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Extensible or expandable garden hoses have become popular. However, their behavior may be surprising to physicists. In this paper, the stress–strain equations that explain this behavior are derived and compared with experiments. The results clearly demonstrate that, since deformation is very large, conventional definitions of strain and stress are not useful and so-called real definitions are needed instead. [ABSTRACT FROM AUTHOR]

In large equivalent explosion tests, the method of calculating blast wave parameters by the plastic deformation angle of a cantilever beam can effectively avoid the problem of power supply, storage, communication, and low survival rate of conventional blast wave sensors. In this paper, by means of theoretical analysis and numerical simulation, the deformation response of a pure aluminum cantilever beam with different scaled distances is calculated, and the relationship between the plastic bending angle and blast wave parameters is obtained, which provides a novel and effective method for the measurement of blast wave parameters. The experimental results show that the deformation of the cantilever beam is mainly dominated by the impulse load and the error of this measurement method is within 15%. This method can provide a complementary approach to more precise but complex sensor measurement and can effectively evaluate the impulse in the explosion accident outside. [ABSTRACT FROM AUTHOR]

Acoustic metamaterials (AMMs) are designed with complex geometrical shapes to obtain unconventional sound-absorbing performances. As additive manufacturing is particularly suited to print complex structures in a more straightforward and controllable way, AMMs often exploit three-dimensional (3-D) printing techniques. However, when exposed to different temperature conditions, such structures can be affected by geometrical deformations, especially when they are polymer-based. This can cause a mismatch between the experimental data and the expected theoretical performance; therefore, it is important to take thermal effects into account. The present paper investigates the influence of thermal deformations on the sound absorption of three geometries: a coplanar spiral tube, a system with double coiled resonators, and a neck-embedded resonator. Measurements were performed on each 3-D printed specimen in the impedance tube after the samples had been placed in a climate chamber to modify the temperature settings (T = 10–50 °C). Numerical models, validated on the measurements, were employed to quantify the geometrical deformation of AMM structures through a multiphysics approach, highlighting the effects of thermal stress on the acoustic behavior. The main outcomes prove that the frequency shifts of sound absorption peaks depend on temperature configurations and follow exponential regressions, in accordance with previous literature on polymeric materials. [ABSTRACT FROM AUTHOR]

Bicontinuous interfacially jammed emulsion gels ("bijels") represent a new class of soft materials made of a densely packed monolayer of solid particles sequestered at the interface of a bicontinuous fluid. Their mechanical properties are relevant to many applications, such as catalysis, energy conversion, soft robotics, and scaffolds for tissue engineering. While their stationary bulk properties have been covered in depth, much less is known about their behavior in the presence of an external shear. In this paper, we numerically study the dynamics of a bijel confined within a three-dimensional rectangular domain and subject to a symmetric shear flow sufficiently intense to break the material. Extensive numerical simulations reveal that the shear flow generally promotes the detachment of a sizable amount of particles from the fluid interface and their accumulation in the bulk. Fluid interfaces undergo large stretching and deformations along the flow direction, an effect that reduces their capability of entrapping particles. These results are supported by a series of quantitative indicators such as (i) curvature of the fluid interface, (ii) spatial distribution of the colloidal particles, and (iii) fluid flow structure within the microchannel. [ABSTRACT FROM AUTHOR]

A whispering gallery mode resonator based magnetometer using chip-scale glass microspherical shells is described. A neodynium micro-magnet is elastically coupled and integrated on top of the microspherical shell structure that enables transduction of the magnetic force experienced by the magnet in external magnetic fields into an optical resonance frequency shift. High quality factor optical microspherical shell resonators with ultra-smooth surfaces have been successfully fabricated and integrated with magnets to achieve Q-factors of greater than 1.1 × 107 and have shown a resonance shift of 1.43 GHz/mT (or 4.0 pm/mT) at 760 nm wavelength. The main mode of action is mechanical deformation of the microbubble with a minor contribution from the photoelastic effect. An experimental limit of detection of 60 nT Hz−1/2 at 100 Hz is demonstrated. A theoretical thermorefractive limited detection limit of 52 pT Hz−1/2 at 100 Hz is calculated from the experimentally derived sensitivity. The paper describes the mode of action, sensitivity and limit of detection is evaluated for the chip-scale whispering gallery mode magnetometer. [ABSTRACT FROM AUTHOR]

A study on dynamical characteristics of a ternary locally resonant phononic crystal (PC) plate (i.e., hard scatterer with soft coating periodically disperse in stiff host matrix) is carried out in this paper. The effect of thermal deformation on the structure stiffness, which plays an important role in the PC’s dynamical characteristics, is considered. Results show that both the start and the stop frequency of bandgap shift to higher range with the thermal deformation. In particular, the characteristics of band structure change suddenly at critical buckling temperature. The effect of thermal deformation could be utilized for tuning of phononic band structures, which can promote their design and further applications. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printing is rapidly becoming an effective means of prototyping and creating custom consumer goods. The most common method for printing a polymer melt is fused filament fabrication (FFF) and involves extrusion of a thermoplastic material through a heated nozzle; the material is then built up layer-by-layer to fabricate a 3D object. Under typical printing conditions, the melt experiences high strain rates within the FFF nozzle, which are able to significantly stretch and orient the polymer molecules. In this paper, we model the deformation of an amorphous polymer melt during the extrusion process, where the fluid must make a 90° turn. The melt is described by a modified version of the Rolie-Poly model, which allows for flow-induced changes in the entanglement density. The complex polymer configurations in the cross section of a printed layer are quantified and visualized. The deposition process involving the corner flow geometry dominates the deformation and significantly disentangles the melt. [ABSTRACT FROM AUTHOR]

Material functions underlie our understanding of rheology. They form the descriptive language of rheologists and require clear definitions. Here, it is shown that the definitions of oscillatory material functions depend on how the oscillating input is mathematically referenced, as a sine or cosine. Depending on this seemingly arbitrary trigonometric reference choice, the (3rd, 7th, 11th, etc.) Fourier coefficients of a nonlinear shear response change sign. Additionally, the even harmonic coefficients of a shear normal stress response are transposed. This impacts large-amplitude oscillatory shear (LAOS) characterization in both shear strain-control (LAOStrain) and shear stress-control (LAOStress) modes. It is important to resolve this issue, because it involves the leading-order nonlinearities and the signs of these higher harmonics convey important information. This paper provides a resolution, in two parts. First, it is shown that the deformation-domain Chebyshev coefficients are immune to the arbitrary trigonometric reference in the time domain, and therefore the Chebyshev-coefficient material functions can be used and interpreted without risk of inconsistency. Second, this paper proposes the convention of referencing to a sine input for strain-control tests (currently the typical convention) and using a cosine input for stress-control (where there is not currently a convention). Finally, clarity is brought to the practical issue of data processing a digital signal, which is required for numerical simulations and every instrument that performs oscillatory characterization. [ABSTRACT FROM AUTHOR]

The conversion of creep compliance to dynamic moduli is one of the promising ways to overcome the limitation of the dynamic measurements for wide range of frequency. Remarkable algorithms were developed by Evans et al. [Phys. Rev. E 80, 012501 (2009)] and Kim et al. [J. Rheol. 59, 237-252 (2015)]. Although the former is independent of any model of creep compliance, it suffers from the instability for experimental error. On the other hand, although the latter is a stable algorithm based on the model of Havriliak and Negami [Polymer 8, 161-210 (1967)], it has a problem of parameter identification. This paper is an effort to improve the approach of Kim et al. [J. Rheol. 59, 237-252 (2015)] by suggesting new approximate functions for the Laplace transform of creep compliance. We compared our algorithm with the two previous ones. [ABSTRACT FROM AUTHOR]

This paper develops a model for fast filament stretching, thinning, and break-up for Newtonian and non-Newtonian fluids, and the results are compared against experimental data where fast filament relaxation occurs. A 1D approximation was coupled with the arbitrary Lagrangian Eulerian (ALE) formulation to perform simulations that captured both filament thinning and break-up. The modeling accounts for both the initial polymer stretching processes from the precise movement of the two moving pistons and also the subsequent thinning when the pistons are at rest. The simulations were first validated for a low viscosity Newtonian fluid matched to experimental data obtained from a recently developed apparatus, the Cambridge Trimaster. A non-Newtonian polymer fluid, with high frequency linear viscoelastic behavior characterized using a piezoaxial vibrator rheometer, was modeled using both an Oldroyd-B and FENE-CR single-mode constitutive models. The simulations of the filament deformation were compared with experiment. The simulations showed a generally reasonable agreement with both the stretch and subsequent relaxation experimental responses, although the mono mode models used in this paper were unable to capture all of the details for the experimental time evolution relaxation profile of the central filament diameter. [ABSTRACT FROM AUTHOR]

The ultrasonic wave velocities in a polycrystalline aggregate are sensitively influenced by texture development due to plastic deformation. According to Sayer's model, it is possible to construct ultrasonic pole figures via the crystallite orientation distribution function (CODF), which can be calculated by using ultrasonic wave velocities. In the previous papers, the theoretical modeling to simulate ultrasonic wave velocities propagating in solid materials under plastic deformation has been proposed by the authors and proved to be a good agreement with experimental results. Generally, wave velocities are dependent upon the propagating wave frequency; hence to evaluate texture development via ultrasonic pole figures it is necessary to examine an influence of frequency dependence on the ultrasonic wave velocities. In the present paper, the proposed theoretical modeling is applied to the texture characterization in polycrystalline aggregates of FCC metals under various plastic strain histories via ultrasonic pole figures, and also the frequency dependence is examined by using Granato-Lücke's dislocation strings model. Then the simulated ultrasonic pole figures are compared with the pole figures analyzed by the finite element polycrystal model (FEPM). The good qualitative agreement between both results suggests the sufficient accuracy of our proposed theoretical modeling. [ABSTRACT FROM AUTHOR]

We derive a constitutive relation to describe the deformation of a two-dimensional strongly aggregated colloidal system by incorporating the interparticle colloidal forces and contact dynamics. The theory accounts for the plastic events that occur in the form of rolling/sliding during the deformation along with elastic deformation. The theory predicts a yield stress that is a function of volume fraction of the colloidal packing, the coordination number, the interparticle potential, coefficient of friction, and the normal and the tangential stiffness coefficients. The predicted yield strain was independent of the particle volume fraction although the compressive yield stress exhibited a power-law relation with the volume fraction. The power-law exponent, however, was lower than that obtained from simulations reported in a paper by Roy and Tirumkudulu ["Yielding in a strongly aggregated colloidal gel. Part I: 2D simulations," J. Rheol. 60(4), 559-574 (2016)]. The cause for the discrepancy was identified to be the nonaffine deformation of the network. To account for such effects, a constitutive relation based on a simple fractal model was developed that predicts yield stress profile close to those obtained from simulations. [ABSTRACT FROM AUTHOR]

In Paper I [J. W. Swan et al., J. Rheol. 58, 307-338 (2014)], we derived an exact theoretical description of medium amplitude oscillatory shear for a semidilute colloidal dispersion. Through solution of the Smoluchowski equation governing the spatial distribution of suspended particles in the semidilute limit, we calculated the stresses that arise from an oscillatory linear flow as an expansion in powers of the rate of deformation. Here, this is extended to calculation of the first departures from linearity in the first and third harmonics of the suspension stress driven by oscillatory deformation. The role of hydrodynamic interactions is investigated via the excluded-annulus model in which particles are given an impenetrable core with a radius larger than their hydrodynamic radius. The ratio of these length scales controls the strength of hydrodynamic interactions. The third harmonic of the suspension stress is predicted to be dominated by hydrodynamic stresses at high frequency, a result that is shown to be valid experimentally for the oscillatory shear response of concentrated near hard-sphere dispersions. The calculations anticipate recent experimental observations on model near hard-sphere colloidal dispersions, and quantitative agreement is demonstrated when the predictions are scaled appropriately to account for volume fraction effects. The first departures from linearity in harmonics of the suspension stress are separated into several material functions that are independent of the flow geometry. These functions are generated from detailed numerical solutions, while asymptotic analysis is shown to predict the values of these functions at high frequency. These exact calculations provide a basis for understanding the onset of nonlinear rheological behavior of colloidal suspensions under dynamic oscillatory flow. [ABSTRACT FROM AUTHOR]

A vision-based on-chip sensor for sensing local pressure inside a microfluidic device is proposed and evaluated in this paper. The local pressure is determined from the change of color intensity in the sensing chamber which is pre-filled with colored fluid. The working principle of the sensor is based on polydimethylsiloxane deformation. The pressure at the point of interest is guided into a deformation chamber, where the structural stiffness is softened by chamber geometry, and thus, the chamber deforms as a result of pressure changes. Such deformation is transmitted to the sensing chamber, a same-layer concentric inside the deformation chamber. The deformation in the sensing chamber causes the colored fluid flowing in or out the chamber and leads to different color intensity from the top view through a microscope. Experimental evaluations on static and dynamic responses by regulated input pressures were conducted. The correlation in static response is 0.97 while the dynamic responses are successfully observed up to 16 Hz. The greatest advantage is that the local pressure can be directly seen without any additional hardware or electricity. The whole sensor is on a single-layer microfluidic design, so that the fabrication is simple, consistent, and low-cost. The single-layer design also provides the convenience of easy integration for existing microfluidic systems. [ABSTRACT FROM AUTHOR]

This paper describes an original imaging technique, named Locadiff, that benefits from the diffuse effect of ultrasound waves in concrete to detect and locate mechanical changes associated with the opening of pre-existing cracks, and/or to the development of diffuse damage at the tip of the crack. After giving a brief overview of the theoretical model to describe the decorrelation of diffuse waveforms induced by a local change, the article introduces the inversion procedure that produces the three dimensional maps of density of changes. These maps are interpreted in terms of mechanical changes, fracture opening, and damage development. In addition, each fracture is characterized by its effective scattering cross section. [ABSTRACT FROM AUTHOR]

Silicon insert is a promising tool for microinjection moulding (MIM). However, its fracture problem induced by impact in MIM creates a bottleneck for application. The purpose of this paper is to investigate the impact behaviour in MIM and the effect on the fracture of silicon inserts. The finite element method is utilised to calculate the crack propagation of silicon inserts with pressure load and thermal load in the MIM process. The simulation result shows that the crack propagation is more easily induced by the increase of pressure load, while the temperature change has little effect on the crack propagation. An experimental platform, including a novel rotatable insert mould, is developed to investigate the dynamic pressure in the MIM process. The result shows that both the maximum pressure and the maximum loading rate occur in the initial period of MIM process. It indicates that the silicon insert is more prone to fracture at the beginning of the MIM process, and spatial pressure peaks are observed in the cavity as well. The nearly consistent distribution between the peak positions and the insert fracture zones shows that the pressure distribution is quite relevant to the fracture of the silicon insert. The result is helpful because it reveals the fracture phenomenon of silicon inserts. [ABSTRACT FROM AUTHOR]

Rheology has achieved a strong position for the characterization of polymeric materials during the last 40 years. Dynamic-mechanical measurements are widely used for this purpose. On several examples, this paper demonstrates the potential of creep-recovery whose application has still been rather limited. In many cases, dynamic-mechanical experiments suffer from the fact that for several reasons, the angular frequencies applied are not chosen low enough to reach the terminal regime for which relationships between rheological quantities and molecular parameters have been established. In creep and a subsequent recovery, the time scales can be extended into the stationary regime in the linear range of deformation, and therefore, creep recovery is an efficient method to directly determine the zero-shear viscosity η0 and the linear steady-state recoverable compliance J0e . For a polymer melt with long relaxation times, it is shown how time-dependent creep data converted into dynamic-mechanical quantities can be used to extend the frequency scale to the terminal regime. The power of J0e and its temperature dependence is demonstrated for the analysis of the branching structure of a polymer. Furthermore, from such kind of measurements, interesting insights into the interactions between particles and matrix molecules in filled polymeric materials were obtained. As shown in elongational experiments, the steady state of deformation at a constant stress is reached at shorter times than at the corresponding constant strain rate. The experimental consequences are discussed. Another interesting aspect of creep is that a constant stress implies a constant capillary number. The advantage of this experimental condition for investigations of the droplet deformation in polymer blends is demonstrated. [ABSTRACT FROM AUTHOR]

We consider in this paper the elastic and viscous properties of Silly Putty and confirm the well known fact that the properties depend on the rate at which the material is deformed. Rapid deformations were studied by dropping masses onto one end of a Silly Putty cylinder, and slow deformations were studied by compressing the cylinder in a materials testing machine. The results were compared with a simple engineering model of viscoelastic materials to estimate the stiffness and the viscosity of the Silly Putty cylinder. It was found that stress induced in Silly Putty relaxes with a time constant of about 0.1 s, Young's modulus for a rapid deformation is about 1.7 x 106N/m², and the viscosity for a slow compression is about 8 x 104pa s. When subject to a short impact, Silly Putty vibrates as a result of compressional wave propagation through the material. [ABSTRACT FROM AUTHOR]

This paper investigates the transmission loss of symmetric and asymmetric laminate composite panels periodically reinforced by composite stiffeners. A comprehensive model based on periodic structure theory is developed. First order shear deformation theory is used and the coupling of the in-plane motion of the panel with its out-of-plane motion is taken into account. Stiffeners interact with the panel through three forces (two in-plane, one out-of-plane) and a torsion moment. Three types of cross sections are investigated for the composite stiffeners: I-shaped, C-shaped, and omega-shaped cross-sections. The model is validated numerically by comparison with the finite element/boundary element method. Experimental validations are also conducted. In both cases, excellent agreement is obtained. Numerical results show that the in-plane coupling effect is increased by increasing the panel thickness and the stiffener's eccentricity. The in-plane coupling effect is also found to increase with frequency. [ABSTRACT FROM AUTHOR]

Using a numerical method based on the boundary-integral technique, we assess the impact of interfacial slip on the dynamics of deformation and breakup of a single drop subjected to a uniaxial extensional flow under creeping-flow conditions. Interfacial slip is incorporated in our continuum development as a jump in the tangential velocity across the interface. This velocity jump is shown to reduce to the Navier-slip boundary condition to leading order and is characterized by a dimensionless slip coefficient α=(dI/μI)(μ/R), where dI is thickness of the diffuse interface between the liquids, μI is the viscosity of the interfacial region, μ is the viscosity of the suspending fluid, and R is the drop radius. A key contribution of this paper is the development of a stable, boundary-integral formulation to incorporate interfacial slip into existing, no-slip boundary-integral frameworks for drop deformation. Slip has a fourfold impact on the drop stretching, relaxation, and breakup phenomena. First, when the capillary number is small, the steady deformation of the drop with slip is smaller than the no-slip result, and the difference increases with the viscosity ratio and the capillary number. Slip thus leads to larger critical capillary numbers beyond which the drop stretches continuously in the extensional flow. Second, for capillary numbers greater than the critical value, we find that the shape of the deformed drop for the same drop elongation is relatively insensitive to the slip coefficient, but the time required to reach this deformation is a strong function of the slip coefficient-slip slows down the deformation process. Third, the end-pinch mechanism of drop breakup leads to a different number and sizes of droplets with the inclusion of slip. Finally, slip causes the capillary-instability mechanism of drop breakup to produce larger drops at faster rates relative to the no-slip case. In addition to the above results, we also show that slip moderates the viscosity and normal stress differences in a sheared, dilute emulsion. Our study has important implications in the area of blending of immiscible polymers and indicates that the drop size distribution, which ultimately governs the material properties of the blend and composites prepared from it, is influenced strongly by interfacial slip. [ABSTRACT FROM AUTHOR]

This paper is concerned with an investigation of the rheological performance of magnetorheological fluids under squeeze flow. Preliminary results on Newtonian fluids are first compared to Stefan's equation. Then, unidirectional monotonic compression tests are carried out in the presence of uniaxial external magnetic fields at slow compression rates under constant volume operation. Results are compared to Bingham plastic, biviscous, and single chain micromechanical squeeze flow models. Measurements using combined deformation modes (compression+small-strain oscillatory shear) suggest a compression-induced shear strengthen effect up to strains of ∼0.5. Particle-level dynamic simulations are in qualitatively good agreement with experimental observations. [ABSTRACT FROM AUTHOR]

Dielectrostriction is a rheo-dielectric phenomenon that relates the variation of dielectric properties of a material to deformation. For an initially isotropic material, two independent material parameters, called the strain-dielectric coefficients, α1 and α2, are required to describe dielectrostriction in terms of strain. Deformation affects a material's dielectric properties in two ways: (a) by introducing anisotropy in the material, which is characterized by α1, and (b) by changing the volume density of the polarizable species, which is associated with (13α1+α2). Purely viscous fluids remain isotropic during any flow-induced deformation, and therefore the coefficient α1 is always zero. In this paper, the dielectrostriction effect is studied in viscoelastic materials that are formulated to possess different degrees of elasticity. A special planar capacitance sensor rosette was employed to measure the coefficients α1 and α2 for these viscoelastic materials. The relationship between the material's elasticity and the coefficient α1 is discussed, together with some potential applications based on this relationship in the conclusion. [ABSTRACT FROM AUTHOR]

In this paper, we experimentally study the deformation and break-up of a micron-sized polydimethylsiloxane drop in a refractive-index-matched suspension of polymethylmethacrylate particles undergoing a planar hyperbolic flow. The particles produce both short-ranged stochastic effects and macroscopic mean-field effects on the deformation and break-up of the drops. In our experiments, the relative influence of these effects was varied by changing the particle to drop-size ratio (dp/d). At small dp/d, the mean-field effects dominate and the drop deformation and break-up are only influenced by an increased effective viscosity of the suspension. At large dp/d, the local flow fluctuations and the direct interactions with particles have the dominant effect on drop dynamics. This leads to pronounced fluctuations in the drop deformation and a higher polydispersity in the drop size after break-up. [ABSTRACT FROM AUTHOR]

Poly(dimethylsiloxane) or PDMS is an excellent material for replica molding, widely used in microfluidics research. Its low elastic modulus, or high deformability, assists its release from challenging molds, such as those with high feature density, high aspect ratios, and even negative sidewalls. However, owing to the same properties, PDMS-based microfluidic devices stretch and change shape when fluid is pushed or pulled through them. This paper shows how severe this change can be and gives a simple method for limiting this change that sacrifices few of the desirable characteristics of PDMS. A thin layer of PDMS between two rigid glass substrates is shown to drastically reduce pressure-induced shape changes while preserving deformability during mold separation and gas permeability. [ABSTRACT FROM AUTHOR]

This paper reports the first predictions of the yield stress of suspensions of non-Brownian magnetic fibers in the presence of uniform magnetic fields. The quasistatic regime of the shear deformation (before the flow onset) of the suspension is studied. Four different structures of the magnetic fiber suspensions are considered—column, zigzag, three-dimensional stochastic and near-planar stochastic structures—and the yield stress is attributed to the failure of the given structure at a critical strain. The main contributions to the yield stress are found to come from the restoring magnetic torque acting on each fiber and from the solid friction between fibers. The enhanced magnetorheological effect of magnetic fiber suspensions observed experimentally [M. T. López-López et al., J. Rheol. 53, 115–126 (2009)] is explained and quantified in terms of interfiber friction. Surprisingly, the dipolar magnetic interactions between fibers do not affect significantly the yield stress. The lowest yield stress is obtained for the zigzag structure and the highest one for the column structure. A reasonable agreement with the experiments is obtained for 5% and 7% fiber volume fractions in the frame of the more realistic model of near-planar stochastic structures. [ABSTRACT FROM AUTHOR]

A new method for measurement of the viscoelastic properties of the liquid with the torsion resonator on forced resonance is presented in this paper. Both theoretical analysis and experiments of different glycerol-water mixtures with our homemade torsion pendulum apparatus demonstrate that this new method avoids the restriction of the common method that the resonator should have the high quality factor both in air and in liquid sample and has the prominent advantage of measuring the concentrated and large-viscous liquid in the low frequency range (≤100 Hz) with a better precision, which is usually unavailable by the common method. Employment of the new method can thus extend the accessible ranges of viscosity and frequency of the torsion resonator apparatus and close the gaps between conventional rheometers and the torsion resonators. [ABSTRACT FROM AUTHOR]

This paper reports finite-element simulations of drop deformation in converging flows in an axisymmetric conical geometry. The moving interface is captured using a diffuse-interface model and accurate interfacial resolution is ensured by adaptive refinement of the grid. We have explored the effects of viscoelasticity on drop deformation when either the drop or the matrix is a Giesekus fluid. Contrary to the popular belief that viscoelasticity in the drop hinders deformation and that in the matrix enhances deformation, we predict a more complex picture in which viscoelasticity in either component may suppress or promote drop deformation depending on the capillary number Ca and the drop-to-matrix viscosity ratio β. Smaller Ca and β are conducive to the behavior mentioned above, while large Ca and β may produce the opposite effect. Both trends are explained by the reaction of the polymer stress to the inhomogeneous and transient deformation in the converging flow field. Finally, this understanding reconciles contradictory results in the literature as opposite limits in the parameter space. [ABSTRACT FROM AUTHOR]

The effect of parametric wave phase conjugation (WPC) in application to ultrasound or acoustic waves in magnetostrictive solids has been addressed numerically by Ben Khelil et al. [J. Acoust. Soc. Am. 109, 75–83 (2001)] using 1-D unsteady formulation. Here the numerical method presented by Voinovich et al. [Shock waves 13(3), 221–230 (2003)] extends the analysis to the 2-D effects. The employed model describes universally elastic solids and liquids. A source term similar to Ben Khelil et al.’s accounts for the coupling between deformation and magnetostriction due to external periodic magnetic field. The compatibility between the isotropic constitutive law of the medium and the model of magnetostriction has been considered. Supplementary to the 1-D simulations, the present model involves longitudinal/transversal mode conversion at the sample boundaries and separate magnetic field coupling with dilatation and shear stress. The influence of those factors in a 2-D geometry on the potential output of a magneto-elastic wave phase conjugator is analyzed in this paper. The process under study includes propagation of a wave burst of a given frequency from a point source in a liquid into the active solid, amplification of the waves due to parametric resonance, and formation of time-reversed waves, their radiation into liquid, and focusing. The considered subject is particularly important for ultrasonic applications in acoustic imaging, nondestructive testing, or medical diagnostics and therapy. [ABSTRACT FROM AUTHOR]

The creep compliance and relaxation functions used in characterizing the mechanical response of linear viscoelastic solids are traditionally found by conducting two separate experiments. Alternatively, one of the functions may be determined from a single experiment while the other is obtained through interconversion. All direct interconversion methods, however, require the solution of an ill-posed problem. The goal of this paper is to present the theoretical framework for developing a new apparatus, based on “spring loading,” which facilitates the determination of both creep and relaxation functions from a single experiment. There is no need for interconversion. Questions of stability with respect to the measured data are discussed and a stable numerical algorithm is presented. [ABSTRACT FROM AUTHOR]

A theoretical analysis is carried out in an effort to understand certain unusual properties of transient guided waves produced in a thin unidirectional graphite/epoxy composite plate by a localized dynamic surface load. The surface motion is calculated using an approximate plate theory, called the shear deformation plate theory (SDPT), as well as a recently developed finite element analysis (FEA), for their mutual verification. The results obtained by the two methods are shown to have excellent agreement. An interesting, nearly periodic "phase reversal" of the signal with propagation distance is observed for each propagation direction relative to the fiber direction. For clarification, a closed form analytical expression for the vertical surface displacement in an aluminum plate to an impulsive point force is obtained using the steepest descent method. It is found that the strong dispersion of the first antisymmetric waves at low frequencies is the main reason behind the phase reversal. This is verified further by measuring the surface response of a relatively thick aluminum plate to a pencil lead break source. The understanding developed in the paper is expected to be helpful in detecting and characterizing the occurrence of damage in composite structures. [ABSTRACT FROM AUTHOR]