Showing papers in "Journal of Composite Materials in 2009"
TL;DR: In this article, different process parameters during pyrolysis were investigated and optimized in order to provide the reclaimed carbon fibers with properties close to new fibers, and a test on a semi-industrial scale was successfully performed to demonstrate the technical viability of the optimized process parameters.
Abstract: Pyrolysis is a well known method to recover carbon fibers from composite waste. In order to bring these recycled carbon fibers back into new composites, and to provide a 'closed loop' for this material, their properties have to be investigated and proved suitable for new products. In a former study a strong influence of the pyrolysis process on the surface of the recovered fibers was found. This in turn influenced other properties like fiber strength, electrical properties and fiber―matrixadhesion. These results offer the possibility to control individual properties of recycled carbon fibers and their composites, but on the other hand they indicate a necessity for process optimization in order to provide a high quality of the recycled fibers. In this study different process parameters during pyrolysis were investigated and optimized in order to provide the reclaimed carbon fibers with properties close to new fibers. The optimization was done by labscale pyrolysis experiments performed in a thermogravimetric analyzer (TGA), with variation of pyrolysis temperature, isothermal dwell time and oven atmosphere, respectively. The recovered fibers were analyzed by scanning electron microscopy and Raman spectroscopy. Finally a pyrolysis test on a semi-industrial-scale was successfully performed to demonstrate the technical viability of the optimized process parameters.
233 citations
TL;DR: The performance of fiber reinforced polymer (FRP) composites at high temperatures is a serious concern that needs investigation before the incorporation of these composites into important engineeri... as mentioned in this paper.
Abstract: The performance of fiber reinforced polymer (FRP) composites at high temperatures is a serious concern that needs investigation before the incorporation of these composites into important engineeri...
218 citations
TL;DR: In this paper, a series of tensile tests were conducted on a Lloyd LRX tensile testing machine for numerous natural fibers deemed potential candidates for development in composite applications, including jute, kenaf, flax, abaca, sisal, hemp, and coir.
Abstract: A series of tensile tests were conducted on a Lloyd LRX tensile testing machine for numerous natural fibers deemed potential candidates for development in composite applications. The tensile tests were conducted on the fibers jute, kenaf, flax, abaca, sisal, hemp, and coir for samples exposed to moisture conditions of (1) room temperature and humidity, (2) 65% moisture content, (3) 90% moisture content, and (4) soaked fiber. These seven fibers were then tested for the four conditions and the mechanical properties of tensile strength, tensile strain to failure, and Young's modulus were calculated for the results. These results were then compared and verified with those from the literature, with some of the fibers showing distinctly promising potential. Additionally, a study on the effect of alkalization using 3% NaOH solution was carried out on flax, kenaf, abaca, and sisal to observe impact that this common fiber pre-treatment process has on fiber mechanical properties. The result of the investigation indicated that over treatment of natural fibers using NaOH could have a negative effect on the base fiber properties. It is consequently apparent that a treatment time of less than 10 min is sufficient to remove hemicelluloses and to give the optimum effect.
208 citations
TL;DR: In this paper, the fracture energy of hybrid carbon fiber reinforced polymers was investigated and the composites were modified by the addition of multi-walled carbon nanotubes into the matrix material.
Abstract: In the present study, the fracture energy of hybrid carbon fiber reinforced polymers was investigated. The composites were modified by the addition of multi-walled carbon nanotubes into the matrix material. The interlaminar fracture properties under Mode I and Mode II remote loading were studied as a function of the carbon nanotube content in the matrix. With the addition of carbon nanotubes in the epoxy matrix, a significant increase in the load bearing ability as well as in the fracture energy was observed, for both Mode I and Mode II tests. It is speculated that carbon nanotubes due to their large aspect ratio have a significant toughening effect since extra energy is needed in order to pull them out from the matrix and start the crack propagation following a kinking out pattern at nanoscale.
198 citations
TL;DR: In this article, a variationally consistent theory is derived from the virtual work principle and employs a piecewise linear zigzag function that provides a more realistic representation of the deformation states of flexible beams than other similar theories.
Abstract: A new refined theory for laminated composite and sandwich beams that contains the kinematics of the Timoshenko Beam Theory as a proper baseline subset is presented. This variationally consistent theory is derived from the virtual work principle and employs a novel piecewise linear zigzag function that provides a more realistic representation of the deformation states of transverse-shear flexible beams than other similar theories. This new zigzag function is unique in that it vanishes at the top and bottom bounding surfaces of a beam. The formulation does not enforce continuity of the transverse shear stress across the beam s cross-section, yet is robust. Two major shortcomings that are inherent in the previous zigzag theories, shear-force inconsistency and difficulties in simulating clamped boundary conditions, and that have greatly limited the utility of these previous theories are discussed in detail. An approach that has successfully resolved these shortcomings is presented herein. Exact solutions for simply supported and cantilevered beams subjected to static loads are derived and the improved modelling capability of the new zigzag beam theory is demonstrated. In particular, extensive results for thick beams with highly heterogeneous material lay-ups are discussed and compared with corresponding results obtained from elasticity solutions, two other zigzag theories, and high-fidelity finite element analyses. Comparisons with the baseline Timoshenko Beam Theory are also presented. The comparisons clearly show the improved accuracy of the new, refined zigzag theory presented herein over similar existing theories. This new theory can be readily extended to plate and shell structures, and should be useful for obtaining relatively low-cost, accurate estimates of structural response needed to design an important class of high-performance aerospace structures.
179 citations
TL;DR: In this paper, a micromechanics model is developed to assess the impact of the effects of electron hopping and the formation of conductive networks on the electrical conductivity of CNT-polymer nanocomposites.
Abstract: The introduction of carbon nanotubes (CNTs) into nonconducting polymers has been observed to yield orders of magnitude increases in conductivity at very low concentrations of CNTs. These low percolation concentrations have been attributed to both the formation of conductive networks of CNTs within the polymer and to a nanoscale effect associated with the ability of electrons to transfer from one CNT to another known as electron hopping. In the present work, a micromechanics model is developed to assess the impact of the effects of electron hopping and the formation of conductive networks on the electrical conductivity of CNT-polymer nanocomposites. The micromechanics model uses the composite cylinders model as a nanoscale representative volume element where the effects of electron hopping are introduced in the form of a continuum interphase layer, resulting in a distinct percolation concentration associated with electron hopping. Changes in the aspect ratio of the nanoscale representative volume element are used to reflect the changes in nanocomposite conductivity associated with the formation of conductive networks due to the formation of nanotube bundles. The model results are compared with experimental data in the literature for both single- and multi-walled CNT nanocomposites where it is observed that the model developed is able to qualitatively explain the relative impact of electron hopping and nanotube bundling on the nanocomposite conductivity and percolation concentrations.
168 citations
TL;DR: In this article, a natural polyol was prepared from castor oil by alcoholysis with triethanolamine, which was subsequently used as the polyol component in the formulation of rigid polyurethane foams.
Abstract: A natural polyol was prepared from castor oil by alcoholysis with triethanolamine. The oil and the oil-based polyol were characterized by infrared spectroscopy and through the analytical determination of their functional groups, both techniques indicating that the hydroxyl content increased significantly after the alcoholysis reaction. The modified oil was subsequently used as the polyol component in the formulation of rigid polyurethane foams. Wood flour was chosen to be incorporated as filler in these materials. Physical, thermal, and mechanical properties of the neat and reinforced foams were measured, analyzed, and compared to a reference commercial system. The chemical reaction between wood flour and isocyanate strongly affected the composites’ response to thermo-gravimetric tests. Compression modulus and yield strength decreased as wood flour content increased. The effect of the foam density on the compression properties was also investigated.
150 citations
TL;DR: The performance of continuum material models for mesolevel modeling of progressive failure in composite laminates is examined in this paper, where two different continuum models are used: a continuum damage model and a softening plasticity model.
Abstract: The performance of continuum material models for mesolevel modeling of progressive failure in composite laminates is examined. Two different continuum models are used: a continuum damage model and a softening plasticity model. It is shown how mesh-independent results can be obtained with both models by introducing a viscosity term. The capability of the models to represent complex intraply failure behavior is assessed by means of an analysis of a notched plate, where interface elements are used to model delamination. Proper results from different modeling approaches are shown, but upon calibration a limitation of the continuum approach in the representation of matrix failure is encountered. With a second example, this limitation is emphasized further and explained as a consequence of the homogenization that is inherent in continuum models, irrespective of the applied failure criteria and material degradation laws.
150 citations
TL;DR: In this paper, the influence of physical treatment on morphology, wettability, fine structure of fibers and its impact on the interfacial adhesion of natural fiber-reinforced thermosets was studied.
Abstract: The aim of this article is to study the influence of physical treatment on morphology, wettability, fine structure of fibers and its impact on the interfacial adhesion of natural fiber-reinforced thermosets. For that purpose, jute fibers were treated with argon cold plasma for 5, 10, and 15 min and processed for composite with unsaturated polyester resin. Scanning electron microscopy (SEM) micrograph had shown the rough surface morphology and degradation of fiber due to etching mechanism causes by plasma. Surface properties of fibers before and after treatment were determined by mean of contact angle determination and fine structural details by Fourier transform infrared-spectroscopy (FT-IR). Plasma treatment resulted in the development of hydrophobicity in fibers, that is contact angle were found increasing with water. This could be due to the decrease in phenolic and secondary alcoholic groups or oxidation of basic structural component, lignin and hemicelluloses after plasma treatment as studied by FTIR...
136 citations
TL;DR: In this paper, the authors presented analytical models for the Mode I interlaminar fracture of laminated composites reinforced with aligned carbon nanotubes (CNTs), where the aligned CNTs enhance toughness mechanistically through either pullout (frictional sliding) from the matrix or sword-in-sheath sliding.
Abstract: Analytical models are presented for the Mode I interlaminar fracture of laminated composites reinforced with aligned carbon nanotubes (CNTs). The models are based on the crack-closure technique for fiber bridging, where the aligned CNTs enhance toughness mechanistically through either pullout (frictional sliding) from the matrix or sword-in-sheath sliding. The models are independent of the scale of reinforcement and demonstrate significant enhanced toughening for nanoscale reinforcement (CNTs) as opposed to typical mm-scale reinforcements (stitches and Z-pins). Complete analytical expressions for crack-growth resistance (GR(Δa)) are obtained including normalized closed-form expressions for steady-state toughness for any scale of z-direction fiber reinforcement. The model is verified by comparison to previous experimental results for Z-pins and also aligned CNTs, and is used to define regimes where the competing mechanisms of toughening are operative. CNT strength is a key parameter limiting toughness enha...
136 citations
TL;DR: In this paper, the effects of tow width, laminate thickness and staggering in combination with tow-drop areas are studied by making use of finite element simulations, and the expressions for implementing the tow drop areas in a finite element model are given.
Abstract: Variable-stiffness laminates that have fiber orientation variation across its planform can be manufactured using advanced fiber placement technology. For such laminates, successive passes of the fiber placement head often overlap resulting in thickness build-up. If a constant thickness is desired, tows will be cut at the course boundary, which can result in small triangular resin-rich areas without any fibers. In this article a theoretical, numerical investigation of the influence of these tow-drop areas on the strength and stiffness of variable-stiffness laminates is performed. The effects of tow width, laminate thickness and staggering in combination with tow-drop areas are studied by making use of finite element simulations. A method for the localization of tow-drop areas is presented, and the expressions for implementing the tow-drop areas in a finite element model are given. Subsequently, progressive failure analyses using the LaRC failure criteria are performed. Failure occurs at tow-drop locations ...
TL;DR: In this article, the effects of chemical modification (silane coupling) and filler loading on the fundamental properties of the bamboo fiber (BF) filled polypropylene (PP) bio-composites were investigated.
Abstract: The effects of chemical modification (silane coupling) and filler loading on the fundamental properties of the bamboo fiber (BF) filled polypropylene (PP) bio-composites were investigated in this study. Mechanical properties of the PP/ BF composites, such as the tensile strength, flexural strength, and impact strength decreased as BF loading increased. However, the tensile modulus, flexural modulus, and water absorption were increased by the increase of the BF loading. The addition of aminopropyltrimethoxysilane (AS) and tetramethoxy orthosilicate (TMOS) after the alkali pretreatment for the BF increased all the tensile, flexural, impact strength, and water desorption of the resultant composites, resulting from the improved adhesion between the BF and PP matrix. This tendency was more obvious with the increase of the BF loading. The melting temperature, melting enthalpy, crystallization enthalpy, and crystallinity were decreased by the increase of BF loading and the AS and TMOS treatments. One the other h...
TL;DR: In this paper, the effect of the particle size of silica colloidal suspension (SCS) in SCS-impregnated plain woven fabrics on the ballistic performance of those fabrics was investigated.
Abstract: This study investigated the effect of the particle size of silica colloidal suspension (SCS) in SCS-impregnated plain woven fabrics on the ballistic performance of those fabrics. In order to examine the particle size effect, spherical silica particles with average diameters of 100 nm, 300 nm, and 500 nm were used to fabricate SCS. The SCS-impregnated fabrics were subjected to ballistic tests under various boundary conditions. The fabric impregnated with SCS produced using silica particles with an average particle diameter of 100 nm showed better impact performance than those of the SCS-impregnated fabrics containing larger particles and untreated fabrics in terms of impact energy absorption and resistance to blunt trauma, while earlier failure of their primary yarns in the impacted zone under fully clamped conditions was also observed. The results of the drop impact test and yarn pull-out tests indicated that SCS-impregnated fabric with smaller particles exhibits the largest increment of inter-yarn fricti...
TL;DR: In this article, a family of router milling tools for the high-performance milling of carbon fiber reinforced plastics is presented, which are shaped by multiple left-hand and right-hand helical edges, which form small pyramids along the cutting length.
Abstract: This article deals with the new development of a family of router milling tools for the high-performance milling of carbon fiber reinforced plastics. The new milling tools are shaped by multiple left-hand and right-hand helical edges, which form small pyramidal edges along the cutting length. Several substrates and coatings have been tested including AlTiN and the new naCO with nanocrystalline structure. After the analysis of tests and modifications on the tool prototypes, the final result is a series of routing endmills optimized for carbon fiber composites defining the influence of each of milling tool features on tool performance, which was not clearly established till date. The specific cutting forces, tool wear, and others aspects are discussed in detail.
TL;DR: In this paper, the elastic modulus of discontinuous carbon fiber/epoxy laminates produced by compression molding of chopped unidirectional prepreg tape is measured by several means.
Abstract: The elastic modulus of discontinuous carbon fiber/epoxy laminates produced by compression molding of chopped unidirectional prepreg tape is measured by several means. Commercial applications for this type of material form already exist, such as Hexcel HexMC®. Although the average elastic modulus of this material has been shown to be as high as that of the continuous fiber quasiisotropic benchmark, its non-homogenous nature gives rise to variations as high as 19% in the measurement by means of strain gage or extensometer. This phenomenon would be attributed to the variability of the manufacturing process, were it not for the fact that strength variation is much lower, with a maximum of 9%. In order to assess whether the variation observed is a result of the measurement technique and not an actual variation in material properties, a series of tensile tests is conducted while systematically varying strain gage length and location. The measurements are then compared relative to each other as well as to multip...
TL;DR: In this article, the effect of voids on the strength of composite laminates has been investigated in terms of the fracture parameters involved in the fracture criterion and the critical void content has been estimated for each case both for void content and ultrasonic attenuation.
Abstract: An experimental program to characterize the effect of voids on the strength of composite laminates is presented. The adequacy of a fracture criterion to represent the experimental data for the effect of voids on the flexure strength, tensile strength, and interlaminar shear strength of composite laminates is assessed. The experimental program investigates the effect of different pressures and dwell times on the critical void content. Laminates produced with carbon fiber/epoxy resin unidirectional prepreg have been produced with an intentionally high void content. Short beam shear, three-point flexure, and tensile testing are used for mechanical evaluation and the results correlate to void volume fraction and ultrasonic absorption coefficient. The ultrasonic absorption coefficient is measured for all the specimens and its variation is approximately linear with the void content, corroborating previous experimental results. The effects of these factors on the strength of the composite laminates are discussed in terms of the fracture parameters involved in the fracture criterion. The critical void content is estimated for each case both in terms of void content and ultrasonic attenuation.
TL;DR: In this article, the authors demonstrate the construction of a multifunctional composite structure capable of energy storage in addition to load bearing, which was assembled and integrated within the co-carrier.
Abstract: This study demonstrates the construction of a multifunctional composite structure capable of energy storage in addition to load bearing. These structures were assembled and integrated within the co...
TL;DR: In this paper, the feasibility of applying two kinds of mudar (Calotropis gigantea) fibers, namely bark fibers and seed fibers, as an alternative raw material for fiber-reinforced composite (FRC) is investigated.
Abstract: In this study the feasibility of applying two kinds of mudar (Calotropis gigantea) fibers, namely bark fibers and seed fibers, as an alternative raw material for fiber-reinforced composite (FRC) is investigated. The chemical analysis of the bark and seed fibers indicates that their main components are holocellulose 76 and 69%, cellulose 57 and 49%, lignin 18 and 23%, and alkali soluble substances 17 and 15%, respectively. There are statistically significant differences in the bark and seed fiber dimensions. The bark fibers are long, with a thin wall relative to their diameter, and are therefore lightweight. The seed and bark fibers are very similar to hard- and soft-woods, in terms of chemical compositions and fiber dimensions, respectively. The mechanical properties of the mudar bark fibers are: tensile strength 381 MPa, strain at break 2.1% and Young's modulus 9.7 GPa. In general, both types of fibers have enough potential for replacing or supplementing other fibrous raw materials as reinforcing agent.
TL;DR: In this article, two kinds of rubber particles, one is the reactive liquid rubber (CTBN) and the other is the core-shell rubber (CSR), were employed to modify the fracture toughness of epoxy resin.
Abstract: The research aims to investigate the interlaminar fracture toughness of glass fiber/epoxy composites, which consist of the silica nanoparticles and the rubber particles. Two kinds of rubber particles, one is the reactive liquid rubber (CTBN) and the other is the core-shell rubber (CSR), were employed to modify the fracture toughness of epoxy resin. In general, the disadvantage of adding rubber particles into polymeric resin is the dramatic reduction of stiffness although the toughness could be modified accordingly. In order to enhance the fracture toughness of the fiber composites without sacrificing their stiffness, the silica nanoparticles in conjunction with the rubber particles were introduced into the epoxy matrix to form a hybrid nanocomposite. Experimental results obtained from tensile tests on bulk epoxy confirm the presumption that the reduction of the epoxy stiffness because of the presence of rubber particles can be effectively compensated by the silica nanoparticles. Furthermore, the fracture ...
TL;DR: In this paper, a review is provided on the underlying mechanisms of and the advantages arising from UV/O3 treatment of polymer substrates and nanoscale carbon materials, and a relation is placed on the relation.
Abstract: Dry oxidizing methods have been widely used to modify surface properties of polymer and ceramic substrates. Compared to other dry oxidizing methods, ultraviolet light/ozone (UV/O3) treatment has hitherto attracted less attention, mainly due to relatively weak oxidizing power. With optimized processing conditions, however, UV/O3 treatment can be better capable of offering desired effects associated with appropriate surface modifications. Incorporation of nanoscale reinforcements, e.g., carbon nanotubes (CNTs) and graphite, into a polymer matrix creates a new class of composites that possess unique mechanical and functional capabilities. A proper surface treatment is critical to dispersing the reinforcements in the matrix, hence to provide adequate adhesion between the reinforcements and the matrix. In this article, a review is provided on the underlying mechanisms of and the advantages arising from UV/O3 treatment of polymer substrates and nanoscale carbon materials. Special focus is placed on the relation...
TL;DR: In this article, the fracture behavior of multilayered unidirectional graphite/epoxy composite (T800/3900-2) materials is investigated under geometrically symmetric loading configurations and impact loading conditions.
Abstract: In this work, fracture behavior of multilayered unidirectional graphite/epoxy composite (T800/3900-2) materials is investigated. Rectangular coupons with a single-edged notch are studied under geometrically symmetric loading configurations and impact loading conditions. The notch orientation parallel to or at an angle to the fiber orientation is considered to produce mode-I or mixed-mode (mode-I and -II) fracture. Feasibility of studying stress-wave induced crack initiation and rapid crack growth in fiber-reinforced composites using the digital image correlation method and high-speed photography is demonstrated. Analysis of photographed random speckles on specimen surface provides information pertaining to crack growth history as well as surface deformations in the crack-tip vicinity. Measured deformation fields are used to estimate mixed-mode fracture parameters and examine the effect of fiber orientation (β) on crack initiation and growth behaviors. The samples show differences in fracture responses dep...
TL;DR: In this paper, the assumption of equal tensile and compressive modulus necessary to determine single fiber axial compressive strength from the elastica loop test is relaxed by deriving a compressivestrength equation based on the analysis of the flexural response of a fiber with different modulus in tension and compression.
Abstract: The assumption of equal tensile and compressive modulus necessary to determine single fiber axial compressive strength from the elastica loop test is relaxed by deriving a compressive strength equation based on the analysis of the flexural response of a fiber with different modulus in tension and compression. Previously determined tensile (E1t) and compressive (E1c ) modulus values for different high performance organic fibers with varying degrees of lateral molecular interactions are used to determine fiber compressive strength. The importance of using the bi-moduli equation becomes evident in the case of fibers that lack strong intermolecular interactions, since calculations done with the original loop test equation can result in an overestimation of the compressive strength on the order of 80%, as seen for the poly-(p-phenylene benzobisoxazole) fiber PBO. Kink band angles measured from looped fiber specimens are documented and correlated to the calculated compressive strength values.
TL;DR: In this paper, the effects of the fiber content (55, 70, and 85 wt%) and compatibilizing agent (0, 2, and 4 wt) concentration on the mechanical properties and water absorption were evaluated.
Abstract: This article deals with experimental investigation of composites based on recycled high-density polyethylene (RHDPE) and poplar fibers (Populus deltoids) formed by air-forming and hot-pressing. The effects of the fiber content (55, 70, and 85 wt%) and compatibilizing agent (0, 2, and 4 wt%) concentration on the mechanical properties and water absorption were evaluated. The use of polyethylene-grafted maleic anhydride (PE-g-MA) improved the compatibility between the fiber and RHDPE. Adding PE-g-MA at 2 and 4 wt% in the composite formulation significantly improved both the stability and mechanical properties. The tensile strength of the composites containing PE-g-MA was superior to those of the composites without compatibilizing agent. As expected, the flexural of the composites increased with the wood content. Low internal bond strength was observed for the panels with different fiber loading and compatibilizing agent content in our study.
TL;DR: Carbon fiber reinforced plastic (CFRP) composite materials are finding increased applications in many industries due to their excellent properties as mentioned in this paper.Drilling of CFRP composites is needed for joining...
Abstract: Carbon fiber reinforced plastic (CFRP) composite materials are finding increased applications in many industries due to their excellent properties. Drilling of CFRP composites is needed for joining...
TL;DR: In this article, the effects of nanoclay (layered silicate) loading (0, 2, 4, 6, 8 wt%) as reinforcement filler and press temperature (165 and 175C) on the properties of laboratory made medium density fiberboard (MDF) boards were investigated.
Abstract: In this study, the effects of nanoclay (layered silicate) loading (0, 2, 4, 6, 8 wt%) as reinforcement filler and press temperature (165 and 175C) on the properties of laboratory made medium density fiberboard (MDF) boards were inves- tigated. Physical (thickness swelling) and mechanical properties of the boards were determined according to the procedure of European Norm standards. The results showed considerable improvement in mechanical properties, specifically in bending strength and internal bond strength of the boards as nanoclay was loaded from 2 to 6 wt% to the boards' furnishes. The boards with 6 wt% nanoclay content showed the optimized mechanical properties. There was a clear trend that both thickness swell- ing (after 2 and 24 h water soaking) decreased with addition of nanoclay and press temperature. The increasing press temperature had strong positive effect on all phy- sicomechanical properties of the boards. Thus, the data showed that nanoclay can enhance mechanical strength and water stability properties of MDF boards.
TL;DR: In this paper, a model for predicting composite material strength degradation under elevated and high temperatures is proposed, which is based on the morphology of the mixture of materials in different states, and the degradation of nominal compressive strength tends to follow the lower bound of strength defined by the inverse rule of mixture.
Abstract: A model for predicting composite material strength degradation under elevated and high temperatures is proposed. This model is based on the morphology of the mixture of materials in different states. The degradation of resin-dominated shear strength can be well described by the rule of mixture while the degradation of nominal compressive strength tends to follow the lower bound of strength defined by the inverse rule of mixture. Composite materials under tension may exhibit fiber- or resin- dominated behavior. In a lower temperature range, strength is dominated by the fiber tensile strength, while at higher temperatures, tensile components may exhibit resin- dominated failure in joint regions. The parameters required in the model can be obtained on the basis of kinetic analysis of dynamic mechanical analysis results. The fitting of experimental curves of material strength degradation is not necessary. The proposed modeling scheme can easily be incorporated into structural theory to predict mechanical responses and time-to-failure. © 2009 SAGE Publications
TL;DR: In this article, a 3D finite element model of a Kevlar KM2® plain woven fabric was developed for examining ballistic impact from a spherical projectile, including friction between the individual yarns as well as the projectile and fabric.
Abstract: This study focuses on developing a global/local three-dimensional (3D) finite element model of a Kevlar KM2® plain woven fabric applicable for examining ballistic impact from a spherical projectile. The impact event is modeled in LS-DYNA® including friction between the individual yarns as well as the projectile and fabric. When compared with the predictive capabilities of a 3D finite element model that includes the detailed undulating representation of the fabric architecture over the entire solution domain, the savings in computational effort afforded by the global/local model become especially attractive. The agreement with fully detailed 3D finite element simulations and ballistic experiments is also demonstrated.
TL;DR: In this article, the chemical composition (cellulose, lignin, hot water, and ethanol/ cyclohexane extractive contents) of acacia, eucalyptus, pine, and oak and the morphological properties such as wood fiber length distribution were determined in order to investigate this effect.
Abstract: Different wood species can be expected to affect the properties of wood—polymer composites (WPCs) differently, as they have different chemical compositions. The chemical composition (cellulose, lignin, hot water, and ethanol/ cyclohexane extractive contents) of acacia, eucalyptus, pine, and oak and the morphological properties such as wood fiber length distribution were determined in order to investigate this effect. Composites of linear low-density polyethylene and 10 wt% of each of the wood species were prepared, using polyvinyl alcohol-co-ethylene as a compatibilizer. Significant differences were found between the wood species in terms of both chemical composition and wood fiber length distribution. These affected the properties of the WPCs in different ways. Use of acacia resulted in a WPC with superior mechanical properties and thermal stability compared with the other species, due to its higher cellulose and lignin contents and a favorable wood fiber length distribution; however, acacia composites a...
TL;DR: In this paper, the analysis of dynamic mechanical properties of hollow particle filled composites, called syntactic foams, was carried out and a theoretical model was developed to predict the dynamic mechanical behavior of these composites.
Abstract: This study entails the analysis of dynamic mechanical properties of hollow particle filled composites, called syntactic foams. A theoretical model is developed to predict the dynamic mechanical beh...
TL;DR: In this paper, the influence of interlayer delaminations on the static and fatigue behavior of composite laminates was investigated using finite element analysis, and the effect of angular misalignments on the laminate stiffness and strength was shown.
Abstract: This article presents the results of a current study on the influence of interlayer delaminations on the static and fatigue behavior of composite laminates. The composite was manufactured by a vacuum molding method using 12 balanced bi-directional carbon fiber layers and epoxy resin. Delaminations with different length were artificially introduced. The specimens with dog bone shape were cut from the original plates having 3 mm thickness and fiber weight fraction of 0.66. Static tests were performed in order to study the influence of delamination size on the laminate stiffness and strength. Complementary finite element analysis was carried out showing the influence of angular misalignments of fiber/matrix delaminations on the laminate stiffness. Fatigue tests were performed in load control for R = 0.05 and R = —1, with a loading frequency of 10 Hz, at room temperature. The artificial interlayer delaminations have a negligible influence on the fatigue strength for tensile cycle loadings, but produce signifi...