Volume 22, Issue 2 (March 1994)
Constant Temperature-Compensated Strain Rate Testing of Aluminum
Temperature and strain rate have long been identified as the external variables dictating material response during deformation. The Zener-Hollomon parameter, Z, is a temperature-compensated strain rate defining the interrelationship between the two variables. Investigation of the constitutive response of a material requires well-defined testing conditions in order to properly identify material behavior. Mechanical testing at constant Z values offers the advantage of using well-defined deformation conditions when isothermal control cannot be maintained during deformation. To perform such tests real time feedback control of the strain rate is required. In addition, at high strain rates where deformation heating becomes significant, thermocouple response is not rapid enough to provide feedback signal adequate for control of the test. Under these circumstances it is necessary to predict deformation heating of the specimen as a function of the test parameters and control the strain rate based upon the estimated specimen temperature. Results of constant Z tests are presented showing the capabilities of the control system. Deformation heating is accounted for by a simple equation assuming a near adiabatic process which predicts the dissipation of heat through the surrounding environment. An application of the constant Z test procedure for modeling material behavior is briefly discussed. The ability to perform deformation experiments at constant Z values offers significant advantages in gaining an understanding of the constitutive response of materials.