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For a relatively new class of linearization of implicit constitutive relations, wherein the linearized strain tensor is assumed to be a function of the Cauchy stress tensor, we write the balance of linear momentum and the time differentiated constitutive relation as a first order system, and we examine conditions for the hyperbolicity of such a system; this procedure is carried out for one and three dimensions. For the one dimensional case we use the characteristic polynomial and find conditions so that our system is hyperbolic. For three dimensions we find conditions so that our system can be put in a symmetric hyperbolic form. • We write the equations as a first order system. • For the one dimensional case we use the characteristic polynomial and find conditions so that our system is hyperbolic. • For three dimensions we find conditions so that our system can be put in a symmetric hyperbolic form. [ABSTRACT FROM AUTHOR]

In this communication a generalized strain approach is proposed to model constitutive equations for nonlinear residually stressed magneto-electric coupled viscoelastic solids with short term memory. This approach is a change with respect to the work that has been done, in the last decades, on the mechanics of nonlinear solids. The generalized strain model uses spectral invariants, where they have a clear physical meaning and hence are attractive for use in experiments. A specific form for a constitutive equation containing single-variable functions is presented, which are easy to deal with, if compared to multivariable functions. The effects of viscosity, residual stress and magneto-electric fields are studied via the results of boundary value problems, and some of these results are compared with experimental data. • A generalized strain approach is proposed to obtain constitutive equations. • A nonlinear residually stressed magneto-electric coupled viscoelastic solid is built. • The generalized strain model uses spectral invariants, all with physical meaning. • The effects of viscosity, residual stress and magneto-electric fields are studied. [ABSTRACT FROM AUTHOR]

In this prospective, randomised, blinded clinical study, we compared the sedative, antinociceptive and cardiorespiratory effects of intranasal (IN) dexmedetomidine at 5 μg/kg (diluted with 0.03 mL/kg NaCl 0.9%, DEX) with or without methadone (0.3 mg/kg; DEXMET), through a mucosal atomization device to one nostril in twenty healthy client-owned dogs. At 5-min intervals over 45 min, sedation score, onset, cardiopulmonary variables, mechanical nociceptive thresholds (MNTs) were assessed, also ease of administration, adverse effects, and response to IV catheterization. Statistical analysis employed t-test, the Mann-Whitney U, repeated measures ANOVA and Chi-square tests as appropriate (P < 0.05). Higher sedation ocurred in DEXMET (7 [5–10]) compared to DEX (5 [2–7]) from 15 to 30 min (P < 0.01, median [interquartile range]). Heart rate was lower in DEXMET (P < 0.01; 65% reduction vs. 41% in DEX, P = 0.001). The MNTs were higher in DEXMET than DEX from 15 to 45 min (P < 0.01), peaking at T30 (17.1 ± 3.8, DEXMET and 8.5 ± 5.4 N, DEX). No differences were observed in mean arterial blood pressure and respiratory rate. Intranasal administration was considered easy for 8 dogs per group. Reverse sneezing (8 dogs; P < 0.001), sialorrhea and retching (4 and 2 dogs, respectively) occurred in DEXMET. Response to catheterisation was lower in DEXMET than DEX (P = 0.039; 2 and 7 dogs, respectively). In conclusion, intranasal methadone (0.3 mg/kg) increased the sedative and antinociceptive effects produced by dexmedetomidine (5 μg/kg) in healthy dogs and resulted in lower heart rate. • Methadone potentiated sedative effect of intranasal (IN) dexmedetomidine. • Methadone IN produced greater antinociceptive effects than dexmedetomidine alone. • Lower heart rate was observed when both drugs were administered IN. [ABSTRACT FROM AUTHOR]

In this paper we study the response of bodies that are residually stressed within the context of a new class of constitutive relations, wherein the strains are assumed to be functions of the stresses. Such bodies are said to have residual stresses if there are stresses within the bodies even though the bodies are unstrained in the configuration of interest in the absence of external traction. Problems within the context of the norm of the gradient of the displacement field being small are considered, with regard to the determination of the residual stresses in an anisotropic cylindrical annulus with two preferred directions, and the nature of residual stresses within an anisotropic slab. The residual stresses in a body that is subject to incremental stresses are also studied. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the effects on mean arterial pressure (MAP) and ventilation of propofol total IV anaesthesia (TIVA) and isoflurane as anaesthetic maintenance in healthy dogs undergoing orthopaedic surgery, with epidural anaesthesia. Dogs were premedicated IM with dexmedetomidine (4 μg/kg) and methadone (0.3 mg/kg), induced with IV propofol (0.65–5 mg/kg) and randomly assigned to be maintained with isoflurane (group I) or propofol (group P). Isoflurane end-tidal concentration (EtISO) and propofol infusion rate were adjusted during the surgery to maintain a suitable anaesthetic depth. All dogs received bupivacaine (1 mg/kg) and morphine (0.1 mg/kg) in the lumbosacral epidural space (total volume 0.2 mL/kg). MAP was recorded every 5 min during the procedure. Statistical analysis was performed using parametric (Student’s t test) and nonparametric (Mann–Whitney U -test, chi-square) tests, as appropriate. Anaesthetic maintenance in groups I and P was accomplished by providing a mean EtISO of 1.12 ± 0.15% and a mean propofol infusion rate of 15.0 ± 4.7 mg/kg/h, respectively. MAP was significantly higher in group P than in group I (92 ± 17 mmHg versus 78 ± 10 mmHg; P = 0.021). Eleven dogs in group P and two dogs in group I reached an EtCO 2 > 7.3 kPa, requiring mechanical ventilation ( P = 0.001). In combination with epidural anaesthesia, propofol TIVA improved MAP and is a suitable alternative to isoflurane in orthopaedic surgery of the hind limb in healthy dogs. Nevertheless, since it was associated with increased respiratory depression, mechanical ventilation should be available. [ABSTRACT FROM AUTHOR]

In this paper we are interested in developing constitutive equations for fiber-reinforced nonlinearly viscoelastic solids. It has been shown that constitutive equations for such bodies can be expressed in terms of a complete minimal set of 18 classical invariants associated with deformation and fiber orientation. In this paper, we give an alternative formulation using a set of spectral invariants. It is shown via the use of spectral invariants that only 11 of the 18 classical invariants are independent. We analyze the spectral invariants for two illustrative deformation gradients: (i) simple tension, and (ii) simple shear. [ABSTRACT FROM AUTHOR]

In this paper we generalize the recent implicit models that have been put into place to describe the elastic response of bodies when thermal effects come into play. The implicit constitutive relations for thermoelastic response presented here provide a very natural way to overcome a serious problem associated with the celebrated model due to Fourier, namely infinite speed of the propagation of temperature. We also study some boundary value problems within the context of the implicit equations that we have developed. We carry out a linearization based on the classical assumption that the displacement gradient is small and obtain constitutive relations that allow the linearized strain to be a non-linear function of the stress and temperature. [ABSTRACT FROM AUTHOR]

Although carbon nanotubes/aluminum (CNT/Al) composites are promising materials in the production of structural components, their mechanical behavior under overaging conditions has not been considered. In this paper the effect of CNTs on the microstructural and mechanical behavior of a 2024 aluminum alloy (Al2024) synthesized by mechanical alloying (MA) and powder metallurgy routes is discussed, as well as the effect of aging heat treatments at different temperatures and aging times. The mechanical behavior of composites was screened by hardness measurements as function of aging time. After 96 h of aging time, composites showed mechanical stability in their hardness performance. Images from transmission electron microscopy showed that the mechanical stability of composites was due to a homogeneous dispersion of CNTs in the aluminum matrix and a subsequent alteration in the kinetics of precipitation is due to their presence in the aluminum matrix. Even though strengthening precipitation took place during aging, this was not the main strengthening mechanism observed in composites. [ABSTRACT FROM AUTHOR]

New sets of spectral invariants are proposed to study the behaviour of electro-elastic bodies composed of a matrix filled with one or two (in general non-orthogonal) families of ‘fibres’, where both the matrix and the fibres can react to the presence of electric fields. [ABSTRACT FROM AUTHOR]

The objectives of this study were to determine: (1) the sedative effects of dexmedetomidine in combination with methadone, midazolam, or both, and (2) the propofol dose required to achieve endotracheal intubation in healthy dogs. Seven healthy Beagle dogs were included in a prospective experimental, crossover, randomised and masked design. All dogs received four treatments IM, with at least 1 week between sessions, as follows: dexmedetomidine 5 µg/kg (D) alone, or combined with methadone 0.3 mg/kg (DMe), midazolam 0.3 mg/kg (DMi), or both (DMeMi). The degree of sedation was evaluated using a numerical scale (maximum 15 points). The dose of propofol required for intubation was also calculated for each group. Recovery time and quality were determined. Statistical analysis was performed using parametric (ANOVA) and nonparametric tests (Friedman, Cochran Q), as appropriate. The degree of sedation obtained with DMe and DMeMi (13, [7–14]; 13, [6–14], respectively) was significantly higher than in the control group (2, [1–4]; P  = 0.023, P  = 0.006, respectively). The required dose of propofol was lower in all groups (DMi, 1.5 ± 0.5 mg/kg, P  = 0.002; DMe, 1.2 ± 0.5 mg/kg, P  <   0.001; DMeMi, 0.9 ± 0.3 mg/kg) than in the control group (2.9 ± 0.9 mg/kg; P  <   0.001). Recovery quality was not different between groups ( P  = 0.137). In healthy dogs, the addition of midazolam did not enhance the sedative effects of dexmedetomidine or a dexmedetomidine–methadone combination at the doses studied, and propofol requirements were reduced. The sedative effect of dexmedetomidine was enhanced with methadone, and the required dose of propofol was reduced. [ABSTRACT FROM AUTHOR]

In this work a new set of principal axis invariants is proposed in order to study the problem of considering large magneto-elastic deformations, for bodies that are isotropic in the un-deformed configuration when no external magnetic induction is applied. The new set of invariants has clear physical meanings and may have an experimental advantage over the standard invariants used in many previous works in this area. The principal axis invariant formulation is also shown to be more general. Some simple boundary value problems are solved, such as the simple shear, and the biaxial extension of a slab, where with the use of these new invariants, it is possible to study in a much simpler manner the effect of different types of deformations on the response of the material. An illustrated simple specific constitutive equation is proposed which compares well with experiment. [ABSTRACT FROM AUTHOR]

Abstract: Recently, a very general and novel class of implicit bodies has been developed to describe the elastic response of solids. It contains as a special subclass the classical Cauchy and Green elastic bodies. Within the class of such bodies, one can obtain through a rigorous approximation, constitutive relations for the linearized strain as a nonlinear function of the stress. Such an approximation is not possible within classical theories of Cauchy and Green elasticity, where the process of linearization will only lead to the classical linearized elastic body. In this paper, we study numerically the states of stress and strain in a finite rectangular plate with an elliptic hole and a stepped flat tension bar with shoulder fillets, within the context of the new class of models for elastic bodies that guarantees that the linearized strain would stay bounded and limited below a value that can be fixed a priori, thereby guaranteeing the validity of the use of the model. This is in contrast to the classical linearized elastic model, wherein the strains can become large enough in the body leading to an obvious inconsistency. [Copyright &y& Elsevier]

Abstract: Incremental equilibrium equations and corresponding boundary conditions for an isotropic, hyperelastic and incompressible material are summarized and then specialized to a form suitable for the analysis of a spherical shell subject to an internal or an external pressure. A thick-walled spherical shell during inflation is analyzed using four different material models. Specifically, one and two terms in the Ogden energy formulation, the Gent model and an formulation recently proposed by Lopez-Pamies. We investigate the existence of local pressure maxima and minima and the dependence of the corresponding stretches on the material model and on shell thickness. These results are then used to investigate axisymmetric bifurcations of the inflated shell. The analysis is extended to determine the behavior of a thick-walled spherical shell subject to an external pressure. We find that the results of the two terms Ogden formulation, the Gent and the Lopez-Pamies models are very similar, for the one term Ogden material we identify additional critical stretches, which have not been reported in the literature before. [Copyright &y& Elsevier]

Abstract: Carbon nanotube/2024 aluminum alloy (CNT/Al2024) composites were fabricated with a combination of mechanical alloying (MA) and powder metallurgy routes. Composites were microstructurally and mechanically evaluated at sintering condition. A homogeneous dispersion of CNTs in the Al matrix was observed by a field emission scanning electron microscopy. High-resolution transmission electron microscopy confirmed not only the presence of well dispersed CNTs but also needle-like shape aluminum carbide (Al4C3) crystals in the Al matrix. The formation of Al4C3 was suggested as the interaction between the outer shells of CNTs and the Al matrix during MA process in which crystallization took place after the sintering process. The mechanical behavior of composites was evaluated by Vickers microhardness measurements indicating a significant improvement in hardness as function of the CNT content. This improvement was associated to a homogeneous dispersion of CNTs and the presence of Al4C3 in the aluminum alloy matrix. [Copyright &y& Elsevier]

Abstract: A variational formulation for an electro-elastic body surrounded by free space in the context of large and nonlinear elastic deformations is developed. The functional depends on the deformation function and the electric scalar potential. The approach presented here introduces an alternative expression for the energy stored by the exterior free space, which is intended to facilitate the (in general troublesome) calculations of the first and the second variations of the functional. [Copyright &y& Elsevier]

Abstract: The wear behavior of the 2024 aluminum alloy and its composites was evaluated through a pin-on-disk system. For this purpose the aluminum alloy was reinforced by carbon nanotubes dispersion produced by milling process. The nanotubes dispersion was carried out using a high energy mill for a fixed milling time. Milled powders were cold consolidated, sintered and then microstructurally and mechanically evaluated. The wear behavior of the alloy and its composites was evaluated considering the different nanotube contents under several abrasive conditions. The composites with higher nanotube concentration (5.0wt%) displayed an improved wear resistance in all cases evaluated in this work. [Copyright &y& Elsevier]

Abstract: A constitutive framework for electro-sensitive materials in the context of non-linear elasticity is analyzed. Constitutive equations are given in terms of energy functions that depend on several invariants. The study includes both the analysis of the invariants, which are present in the energy functions, and the analysis of constitutive restrictions that have to be obeyed by the constitutive functions. Isotropic as well as non-isotropic electro-sensitive elastomers are studied. The set of invariants that describe each material model is analyzed under two homogeneous deformations: (i) an uniaxial elongation and (ii) a simple shear deformation. These deformations are chosen since they are relevant to specific experiments, from which one may try to fit constitutive equations. The constitutive restrictions developed are based on classical ones used for isotropic non-linear elastic materials, in particular, are based on the Baker–Ericksen inequality and the ellipticity condition. [Copyright &y& Elsevier]

Abstract: In the present work, the 2024 aluminum alloy (Al2024) alloy has been produced by mechanical alloying (MA). The alloy was then strengthened by dispersion of carbon nanotubes (CNTs) during different times. Thus, the effect of CNTs concentration and milling time on the microstructure of the Al2024-CNTs composites was studied. The results show a homogeneous dispersion of CNTs into the Al-matrix phase by mechanical milling (MM). It was observed that the increment in the milling time, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MA. The finest particle size was obtained at 20h of milling. These observations were confirmed by scanning and transmission electron microscopy. After 10h of milling, Cu, Mg and other alloying elements constituting the Al2024 alloy, form a solid solution and only some remnant Mn particles were observed but not detected by X-ray diffraction. [Copyright &y& Elsevier]

Abstract: This paper provides examples of the numerical solution of boundary-value problems in nonlinear magnetoelasticity involving finite geometry based on the theoretical framework developed by Dorfmann and co-workers. Specifically, using a prototype constitutive model for isotropic magnetoelasticity, we consider two two-dimensional problems for a block with rectangular cross-section and of infinite extent in the third direction. In the first problem the deformation induced in the block by the application of a uniform magnetic field far from the block and normal to its larger faces without mechanical load is examined, while in the second problem the same magnetic field is applied in conjunction with a shearing deformation produced by in-plane shear stresses on its larger faces. For each problem the distribution of the magnetic field throughout the block and the surrounding space is illustrated graphically, along with the corresponding deformation of the block. The rapidly (in space) changing magnitude of the magnetic field in the neighbourhood of the faces of the block is highlighted. [Copyright &y& Elsevier]

Abstract: Some simple boundary value problems are studied, for a new class of elastic materials, wherein deformations are expressed as non-linear functions of the stresses. Problems involving ‘homogeneous’ stress distributions and one-dimensional stress distributions are considered. For such problems, deformations are calculated corresponding to the assumed stress distributions. In some of the situations, it is found that non-unique solutions are possible. Interestingly, non-monotonic response of the deformation is possible corresponding to monotonic increase in loading. For a subclass of models, the strain–stress relationship leads to a pronounced strain-gradient concentration domain in the body in that the strains increase tremendously with the stress for small range of the stress (or put differently, the gradient of the strain with respect to the stress is very large in a narrow domain), and they remain practically constant as the stress increases further. Most importantly, we find that for a large subclass of the models considered, the strain remains bounded as the stresses become arbitrarily large, an impossibility in the case of the classical linearized elastic model. This last result has relevance to important problems in which singularities in stresses develop, such as fracture mechanics and other problems involving the application of concentrated loads. [ABSTRACT FROM AUTHOR]

Abstract: We present a variational formulation for an electro-elastic body in contact with two semi-infinite rigid bodies, which are electric conductors and have a distribution of free charge. These three bodies are surrounded by free space, where far away we have a given electric displacement and an electric potential on disjoint surfaces. [Copyright &y& Elsevier]

Abstract: From electrochemical methods, polarization resistance and electrochemical impedance spectroscopy, the corrosion susceptibility of pipeline steel samples immersed in 1M H2SO4 was determined using nil and different concentrations of the molecule 2-mercaptoimidazole (2MI). It was found that a corrosion inhibiting efficiency, IE, value of 98.5% was reached when the 2MI concentration in the system increased to 25ppm. Moreover, at this concentration, the 2MI IE was measured as a function of time finding that the IE kinetics follows the relationship: %IE=98.5−0.03t after 800h of evaluation. During the first 200h 2MI IE was higher that 90% then, it decreased to 70% and it remained constant up to 1200h. It is shown that this compound can affect both the anodic and cathodic processes, thus it can be classified as a mixed-type inhibitor however, from variation of both corrosion potential and polarization resistance with [2MI] it was possible to state that the anodic reaction rate, of the corrosion process, decreases at a greater proportion than the cathodic one. 2MI follows an adsorption mechanism, which can be adequately described by the Langmuir isotherm with an adsorption standard free energy difference (ΔG°ads) of −26.8kJmol−1. In order to analyze the influence of substituting groups, both electron-donating and electron-attracting and the number of π-electrons on the corrosion inhibiting properties of organic molecules, an electrochemical study was carried out on four different molecules having similar chemical framework structure: 2-mercaptoimidazole (2MI), 2-mercaptobenzoimidazole (2MBI) 2-mercapto-5-methylbenzimidazole (2M5MBI) and 2-mercapto-5-nitrobenzimidazole (2M5NBI). It was found that the IE order followed by the molecules tested was 2MI>2MBI>2M5MBI>2M5NBI. Thus 2MI turned out to be the best inhibitor, even superior to the 2MBI. This fact strongly suggests that, contrary to a hitherto generally suggested notion, an efficient corrosion inhibiting molecule does not require to be a large one, also bearing an extensive number of π-electrons. [Copyright &y& Elsevier]

A new constitutive equation is proposed for rubber, based on expressing the Cauchy stress as a function of the Hencky strain tensor. The model is used for isotropic bodies considering the classical invariants of Rivlin and Spencer. The predictions for the extension and compression of a cylinder, and the inflation of a hollow sphere, are compared with the predictions of the constitutive equation for rubber by Ogden. • A new model is presented for rubber. • A comparison with the Ogden's model is provided. • The behaviour of a hollow sphere is studied. obtained. [ABSTRACT FROM AUTHOR]

Abstract: Novel Al-based nanocomposites reinforced with multi-walled carbon nanotubes were produced by mechanical milling followed by pressure-less sintering at 823K under vacuum. The interface between Al matrix and the multi-walled carbon nanotubes was examined using transmission electron microscopy. These observation showed that the multi-walled carbon nanotubes were not damaged during the preparation of the nanocomposite and that no reaction products were detected after sintering. The mechanical properties of sintered nanocomposites specimens were evaluated by a compression test. The yield stress (σ y) and the maximum strength (σ max) obtained were considerably higher than those reported in the literature for pure Al prepared by the same route. The values for σ y and σ max increase as the volume fraction of multi-walled carbon nanotubes increases. The milling time and the concentration of multi-walled carbon nanotubes have an important effect on the mechanical properties of the nanocomposite. [Copyright &y& Elsevier]

A constitutive relation was developed in Part I for describing the response of a class of visco-elastic bodies, wherein the left Cauchy–Green tensor, the symmetric part of the velocity gradient, and the Cauchy stress tensor are related through an implicit constitutive relation. Here, we study a boundary value problem within the context of the model namely the inhomogeneous deformation of the body, corresponding to the response of an infinitely long slab due to the influence of gravity. • A constitutive model that depends on the stresses is presented. • The behaviour of a slab when varying different material is studied. • An exact solution is found for the boundary value problem under special conditions. [ABSTRACT FROM AUTHOR]

A constitutive relation is proposed for viscoelastic bodies that is a generalization of the classic Kelvin–Voigt model, wherein the left Cauchy–Green tensor, the symmetric part of the velocity gradient, and the Cauchy stress tensor are implicitly related. The model developed includes several models that are being used in the literature to describe the elastic and viscoelastic response of bodies. In this paper, we study special homogeneous deformations of a slab within the context of the implicit viscoelastic model. • An implicit constitutive model is presented for viscoelastic media, where the stresses can have influence in the behaviour of the body. • A boundary value problem is solved in detail using the constitutive model, studying the behaviour of a slab when varying different material constants. • Some exact solutions are found for the boundary value problem for some especial cases for the material constants. [ABSTRACT FROM AUTHOR]

A nonlinear spectral formulation, which is more general than the traditional classical-invariant formulation, is used to describe the mechanical behaviour of a residually stressed electro-elastic body with two preferred directions (ESTPD); the generality of the spectral formulation could facilitate the quest for good constitutive equations for ESTPDs. The strain energy is a function of spectral invariants (each with a clear physical meaning) that depend on the right stretch tensor, the residual stress tensor, two preferred-direction-structural tensors and one of the electric variables; clear meaningful physical invariants are useful in aiding the design of a rigorous experiment to construct a specific form of constitutive equation. Separable finite strain constitutive equations containing general single-variable functions, which depend only on a principal stretch or the electric field, are proposed and, in view of this, the corresponding infinitesimal strain energy functions can be easily constructed. A specific form for the strain energy function is generally easier to obtain from the general strain energy function via experiment if it is expressed in terms of general single-variable functions. The proposed constitutive equations can be easily converted to allow the mechanical influence of compressed fibres to be excluded or partially excluded and to model fibre dispersion in collagenous soft tissues. With the aid of spectral invariants, we easily prove that at most 15 of the 98 classical invariants in the corresponding minimal integrity basis are independent; this proof cannot be found in the literature. A simple tension boundary value problem with cylindrical symmetry is studied, where the residual stress is assumed to depend only on the radial position. [ABSTRACT FROM AUTHOR]

Graphene can be considered as an ideal reinforcement for the production of composites due to its outstanding mechanical properties. These characteristics offer an increased opportunity for their study in the production of metal matrix composites (MMCs). In this research, the studied composites were produced by mechanical alloying (MA). The employed milling times were of 1, 3 and 5 h. GNPs were added in 0.25, 0.50 and 1.0 wt% into an aluminum powder matrix. Milled powders were cold consolidated and subsequently sintered. Composites were microstructurally characterized with Raman spectroscopy and electron microscopy and X-ray diffraction. The hardness behavior in composites was evaluated with a Vickers micro-hardness test. A homogeneous dispersion of graphene during MA and the proper selection of sintering conditions were considered to produce optimized composites. The obtained results with electron microscopy indicate a homogeneous dispersion of GNPs into the aluminum matrix. Analyses showed GNPs edges where the structure of the graphene layers conserved after MA is observed. [ABSTRACT FROM AUTHOR]