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

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(e)

(f)

(g)

(a)

(b)

(c)

(d)

(j)

(l)

(k)

(h)

(i)

Fig. 1. Di ff erent specimens taken from literature for uniaxial and biaxial loading

Dog bone specimens (Fig. 1(a)) are commonly used to determine the elastic–plastic material parameters. Due to the geometry a homogenous stress state occurs throughout the experiment and is only disturbed by necking which appears towards the end of the experiment. With di ff erently notched specimens (b) a first influence of the stress state on the material behavior can be studied. The stress triaxiality increases with decreasing notch radius whereas it is worthy to notice, that the stress state is not homogeneous in the critical region (Bai and Wierzbicki (2008); Bru¨nig et al. (2008); Gao et al. (2010)). By introducing a central hole (Mohr and Henn (2007)) (c) a similar e ff ect is achieved whereas the stress state is inhomogeneous to a greater extent due to the deformation of the initially flat sides. Gao et al. (2009) (d) used plane strain specimens with notches in thickness direction which show a rather uniform stress state in width direction. With the geometries shown in (a-d) tension dominated stress states with stress triaxialities from 0.33 to 0.57 can be achieved. To study shear dominated stress states in a one–dimensional testing device di ff erent geometries with one shear zone have been proposed, see e.g. (e) (Bru¨nig et al. (2008); Gao et al. (2010); Gruben et al. (2012)). Unfortunately this type of specimen shows rotations of the central part before fracture which leads to tension dominated stress states. This e ff ect could be reduced by notches in thickness direction (Driemeier et al. (2010)) whereas a homogeneous material in thickness direction is assumed. Another solution has been presented by Roth and Mohr (2016) (f) with a double shear specimen which avoids major rotations of the shear part. The central idea of a double shear specimen goes back to Miyauchi (1984) (g) and has been presented in the overview paper of Kuwabara (2007). In addition this specimen can even be used for cyclic loading. Arcan et al. (1978) presented the idea to use one specimen under di ff erent loading angels (h) causing in the central part shear which can be superimposed with compression. This idea was followed up by Dunand and Mohr (2011) for the design of the butterfly specimen (i). By the use of a specially designed testing device di ff erent shear–tension loading conditions can be applied. Furthermore, Yin et al. (2015) designed a circular specimen (l) whereas notches on both sides are arranged in a circular way. By rotating the outer and inner parts in opposite directions shear loading is forced within the notches.