Figure 7: Slice through the sample in the \(y,z\) projection showing in (a ) the untreated sample close to peak stress (Figure 4O) and (b ) the heat-treated sample at peak stress (Figure 5O) the formation of tensile (c ) en-echelon (Olson and Pollard, 1991; Thomas and Pollard, 1993) and (d ) wing-cracks (Fairhurst and Cook, 1966; Fig. 15 in Damjanac and Fairhurst, 2010).