PSI - Issue 13

Steffen Gerke et al. / Procedia Structural Integrity 13 (2018) 39–44 S. Gerke et al. / Structural Integrity Procedia 00 (2018) 000–000

43

5

(a)

(b)

F [kN]

8

6

axis1 1/-2 axis2 1/-2 axis1 1/-1 axis2 1/-1 axis1 1/-0.5 axis2 1/-0.5

4

axis1 1/0 axis2 1/0

2

0

axis1 1/+0.5 axis2 1/+0.5 axis1 1/+1 axis2 1/+1 axis1 1/+2 axis2 1/+2

-2

-4

Δ u [mm] ref

-6

-1

0

1

Fig. 4. (a) Load–displacement–curves for di ff erent load ratios. (b) corresponding load–load-curves

Fig. 5. Upper row: fractures specimens for di ff erent load ratios; lower row: first principal strain before fracture measured by DIC

as shown underneath. Here only the marked notch (see Fig. 3(b)) is displayed, i.e. if that notch did not fracture, the results of a fractured notch have been reflected in order to facilitate the comparability. By this representation it can be nicely seen how the direction of the crack and the corresponding area with elevated deformations changes: For more shear like loading ( 1 / − 2 , 1 / − 1 and 1 / − 0 . 5 ) the deformations are concentrated in a narrow band and for more tension dominated load cases ( 1 / + 0 . 5 , 1 / + 1 and 1 / + 2 ) the zone becomes more extended. For the load cases 1 / − 0 . 5 and 1 / − 1 the inclination of the crack is in notch direction while for the other load cases the inclination changes. For 1 / 0 the orientation of the extremal principal strain band corresponds nicely with the fracture orientation and for 1 / − 0 . 5 the principal strain before fracture and the fracture surface have a very similar tilted curvature. For 1 / + 1 the principal strain is distributed in a elliptic shape with minor values in its center. Therefore fracture may not be able to align on a straight section of principal strain maxima and it forms on a relief-like plane. Furthermore, the ductile behavior of the load cases 1 / − 0 . 5 and 1 / − 1 is clearly reflected with high strain values of 0 . 5 while for 1 / + 2 only 0 . 075 is reached.

4. Conclusions

Within this paper a series of experiments with the biaxial X0-specimen under proportional loading conditions has been presented. The new geometries have been motivated by a literature overview on specimen geometries for sheet metals with in-plane loading. Furthermore, the corresponding continuum damage model has been presented. The experimental results clearly indicate that the X0-specimen is suitable to study the damage and fracture behavior within a wide range of stress triaxialities. For di ff erent load cases the damage and fracture behavior changes: For