THE STRUCTURE OF CONTROLLED SHEAR BANDS IN DYNAMICALLY DEFORMED REACTIVE MIXTURES

The structure of controlled high-strain-rate shear bands generated in heterogeneous reactive porous materials (Nb + Si, Mo + Si + MoSi2) has been investigated using axially symmetric experimental configurations in which the source of energy is the detonation of low velocity explo sives. The deformation was highly localized, with profuse formation of shear bands, which have thicknesses of 5 to 20 mu m. The experimental method generated overall strains up to 100 and strain rates gamma of approximately 10(7) s(-1). Changes in particle morphology, melting, an d regions of partial reaction on three different length scales were ob served. The shear band thickness is smaller than the initial character istic particle size of the porous mixture (less than or equal to 44 mu m), ensuring a cooling time of the deformed material on the same orde r of magnitude as the deformation time (10(-5) s). In the shear locali zation regions, two characteristic phenomena were observed: (a) a shea r fracture subdividing the Nb particles into thin parallel layers and (b) the formation of vortices. A mechanism for the reaction inside the shear bands is proposed, and an expression for the largest size of ch emical products as a function of shear deformation is obtained.