Residual Strain State Research Articles

Dislocation structure for one-dimensional strain in a shocked crystal.

Dislocation structures proposed to model plastic deformation at a shock front are analyzed. The creation and glide movement of the dislocations are considered. Glide-type movement violates the condition of one-dimensional strain except if dislocation dipoles with Burgers vectors parallel and antiparallel to the shock propagation direction are directly generated by alternating shear stresses as in a punching action. The stress, strain, and dilatation characteristics are presented for a dislocation structure proposed by Armstrong, Miller, and Sandusky (AMS) to give a residual one-dimensional strain state. The AMS dislocation structure is related to independent results from a molecular-dynamics description of shear displacements in a shocked triangular lattice and is used as a basis for estimating the extent of postshock strengthening levels. The shock-strengthening predictions are in reasonable agreement with postshock deformation measurements.

Upper critical fields and critical current densities in bronze processed commercial multifilamentary Nb/sub 3/Sn wires

The T/sub c/, B/sub c2/, and J/sub c/ were investigated for superconductors in a residual strain state for bronze processed commercial multifilamentary Nb/sub 3/Sn wires. It was found that the temperature dependence of B/sub c2/ under strain obeys (1-(2/3)( pi T/1.75T/sub c/)/sup 2/) near T=0 and (1-T/T/sub c/) near T/sub c/. The establishment of the temperature scaling law of a global pinning force F/sub p/=J/sub c/*B was confirmed in commercial Nb/sub 3/Sn wires.

ブロンズ法極細多芯Ｎｂ３Ｓｎ線材における上部臨界磁場と臨界電流密度

We investigated Tc, Bc2 and Jc in a residual strain state of pre-strain for bronze processed multifilamentary Nb3Sn wires. The influence of a sample holder to the measured Jc value due to the thermal contraction and the relationship between a Jc criterion and an n-value in the form of V=KIn were clarified. It turned out that the temperature dependence of Bc2 under strain obeys [1-(2/3)(l.c.T/1.75 Tc)2] near T=0 and (1-T/Tc) near Tc. Moreover, the establishment of the temperature scaling law on the global pinning force Fp was confirmed in practical Nb3Sn wires.

切削加工した鋼材の表面残留応力に及ぼすカッター速度の影響に関するＸ線的研究

It is well known that the curved and splitted 2θ vs. sin2ψ distributions are often observed in the surface layers of the uni-directionally machined metallic materials in the case of the X-ray stress measurement. In order to solve this problem, a new X-ray method which provides more informations was proposed previously by Dölle and Hauk.The present experiments were carried out to determine the influence of cutting speed on the residual strain state, half value width of X-ray diffraction lines, micro-vickers hardness and surface roughness in the cut layer of carbon steel S50C.The experimental results showed that the changes in residual strain tensor components ε11, ε22 had similar tendency to those in half value width, micro-vickers hardness and centerline average height roughness in the machining direction.It was also clarified that with an increase in cutting speed, i.e. with a decrease in cutting volume, the residual strain tensor components ε11 and ε22 increased. In some cases, however, the strain increased discontinuously, which was explained by the formation of built-up edge.These results show that the present method of measuring strain tensor is one of the powerful methods to investigate the machining mechanism and surface layer state.

A strain-induced phase transformation in bronze-processed Nb3Sn?

The superconducting critical temperatures and magnetic fields of bronze-processed monofilamentary Nb3Sn wires flattened by rolling before reacting were, respectively, ∼13.5 K and 12 T, compared with values ∼16 K and 18 T for similarly processed circular (unflattened) wires. The interpretation of these results is discussed as either (i) the consequence of a strain- induced phase transformation or (ii) the result of the normal strain dependence of the critical properties of Nb3Sn and the triaxial nature of the residual strain state of the composite. A clear choice between the two possibilities is not possible on the basis of the present evidence, but the results underscore the inadequacy of describing the state of internal strain produced by differential thermal contraction in terms of a single value of ’’precompression,’’ as is commonly done.

Thermal cracks in unconfined sioux quartzite : Friedman, M; Johnson, B Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P423–430. Publ Reno: University of Nevada, 1978

The morphology, orientation, and abundance of thermal cracks are characterized in unconfined specimens of Sioux quartzite subjected to (1) slow thermal cycling (< 2 C/min) to 385, 560 and 685 C; and (2) slow heating at the same rate followed by quenching from 400 C. In both, all the thermal cracks are microscopic in size and occur primarily along grain boundaries and secondarily as intragranular microfractures. The latter intersect parted grain boundaries. In the slowly cycled specimens the intragranular cracks are strongly oriented at 60 to 90 to the axis of the greatest principal elongation (100 x 10/sup -6/, elongations counted positive) of the average state of residual elastic strain in the rock prior to thermal treatment, as measured by x-ray diffractometry. This geometry suggests a genetic relation between the cracks and the net stresses resulting from superposition of the residual stresses and the thermoelastic stresses developed from differential expansions of anisotropic nearest-neighboring grains. 17 references.

A Study of Relations between Rock Fabric and Joints in Sandstone

Significant relations are visible between properties of sedimentary rock fabric determined by microscopic and experimental study of sandstone and the pattern of jointing in these rocks where observed on structures in the field. Fine-grained sandstones in the Cardium Formation were studied in fold and fault structures along South Ram River in the central Alberta Foothills.X-ray diffraction determination of lattice-spacing in the quartz component of samples from the outcrop indicates that a state of residual elastic strain resides in grains comprising the rock fabric. The direction of relative compression in grains is parallel to regional trend of structure. Results of uniaxial compression experiments at low levels of strain, and of point-loading tests on discs cored from Cardium sandstone suggest a preferential orientation of microfractures parallel to this regional trend. These and other experimentally measured parameters of the rock fabric bear a direct geometrical relation to the pattern of joints observed and measured at various sites.These relations have importance for interpretation of jointing because they suggest how joint sets, though formed primarily during later stages of a tectonic cycle—during uplift and unloading of strata—have their directions influenced by earlier stages in that cycle, namely basin subsidence, sediment diagenesis, and initial tectonic loading. The relations observed in the present study also have importance wherever an understanding of joint patterns is a matter of economic importance. Two relevant examples are the interpretation of in situ stress measurements and the evaluation of fracture permeability in rock masses.

Influence of residual elastic strain on the orientation of experimental fractures in three quartzose sandstones

This study is to evaluate the influence of residual elastic strain on the orientations of tensile and shear fractures in rock. As a first step, the three-dimensional state of residual elastic strain was measured by X-ray diffractometry. Principal strains (×10−6, expansions positive) are 0, 50, and 90 in the Tennessee sandstone, −250, −30, and 100 in the Uinta Mountain quartzite, and −130, −17, and 140 in the Tensleep sandstone. These values are converted to stresses by multiplying each by 0.89×106 bars, the elastic compliance normal to in quartz. A prediction was then made concerning the orientations of fractures that would be induced in each rock by loading normal to bedding. The prediction was based on a knowledge of the prestrain, the applied loads, the maximum tensile stress, and Coulomb Mohr criteria. Each prediction was then tested by experimentally fracturing the rocks. Tensile fractures, induced in disks of Tennessee sandstone and Uinta Mountain quartzite by point-loading normal to bedding, exhibit a marked preferred orientation. Also strongly oriented are shear fractures induced in triaxial compression tests (ė of 10−4/sec, 25°C) on cylinders of Tennessee sandstone (to 2000 bars confining pressure), Uinta Mountain quartzite (1500 bars), and Tensleep sandstone (1000 bars). In each rock the tensile fractures strike parallel to the shear fractures, and both follow the predicted trend. To identify other possible causes for the fracture anisotropy, (1) apparent grain elongation, especially the trend of long axes within the bedding plane, (2) orientation of grain boundaries, (3) crystallographic orientation of quartz grains, and (4) orientation of quartz microfractures and deformation lamellae were investigated. All aspects of the fabric are randomly oriented except the trend of apparent long axes. The induced fractures cut across the trend of the long axes in two of the three rocks. It is concluded that the state of prestrain is controlling the oriontations of the fractures. The anisotropy manifest by the prestrain persists to at least moderate confining pressures.

Superconductivity in Indium Antimonide

Two samples of the metallic phase of indium antimonide were stabilized at atmospheric pressure by cooling semiconductor grade material from 100\ifmmode^\circ\else\textdegree\fi{}C to 77\ifmmode^\circ\else\textdegree\fi{}K at a pressure of 27 kbars, and then removing the pressure. Measurements of the magnetic moment of these samples down to 1.1\ifmmode^\circ\else\textdegree\fi{}K were made using a sample-motion technique in a uniform magnetic field. Below 1.89\ifmmode^\circ\else\textdegree\fi{}K, the samples exhibited bulk superconducting properties, in agreement with previous work. A high-field tail on the magnetization curves and the existence of considerable locked-in flux as the magnetic field was reduced were taken to be indications of a high state of residual strain in the sample. The slope of the critical field curve at 1.89\ifmmode^\circ\else\textdegree\fi{}K was found to be ${(\frac{\ensuremath{\partial}{H}_{c}}{\ensuremath{\partial}T})}_{\mathrm{Tc}}=\ensuremath{-}103$G/\ifmmode^\circ\else\textdegree\fi{}K. This is consistent with values found for soft superconductors with similar transition temperatures, and implies a normal state electronic specific heat per ${\mathrm{cm}}^{3}$, which is roughly half that of white tin. White tin has the same average ionic mass as metallic indium antimonide, and presumably the same electronic density.