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Due to the thickness of the spacer fabric, it is usually assembled in a multi-layered manner as a cushion material. However, few studies have been conducted on the compression properties of the multi-layered spacer fabrics. Firstly, this paper analyzes the factors affecting the compression properties of multi-layered spacer fabrics, and explains the influencing mechanisms. Results show that the fixing condition between the sample and the indenter, the fixing condition between layers, the overlaying direction and the compression speed have little effect on the compression property. However, when overlaying spacer fabrics with different moduli, a better compression property can be obtained by placing the fabric with a higher modulus on top. Secondly, this paper focuses on the relationship between the layers and the compression property of the spacer fabrics. It shows that the relation between the compression work and the number of layers is linear, with a high correlation coefficient. The relationship between the modulus and the number of layers is in the form of a cubic function with a good correlation coefficient. Finally, the Kelvin model is modeled and is found to be suitable for characterizing the stage II compressive properties of multi-layered spacer fabrics. The above quantitative analysis provides theoretical support for the design of cushion materials with different moduli and support performance in different regions, and has practical guiding significance. [ABSTRACT FROM AUTHOR]

New generation nano-filler polymer composites have many applications including biomedical, electronic and maritime related applications because of their mechanical, electronic and optical properties. The properties of composites were investigated as a function of nano-filler content. Among these, tungsten disulfide (WS2) has the potential to be used as a component in electronic devices owing to its high electron mobility and easily tunable optical band gap energy. Tungsten disulfide (WS2)- Polyacrylamide (PAAm) composite was prepared using free radical co-polymerization and wet laboratory methods with WS2 content. Composites were characterized for mechanical and optical properties using an Elasticity Instrument and UV-vis Spectrophotometer, respectively. Elastic modulus was modeled by a statistical thermodynamics model. Tauc's and Urbach's Tail model for direct transition were used to model for the optical band gap. In this study, the swelling and WS2 effect on the optical band gap and elasticity of WS2 - PAAm composites were investigated. It was observed that the elasticity presented a reversed behavior of optical band gap energies with respect to WS2 content. For the applications of nano-filler doped polymer composites in flexible electronic devices, WS2 content strongly influences the mechanical and optical properties. [ABSTRACT FROM AUTHOR]

This article presents a new micromechanical model to predict biaxial tensile moduli of plain weave fabric composites by considering the interaction between the orthogonal interlacing strands. The two orthogonal yarns in micromechanical unit cell were idealized as curved beams with a path depicted using sinusoidal shape functions. The biaxial tensile moduli of plain weave fabric composites were derived by means of the minimum total complementary potential energy principle founded on micromechanics. Biaxial tensile tests were conducted on the resin transfer molding–made EW220/5284 plain weave fabric composites at five biaxial loading ratios of 0, 1, 2, 3 and ∞ to validate the new model. Predictions from the new model were compared with experimental data. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed model. Using the new model, the biaxial tensile moduli of plain weave fabric composites can be predicted based only on the properties of basic woven fabric. [ABSTRACT FROM AUTHOR]

Wool, cotton and ramie thermal properties are qualitatively studied by temperature-dependent Fourier transform infrared (TD-FTIR) spectroscopy, and quantitatively investigated by thermogravimetry coupled with a differential thermal analyzer (TG-DSC). TD-FTIR results indicate that although cotton, ramie and wool exhibit significant water loss, they have no detected degradation within the temperature range from 25℃ to 210℃. These data are confirmed by TG-DSC analysis. Dynamic mechanical thermal analysis provides comparative study of cotton, ramie and wool bundles’ dynamic mechanical thermal properties. The four-fiber-bundle has a much lower storage modulus due to its larger fiber contact surface and twisting deformation; heating reduces the storage modulus significantly for cotton and ramie instead of wool fiber bundles in the temperature range from 25℃ to 100℃. Key E′-T and tan δ-T curve information reveals that ramie fiber bundles have the strongest temperature sensitivity, while wool fiber bundles express the weakest temperature sensitivity. [ABSTRACT FROM AUTHOR]

Investigations were carried out on glass-epoxy composite specimens with varied fibre orientations (±2° to ±88°), prepared by both braided and filament winding techniques. The experimental strength and stiffness of these composites while exhibiting similar trends, correlated well with those predicted by classical laminate theory. The filament wound composites exhibited (20–40%) initial higher properties vis-a-vis the braided composites, while a correlation index between the experimental and theoretical values has been evolved. [ABSTRACT FROM AUTHOR]

In this study, the behavior of thick magnetorheological elastomers is experimentally investigated. Two types of magnetorheological elastomer specimens of varying concentrations, with circular and rectangular shapes having thicknesses from 6.35 mm to a maximum of 25.4 mm, are prepared. The magnetorheological elastomer samples are studied under quasi-static compression and double lap-shear tests. The shear and the Young’s moduli of the magnetorheological elastomers are obtained under different applied magnetic fields. It is observed that the field-induced change in the modulus is independent of the thickness of the magnetorheological elastomer and is only dependent on the iron particle concentration and the magnetic field strength. With the increase in the applied magnetic field, it is observed that the change in modulus varies from a linear behavior at lower applied magnetic fields to a nonlinear one at higher magnetic fields. It is found that compressive and shear moduli only depend on the applied magnetic fields and are independent of the sample thickness. In addition, the maximum induced change in material modulus under compression is shown to be 99%, whereas in shear it is found to be 68% when compared to its off-state. [ABSTRACT FROM AUTHOR]

Braided and filament wound CFRP were fabricated with varied fiber orientations. These composites exhibited not only similar trends in their experimental strength and stiffness properties but also good correlations with predictions made by CLT. [ABSTRACT FROM PUBLISHER]

Hybridization, especially where only variant natural lignocelluloses are combined, is fast receiving encouraging attention because it offers a range of properties that may be difficult to obtain with a single kind of reinforcement. In this study, tensile, flexural, and impact properties of hybridized kenaf/PALF-reinforced HDPE composite were studied. Sheets from which tensile, flexural, and impact specimens were cut out were produced from the compression molding of composite pellets and subsequently conditioned in an oven for 21 h at 103°C. The tensile and flexural specimens were tested according to ASTM D638 and ASTM D790 using a 5-kN INSTRON bluehill universal testing machine accordingly. While a notched Izoid impact test was conducted using a 1-J universal pendulum according to ASTM D256. All specimens were prepared at a fiber ratio of 1:1 kenaf:PALF and fiber lengths of 0.25, 0.5, 0.75, and 2 mm; fiber loadings of between 10% and 70% were utilized for the study. About 0.25 mm fiber showed the best tensile and flexural properties with a linear increase in properties up to 60% fiber loading while impact strength showed better property with 0.75 and 2 mm fiber lengths. At 0.25 mm fiber length, tensile strength of 32.24 MPa, flexural strength and modulus of 34.01 MPa and 4114.11 MPa, respectively, were observed at 60% fiber loading. Moduli results of all the composites formulated generally obeyed the ROM. SEM was used to examine the surface of composites produced. Tensile and impact strengths result showed inverse proportionality while flexural strength of the composite generally adhered to the ROM. However, a positive effect was observed in the case of composite’s impact strength in respect of increasing fiber length. Thus, reduction in some mechanical properties of the composite with respect to increasing fiber length is attributed more to fiber entanglement rather than attrition. [ABSTRACT FROM AUTHOR]

This article discusses a simplified approach to analyze mechanical properties of randomly distributed short fiber composites. Mechanical properties of three different randomly oriented short fiber composites, cotton, nylon, and aluminium with vinylester resins, were experimentally investigated. The analytical results were compared with experimental results and a very good correlation was found. Further, the experimental results and the predictions showed that the strength of the composites is less than the strength of the matrix material, for all three composites tested. [ABSTRACT FROM AUTHOR]

Total joint replacements (TJRs) have a limited lifetime, but the introduction of devices that exhibit good lubricating properties with low friction and low wear could well extend this. A novel tibial bearing design, using polyurethane (PU) as a compliant layer, to mimic the natural joint, has been developed. To determine accurately the mode of lubrication under which these joints operate, a synthetic lubricant was used in all these tests. Friction tests were carried out to assess the effects of material modulus and surface roughness, together with bearing design parameters such as bearing thickness and conformity, on lubrication. Corethane 80A was the preferred material and was chosen as the compliant layer for subsequent testing. A low surface roughness resulted in lower asperity contact as the asperities were depressed by the pressurized entraining fluid and full-fluid-film lubrication was approached. The three different tibial bearing conformities (low, medium, and high) did not appear to influence the mode of lubrication and all these bearings performed with extremely low friction. Similarly, the bearing thickness effects on lubrication at the levels tested (2mm, 3mm, and 4mm) were minimal, although the effects of layer thickness on interface shear stress could be expected to be significant. This study describes a series of friction tests that have been used to select the most appropriate material and to optimize the design parameters to establish optimum conditions for these compliant layer joints. [ABSTRACT FROM AUTHOR]

Good theoretical composite models have been developed to address the modulus as a function of filler volume fraction and tensile strength as a function of time. However, very little has been done to understand the observation that the tensile yield strength appears to go through a maximum as a function of the volume fraction of filler for a particulate composite. While several factors undoubtedly influence the location of this maximum, it is apparent that the necessary generation of voids in the formulation has been largely overlooked as a primary source for this maximum. A simple parallel strain composite tensile strength model is developed from the different tensile strength components in the composite. For this simple model the tensile strength of the composite is set to go to zero at the 'zero limit' packing fraction. The most important result from this simple model is that a maximum in composite tensile strength is clearly indicated when the tensile strength of the filler is greater than that of the matrix and the transfer efficiency from the filler to the matrix is not near zero. A more detailed generalized tensile strength model is also developed from the existing modulus models. This derivation is initiated from the definition of modulus which includes both stress and strain. The ratio of the tensile yield strength of the composite to that of the matrix is equated to corresponding ratios for yield strain and secant yield modulus. It is assumed that the strain ratio could be described by the reciprocal of a modified Kerner equation and the modulus ratio could be described by the generalized modulus equation developed earlier by this author. This new tensile strength model nicely describes a maximum tensile strength as well as a minimum tensile strength at the zero limit packing fraction. It is clearly shown that the new generalized tensile strength model developed in this study gives a much better fit of four sets of tensile strength data than the Turcsanyi model, the Dibenedetto model and a second-order polynomial model. This result applies equally for data that shows a clear maximum as well as data where the tensile strength decreases steadily from the tensile strength of the matrix itself. [ABSTRACT FROM AUTHOR]

This paper proposes a method of deriving the engineering and strength properties of unidirectional lamina from laminate properties. Simple straight-sided untabbed tension and compression specimens are used to obtain the laminate properties. The derivation approach is an extension of existing methods that use cross-ply or angle-ply test specimens and back-out factors (also known as cross-ply factors) to derive unidirectional lamina strengths in the fiber direction. This method may reduce the cost of testing and improve the accuracy of strength predictions. It may be used to characterize some newer material forms such as two-dimensional braids. [ABSTRACT FROM AUTHOR]

New models for the elastic properties (Young's and shear moduli, bulk modulus, and Poisson s ratio) of two-phase pore-solid composites are developed using the differential effective medium approach (DEMA). Out of the four models developed in the paper, two models predict the elastic properties to be a function of only one variable, that is, porosity (volume fraction of pores). The remaining two models include an additional parameter, namely the maximum packing volume fraction of pores. The proposed models are evaluated using published experimental data on pore-solid composites, covering a broad range of porosity. [ABSTRACT FROM AUTHOR]

The relationship between the statistical characteristics of the microstructure, the stress state in the matrix and the effective properties of unidirectional composites have been studied. A representation of the stress state in the form of stress spectra is introduced. The skewness of spectra derived for the four basic regular periodic fiber arrays reflects the degree of order in the microstructure. A hybrid array combining features of these arrays was developed to approximate a random array. All stress components in the matrix of such a pseudo-random composite under transverse load exhibit an approximately Gaussian distribution. The stress state in the matrix determines the effective elastic modulus and the viscoelastic relaxation strength. This has led to a stress-based mechanical analysis using the moments of the stress spectrum for a representative, pseudo-random fiber arrangement. [ABSTRACT FROM PUBLISHER]

Recently, there has been a growing interest in the use of particulate reinforced composites in a wide variety of applications. Particle reinforced composites are candidate materials for structures where shock or impact loading is expected. The ICAN (Integrated Composites Analyzer) computer code developed at NASA-Glenn Research Center has been modified to include micromechanics equations for particle reinforced composites. In this work, the simplified micromechanics of particulate reinforced composites and a fast probability integration (FPI) technique have been used to obtain the probabilistic composite behavior of a Al/Si Cp (silicon carbide particles in aluminum matrix) composite. The probability density functions for composite moduli, thermal expansion coefficient and thermal conductivities along with their sensitivity factors are computed. The effect of different assumed distributions in constituent properties and the effect of reducing scatter in input random variable on a select composite property-namely the thermal expansion coefficient are also evaluated. The variations in the constituent properties that directly effect these composite properties are accounted for by assumed probabilistic distributions. The results show that the present technique provides valuable information about the scatter in composite properties and sensitivity factors, which are useful to test or design engineers. [ABSTRACT FROM PUBLISHER]

The compressional resilience of Acrilan, Terylene, and Tricel fibers at pressures ranging from 0.001 to 1.0 psi is reported, and the effects on the resilience of various fiber properties are determined experimentally. The behavior of a mass of fibers in compression can be adequately described by an equation of the form: T = aP-b, where T is thickness of the fibrous mass, P is the pressure, and a and b are constants which depend on fiber properties and also on the experimental conditions. Fiber properties investigated were staple length, fineness, crimp and interfiber friction. Crimp has the highest influence on resilience, whereas fiber friction and fineness indicate comparatively less effect. Fiber length shows no correlation with resilience. There is little difference between Acrilan, Terylene, and Tricel as suitable materials for fiberfill. [ABSTRACT FROM PUBLISHER]

Filament winding is an efficient process for manufacturing composite pressure vessels that take advantage of the high structural efficiency of graphite fiber. One critical parameter in evaluating the performance of composite pressure vessels is burst strength. Burst failure in such vessels is primarily a result of fiber breakage. Once fibers start to break, the role of the matrix material becomes increasingly important. The major objective of this study was to investigate the influence of preselected epoxy matrix proper ties on delivered fiber strength and strength variability. It is shown that important matrix variables in determining delivered fiber strength and strength variability are the neat resin fracture toughness** (GIc); elongation at yield (εys); initial modulus (Eo); and strength yield (σ ys) . [ABSTRACT FROM PUBLISHER]

Load-extension measurements were made on wool fibers and yams in steam, air at 100°C, and water at different tem peratures in the range 20-90°C. Samples were subjected to the action of steam, air at 100°C, and water at 90°C for different periods before being loaded in the respective media. It was found that for all three heating media, extensibility passed through a maximum value when wool was elongated in the process of heat absorption. Temperature-dependent transitions in water were found to be around 40° and 70°C for reduced wool. Load-extension measurements of wool in steam showed that the effect of crosslinking treatment can be seen, if comparison is made between the load-extension curves of crosslinked and pretreated wool and not between crosslinked and untreated wool. [ABSTRACT FROM PUBLISHER]

For maximum liquid-holding capacity, an uncompressed fibrous assembly requires wettable fibers of high wet modulus. Tests with rayons of various denier, state of finishing, and modulus indicate that, for compressed absorbents, it also is desirable to minimize the required compaction forces by reducing the dry modulus and resilience of the fibers. The use of wet crosslinked rayon, which has the requisite combination of wet and dry properties, leads to significant improve ments in absorbency.The effect of increasing bulk density on the liquid capacity per unit weight and capacity per unit volume of absorbents is discussed, and a mechanistic description of the latter is presented. [ABSTRACT FROM PUBLISHER]

On treatment with a variety of swelling agents, polyhexamethylene terephthalamide (nylon 6-T) fibers undergo char acteristic changes in tensile properties, x-ray pattern, and dyeability. Microscopically visible voids are permanentlv removed and the uptake of acid and disperse dyestuffs is increased in that portion of the fiber penetrated by the swotting agent. The molecular rearrangement which occurs during this "relaxation" consists of disorientation and probably in volves a change in the relative positioning of successive hydrogen-bonded sheets. It is suggested that the change in dyeing behavior on relaxation consists in general of an increase in extent of the so-called "overdyeing" resulting from the genera tion of additional "vacancies." [ABSTRACT FROM PUBLISHER]