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Experimental determination of the void volume fraction for S235JR steel at failure in the range of high stress triaxialities

Kossakowski P. G.

Archives of Metallurgy and Materials

2017

Vol. 62, iss. 1

167--172

This paper is concerned with the critical void volume fraction fF representing the size of microdefects in a material at the time of failure. The parameter is one of the constants of the Gurson-Tvergaard-Needleman (GTN) material model that need to be determined while modelling material failure processes. In this paper, an original experimental method is proposed to determine the values of fF. The material studied was S235JR steel. After tensile tests, the void volume fraction was measured at the fracture surface using an advanced technique of quantitative image analysis The material was subjected to high initial stress triaxialities T0 ranging from 0.556 to 1.345. The failure processes in S235JR steel were analysed taking into account the influence of the state of stress.

Effect of initial porosity on material response under multi-axial stress state for S235JR steel

Kossakowski P. G.

Archives of Civil Engineering

2012

Vol. 58, nr 4

445-462

The effect of the initial porosity on the material response under multi-axial stress state for S235JR steel using the Gurson-Tvergaard-Needleman (GTN) material model was examined. Three levels of initial porosity, defined by the void volume fraction f0, were considered: zero porosity for fully dense material without pores, average and maximum porosity according to the metallurgical requirements for S235JR steel. The effect of the initial porosity on the material response was noticed for tensile elements under multi-axial stress state defined by high stress triaxiality sigma m/sigma e = 1.345. This effect was especially noticeable at the range of the material failure. In terms of the load-bearing capacity of the elements, the conservative results were obtained when maximum value of f0 = 0.0024 was used for S235JR steel under multi-axial stress state, and this value is recommended to use in the calculations in order to preserve the highest safety level of the structure. In usual engineering calculations, the average porosity defined by f0 = 0.001 may be applied for S235JR.

The analysis of influence of Tvergaard's parameters on S235JR steel response in high stress triaxiality

Kossakowski P.

Advances in Materials Science

2012

Vol. 12, nr 1(31)

27-35

The influence of Tvergaard’s parameters qi of Gurson-Tvergaard-Needleman (GTN) material model on S235JR steel response was considered in the study. The analysis concerns the strength curves simulated numerically for notched tensile elements under static tension in complex stress state defined by high initial stress triaxiality > 1. Typical and material-dependent values of Tvergaard’s parameters qi were examined. The influence of the Tvergaard’s parameters qi on material response was noticed at the failure range for S235JR steel in the case of high stress triaxiality.