The adiabatic correction factor for deformation heating during the uniaxial compression test

The isothermal uniaxial compression test is a common method to determine the flow stress of metals. For accurate flow stress data at strain rates > 10(-3) s(-1), the data must be corrected for now softening due to deformation heating. The first step in the correction is to determine the increase in temperature. An adiabatic correction factor, eta, is used to determine the temperature between strain rates of 10(-3) to 10(1) s(-1). The adiabatic correction factor is the fraction of adiabatic heat retained in the workpiece after heat loss to the dies, eta = (DeltaT(ACTUAL))/(DeltaT(ADIABATIC)) where DeltaT(ADIABATIC) = (0.95 integral sigmad epsilon)/(pC(p)). The term eta is typically taken to be constant with strain and to vary linearly (0 to 1) with log (epsilon) between 10(-3) and 10(1) s(-1). However, using the finite element method (FEM) and a one-dimensional, lumped parameter method, eta has been found to vary with strain, die and workpiece thermal conductivities, and the interface heat-transfer coefficient (HTC). Using the lumped parameter method, an analytical expression for eta was derived. In this expression, eta is a function of the die and workpiece thermal conductivities, the interface heat-transfer coefficient, workpiece heat capacity, strain, and strain rate. The results show that an increase in the HTC or thermal conductivity decreases eta.