Experimental-numerical evaluation of a new butterfly specimen for fracture characterisation of AHSS in a wide range of stress states

On modelling of shear fracture in deep drawing of a high-strength dual-phase sheet steel

“…As can be seen, the critical element at the inner radius experiences a strongly pressure-superimposed stress state with stress triaxialities η below −0.33. Taking into consideration the fact that fracture strains of the studied material used for the parameterisation of the MMC fracture model were determined at stress triaxialites of η ≥ 0 [14] and findings of Bao and Wierzbicki [15] who postulated no damage accumulation in metallic materials at stress triaxialities of η ≤ −0.33, the MMC fracture model was adjusted to yield infinitely high fracture strainsε f pl = +∞ at η ≤ −0.33 (compare figure 4, left and right). The adjustment of the MMC fracture model lead, as expected, to a delay in crack initiation in critical elements in the middle plane and at the inner radius, as can be seen in figure 8 and figure 9.…”

“…An evaluation of the fracture characterisation method based on a tensile test on a novel butterfly specimen, which was previously proposed by the authors [14], on an FEA of a deep-drawing process of a dual-phase sheet steel DP600 is presented. The results reveal that shear fracture of this material is predicted too early by the used MMC fracture model.…”

“…The fracture behaviour was described by the MMC fracture model according to equation 4 with A/C 2 = 1.667, n = 0.635, C 1 = 0.291,C 3 = 1.070 as proposed in [14] for a virtual strain gauge length of l 0 = 0.2 mm. Furthermore, following results of Bao and Wierzbicki [15], who pointed out at a cut-off value of the stress triaxiality of η = −0.33, below which fracture in a steel material never occurs, the fracture behaviour was also described by an adjusted MMC fracture model, which yields infinitely high fracture strainsε f pl at stress triaxialities of η ≤ −0.33 as shown in figure 4, right.…”

“…It was shown that the MMC fracture model gives more flexibility in approximation of fracture strains and can thus yield a more accurate description of the fracture behaviour of a high-strength dual-phase sheet steel DP600 [14]. The fracture strainε f pl is given by this model as follows:ε…”

“…The aim of the present paper is to evaluate the fracture characterisation method based on a tensile test on a novel butterfly specimen, which was proposed by the authors in a previous publication [14], on an FEA of a deep-drawing process of a dual-phase high-strength sheet steel DP600. In case of considerable discrepancies between the experiment and simulation with respect to the time moment and location of shear fracture initiation, novel improvements of the characterisation method or the used fracture modelling approach are to be proposed.…”