Testing of Materials at Medium rates of Strain

Abstract

The problems involved in the measurement of the mechanical properties of rate-dependent materials are discussed, with special reference to the role of the elastic stiffness of the testing machine and specimen. A description is given of a newly developed universal testing machine, operated by hydraulic pressure and capable of testing at crosshead velocities up to about 40 in/s. The machine has been used in two ways: for tensile tests at approximately constant strain rates in the range 10-1 to 10-2 s-1; and for compression tests in which a load is applied in a few milliseconds and maintained at a nearly constant value while the specimen is plastically deformed. The machine is instrumented so that the applied load and cross-head velocity are recorded throughout the test. The testing technique and the accuracy of measurement are discussed with reference to experimental results obtained in tests on annealed copper, mild steel, silicon-iron, and a high-strength aluminium alloy.