Constant Strain Rate Compression Tests Research Articles

The Mechanical Properties of Single Crystals of Pure Ice

Abstract Results obtained from tensile and compressive tests on pure ice single crystals at various temperatures down to −90°C are reported. At −50°C tensile creep tests give a continually increasing creep rate until fracture, as observed at higher temperatures. The stress dependence of the strain-rate is discussed. Fracture stress increases with decreasing temperature. Results from constant strain-rate compressive tests are compared with theoretical curves computed from Johnston’s (1962) theory of dislocation multiplication. A dislocation velocity of the order of 0.5×10−8 m s−1 is deduced for ice at −50°C.

An investigation of the mechanism of thermally activated deformation in tantalum and tantalum-base alloys

The activation energy and activation volume of tantalum and tantalum-base solid-solution alloys were obtained from both constant stress (creep) tests and constant strain rate (tensile or compression) tests. These parameters were investigated as a function of stress, temperature and interstitial concentration. The agreement between the activation parameters obtained from creep and tensile or compression tests supports many assumptions that have been made in the past about the differential technique. The functional dependence of the activation energy with changes in modulus (produced by an alloying element) is in agreement with that predicted from calculations of the energy of formation of a double kink over the Peierls' stress barriers. Electron-transmission micrographs show a predominance of screw dislocations in samples deformed at large effective stresses. This observation is explained in terms of a larger Peierls' stress of the screw dislocations. It is concluded that experimental results support the double-kink mechanism as the rate-controlling mechanism of low-temperature deformation in b.c.c. metals.