Hexagonal Array Model Research Articles

Fabrication and Characterization of Quinoa Protein Nanoparticle-Stabilized Food-Grade Pickering Emulsions with Ultrasound Treatment: Interfacial Adsorption/Arrangement Properties.

The natural quinoa protein isolate (QPI) was largely reflected in the nanoparticle form at pH 7.0 (∼401 nm), and the ultrasound at 20 min progressively improved the contact angle (wettability) and surface hydrophobicity of the nanoparticles. Ultrasound process also modified the type of intraparticle interaction, and the internal forces of sonicated particles were largely maintained by both disulfide bonds and hydrophobic interaction forces. In emulsion system, the ultrasound progressively increased the emulsification efficiency of the QPI nanoparticles, particularly at high protein concentration ( c > 1%, w/ v) and higher emulsion stability against coalescence. As compared with the natural QPI-stabilized emulsions, the 20 min sonicated emulsions exhibited higher packing and adsorption at the protein interface. The microstructure of emulsions that occurs is bridging flocculation of droplets at low c (≤1%, w/ v), while the amount of protein particles could be high enough to cover the droplet surface at high c ( >1%, w/ v) with hexagonal array model arrangement. Thus these results illustrated that both natural and sonicated QPI nanoparticles could be performed as effective food-grade stabilizer for Pickering emulsion; however, the sonicated QPI nanoparticles exhibited much better emulsifying and interfacial properties.

Poroelastic properties of anisotropic cylindrical composite materials

The present work is devoted to the determination of the effective poroelastic properties of anisotropic materials, such as porous nanocomposites and microbiotissues. The poroelastic field of composite materials in a transversely isotropic medium is determined by using the general self-consistent method (GSCM), and the dependence of material properties of the composites on porosity is considered. A hexagonal transversely isotropic model is used and treatment processes are proposed for application to microstructures or macrostructures. Several numerical examples are presented to validate the proposed model, and the results obtained from the model are compared with those obtained from a random-array model, a hexagonal-array model using the strain energy approach (SEA), the dilute suspension of the GSCM, the self-consistent method (SCM) and the effective self-consistent method (ESCM). An explicit solution of poroelasticity is provided, and the effects of the solid matrix anisotropy and pore space on the effective poromechanical properties considered. The numerical results for the hexagonal microstructure using the GSCM agree much better with those obtained from experimental investigation in both wet and dry situations than those obtained from other methods. Finally, the influences of fatigue on micromechanical properties for wet and dry conditions are also described.

Strength evaluation and failure analysis of unidirectional composites using Monte-Carlo simulation

Tensile strength and failure process of composite materials depend on the variation in fiber strength, matrix properties and fiber–matrix interfacial shear strength. A Monte-Carlo simulation considering variation in these factors has been widely used to analyze such a complicated phenomenon as a strength and simulate the failure process of unidirectional composites. In this study, a Monte-Carlo simulation using 2-D and 3-D (square and hexagonal array) model was performed on unidirectional graphite/epoxy and glass/polyester composites. The results simulated by using 3-D hexagonal array model have a good agreement with the experimental data which were tensile strength and failure process of unidirectional composites.

Evaluation of Transverse Young's Modulus of Unidirectional Carbon Fiber Reinforced Plastics.

The transverse Young's modulus of unidirectional carbon fiber reinforced plastics(CFRP) was measured by three points bending tests and compared with values calculated using finite element method(FEM). To calculate the transverse Young's modulus, we developed a 3-dimensional finite element method program by modifying the hexagonal array model in consideration of the anisotropy of carbon fiber and the effect of interface between carbon fiber and matrix. The values calculated without consideration of the effect of interface were smaller than the experimental data. The FEM analysis indicated that the transverse Young's modulus of CFRP was changed largely with the change of the Young's modulus of the interface layer when the modulus of the interface was less than that of the matrix.

Strength Evaluation and Eailure Analysis of Unidirectional Composites Using Monte-Carlo Simulation

Tensile strength and failure process of composite materials depend on the variation in fiber strength, matrix properties and fiber-matrix interfacial shear strength. A Monte-Carlo simulation considering variation in these factors has been widely used to analyze such a complicated phenomenon as a strength and simulated the failure process of unidirectional composites. In this study, a Monte Carlo simulation using 2-D and 3-D(square and hexagonal array) model was performed on unidirectional graphite/epoxy and glass/polyester composites. The results simulated by using 3-D hexagonal array model have a good agreement with the experimental data which were tensile strength and failure process of unidirectional composites.

Approximate upper and lower bounds for the strength of unidirectional composites

This paper addresses the problem of determining the probabilistic strength of unidirectional composites. We first calculated the stress-concentration factors (SCFs) around broken fibers in a three-dimensional, hexagonal-array model. Two approaches were tried to calculate the SCFs. One is a shear-lag analysis originated by Hedgepeth and Van Dyke and the other is close to a local load-sharing rule (LLS). These two sets of SCFs provide the upper and lower bounds of the strength. With these SCFs, we next carried out a Monte Carlo simulation to evaluate the strength of unidirectional composites in which a chain-of-bundles probability model and a Weibull distribution were used. Parametric studies were first conducted and a comparison with experiments and other existing theories was next done. Our `approximate' upper bound was lower than Rosen's prediction and lower bound, higher than Zweben's value. The value from the simulation was also close to the experimental results.

Discreteness of Charge and Ion Association Effects on Electroactive Self-Assembled Monolayers

The voltammetric response of an electrode covered with an electroactive self-assembled monolayer is modeled including discreteness of charge effects and interfacial ion association. Discreteness of charge potentials are estimated according to the hexagonal array model of Macdonald and Barlow, and results are compared with those obtained in previous work with the cutoff disk model. As a consequence of the slower variation of the discreteness of charge potential on the applied electrode potential, voltammetric waves are predicted to be asymmetrical and wider than those computed from the cutoff disk model. For relatively high redox coverage and/or small values of the integral capacities of the inner and outer part of the monolayer, a negative differential capacity is predicted. This is a consequence of the additional stabilization provided by the discreteness of charge effect, which allows the charge density at the redox plane to increase faster than the charge density on the electrode surface when the monolayer is being oxidized. Comparison with experimental results shows that inclusion of the discreteness of charge effects results in a variation of the absolute value of the interfacial parameters, while their qualitative trends are the same as those obtained on the basis of an average potential model. Therefore, only the physical significance of the fitting parameters may help to discriminate among the different models.

A Comparative Study of Square Cell and Circular Cell Micro-Models

Accuracy and computational simplicity are both sine qua non for micro-mechanical models which would be candidates for incorporation in structural analysis treating combined nonlinearities. To date there are a number of micro-models and most of these employ either a square cell or a circular cell as the representative volume element. The present paper discusses the accuracy of typical micro-models belonging to either category. A simplified square cell model (SSCM) derived from elementary mechanics is presented and this model is shown to give results almost identical to those of Aboudi's method of cells (AMC). A finite element-based 3-phase cylindrical fiber model (FECM) is developed with the primary object of determining the stress variation at the micro-level and thus the initiation of local failure. This model is apparently the most accurate in the set of models considered in the paper. It is confirmed that the closed form expressions of Hashin and Rosen in conjunction with the expressions to determine the transverse shear modulus given by Christensen and Lo offer a viable approach to the determination of elastic constants. The AMC and SSCM too provide sufficiently accurate prediction of plastic constants. However for the determination of initial yielding under combined loading, a micro-model which gives the variation of stresses across the model is required. The problem of the prediction of first yield of a metal matrix composite is considered and the results of the FECM are compared with those of the simpler square cell models and the hexagonal array model of Dvorak. The square cell models fail in the prediction of the first yield in the context of stress states which are nearly hydrostatic. The present FECM model is seen to be very effective because of the uncoupling of harmonics in the solution process and promises to be an effective tool for the inelastic analysis of the composites.

Mechanics of hot isostatic pressing in intermetallic matrix composites

Thermal residual and mechanical stresses generated by hot isostatic pressing, cooling and subsequent mechanical loading of SCS6/Ni3Al and SCS6/Ti3Al composites with uncoated and carbon-coated fibres have been simulated by micromechanical modelling. The solutions were found in a periodic hexagonal array model of the microstructure with the finite element method. The intermetallic matrices were assumed to be elastic-plastic, with temperature-dependent properties. The fibre and coating were assumed to be elastic. Local stress fields and overall response were found for several processing sequences. The results suggest that plastic deformation of the matrix during cooling from fabrication temperatures reduces residual stresses. The Ni3Al matrix system yields more easily than the Ti3Al system. HIP programmes that promote such yielding are proposed and analysed in both systems. Compliant and expansive fibre coatings tend to reduce the thermal stresses, but may also enhance the interface stresses in the matrix under overall mechanical loads.

Analysis of thermoviscoelastic behavior of unidirectional fiber composites

A method of analysis of the thermoviscoelastic properties of unidirectional fiber composites consisting of transversely isotropic elastic fibers and thermoheologically complex matrix is presented. The composite is modeled by the composite cylinder assemblage to obtain certain properties and by the periodic hexagonal array model to obtain others. Analysis capability includes any temperature variation and any thermorheological matrix. Specific numerical results were obtained for relaxation and creep functions and for material response associated with cyclic temperature variation as occurs in an orbiting space structure.