A tubular tension-torsion specimen is proposed to characterize the onset of ductile fracturein bulk materials at low stress triaxialities. The specimen features a stocky gage section of reduced thickness. The specimen geometry is optimized such that the stress and strain fields within the gage section are approximately uniform prior to necking. The stress state is plane stress while circumferential strain is approximately zero. By applying different combianations of tension and torsion, the material response can be determined for stress triaxialities ranging from zero (pure shear) to about 0.58 (transverse plane strain tension) and Lode angle parameters ranging from 0 to 1. The relative displacement and rotation of the specimens shoulder as well as the surface strain field witing the gage section are determined through stereo digital image correlation. Multiaxial fracture experiments are performed on a 36CrNiMO16 high strenght steel. A finite element model is built to determine the evolution of the local stress and strain fields all the way to fracture. Furthermore the newly-proposed Hosford-Coulomb fracture initiation model is used to describe the effect of stress state on the onset of fracture.