Fluid mechanics of copper: Viscous energy dissipation in impact welding

Abstract

The aim of this paper is twofold; to explain the parametric bounds for successful impact welding, and thereby to confirm the existence of a new region V of inviscid fluid behavior of metals. The assumption of two regions of fluid behavior (viscid and inviscid) has previously permitted a description of wave formation in impact welding and has provided an estimate of about 107 s-1 for the critical strain rate dividing the two regimes. The model is extended here to a consideration of viscous energy dissipation. It is predicted that for sufficiently high impact velocities there will be some melting, and that for sufficiently low velocities the dissipation will prevent the formation of the reentrant jet needed to remove surface impurities and permit a bond to form. In this way upper and lower bounds to a bonding region are established. Fits to data of Cu-Cu bonding provide two estimates of the coefficient of viscosity, 102 and 2.2×102 N s m -2. These values of the critical strain rate and viscosity combine to give a critical strength of (1-2.2) ×109 N m-2. A theoretical value of 1.2×109 N m-2 lies in this range.