Showing papers on "Elasticity (economics) published in 1994"

Musculotendinous stiffness: its relationship to eccentric, isometric, and concentric performance

Abstract: The purpose of this study was to quantify the relationship between musculotendinous stiffness and performance in eccentric, isometric, and concentric activities. Thirteen trained subjects performed...

Failure mechanisms of 3D woven composites in tension, compression, and bending

Abstract: Observations of failure mechanisms in monotonic loading are reported for graphite/epoxy composites containing three-dimensional (3D) interlock weave reinforcement. The key phenomena are delamination and kink band formation in compression, tow rupture and pullout in tension, and combinations of these in bending. The materials exhibit great potential for damage tolerance and notch insensitivity. This is partly due to the presence of geometrical flaws that are broadly distributed in strength and space; and partly to the coarseness of the reinforcing tows, which leads to extensive debonding and reduced stress intensification around sites of failure. Rules of mixture corrected for the effects of tow irregularity suffice to estimate elastic moduli. Rough estimates of the stress at which the first failure events occur in compression or tension can be made from existing micromechanical models. Ultimate tensile failure might be modeled by regarding failed tows that are being pulled out of the composite as a cohesive zone. The characteristic length estimated for this zone, which is a direct measure of damage tolerance and notch insensitivity, has very large values of order of magnitude 0.1–0.5 m.

Force Microscopy Study of Friction and Elastic Compliance of Phase-Separated Organic Thin Films

Abstract: A correlation between friction and elasticity is drawn from measurements on organic thin films with a modified scanning force microscope (SFM). Local elastic compliance has been measured simultaneously with both topography and friction on the submicrometer scale on thin films of phase-separated mixtures of fluorocarbons and hydrocarbons. On the fluorocarbon domains, higher friction and lower Young`s modulus than on the hydrocarbon domains have been found. Variations in pH during sample preparation lead to differences in film formation, detected with the SFM as changes in topography, elasticity, and friction. On increasing pH, both the Young`s modulus and friction force are found to decrease. This unexpected result is discussed in terms of film formation and cohesive energy mechanisms.

Aspects of the formulation and finite element implementation of large strain isotropic elasticity

Abstract: The paper presents a formulation of isotropic large strain elasticity and addresses some computational aspects of its finite element implementation. On the theoretical side, an Eulerian setting of isotropic elasticity is discussed exclusively in terms of the Finger tensor as a strain measure. Noval aspects are a direct representation of the Eulerian elastic moduli in terms of the Finger tensor and their rigorous decomposition into decoupled volumetric and isochoric contributions based on a multiplicative split of the Finger tensor into spherical and unimodular parts. The isochoric stress response is formulated in terms of the eigenvalues of the unimodular part of the Finger tensor. A constitutive algorithm for the computation of the stresses and tangent moduli for plane problems is developed and applied to a model problem of rubber elasticity. On the computational side, the implementation of the constitutive model in three possible finite element formulations is discussed. After pointing out algorithmic techniques for the treatment of incompressible elasticity, several numerical simulations are presented which show the performance of the proposed constitutive algorithm and the convergence behaviour of the different finite element fomulations for compressible and incompressible elasticity.

Global uniqueness for an inverse boundary value problem arising in elasticity

Abstract: We prove that we can determine the Lame parameters of an elastic, isotropic, inhomogeneous medium in dimensionsn≧3, by making measurements of the displacements and corresponding stresses at the boundary of the medium.

Theoretical analysis and verification of ultrasound displacement and strain imaging

Abstract: Evaluation of internal displacement and strain distributions in tissue under externally applied forces is a necessary step in elasticity imaging To obtain a quantitative image of the elastic modulus, strain and displacement fields must be measured with reasonable accuracy and inverted based on an accurate theoretical model of soft tissue mechanics In this paper, results of measured internal strain and displacement fields from gel-based phantoms are compared with theoretical predictions of a linear elastic model In addition, some aspects of elasticity reconstruction based on measured displacement and strain fields are discussed >

Soft elasticity : deformation without resistance in liquid crystal elastomers

Abstract: Polymeric nematic liquid crystals crosslinked into elastomers (solid liquid crystals) are shown to display novel and complex elasticity. The internal (nematic) direction can experience a barrier to its rotation which couples to standard elasticity. We predict a new phenomena unique to anisotropic rubber - a «soft elastic response»; uniaxial strain is developed without resistance below a critical deformation λ * due to the relaxation of related shear strains and reorientation of the nematic director. We discuss possible experiments to verify this prediction and interpret the existing experimental observation in terms of the concept of «soft elasticity»

Double-Inclusion Model and Overall Moduli of Multi-Phase Composites

Abstract: The double inclusion model consists of an ellipsoidal inclusion of arbitrary elasticity, containing another ellipsoidal heterogeneity of arbitrary elasticity, size, and orientation, which are embedded in an infinitely extended homogenous domain of yet another arbitrary elasticity. Average field quantities for the double inclusion are obtained analytically, and used to estimate the overall moduli of two phase composites. The technique includes the self consistent and other related methods as special cases. Furthermore, exact bounds for the overall moduli are obtained on the basis of the double inclusion model

Forward and inverse problems in elasticity imaging of soft tissues

Abstract: In elasticity imaging, a surface deformation is applied to an object using small pistons, and the resulting induced strains in the interior of the object are measured using ultrasonic imaging. Two important problems are considered: (1) the forward problem of determining the strains induced by a known deformation of an object with known elasticity; and (2) the inverse problem of reconstructing elasticity from measured strains and the equations of equilibrium. The method of finite differences is used to solve the forward problem for a given piston configuration; some nontrivial issues arise in determining boundary conditions. The finite difference equations are then rearranged into a linear system of equations which formulates the inverse problem; this system can be solved for the unknown elasticities. This formulation of the inverse problem is completely consistent with the forward problem; this is useful for iterative methods in which the deformation is adaptively changed. A comparison between simulated and actual measured results demonstrate the feasibility of the proposed procedure. >

Disposable absorbent garment and a continuous, selectively elasticized band joined there to

Abstract: A disposable absorbent garment comprises a pair of elastic side sections, front and back sections, and a continuous, selectively elasticized waistband operatively joined thereto. The waistband does not substantially inhibit the elasticity of the elastic side sections, and provides the same or different elasticity to the front and back sections.

Determination of the moduli of elasticity of rocks. Comparison of the ultrasonic velocity and mechanical resonance frequency methods with direct static methods

Abstract: In the present investigation, dynamic methods for the determination of moduli of elasticity were compared with direct static methods. The dynamic moduli of rocks, such as Young's modulus (E) and Poisson's ratio (v) were determined, using both mechanical resonance frequency and classic P and S wave ultrasonic velocity techniques. For this purpose rock samples from different areas of France, covering a wide range of velocity values, were used. The mechanical resonance frequencies were investigated using a Grindo-Sonic machine while the P and S wave ultrasonic velocities were measured using a Pundit ultrasonic machine, connected to an oscilloscope. The static moduli were determined using deformation gauges. Statistical interpretation of the test results indicated significant correlation between these dynamic and static methods. Accordingly, the above non-destructive dynamic methods are suitable for the determination of static moduli of elasticity.

Complex hypersingular integrals and integral equations in plane elasticity

Abstract: Complex hypersingular (finite-part) integrals and integral equations are considered in the functional class of N. Muskhelishvili. The appropriate definition is given. Three regularization (equivalence) formulae follow from this definition. They reduce hypersingular integrals to singular ones and allow to derive hypersingular analogues for Sokhotsky-Plemelj's formulae and for conditions that are necessary and sufficient for the function to be piecewise holomorphic. Two approaches to get and investigate complex hypersingular equations follow from these results: one of them is based on the equivalence formulae; as to the other, it is based on above-mentioned conditions. As an example, authors' equation for plane elasticity is studied. The existence of a unique solution is stated and some advantages over singular equations are outlined. To solve hypersingular equations the quadrature rules are presented. The accuracy of different quadrature formulae is compared, the examples being used. They confirm the need to take into account asymptotics and to carry out a thorough analytical investigation to get safe numerical results.

The Rayleigh multipole method for linear elasticity

Abstract: A plane-strain elasticity problem is studied by means of an adaptation of the Rayleigh multipole method for a domain with a set of circular elastic inclusions. The complex potentials of Kolosov-Muskhelishvili are obtained in the form of Laurent series outside the inclusions. The results of the calculation of the multipole coefficients have been compared with those obtained by means of an integral approximation for two cases: a pair of identical inclusions and a square array of inclusions.

Deformation of single-mode optical fibers under static longitudinal stress

Abstract: The deformation of single-mode fibers resulting from a longitudinally applied static force has been measured experimentally by means of high resolution heterodyne interferometry and analyzed theoretically using the second-order theory of elasticity and the photoelastic effect. Both the elongation of the fiber and the phase change of light propagating through the fiber have been measured as a function of tensile force. The values of the elastic constants measured for fibers with pure silica core and B 2 O 3 doped cladding are E = 6.41 \times 10^{10} N/m2for the Young's modulus, \delta = -4.0 for the nonlinearity constant of the longitudinal strain, and \beta = -2.3 for the nonlinearity constant of the transverse strain. For unit elongations up to 0.3 percent, no creep, hysterisis, or relaxation effects have been observed within a resolution of one part in 104.

Junction dynamics and the elasticity of networks

Abstract: The restrictions on the configurations available to the cross-link junctions of a network, arising from its presence in a dense phase, have a well-established effect on the mechanical properties of elastomers. These constraints give rive to intermolecular cooperativity of the junction motions and hence can be well described by models of constraint dynamics in relaxation phenomena. This connection between junction dynamics and elasticity of networks is illustrated by comparing the predictions of the coupling model of relaxation with the constrained junction model of Flory. The comparison is borne out by recent 31 P NMR results on network

The heel-pad compressibility.

Abstract: Heel-pad thickness and compressibility were studied in the feet of 400 normal subjects by loaded and unloaded lateral radiographs. The normal unloaded heel-pad thickness was 18.70 +/- 2.46 mm. The thickness was greater in men than in women and increased with age. The heel-pad compressibility index was 0.53 +/- 0.09. The compressibility increased with age, but there was no significant difference with gender. An increase in body weight led to an increase in heel-pad thickness and loss of elasticity.

Equilibrium Swelling of Highly Cross-Linked Polymeric Resins

Abstract: A modified expression for the change in chemical potential of a solvent, in a polymer network, due to isotropic swelling was obtained by substituting a non-Gaussian chain length probability distribution in Flory's statistical analysis of rubber elasticity. The affine non-Gaussian expression for the free energy change due to elastic deformation was compared to both the traditional Flory and the James-Guth phantom network expressions for the free energy change due to elastic deformation using available experimental data for the swelling of highly cross-linked polymeric resins. Among the different models for the elastic contribution to the free energy change resulting from isotropic swelling, the non-Gaussian elasticity expression was found to be as good as, or slightly better than the Flory expression, and clearly superior to the James-Guth phantom network expression. Both of the two different expressions used to represent the free energy of mixing, the Flory-Huggins expression and a modified version of the quasi-chemical mixing expression, were found to be equally successful when describing the isotropic swelling of cross-linked polymeric resins

Chitosan foil for wound sealing and process for its preparation

Abstract: The invention relates to a foil of chitosan for wound sealing. According to the invention this foil contains glycerin as an elasticity enhancing additives and has a perforated surface promoting gas exchange.

Three-dimensional modelling of thermal residual stresses and mechanical behavior of cast SiC/A1 particulate composites

Abstract: Thermal residual stresses developed during casting of SiC/aluminum particulate-reinforced composites were investigated as a function of cooling rate and volume fraction of particles using thermo-elastoplastic finite element analysis. The phase change of the matrix during solidification and the temperature-dependent material properties as the composite is cooled from the liquidus temperature to room temperature were taken into account in the model. Further, the effect of thermal residual stresses on the mechanical behavior of the composites was also studied. Based on the study, it was found that the matrix undergoes significant plastic deformation during cool down and has higher residual stress distribution as the cooling rate increases. The model which does not include the solidification of the matrix tends to overestimate the residual stresses in the matrix and underestimate the tensile modulus of elasticity of the composites. In addition, the presence of thermally induced residual stresses tends to decrease the apparent modulus of elasticity and increase the yield strength of the composites compared to those without residual stresses.

Viscoelastic free-surface flows - spin-coating and dynamic contact lines

Abstract: The effect of elasticity on the spreading of a spinning drop of fluid is investigated in the context of lubrication theory. It is shown that the Oldroyd-B constitutive equation permits a solution in which the free surface of the central part of the drop thins uniformly in space. Perturbation results for small effects of elasticity indicate an increased thinning rate of the free surface compared to Newtonian results for the central part of the spinning drop, and that this enhanced thinning rate persists only over a few characteristic relaxation times. Elastic effects in the capillary region near the moving contact line are also investigated by perturbation theory for small elasticity. Two methods for resolving the contact line singularity are chosen: matching the free surface profile to a precursor film of thickness b, and introducing slip at the spinning plate. For the precursor film model, the free surface correction changes character from a net enhancement of the capillary ridge near the contact line for large b, to a negative correction over most of the profile for small b. With the slip model, the free surface correction gives a net enhancement of the capillary ridge for all values of the slip parameter α. The difference between the models for thin precursor films or slight slip is explained by examining the manner in which the stress relaxes near the contact line. The results suggest that viscoelastic contact line dynamics may be more sensitive to the local molecular physics than the Newtonian counterparts.