Rupture mechanisms in combined tension and shear—Experiments

Abstract

An experimental investigation of the rupture mechanisms in a mid-strength and a high-strength steel were conducted employing a novel test configuration. The specimen used was a double notched tube specimen loaded in combined tension and torsion at a fixed ratio. The effective plastic strain, the stress triaxiality and the Lode parameter were determined in the centre of the notch at failure. Scanning electron microscopy of the fractured surfaces revealed two distinctively different ductile rupture mechanisms depending on the stress state. At high stress triaxiality the fractured surfaces were covered with large and deep dimples, suggesting that growth and internal necking of voids being the governing rupture mechanism. At low triaxiality it was found that the fractured surfaces were covered with elongated small shear dimples, suggesting internal void shearing being the governing rupture mechanism. In the fractured surfaces of the high-strength steel, regions with quasi-cleavage were also observed. The transition from the internal necking mechanism to the internal shearing mechanism was accompanied by a significant drop in ductility.

Influence of Stress State on the Mechanical Impact and Deformation Behaviors of Aluminum Alloys

“…This behavior is in agreement with the numerical results published by other authors [11,27]. Several authors [22][23][24][25][26] have assumed a symmetric failure criterion concerning the Lode parameter.…”

Experimental characterization and numerical modeling of micromechanical damage under different stress states

“…Recently, several studies [12][13][14][15][16][17][18][19][20][21] have shown that the Lode angle, associated with the third invariant of the deviatoric stress tensor, is an essential parameter in ductile fracture. It characterizes the effect of the stress state on plastic flow and the ductile rupture of the material.…”

Ductile Shear Damage Model for Porous Materials

“…The true fracture strain is the most physical experimental indicator for quantifying the resistance to damage and fracture of a material subjected to tensile loading conditions. An average true fracture strain measure f  using the diameter reduction is usually used to quantify the ductility [9,10]. It is defined as 2 log ⁄ .…”

“…In addition, if void nucleation is disregarded, the GTN model cannot describe ductile failure evolution for shear stress close to zero since, according to this constitutive model, the void growth mechanism requires hydrostatic tension within the material. However, continued softening and then ductile failure is known to occur at low triaxiality and even in situations of pure shear [9,10].…”