Showing papers in "Journal of Composite Materials in 2010"
TL;DR: In this paper, a program of scaled tests on unnotched and open-hole tension and compression specimens is summarized, with both strength and failure mechanisms changing with specimen size and the thickness scaling method having a particularly important effect.
Abstract: A program of scaled tests on unnotched and open-hole tension and compression specimens is summarized. Quasi-isotropic IM7/8552 carbon-fiber epoxy specimens have been tested using two different scaling techniques: sub-laminate-level ([45/90/ - 45/0]ns) and ply-level scaling ([45n/90 n/ - 45n/0n]s), independently varying the thickness and in-plane dimensions. Significant scaling effects are shown, with both strength and failure mechanisms changing with specimen size and the thickness scaling method having a particularly important effect. Failure mechanisms and scaling behavior are compared between tension and compression and models presented that predict the observed size effects from fundamental material parameters without any fitting factors.
141 citations
TL;DR: In this article, the properties of kenaf/phenol-formaldehyde (PF), fiberfrax/PF, and hybrid PF composites have been investigated as a function of fiber loading.
Abstract: In this study, mechanical properties such as tensile characteristics, flexural characteristics, impact strengths, and hardness of kenaf/phenol-formaldehyde (PF), fiberfrax/PF, and kenaf/fiberfrax hybrid PF composites have been investigated as a function of fiber loading. Composite samples were prepared by mixing the fibers and resin in a mixing chamber for 5 min. The composite sheets were prepared by pressing fiber-resin material in a steel mold at 120°C for 30 min at 10 MPa pressure. The test samples were cut from the composite sheets. At least five specimens were tested and mean value was taken for each composite according to ASTM standards. The reinforcing effects of kenaf and fiberfrax fibers were evaluated at various fiber loadings, that is, 19, 28, 36, 43, 52, and 62 vol. %. The hybrid effect of kenaf and fiberfrax fiber on the tensile, flexural, impact strengths, and hardness was also investigated for various ratios of kenaf/fiberfrax fiber loadings ranging between 1 : 0 and 0 : 1. Total fiber load...
115 citations
TL;DR: In this article, a comprehensive methodology is presented to characterize the main processing properties of a thermoset resin system, including thermal, chemorheological, and thermomechanical properties of the CYCOM 890 RTM epoxy resin.
Abstract: The resin characterization is a key element in the manufacturing of composite materials. Resin processing properties and their associated constitutive models are essential in order to define and optimize the processing parameters and predict the final properties of a composite structure. In this article, a comprehensive methodology is presented to characterize the main processing properties of a thermoset resin system. As a case study, the thermal, chemorheological, and thermomechanical properties of the CYCOM 890RTM epoxy resin were investigated. A cure kinetics model taking into account the diffusion was found to accurately predict resin cure kinetics behavior within the processing condition range. The developed resin rheological model accurately predicted the onset of resin gelation and the evolution of resin viscosity with temperature and degree-of-cure. The glass transition temperature and instantaneous elastic modulus were determined using also a rheometer in a solid torsion mode. Finally, volumetri...
111 citations
TL;DR: In this paper, the epoxy-based hybrid composites were developed by combining the sisal and glass fibers into epoxy matrix, and the aforementioned properties were optimally improved at 2 cm fiber length when compared with 1 and 3 cm fiber lengths.
Abstract: In this article, the epoxy-based hybrid composites were developed by combining the sisal and glass fibers into epoxy matrix. Hardness, impact strength, frictional coefficient, and chemical resistance of hybrid composites with and without alkali treatments were studied. Variation of the aforementioned mechanical proper- ties and chemical resistance was studied with different fiber lengths such as 1, 2, and 3 cm. A 9 vol.% of the sisal and glass fibers was reinforced into the epoxy matrix. The aforementioned mechanical properties were optimally improved at 2-cm fiber length when compared with 1 and 3 cm fiber lengths. Chemical resistance was also significantly improved for all chemicals except sodium carbonates and toluene.
109 citations
TL;DR: In this article, a hyperelastic constitutive model for textile composite reinforcement at large strain is proposed, which is the addition of two tension and one shear energies, which exhibits weak elongations in the fiber directions and large angular variations in the fabric plane.
Abstract: A hyperelastic constitutive model is developed for textile composite reinforcement at large strain. A potential is proposed, which is the addition of two tension and one shear energies. The proposed potential is a function of the right Cauchy Green and structural tensor invariants whose choice corresponds to textile composite reinforcement mechanical behavior which exhibits weak elongations in the fiber directions and large angular variations in the fabric plane.The model is implemented in a Vumat user routine of ABAQUS/Explicit. Some elementary tests are performed in order to identify the model and verify its validity. It is then used to simulate the hemispherical punch forming of balanced and unbalanced fabrics. A correct agreement is obtained with experimental forming processes.
106 citations
TL;DR: In this paper, Al-45% Cu alloy was used as the matrix and fly ash and silicon carbide (SiC) as reinforcements for the hybrid metal matrix composite was produced using conventional foundry techniques.
Abstract: Metal matrix composites are engineered materials with a combination of two or more dissimilar materials, (at least one of which is a metal) to obtain enhanced properties In the present investigation Al-45% Cu alloy was used as the matrix and fly ash and silicon carbide (SiC) as reinforcements The hybrid metal matrix composite was produced using conventional foundry techniques The fly ash and SiC were added in 5%, 10%, and 15% by weight (equal proportion) to the molten metal The hybrid composite was tested for fluidity, hardness, density, mechanical properties, impact strength, dry sliding wear, slurry erosive wear, and corrosion The microstructure examination was done using scanning electron microscope to assess the distribution of particulates in the aluminum matrix The results show that there is an increase in hardness with increase in the particulates content The density decreases with increase in fly ash and SiC content The tensile strength, compression strength, and impact strength increases
101 citations
TL;DR: In this article, a solution based on an artificial neural network is employed in the analysis of the radiographic images to evaluate the delamination caused by carbon/epoxy laminates by drilling.
Abstract: Drilling carbon/epoxy laminates is a common operation in manufacturing and assembly. However, it is necessary to adapt the drilling operations to the drilling tools correctly to avoid the high risk of delamination. Delamination can severely affect the mechanical properties of the parts produced. Production of high quality holes with minimal damage is a key challenge. In this article, delamination caused in laminate plates by drilling is evaluated from radiographic images. To accomplish this goal, a novel solution based on an artificial neural network is employed in the analysis of the radiographic images.
98 citations
TL;DR: In this paper, a model predicting the effective thermal conductivity of filled polymer composites is proposed on the basis of the percolation theory, which is based on the shape and distribution of fillers.
Abstract: In view of the shape and distribution of fillers, a model predicting the effective thermal conductivity of filled polymer composites is proposed on the basis of the percolation theory. Compared to other models proposed in the literatures, theoretical results obtained with the percolation model agree better with the experimental data. Methods of determining the percolation threshold Vc and the exponent n in the percolation model are also discussed.
91 citations
TL;DR: In this article, the properties of flax fiber-reinforced composites were discussed with respect to their tensile properties and their properties of the fiber and the matrix (unsatured polyester), and the similarity of the tensile curves of the composites and of the elementary fibers was attributed to the good adhesion of the fibers with the matrix.
Abstract: Flax fibers were used to process unidirectional composites by two different methods. Their mechanical properties obtained by tensile testing are discussed with respect to the properties of the fibers and those of the matrix (unsatured polyester). The similarity of the tensile curves of the composites and of the elementary fibers is attributed to the good adhesion of the fibers with the matrix. Moreover, as there is almost a linear evolution of the composite properties with the fiber volume fraction, these properties are used to estimate those of the real reinforcement material, that is, the flax bundles: the calculations lead to a fiber strength of 500-800 MPa and a fiber modulus of roughly 30 GPa, which is half the values obtained by tensile testing elementary fibers. These data may be helpful when trying to model the deformation behavior of flax fiber-reinforced composites.
89 citations
TL;DR: In this paper, a new type of bistable laminate is presented which has a symmetric lay-up, which derives from an unsymmetric fiber prestress applied to the laminate.
Abstract: The bistability of unsymmetric cross-ply [0n/90n] T laminates has already been investigated in much detail. In this work a new type of bistable laminate is presented which has a symmetric lay-up. Bistability derives from an unsymmetric fiber prestress applied to the laminate. The experimental procedure used to apply this fiber prestress is presented in detail. Experimental results are compared with analytical and finite element models which have the ability to model fiber prestress accurately. As well as having minimal hygrothermal variability, it is noted that the snap-through loads for a prestressed symmetric laminate can be much higher than its unstressed [0n/90n]T equivalent.
87 citations
TL;DR: In this paper, the flexural behavior of a new sandwich panel proposed for cladding of buildings is studied, which is fabricated by laminating two glass fiber-reinforced polymer skins to a prefabricated polyurethane foam core.
Abstract: The flexural behavior of a new sandwich panel proposed for cladding of buildings is studied. The panel is fabricated by laminating two glass fiber-reinforced polymer skins to a prefabricated polyurethane foam core. Two different densities for the core are explored, namely; a 0.31 kN/m3, referred to herein as ‘soft’ foam, and a 0.63 kN/m3, referred to as ‘hard’ foam. Ten 1500 × 300 × 76 mm3 panels were tested in flexure. For each core density, three similar panels were tested to establish the reproducibility of test results as a measure of quality control of fabrication. The panels were tested in three-point and four-point bending as well as under uniform load. The effect of wind pressure and suction was simulated for some panels by applying cyclic bending. It was shown that flexural strength and stiffness increased substantially, by 165% and 113%, respectively, as the core density was doubled. The contributions of shear deformation of the soft and hard cores to mid-span deflection were 75% and 50%, respec...
TL;DR: In this paper, a thermosetting epoxy-polymer was modified by incorporating 9 wt% of carboxyl-terminated butadiene-acrylonitrile rubber microparticles and 10 wt percent of silica nanoparticles.
Abstract: A thermosetting epoxy-polymer was modified by incorporating 9 wt% of carboxyl-terminated butadiene-acrylonitrile rubber microparticles and 10 wt% of silica nanoparticles. The tensile fatigue behavi...
TL;DR: In this paper, the behavior of concrete cylinders externally wrapped with fiber-reinforced polymer (FRP) composites and internally reinstalled with concrete blocks is investigated. But the results of an experimental and analytical study are limited.
Abstract: This article presents the results of an experimental and analytical study on the behavior of concrete cylinders externally wrapped with fiber-reinforced polymer (FRP) composites and internally rein...
TL;DR: In this article, the impact behavior of hybrid laminates manufactured by RTM with woven carbon and glass fabrics was studied using X-ray microtomography, and the results of these analyses, together with those of the impact tests, were used to elucidate the role played by glass fiber hybridization on the fracture micromechanisms and on the overall laminate performance under low-velocity impact.
Abstract: The low-velocity impact behavior was studied in hybrid laminates manufactured by RTM with woven carbon and glass (S2) fabrics. Specimens with different thicknesses and glass fiber content (from 0 to 21 vol.%) were tested with impact energies in the range 30-245 J and the resulting deformation and fracture micromechanisms were studied using X-ray microtomography. The results of these analyses, together with those of the impact tests (maximum load and energy absorbed), were used to elucidate the role played by glass fiber hybridization on the fracture micromechanisms and on the overall laminate performance under low-velocity impact.
TL;DR: In this article, the authors investigated the mechanical properties of epoxy-based nanocomposites reinforced with spherical nanoparticles and found that the in-plane shear strength increases with the increment of particulate inclusions.
Abstract: The research is aimed to investigate the mechanical behaviors of epoxy-based nanocomposites reinforced with spherical nanoparticles. Five differ- ent contents of silica nanoparticles 5, 10, 15, 20, and 40 wt% were introduced in the samples. Through a solgel technique, the silica particles with a diameter of 25 nm were exfoliated uniformly in the epoxy matrix. Experimental results obtained from tensile tests indicate that the modulus of nanocomposites increases with the increment of particulate inclusions, and the enhancing behavior is coincided with the model predictions obtained from the MoriTanaka micromechanical model. In addition, the fracture tests conducted on single-edge-notch bending specimens reveal that the inclusion of nanoparticles can effectively increase the fracture tough- ness of the nanocomposites. Furthermore, the extent of the enhancement is more appreciable in the brittle matrix system rather than in the ductile matrix system. Subsequently, by inserting the silica epoxy mixture into the unidirectional glass fiber through a vacuum hand lay-up process, the glass fiber/silica/epoxy composite samples were fabricated. Results depicted that the in-plane shear strength increases until the increment of particle loadings are up to 10 wt%. In addition, results obtained from the compression tests revealed that the glass/epoxy specimens with 20 wt% silica loading exhibit superior compressive strengths than those that do not contain any silica particles.
TL;DR: In this paper, the effect of silane concentrations (0.1, 0.3, and 0.5%) on tensile properties, flexural properties, and interlaminar shear strength was investigated.
Abstract: In this study, jute/polyester composites were fabricated. To improve the adhesion between jute fabric and polyester alkali-treated jute fabrics were treated with γ-methacryloxypropyltrimethoxysilane (γ-MPS). The effect of silane concentrations (0.1%, 0.3%, and 0.5%) on tensile properties, flexural properties, and interlaminar shear strength was investigated. Once jute fabrics were treated with 0.1% and 0.3% silane concentrations, the tensile properties of silane-treated jute polyester composites increased. However, when 0.5% γ-MPS was used in silane treatment, the tensile properties of jute/polyester composites decreased. 0.3% silane-treated jute/polyester composites exhibited superior improvements in terms of the flexure properties among the fabricated composites. Interlaminar shear strength measurements showed that best adhesion was provided by using 0.3% silane-treated jute/polyester composites. Good adhesion between silane-treated jute fabric and polyester was also confirmed by scanning electron micro...
TL;DR: In this paper, the authors examine the advances in fabrication techniques, characterization, and new theoretical and computational tools for guiding design that are leading to systems with greater functionality and complexity, which can be used for self-healing, self-cooling, and structural damage sensing.
Abstract: Microvascular networks show promise for applications such as self- healing, self-cooling, and structural damage sensing. Fluid-filled micro-scale channels have been investigated extensively in the field of microfluidics, but three- dimensional networks in polymeric structural materials have been achieved only recently. The purpose of microvascular network integration is to provide a vehicle for the distribution and replenishment of active fluids throughout a matrix material enabling multifunctional operation. This perspective seeks to examine the advances in fabrication techniques, characterization, and new theoretical and computational tools for guiding design that are leading to systems with greater functionality and complexity.
TL;DR: In this article, a series of papers on the thermo-mechanical responses of fiber-reinforced composites at elevated temperatures reports the exper- imental results required as input data in order to validate the kinetic, heat transfer, and thermodynamic models being developed.
Abstract: This first part of a series of papers on the thermo-mechanical responses of fiber-reinforced composites at elevated temperatures reports the exper- imental results required as input data in order to validate the kinetic, heat transfer, and thermo-mechanical models being developed and to be discussed in subsequent papers. Here the experimental techniques used for the determination of physical, thermal, and mechanical properties and their significance for particular models are discussed. The fire retardant system used to improve the fire performance of glass fiber-reinforced epoxy composites is a combination of a cellulosic charring agent and an interactive intumescent, melamine phosphate. Thermogravimetry is used to obtain kinetic parameters and to evaluate the temperature-dependent physical prop- erties such as density, thermal conductivity, and specific heat capacity, determined using other techniques. During flammability evaluation under a cone calorimeter at 50 kW/m 2 heat flux, thermocouples are used to measure temperatures through the thicknesses of samples. To investigate their thermo-mechanical behavior, the com- posites are exposed to different heating environments and their residual flexural modulus after cooling to ambient temperatures determined. At a low heating rate of 10 � C/min and convective conditions, there was a minimal effect of fire retardant additives on mechanical property retention, indicating that fire retardants have no effect on the glass transition temperature of the resin. On the other hand, the fire- retarded coupons exposed to a radiant heat from cone calorimeter, where the heating rate is about 200 � C/min, showed 60% retention of flexural modulus after a 40-s exposure, compared to 20% retention observed for the control sample after cooling specimens to ambient temperatures.
TL;DR: In this article, the effect of atmospheric plasma treatments on the surface chemistry, morphology, and mechanical properties of graphite/epoxy composites was evaluated using contact angle measurements, XPS, FTIR, SEM and AFM.
Abstract: A study was undertaken to evaluate the effect of atmospheric plasma treatments on the surface chemistry, morphology, and mechanical properties of graphite/epoxy composites. Characterization included contact angle measurements, XPS, FTIR, SEM and AFM. Treatment was shown to increase strength by as much as 50% relative to untreated specimens. The improvement was related to the number of passes and can be attributed to chemical surface modifications. While the total amount of oxygen on the surface stabilized quickly after a few plasma passes, the concentration of the carboxyl groups was shown to continuously increase, and correlated well with observed increases in strength.
TL;DR: In this paper, the authors describe a self-sealing plain weave E-glass epoxy composite with the healing components, microencapsulated dicyclopentadiene (DCPD), and paraf- fin wax coated Grubbs' catalyst dispersed throughout the matrix.
Abstract: We describe a self-sealing plain weave E-glass epoxy composite with the healing components, microencapsulated dicyclopentadiene (DCPD), and paraf- fin wax coated Grubbs' catalyst dispersed throughout the matrix. In this work, sealing is assessed through use of a pressure cell apparatus to detect nitrogen flow through the thickness direction of a damaged composite. A controlled amount of microcracking is introduced through cyclic indentation of opposing surfaces of the sample. The resulting damage zone is proportional to the indentation load. We investigate the effect of DCPD microcapsule size and concentration on the self-sealing ability of plain weave E-glass epoxy composites. For 51mm diameter capsules (6.5wt%), 67% of the self-sealing composite panels fully seal with no leaking, compared to 0% of the control panels with no sealing ability. When the amount of damage is reduced, 100% of the self-sealing samples resealed. Sealing performance decreases with smaller diameter capsules (18mm diameter) and lower capsule concentrations (2.7wt%), indicating that there is a minimum capsule size and concentration to deliver enough healing agent to seal a given damage volume.
TL;DR: In this article, an experimental study on the mode I interlaminar fracture of glass/polyester composites by using acoustic emission (AE) to analyze the damage evolution and evaluate the intra-laminar performance of polymeric composites.
Abstract: This article proposes an experimental study on the mode I interlaminar fracture of glass/polyester composites by using acoustic emission (AE) to analyze the damage evolution and evaluate the interlaminar performance of polymeric composites. A delamination process simulated with a double cantilever beam in opening mode (Mode I) coupled with an AE technique has been employed. The microscopic observation (scanning electron microscopy) is used to determine the correlation between different fracture mechanisms and their corresponding AE signal frequency content. Selected emissions are classified as matrix cracking, fiber breakage, or interface processes (fiber—matrix debonding) based on their total power in defined frequency intervals of the spectral power density. A correlation was established between the mechanical energy release rate and the AE energy rate. Analysis in the frequency domain shows AE parameters are powerful indicators of the intensity of the damage.
TL;DR: In this article, the surface chemistry and bonding behavior of graphite-epoxy composite joints were investigated using X-ray photoelectron spectroscopy (XPS) and the carboxyl concentration on the surface was measured as a function of these changes and correlated to lap shear strengths.
Abstract: Atmospheric plasma treatment for the surface preparation of adhesively bonded composite joints appears promising as a replacement to current surface preparation techniques. However, questions remain regarding the sensitivity and optimization of various plasma processing parameters on final composite bond properties. In this study, we continue to investigate how plasma surface treatment processing variables ultimately affect the surface chemistry and bonding behavior of a graphite-epoxy composite. The plasma power level, the working distance of the plasma head, the carrier gas (helium) flow rate, the duration of plasma exposure, and the active gas (oxygen) concentration within the plasma were varied and correlated to surface chemistry variations using X-ray photoelectron spectroscopy (XPS). The carboxyl concentration on the surface was then measured as a function of these changes and correlated to lap shear strengths. In addition, samples were monitored using XPS to evaluate the decay behavior of the surfa...
TL;DR: For three 3D woven carbon fiber reinforcements with different architectures, the compressibility, geometrical structure, and permeability were studied in this paper, where the in-plane permeability was modeled by superimposing a disturbance caused by the binder yarns to the permeability of a regular layered fiber structure.
Abstract: For three 3D woven carbon fiber reinforcements with different architectures, the compressibility, geometrical structure, and permeability were studied. At low levels of compression, the thickness of an angle-interlock weave is reduced mainly by local reduction of the height of inter-bundle voids and permanent reordering of the fiber bundles. At higher compression levels, bundle compaction is dominant. For an orthogonal weave fabric, the main compression mechanism is compaction of the fiber bundles. The in-plane permeability is modeled by superimposing a disturbance, caused by the binder yarns, to the permeability of a regular layered fiber structure. It is characterized mainly by the dimensions of the inter-bundle voids in each layer, and the pattern and dimensions of the binder yarns. Because of the dependence on the inter-bundle void dimensions, the fabric compression behavior is reflected. The through-thickness permeability is determined by flow-enhancing channels in the structure of the reinforcement,...
TL;DR: In this article, thermal conductivity measurements of carbon nanotube (CNT) copper nanocomposite fabricated with a novel electrochemical co-deposition method were carried out.
Abstract: In this study, thermal conductivity measurements of carbon nanotube (CNT) copper nanocomposite fabricated with a novel electrochemical co-deposition method were carried out. The measured thermal conductivity of a Cu-CNT nanocomposite is about 180% greater than that of pure copper. The resultant thermal conductivity of Cu-CNT composite is found to be proportional to the CNT addition.
TL;DR: In this paper, the effect of SiC volume fraction on the strength of Al-SiC nanocomposites was studied using high resolution scanning electron microscopy and X-ray diffraction method.
Abstract: Al—(1, 3, 5, 7, 10 vol%) SiC nanocomposites were produced by mechanical alloying (MA) and double pressing/sintering route. The characteristics of the milled powders and the consolidate specimens were examined using high resolution scanning electron microscopy and X-ray diffraction method. Compression and hardness tests were used to study the effect of SiC volume fraction on the strength of Al—SiC nanocomposites. It was shown that with increasing the SiC volume fraction, finer particles with narrower size distribution and smaller crystallite size are obtained after MA. During sintering close to the melting point of aluminum, the presence of nanometer-scaled SiC particles was found to hinder the grain growth significantly. The Al matrix with a higher SiC content exhibited more potential for grain boundary pinning, i.e., smaller grain size was obtained at higher SiC volume fractions. Consequently, an improved mechanical strength was obtained. The processing method (MA/pressing/sintering) can be used for fabr...
TL;DR: In this paper, the effect of nonlinear interlaminar shear stress-strain relations on delamination failure prediction for thick IM7/8552 carbon/epoxy tape laminates with wavy plies was shown.
Abstract: Accurate matrix-dominated constitutive properties can be a key to accurate failure models for polymer-matrix composites. This work shows the effect of nonlinear interlaminar shear stress-strain relations on delamination failure predictions for thick IM7/8552 carbon/epoxy tape laminates with wavy plies. Nonlinear finite element model (FEM) predictions and subsequent test correlations are presented. The interlaminar shear stress-strain relations are generated using short-beam shear tests and a digital image correlation full-field strain measurement technique. Test data for the wavy-ply coupons show that nonlinear shear stress-strain response is required for accurate failure prediction.
TL;DR: In this article, it was shown that the compaction of flax mats requires a higher load than for glass mat composites of similar areal weight, and the transverse permeability of the flax mat is lower than that of glass mat.
Abstract: Nowadays, the market demand for environmentally friendly materials is rapidly increasing. Biodegradable fibers and biodegradable polymers, mainly extracted from renewable resources, are expected to be a major contribution to the production of new industrial high performance biodegradable composites, partially solving the problem of waste management. At the end of its lifetime, a structural biodegradable composite can be crushed and recycled through a controlled industrial composting process. Bodros et al. [1] showed that biodegradable L-polylactide acid (PLLA)/flax fibers mat composites exhibiting specific tensile properties equivalent to glass fiber polyester composites can be manufactured by an un-optimized film-stacking process. In our study, the process has been investigated more extensively. Indeed, the compaction of flax mats requires a higher load than for glass mats of similar areal weight. The transverse permeability of flax mats has also been shown to be lower than for glass mats. In both cases,...
TL;DR: In this paper, the authors studied the transverse failure response of unidirectional fiber-epoxy systems by means of finite element simulations and found that the failure response depends on the relative strength and relative toughness of the interface and the epoxy matrix.
Abstract: The transverse failure response of unidirectional fiber-epoxy systems is studied by means of finite element simulations. An interface damage model is used for modeling fiber debonding and epoxy cracking. The convergence of the numerical results upon mesh refinement is analyzed. It is found that the failure response depends on the relative strength and relative toughness of the fiber-epoxy interface and the epoxy matrix. The tensile failure response of epoxy systems containing multiple fibers is also analyzed. In addition, the simulations demonstrate the influence on the failure response by the relative strength of the fiber-epoxy interface and the epoxy matrix, and by the fiber volume fraction and fiber distribution. The simulated fracture patterns are shown to be in good agreement with experimental observations reported in the literature.
TL;DR: In this article, mode I interlaminar fracture toughness (GIC) of a Vectran-stitched laminated composite is determined experimentally and computa- tionally.
Abstract: In this article, mode I interlaminar fracture toughness (GIC )o f Vectran-stitched laminated composite is determined experimentally and computa- tionally. Critical strain energy release rates are measured by performing double can- tilever beam test on composites stitched with Vectran as stitch fiber, and are found to increase with increasing stitch thread thickness and stitch density. It is also revealed that the relationship between GIC and stitch density or stitch thread volume fraction appears to be linear. Interlaminar tension test is conducted to identify important fracture behavior of a single Vectran stitch fiber thread. The finite-element (FE) model of the stitched composite incorporates the novel four-step stitch fracture pro- cess, namely, interfacial debonding, slack absorption, fiber breakage, and pullout friction. The FE predictions of loaddisplacement curves and critical mode I strain energy release rates show good agreement with the experimental results. The differ- ences in interdependent stitch mechanisms between moderately stitched and densely stitched composites are discussed.
TL;DR: In this article, a constitutive model for fibrous polymer composites was established based on an elasticplastic approach, where the potential function is a linear combination of functions related to deviatoric and dilatational deformations.
Abstract: A constitutive model for fibrous polymer composites was established based on an elasticplastic approach. The proposed potential function is a linear combination of functions related to deviatoric and dilatational deformations. A uni- directional carbon/epoxy composite, AS4/3501-6, and a woven-glass/vinylester com- posite were fabricated and tested under quasi-static off-axis tension and compression and used in developing and verifying the model. Model parameters were determined from the off-axis test results. Stressstrain curves predicted by the model were in good agreement with experimental results. The constitutive model established can describe the nonlinear orthotropic mechanical behavior of the composites, and it accounts as well for their tensioncompression behavior. HARACTERIZATION AND PREDICTION of the mechanical behavior of fiber-reinforced composites are essential for design and their structural applications. Numerous con- stitutive models of composites have been proposed for prediction of their nonlinear mechanical behavior. The approaches followed in those models can be categorized in terms of the scale of analysis and the assumptions made about the mechanical behavior. Micromechanical models (15) are based on the microstructure and mechanical char- acteristics of the constituents, fiber, and matrix of the composite. These models are used to predict effective mechanical properties of the composite and provide insight into the contributions of each constituent to the properties and the interactions between fibers and matrix. However, in mechanical analysis of composite structures, microscopic models may require expensive computations and are hampered by insufficient data of the