Showing papers on "Deformation (meteorology) published in 1990"

Extended free-form deformation: a sculpturing tool for 3D geometric modeling

Abstract: Current research efforts focus on providing more efficient and effective design methods for 3D modeling systems. In this paper a new deformation technique is presented. Among other things, arbitrarily shaped bumps can be designed and surfaces can be bent along arbitrarily shaped curves.The purpose of this research is to define a highly interactive and intuitive modeling technique for designers and stylists. A natural way of thinking is to mimic traditional trades, such as sculpturing and moulding.Furthermore, with this deformation technique, the modeling tool paradigm is introduced. The object is deformed with a user-defined deformation tool.This method is an extension of the Free-Form Deformation (FFD) technique proposed by Sederberg and Parry [17].

A process for making microcellular thermoplastic parts

Abstract: A novel process to produce microcellular thermoplastic parts is described This is achieved by integrating the deformation process in the foaming cycle in such a way that the cell nucleation and growth processes are effectively uncoupled from deformation The nitrogen-polystyrene system is studied and the relationships between the essential process parameters are established It is experimentally shown that the pressures associated with deformation do not reduce the number of bubbles nucleated The process synthesized is demonstrated by making a microcellular polystyrene container

Extended free-form deformation: a sculpturing tool for 3D geometric modeling

Abstract: Current research efforts focus on providing more efficient and effective design methods for 3D modeling systems. In this paper a new deformation technique is presented. Among other things, arbitrar...

Cold deformation microstructures

Abstract: The evolution of the cold deformation microstructure is described for medium to high stacking fault energy, single phase fcc metals. Macroscopic strain accommodation for polycrystalline metals is considered, and it is suggested that grains subdivide during deformation on a smaller and smaller scale, and that each volume element is characterised by an individual combination of slip systems. A number of microstructural observations (especially of aluminium, nickel, and copper) are described, and dislocation arrangements are discussed on the basis of the general principle that they are low energy dislocation structures. It is shown that the microstructural evolution is quite similar in polycrystalline metals and in single crystals deforming by multislip, and ways in which metallurgical parameters such as stacking fault energy and grain size can affect the microstructure are examined. The general principle of grain subdivision during cold deformation is discussed with reference to the microstructural ...

Two valve micropump with improved outlet

Abstract: Pumping takes place within the micro-pump as a result of the deformation of a plate (12) using a piezo-electric pad (13). The deformation produces a variation in volume within a pumping chamber (15) defined inside a plate (11) which is made of a material which can be machined using photolithographic processes. The pump outlet (3) is blocked off, selectively, by a membraned check-valve (18) which is in direct communication with another check-valve (16) via the pumping chamber. The check-valve (16) selectively enables the pumping chamber to communicate with the pump inlet (2). The outlet valve membrane (18) has a layer of oxide (17) providing a pretension on closing. The check-valve thus has a regulatory effect on the pump operation, making the flow almost independent of the outlet (3) pressure. Application: injection of exact doses of medication.

Instability, softening and localization of deformation

Abstract: Abstract Material strain softening is commonly taken as a necessary and sufficient condition for localization in deforming rocks. However, there is a wide range of experimental and theoretical information which shows that localization can occur in sands, brittle rocks and ductile metals under strain-hardening conditions. This paper aims to bring these two contrasted views together. Three separate criteria are necessary in order to understand localization behaviour. The first involves the stability of the deforming system. The second determines whether a deforming system will undergo bifurcation so as to cease deforming in a homogeneous mode and instead deform in an inhomogeneous mode such as barrelling or localization. The stability and bifurcation criteria are independent of each other since barrelling is a stable mode whereas localization is unstable. The third criterion establishes if the unstable bifurcation mode is one of localization or of some other kind. Localization may arise from the presence of vertices on the yield surface (as in the case of pressure insensitive, rate dependent metals and in brittle rocks due to the development of preferred microfractures for slip) or from the constitutive relation being such that the plastic strain-rate vector is not normal to the yield surface (as in the cases of pressure sensitive, dilatant rocks, of materials deforming by crystal-plastic processes involving dislocation cross-slip and/or climb, and of visco-plastic materials in which voids are forming due to diffusive processes). It is important to distinguish between material and system softening (or hardening) behaviour. The theory for a kinematically unconstrained shortening experiment (that is, rigid, frictionless platens) indicates that localization can occur in strain-hardening materials but the system must strain-soften from then on; that is, localization occurs at peak stress for the system even though the material may continue to harden (or soften). However, the addition of kinematic constraints (such as friction at elastic platens, a constraint to deform in plane strain or at constant volume) means that localization may occur in a system that is monotonically strain hardening. Shear zones in naturally deformed rocks show ample evidence of dilatant behaviour in that evidence for the passage of large volumes of fluid during localization is common as is the development of dilatant vein systems. As such, since shear zones are strongly constrained by the elastic and (limited) plastic response of the relatively undeformed rocks surrounding the shear zones, strain-hardening behaviour of the system is to be expected as the norm, even if the rocks within the shear zones are undergoing material strain-softening.

Geometric factors affecting the internal stress distribution and high temperature creep rate of discontinuous fiber reinforced metals

Abstract: The creep deformation behavior of metal-matrix composites has been studied by a continuum mechanics treatment utilizing finite element techniques. The objective of the work has been to understand the underlying mechanisms of fiber reinforcement at high temperatures and to quantify the importance of reinforcement phase geometry on the overall deformation rate. Internal stress distributions are presented for a material that consists of stiff elastic fibers in an elastic, power law creeping matrix. Results indicate that large triaxial stresses develop in the matrix, and that these stresses have a strong effect on reducing the creep rate of the composite. Reinforcement phase geometry, as measured by the fiber volume fraction, aspect ratio, separation, and overlap, greatly influences the degree of constraint on the flowing matrix material and the overall deformation rate. Theoretical predictions from this modeling are compared to experimental results of creep deformation in metal-matrix composite systems with varying degrees of agreement.

Tissue hardness measurement using the radiation force of focused ultrasound

Abstract: A technique for measuring hardness in which the impulsive radiation force is focused ultrasound is used to generate localized deformation of the tissue and the applied force and/or the deformation are measured as a function of time by a conventional pulse-echo technique is proposed An attempt is made to derive some characteristic values from the curve as figures of tissue hardness The decay of applied force measured while keeping the deformation constant proved to give a good figure This preliminary experiment indicates that the proposed technique is feasible >

A computational model for face location

Abstract: The authors adopted a model-based approach, where the shape of the object is defined in terms of several mini-templates. The mini-templates are abstract descriptions of simple geometric features like arcs and corners. Relationships between mini-templates are not rigid. Rather, they are represented by springs that allow deformation of a template in terms of its size and orientation. Cost functionals are determined empirically. The authors expect their system to generate candidate regions in a given photograph associated with a rank of its goodness. >

Thermodynamics of rock deformation by pressure solution

Abstract: Geologists are indebted to Sorby (1863) for the recognition of the fact that rock deformation in the presence of water is often accomplished by processes in which ‘mechanical force is resolved into chemical action’. Sorby later coined the term ‘pressure solution’ in ascribing phenomena such as the pitting of pebbles (Mosher 1981) to stress-enhanced solubility, with which he was familiar from contemporary work in physical chemistry (Durney 1978). In recent work on deformation mechanisms, the terms Solution precipitation creep’ and ‘solution transfer’ or ‘transport creep’ have become customary, the former being more familiar from the metallurgical literature. In this chapter the term ‘pressure solution’ will be used to examine a principal mechanism of ductile rock deformation in the upper crust, which operates under diagenetic and low metamorphic grade conditions up to 200–400°C, depending upon grain size and mineralogy (Weyl 1959, Durney 1972, Elliott 1973, Rutter 1983).

Application of Three Dimensional Finite Element Analysis to Shape Rolling Processes

Abstract: In the present investigation, an FEM code SHPROL has been developed for three-dimensional simulations of shape rolling processes SHPROL is capable of handling arbitrary roll profiles and follows the deformation path incrementally so that even the end deformation that causes the crop loss can be predicted At the present time, SHPROL can be applied to isothermal rolling processes which consist of two equivalent rolls The rigid-viscoplastic formulation is used and the constant shear friction, variable between sticking and frictionless, is utilized at the roll-billet interface The roll profile is described as a combination of straight lines and arcs To demonstrate the simulation capability of SHPROL, three rolling processes have been simulated: plane-strain rolling, plate rolling, and shape rolling from square to oval cross-section Discussions were mostly made by comparing the simulation results to general observations in practice The results show that SHPROL is a valuable tool for designing rolling processes in industrial importance

Three-dimensional crack front fields in a thin ductile plate

Abstract: Based on detailed finite element solutions, various aspects of the 3-D fields near a crack front in a thin ductile plate are analysed. In particular, the stress field in the immediate crack front vicinity is carefully investigated. The existence and size of local J-dominated fields are determined from a comparison of the complete near tip stress field with the plane strain HRR solutions using a dominance parameter. In conjunction with an estimated size of the finite deformation zone, the loss of HRR-dominance along the crack front is also studied. Physically, the loss of HRR-dominance at higher load occurs when the finite deformation region outgrows the (local) plane strain region, the size of which is essentially limited by the geometry of a thin plate. Alternatively, the existence (at the mid-plane) of plane strain HRR-dominance in a low hardening material under (in-plane) small scale yielding requires the thickness of a thin plate to exceed 0.5(K1/σ0)2, thus limiting the maximum in-plane extent of the plastic zone to a fractio of plate thickness. Furthermore, such a restriction on the plastic zone size precludes the coexistence of local plane strain and surrounding plane stress HRR-fields within a thin plate.

Deformation and Grain Growth of Low‐Temperature‐Sintered High‐Purity Alumina

Abstract: 9 = 0.6 I / s ' 7 = 6.0 0 7 = 2 4 i ti 3 = 6 0 Through close control over green-state powder processing, pure alumina ceramics of 0.5-pm grain size were obtained by sintering at 1250°C. The static grain growth of this material was modest at temperatures below 1300°C. However, dynamic grain growth occurred rapidly during superplastic deformation. Therefore, although the ultrafine-grained alumina exhibited rather low initial flow stress at relatively low deformation temperatures, dynamic grain-growth-induced strain hardening gave rise to high flow stress causing cavitation and cracking. As a result, superplastic deformation could not be achieved for the ultrafine-grained pure alumina. [

Three-Dimensional Computation of Flow and Bed Deformation

Abstract: A three-dimensional (3D) flow model is developed to improve the defects of a two-dimensional (2D) model proposed by Shimizu and Itakura. Calculated results are compared with experiments as well as with results calculated by the 2D model. The flow field is predicted more correctly by the 3D model than the 2D model. A simplification of the full 3D model is made, in which the depth-wise profile of the velocity is assumed to be logarithmic. This approach is favorably tested in the calculation of flow in a meandering bend. The simplified 3D model is applied to the computation of bed deformation by bed load as well as suspended load transport in meandering channels. Good agreements are found in comparison with the experimental results. A definite difference between the 3D and 2D models is found in the predicted bed deformation with suspended load. Evaluations of the flow and bed deformation by the proposed model are clearly demonstrated through application examples, and the validity of the new calculation model is verified.

Transition between seismic and aseismic deformation in the upper crust

Abstract: Abstract Displacement on faults is often accommodated by a succession of two mechanical processes: aseismic sliding mass transfer and seismic cataclastic events. Pressure solution is attested both by dissolution markers of asperities which prevent sliding on and around the fault zone, and by the mechanism of growth of the mineral fibres by aseismic crack-seal in cavities opened by sliding. The cataclastic process is attested by observations of broken and kinked fibres, and by observations of euhedral crystals in the cavities opened by fault sliding. Natural examples are given to recognize and balance the mass transfers. Finally, a model is proposed to explain seismic/aseismic transitions on a given fault based on a gradual reduction in the cataclastic strength of the fault during sliding by successive breaking of asperities, and on the principle of minimum work consumed during the slip since the energy needed either for pressure solution sliding or for the cataclastic event may vary differently with the progressive sliding. Depending on the limiting processes for pressure solution slip, stable aseismic or unstable slip with seismic/aseismic transition is predicted.

The Alpine deformation of the Central Oman Mountains

Abstract: Abstract The Saih Hatat, Jebel Nakhl, Jebel Akhdar and the Hawasina Window structures of the Oman Mountains developed as culminations above a major sole thrust associated with late stage emplacement of the ophiolite from the northeast onto the Arabian margin. The outcrop of a pre-Permian sequence in the cores of Jebel Akhdar, Jebel Nakhl and Saih Hatat implies that the major sole thrust is located within the pre-Permian succession. This thrust is emergent in the southern foothills of the mountains south of the Jebel Salakh Range. In the Hawasina Window, however, the thrust is at a higher level and is located within the slope and oceanic sediments. An extensional regime due to the gravity sliding of the Semail ophiolite is recognized from the occurrence of surge zones, extensional duplexes, extensional cleavage and gravity folds. The development of the extensional faults, which occur in the frontal, dorsal, lateral and oblique walls of the above culminations, may account for the absence and locally thinning of the Tethyan thrust sheets around the flanks of these structures. The extensional tectonic regime is also believed to be responsible for the final extensional nature of the ‘Semail Thrust’. The Oman Mountains foreland fold and thrust belt mostly consists of a series of thrust sheets of oceanic sediments (Hawasina) together with widespread exposures of syntectonic (Aruma) deposits. The belt is dominated by imbricate stacks of both Hawasina and Aruma units. These imbricate stacks have been folded around major culminations arranged in a characteristic en echelon pattern. Late Alpine (Tertiary) deformation is largely attributed to an extensional regime of culmination collapse. Folds and thrusts were developed at the leading edge of the extensional faults (surge zones). Tertiary folding and thrusting may reactivate the pre-existing Early Alpine (Late Cretaceous) structures.

A strategy for the analysis of the stability of reference points in deformation surveys

Abstract: Confirmation of the stability of reference points is one of the main problems in deformation analysis. The difficulty lies in the datum defects of monitoring networks. A strategy has been developed...

The role of second phase in localizing deformation

Abstract: Abstract Small fractions of second phases may play a major role in localizing deformation in rocks. Second phases inhibit the migration of grain boundaries and hence may prevent grain growth. Since flow laws for many deformation mechanisms show a grain size dependence, second phases may indirectly control deformation rate. To illustrate this, a hypothetical sequence of micritic limestones, two impure layers sandwiched between two pure calcite layers, are metamorphosed and then deformed. The initial grain size is assumed to be less than 5 μm. The thermo-mechanical behavior of this sequence is predicted based on three types of experimental data: (1) calcite grain growth kinetics; (2) calcite grain size as a function of second phase; (3) plastic flow laws on natural and synthetic calcite rocks under conditions for grain-size insensitive (GSIC) and grain-size sensitive creep (GSSC). Extrapolations of the results predict that metamorphism at 400°C will increase the grain size in the pure calcite layers to 780 μm in 10 000 years. In a layer containing 5% of 0.3 μm particles, however, the grain size will increase to only 6 μm. Under a differential stress of 100 MPa, the coarser-grained layers deform by GSIC at a strain rate of 10−14 s−1 while the 6 μm layer deforms by GSSC at 10−9 s−1. This large difference in deformation rate insures that virtually all of the strain will be localized in the fine-grained layer.

Control of fluids on deformation of rocks

Abstract: Abstract Fluids of many compositions, concentrations and pressures, are ubiquitous throughout the continental lithosphere, exerting strong control on the deformation properties and processes of rocks both by mechanical means and by complex chemical rock-fluid interactions. Fluids of meteoric and juvenile origin, released by compaction, dehydration reactions, melting, and degassing, commonly during large-scale tectonic events, flow by means of thermal convection, advection (infiltration), and surface and intracrystalline diffusion. These fluids transport mass for distances ranging from the grain scale to hundreds of kilometres; fracture zones provide favourable conduits for flow. Abnormal pore pressures, recorded at all metamorphic grades, develop intermittently during syntectonic deformation, enhancing fluid infiltration by promoting increased porosity and permeability, hydraulic fracturing and severe grain size reductions. The infiltrating fluids enhance hydrolytic weakening, several grain boundary mechanisms, and reaction kinetics in a feedback manner so that strain is commonly localized into semibrittle and ductile shear zones. Large-scale detachments may take place along these shear zones at virtually any depth below the uppermost few kilometres, which, when combined with softening resulting from depth-dependent petrological and geochemical segregations, form a rheological stratigraphy. The rheology of the lithosphere through time has been governed by a combination of bulk rock flow and localized deformation is shear zones, both of which have been aided or controlled by pervasive dynamic rock-fluid interactions.

Quantum deformations of SU(2)

Abstract: Explicit representations of two deformations of SU(2), one in the Cartan basis, and one in the Cartesian basis, are constructed. The Cartan deformation subsumes previously known cases, while the Cartesian deformation appears to be new. In the latter case, explicit reversible mappings in terms of representations of SU(2) and a Casimir for the algebra are constructed.

Geostrophic turbulence and emergence of eddies beyond the radius of deformation

Abstract: Geostrophic turbulence has traditionally been studied within the framework of the classical, quasi-geostrophic equation. This equation, valid only when vertical displacements are weak, possesses a symmetry between cyclonic and anticyclonic vortices that is not present in the primitive equations. Moreover, previous studies were restricted by length scales not in excess of the deformation radius. In an attempt to advance the study of unforced geostrophic turbulence, we address here the following questions: How is the energy cascade toward longer length scales affected beyond the deformation radius? And, what is the result of the cyclonic-anticyclonic asymmetry brought on by finite vertical displacements? Some answers are provided by numerical experiments using a generalized geostrophic equation. The energy cascade is found to come to a halt beyond the deformation radius. There, a statistical equilibrium is reached at a length scale prescribed as a combination of the deformation radius, the beta eff...