The Effect of Specimen Size and Interface Lubrication on the Compressive Flow Stress of Copper and Steel

摘要

Test variables were examined to determine their significance in the cylindrical compression test with overhanging dies. The variables investigated were specimen diameter-to-height ratio (D/H) and interface lubricants for OFHC copper and AISI 1018 steel. For the purpose of evaluating the compressive flow curves, specimens 2.0, 2.5, and 3.0 inches in diameter, and 2.0 to 5.0 inches high were forged in a 500-ton forge press. Tensile flow was also examined for AISI 1018 steel. For the purpose of evaluating the behavior of interface lubricants, specimens 2.0, 2.5, and 3.0 inches in diameter, and 0.67 inch high were forged. Smaller copper specimens with dimensions proportional to those above were pressed in a 200,000-pound laboratory testing machine. Finally, the relative ranking of lubricants determined by pressing short specimens was compared to that determined by the ring compression test. Generally, the compressive flow stress of steel at 1800F with little or no influence of end effects was determined using specimen D/H values of approximately 0.6 or less. The evaluation of interface lubricant was satisfactorily examined using specimen D/H values of 3.0 or greater. The test, however, was sensitive to specimen diameter as well as lubrication. Thus, the relative rank of lubricants was altered somewhat by specimen diameter. The results failed to follow theoretically predicted behavior of applied pressure versus specimen D/H assuming either constant shear stress or constant coefficient of friction at the interface. (Author)