Effects of the constraint parameter triaxial stress on the failure behaviour of steels

Abstract

The constraint parameter triaxial stress which results from loading types and component geometries plays an important role in the failure behaviour of materials. Especially the local failure initiation of materials depends very strongly on triaxial stress. The failure behaviour of a material under different stress states (i.e. different constraint) differs. In this paper effects of triaxial stress on the failure behaviour of steels are presented by means of theoretical analysis, experiments and finite‐element‐calculations. A theoretical model describing the effects of triaxial stress on failure initiation of materials has been developed based on theoretical analysis. Corresponding experiments were conducted to determine the material constants in the failure model of materials. In order to obtain local damage parameters finite‐element calculations have been conducted. According to the results from theoretical analysis, experiments and finite‐element calculations the damage curves of materials, in which the critical equivalent plastic strain is plotted as a function of triaxial stress, have been obtained. Furthermore, the failure behaviour of materials under different triaxial stresses has been discussed.

Damage and Fracture of Perforated Aluminum Alloys

“…The finite-element calculations were performed with the finite-element program NASTRAN for WINDOWS using 3D eight-node elements. The calculations demonstrate the different values of the triaxial stress state in the environment of the pore calculated by means of Equation 1. Figure 8 illustrates the distribution of the stresses and triaxiality along the web between two holes.…”

“…Using the equivalent plastic strain at failure initiation as a characteristic parameter, socalled ªfailure curvesº can be introduced as a function of triaxiality. [1,2] Experimental investigations on Al-alloys show that pores can develop during plastic deformation, depending on the microstructure. Within the range of the highest multiaxiality a macrocrack finally develops that leads to failure of the specimen.…”

Modelling of ductile failure in aluminium sheet forming simulation

“…This may be explained by the fact that hydrostatic tension (compression) tends to open (close) voids, see e.g. [44,57,67]. Usually, the higher the strength/stiffness of a material the lower is the ductility, because in a material exhibiting a high stiffness the stresses are high as well thereby promoting fracture.…”

A note on calibration of ductile failure damage indicators

“…However, the experimental data in [9] point to higher values of k. For typical steels go is given in the range between 0,06 and 0,30. Very recently the Aachen group, see Kong et al [40], published a relation for e] taking explicitly into account the strain hardening by the strain hardening coefficient n(n ~ c~ elastic-perfectly plastic material). This relation can be modified in analogy to (9a) as:…”

“…However, the authors of this paper prefer (9a) since Kong et al [40] apply n simultaneously as a strain as well as a strain rate hardening coefficient. The damage indicator Di is now changed due to (9a) to…”