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Introduction: Typical practitioners choose from among only two to three products when selecting liners for their patients. A lack of comparable objective information about similarities and differences among elastomeric liner products may be part of the reason. Methods: Commonly used, commercially available polyurethane, silicone, and thermoplastic elastomer (TPE) liners were tested for their compressive, shear, tensile, and volumetric elasticities as well as their coefficients of friction (CoFs) and thermal conductivities. Results: Polyurethane and silicone liners tended to be stiffer in compression and shear than TPE liners. Fabric backings contributed primarily to increased tensile elasticity (and thus reduced pistoning). Polyurethane liners demonstrated relatively low CoFs, whereas silicone and TPE liners had higher CoFs and wider ranges. All materials tested were essentially incompressible. Thermal conductivities of all materials were comparable and similar to that of leather. Conclusions: Polyurethane liners are softer and less sticky than 16 years ago, and TPE liners have higher tensile stiffness than previously. A stiff fabric backing can increase tensile stiffness by more than 200%. Compressive stiffness may be used to characterize a liner's ability to flow. Elastomeric liners move heat almost exclusively via conduction. [ABSTRACT FROM AUTHOR]

This study describes detailed investigation on dynamic swelling of cationic copolymeric hydrogels prepared by N , N -dimethylaminoethyl methacrylate (DMAEMA) and 2-Hydroxyethyl methacrylate (HEMA). The effect of pH on the copolymer structure and dynamic swelling kinetics of poly( N , N -dimethylaminoethyl methacrylate-co-2-Hydroxyethyl methacrylate) (P(DMAEMA-co-HEMA)) hydrogels was investigated under various experimental conditions. The pH as well as the temperature-dependent swelling results showed that the copolymeric hydrogels have strong desire to respond to the external temperature- and pH-stimuli. P(DMAEMA-co-HEMA) hydrogels exhibit excellent compositional and mechanical features as well as the unique tunable time-dependent swelling behavior. In methacrylate-based hydrogels, the hydrophilicity of monomers and the degree of crosslinking are not only the factors that determine the degree of swelling of resultant copolymeric hydrogels, the elastic property is a third factor that should be taken into account when discussing the swelling behavior. P(DMAEMA-co-HEMA) hydrogels possess tunable physico-chemical properties that can be adjusted by the changing the copolymer composition. [ABSTRACT FROM AUTHOR]

The use of carbon nanofibers (CNFs) in cement systems has received significant interest over the last decade due to their nanoscale reinforcing potential. However, despite many reports on the formation of localized CNF clusters, their effect on the cement paste micromechanical properties and relation to the mechanical response at the macroscopic scale are still not fully understood. In this study, grid nanoindentation coupled with scanning electron microscopy and energy dispersive spectroscopy was used to determine the local elastic indentation modulus and hardness of a portland cement paste containing 0.2% CNFs with sub-micro and microscale CNF clusters. The presence of low stiffness and porous assemblage of phases (modulus of 15–25 GPa) was identified in the cement paste with CNFs and was attributed primarily to the interfacial zone surrounding the CNF clusters. The CNFs favored the formation of higher modulus C–S–H phases (>30 GPa) in the bulk paste at the expense of the lower stiffness C–S–H. Nanoindentation results combined with a microscale–macroscale upscaling homogenization method further revealed an elastic modulus of the CNF clusters in the range from 18 to 21 GPa, indicating that the CNF clusters acted as compliant inclusions relative to the cement paste. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers a functionally graded cantilever beam with different modulus in tension and compression. The beam is subjected to bending loads, including pure bending, shear force at the free end and uniform pressure on the upper lateral, respectively. Its modulus values in tension and compression both change with the thickness coordinate as arbitrary functions, which could bring the beam a broader range of applications in engineering. The problem is treated as a plane stress case and described by Airy stress function. By using semi-inverse method, the elastic solutions for the beam are obtained, which can be easily degenerated into the ones for homogeneous beams. An example is finally presented to show the effect of nonhomogeneous materials with different modulus on the elastic field in a cantilever beam. [Copyright &y& Elsevier]

[Display omitted] The small atomic region containing a defect in a crystalline solid is nonlinear elastic. In this paper, we consider a solid containing defects as a composite wherein the defected regions have a bulk modulus, K , different from that of the perfect crystal. If the volume fraction of the defected regions is sufficiently small, a rule of mixtures should apply so that K of the composite depends linearly on the volume fraction of the defected region. We identify the slope of that linear dependence as the signature, denoted S. We further show that S is related to a property of the linear elastic fields of point defects described by elastic dipole tensors, P ij. To first order, the P ij of such defects depend linearly on external strain and the strength of that dependence is the diaelastic polarizability tensor, α. We show that S is simply related to α. Atomistic models of EAM Ni were used to compute K versus reciprocal volume for several kinds of defects, namely single, di-, and tri-vacancies and interstitials, dislocations, and grain boundaries. The results show 1) when the volume fraction of the defected region is small, a rule of mixtures applies, and 2) S has a distinct value for each defect and is negative for vacancies but positive for the other defects. Thus, S depends on the effective modulus of the nonlinear region and its size. The effective bulk modulus of a spherical ball-in-hole composite model derived in the Appendix predicts that the variation of K with volume fraction is very nearly linear. The magnitudes of S , although quite small, are discussed as a potential means of monitoring defect changes in their concentration via sensitive experimental measurements of the bulk modulus. [ABSTRACT FROM AUTHOR]

We propose a theory which describes the mechanical behaviour of magneto-sensitive elastomers (MSEs) under a uniform external magnetic field. We focus on the MSEs with isotropic spatial distribution of magnetic particles. A mechanical model is used in which magnetic particles are arranged on the sites of three regular lattices: simple cubic, body-centered cubic and hexagonal close-packed lattices. By this we extend our previous approach [Ivaneyko D. et al., Macromolecular Theory and Simulations, 2011, 20, 411] which used only a simple cubic lattice for describing the spatial distribution of the particles. The magneto-induced deformation and the Young's modulus of MSEs are calculated as functions of the strength of the external magnetic field. We show that the magneto-mechanical behaviour of MSEs is very sensitive to the spatial distribution of the magnetic particles. MSEs can demonstrate either uniaxial expansion or contraction along the magnetic field and the Young's modulus can be an increasing or decreasing function of the strength of the magnetic field depending on the spatial distribution of the magnetic particles. [ABSTRACT FROM AUTHOR]

Abstract: This paper compares the important mechanical properties and the electrical conductivities from room temperature to 800°C of four LaCoO3 based cobaltite compositions with 0, 20, 40 and 55% Ca2+ ions substituted on the A site of the perovskite structure respectively. Ca2+ doped lanthanum cobaltite materials are strong candidates for use as cathodes in lower temperature solid oxide fuel cells operating at or below 800°C. Among these four cobaltite compositions, two (LaCoO3 and La0.8Ca0.2CoO3) were found to be phase pure materials, whereas the remaining two compositions (La0.6Ca0.4CoO3 and La0.45Ca0.55CoO3) contained precipitation of secondary phases such as CaO and Co3O4. The mechanical properties of the four compositions, in terms of Young''s modulus, four-point bending strength and fracture toughness measurements, were measured at both room temperature and 800°C. At room temperature, doping with Ca2+ was found to substantially increase the mechanical properties of the cobaltites, whereas at 800°C the pure LaCoO3 composition exhibited higher modulus and strength values than La0.8Ca0.2CoO3. All of the four compositions exhibited ferroelastic behavior, as shown by the hysteresis loops generated during uniaxial load–unload compression tests. Electrical conductivity measurements showed the La0.8Ca0.2CoO3 composition to have the highest conductivity among the four compositions. [Copyright &y& Elsevier]

Abstract: There has been an increasing interest in understanding how the mechanical properties of the microenvironment influence stem cell fate. We describe studies of the proliferation and differentiation of neural stem cells (NSCs) encapsulated within three-dimensional scaffolds – alginate hydrogels – whose elastic moduli were varied over two orders of magnitude. The rate of proliferation of neural stem cells decreased with increase in the modulus of the hydrogels. Moreover, we observed the greatest enhancement in expression of the neuronal marker β-tubulin III within the softest hydrogels, which had an elastic modulus comparable to that of brain tissues. To our knowledge, this work represents the first demonstration of the influence of modulus on NSC differentiation in three-dimensional scaffolds. Three-dimensional scaffolds that control stem cell fate would be broadly useful for applications in regenerative medicine and tissue engineering. [Copyright &y& Elsevier]

The temporal development of the modulus of elasticity and its profile were studied in water-borne alkyd coatings during the drying process of the coating films. Values of the Young’s moduli of elasticity of free coating films were measured using tensile tests. Since the elastic modulus is related to cross-link density, the values of the moduli give information on the advancement of the drying process. A mathematical model was developed to predict the degree of effective cross-linking and the mechanical behaviour of the drying coating films with different thicknesses. This model is based on trends observed by confocal Raman microspectroscopy, which exhibit the profile of the consumption of double bonds and thus can be used to monitor the development of cross-link density as a function of depth from the film surface. The average values of the Young’s measured moduli were successfully described by the numerical model as a function of drying time. [Copyright &y& Elsevier]