Showing papers on "Hydrostatic stress published in 1975"

Creep and swelling deformation in structural materials during fast-neutron irradiation. Discussion

Abstract: Radiation-induced creep and swelling is formulated in terms of the segregation of vacancies and interstitials to the microstructural sinks, such as voids, dislocations, and dislocation loops, in order to provide the physical basis for the effect of stress on swelling, radiation-induced creep, and the interrelationship between swelling and irradiation creep. It is first shown that the segregation is caused by the interaction between the point defects and the sinks and that the size interaction as well as the inhomogeneity interaction have to be considered. The latter interaction depends both on the external and the internal stresses. The segregation is then expressed in terms of bias factors for each sink type, and these factors are given for voids, small dislocation loops, and edge dislocation multipoles. The bias factors for voids are shown to depend on the hydrostatic stress leading to a stress-dependent incubation time for void nucleation as well as a stress-dependent swelling rate. The bias factors for dislocation loops depend on the deviatoric stress. Thus, the loop growth rate becomes orientation-dependent in a stress field, which gives rise to irradiation creep. The comparison between the bias factors of voids and dislocation multipoles reveals that void nucleation is suppressed in cold-worked materials until sufficient recovery has occurred. By including the bias factors for voids, dislocations, and dislocation loops into the models for swelling and irradiation creep, a constitutive law for radiation-induced deformation is obtained which includes the rates for stress-free swelling, stress-induced swelling, swelling-independent and swelling-dependent irradiation creep.

Creep and Swelling Deformation in Structural Materials During Fast-Neutron Irradiation

Abstract: Radiation-induced creep and swelling is formulated in terms of the segregation of vacancies and interstitials to the microstructural sinks, such as voids, dislocations, and dislocation loops, in order to provide the physical basis for the effect of stress on swelling, radiation-induced creep, and the interrelationship between swelling and irradiation creep. It is first shown that the segregation is caused by the interaction between the point defects and the sinks and that the size interaction as well as the inhomogeneity interaction have to be considered. The latter interaction depends both on the external and the internal stresses. The segregation is then expressed in terms of bias factors for each sink type, and these factors are given for voids, small dislocation loops, and edge dislocation multipoles. The bias factors for voids are shown to depend on the hydrostatic stress leading to a stress-dependent incubation time for void nucleation as well as a stress-dependent swelling rate. The bias factors for dislocation loops depend on the deviatoric stress. Thus, the loop growth rate becomes orientation-dependent in a stress field, which gives rise to irradiation creep. The comparison between the bias factors of voids and dislocation multipoles reveals that void nucleation is suppressed in cold-workedmore » materials until sufficient recovery has occurred. By including the bias factors for voids, dislocations, and dislocation loops into the models for swelling and irradiation creep, a constitutive law for radiation-induced deformation is obtained which includes the rates for stress-free swelling, stress-induced swelling, swelling-independent and swelling-dependent irradiation creep.« less

Stress effects in ion bombardment experiments

Abstract: Ion bombardment is employed to simulate the neutron damage that will occur in fusion reactor structural materials. These experiments usually involve specimens whose thickness is large compared to the ion range. The correct interpretation of such experiments requires inclusion of the impact of swelling- induced stresses, which arise from the rigidity of the non-swelling region beyond the ion range. An initial low level of swelling is accommodated by elastic compression of the voided region, giving rise to anisotropic stresses whose deviatoric components lead to plastic deformation by various irradiation creep mechanisms. Swelling generates the stresses which lead to creep, which in turn limits the magnitude of stress. The hydrostatic stress along the ion range eventually saturates at a level which reduces the swelling rate from the anticipated stress-free value. The swelling is fully anisotropic, two-thirds of the deformation having been diverted from directions normal to the ion beam. Crystalline anisotropy further modifies the relative rates of creep processes, and radiation-hardening of the lattice imposes an additional fluence dependence. Stress reversal at denuded zones leads to second-order stress effects. The use of step height measurements allows observation and measurement of these phenomena. Estimates of the stress levels and swelling rates canmore » be made using swelling and creep coupling coefficients derived from fission reactor data. A significant reduction in swelling rate is predicted by this analysis. (auth)« less

Measuring Photoelastic and Elastic Constants of Transparent Materials by Application of Static Stress

Abstract: The shift of Twyman-Green and Fizeau fringes as a function of applied uniaxial and hydrostatic stress have been measured on transparent solids. These data permit us to calculate all the photo-elastic and elastic constants of a material. At the wavelength 10.6 μm, where fringe shifts are small, we have measured photo-elastic constants using a modified Twyman-Green interferometer, which is capable of detecting fringe shifts ~0.01 λ by electronic means. Data on polycrystalline ZnSe grown by chemical vapor deposition are presented.

Mechanical Behavior of 6061-T651 Aluminum

Abstract: Theme A experimental testing program was conducted to determine the effects of stress state and temperature on the mechanical properties of 6061-T651 aluminum. From the data obtained at the yield and ultimate points, a 3-parameter plot was developed based upon the parameters effective stress, effective strain, and the hydrostatic component of stress. This plot illustrates the onset of plastic deformation and the occurance of fracture, and, was obtained solely from the data acquired from uniaxial tensile specimen tested at various pressures and temperatures. Two other loading pathsbiaxial tension and torsion — were used to verify the accuracy of the plot. From the test program, data were also obtained regarding the effects of the pressure and temperature environments on the other material properties such as Young's Modulus, Poisson's Ratio, toughness, and ductility.

Transfer of hydrostatic loading from one boundary to another

Abstract: If a portion of the surface of a body subjected to uniform pressure is let free, and if that same amount of pressure is applied to the rest of the surface which was originally free, the resultant stress field is the same in both cases but for a sign and a hydrostatic component. Applications may be important especially in experimental work.

Allowance for the effect of hydrostatic pressure in calculating the deformation of polymer structural elements

Abstract: Simple equations of state of hereditary type are introduced and the results of analyzing certain experiments are presented. A solution of the problem of determining the stresses and strains in the case where the average stress does not depend on the coordinates is given for the equations of state in question.