Bianchi Type VI Cosmological Model with Dynamical Cosmological Parameters G and ⩘ in the presence of Bulk Viscous Stress

In the present study, we have obtained Bianchi type VI anisotropic model of the universe filled with a bulk viscous stress in the presence of variable gravitational and cosmological constants. Here we have assumed the cosmological term in the form Λ∝H to discuss the effect of cosmological variables. It is found that the bulk viscosity coefficient (ξ) is a decreasing function of time. The expression for proper distance, luminosity distance, angular diameter distance, look back time and distance modulus curve have been analyzed and also the distance modulus curve of derived model nearly matches with Supernova Ia (SN Ia) observations.

Thermal Modulus Evaluation of Arenga pinnata Fibre Reinforced Epoxy Composite: Effect of Moisture Absorption

This paper presents the effect of moisture absorption towards thermal modulus evaluation of Arenga Pinnata fibre reinforced epoxy composite. The specimens are produced by hand lay-up method for practically with the ratio of combination of fibre with epoxy and hardener. The fibres were treated with sodium hydroxide (NaOH) prior the composites fabrication. Then, it were submerged in the water for moisture absorption and left for 8 days, 16 days and 30 days. The flexural modulus indicates there is reduction of elastic modulus values over the submerged period. Thermal analysis depicted by storage modulus curve showed the submerged specimens were not affected too much as compared to the control specimens. In fact, their performances were remaining the same across the temperature across from-10°C to 100°C. It is suggested from the experimental result that Arenga Pinnata fibres have a potential prospect as fibre reinforcement composites in many application.

The variation of comonomers feeding profile to design the distribution of chains composition for the optimization of the mechanical properties in copolymer systems

Semicontinuous seeded emulsion copolymerizations, using 5 different types of feeding profiles of comonomers (styrene/butyl acrylate, S/BA) were carried out, to vary in a gradual manner the composition of the copolymer chains formed throughout the reactions (gradient composition copolymer, GCC). For comparison, equivalent core-shell type polymeric materials were synthesized in two stages (TS). In all reactions, the S/BA global mass ratio was: 70/30. To estimate the weight composition distribution (WCD) of the copolymer chains, the cumulative styrene content in the polymer mass was followed throughout the reaction (1H-NMR). Average molecular weights were determined using SEC. The differences in mechanical performance were established, carrying out a mechanodynamic (DMA), and mechanostatic characterization (stress-strain at several temperatures and, Izod testing). The area under the loss modulus curve (LA) was correlated with Izod impact strength, showing the damping superiority of the GCCs over the T-S material. At all tested temperatures (between 25 and 70 °C), the GCC materials exhibited yielding and plastic deformation, while the T-S material presented brittle fracture in that temperature interval. The WCDs were used to elucidate the differences in mechanical behaviour among GCC materials. The feeding profile variation in combination with the WCD analysis represents a novel methodology to produce tailor made copolymers.

Nanomechanical Properties of Prepared-TiO2 Films Using Nanoindentation Technique

Nanoindentation was used to measure the hardness and Young’s modulus of prepared-TiO2 films. The thickness and refractive index of the TiO2 films were measured using ellipsometry with a monochromator. Scanning electron microscopy was used to determine the micrography of the TiO2 films. Pure TiO2 films were prepared from sols made by 3 % (w/w) of prepared-TiO2 suspension solution coated onto silicon wafers. After the dip-coating was completed, the coatings were further treated by various procedures, natural air-drying, water-vapor exposure, and calcinations. The prepared-TiO2 films were smooth and free of macro cracking. The grain sizes of these films were uniform and in the range of 50–100 nm and the films were of rutile structure. The prepared-TiO2 coatings exhibited more favorable porosity in water-vapor exposure than those under other conditions. The T-H2SO4 coatings exhibited higher hardness and modulus than those with T-H2O and T-NH4OH coatings after high temperature calcination. The values of hardness and modulus for T-H2SO4 coatings were 11.93 GPa and 226.25 GPa, respectively. Curves of hardness and modulus as a function of depth (0–2200 nm) of the coatings under calcination conditions show a peak at shallow contact depth within 100 nm and then demonstrate being rather constant. The hardness and modulus curve obtained from T-H2SO4 coatings in water-vapor exposure are rather constant.

An Anisotropic Hardening Rule for Elastoplastic Solids Based on Experimental Observations

A hardening rule is described based on yield and memory surfaces. A memory surface indicates the extent of loading, and a yield surface is the locus of the elastic region. We define a hardening modulus curve which relates the change in size of the yield and memory surfaces to the tangent modulus of the material at the maximum load. The evolution of the yield surface is described for both the proportional and nonproportional loading paths. Both quasi-static and stable cyclic loading is considered. An attractive feature of this nonlinear hardening law is that the material constants associated with it are limited—three in all—and they can be easily determined from a simple test. The predictions of the proposed hardening law are compared with the experimental data for proportional and nonproportional loading paths, and are found to be in good agreement.

The Effect of Crosslink Structure on the Tensile Strength and Oxygen Absorption Characteristics of Natural Rubber Vulcanizates

The chemical nature of crosslinks in natural rubber—sulfur—diphenylguanidine vulcanizates was modified by reaction with triphenylphosphine under nitrogen to determine the effect of this change on tensile strength and oxygen absorption characteristics of the vulcanizates. The vulcanizates were characterized by organically combined sulfur and polysulfidic sulfur. Polysulfidic crosslinks, i.e., crosslinks containing three or more sulfur atoms in the crosslink, were found not to be essential for the attainment of high tensile strength in these vulcanizates. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted the tensile strength versus 300% modulus curve for the control samples. Vulcanizates which had been reacted with triphenylphosphine for 16 days at 80° C, had lost 95–99.6% of their polysulfidic sulfur. These triphenylphosphine-reacted vulcanizates exhibited significantly lower rates of oxygen absorption at 100° C as compared to the untreated vulcanizates. This suggests that polysulfidic structures in the original vulcanizates act as oxidation initiators.