Showing papers on "Deformation (meteorology) published in 1974"

Stress-deformation and strength characteristics of soil under three different principal stresses

Abstract: The concept that the deformation of soil is governed by the shear-normal stress ratio on the mobilized plane of soil particles has already been discussed on the basis of the microscopic analysis of the behaviors of soil particles under shear. 5 This discussion originates in an idea that soil is one of the materials to which the frictional law in its broad sense of word applies. In the present paper, the authors expand the formerly proposed concept2),4 of three mobilized planes (compounded mobilized planes) among the three principal stress axes into a new postulate that a stress plane called "spatial mobilized plane" occurs in the three-dimensional stress space. Then, they propsse to verify, with various test data, the fact that stress-strain relationships of soil under three different principal stresses can uniquely be expressed by interpreting the relationships with respect to this plane. They also propose a new yield condition (failure criterion) of soil that soil yields when the shear-normal stress ratio on this plane has reached a fixed value.

Deformation mechanisms in crystalline polymers

Abstract: The mechanisms which have been suggested to explain the deformation of crystalline polymers are reviewed. Emphasis has been placed upon the type of information that can be gained from experimental observations and on the extent to which those observations are consistent with suggested deformation mechanisms and current ideas on polymer structure and morphology.

Bone deformation recorded invivo from strain gauges attached to human tibial shaft

Abstract: A strain gauge rosette was attached to the midshaft of a man's tibia. This demonstrated that during every stride the bone surface was subjected to a number of discrete deformation cycles. During each cycle the bone was deformed from a particular direction, released at least partially and then deformed from another direction. This feature has been observed from a number of sites in experimental animals. The largest deformation occurred while the subject was running; the principal tension then reached 850 microstrain applied in line with the bone's long axis at 13 times 10-3 microstrain per second. When walking the largest deformation occurred prior to 'toe off'; compression was then the larger principal strain about minus 400 microstrain applied at 37 degrees to the bone's long axis at minus 4 times 10-3 microstrain per second. These strain values are the same order of size as those recorded from the long bones of sheep and pigs during their locomotion.

Postseismic Viscoelastic Rebound

Abstract: The sudden appearance of a dislocation, representing an earthquake, in an elastic layer (the lithosphere) overriding a viscoelastic half space (the asthenosphere) is followed by time-dependent surface deformation, which is very similar to in situ postseismic deformation. The spectacular postseismic deformation following the large Nankaido earthquake of 1946 yields for the asthenosphere a viscosity of 5 x 10 19 poise and a 50 percent relaxation of the shear modulus. Large thrust type earthquakes may provide, in the future, a new method for exploring the rheology of the earth9s upper mantle.

Deformation mechanism maps based on grain size

Abstract: A new form of deformation mechanism map is introduced based on grain size. Maps are developed for pure aluminum at two different homologous temperatures, and the relative contributions of the various deformation processes are estimated as a function of stress at different grain sizes. A simple method of constructing these maps is presented, requiring only a knowledge of the relevant constitutive equations for the various mechanisms and a minimum of calculation.

Stretching limits in sheet metals: In-plane versus out-of-plane deformation

Abstract: Limiting principal strains were measured by two different techniques of biaxial stretching of sheets, one of which permits free deformation in a flat plane, while the other causes constrained deformation in contact with a rigid or rubber punch. The latter method, which relates well with industrial experience, produces larger limiting strains under identical degrees of biaxiality. A possible explanation is based on the process of instability and strain localization.

Erythrocyte Deformation in Human Muscular Dystrophy

Abstract: Erythrocytes from patients with congenital muscular dystrophy exhibit dramatic surface deformation when observed with a scanning electron microscope. A similar alteration, but one affecting a smaller proportion of cells, occurs in the case of female carriers of the sex-linked Duchenne dystrophic condition. These observed changes in the erythrocyte surface may reflect a systemic defect in membrane properties.

Infrared studies on segmented polyurethane-urea elastomers

Abstract: Structural studies on hydrogen bonding in segmented polyurethane-urea elastomers were made using IR spectroscopy. Further, the orientation behavior of both the hard and soft segments on deformation was investigated using IR dichroism measurements. Hydrogen bonding was found to be formed not only between the hard segments but also between the soft segments, through urea and urethane groups, respectively. Changes in the extent of hydrogen bonding on deformation were related to segmental orientation behavior, and mechanical properties such as stress-strain and stress hysteresis. The hard segments orient preferably transverse to the stretch direction to high elongations, and show hysteresis of orientation on cyclic straining. The orientation behavior of the soft segments is approximately reversible on repeated deformation. In the range of comparatively small elongation, however, the deformation of the soft segments is larger than the external deformation. From these experimental facts, the mechanism ...

Elastic-plastic analysis of deformation induced by thermal stress in eutectic composites: I. theory

Abstract: Understanding the deformation of eutectic composites under conditions of changing temperature with or without externally applied loading is important to the utilization of these materials. Here a method of calculating elastic-plastic deformation parameters in such materials is derived and its use demonstrated. The method uses stress equilibrium, strain continuity, and component constitutive relations to derive expressions for matrix stress as a function of temperature during heating and cooling or hold time at constant temperature. From that quantity several deformation parameters of interest can be calculated. Because numerical techniques must be used to determine solutions, great flexibility is available in the selection of cycling conditions and material constants. An illustrative calculation is presented and its results are discussed.

Isotope shifts in the atomic spectrum of xenon and nuclear deformation effects

Abstract: Optical isotope shifts of four lines in the atomic spectrum of xenon have been measured using enriched samples of all stable xenon isotopes The spectrograms were recorded with the aid of a pressure-scanned Fabry-Perot interferometer and analysed by digital data techniques The measured isotope shifts are shown to be self-consistent by means of a King plot An estimate of the specific mass effect is given and the changesδ 〈r 2〉 of the mean square radius of the nuclear charge distribution are extracted from the measured shifts These changesδ 〈r 2〉 are discussed in terms of the nuclear deformation parameterβ 2 The results for the deformation of the stable even xenon isotopes are shown to be in good agreement with the systematic of deformation found for the neighbouring elements from Coulomb excitation experiments

Deformation Pattern of Twisted Nematic Liquid Crystal Layers in an Electric Field

Abstract: At rest between two metallized glass plates a nematic liquid shows a screw-like deformation pattern if one turns the plates by an angle ωm around an axis perpendicular to the plates. If a voltage U is applied, the molecules are tilted with respect to the electric field when U exceeds a threshold voltage. With increasing amount of twist ωm the maximum angle of tilt γ m increases to almost π/2 even in a weak field. Numerical results are given for the Schadt-Helfrich-cell, i.e. ωmλπ/2. The effect of piezc-electricity on deformation in a Schadt-Helfrich-cell is discussed.

Elasto-Plastic Indentation of a Layered Medium

Abstract: H. A. FRANCIS. The development of numerical finite-element models is undoubtedly the most fruitful theoretical approach for predicting and analyzing the complex strain field produced by plastic indentation. The authors' model for spherical indentation of an elastic-plastic semi-infinite layered body has yielded many interesting results. I t is felt: that some of these results can be enhanced by clarification of several points. The results have been presented as functions of the independent geometric variable D/H (indentation depth/layer thickness). However, the ratio D/H alone does not completely define the contact. The deformation mechanics must also depend on the geometry of the spherical segment of material displaced by the indenter (radius R), as specified by the ratio D/R. For Fig. 9, R/H = 20; was this value used for the other results as well? Fig. 8, which purports to show that the shape of the plastic boundary under load is strongly dependent on Yz/Yi, in fact represents a contradiction. As long as (1) the substrate is not softer than the layer (F2 > Y{), (2) the stress invariant J? decreases with depth z (which seems intuitively reasonable, considering the geometry of the plastic boundary), and (3) the plastic boundary does not extend to the layer-substrate interface, the solution must be independent of the substrate yield stress Y2. It can therefore be concluded solely from the loaded plastic boundary for Yi/Y\\ = 4.75 in Fig. 8 that during loading up to this load the solution is the same as for a homogeneous body (Ei = Ei, Y\\ = Y2). Thus, the two plastic boundaries shown for Y2/Y\\ = 1.0, 4.75 are mutually inconsistent. The surface profiles shown in Fig, 9 demonstrate that the deformation depends on the rigidity of the substrate and the fractional characteristics of the layer-substrate interface. I t is well known that the nature of the irreversible changes in surface shape outside the contact also depends on the strain-hardening rate Er. For plastic spherical indentation, the residual normal surface displacement sir) (measured positive outward) always has a positive maximum which for low ET is near or at r = a and whose distance from r = a in general increases with ET [I, 2]. For low ET, s(a) > 0 (\"piling up\"), and for high ET, s(a) < 0 (\"sinking in\") [3, 4, 5]. Thus the residual displacement field is strongly dependent on the flow stress gradient in the plastic, zone. For Y/E = 0.00084, the value ET/E = 0.244 given in Fig. 3 gives, practically speaking, a very high strainhardening rate: at a uniaxial plastic strain of 0.01, the uniaxial flow stress is 4.8 F. Assuming ET/E = 0.244 for Fig. 9, it is, therefore, realistic that, the unloaded contact perimeter lies below the original surface level. Did the authors investigate the nonstrain-hardening case Er = 0, and, if so, did it give the expected \"piling u p \" behavior (s(n) > 0)? Were any other results of the model found to be dependent on ET/E? For example, the di-

Deformation of lipid bilayer spheres by electric fields.

Abstract: In two previous publications1; 2 we have pro­ posed an elastic theory for simple lipid bilayers which may be viewed as two-dimensional fluids. In particular, we have shown that bilayer spheres in an aqueous medium can be deformed into ellipsoidal bodies if they are submitted to a magnetic field or excess outside pressure. Here we consider a possible deformation by electric fields. It will be seen that the electric effect can be quite strong for large vesicles. As before, we restrict ourselves to small deforma­ tions, assuming the bilayer to be unstretchable and the sphere to become an ellipsoid of revolution. To calculate the ellipticity we minimize the total ener­ gy consisting of curvature-elastic and electric parts. The conductivity of the bilayer will in general be very much smaller than that of the aqueous environ­ ment, so it seems permissible to treat the membrane as a perfect insulator. The electric energy of deformation may be ob­ tained from the Maxwell stresses. Those inside the membrane will be balanced by equal but opposite elastic stresses. The membrane is likely to sustain the latter without undergoing an appreciable defor­ mation as they induce neither curvature nor shear flow in the bilayer. The only unbalanced force is due to the Maxwell stress exerted by the electric field just outside the vesicle, since in the enclosed water the field must be identical to zero. We assume here that the membrane is dielectrically isotropic, which implies that the forces caused by the Maxwell stresses are confined to the interfaces with water. If it is not, electrical torque densities may be ex­ pected within the bilayer. The torques may induce curvature, but this should be negligible as the polarizabilities of the bilayer should be very much smaller than that of water. The standard expression for the electric potential Ue around a sphere in a uniform applied field is

DEFORMATION MODES γ' PRECIPITATION HARDENED NICKEL-BASE ALLOYS

Abstract: By a detailed consideration of the geometrical consequences of shear displacements in Llz y' and the requirement of compatibility with the fcc y matrix, it has been possible to define the shear modes potentially operative in y' precipitation hardened nickel-base alloys. Most of these geometrically possible deformation modes have, in fact, been observed. The predominant mechanisms are planar glide on { 111 ) of paired a12 < 110 > dislocations at low temperature and viscous cutting of y' by paired a12 < 110 > in climb configurations at high temperature. The a/3 < 112 > stacking fault modes of shear are of secondary importance, except in primary creep at intermediate temperatures where the motion of superlattice intrinsiclextrinsic stacking fault pairs is rate controlling.