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Mooney-Rivlin is the most frequently used model from all models used for mechanical characterization of the hyperelestic materials. Simplicity, applicability in a large rage of strains are the key reasons for regular use of this model. However, depending on the number of parameters, the Mooney model can take several forms. While, nine parameter being the highest order noticed, two parameter model is the most commonly found form in the current research domain. Since two parameter model used repetitively, we investigated the effect of incremental change in two material constant values one at a time, on model curve. As Drucker Stability Criterion is governing the extreme values of material parameters, changes in the model curves are discussed related to it. Resultant effects on stress-strain curves due to change in parameter values were examined and physical effect on the characterization is interpreted accordingly.

A simple plasticity model is proposed to model the stabilized cyclic stress‐strain by introducing the non‐proportionality factor and additional hardening coefficient. The two introduced factors take into account the effects of non‐proportional additional hardening. The proposed model is convenient for engineering application since only six material constants are necessary for modeling.

In order to find hyperelastic material model constants, data fitting technique is often used. For this task, the data is collected through different laboratory tests, namely, the uniaxial, the biaxial and the pure shear. However, due to the difficulty in getting biaxial data, often only uniaxial data was used for the fitting. Despite frequent use, it was established that this practice creates erroneous results. With a view to improve the data fitting results and at the same time to overcome the difficulty of collecting primary biaxial data, uniaxial data was used to generate a secondary biaxial data set. The data derived through this method was then tested with four common models as to examine the compatibility of the method. Subsequently, real biaxial data was used to compare with the data fitting results obtained through the proposed method. As results indicated combined data fitting for both instances were very much identical with respect to all tested models. Cases where somewhat higher deviation observed between experimental curves and data fitted curves for biaxial data, gave similar results for adjusted data driven data fitting too. However, such deviation could be attributed to mismatch between models with the particular material behaviour rather than the generated data.

Concrete tensile strength and fracture toughness are two important material constants that should be independent of specimen size, geometry or type. In this study, on the basis of the improved boundary effect model, independent tensile strength and fracture toughness of concrete, which are unaffected by the specimen type, were determined by using various specimens, e.g., three-point-bending and wedge-splitting specimens. The concrete structural failure was fully predicted using independent material constants, and the constructed safe design diagrams with upper and lower limits (±15%) can cover all experimental results. The theoretical minimum size of the concrete meeting the linear elastic fracture mechanics were quantified, and the peak loads of concrete specimens were predicted using various average fictitious crack growth length.

Duplex and super duplex stainless steels have high corrosion resistance, excellent mechanical properties, and high impact strength. Such characteristics make these steels able to operate in various segments of the industry, especially in aggressive environments. These alloys have higher strength than austenitic and ferritic stainless steels and their operation is generally restricted to temperatures lower than 300 °C. Most steels and alloys only exhibit elasto-viscoplastic behavior at temperatures higher than 1/3 of the absolute melting temperature. The objective of this work was to make an experimental study showing that the duplex and superduplex steels present a rate-dependent behavior even at room temperature (around 25 °C). Two different alloys: duplex stainless steel UNS 31803F51 and super duplex UNS S32760GRF55 were used in the study. Simple models were proposed to describe how the rate-dependent portion of the stress (called at this paper “the viscous term”) depends on the strain rate. A simple procedure to identify experimentally all material constants that appear in the theory is presented. The experimental results are in very good agreement with the model predictions.

In the metal plastic forming process, ductile fracture is an important factor influencing the forming properties of materials, and the ductile fracture criterion can effectively predict the moment and location when the material fracture. When using the ductile fracture criterion predicts the fracture of materials, the material constants expressed in integral form is an important index that affect the prediction accuracy. At present, the method to determine the material constants in the ductile fracture criterion is mostly combined with basic test. Therefore, the method to determine the material constants in ductile fracture criterion is introduced in this paper. These methods are divided into numerical calculation methods, finite element simulation method and the M-K theory model method.

These data include detailed calculations and graphs based on our manuscript submitted to Journal of Magnetism and Magnetic Materials, entitled "Predicting New Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy". These data are organized in two parts; first, we present the calculated plots of sensitivity of magnetic anisotropy field and anisotropy energy density for 49 epitaxial rare earth iron garnet (REIG) film/substrate pairs (a total of 98 plots, Figs. 1-15). In the second part, we present in Table 1 the complete details on the calculations for total magnetic anisotropy and all material constants used for each of 50 film/substrate pairs. The comparison with the previous experimental demonstrations is also shown in Table 1 (last column) and 2 with an accompanying discussion confirming the reliability of our model. (C) 2019 The Author(s). Published by Elsevier Inc.

The risk of error in using only uniaxial data for fitting constitutive model curves is emphasized by many hyperelastic material researchers over the years. Unfortunately, despite these indications, often the method is utilized in finding material constants for mathematical models. The reason behind this erroneous practice is the difficulty in obtaining biaxial data. Therefore, as a remedial measure, in this research work we suggest a method of forecasting biaxial data from uniaxial data with a reasonable accuracy. Initially, a set of data is collected through standard uniaxial test. A predefined generalized function is then used to generate a set of values which subsequently used as multiplication factors in order to get biaxial tension data. Eventually, with availability of two data sets, Mooney-Rivlin two parameter model was used for combined data fitting. Material constants were then obtained through least squares approach and thereby theoretical load curves namely uniaxial, equi-biaxial tension and pure shear were drawn. The results of this work suggest a definite improvement related to three curves when compared with only uniaxial test data fitted outcomes. For validation of secondary biaxial data, separate eqi-biaxial test was done and resulting curves were compared. Biaxial primary data curve and forecasted data driven curve show identical data distribution pattern though there is a shift and therefore provide a basis for further research in this direction.

This paper deals with the reflection and transmission of SH waves at a very rough interface separating two dissimilar isotropic elastic solids. The interface oscillates between two straight lines. By means of homogenization, the domain containing the very rough interface is replaced by an effective material layer whose elastic constants depend on the thickness variable. The reflection and transmission of SH waves at the very rough interface is then reduced to the ones at a FGM layer. The exact analytical formulas for the reflection and transmission coefficients have been derived. Based on them, the dependence of the reflection and transmission coefficients on the incident angle, the wave frequency, the material constants and the geometry of the rough interface are examined. Remarkably, it has been shown that a very rough interface of comb-type with the comb-tooth width varying periodically can produce band-gaps to SH waves. With this fact, many potential applications can be expected coming from very rough interfaces of comb-type with periodic comb-tooth width. It is also shown that the width and the location of band-gaps depend strongly on the contrast of rigidities of two half-spaces, the amplitude of the variation of the comb-tooth width, the incident angle of SH waves and the number of periods of comb-tooth.

The influences of process parameters on mechanical properties of AA6082 in the hot forming and cold-die quenching (HFQ) process were analysed experimentally. Transmission electron microscopy was used to observe the precipitate distribution and to thus clarify strengthening mechanism. A new model was established to describe the strengthening of AA6082 by HFQ process in this novel forming technique. The material constants in the model were determined using a genetic algorithm tool. This strengthening model for AA6082 can precisely describe the relationship between the strengths of formed workpieces and process parameters. The predicted results agree well with the experimental ones. The Pearson correlation coefficient, average absolute relative error, and root-mean-square error between the calculated and experimental hardness values are 0.99402, 2.0054%, and 2.045, respectively. The model is further developed into an FE code ABAQUS via VUMAT to predict the mechanical property variation of a hot-stamped cup in various ageing conditions.

The fragility parameter is one of the most important material constants that is extensively used in glass science, playing a central role in the enhancement of the understanding the glass formation process of disordered systems. Although fragility has been widely used, this concept has never been precisely defined and evaluated in relaxor ferroelectrics. Here, we have filled up this scientific gap. Based on a generalized Vogel-Fulcher-Tammann equation, the fragility parameter is introduced for relaxor ferroelectrics. The new formulation has been quantitatively assessed by combining dielectric spectroscopy and pyroelectric measurements on canonical relaxors. A clear correlation between the fragility and a new local structural heterogeneity related order parameter elucidates new information about the ferroelectric order of relaxor ferroelectrics. A new pathway to disentangle relaxation phenomena in other relaxor ferroics could have opened.

A long-standing puzzle in the understanding of magnetic materials is the “Permalloy problem,” i.e., why the particular composition of Permalloy, Fe 21.5 Ni 78.5, achieves a dramatic drop in hysteresis and concomitant increase in initial permeability, while its material constants show no obvious signal of this behavior. In fact, the anisotropy constant κ1 and the magnetostriction constants λ 100 , λ 111 all vanish at various nearby, but distinctly different, compositions than Fe 21.5 Ni 78.5. These compositions are in fact outside the compositional region where the main drop in hysteresis occurs. We use our newly developed coercivity tool [A. Renuka Balakrishna and R. D. James, Acta Mater. 208, 116697 (2021)] to identify a delicate balance between local instabilities and magnetic material constants that lead to a dramatic decrease in coercivity at the Permalloy composition Fe 21.5 Ni 78.5. Our results demonstrate that specific values of magnetostriction constants and anisotropy constants are necessary for the dramatic drop of hysteresis at 78.5% Ni. Our findings are in agreement with the Permalloy experiments and provide theoretical guidance for the development of other low hysteresis magnetic alloys.

Modelling creep deformation of tempered martensitic P9 steel in quenched and tempered, and simulated post weld heat treatment conditions has been performed in the framework of improved Dyson–McLean approach for wide range of stresses at 873 K. In this approach, kinetic creep law coupled with the set of first-order differential equations representing the evolution of microstructural internal-state-variables with strain/time has been employed to describe creep deformation behaviour of tempered martensitic steel. The optimised material constants associated with the model such as dislocation storage parameter (Kd) and rate constants associated with the precipitate coarsening (Kp) and solute depletion (Ks) reflect the influence of two different heat treatments on creep characteristics examined in the present investigation. At all test conditions, good agreement between the predicted and experimental creep strain/strain rate-time data at 873 K has been observed. Further, good correlations have been obta...

The Jiles-Atherton (JA) model explains hysteresis phenomenon in a ferromagnetic material through domain wall transitions with five material constants called the JA parameters. These parameters describe the magnetic characteristics of a ferromagnetic material and are identified from the measured saturated B-H loop. However, the JA parameters cannot predict the inner loops accurately and this presents a serious problem for the JA model to be used in finite element based computer-aided design simulations. In this paper, we have proposed a new approach which assumes one of the JA parameters to be a function of magnetic field intensity H, or magnetic flux density B, and requires knowledge of the inner loops. The improvement in the accuracy of the modified JA model has been demonstrated by comparing its predictions with measurements and one of the already published works.

To date, the complete sets of electromechanical-related coefficients of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals have been reported only at room temperature (RT). To meet the demands of practical applications, the full sets of elastic, piezoelectric, and dielectric constants of [001]-poled rhombohedral PIN-PMN-PT single crystals were measured as a function of temperature ranging from −10 °C to 70 °C by the resonance method. Variation trends of the material constants with temperature are discussed, and the corresponding mechanisms are analyzed. With increasing temperature, absolute values of the elastic compliance constants, the piezoelectric coefficients $d_{\mathrm {ij}}$ , and the dielectric permittivities $\varepsilon _{\mathrm {ij}}$ increase, but the piezoelectric voltage coefficients $g_{\mathrm {ij}}$ and the characteristic frequencies decrease. The electromechanical coupling factors $k_{\mathrm {ij}}$ are not sensitive to temperature, of which $k_{33}$ keeps 91% in the temperature range of −10 °C to 70 °C. Compared with other coefficients, the piezoelectric coefficients $d_{31}$ , $d_{33}$ , and $d_{15}$ , and the dielectric permittivities $\varepsilon _{11}^{T}$ , $\varepsilon _{33}^{T}$ , $\varepsilon _{11}^{S}$ , and $\varepsilon _{33}^{S}$ , show the largest enhancements with increasing temperature. For example, the piezoelectric coefficients $d_{31}$ and $d_{33}$ , and the dielectric permittivities $\varepsilon _{11}^{T}$ and $\varepsilon _{33}^{T}$ change from −560 pC/N, 1130 pC/N, 1050, and 3300 at −10 °C to −890 pC/N, 1700 pC/N, 2030, and 6140 at 70 °C, increasing by more than 50% from −10 °C to 70 °C.

The present paper examines the effective macroscopic behavior of a microscopically damaged interface between an infinitely long piezoelectric layer and a piezoelectric half-space under antiplane deformation. The interface is modeled as containing a periodic array of micro-cracks. The lengths and the positions of the micro-cracks on a period interval of the interface are randomly generated. The micro-statistical model is formulated in terms of hypersingular integral equations and used to investigate in detail the influences of the material constants of the piezoelectric layer and the half-space and the width of the layer on the effective properties of the interface.

The behavior of material constants in ferroelectric Ba0.8Sr0.2TiO3 thin films is studied depending on the misfit strain at room temperature in the context of nonlinear thermodynamic potential of the phenomenological theory. Some constants are found to undergo drastic changes with the alternating strain at the interfaces. The gathered results allow one to evaluate the material constants for a specific film and to outline the direction in searching the ways to synthesize films with the needed properties.

Based on the Stroh formalism of one-dimensional quasicrystals with piezoelectric effect, the problems of an infinite plane composed of two different quasicrystal half-planes are taken into account. The solutions of the internal and interfacial Green's functions of quasicrystal bi-material are obtained. Moreover, numerical examples are analyzed for a quasicrystal bi-material subjected to line forces or line dislocations, showing the contour maps of the coupled fields. The impacts of changing material constants on the coupled field components are investigated.

Determination of material constants describing its behavior during superplastic gas forming is the main subject of this study. The main feature of free bulging tests is the stress-strain conditions which are very similar to ones occurring in the most of gas forming processes. On the other hand, the interpretation of the results of such tests is a complicated procedure. The paper presents a simple technique for the characterization of materials superplasticity by free bulging tests, which is based on inverse analysis. The main idea of this technique is a semianalytical solution of the direct problem instead of finite element simulation which allows one to reduce the calculation time significantly. At the same time the results this simplified solution are accurate enough to obtain realistic material constants.

Low cycle fatigue tests were carried out for a 304 stainless steel at room temperature. A series of experimental characterisations, including SEM, TEM, and XRD were conducted for the 304 stainless steel to facilitate the understanding of the mechanical responses and microstructural behaviour of the material under cyclic loading including nanostructure, crystal structure and the fractured surface. The crystal plasticity finite element method (CPFEM) is a powerful tool for studying the microstructure influence on the cyclic plasticity behaviour. This method was incorporated into the commercially available software ABAQUS by coding a UMAT user subroutine. Based on the results of fatigue tests and material characterisation, the full set of material constants for the crystal plasticity model was determined. The CPFEM framework used in this paper can be used to predict the crack initiation sites based on the local accumulated plastic deformation and local plastic dissipation energy criterion, but with limitation in predicting the crack initiation caused by precipitates.

Strain tuning of polarization states and dielectric properties in (001) epitaxial (Pb, Sr)TiO3 (PST) films is investigated using a thermodynamic phenomenological model. We find that our calculations of anisotropic dielectric properties and their electric field tunability at various in-plane strained states are in good agreement with relevant experimental data for epitaxial Pb0.35Sr0.65TiO3 films when material constants are properly determined. Our modeling further suggests that dielectric tunability can be optimized by combined control of epitaxial strain and PST composition.

Analysis of thermoelastic damping (TED) of micro and nano-beam resonators plays a very important role in designing the resonator with high-quality factors. TED of micro and nano-beam resonators has therefore been an interesting and challenging area of research in recent years. Prediction of TED is more challenging under the effect of non-Fourier heat conduction. In the past, several works have been dedicated to TED modeling with the influence of non-Fourier heat conduction in view of the fact that non-Fourier heat conduction model is more relevant for analysis of TED for small scale devices. The present work aims to investigate TED in micro and nano-mechanical resonators utilizing non-Fourier heat conduction model with a single delay term introduced by Quintanilla in 2011. We derive an explicit formula of the quality factor for TED based on the entropy generation approach. With the help of numerical results, we present the influence of TED in the context of normalized frequency as well as beam thickness. Further, the effects of the time delay parameter and the material constants on TED have been discussed in detail. The results of the present model are compared to those obtained for GN-III model. It has been observed that the current model offers a high-quality factor as compared to GN-III model.

We analyse the circular Couette flow of Herschel–Bulkley fluids to investigate the validity of the assumption that the rate of strain distributions across the gap share a common point. It is demonstrated that this is true only with fully-yielded Bingham -plastic flow. In other cases, e.g., in partially-yielded Bingham-plastic flow or fully-yielded Herschel–Bulkley flow, the common point for the fully-yielded Bingham case provides a good approximation for determining material constants only if the gap is sufficiently small. We also revisit the important issue of determining material properties of viscoplastic fluids by using “true values” for the rate of strain and demonstrate that the material properties can be very different from those obtained using “apparent’ values for the rate of strain. 260 101 108

The nonlinear properties of barium titanate lead to changes in the material constants of the linear equations for the piezoelectric effect in thin films. The behavior of the material constants of single-crystal barium titanate thin films at room temperature has been studied as a function of the misfit strain in terms of the Landau potential of the phenomenological theory. Most of material constants exhibit anomalies at the interfaces with variations in the strain. In the r phase, some elastic and electroelastic constants reach an extremum. The obtained results indicate lines of the search for obtaining films with necessary properties.

In order to predict the creep life of a component at high temperature both accurately and economically, continuum damage mechanics approach is used based on experimental creep data. However, material constants used in the models have a great relationship with the performed stress range of creep tests. In this paper, several sets of material constants were obtained from a wide range of stresses on P91 steel. The creep damage tolerance parameter was used to classify these sets, and the modified continuum damage mechanics model was used to investigate a pipe under closed-end condition. Results have illustrated the main difference lies on the tertiary stage while slight difference on the primary and secondary stages, and the contribution of the tertiary stage to the total damage decreased when using material constants from higher stress region.

New derivations of origin-independent expressions for the electric permittivity are presented, starting either from the response function of the current density that defines the absorption coefficient, or from the off-resonance single-photon scattering amplitude that leads to the Kramers–Heisenberg dispersion formula. The resulting expression for the permittivity is compared with earlier work on the origin dependence of the material constants. Different origin-independent expressions for the permittivity, the inverse permeability and the magnetizability are calculated and discussed. By considering electromagnetic plane waves in the absence of external sources, the macroscopic Maxwell equations are used to describe the response of matter to external fields. In combination with the constitutive relations, a wave equation expressed in terms of the material constants is derived. It is shown that the different definitions of the material constants lead to the same wave equation. The non-uniqueness of the definitions of the material constants is discussed in this context. Finally, based on the discussions, we propose a possible unique, origin-independent definition of the material constants.

In present paper, 3D finite element (FE) method is used to determine plastic limit load solutions for pipe bends under combined bending and torsion moment. With a detailed analysis and comparison, a common awareness for loading effect is showing which will raise researchers concern. By the way, past solutions are not appropriate to estimate FE results. In this respect of finite element analysis, overall yielding considering the spread process of yield region from crown to the straight pipe shows these promising finite element results. A wide range of non-dimensional parameters for pipe bends are considered and plastic limit load solutions are suggested. The results show that r/t is the main factor affecting the limit loads. Plastic limit load is independent on the loading path and material constants by normalizing. Results show that the circular interaction rule is a great approximation for pipe bends under combined bending and torsion moment. A series of approaches are confirmed in order to validate our finite element method on plastic limit analysis. Based on the finite element results, approximate plastic limit load solutions are proposed. Present work will further improve the limit load solution for pipe bends under complex loading conditions.

A method for calculating the macroscopic elastic moduli of isotropic composites with isolated inclusions is proposed. The distinctive feature of the method is calculation of the concentration factors of average strains and stresses by using the effective volumes of averaging of phases. The effective volumes are found by solving the boundary-value problem of elastic deformation of the representative cell of a two-phase composite. In this case, the limiting version of a conventionally porous composite with zero material constants of inclusions is taken into account. A good agreement between calculation results and experimental data is obtained for various combinations of the elastic moduli and volume fraction of inclusions.

The compositional dependence of the large-field behavior of [001]C-cut relaxor ferroelectric xPb(In1/2Nb1/2) O3-(1-x-y)Pb(Mg1/3Nb2/3)O3-yPbTiO3 (PIN-PMN-PT) single crystals that are on the rhombohedral side of the morphotropic phase boundary was characterized under electrical, mechanical, and thermal loading. The effects of varying the concentrations of PIN and PT are discussed. Composition was found to impact the material constants and the field-induced phase transformation threshold in the piezoelectric d333-mode configuration.

The present investigation provides the assessment of stationary points and uniform film thickness for the thin film flow of Sisko fluid model on a vertically upwards moving belt. The conditions for the stationary points, uniform film thickness and net upwards flow are specified. It is observed that the locations of stationary points are shifted towards the belt with an increase in the fluid behaviour index, Sisko fluid parameter and Stokes number. The behaviour of uniform film thickness is investigated by giving certain realistic values to the fluid behaviour index and material constants. Furthermore as special cases, locations of the stationary points and uniform film thickness for the Newtonian fluid film are discussed.

Cochleates are self-assembled cylindrical condensates that consist of large rolled-up lipid bilayer sheets and represent a novel platform for oral and systemic delivery of therapeutically active medicinal agents. With few preceding investigations, the physical basis of cochleate formation has remained largely unexplored. We address the structure and stability of cochleates in a combined experimental/theoretical approach. Employing different electron microscopy methods, we provide evidence for cochleates consisting of phosphatidylserine and calcium to be hollow tubelike structures with a well-defined constant lamellar repeat distance and statistically varying inner and outer radii. To rationalize the relation between inner and outer radii, we propose a theoretical model. Based on the minimization of a phenomenological free energy expression containing a bending, adhesion, and frustration contribution, we predict the optimal tube dimensions of a cochleate and estimate ratios of material constants for cochleates consisting of phosphatidylserines with varied hydrocarbon chain structures. Knowing and understanding these ratios will ultimately benefit the successful formulation of cochleates for drug delivery applications.

A unified macro- and micromechanics constitutive model of fully coupled electro-magneto-thermo-elastic multiphase functional composites is developed. The model is based on the hypothesis of periods, the theory of uniformity, and the finite-volume direct averaging micromechanics (FVDAM). By introducing quadratic displacements and electric and magnetic potentials into the constitutive model, its accuracy is improved. The efficiency of the model is also raised by adopting surface-averaged quantities to be the primary variables of the original FVDAM. A numerical example is presented, and a relation between material constants and the fiber volume fraction is obtained.

A new theoretical approach based on the modified three-element Eyring-Halsey model was developed for the derivation of an equation describing the thermally induced recovery of predeformed and crystallized crosslinked polymers. The proposed approach takes into account the influence of crystallizable covalent network and of entangled slipped molecular chains. Modeling of thermally induced shape-memory (SM) recovery strain and SM recovery rate detected at constant heating rate has been successfully performed for nearly linear and two short-chain branched polyethylenes, which were crosslinked by peroxide. The values of material constants determined by fitting agree with the estimations existing in literature. Fitting results have shown that increase of degree of branching and crosslink density accompanied with reducing crystallinity results in increasing contribution of the entangled slipped chains to the total stored SM strain. The physical sense of main fitting parameters and their dependences on the material constants such as crystallinity are discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 815–822

The flow behaviors of CLAM steel were investigated to obtain the forming simulation parameters. The hot deformation experiment was performed under the strain rate of 0.001–5 s −1 and the temperature of 850–1050 °C on Gleeble-1500 thermo-simulation machine. The results showed that the flow stress decreased with the increasing deformation temperature but increased with the increasing strain rate. Moreover, material constants α , n , ln A and activation energy Q were calculated as a function of strain. Constitutive equation of Arrhenius-type allowing for the effects of strain, strain rate and temperature was developed to describe the hot deformation behaviors of CLAM steel. The flow stress of CLAM steel predicted by the proposed constitutive equation highly coincided with the experimental results, which demonstrated that the developed constitutive equation could precisely predict the flow behaviors of CLAM steel.

In this paper, the stress relaxation tests were performed on Ti-6Al-4V alloy sheet with different initial total strains and different temperatures. Based on the experimental data, a novel empirical equation for predicting the stress versus time curves was proposed, and then an explicit constitutive model for describing the stress relaxation behaviours was further developed. The average prediction error was less than 8.27%, proving the proposed prediction curves were valid. In addition, two material constants which depend on initial stresses and total strains were introduced to accurately describe the stress relaxation curves. Then the methods for solving these two material constants under different initial conditions were presented. Finally, a simple method for dividing the stress relaxation stages was proposed. There are three stages in the stress relaxation curve studied in this paper, including the loading stage, stress relaxation-I and stress relaxation-II. A symbol called ηi which represents the normalized ratio of instantaneous stress to initial stress was used. When time τ is equal to α, the ratio of instantaneous normalized stress to normalized initial stress is reduced to η1 = 1/e, and the instantaneous plastic strain at this moment is (1 − η1) of the total plastic strain.

Quasi-static and dynamic tensile tests were conducted to measure diffusion bonding (DB) interface strength of Ti6Al4V alloy at different strain rates. The effect of strain rate on fracture mode was analyzed by the fractography analyses. A modified Johnson-Cook (JC) model was proposed to describe the stress-strain behavior of DB interface, where the strain rate hardening coefficient had a nonlinear relationship with the strain and the strain rate. The JC failure model with calibrated material constants was used to predict the failure strain of DB interface. Using Abaqus/Explicit through a VUHARD subroutine, the modified JC model and the JC failure model were verified by predicting load-elongation curves and failure strains at three strain rates. The models are capable of describing the mechanical behavior of DB interface for Ti6Al4V alloy.

With consideration of the static bulk flexoelectric effect, dynamic bulk flexoelectric effect, strain gradient elastic effect and micro-inertia effect, Rayleigh wave propagation in semi-infinite centrosymmetric flexoelectric dielectrics is investigated and the dispersion relation is derived. Numerical results of the Rayleigh wave propagation in single crystal SrTiO3 indicate that, the strain gradient elastic effect and the micro-inertia effect have competing influences on the wave velocity, and the ratio of the corresponding two internal length scales is essential to the dispersion curve. However, these effects are remarkable only when the wave number is relatively large. In addition, the static bulk flexoelectric effect is found to reduce the Rayleigh wave velocity especially when the static bulk flexocoupling coefficient is large. Furthermore, influences of the dynamic bulk flexoelectric effect and the polarization gradient effect on the Rayleigh wave propagation are also examined that they both hinge on the flexocoupling coefficient other than the related material constants.

A mathematical model of magnetomechanical compression-extension oscillations of a ferrimagnet having the shape of a right parallelepiped in a polarizing magnetic field is constructed. The solution to the equation derived here makes it possible to determine the resonance frequencies of oscillations for various relations between the length and the cross section of the sample and for various values of the polarizing magnetic field. The results of computations for an yttrium ferrite-garnet sample are compared with the results of measurements. The experimental value of the elastic tensor component for yttrium ferrite-garnet is obtained.

SnSb x O2 (x = 0.003, 0.01, 0.02, 0.05 and 0.07) ceramics and SnSb0.05O2–BaTi0.8Fe0.2O3-δ composite ceramics were prepared by using wet-chemical synthesis methods. The phases and related electrical properties of the ceramics were investigated. The results show that all the prepared ceramics have the effect of negative temperature coefficient (NTC) of resistivity over a wide temperature range. The room-temperature resistivities (ρ 25) and material constants (B 25/85) of the SnSb x O2 NTC ceramics increase with the Sb concentration increases. The B 25/85 of the ceramics can be enhanced obviously when a certain content of BaTi0.8Fe0.2O3-δ was added in SnSb x O2. The analysis of impedance spectra reveals that both grain and grain boundary contribute to the NTC effect of the ceramics. The conduction mechanisms combining the electron-hopping model and band conduction are proposed for the NTC effect in the SnSb0.05O2–BaTi0.8Fe0.2O3-δ composite ceramics.

The propagation of SH waves is studied in two bonded semi-infinite material, one piezoelectric and the other piezomagnetic. Both materials are functionally gradient materials. The material properties of the two materials vary in two directions, one parallel to the interface and the other perpendicular to the interface. The dispersion relations are obtained in explicit forms for different forms of the non-homogeneities. The effects of gradient variation about material constants on the frequency of SH waves and on the wave numbers are shown graphically.

The electroelastic effect describes the shift in resonant frequency that a resonator experiences as a result of the application of a dc electrical field. We report on experimental measurements of the electroelastic effect observed in fourteen plano-plano configuration thickness-mode langasite (La3Ga5SiO14) resonators. The orientations of the fourteen samples provide a sufficient data set to extract all eight of the third-order piezoelectric constants of this material. The role of this type of measurement in determining third-order piezoelectric constants is discussed. We compare the experimentally observed behavior to that predicted when using the langasite material constants currently available in the literature.

The phenomenological theory of solid solution is used to calculate the material constants (elastic compliances, susceptibilities, piezoelectric moduli, pyroelectric constants) of Ba x Sr1 − x TiO3 solid solutions over the entire range of concentrations x at room temperature. The phenomenological potential constants and the numerical values of the material constants are given for specific concentrations.

An experimental research and numerical simulation of thermomechanical behavior of glassy polymers at large deformations are considered. The obtained constitutive equations are linearized for numerical implementation and applied to uniaxial compression case. A series of thermomechanical experiments for lightly-linked epoxy specimens has been conducted. Material constants for constitutive model are obtained. A satisfying accordance of numerical and experimental data is shown.

A constitutive model is developed for the elastic behavior of a thermo-responsive gel subjected to swelling in a water bath to which hydrostatic pressure is applied. Material constants are found by fitting experimental data on poly(N-isopropylacrylamide) gel under unconstrained swelling. Good agreement is demonstrated between the observations and results of simulation. The effects of temperature and pressure on equilibrium water uptake are studied numerically.

In this work we revisit the issue of obtaining true material constants for semisolid slurries. Therefore, we consider the circular Couette flow of Herschel-Bulkley fluids. We first show how true constants can be obtained using an iterative procedure from experimental data to theory and vice versa. The validity of the assumption that the rate-of-strain distributions across the gap share a common point is also investigated. It is demonstrated that this is true only for fully-yielded Bingham plastics. In other cases, e.g., for partially-yielded Bingham plastics or fully-yielded Herschel-Bulkley materials, the common point for the fully-yielded Bingham case provides a good approximation for determining the material constants only if the gap is sufficiently small. It can thus be used to simplify the iterative procedure in determining the material constants. © 2016 Trans Tech Publications, Switzerland. 256 153 172 Sponsors: Conference code: 184809

In a lattice spring model (LSM), the material is discretised into particles linked by springs. However, LSMs always adopt linear springs, which results in a stiff approximation of the corresponding elastic solution. In this work, a high order LSM is proposed to overcome this limitation by introducing additional degrees of freedoms (DOFs) to the particles. Based on the energy minimisation principle and the local strain technique, equations for the stiffness matrices of high order LSM are derived. Relationships between micro spring parameters and macro material constants are derived from the Cauchy-born rules and the hyperelastic theory. Numerical examples show that the high order LSM can provide a better solution than that of the linear LSM and that the LSM is more suitable for modelling singularity and fracture problems.

This report gives a discussion of a new wave characteristic as a material parameter for a composite with the magnetoelectric effect. The new parameter depends on the material constants of a piezoelectromagnetic composite. It can be implemented on: (A) mechanically free, electrically and magnetically open surface and (B) mechanically free, electrically and magnetically closed surface. These theoretical investigations are useful for researchers in the fields of acousto-optics, photonics and opto-acousto-electronics. Some sample calculations are carried out for BaTiO3–CoFe2O4 and PZT-5H–Terfenol-D composites of class 6 mm. Also, the first and second derivatives of the new parameter with respect to the electromagnetic constant α are graphically shown.

In this study, a free bulge test simulation was performed with conditions corresponding to experiments for a cobalt-alloy tube hydroforming. A 3D strain measurement scheme was introduced to obtain strain data after free bulge tests, and the measured strain values were used in the evaluation of ductile fracture criteria. Cockcroft ductile fracture criterion, Oyane ductile fracture criterion and the modified Cockcroft criterion were adopted for establishing the material constants by simple tensile test and notched tensile test. Experimental data from free bulge tests were used for fracture prediction with these criteria. The results revealed that for the purpose of tube hydrofoming, the modified Cockcroft criterion with strain paths is more accurate than either the Cockcroft ductile fracture criterion or the Oyane ductile fracture criterion. [doi:10.2320/matertrans.MF201119]

The paper presents a ratchetting model, based on the non-linear kinematic-isotropic hardening law of Leimatre and Chaboche, able to predict the shear strain accumulation during rolling contact loading and including wear as a competitive phenomenon. A procedure was proposed to calibrate the model with the material constants suitable for rolling contact problems, obtaining them from bi-disk contact tests. For this aim and to study the damage evolution at the wheel–rail interface, some twin disk rolling contact tests were carried out on a common wheel–rail material couple under a dry rolling–sliding condition typical of normal service. The tests were stopped at progressive cycles numbers for different couples of specimens, which were then cut and observed with optical and electron microscope in order to analyse the damage evolution in the zone near to the contact interface. A wear-rolling contact fatigue competition was observed with a progressive crack tip advance following a shear band cracking mechanism and crack tail removal due to wear. The numerical model allowed predicting the experimental strain profile along the depth as a function of contact cycles number, also demonstrating through the critical strain approach that in the analysed conditions wear was able to prevent deep crack formation.

International audience; The characteristic dimensions of the hot, liquid zone behind a moving shear-band front in a metallic glass are analyzed. In addition to the expected dependence on material constants, the thickness of the zone is proportional to the shear offset, while its width is proportional to the square of the offset. Considering the bending of a plate, the size and shape of the hot zone are found to be strongly dependent on plate thickness. For shear offsets << 1 mu m, typical of plate thickness << 100 mu m, local temperature rises are insignificant. For larger dimensions, local temperature rises give a liquid zone centered on the shear plane with width comparable to the sample dimensions. The scaling of characteristic lengths and times with plate thickness facilitates the interpretation of the transitions observed in mechanical behavior, and the variation in behavior from glass to glass. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved