Showing papers on "Deformation (meteorology) published in 1995"

Deformation Constraints in a Mass-Spring Model to Describe Rigid Cloth Behavior

Abstract: This paper describes a physically-based model for animating cloth objects, derived from elastically deformable models, and improved in order to take into account the non-elastic properties of woven fabrics . A cloth object is first approximated to a deformable surface composed of a network of masses and springs, the movement of which is evaluated using the numerical integration of the fundamental law of dynamics. We show that when a concentration of high stresses occurs in a small region of the surface, the local deformation becomes unrealistic compared to real deformations of textiles . With such an elastic model , the only solution to decrease these deformations has been so far to increase the stiffness of the deformed springs, but we show that it dramatically increases the cost of the algorithm. We present therefore a new method to adapt our model to the particularly stiff properties of textiles, inspired from dynamic inverse procedures. R esume Cet article decrit un modele physique d'animation des tissus, variante des modeles elastiques deformables, et ameliore de fa<;on a prendre en compte les proprietes non elastiques des textiles . Nous modelisons tout d 'abord une piece de tissu par une surface deformable, constituee d 'un reseau de masses et de ressorts. Son mouvement est evalue grace a I'integration numerique de la loi fondamentale de la dynamique. Nous montrons que lorsqu'une forte concentration de contraintes apparait a certains endroits de la surface, la deformation locale y devient irrealiste comparee aux deformations rencontrees dans les tissus reels . A vec un tel modele elastique, la seule solution permettant d'attenuer cette deformation etait jusqu'a present d 'augmenter la raideur des ressorts deformes, mais nous montrons que ceci faisait croitre dramatiquement le cout de I'algorithme. Nous presentons donc ici une nouvelle methode permettant d 'adapter notre mode le aux proprietes particulierement rigides des textiles, inspiree des procedures de dynamique inverse.

Wetting effects on the spreading of a liquid droplet colliding with a flat surface: Experiment and modeling

Abstract: In this paper an experimental and theoretical study of the deformation of a spherical liquid droplet colliding with a flat surface is presented. The theoretical model accounts for the presence of inertia, viscous, gravitation, surface tension, and wetting effects, including the phenomenon of contact‐angle hysteresis. Experiments with impingement surfaces of different wettability were performed. The study showed that the maximum splat radius decreased as the value of the advancing contact angle increased. The effect of impact velocity on droplet spreading was more pronounced when the wetting was limited. The experimental results were compared to the numerical predictions in terms of droplet deformation, splat radius, and splat height. The theoretical model predicted well the deformation of the impacting droplet, not only in the spreading phase, but also during recoiling and oscillation. The wettability of the substrate upon which the droplet impinges was found to affect significantly all phases of the spre...

Scaling Properties of Stretching Ridges in a Crumpled Elastic Sheet

Abstract: Strong deformation of a sheet of solid material often leads to a crumpled state having sharp points of high curvature. A scaling property governing the crumpled state has been numerically demonstrated by an examination of the ridges joining pairs of sharp points in a range of simple geometries of variable size. As the linear size X increases sufficiently, the deformation energy grows as X1/3 and consists of similar amounts of bending and stretching energy. The deformation energy becomes concentrated in a fraction of the sheet that decreases as X1/3. Despite this concentration, the local strain in the ridge decreases as X2/3. Nearly all the deformation energy in thin, crumpled elastic sheets was found to be concentrated in ridges that obey these scaling laws.

The accommodation of Arabia-Eurasia Plate convergence in Iran

Abstract: Continental convergence between Arabia and Eurasia is taken up by distributed deformation in Iran. At wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field. The only quantitative source of information on the spatial distribution of strain rates within Iran is the record of earthquakes. We find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the Arabia-Eurasia plate motion between the defined shapes of Iran's rigid borders. When, in addition, we specify central Iran, Azerbaijan, and the southern Caspian basin to be relatively rigid blocks within the deforming zone, then the fit to the style of the observed strain rate distribution is even better. We conclude that much of the pattern of deformation in Iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it. This is likely also to have been a common occurrence in older orogenic belts. We confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part (∼10–20%) of the total deformation required by the convergence between the Arabia and Eurasia plates. We then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes. There is therefore no requirement that the large proportion of aseismic deformation in Iran is substantially different in style, orientation, or distribution from that released seismically in the earthquakes.

Tracking and finite element analysis of stripe deformation in magnetic resonance tagging

Abstract: Magnetic resonance tissue tagging allows noninvasive in vivo measurement of soft tissue deformation. Planes of magnetic saturation are created, orthogonal to the imaging plane, which form dark lines (stripes) in the image. The authors describe a method for tracking stripe motion in the image plane, and show how this information can be incorporated into a finite element model of the underlying deformation. Human heart data were acquired from several imaging planes in different orientations and were combined using a deformable model of the left ventricle wall. Each tracked stripe point provided information on displacement orthogonal to the original tagging plane, i.e., a one-dimensional (1-D) constraint on the motion. Three-dimensional (3-D) motion and deformation was then reconstructed by fitting the model to the data constraints by linear least squares. The average root mean squared (rms) error between tracked stripe points and predicted model locations was 0.47 mm (n=3,100 points). In order to validate this method and quantify the errors involved, the authors applied it to images of a silicone gel phantom subjected to a known, well-controlled, 3-D deformation. The finite element strains obtained were compared to an analytic model of the deformation known to be accurate in the central axial plane of the phantom. The average rms errors were 6% in both the reconstructed shear strains and 16% in the reconstructed radial normal strain. >

Effects of microstructure on the deformation and fracture of γ-TiAl alloys

Abstract: Deformation and fracture behavior of two-phase γ-TiAl alloys were investigated under monotonic tension loading conditions for duplex and lamellar microstructural forms. The effects of microstructure on tensile properties and deformation-fracture behavior are analyzed for deformation temperatures below and above the brittle-ductile transition. The crack initiation toughness and associated strains near the crack tip are used to explain the inverse relationship between ductility and toughness observed at room temperature. Fracture resistance behavior and toughening mechanisms at room temperature are explained in terms of microstructure and deformation anisotropy. The competition between the effects of grain size and lamellar spacing or tensile and toughness properties is discussed.

A real-time simultaneous small- and wide-angle X-ray scattering study of in-situ deformation of isotropic polyethylene

Abstract: Small- and wide-angle X-ray scattering patterns were measured in real time during in situ deformation of isotropic polyethylene at room temperature. A linear low-density polyethylene (LLDPE) was compared with a high-density polyethylene (HDPE) of approximately the same molecular weight. SAXS showed that the start of cavitation in the HDPE coincided with the onset of a stress-induced martensitic transformation detected by WAXS at a low macroscopic strain (∼0.06). It is proposed that the transformation mechanism was the T2 2 mode. It was found that in the HDPE possible lamellar stack rotation occurred whereas in the LLDPE interlamellar shear was active. Altering the thermal history to change the degree of crystallinity and lamellar population altered the strain at which the martensitic transformation occurred. In the annealed LLDPE a higher crystallinity delayed the onset of the transformation by allowing a greater amount of deformation to occur via other deformation mechanisms. In annealed HDPE, however, the transformation was activated at lower strains since less deformation of the amorphous component was possible.

Tissue supporting devices

Abstract: A new multiple component stent arrangement which allows for initial self-expansion and subsequent deformation to a final enlarged size.

Deformation-induced martensitic characteristics in 304 and 316 stainless steels during room-temperature rolling

Abstract: The effect of grain size on the deformation-induced martensite (α′) in 304 and 316 stainless steels (SS) during room-temperature rolling has been studied. Samples of four grain sizes of 52, 180, 229, and 285 μ in 304 and three grain sizes of 77, 125, and 200 /μm in 316 SS have been rolled from 16 to 63 pct reduction in thicknesses to characterize the microstructures during the rolling deformation. The amount of α′ formed increases with increase in the amount of deformation in both SS for a given grain size. The volume fraction of martensite formed increases with a decrease in grain size in 304 SS, while the α’ martensite formation has been found to be grain size insensitive in 316 SS. The volume fraction of α’ formed in 304 SS is always higher than that in 316 SS for a fixed percent reduction in thickness and grain size. This is attributed to the higher number of shear band intersections observed in 304 SS, which are considered to be the nucleation sites for the α’ embryos. The lath martensite obtained at small true rolling strains changes to blocky type at higher true strains. The morphology of α′ formed has been discussed and its characteristics obtained from rolling deformation have been compared with those earlier reported from the room-temperature tensile deformation.

Finite Element Simulation of Orthogonal Metal Cutting

Abstract: The development and implementation of a plane-strain finite element method for the simulation of orthogonal metal cutting with continuous chip formation are presented. Detailed work-material modeling, including the effects of elasticity, viscoplasticity, temperature, large strain, and high strain-rate, is used to simulate the material deformation during the cutting process. The unbalanced force reduction method and sticking-sliding friction behavior are implemented to analyze the cutting process. The deformation of the finite element mesh and comparisons of residual stress distributions with X-ray diffraction measurements are presented. Simulation results along the primary and secondary deformation zones and under the cut surface, e.g., the normal and shear stresses, temperature, strain-rate, etc., are presented revealing insight into the metal cutting process

Large deformation and fracture behaviour of gels.

Abstract: When gels are used in practice, their large-deformation and fracture characteristics are mostly far more relevant than small-deformation characteristics. In this paper fracture behaviour is discussed of various types of gels, viz. polymer and particle gels, the latter with fairly low and very high volume fraction of particles. First, a general introduction is given on theoretical aspects of fracture mechanics of gels, which involves an essential extension of classical fracture theories. The relationship between large-deformation and fracture behaviour of a gel and its structure proves to be far more complicated than for small-deformation properties. The main reasons for this difference are: (i) the much more important effect of relatively large inhomogeneities on fracture properties and (ii) some very different causes for the strain rate dependence. Not only are the average distance between cross-links and the average stiffness of the strands connecting them of importance, but also the distribution of these parameters. Moreover, inhomogeneities, be it defects (of µm to mm scale) or weak regions (e.g. in composite gels) may have an overriding effect on the fracture properties. To understand the strain rate dependence, one should consider the energies involved as a function of the deformation rate and distinguish between the amount elastically stored during deformation, the amount dissipated due to viscous flow or due to friction processes and the net fracture energy. Moreover crack initiation and fast ‘spontaneous’ crack growth (crack propagation) have to be distinguished. The factors mentioned cause large deformation and fracture properties to be much more strongly dependent on the physical structure of a gel than are the small deformation properties.

Force activated touch screen measuring deformation of the front panel

Abstract: A touch screen device includes a panel; a sensor coupled to the panel for detection of a force applied to the panel and a data processor coupled to the sensor for processing data transmitted by the sensor upon detection of the force. The sensor is provided to be co-deformable with the panel for detecting a deformation of the panel itself as a result of the force being applied. This avoids the use of a rigid frame as in conventional devices, saving weight, costs and components, and reducing manufacturing problems. The sensor means may comprise strain gauges that are physically integrated with the panel. Combined with a display such device presents a minimum parallax.

Structural interpretation of the nucleation and growth of deformation twins in Zr and Ti—II. Tem study of twin morphology and defect reactions during twinning

Abstract: A TEM study of mechanical twinning in Ti and Zr was performed. A large number of [0001]-dislocations which are rarely seen in the matrix, and a new type of stacking fault were found within deformation twins in both materials. Matrix dislocations were observed to actively interact with the tips of twin embryos and step ledges of growing twin lamellae. Twin embryos bounded by straight coherent and inclined semi-coherent boundaries were observed. These results as well as the morphological variation of twin lamellae during deformation do not agree with twinning dislocation theories but support a step-wise nucleation and growth mechanism proposed for deformation twinning in h.c.p. structures. Extended discussions are provided to address unanswered questions in the literature concerning deformation twinning.

Monitoring Deformation Processes in High-performance Fibres using Raman Spectroscopy

Abstract: It is demonstrated that Raman spectroscopy is a powerful technique for the analysis of the relationship between structure and deformation processes in high-performance fibres A brief review is presented of the developments in instrumentation that have enabled Raman spectroscopy to become so powerful for such studies Examples are given of the application of the technique to follow molecular deformation processes in different aramid fibres It is demonstrated that the behaviour is consistent with the deformation being controlled by a uniform stress series-type model where deformation takes place through a combination of crystal stretching and crystal rotation The stress-induced Raman band shifts are a direct measure of crystal stretching It is further demonstrated that the deformation of polyester fibres can be interpreted in a similar way The Raman technique is extended to the analysis of the relationship between structure and mechanical properties on carbon fibres where it is again shown that the beh

Deformation of liquid capsules with incompressible interfaces in simple shear flow

Abstract: The transient deformation of liquid capsules enclosed by incompressible membranes whose mechanical properties are dominated by isotropic tension is studied as a model of red blood cell deformation in simple shear flow. The problem is formulated in terms of an integral equation for the distribution of the tension over the cell membrane which is solved using a point-wise collocation and a spectral-projection method. The computations illustrate the dependence of the deformed steady cell shape, membrane tank-treading frequency, membrane tension, and rheological properties of a dilute suspension, on the undeformed cell shape. The general features of the evolution of two-dimensional cells are found to be similar to those of three-dimensional cells, and the corresponding membrane tank-treading frequency and maximum tension are seen to attain comparable values. The numerical results are compared with previous asymptotic analyses for small deformations and available experimental observations, with satisfactory agreement. An estimate of the maximum shear stress for membrane breakup and red blood cell hemolysis is deduced on the basis of the computed maximum membrane tension at steady state.

A study of fabric deformation using nonlinear finite elements

Abstract: Fabric deformation characterized by large displacements and rotations but small strains is analyzed using a geometric nonlinear finite element method. The fabrics are modeled by shell/plate elements. Special considerations for applying the finite element method to fabric analysis are discussed and several examples of fabric deformation presented. The results from the finite element model are compared with experimental data and are in good agreement.

Experimental and Numerical Studies of a Laminated Composite Single-Lap Adhesive Joint

Abstract: The problem of a single-lap bonded joint with laminated polymeric composite adherents and with a spew fillet, subjected to tensile loading, is investigated. Experimental and numerical analyses of this problem are presented to address the mechanics and deformation of such material and bonding configuration. Strain gages are employed to record the geometrically nonlinear deformation of the specimen. Full-field moire interferometr is used to measure the surface deformation of the adherends and adhesive (including a spew fillet). A geometrically nonlinear, two-dimensional finite element analysis is performed to check the mechanics assumptions by comparing with the experimental measurement. A good correlation between experimental and numerical solutions is obtained. It is observed that the composite single-lap joint deforms nonlinearly when subjected to tensile loading. The resulting displacement and strain fields for the adherend and adhesive layer are also presented. The moire results show that the transvers...

Seismic deformation in the Mediterranean area estimated by moment tensor summation

Abstract: SUMMARY Theoretical relationships allow the distributed deformation due to seismic activity to be quantified on the basis of the analysis of moment tensors. We apply this method to a data set consisting of seismic events that have occurred in the past 85 yr (1908- 1992) along the most important seismogenic zones of the Mediterranean region. We use the Centroid Moment Tensor (CMT) Catalog prepared at Harvard University, covering the last 16yr, and older data from Jackson & McKenzie (1988). We determine the seismic deformation and compare it to estimates of the overall deformation as obtained from global plate motion and geological studies. We generally find that the geometry of seismic deformation is similar to tectonic predictions. Even though spanning a shorter time interval, the CMT Catalog often gives a better estimate of deformation geometry than the whole data set (85yr). Seismic deformation generally ranges from less than 10 per cent to more than 90 per cent of the total deformation. Uncertainties arise because data sets may not be representative of the long-term seismic behaviour of each zone. More reliable estimates for comparison with geodynamic processes should result from analysis of a longer time period, for which no instrumental data are available. The similarity of the deformation geometry using CMT data with tectonic expectations suggests, for several zones, the possibility of using historical data to infer longer term deformation rates based on current deformation geometry.

Initiation and propagation of shear zones in a heterogeneous continental lithosphere

Abstract: Continental plates represent rheologically heterogeneous media in which complex finite strain fields may develop due to interaction of plate tectonic processes with intraplate heterogeneities. Such a deformation pattern is displayed by the Borborema shear zone system in northeastern Brazil. It involves continental-scale, curvilinear, E-W trending right-lateral transcurrent shear zones that branch off from a major NE trending, right-lateral strike-slip deformation zone formed at the northern termination of the Sao Francisco craton and that finally terminate in transpressive metasedimentary belts. We suggest that this strain field results from the compressional deformation of a highly heterogeneous continental lithosphere composed of a stiff domain (craton) and rheologically weaker domains (basins). The effect of a low-viscosity domain on the deformation of a continental plate and, in particular, the perturbation induced by this domain on the development of a shear zone formed at the termination of a stiff block were investigated using numerical modeling. The low-strength domain induces an enhanced strain localization, and the geometry of the shear zone is significantly modified. It is either split, forming a branched shear zone system in which one branch maintains its original orientation while the other rotates toward the low-viscosity domain, or completely rotated toward the weak block. The perturbation of the finite strain field depends on the ability of the weak domain to accommodate deformation, which is controlled by its initial viscosity contrast relative to the surrounding lithosphere, its orientation relative to the convergence direction, and its distance from the shear zone initiated at the termination of the stiff block. The interaction between imposed boundary conditions (tectonic forces and plate geometry) and the internal structure of the plate may give rise to highly heterogeneous strain fields, as exhibited by the Borborema shear zone system, in which intraplate rheological heterogeneities induce the development of branched or sinuous shear zones. A heterogeneous continental plate subjected to a normal convergence may therefore display significant lateral variations in strain intensity, with shear zones bordering nearly undeformed blocks, and in deformation regimes and vertical strains that would result in contrasting metamorphic and uplift histories.

The double yield in the tensile deformation of the polyethylenes

Abstract: Double yields, as well as other complex yielding behavior, that are observed during the tensile deformation of the polyethylenes have been studied in a systematic manner. The conditions under which such yielding is observed were established by studying a set of linear polyethylenes and well-characterized ethylene copolymers of narrow molecular weight and composition distributions. A wide range in crystallinity levels were developed and the rate of deformation and the deformation temperature were varied. These experimental results make clear why such complex yielding processes are not always observed. A qualitative explanation, based on the postulate of a partial melting-recrystallization process during deformation, is given that encompasses all of the experimental data.

Cohomology and deformation of Leibniz pairs

Abstract: Cohomology and deformation theories are developed for Poisson algebras starting with the more general concept of a Leibniz pair, namely of an associative algebraA together with a Lie algebraL mapped into the derivations ofA. A bicomplex (with both Hochschild and Chevalley-Eilenberg cohomologies) is essential.