Journal of Composite Materials

Multifunctional structure-battery composites were developed using fiber reinforced marine composites for structure function and rechargeable lithium-ion cells for energy storage and structure function. Laminate, sandwich, and modular beam configurations were fabricated and tested to determine flexural stiffness and strength, energy storage capacity versus discharge rate, and buoyancy (density). The structure-battery composites exhibited higher flexural stiffness but lower strength than equivalent unifunctional designs, energy storage capacities between 40 and 60 Wh/L, and buoyancies bracketing the unifunctional specimen values. Issues requiring further attention include: improved bending strength, simplified fabrication, reversible attachments for modular components, electrical wiring and connections, and battery management circuitry.

This article discusses the design of airborne dye-sensitized solar cell (DSSC) panel integrated in the airplane composite panel which is subjected to mechanical dynamic loading so that the DSSC will function continuously as airborne energy harvester. This article consists of two parts, first synthesis of more rubut DSSC, and then its integration into a composite panel with durability demonstrated.

A novel three-component composite electrode consisting of a carbon current collector with conductive polymer and silver coating is described here. The composite electrode fabrication strategy is described and the composite electrode is evaluated as a cathode for oxygen reduction in non-aqueous media. This approach is utilized for the first time to prepare three-dimensionally structured carbon–conductive polymer–silver composites, yielding composite electrodes with ∼4× the oxygen reduction capacity of their planar counterparts. Improvement of cathode oxygen reduction activity will increase current capability and power output of metal air batteries, facilitating future development of small, lightweight, and long-life power sources.

Preparation and electrochemical evaluation of battery cathodes made from carbon nanotube substrates and lithium trivanadate (LiV₃O₈) are reported in this study. Our carbon nanotube substrate–LiV₃O₈ (CNT-SI) cathodes displayed good rate capability (>140 mAh/g on 1C discharge) and improved capacity retention (>280 mAh/g after 30 cycles at C/20) when utilized in lithium-based batteries. The use of the CNT-SI composite where the electrodes are comprised of a carbon nanotube substrate and active material with no addition of binder, additional carbon additives, and without a foil backing provides the opportunity for a 25% increase in the percentage of active mass and a 36% reduction in the total electrode mass. These benefits demonstrate that considering electrode configuration as well as active material is a key strategic approach to enhance battery energy density.

Recent experimental investigations demonstrated that by incorporating magnetic particles into shape memory polymer matrices, a fast and remote heating of materials and shape recovery could be achieved by exposing the shape memory polymer composite to an electromagnetic field. The particles served as internal mini-antennas to transform the electromagnetic energy to inductive Joule heat, and subsequently to initiate the recovery of shape memory polymers (SMPs). In this paper, a three-dimensional computational study was carried out to study the coupling between heat transfer from spherically shaped particles and heat-induced shape recovery of SMP composites. The influence of particle size, particle volume fraction, particle heating temperature and rate to the magnetically induced shape recovery behavior was studied. The results in this paper provided a meaningful guidance for further designs and applications of the magnetic particles reinforced shape memory polymer composites.

We report a novel strategy that exploits the unique mechanical characteristics of microscale liquid elements to enable versatile multifunctional integration of brittle components into load-bearing structures. The preliminary feasibility of this integration strategy is demonstrated experimentally using chemically patterned 500 -µm-thick silicon chips to emulate brittle functional components. A systematic study of the mechanical characteristics of microscale liquid bridges, including the force-gap relations under axial loading and the control of rupture distances, is discussed to help guide the systematic design of liquid-based mechanical elements for multifunctional integration.

This paper reports development and thermal characterization of tin-capped vertically aligned multiwalled carbon nanotube array composites for thermal energy management in load-bearing structural applications. Three-omega voltage measurements are used to characterize thermal conductivity in the vertically aligned multiwalled carbon nanotube-epoxy composites as well as in its individual constituents, i.e. bulk epon-862 (matrix) and tin thin film in the temperature range 240 K–300 K, and in individual multiwalled carbon nanotubes at room temperature taken from the same vertically aligned multiwalled carbon nanotube batch as the one used to fabricate the carbon nanotube-epoxy composites. A 1-D multilayer thermal model that includes effects of thermal interface resistance is developed to interpret the experimental results. The thermal conductivity of the carbon nanotube-epoxy composite is estimated to be ∼5.8 W/m-K and exhibits a slight increase in the temperature range of 240 K to 300 K. The study suggests that morphological structure/quality of the individual multiwalled carbon nanotubes as well as thin tin capping layer are dominating factors that control the overall thermal conductivity of the thermal interface materials. These results are encouraging in light of the fact that thermal conductivity of a vertically aligned multiwalled carbon nanotube array can be increased by an order of magnitude by using a standard high-temperature post-annealing step. In this way, multifunctional (load bearing) thermal interface materials with effective through-thickness thermal conductivities as high as 25 W/m-K can potentially be fabricated.

The human skin hosts an array of sensors that are capable of detecting and interpreting many traits important to how we function and survive. The goal of mimicking this capability in composites to create intelligent composite materials has led to the development of a bio-inspired stretchable network composed of numerous micro-fabricated sensors capable of detecting multiple stimuli. The components of the network are small scale and flexible making the network embeddable within complexly shaped composite layups and flexible structures with minimal impact on the host structure. This paper outlines recent progress in ongoing work to develop the bio-inspired network in order to create intelligent composite materials.

The erosive effect of ultraviolet radiation and atomic oxygen at the lower earth orbit space environment of the International Space Station on Epon 862 based epoxy composites with 12 and 100 nm silica particles was investigated. Although exposure to ultraviolet radiation had a small effect on surface erosion, restricted to 2 µm of the top surface, concurrent exposure to ultraviolet radiation and atomic oxygen resulted in significant erosion. Atomic oxygen erosion of nanocomposites with 1–5 wt% silica particles resulted in a carpet-like residual surface layer whose thickness and morphology were dependent on the size and concentration of the embedded silica particles. The eroded surface of the control epoxy had high surface roughness in the form of 10–40 µm long conical protrusions. With the addition of silica particles, the residual surface layer became fibrous and rich in silica particles, and its density increased with the weight fraction and size of the silica particles. The large and uneven erosion depth of samples exposed to atomic oxygen and ultraviolet radiation resulted in a surface damage layer with average thickness between 5 and 100 µm with significantly reduced mechanical properties compared to the surface of the as-fabricated nanocomposites. The erosion yield of the control epoxy due to atomic oxygen was 4.36 × 10⁻²⁴ cm³/atom and the addition of silica nanoparticles reduced it significantly to 1.78 × 10⁻²⁵ cm³/atom. In particular, silica nanoparticles of diameter 12 and 100 nm and weight fraction 5% reduced the erosion yield of the control epoxy by 90% and 96%, respectively.

We have developed a new method of electron beam cross-linking to improve electrical conductivity without deteriorating optical transparency of carbon nanotube films. Nano- and micro-patterning on carbon nanotube films are found to be effective in improving optical transparency, but comes at a cost of reducing electrical conductivity. Thermal conductivity of carbon nanotube films can be significantly reduced by nanopatterning. A decreased thermal conductivity may not be all negative, as it could help thermal energy harvesting through increasing Seebeck coefficient and ZT. Multifunctional nanocomposites of carbon nanotube and poly(N-isopropylacrylamide) were prepared and they showed high electromagnetic interference shielding efficiencies and thermal signature reduction while remain optically transparent.

This article examines the concept and design of a multifunctional composite sandwich structure for simultaneous energy harvesting and vibration control. The intention is to design a composite wing spar for a small unmanned aerial vehicle which is able to harvest energy itself from ambient vibrations during normal flight along with available sunlight. If the wing experiences any strong wind gust, it will sense the increased vibration levels and provide vibration control to maintain its stability. The proposed multifunctional composite wing spar integrates a flexible solar cell array, piezoelectric wafers, a thin film battery, and an electronic module into a composite sandwich structure. The piezoelectric wafers act as sensors, actuators, and harvesters. The basic design factors are discussed for a beam-like multifunctional wing spar with energy harvesting, strain sensing, and self-controlling functions. The configurations, locations, and operating modes of piezoelectric transducers are also discussed for optimal power generation. The equivalent electromechanical representations of a multifunctional wing spar is derived theoretically and simulated numerically. Special attention is given to the self-contained gust alleviation with the goal of using available energy harvested from ambient vibrations. A reduced energy control law is implemented to reduce the actuation energy and the dissipated heat. This law integrates saturation control with a positive strain feedback controller and is represented by a positive feedback operation amplifier and a voltage buffer operation amplifier for each mode. This study builds off of our previous research and holds promise for improving unmanned aerial vehicle performance in wind gusts. Here, we also include, but not use, a flexible solar panel in our modeling.