Abstract
Mechanical properties of hydrogels are of considerable interest for applications including tissue engineering and drug delivery. However, mechanical characterization of hydrogels is ...inherently challenging due to their multiphasic construction. Under mechanical loading, internal fluid redistribution affects the gel response, leading to a time- and length-scale-dependent material behavior, known as poroelasticity. Traditional mechanical tests are effective for determining instantaneous flow-independent gel response, and they are limited in characterizing poroelastic behavior as a function of loading time- and length-scales. Here, micro- and nanoindentation experiments are combined to characterize the full range of poroelastic behavior of a hydrogel. A master curve is presented to demonstrate that the relative competition of poroelastic relaxation time with ramp loading time determines gel response across different time- and length-scales. The master curve provides a novel mechanism to establish the instantaneous and equilibrium limits on the elastic modulus for a material, useful for designing hydrogel biomaterials.
First-principles calculations were performed to study the structural, elastic, electronic properties and Debye temperature of D022-Ni3V under pressure. The obtained structural parameters are in ...accord with previous data. The calculated elastic constants manifest that Ni3V binary compound is mechanically stable. Using the Voigt–Reuss–Hill method, elastic properties such as bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio υ are calculated. And results indicate that pressure can improve the hardness of Ni3V compound. Moreover, the density of states as a function of pressure is analyzed, and Population analysis explain the improvement of hardness by pressure from the view of chemical bonds. The Debye temperature ΘD calculated from elastic constants goes up with the increasing pressure.
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•Structural, elastic, electronic properties and Debye temperature under various pressures.•Higher hardness of Ni3V compound may be obtained when pressure increases.•The electronic properties under pressure reveal the reason for improvement of hardness.•Debye temperatures increase with increasing pressure.
Cerium-doped glasses usually contain a mixture of Ce3+ and Ce4+ species, with the trivalent state being dominant. Quantitative determination of the redox ratio is complicated by the narrow energy gap ...between both states, leading to spectral overlap in optical absorption studies, and strong beam sensitivity in other techniques. However, it also indicates a way to induce electric conduction through electron hopping, with the additional benefit of visual transparency. Here, cerium phosphate glasses are reported in which the local optical basicity is varied through substitution of cerium by highly polarizable rubidium ions. This is done in order to control the Ce3+/ Ce4+ ratio. Electrical impedance spectroscopy is considered as an alternative means to assess the redox ratio by exploring the extent of polaron conduction. Complementary Raman and 31P MAS NMR spectroscopic studies provide structural insight on the process of mixed electronic and ionic charge transport. Meanwhile, a monotonic decrease in the elastic modulus and an abnormal change in Poisson's ratio when varying the composition corroborate structural interpretations.
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•Heterogeneous honeycombs with bio-inspired line defects are designed and analyzed.•Structure with octagon-pentagon defects own 12.7% higher Young’s modulus than the benchmark.•The ...structure with pentagon-trigon defects exhibit about 56.5% higher SEA than the benchmark.•Composite-lattice honeycombs own non-uniform collapse bands under compression.
Taking inspiration from geometric defects in hexagonal lattices existing in nature (beehive and graphene), this work explains how defects in the form of channels can improve the effective Young’s modulus and specific energy absorption properties of hybrid-lattice hexagonal honeycombs under compression due to non-uniform collapse band behavior and strain delocalization. The results reveal that in terms of effective Young’s modulus, honeycombs with octagon-pentagon and pentagon-trigon defected cells outperform the benchmark structure by roughly 13% and 20%, respectively. In terms of specific energy absorption (SEA), all composite-lattice honeycombs show superior behavior to the benchmark honeycomb, especially the pentagon-trigon defective honeycomb with about 56.5% higher SEA. The novel structures show promising design prospects for applications in various industries, especially automotive and construction with cost-effective advantage in customized or low-volume production cases.
The effects of state of charge (SOC) on the elastic properties of 3D structural battery composites are studied. An analytical model based on micromechanical models is developed to estimate the ...effective elastic properties of 3D structural battery composite laminae at different SOC. A parametric study is performed to evaluate how different design parameters such as volume fraction of active materials, stiffness of constituents, type of positive electrode material, etc. affect the moduli of the composite lamina for extremes in SOC. Critical parameters and configurations resulting in large variations in elastic properties due to change in SOC are identified. As the extreme cases are of primary interest in structural design, the effective elastic properties are only estimated for the electrochemical states corresponding to discharged (SOC = 0) and fully charged (SOC = 1) battery. The change in SOC is simulated by varying the volume and elastic properties of the constituents based on data from literature. Parametric finite element (FE) models for square and hexagonal fibre packing arrangements are also analysed in the commercial FE software COMSOL and used to validate the analytical model. The present study shows that the transverse elastic properties E2 and G23 and the in-plane shear modulus G12 are strongly affected by the SOC while the longitudinal stiffness E1 is not. Fibre volume fraction and the properties of the coating (such as stiffness and Poisson's ratio) are identified as critical parameters that have significant impact on the effect of SOC on the effective elastic properties of the composite lamina. For configurations with fibre volume fraction Vf ≥ 0.4 and Young's modulus of the coating of 1 GPa or higher, the transverse properties E2 and G23 change more than 30% between extremes in SOC. Furthermore, for configurations with high volume fractions of electrode materials and coating properties approaching those of rubber the predicted change in transverse stiffness E2 is as high as +43%. This shows that it is crucial to take effects of SOC on the elastic properties into account when designing 3D structural battery composite components.
Transition-metal (TM) carbides are an important class of hard, protective coating materials; however, their brittleness often limits potential applications. We use density functional theory to ...investigate the possibility of improving ductility by forming pseudobinary cubic M1M2C alloys, for which M1 = Ti or V and M2 = W or Mo. The alloying elements are chosen based on previous results showing improved ductility of the corresponding pseudobinary nitride alloys with respect to their parent compounds. While commonly-used empirical criteria do not indicate enhanced ductility in the carbide alloys, calculated stress/strain curves along known slip systems, supported by electronic structure analyses, indicate ductile behavior for VMoC. As VMoC layers are sheared along the 11¯0 direction on {111} planes, the stress initially increases linearly up to a yield point where the accumulated stress is partially dissipated. With further increase in strain, the stress increases again until fracture occurs. A similar mechanical behavior is observed for the corresponding TM nitride VMoN, known to be a ductile ceramic material 1. Thus, our results show that VMoC is a TM carbide alloy which may be both hard and ductile, i.e. tough.
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The evolution of Young’s modulus and damping is investigated for Czech kaolins in situ via the impulse excitation technique (IET) from room temperature to 1250 and 1400 °C. During heating the ...processes of drying, dehydroxylation, spinel formation, mullitization, silica release and glass melting are clearly discernible. During cooling Young’s modulus increases, exhibiting a flat maximum around 800 °C and a steep decrease below 200 °C when the cristobalite content is high. Differential IET curves are introduced as a new representation of IET results, and damping curves are shown to provide additional information. The phase composition is determined via XRD, including the glass phase. Based on the densities, Young’s moduli and volume fractions of the individual phases, the densities and Young’s moduli of the kaolin-based ceramics are calculated and compared to theoretical predictions, showing that Young’s modulus is nicely predicted by a benchmark relation for partially sintered ceramics with concave pores.
Ceramics from the magnesia-alumina-silica (MAS) system are common products of the ceramic industry. The phase composition of these systems can be rather complex, especially when feldspar is added as ...a flux, and thus attempts to correlate the composition and structure of these ceramics to their properties are quite rare, especially when considerable amounts of glass phase and sapphirine appear after firing. In this paper an attempt is made to correlate, for a talc-kaolin-alumina-feldspar mixture resulting in cordierite-sapphirine ceramics after firing to 1250 °C, the resulting elastic properties (Young’s modulus), as determined via the impulse excitation technique (IET), with the phase composition, determined via X-ray diffraction (XRD). Moreover, it is shown how the evolution of the phase composition and microstructure is reflected in the temperature dependence of Young’s modulus and damping during heating-cooling cycles with maximum temperatures ranging from 1000 to 1250 °C.
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