Figure 4. Force F 1 vs. force F 2 ; solid lines proportional and dashed lines non-proportional experiments

Figure 5. Load-displacement curves for the final load ratio F 1 = F 2 = 1 / + 1

4. Experimental results

In the present paper, experimental results of di ff erent loading paths for the representative final load ratio F 1 / F 2 = 1 / + 1 (tension loading) have been selected and will be discussed in detail. With this load ratio experimental data for di ff erent stress histories will be obtained leading to di ff erent damage and fracture mechanisms on the micro-level. Focus will be on the e ff ect of the loading path on deformation, damage and fracture behavior. Therefore the test results for the biaxially loaded X0-specimen obtained from proportional loading paths (P) will be compared with those based on non-proportional ones (NP) and among themselves. Load-displacement curves for the proportional and two di ff erent non-proportional loading paths are shown in Fig. 5. In particular, in the case of proportional loading of the X0-specimen the maximum load is F 1 = 7 . 3 kN and the dis placements at final fracture are ∆ u ref.1 = 0 . 27 mm in axis 1. For the non-proportional loading path 1 / 0 s + 1 the maximum load is 3% higher and the displacement at fracture in axis 1 is 44% larger compared to the proportional loading path whereas a decrease in final displacement in axis 2 of 63% has been observed in the biaxial tests. For the case of non proportional loading 1 / − 1 s + 1 a slightly bigger increase in maximum load (5%) has been measured and the displacement at fracture in axis 1 is 22% larger compared to the proportional loading path whereas the displacement at fracture in axis 2 is 75% smaller. Furthermore, Fig. 6 shows the principal strains in the top notched part of the X0-specimen shortly before final fracture occurs. In particular, the first principal strain based on the proportional loading path develops in broad strain bands with elliptic shaped strain maxima of 15%. For the non-proportional path ( 1 / 0 s + 1 ) in similar broad strain bands