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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.

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.

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.

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.

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.

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.

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.