School of Civil Engineering, Chongqing University
National Natural Science Foundation of China
The true stress-strain relationship and ductile fracture characteristics of Chinese Q690 high strength structural steel were investigated at different low strain rates. Sheet specimens with one un-notched and two different notch geometries were used for uniaxial tensile tests and pure shear sheet specimens were also adopted for shear tests. These specimens were loaded to obtain a wide range of stress states. A hybrid experiment-simulation approach was used to determine the equivalent plastic strain to fracture, the stress triaxiality and the Lode parameter. The results showed that the stress triaxiality and the Lode parameter are the key factors controlling fracture and that strain is more sensitive to strain rate compared to stress. It was observed that the equivalent plastic fracture strain increases with increasing the strain rate. In addition, further studies are required to design the pure shear specimens since the tensile stress or tensile-shear stress will be dominated on the fracture sections in most of pure shear tests due to the obvious deformation and stress concentration before fracture at the gauge area.