Surface stress and agglomeration effects on nonlocal biaxial buckling polymeric nanocomposite plate reinforced by CNT using various approaches

In this article, the surface stress effect on the biaxial critical buckling load of nonlocal polymeric nanocomposite rectangular plate reinforced by carbon nanotubes (CNTs) is presented. Various approaches such as Eshelby–Mori–Tanaka, the extended mixture rule, Halpin–Tsai, and micromechanical are used to determine the effective material properties of polymeric nanocomposite plate. The governing equations of equilibrium are obtained by using Hamilton’s principle. The Navier’s method is considered to obtain the biaxial critical buckling load of polymeric nanocomposite rectangular plate for simply supported boundary conditions. A detailed parametric study is conducted to explain the effects of aspect ratio, elastic foundation, surface stress and agglomeration on the biaxial buckling of nanocomposite plate. The results show that surface stress effect plays an important role at nanoscale. Also, the biaxial critical buckling load decreases with increasing the CNTs volume fraction in the inclusion (agglomeration effect). The results of this research can be used for micro-electro-mechanical and nano-electro-mechanical devices.     

Optimization of sintering conditions for improved microstructural and mechanical properties of dense Ce0.8Gd0.2O2-δ-FeCo2O4 oxygen transport membranes

Ce_0.8Gd_0.2O_2-δ-FeCo₂O₄ composite is an excellent oxygen transport membrane material with good chemical stability for applications in oxygen separation and membrane reactors. To improve microstructural and mechanical properties, sintering profiles for Ce_0.8Gd_0.2O_2-δ-FeCo₂O₄ composites were optimized. Different sintering temperatures are selected based on our study of phase interactions among the initial powder mixtures using high-temperature X-ray diffraction. The results reveal that the phase interaction at ～1050 ℃ accelerates densification process, and a further increase of sintering temperature to 1200 ℃ contributes to the homogenization of the pore distribution. A higher density and an improved homogeneity of pore distribution result in enhanced mechanical strength. However, the density decreases once the sintering temperature reaches 1350 ℃. Hence, the optimal sintering temperature considering both microstructural and mechanical properties appears to be 1200 ℃. Sintering at this temperature results in a microstructure with a density exceeding 99 % with only small surface defects and a high average flexural strength of approximately 266 MPa.     

High temperature compressive creep behavior of BaCe0.65Zr0.2Y0.15O3−δ in air and 4% H2/Ar

The proton conductive material BaCe_0.65Zr_0.2Y_0.15O_3−δ has great potential for the separation and purification of hydrogen. However, due to the demanding application conditions regarding both temperature and atmosphere, the elevated temperature structural stability needs to be characterized and warranted. Hence, in this research work, the elevated temperature compressive creep behavior of BaCe_0.65Zr_0.2Y_0.15O_3−δ in the temperature regime of 850°C to 1200°C was studied in both air and 4% H₂/Ar as a function of the applied stress. The results indicate different creep mechanisms depending on atmosphere and temperature range. While dislocation creep was observed in 4% H₂/Ar over the full range, a dislocation creep mechanism was observed in air at temperatures ≤1050°C and a diffusional creep mechanism at temperature ≥1100°C. A detailed microstructural analysis of the post-creep test specimens revealed that the exposure to oxygen leads to localized stoichiometric changes and a decomposition at the surface.     

Time-dependent creep stress redistribution analysis of thick-walled functionally graded spheres

Time-dependent creep stress redistribution analysis of thick-walled spheres made of functionally graded material (FGM) subjected to an internal pressure and a uniform temperature field is performed using the method of successive elastic solution. The material creep and mechanical properties through the radial graded direction are assumed to obey a simple power-law variation. Total strains are assumed to be the sum of elastic, thermal and creep strains. Creep strains are time, temperature and stress dependent. Using the equations of equilibrium, compatibility and stress–strain relations a differential equation, containing creep strains, for radial stress are obtained. Ignoring creep strains, a closed-form solution for initial thermoelastic stresses at zero time is presented. It has been found that the material in-homogeneity parameterβ has a substantial effect on thermoelastic stresses. From thermoelastic analysis the material identified by β=2 in which a more uniform shear stress distribution occurs throughout the thickness of the FGM sphere is selected for time-dependent stress redistribution analysis. Using the Prandtl–Reuss relations and Norton’s creep constitutive model, history of stresses and strains are obtained. It has been found that radial stress redistributions are not significant, however, major redistributions occur for circumferential and effective stresses. It has also been concluded that stresses and strains are changing with time at a decreasing rate so that there is a saturation condition beyond which not much change occurs. Indeed after 50 years the solution approaches the steady-state condition.     

Flutter and bifurcation instability analysis of fluid-conveying micro-pipes sandwiched by magnetostrictive smart layers under thermal and magnetic field

International Journal of Mechanics and Materials in Design - Fluid-conveying micro/Nano structures are key tools in MEMS and NEMS applications especially for drug delivery systems to attack a...     

Definition of requirements for accessing multilingual information opinions

Multimedia Tools and Applications - In this paper, we will present a study concerning the understanding of the needs of people using Internet in order to access to multilingual information. In...     

Evaluation of (4‐Arylpiperidin‐1‐yl)cyclopentanecarboxamides As High‐Affinity and Long‐Residence‐Time Antagonists for the CCR2 Receptor

Animal models suggest that the chemokine ligand 2/CC‐chemokine receptor 2 (CCL2/CCR2) axis plays an important role in the development of inflammatory diseases. However, CCR2 antagonists have failed in clinical trials because of a lack of efficacy. We previously described a new approach for the design of CCR2 antagonists by the use of structure–kinetics relationships (SKRs). Herein we report new findings on the structure–affinity relationships (SARs) and SKRs of the reference compound MK‐0483, its diastereomers, and its structural analogues as CCR2 antagonists. The SARs of the 4‐arylpiperidine group suggest that lipophilic hydrogen‐bond‐accepting substituents at the 3‐position are favorable. However, the SKRs suggest that a lipophilic group with a certain size is desired [e.g., 3‐Br: K_i=2.8 nM , residence time (t_res)=243 min; 3‐iPr: K_i=3.6 nM , t_res=266 min]. Alternatively, additional substituents and further optimization of the molecule, while keeping a carboxylic acid at the 3‐position, can also prolong t_res; this was most prominently observed in MK‐0483 (K_i=1.2 nM , t_res=724 min) and a close analogue (K_i=7.8 nM ) with a short residence time.     

The effect of CNT volume fraction on the magneto-thermo-electro-mechanical behavior of smart nanocomposite cylinder

In this article, using analytical approach, the stress analysis of a long piezoelectric polymeric hollow cylinder reinforced with carbon nanotube (CNT) under combined magneto-thermo-electro-mechanical loading is investigated. Considering three combined loading conditions such as pressure-electric, pressure-electric magnetic and pressure-electric thermal, the governing equation of the problem is obtained. The rule of mixture and modified multiscale bridging model are used to predict effective properties of nanocomposite. The magneto-thermo-electro-mechanical stresses in hollow cylinder are discussed in detail. It can be concluded that increasing CNT volume fraction enhances strength of the nanocomposite cylinder. The results of this work could be useful in view of optimum design of the smart nanocomposite cylinder under magneto-thermo-electro-mechanical loadings and could also be as a reference for future related works.     

Nonlocal electro-thermal transverse vibration of embedded fluid-conveying DWBNNTs

Electro-thermal transverse vibration of fluid-conveying double-walled boron nitride nanotubes (DWBNNTs) embedded in an elastic medium such as polyvinylidene fluoride (PVDF) which is a piezoelectric polymer is investigated. The elastic medium is simulated as a spring and van der Waals (vdW) forces between inner and outer nanotubes are also taken into account. Zigzag structure of boron nitride nanotubes (BNNTs) is described based on the nonlocal continuum piezoelasticity cylindrical shell theory, and Hamilton??s principle is employed to derive the corresponding higher-order equations of motion. In this model, DWBNNTs are placed in uniform temperature and electric field, the latter being applied through attached electrodes at both ends. Having considered the small scale effect, aspect ratio (L/R), densities of fluid and elastic medium, four different cases of loading are assumed in this study, including: a) direct voltage and heating (DVH), b) direct voltage and cooling (DVC), c) reverse voltage and heating (RVH), and d) reverse voltage and cooling (RVC). Numerical results indicate that increasing nonlocal parameter (e ₀ a), for the four above mentioned cases, decreases the critical flow velocity of fluid. The results could be used in design of nano-electro-mechanical devices for measuring density of a fluid such as blood flowing through such nanotubes with great applications in medical fields.