D.C. Barton

The effect of stress triaxiality and strain-rate on the fracture characteristics of ductile metals

Notched tensile tests have been carried out on three common metals (pure iron, mild steel and aluminium alloy BS1474) over a wide range of strain-rates (10−3 to 104 s−1) and the strain-to-failure measured. The ductility of all three materials was found to be strongly dependent on the level of stress triaxiality in the specimen, this dependency being greatest for the ferrous materials and least for the aluminium alloy. No significant effect of strain-rate could be ascertained from the experimental results provided fracture remained fully ductile. However, for mild steel, a transition to a brittle fracture mode was observed for a given level of stress triaxiality as the strain-rate was increased. Numerical simulations of the experiments have been used to derive constants of a semi-empirical fracture model from the measured results. This model was found to give reasonable predictions of fracture over the range of conditions investigated.

A numerical study of ductile void growth under dynamic loading conditions

A numerical study of void growth at differing global strain rates in the range 149 s−1–2240 s−1 and at start temperatures between 173 K and 573 K has been carried out for a material containing a three-dimensional periodic array of equally spaced, initially spherical voids. To take account of the effect of strain rate and temperature on the flow stress under dynamic adiabatic conditions, the well-established Zerilli-Armstrong constitutive relations for pure copper and iron have been employed. An instability criterion based on the maximum mean tensile stress has been used to identify the point at which unstable void growth occurs. For both materials, the strain at instability has been found to be dependent on stress triaxiality and start temperature but only weakly affected by strain-rate

THE EFFECTS OF STATE-OF-STRESS AND STRAIN-RATE ON THE DEFORMATION AND FRACTURE BEHAVIOUR OF REMKO IRON AND PURE COPPER

ABSTRACT Notched specimens in pure copper and Remko iron were tested over a range of stress-rate conditions and strain-rates. Copper showed reducing failure strains with increased stress triaxiality, strain-rate having little effect. Remko iron, however, exhibited a ductile-brittle transition at high states of stress intensity and at the higher strain-rates.