Influence of the Stress State on Various Fracture Modes

Abstract

<p>The influence of superimposed pressure on the damage accumulation processes leading to various tensile fracture modes has been studied on axisymmetric samples of different materials.</p> <p>For ductile fracture damage accumulated in both smooth and notched tensile samples had been characterized in a variety of spheroidized steels tested under superimposed pressures ranging from 0.1 MPa to 1100 MPa by counting the number of voids existing at the cementite-iron interfaces and measuring their area fraction. A quantitative model accounting for the size dependence of void nucleation has been developed to describe these results.</p> <p>The shear fraction mode has been investigated by performing tensile tests on an Al-Zn-Mg alloy under superimposed pressures up to 1100 MPa. The pressure does not affect the onset of shear bands, but changes their growth as it opposes and dilational damage created in the bands. This allows the occurrence of the further plastic deformation process to take place. The microscopic observation of the shear bands, but changes their growth as it opposes any dilational damage created in the bands. This allows the occurrence of the further plastic deformation to take place. The microscopic observation of the shear bands has revealed that they are created by structural softening events, and that they involve a complex spatial correlation of crystallographic slip events over the entire cross-section.</p> <p>Brittle fracture has been studied in both Al-Au and Fe-P alloys, displaying intergranular fracture and transgranular cleavage. The pattern of microcrack development and the changes in fracture modes have been characterized for these two alloys.</p> <p>Finally, two types of fracture maps in stress space are presented, where the various fracture mechanisms are represented by lines, and which can also be used as damage contour maps. These maps are constructed either by considering a complete model of damage accumulation and fracture criterion, or simplified analytical relationships to express damage development and occurrence of failure.</p>