Search

For the past six years, we have been benefiting from the discovery by Tsai and Melo (2014) that the trace of the plane stress stiffness matrix ( tr ( Q ) ) of an orthotropic composite is a fundamental and powerful scaling property of laminated composite materials. Algebraically, tr ( Q ) turns out to be a measure of the summation of the moduli of the material. It is, therefore, a material property. Additionally, since tr ( Q ) is an invariant of the stiffness tensor Q , independently of the coordinate system, the number of layers, layup sequence and loading condition (in-plane or flexural) in a laminate, if the material system remains the same, tr ( Q ) = tr ( A ∗ ) = tr ( D ∗ ) is still the same. Therefore, tr ( Q ) is the total stiffness that one can work with making it one of the most powerful and fundamental concepts discovered in the theory of composites recently. By reducing the number of variables, this concept shall simplify the design, analysis and optimization of composite laminates, thus enabling lighter, stronger and better parts. The reduced number of variables shall result in reducing the number and type of tests required for characterization of composite laminates, thus reducing bureaucratic certification burden. These effects shall enable a new era in the progress of composites in the future. For the above-mentioned reasons, it is proposed here to call this fundamental property, tr ( Q ) , as Tsai’s Modulus.

Hierarchical +1 composites consisting of carbon fibers with carbon nanotubes (CNTs) grown onto them and an epoxy matrix were processed, and the mode I fracture toughness of these composites was evaluated. The mode I fracture toughness of the initial batches of the hierarchical composites was lower than that of the baseline samples without CNTs. Hence, efforts to enhance the adhesion between carbon fibers and CNTs were made, resulting in enhanced adhesion. The enhanced adhesion was confirmed by Scotch tape tests and mode I fracture toughness tests followed by fractographic studies. The mode I fracture toughness of the hierarchical composites with enhanced adhesion was 51% and 89% higher than those of the baseline samples and hierarchical composites with poor adhesion, respectively. Moreover, fractographic studies of the fracture surfaces of the hierarchical composites with enhanced adhesion showed that CNTs were still attached to carbon fibers even after the mechanical tests.

Two-dimensional mapping of the laser-induced breakdown spectroscopy (LIBS) signal of chemical species information in liquefied petroleum gas (LPG) and electrolytic oxy-hydrogen (EOH) flames was performed with in situ flame diagnostics. Base LIBS signals averaged from measurements at wavelengths of 320 nm to 350 nm describe the density information of a flame. The CN LIBS signal provides the concentration of fuel, while the H/O signal represents the fuel/air equivalence ratio. Here, we demonstrate the meaningful use of two-dimensional LIBS mappings to provide key combustion information, such as density, fuel concentration, and fuel/air equivalence ratio.

The aim of this study was to investigate the effects of adding maleic anhydride grafted polypropylene (MA-PP) and graphite nanoplatelets (GNPs) into polypropylene. The tensile strength and flexural properties of the GNP/PP composite were enhanced with an increase in the MA-PP content and the GNP content. The maximum increase of mechanical properties was shown at 10 wt.% of MA-PP having a constant GNP content of 8 wt.% and at 20 wt.% of GNP having a constant MA-PP content of 5 wt.%, whereas a decrease in tensile strength and flexural properties was observed at 20 wt.% of MA-PP. The impact strength was decreased by increasing the MA-PP content and the GNP content. The electrical resistivity of the GNP/PP composite exhibited an anisotropic characteristic due to the direction of the injection molding flow. Electrical resistivity of less than 106 Ω cm regardless of the direction of the resin flow could be obtained by adding more than 20 wt.% of GNP when the MA-PP content was 5 wt.%. The differential scanning calorimetry results suggest that an increase of the GNP content makes it act as a nucleating agent and thus causes an increase in the crystallinity of the PP.

We report the synthesis of graphene/fullerene-capped gold nanoparticle nanocomposite film which was used to construct supercapacitor electrodes. The fullerene-based self-assembled monolayers on gold nanoparticles (AuNPs) were attained via the fullerene(C60)-gold interaction. The fullerene-capped AuNPs effectively separated the graphene sheets preventing aggregation. A synergistic effect was observed—the specific capacitance of graphene/fullerene-capped AuNP electrode is197 F/g, which is higher than that of graphene electrode (31 F/g), graphene/AuNP electrode (126 F/g), and graphene/fullerene electrode (118 F/g). The results render a novel route of synthesis and modification of graphene-based materials for the construction of electrochemical energy storage devices.

This paper aims to develop an autonomic thermal management system of graphite fiber/polymer composite structures using their electrical property. A number of copper tapes are integrated on top and bottom surfaces of a composite plate, and through the thickness resistances between these tapes are measured on a hotplate for temperature monitoring. The resistance at warmer area successfully reflected the temperature distribution taken by an IR imaging camera. The same copper tapes are subsequently used for generating resistive heat by supplying a large amount of current. The effective heat generation is investigated by a finite element analysis, showing that the temperature of a laminate can be controlled by adjusting the conductivity in the fiber and thickness directions.

Epoxy resin nanocomposites reinforced with three different ionic liquid functionalized carbon nanotubes (f-CNTs) were fabricated by an in situpolymerization method. The influence of the anions on the curing process was studied through differential scanning calorimetry (DSC) and normalized Fourier transform infrared (FTIR) spectroscopy. The composition of the nanocomposites was analyzed by X-ray photoelectron spectroscopy. Two different mechanisms are proposed to explain the curing process of the neat epoxy and its composites. The electric conductivity and mechanical properties of the nanocomposites are also reported. The tensile strength was increased dramatically due to the insertion of f-CNTs. Scanning electron microsopy fracture surface analysis indicates a strong interfacial bonding between the carbon nanotubes and the polymer matrix.

Vacuum filtration process to fabricate a transparent conducting carbon nanotube (CNT) film is reported. A CNT mat, which is a fibrous sheet of long multi-walled carbon nanotubes (MWNT), was prepared and dispersed in oleum by solution-sonication. The suspension was then vacuum filtered to obtain a thin MWNT layer with improved dispersion. Sheet resistance of the obtained MWNT layer was increased despite the improved dispersion. SEM micrographs and energy dispersive spectroscopy results indicated that the increase of the sheet resistance could be attributed to degradation and oxidation of the MWNT bundles. Though the chemical approach in this study did not improve the electrical property of the CNT mat, a mechanical approach proposed in our recent work was deemed suitable to enhance optical and electrical properties of the CNT mat.

We describe in this paper a transparent conducting film (TCF). It is a fibrous layer of multiwalled carbon nanotubes (MWNTs), labeled a dilute CNT mat, that was prepared and unidirectionally stretched to improve both the optical and electrical properties. After stretching by 80% strain, transmittance at 550 nm wavelength was improved by 37% and sheet resistance was reduced to 71% of the original value. The improvement of the transmittance can be explained by increased area of the CNT mat after stretch, and the reduced sheet resistance can be explained by increased density of the CNT alignment in lateral direction due to contraction. Based on the microscopic observation before and after stretch, models to describe the phenomena are proposed. By further expanding on this method, it may be possible to obtain a transparent conducting carbon nanotube film which is crack-resistant for solar cell applications.

This study presents the first stage of a multi-scale numerical framework designed to predict the non-linear constitutive behavior of metal-composite interfaces in titanium-graphite fiber metal laminates. Scanning electron microscopy and x-ray diffraction techniques are used to characterize the baseline physical and chemical state of the interface. The physics of adhesion between the metal and polymer matrix composite components are then evaluated on the atomistic scale using molecular dynamics simulations. Interfacial mechanical properties are subsequently derived from these simulations using classical mechanics and thermodynamics. These molecular-level property predictions are used in a companion study to parameterize a continuum-level finite element model of the interface by means of a traction-separation constitutive law. Extension of the proposed approach to other dissimilar metal- or metal oxide-polymer interfaces is also discussed.

Self-healing composites using a thermally mendable polymer, bis-maleimide tetrafuran (2MEP4F), based on Diels–Alder reaction and electrical resistive heating were fabricated using a vacuum assisted injection molding method. Delaminations were induced using short span three point bending on composite coupons. The induced damage and permanent deformation of the composite coupons were observed using X-ray micro-tomography. The same procedure was repeated to confirm multiple healings after electrical resistive heating and healing efficiency of the samples was determined. The permanent deformations and induced delaminations were repaired after the heating process, which is due to both healing and shape memory effects. The multiple healing ability and shape memory effect of the fabricated composite combined with electrical resistive heating realizes a noble self-healing composite.

We demonstrated a novel method for the formation of alloy nano-islands on carbon nanotube (CNT). The two metal layers (Pt, Au) were sputtered on CNTs and the intense pulsed light (IPL) was irradiated on the metal layers. The absorbed light provides enough energy for the diffusion mixing between Pt and Au, forming Pt–Au alloy phase. While the alloy is being formed by the IPL irradiation, the metal layers are broken into nano-islands on CNT due to the surface energy minimization between the metal layers and CNT. The surface characterizations of the Pt–Au/CNT were performed with X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy. Different compositions of alloy nanoparticles were obtained by adjusting the deposition thicknesses of Pt and Au on CNT. Pt 50 Au 50 /CNT electrode showed the highest glucose oxidation current peak among Pt, Pt 70 Au 30 , Pt 50 Au 50 , Pt 30 Au 70 , and Au/CNT electrodes while the electroactive surface areas of them are kept to be similar (average surface area = 7.00 cm 2 , coefficient of variation = 0.06). The amperometric response of Pt 50 Au 50 /CNT electrode to the glucose concentrations showed a wide linear range up to 24.44 mM with a high detection sensitivity of 10.71 μA mM −1 cm −2 . Reproducibility and long-term stability of the Pt–Au/CNT electrode were also proven in the experiments.

Most commercial copper nanoparticles are covered with an oxide shell and cannot be sintered into conducting lines/films by conventional thermal sintering. To address this issue, past efforts have utilized complex reduction schemes and sophisticated chambers to prevent oxidation, thereby rendering the process cost ineffective. To alleviate these problems, we demonstrate a reactive sintering process using intense pulsed light (IPL) in the present study. The IPL process successfully removed the oxide shells of copper nanoparticles, leaving a conductive, pure copper film in a short period of time (2 ms) under ambient conditions. The in situ copper oxide reduction mechanism was studied using several different experiments and analyses. We observed instant copper oxide reduction and sintering through poly(N-vinylpyrrolidone) functionalization of copper nanoparticles, followed by IPL irradiation. This phenomenon may be explained by oxide reduction either via an intermediate acid created by ultraviolet (UV) light irradiation or by hydroxyl (-OH) end groups, which act like long-chain alcohol reductants.

A novel method using intense pulsed light (IPL) for the metal nano-island formation on carbon nanotube (CNT) was introduced. The IPL-induced photothermal dewetting process improved platinum (Pt) catalyst utilization by transforming nano-islands from Pt film on CNT and increasing the surface area for the subsequent sputtering. The irradiation of high intensity of light on the Pt film causes surface-energy-driven diffusion of Pt atoms and forms the array of nano-islands on CNT. The thickness of Pt film can change the size of nano-islands. Cyclic voltammetry showed a dramatically improved glucose oxidation at the IPL morphology modified Pt-CNT electrode compared to the Pt sputtered CNT electrode without IPL irradiation. The power densities of glucose/air biofuel cell based on the morphology modified Pt-CNT electrode and the as-sputtered Pt-CNT electrode were 0.768 microW/cm(2) and 0.178 microW/cm(2), respectively. The biofuel cell based on morphology modified Pt-CNT electrode showed highly stable output in long-term performance. The power density dropped 14.1% in 30 days. Efforts are underway to improve the interface transfer to achieve higher potential and current output.

Inkjet printing of electrode using copper nanoparticle ink is presented. Electrode was printed on a flexible glass epoxy composite substrate using drop on demand piezoelectric dispenser and was sintered at 200 °C of low temperature in N2 gas condition. The printed electrodes were made with various widths and thickness. In order to control the thickness of the printed electrode, number of printing was varied. Resistivity of printed electrode was calculated from the cross-sectional area measured by a profilometer and resistance measured by a digital multimeter. Surface morphology of electrode was analyzed using scanning electron microscope (SEM) and atomic force microscope (AFM). From the study, it was found that 10 times printed electrode has the most stable grain structure and low resistivity of 36.7 nΩ m.

Copper nano-ink with a drop-on-demand (DOD) piezoelectric inkjet printing method was introduced. The printed electrodes were thermally sintered to ensure high-quality electrical and mechanical performances. To check the reliability of the printed electrodes on a polymer layer, resistance changes were measured under static loading. The electrodes with various widths and thicknesses were used to find the optimal dimensions. A multifunctional composite laminate which can harvest and store a solar energy was fabricated using printed electrodes. An amorphous silicon solar cell and a thin film solid state lithium-ion battery were adhesively joined and electrically connected to a thin flexible printed circuit board (PCB). Then, the passive components such as resistor and diode were electrically connected to the printed circuit board by silver pasting. The integrated PCB was co-cured with a carbon/epoxy composite laminate by the vacuum bag molding process in an autoclave. The structural and functional performance of the final energy harvesting/storage composite laminate was tested under mechanical loading.

The cure kinetics of a thermally mendable polymer based on Diels-Alder (DA) and retro-Diels-Alder (rDA) reactions, mendomer 401, was investigated using dynamic differential scanning calorimetry (DSC). The resulting behavior was modeled using a conventional cure kinetic model for thermosetting polymers. A composite panel with two layers of carbon fabric and mendomer 401 was fabricated following the cure cycle suggested by the cure kinetics model. Micro-indentation tests were performed to investigate mechanical properties and dynamic mechanical thermal analysis (DMTA) was conducted to study thermal behavior and to find the trigger temperature for healing. Self-healing behavior of the carbon fiber/mendomer composite was demonstrated using electrical resistive heating over the glass transition temperature.

A novel dispersant “mono-2-(methacryloyloxy)ethyl succinate” was formulated for dispersing 30-nm SiC nanoparticles in vinyl ester resin. The eight carbon rule was used as the guideline to achieve a particle–particle separation of 20 to 60 nm for colloid stability. Fourier transform infrared spectroscopy was performed to characterize the SiC particle surfaces. Only a negligible amount of oxidized layer was observed; which illustrates that the SiC surface is basic. Thus, the Lewis base-Lewis acid reactions make the functional group –COOH an effective adsorbate to the SiC nanoparticle surface. The organofunctional group “methacrylates,” which exhibits the best wet strength with polyester copolymerizes with styrene monomers in the vinyl ester during cure. Hence, this novel dispersant also acts as an efficient coupling agent that reacts with both SiC and vinyl ester. The monolayer coverage dosage of 62 fractional wt% of the dispersant was used to attain the minimum filled resin viscosity. The multicomponent compositional imaging using atomic force microscopy confirmed the monodisperse SiC nanoparticles in vinyl ester. The 3 vol% SiC reinforced vinyl ester achieved a 75% increase in modulus, 42% increase in strength, and 75% increase in toughness as compared with the neat resin without nanofiller reinforcement.

This paper presents a finite element model used to predict the bearing strength of hybrid titanium composite fiber-metal laminates. The model is used to examine the effects of material parameters such as titanium content and edge-distance ratio on specific bearing strength. In addition, a three-dimensional progressive failure user material subroutine is implemented into the commercial finite element code ABAQUS to model stiffness degradation in the graphite-polyimide layers of the hybrid laminate. These results are used to optimize the fiber-metal laminate layup by determining to the ideal tradeoff between joint strength and structural weight.

This paper reports on the recent progress towards the development of power composite structures capable of energy harvesting and storage in addition to load bearing. The process of physically embedding all-solid-state thin-film lithium energy cells into a carbon fiber reinforced plastic (CFRP) and the performance of the resulting power composites are reported. The embedded thin-film lithium-ion energy cells did not significantly alter the mechanical properties of the composite (modulus and strength) under quasi-static uniaxial loading conditions. The embedded energy cells performed at baseline charge/discharge levels up to a loading of about 50% of the CFRP tensile strength.

Robust magnetic vinyl ester resin nanocomposites reinforced with iron oxide (Fe2O3) nanoparticles were fabricated. The particle functionalization with a bi-functional coupling agent methacryloxypropyl-trimethoxysilane (MPS) was observed to have a significant effect on the curing process and subsequent physical properties of the nanocomposites. Particle functionalization favors the composite fabrication with a lower curing temperature as compared to the as-received nanoparticles filled vinyl ester resin nanocomposites. Thermo-gravimetric analysis showed an increased thermo-stability in the functionalized nanoparticles filled vinyl ester resin nanocomposites as compared to the unmodified nanoparticle filled counterparts. The more uniform particle dispersion and the chemical bonding between nanoparticle and vinyl ester resin matrix were found to contribute to the increased thermal stability and enhanced tensile strength. The nanoparticles become magnetically harder after incorporation into the vinyl ester resin matrix.

Silicon carbide reinforced polyurethane nanocomposites were fabricated by a facile surface-initiated-polymerization (SIP) method. The particle loading was tuned to up to 35 wt% without any obvious shrinkage and breakage as compared with the conventional direct mixing method. An increased thermal stability of the composites was observed with the addition of the silicon carbide nanoparticles under thermo-gravimetric analysis (TGA). Tensile strength was observed to increase dramatically with the increase of the particle loading. Both the uniform particle dispersion and the strong chemical bonding between the nanoparticles and the polymer–matrix contributed to the enhanced thermal stability and improved mechanical properties.

Fiber metal laminates are an advanced hybrid materials system being evaluated as a damage tolerance and light weight solution for future aircraft primary structures. This paper investigates the impact properties and damage tolerance of glass fiber reinforced aluminum laminates with cross-ply glass prepreg layers. A systematic low velocity impact testing program based on instrumented drop weight was conducted, and the characteristic impact energies, the damage area, and the permanent deflection of laminates are used to evaluate the impact performance and damage resistance. The post-impact residual tensile strength under various damage states ranging from the plastic dent, barely visible impact damage (BVID), clearly visible impact damage (CVID) up to the complete perforation was also measured and compared. Additionally, the post-impact fatigue behavior with different damage states was also explored. The results showed that both GLARE 4 and GLARE 5 laminates have better impact properties than those of 2024-T3 monolithic aluminum alloy. GLARE laminates had a longer service life than aluminum under fatigue loading after impact, and they did not show a sudden and catastrophic failure after the fatigue crack was initiated. The damage initiation, damage progression and failure modes under impact and fatigue loading were characterized and identified with microscopy, X-ray radiography, and by deply technique.

Electrospinning was used to spin nanocomposite fiber mats from polymer solutions containing nanoparticles. The base polymer was polyacrylonitrile (PAN), and the nanoparticles included iron oxide, antimony tin oxide and zinc oxide with diameters ranging from 10 to 70 nm. The electrospun nanocomposite fiber mats were characterized by scanning electron microscopy (SEM), scanning probe microscopy (SPM) and Fourier transform infrared (FTIR) spectroscopy. The average fiber diameter was found to decrease from 200 nm for neat PAN fibers to 50–150 nm for nanocomposite fibers. The porosity increased from 70% for PAN fiber mat to an average of 86% for nanocomposite fiber mats. The fiber mats were used as a sensor in conjunction with FTIR spectroscopy to detect CO2 gas. The absorbance spectra showed a higher sensitivity with a fiber mat, regardless of its type, than without, indicating gas adsorption on the fiber mat. The highest sensitivity was obtained with PAN/Fe2O3 fiber mat. As the underlying mechanism is physisorption rather than chemisorption, the response time was short and the sensor could be used repeatedly.

The effect of temperature and humidity on equilibrium moisture content of laminates was studied by response surface design. Two glass fabric-reinforced laminated composite materials with different epoxy matrix resins, laminates A and B, were studied. Laminates A and B used are cyanate ester and polyphenylene oxide modified epoxy based laminate, respectively. The results show that the response surface profiles of moisture absorption for the two laminate materials are similar though their amounts of moisture absorption are different. The temperature-humidity interaction effect and the quadratic effect of temperature are significant for laminate A. However, only the linear effects of temperature and humidity are significant for laminate B. Predictive models relating the important factors to the equilibrium moisture content were proposed in the article. The models developed can be used to predict and assess the reliability of the laminates for moisture related failures.

Nanoimprint lithography (NIL) process at the room temperature has been proposed newly to achieve the shape accuracy and to overcome the sticking problem induced in conventional NIL processes. Success of the room temperature NIL relies on the complete understanding of the mechanical behavior of the polymer. Since a conventional NIL process has to heat a polymer above the glass transition temperature to deform the physical shape of the polymer with a mold pattern, visco-elastic properties of the polymer have major effect on the NIL process. The rate dependent behavior of the polymer is also important in the room temperature NIL process because a mold is rapidly pressed onto the polymer while there has been no study on the rate-dependent NIL process. In this paper, finite element analysis of the room temperature NIL process is performed with the consideration of the strain-rate dependent behavior of the polymer. The analyses with the variation of the imprinting speed and the imprinting pattern are carried out in order to investigate the effect of the process parameters on the room temperature NIL process. The analysis results show that the deformed shape and the imprinting force are diversified with the variation of the imprinting speed due to the dynamic behavior of the polymer with the rate dependent plasticity model. The results provide a guideline to determine the process conditions in the room temperature NIL process.

Silicon carbide (SiC) nanoparticles with no surface treatment raise the viscosity of a vinyl ester resin much more intensely than micrometer-size SiC particles. An effective dispersant generally causes a reduction in the resin viscosity attributed to its surface-active properties and thereby increases the maximum fraction of particles that can be introduced. This article assesses the rheological behavior of SiC-nanoparticle-filled vinyl ester resin systems with the Bingham, power-law, Herschel–Bulkley, and Casson models. The maximum particle loading corresponding to infinite viscosity has been determined to be a 0.1 volume fraction with the (1 − η r −1/2)–ϕ dependence (where η r is the relative viscosity and ϕ is the particle volume fraction). The optimum fractional weight percentage of the dispersants (wt % dispersant/wt % SiC) is around 40% for 30-nm SiC nanoparticles, which is much higher than 1–3% for micrometer-size particles. SiC nanoparticles at a concentration of 9.2 wt % (0.03 volume fraction) cause a fourfold increase in the resin viscosity. The addition of a dispersant at the optimum dosage lowers the viscosity of SiC/vinyl ester suspensions by 50%. The reduction in the viscosity is substantial to improve the processability of SiC/vinyl ester nanocomposites.

The effect of dispersants on particle dispersion and flexural properties of SiC/vinyl ester nanocomposites was studied by factorial and response surface designs. The results show that the coupling agent 'gamma-methacryloxy propyl trimethoxy silane (MPS)' has no adverse side effect on the flexural properties as illustrated by the good correlation between maximizing the flexural strength and minimizing the agglomerates. However, the dispersant 'BYK-W 966' has a slight adverse side effect on the flexural properties although it improves dispersion at higher dosage. With an optimal dosage of MPS and W966, a small amount of SiC in 0.5 wt% results in 8% increase in strength and 14% increase in modulus. The flushing operation using the dispersant '1-octanol/decane' achieves an excellent SiC dispersion but it does not result in improved flexural properties. This confirmed that a better state of nanoparticle dispersion does not necessarily lead to improved flexural properties. A good dispersion coupling with a strong filler/matrix interfacial bonding is the key to obtain enhanced flexural properties.

The feasibility of improving polymer composites was investigated using 30 nm SiC nanoparticles in a vinyl ester resin. Even when the particle loading was less than 4% by weight, the viscosity of the nanoparticle suspension was found to increase much higher than that of microparticle suspension. This phenomenon may be the result of association between nanoparticles and polymer molecules, effectively making the nanoparticles larger. The resulting reduction in the mobility of polymer molecules also led to delayed curing. Ultrasonic mixing did not fully disperse the particles. As a result, the composite strength did not improve although the modulus increased. The use of a dispersant, methacryloxy propyl trimethoxy silane (MPS), improved the dispersion quality and hence the composite strength. The paper discusses the issues involved with processing, characterization and properties of SiC/vinyl ester nanocomposites. Methods of improving the nanocomposite quality are proposed in the paper as well.

In this paper, a wear-out model, which is based on the concept ofdeterministic strength degradation and equal ranking between static and residualstrengths, is used to assess the fatigue behaviors of several different sandwich beams.The model requires only two parameters to describe the strength degradation infatigue. One parameter represents the rate of strength degradation and the othera relative fatigue life. A new approach is used to determine these parameters fromexperimental data. The model is shown to be able to describe rather well both thestatic strength distributions and the fatigue stress-life relations of the sandwichbeams. The residual strength distribution after 5000 cycles was predicted for theEglass–vinylester–D100 balsa wood sandwich at 60% maximum stress level with thef and s obtained through the fitting method developed in this paper. There is a goodagreement between prediction and experiment.

The static and fatigue behavior of vacuum-assisted resin transfer molded sandwich panels has been experimentally investigated under flexural loading. Two core materials, D-100 balsa wood and H 250 PVC foam, were used to study the effect of core material on static failure in 3-point and 4-point bending. The face consisted of a quasi-isotropic E-glass non-woven fabric cured in Derakane 441-400 epoxy vinyl ester resin. The stresses in the face and core at failure were calculated from failure loads using the simple beam theory and compared with their respective strength values to identify underlying failure mechanisms. For short beams, core failure led to failure of the beam as a whole. In long beams, however, failure of the wood core could be contained until the face failed. Only D-100 end grain balsa wood was used as core for fatigue tests. A good similarity was seen between the static and fatigue failure modes for both short span and long span specimens.

Models to predict the split growth in notched AS4/3501-6 graphite/epoxy quasi-isotropic laminates under tension-dominated fatigue are presented. First, a power law model and an artificial neural network (ANN) model are developed to describe the split growth under constant-amplitude fatigue. They are then applied in conjunction with a linear damage growth model to predict the split growth under spectrum fatigue. The ANN model is found to work better than the power law model as a predictive tool for split growth.

The subcritical damage growth in notched AS4/3501-6 graphite/epoxy quasi-isotropic laminates under compression–compression and compression-dominated spectrum fatigue was investigated using the longitudinal split length as a damage measure. A linear split growth model was successfully used to predict the split growth in spectrum fatigue using the corresponding data under constant-amplitude fatigue. However, a linear degradation assumption was found to be inappropriate as it overpredicted lifetime under spectrum fatigue. The residual compressive strength did not show any sign of gradual reduction. The damage mode near the hole changed from longitudinal splitting to transverse extension of fiber failure and delamination as the fatigue stress increased. Thus, while the longitudinal split may serve as a measure of damage in high-cycle fatigue, the extent of transverse fiber failure is a better indication of residual compressive strength. It was shown that a compression-dominated fatigue loading spectrum could be shortened substantially by omitting the two lowest load levels at which no significant damage growth was seen under constant-amplitude fatigue.

This paper explains the development of a concurrent engineering system for the design of composite structures. The concurrent engineering system is developed to meet the demand for the better quality products with lower production cost and time. In this study, to compose the architecture of concurrent engineering system, the commercial and non-commercial programs related to design and analysis of composite structures are surveyed and classified. The concurrent engineering system includes various design modules such as design/analysis of composite structures using CLPT and finite-element method (FEM), buckling and postbuckling analysis, thermo-elastic analysis of carbon–carbon composite and optimum design using expert system. For the integration and management of softwares, a graphic-based design environment that provides multi-tasking and graphic user interface capability is built.

Voids in a composite part are deleterious because they degrade its strength and modulus. In resin-transfer molding (RTM), voids result mainly from inhomogeneous fiber architecture. Such inhomogeneity leads to non-uniform permeability of the fiber preform, which in turn causes the resin velocity to vary from point to point at a micro scale. The capillary pressure, which also prevails at this length scale, exacerbates the spatial variation of the resin velocity. The combined effect of pressure gradient and capillary pressure can be described by the capillary number. The resulting microscopic perturbations in the resin-flow front allow voids to form. The present paper proposes a mathematical model to describe the mechanisms of void formation. The existing data are used to validate the assumptions introduced. The model is then used to analyze new data from one-dimensional RTM experiments.

Convection problems governed by hyperbolic equations cannot be solved by conventional finite element methods. Various upwind schemes introduced into finite element methods to solve this class of problems suffer from a numerical error called the artificial diffusion. The amount of artificial diffusion depends not only on the mesh size but also on the flow rate. To minimize artificial diffusion the method of internal nodes is introduced. In this method, which is based on the Lagrangian interpretation of the first order upwind scheme, the flow within each nodal volume can be considered as an one-dimensional flow regardless of the number of upstream or downstream nodes. The use of internal nodes can provide an accurate solution to the degree of cure convection problem on a more coarse mesh with significantly reduced CPU cost. Sample problems are solved to validate the accuracy and efficiency of the method. When incorporated with the heat transfer equations, the use of internal nodes underscores the fact that some RTM problems are very sensitive to errors caused by artificial diffusion.

A study has been made of ply cracking in quasi-isotropic AS4/3501-6 laminates under tension–tension (T–T) and tension–compression (T–C) constant-amplitude (CA) fatigue loading and two-block loading. The CA fatigue and two-block fatigue tests were performed on unnotched laminates having two different lay-ups: [0/±45/90]S3 and [0/±45/90]S4. The thinner lay-up was tested in T–T fatigue, and the thicker lay-up in T–C fatigue to preclude buckling. Load levels of 20–50% of ultimate tensile strength (UTS) were used for CA T–T fatigue tests while 20 and 30% UTS were used for CA T–C fatigue tests. Load mixes of 20/40% and 30/40% UTS were used for T–T block loading while 20/30% UTS mix was used for T–C fatigue. The ply crack densities were measured by using the edge-replication technique. The block order was changed to assess the load sequence effect. The ply cracking in T–C fatigue was much more severe than in T–T fatigue even when the maximum tensile stress was kept the same. In both T–T and T–C, low/high sequence resulted in a higher crack densities than high/low sequence. The crack-density data from constant-amplitude T–T fatigue were used in conjunction with a stiffness reduction scheme to establish in situ S–N (stress–life) curves for the 90° and −45° plies. The S–N curves were further condensed into a master S–N curve by the use of a polynomial failure function. A cumulative damage model was then established under the assumption that the stress redistribution during ply cracking takes place in such a way that the failure function remains on the master S–N curve. The cumulative damage model was applied to predict ply cracking under block fatigue, under T–C fatigue, and also under T–T fatigue in two cross-ply laminates. A concept of equivalent root-mean-square power was used to relate the damage under T–T fatigue to that under T–C fatigue. In general, the cumulative damage model was shown to provide reasonable estimates of crack densities under the test conditions studied.

This paper investigates the bearing properties of mechanically fastened glass-fiber/vinyl-ester composite joints. Two glass composites of different fabrics and lay-ups were fabricated by vacuum-assisted resin-transfer molding (VARTM) and tested by using a double-lap joint configuration. The results of this study are presented as experimental characterization and analytical prediction. The major focus of the experimental part of the paper was to characterize the bearing failure behavior of these composites. The effects of geometric parameters were evaluated and correlated with the resulting bearing strength and failure modes by the statistical method of analysis of variance. From the experimental results obtained, it is concluded that the edge-distance ratio (e/d) and thickness of the specimen strongly affect the bearing strength of the composites. On the other hand, the failure mode is determined by the width ratio (w/d). In the analytical part of the study, Chang’s strength-prediction model, which is based on a two-dimensional finite-element analysis, was utilized to predict the bearing strength of these composite joints. The predicted values were compared with the experimental data obtained from this study and the results suggest that this model can be used to give accurate predictions of the bearing strength of these composites.

An expensive and time consuming aspect of a product development cycle is manufacturing the prototype of the design concept. The goal of current research is to devise a methodology for the rapid process development of resin transfer molding (RTM) in order to reduce product development cycle time and lower the cost of developing composite parts. As a first step towards this goal the feasibility of an alternative rapid prototyping technique, namely laminated object manufacturing (LOM), to fabricate molds has been investigated. The durability and dimensional stability of such a mold, as well as its economic practicality in the RTM manufacturing of a composite I-beam were considered. To keep tooling and fixturing simple, vacuum pressure was used to draw resin into the mold. However, injection at this low pressure proved difficult. To remedy the situation a high permeability layer (HPL) was incorporated into the process. The benefits and drawbacks of utilizing such a layer are also discussed in the paper. Furthermore, an RTM simulation program developed at UCLA was employed to determine optimum gate locations. Finally, the total hours to manufacture the first acceptable part were quantified for comparison with future studies.

A finite element (FEM) approach using an implicit time integration algorithm has been developed to simulate isothermal resin transfer molding process. The finite element formulation is based on the concept of partial saturation at the flow front. The discretized equation is essentially the same as is obtained by a finite element/control volume formulation. The FEM approach is easier to implement for different types of elements. Unlike the explicit time integration schemes, the proposed implicit algorithm uses fixed time steps and allows the flow to advance farther than a layer of flow front elements in a single time step. The resulting code RTMSIM has been validated by comparing its predictions with closed-form solutions for flat plates. A wicking analysis is provided to show the code's ability to deal with the effect of capillary pressure. Several other simulations are provided to demonstrate the accuracy and efficiency of the code.

Chemically Bonded Ceramics (CBCs) have been extensively used many applications. These include: radiation shielding systems, nuclear waste solidification and encapsulation; high temperature structural applications; composites and biomedical applications. The objective of this chapter is to present the science, manufacturing and mechanical properties of the Wollastonite (CaSiO3) based Chemically Bonded Phosphate Ceramics (Wo-CBPCs) composites, Fig. 1. In general, the CBPCs belong to the broader field of Chemically Bonded Ceramics (Della Roy, 1987; Jeong & Wagh, 2002; Wagh, 2004) where the name CBPC refers to ceramic materials that reach their final mechanical properties by chemical reactions at low temperatures (typically less than 300 C) instead of the high temperature processing (by thermal diffusion or melting) as is normally done in traditional ceramics and cements. The Wo-CBPCs are composite materials themselves, they belong to Chemical Bonded Ceramics (CBCs) consolidated by an acid base reaction (Wilson & Nicholson, 1993). Wo-CBPCs are multiphase materials with silica, Wollastonite and brushite grains in a matrix of amorphous calcium phosphates. Reinfocing materials such as graphite nanoplateles, glass fibers and carbon fibers have been successfully incorporated into – CBPCs, realizing high performance composites.

An intense pulsed light (IPL) from a xenon flash lamp was used to sinter copper nanoink printed on low-temperature polymer substrates at room temperature in ambient condition. The IPL can sinter the copper nanoink without damaging the polymer substrates in extremely short time (2 ms). The microstructure of the sintered copper film was investigated using X-ray powder diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), X-ray micro tomography, and atomic force microscopy (AFM). The sintered copper film has a grainy structure with neck-like junctions. The resulting resistivity was 5 μΩ cm of electrical resistivity which is only 3 times as high as that of bulk copper. The IPL sintering technique allows copper nanoparticles to be used in inkjet printing on low-temperature substrates such as polymers in ambient conditions.

We report the first demonstration of the growth of giant graphene domains on platinum (Pt), which results in a uniform bilayer graphene film with domain sizes of millimetre scale. These giant graphene domains are attributed to the giant Pt grains attained in post-deposition annealed Pt thin films that exhibit a strong dependency on the Pt film thickness. Giant grains have been claimed to occur in other metallic materials under appropriate film thicknesses and processing conditions. Our findings demonstrate a route towards rational large-scale uniform graphene synthesis for applications in nanoelectronics and sensing.

In laminated object manufacturing process (LOM) as a rapid manufacturing technique, the key process parameters for achieving a successful prototype are the roller temperature, the roller speed, the roller indentation and the laser cutting time. In addition to these basic process parameters, the material properties and the configuration of the parts affect the internal stresses, local deformations built during the process and the bonding quality. A finite element method was adopted to simulate the thermal aspects of the bonding process along with the structural deformation of the part. Thermal and stress analysis was carried out to calculate the interlaminar shear strength between layers. Experiments were conducted to verify the simulation result for the internal temperature profiles. The finished prototype was tested mechanically to measure interlaminar shear strength to estimate the bonding quality. The calculated bonding quality was compared with the bonding strength converted from the measured interlaminar shear strength, showing a good agreement between the two. In compliance with the increasing demand for high-strength working prototypes, the developed simulation code can simulate the incorporation of new material for the LOM process.

The effect of ductility on fatigue behavior was studied using two DGEBA-based (diglycidyl ether of bisphenol A) epoxies: a ductile Epon 815/Versamid 140 and a brittle Epon 828/Epon Z. Failure modes were different although normalized stress-life relations were similar for both resins. Two competing failure mechanisms were identified: viscoelastic creep, and nucleation and coalescence into a main crack of microcracks. No signs of crazing or fibrillation were detected. The plastic elongation during fatigue was larger in Epon 815/Versamid 140. Fracture sources showed cracked material surrounded by a region of stable growth of the main crack. In the brittle Epon 828/Epon Z cracked material was scarce and the crack initiation region was clean, especially at high stress levels. Discontinuous crack growth bands and striations were seen in the stable crack growth regions. During unstable propagation the crack advanced at different levels joined by deep cleavage steps. Branching of the main crack occurred only in the brittle resin at the final stage of propagation.

The main contribution of this paper is the development of a novel process for the formation of copper indium gallium diselenide (CIGS) films. CIGS films with a thickness of 4 μm and grain size from 0.3 μm to 1 μm were prepared from a Cu(In0.7Ga0.3) (CIG) metallic alloy and Se nanoparticles by the intense pulsed light (IPL) technique. The melting of the CIG and Se nanoparticles and nucleation of CIGS occurred in a very short reaction time of 2 ms. It is believed that the Se diffuses into the CIG lattice to form the CIGS chalcopyrite crystal structure. The tetragonal chalcopyrite crystal structure was confirmed by x-ray powder diffraction (XRD), while the microstructure and composition were determined by field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy (EDAX), and x-ray fluorescence (XRF) spectroscopy.