Problems of the stability of composite materials in compression along interlaminar cracks: Periodic system of parallel macrocracks

1995 ◽  
Vol 31 (7) ◽  
pp. 551-557 ◽  
Author(s):  
I. A. Guz'
Keyword(s):  
Composite Materials ◽  
Periodic System ◽  
The Stability

The stability of heavy nuclei and the limit of the periodic system of elements

1970 ◽  
Vol 100 (1) ◽  
pp. 45-92 ◽  
Author(s):  
G.N. Flerov ◽  
V.A. Druin ◽  
A.A. Pleve
Keyword(s):  
Periodic System ◽  
Heavy Nuclei ◽  
The Stability

scholarly journals Survey Summary on Salts Hydrates and Composites Used in Thermochemical Sorption Heat Storage: A Review

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3105
Author(s):  
Mohamed Zbair ◽  
Simona Bennici
Keyword(s):  
Composite Materials ◽  
Energy Density ◽  
Low Temperature ◽  
Mass Transport ◽  
Lower Energy ◽  
Heat Storage ◽  
Porous Matrix ◽  
Salt Hydrates ◽  
Sorption Heat ◽  
The Stability

To improve the proficiency of energy systems in addition to increasing the usage of renewable energies, thermal energy storage (TES) is a strategic path. The present literature review reports an overview of the recent advancements in the utilization of salt hydrates (single or binary mixtures) and composites as sorbents for sorption heat storage. Starting by introducing various heat storage systems, the operating concept of the adsorption TES was clarified and contrasted to other technologies. Consequently, a deep examination and crucial problems related to the different types of salt hydrates and adsorbents were performed. Recent advances in the composite materials used in sorption heat storage were also reviewed and compared. A deep discussion related to safety, price, availability, and hydrothermal stability issues is reported. Salt hydrates display high theoretical energy densities, which are promising materials in TES. However, they show a number of drawbacks for use in the basic state including low temperature overhydration and deliquescence (e.g., MgCl2), high temperature degradation, sluggish kinetics leading to a low temperature rise (e.g., MgSO4), corrosiveness and toxicity (e.g., Na2S), and low mass transport due to the material macrostructure. The biggest advantage of adsorption materials is that they are more hydrothermally stable. However, since adsorption is the most common sorption phenomenon, such materials have a lower energy content. Furthermore, when compared to salt hydrates, they have higher prices per mass, which reduces their appeal even further when combined with lower energy densities. Economies of scale and the optimization of manufacturing processes may help cut costs. Among the zeolites, Zeolite 13X is among the most promising. Temperature lifts of 35–45 °C were reached in lab-scale reactors and micro-scale experiments under the device operating settings. Although the key disadvantage is an excessively high desorption temperature, which is problematic to attain using heat sources, for instance, solar thermal collectors. To increase the energy densities and enhance the stability of adsorbents, composite materials have been examined to ameliorate the stability and to achieve suitable energy densities. Based on the reviewed materials, MgSO4 has been identified as the most promising salt; it presents a higher energy density compared to other salts and can be impregnated in a porous matrix to prepare composites in order to overcome the drawbacks connected to its use as pure salt. However, due to pore volume reduction, potential deliquescence and salt leakage from the composite as well as degradation, issues with heat and mass transport can still exist. In addition, to increase the kinetics, stability, and energy density, the use of binary salt deposited in a porous matrix is suitable. Nevertheless, this solution should take into account the deliquescence, safety, and cost of the selected salts. Therefore, binary systems can be the solution to design innovative materials with predetermined sorption properties adapted to particular sorption heat storage cycles. Finally, working condition, desorption temperature, material costs, lifetime, and reparation, among others, are the essential point for commercial competitiveness. High material costs and desorption temperatures, combined with lower energy densities under normal device operating conditions, decrease their market attractiveness. As a result, the introduction of performance metrics within the scientific community and the use of economic features on a material scale are suggested.

Experimental Description of Aging of Coconut Shell Powder/Epoxy Composite

2019 ◽  
Vol 287 ◽  
pp. 64-68
Author(s):  
Petr Valášek ◽  
Karolína Habrová
Keyword(s):  
Tensile Strength ◽  
Shear Strength ◽  
Composite Materials ◽  
Current Trend ◽  
Natural Material ◽  
Environmentally Sensitive ◽  
The Stability ◽  
Coconut Shells ◽  
Coconut Shell Powder ◽  
Degradation Time

In the field of composite materials, in some areas, the current trend is the substitution of synthetic reinforcement by natural material. Biological reinforcements thus optimize the resulting mechanical characteristics in a number of cases, where the resulting material can be labeled as environmentally sensitive. The problem of biological materials can be their aging. For the specification of application areas of composite materials with biological reinforcement, it is necessary to know the stability of these materials over time. The paper describes the composite material with epoxy matrix and filler in the form of microparticles (100-200 μm) prepared from coconut shells (CSP/epoxy). Epoxy resin for joining materials in engineering was filled with 2.5, 5.0 and 10.0 wt.% of CSP, and resin used for vacuum infusion was filled with 30 wt.% of CSP (different kind of preparation of composite systems) . For an experimental description of aging was used degradation chamber, where both, the humidity and temperatures in each cycle were changed + 70 °C/-40 °C. An important indication of mechanical aging was used to describe aging, namely shear strength and tensile strength. The degradation period was 5 weeks, corresponding to 35 cycles, i.e. 840 hours of degradation. During the degradation time, the shear strength of the CSP composite dropped to 42.2%, the tensile strength of the prepared infusion system dropped by 49.6%.

Effect of RuO2 on Piezoresistive Properties of CB/MVQ Composite Materials

2014 ◽  
Vol 609-610 ◽  
pp. 124-129
Author(s):  
Ju Ying Wu ◽  
Jing Hui Fan ◽  
Yu Hong Huang ◽  
Jing Guo ◽  
Kai Zhang
Keyword(s):  
Composite Materials ◽  
Carbon Black ◽  
Silicone Rubber ◽  
Oxidation Reaction ◽  
Resistance Testing ◽  
Test Results ◽  
Sem And Tem ◽  
Pressure Resistance ◽  
The Stability

In this paper, RuO2-CB/MVQ composites were prepared through following steps. First, the nanoruthenium particles had been prepared by solvent thermo-deoxidization ways. Secondly, the nanoRuO2 particles had been formed by oxidation reaction of nanoruthenium particles in air. Thirdly, the carbon black/silicone rubber mixed rubber was prepared by solvent mixing. Fourthly, the nanoruthenium particles were mixed into carbon black/silicone rubber mixed rubber by rubbing dispersion. Finally, vulcanization molding was carried out at certain preasure and temperature. The piezoresistive properties of CB/MWQ composite materials were tested with pressure-resistance testing systems designed ourselves. The test results showed that suitable amounts of RuO2 could enhance the stability and creep of piezoresistive properties of CB/MWQ composite materials. The microstructure of CB/MWQ composite materials were analyzed with SEM and TEM. The characterization results showed that nanoRuO2 particles dispersed in composite materials in nanolevel. These nanostructure could improve conductive net of carbon black, and reinforce crosslink net of silicone rubber. These factors had advantage to the stability of piezoresistive properties of CB/MWQ composite materials.

An Approximate Analysis of Quasi-Periodic Systems Via Floquét Theory

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Ashu Sharma ◽  
S. C. Sinha
Keyword(s):  
Parametric Excitation ◽  
Periodic System ◽  
Floquet Theory ◽  
Picard Iteration ◽  
Periodic Systems ◽  
Transition Matrices ◽  
Frequency Spectra ◽  
Periodic Coefficients ◽  
Stability Diagrams ◽  
The Stability

Parametrically excited linear systems with oscillatory coefficients have been generally modeled by Mathieu or Hill equations (periodic coefficients) because their stability and response can be determined by Floquét theory. However, in many cases, the parametric excitation is not periodic but consists of frequencies that are incommensurate, making them quasi-periodic. Unfortunately, there is no complete theory for linear dynamic systems with quasi-periodic coefficients. Motivated by this fact, in this work, an approximate approach has been proposed to determine the stability and response of quasi-periodic systems. It is suggested here that a quasi-periodic system may be replaced by a periodic system with an appropriate large principal period and thus making it suitable for an application of the Floquét theory. Based on this premise, a systematic approach has been developed and applied to three typical quasi-periodic systems. The approximate boundaries in stability charts obtained from the proposed method are very close to the exact boundaries of original quasi-periodic equations computed numerically using maximal Lyapunov exponents. Further, the frequency spectra of solutions generated near approximate and exact boundaries are found to be almost identical ensuring a high degree of accuracy. In addition, state transition matrices (STMs) are also computed symbolically in terms of system parameters using Chebyshev polynomials and Picard iteration method. Stability diagrams based on this approach are found to be in excellent agreement with those obtained from numerical methods. The coefficients of parametric excitation terms are not necessarily small in all cases.

Stability of Fibrous Composites

1992 ◽  
Vol 45 (2) ◽  
pp. 61-80 ◽  
Author(s):  
I. Yu. Babich ◽  
A. N. Guz’
Keyword(s):  
Composite Materials ◽  
Fibrous Composite ◽  
Homogeneous Medium ◽  
Stability Loss ◽  
Critical Parameters ◽  
Filler Concentration ◽  
Arbitrary Form ◽  
Fibrous Materials ◽  
Low Concentration ◽  
The Stability

In this review article the three-dimensional linearized theory is presented of the internal and the surface instability of fibrous composite materials. The possible mechanisms of the stability loss in the structure of these materials are investigated. In this investigation the strict model is used of the nonlinearly elastic compressible and incompressible piecewise-homogeneous medium with the arbitrary form of the elastic potential for the theory of finite deformation and for two variants of the theory of small precritical deformations. Problems for a single fiber (fibrous materials with low concentration of the filler, when at stability loss the interaction between fibers is not accounted for), for two fibers (fibrous materials with low concentration of the filler, when as a result of the structure irregularity at the stability loss two neighbouring fibers may interact) for the infinite row and for a doubly periodic system of fibers (fiber materials with nonsmall filler concentration, taking into account fiber interaction), in the infinite and semiinfinite matrix, are considered. Results are obtained for these cases, predominantly when conditions are satisfied of the complete contact on the fiber and matrix polymer or metal interfaces. In the case of the metal matrix at plastic deformations the conception of continuing loading is used, and the change of the unloading zones in the process of stability loss is not accounted for. The influence of the inhomogeneity of the precritical stressed state, resulting from the difference of coefficients of the transverse expansion, of the mechanical properties, and of the volume concentrations of the fibers and the matrix, on the critical parameters is investigated. Application is presented of the obtained results in the fracture mechanics of fibrous composite materials under compression along the reinforcing elements.

scholarly journals Hybrid Sorbents for Removal of Arsenic

2022 ◽  
Vol 320 (1) ◽  
pp. 32-41
Author(s):  
L. A. Zemskova ◽  
◽  
D. H. Shlyk ◽  
N. N. Barinov ◽  
◽  
...  
Keyword(s):  
Composite Materials ◽  
Transition Metal Oxides ◽  
Large Scale ◽  
Arsenic Removal ◽  
Tap Water ◽  
Carbon Composite ◽  
Low Concentrations ◽  
Carbon Composite Materials ◽  
The Stability ◽  
Removal Of Arsenic

The paper analyzes data on the removal of arsenic by sorption methods using materials that have prospects for large-scale application in water treatment. These materials include transition metal oxides in the micro- and nano-dimensional form, including those in the composition of composite materials with inorganic matrices, or hybrid sorbents in the composition with polymer resins or natural biopolymers. Examples of the use of composite (hybrid) sorbents for the removal of arsenic from solutions with low concentrations (at the level of MPC) are given. The objective of this article was to sum the up-to-date information about the most important features of chitosan-containing and chitosan-carbon materials we developed in view their use in arsenic removal processes at low concentrations to concentrations that meet WHO requirements. The paper presents data on the sorption properties of Mo-containing activated carbon fibers and chitosan-carbon composite materials towards arsenic (V) when it is extracted from bidistilled and tap water under static and dynamic conditions. The factors of the different behavior of the sorbents depending on the form of a biopolymer deposited on the fiber and the stability of the sorbents during the sorption of arsenic are discussed.

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