TENSILE FRACTURE AND SHEAR LOCALIZATION UNDER HIGH LOADING RATE IN TUNGSTEN ALLOYS

The influence of loading rate and microstructure on the tensile and compressive failure properties of three microstructurally dissimilar tungsten alloys has been investigated. Dynamic tensile fracture properties were characterized through fracture toughness tests performed at a stress intensity loading rate of 10(6) MPa square-root m s-1, and by tensile testing at a strain rate of 10(3) s-1. Shear banding phenomena were investigated by means of compression tests performed at strain rates of 5 x 10(3) s-1. Under rapid loading conditions, nickel-cobalt-tungsten alloys were found to be tougher than nickel-iron-tungsten alloys ; the tungsten/tungsten interface was identified as the governing microstructural factor. Quantitative micromodeling using simple fracture models was found to provide a mean of correlating toughness with microstructures. Compression-indUced shear localization was found to be facilitated within systems characterized by either elongated tungsten particles or an adiabatic shear-prone matrix. The shear band width was observed to be proportional to tungsten particle size.