Thermal buckling optimisation of composite plates using firefly algorithm

Abstract

Composite plates play a very important role in engineering applications, especially in aerospace industry. Thermal buckling of such components is of great importance and must be known to achieve an appropriate design. This paper deals with stacking sequence optimisation of laminated composite plates for maximising the critical buckling temperature using a powerful meta-heuristic algorithm called firefly algorithm (FA) which is based on the flashing behaviour of fireflies. The main objective of present work was to show the ability of FA in optimisation of composite structures. The performance of FA is compared with the results reported in the previous published works using other algorithms which shows the efficiency of FA in stacking sequence optimisation of laminated composite structures.     

Conductive and flexible multi-walled carbon nanotube/polydimethylsiloxane composites made with naphthalene/toluene mixture

Conventional conductive materials face challenges when utilizing them for flexible and wearable electronics and soft robotics. Carbon nanotube/polydimethylsiloxane (CNT/PDMS) composites are a promising alternative to the conventional hard conductors because they are light and can realize large deformation. To date, well dispersion of CNTs into PDMS to increase conductivity while maintaining flexibility remains challenging. We aimed at developing highly electrically conductive and flexible multi-walled carbon nanotube/PDMS (MWCNT/PDMS) composites. To this end, we proposed a method to enhance the dispersion of MWCNTs into PDMS using naphthalene and toluene. Our results showed that the addition of naphthalene and toluene into the composites improved dispersion of the MWCNTs and increased the direct current (DC) electrical conductivity. We also found that the morphology of primary aggregates of the MWCNTs influenced the DC electrical conductivity of the composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48167.     

Novel mixed ligand complexes of Co(II), Ni(II), Cu(II), and Zn(II) with 1,10-phenanthroline and acesulfame. Synthesis,structural analysis and hydrogen adsorption study

Four novel metal organic framework (MOF) structures containing acesulfame (ace) and 1,10-phenanthroline (phen) ligands of Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ metal cations were synthesized. The crystal structure analysis of three compounds (1, 2, and 3) was also performed. The structural formula for complex 4 is proposed based on spectroscopic and thermal analysis data. It has been determined that structures 1, 2, and 4 are in a distorted octahedral geometry. It has been suggested that the charge balance of the coordination sphere with 2+ is provided by two monoanionic ace ligands located outside the coordination sphere as counter-ion. In structure 3, there are two Cu^II metal cations, two phen ligands coordinated as bidentate to each metal cation and ace ligand that provides monoanionic-monodentate coordination. The Cu²⁺ cation has distorted bipyramidal geometry. The maximum hydrogen gas adsorption has been found 1.4575 mL/g (0.046 wt%) for the Ni complex.     

Three-dimensional carbon nanotube based polymer composites for thermal management

In this study, the porous multiwall carbon nanotube (MWCNT) foams possessing three-dimensional (3D) scaffold structures have been introduced into polydimethylsiloxane (PDMS) for enhancing the overall thermal conductivity (TC). This unique interconnected structure of freeze-dried MWCNT foams can provide thermally conductive pathways leading to higher TC. The TC of 3D MWCNT and PDMS composites can reach 0.82 W/m K, which is about 455% that of pure PDMS, and 300% higher than that of composites prepared from traditional blending process. The obtained polymer composites not only exhibit superior mechanical properties but also dimensional stability. To evaluate the performance of thermal management, the LED modulus incorporated with the 3D MWCNT/PDMS composite as heat sink is also fabricated. The composites display much faster and higher temperature rise than the pristine PDMS matrix, suggestive of its better thermal dissipation. These results imply that the as-developed 3D-MWCNT/PDMS composite can be a good candidate in thermal interface for thermal management of electronic devices.     

Imaging the Curie Point isothermal surface and predicting its impact on the geothermal regime within the Nile Delta,Egypt

The available aeromagnetic data together with information from some available wells have been used in the current study to shed the light on the geothermal setup of the Nile Delta Province. The aeromagnetic data was reduced-to-pole and critically analyzed using the Spectral Analysis Technique through the Fast Fourier Transform (FFT), to determine the expected depths to the Basement and Curie Point (CPD) surfaces. The geothermal gradient between CPD and earth's surface was estimated, and accordingly the heat flow was evaluated using the proposed thermal conductivity. Then, the Basement Surface Temperature (BST) was estimated, by which the geothermal gradient and heat flow for the igneous-rocky basement and sedimentary-rocky horizon was independently predicted. By which, it could be possible to distinguish between the heat flow contribution from each horizon separately.     

The effect of slightly warm temperature on work performance and comfort in open‐plan offices – a laboratory study

The aim of the study was to determine the effect of a temperature of 29°C on performance in tasks involving different cognitive demands and to assess the effect on perceived performance, subjective workload, thermal comfort, perceived working conditions, cognitive fatigue, and somatic symptoms in a laboratory with realistic office environment. A comparison was made with a temperature of 23°C. Performance was measured on the basis of six different tasks that reflect different stages of cognitive performance. Thirty‐three students participated in the experiment. The exposure time was 3.5 h in both thermal conditions. Performance was negatively affected by slightly warm temperature in the N‐back working memory task. Temperature had no effect on performance in other tasks focusing on psychomotor, working memory, attention, or long‐term memory capabilities. Temperature had no effect on perceived performance. However, slightly warm temperature caused concentration difficulties. Throat symptoms were found to increase over time at 29°C, but no temporal change was seen at 23°C. No effect of temperature on other symptoms was found. As expected, the differences in thermal comfort were significant. Women perceived a temperature of 23°C colder than men.     

Effect of scandia content on the thermal shock behavior of SYSZ thermal sprayed barrier coatings

Nanostructured 4SYSZ (scandia (3.5 mol%) yttria (0.5 mol%) stabilized zirconia) and 5.5 SYSZ (5 mol% scandia and 0.5 mol% yttria) thermal barrier coatings (TBCs) were deposited on nickel-based superalloy using NiCrAlY as the bond coat by plasma spraying process. The thermal shock response of both as-sprayed TBCs was investigated at 1000 °C. Experimental results indicated that the nanostructured 5.5SYSZ TBCs have better thermal shock performance in contrast to 4SYSZ TBCs due to their higher tetragonal phase content and higher fracture toughness of this coating     

Benchmarking thermoception in virtual environments to physical environments for understanding human-building interactions

Thermal comfort influences occupant satisfaction, well-being and productivity in built environments. Several decisions during the design stage (e.g., heating, ventilation, air conditioning design, color and placement of furniture, etc.) impact the building occupants’ thermoception (i.e., the sense by which animals perceive the temperature of the environment and their body). However, understanding the influence of design decisions on occupant behavior is not always feasible due to the resources needed for creating physical testbeds and the need for controlling several contributing factors to comfort and satisfaction. Virtual environments (environments created with virtual reality technology) are novel venues for studying human behavior. However, in order to use virtual environments in the thermoception domain, validation of these environments as adequate representations of physical environments (built environments) is imperative. As the first step towards this goal, we benchmarked virtual environments to physical environments under different thermal stimuli (i.e., hot and cold indoor air temperature). We identified perceived thermal comfort and satisfaction, perceived indoor air temperature, number and type of interactions as markers for the thermoceptive comparison of virtual and physical offices. We conducted an experiment with 56 participants and pursued a systematic statistical analysis. The results show that virtual environments are adequate representations of physical environments in the thermoception domain, especially for subjective perceived thermal comfort and satisfaction assessment. We also found that the type of first adaptive interactions could be used as the markers of thermoception in virtual environments.     

Enhanced flame-retardant property of epoxy composites filled with solvent-free and liquid-like graphene organic hybrid material decorated by zinc hydroxystannate boxes

A polyether amine (M2070) was covalently grafted onto the surface of graphene nanosheets (GNS) decorated by zinc hydroxystannate boxes (ZHS) to obtain an organic hybrid material (GNS-ZHS-M2070) with solvent-free and liquid-like behavior. It was subsequently incorporated into epoxy resin (EP) to investigate the flame-retardant property. The GNS-ZHS-M2070, which was a homogeneous sticky fluid at room temperature without any solvent, could stably disperse in a broad spectrum of solvents. Most importantly, the GNS-ZHS-M2070/EP composites possessed superior flame-retardant performance, such as the lowest peak heat release rate and fire growth rate index values. Furthermore, it had been demonstrated that the superior flame-retardant performance of GNS-ZHS-M2070/EP should be ascribed to the excellent processability and good compatibility of GNS-ZHS-M2070 derived from the unique flowability and soft organic shell. All of these advantages along with the solvent-free nature of GNS-ZHS-M2070 provided a green, efficient and environment-friendly way to fabricate high flame-retardant performance composite materials.     

Enhanced intrinsic stability of the bulk heterojunction active layer blend of polymer solar cells by varying the polymer side chain pattern

Organic photovoltaics (OPVs) have acquired huge attention over the past years as potential renewable energy sources, adding attractive features such as aesthetics, semi-transparency, flexibility, large area printability, improved low-light performance, and cost-effectiveness to the well-known Si-based photovoltaics. Steady improvements in OPV power conversion efficiencies are continuously reported, notably for bulk heterojunction solar cells based on conjugated polymer:fullerene blends. However, apart from efficiency and cost, the stability of organic solar cell devices is of particular concern. Among the different factors contributing to OPV instability, gradual loss of the optimum phase-separated nanomorphology of the photoactive layer blend is a critical parameter. In this paper, we present the results of ‘shelf-life’ accelerated lifetime tests performed for devices containing a range of functionalized poly(3-alkylthiophene) (P3AT) donor polymers upon prolonged thermal stress. By the incorporation of functional moieties on the side chains of P3HT-based copolymers, a remarkable improvement of the intrinsic stability of the active layer blend morphology is accomplished, even for fairly low built-in ratios (5–15%) and without crosslinking to covalently anchor the polymer and/or fullerene molecules. Moreover, these alterations do not influence the initial power conversion efficiencies to a large extent. As such, the presented approach can be regarded as an attractive paradigm for OPV active layer stability.