Experimental investigation and fracture simulation of welded steel connections

Abstract

This thesis aims to investigate the mechanical properties and fracture performance of welded steel connections. First, the effects of stress triaxiality and Lode angle on fracture of steels, are discussed based on the experimental data collected from the literature and test results of two newly designed specimen types. It is observed that the void growth exponential function can accurately describe the stress triaxiality effect in the whole stress state, and the Lode angle effect can be considered using an exponential function, based on which a new fracture model is proposed and termed Lode angle modified void growth model (LMVGM). Second, the mechanical properties in the weld zone and the weld residual stresses (WRS) are measured from welded connections. The mechanical properties of the weld, heat affected zone (HAZ) and base metal, including their stress-strain relationships and fracture strains under various stress states, are measured in longitudinal and transverse directions by conducting tensile tests on miniature coupons extracted from butt-welded plates. The test results show that the strength and ductility of the HAZ are generally in-between those of the base metal and the weld. The magnitude and distribution of WRS of fillet welds with different weld sizes and butt welds are measured from welded cruciform specimens and an end-plate connection using the neutron diffraction method. Finally, experimental investigation and numerical simulation of the fracture in welded cruciform specimens are conducted, and it is concluded that (ⅰ) material inhomogeneity in the weld zone has a significant effect on the performance of the welded connections, and (ⅱ) ignoring the properties of the weld and HAZ will underestimate the capacity of the connection. Based on the measurement results of the mechanical properties in the weld zone, the fracture process of the cruciform specimens is simulated using the calibrated LMVGM.