Graphite Composite Plates Research Articles

Study on Properties of Graphite Polystyrene Permeable Composite Insulation Board

In order to further optimize the properties of polystyrene permeable flame retardant composite insulation board, the composition, properties and flame retardant mechanism of graphite polystyrene permeable flame retardant composite insulation board were discussed in this paper. The properties of graphite polystyrene substrate and permeable flame retardant, the optimum ratio of permeable flame retardant. The tensile strength, compressive strength, thermal conductivity and softening coefficient perpendicular to the plate surface are discussed, and the endothermic flame retardant mechanism of osmotic flame retardant was discussed. The results show that graphite polystyrene permeable flame retardant composite insulation plate does not reduce its combustion and mechanical properties when reduces the density and thermal conductivity.

Impact-Induced Delamination Detection of Composites Based on Laser Ultrasonic Zero-Lag Cross-Correlation Imaging

This paper presents impact-induced delamination visualization by zero-lag cross-correlation (ZLCC) imaging computed using fully noncontact laser scanned ultrasonic wavefields. The proposed technique enables instantaneous visualizing of invisible delamination of composite materials without any sensor installation. Moreover, it provides robust damage diagnosis without comparing with baseline data obtained from the undamaged condition of a target structure, making it possible to minimize false alarms. First, the existence of internal delamination-induced standing waves is proven by employing a finite element analysis. Then, how ZLCC can physically isolate and visualize only the standing wave feature from the measured ultrasonic wavefields is shown. To experimentally validate the proposed technique, a fully noncontact laser ultrasonic imaging system is introduced, and the internal delamination is visualized by laser scanning in a graphite fiber composite plate. The experimental results reveal that hidden delamination is successfully and automatically visualized and quantified without any users’ intervention.

Performance Investigation of Polymer Electrolyte Membrane Fuel Cells Using Graphite Composite Plates Fabricated by Selective Laser Sintering

Selective laser sintering (SLS) was used to fabricate graphite composite plates for polymer electrolyte membrane fuel cells, which has the advantages of reducing time and cost associated with the research and development of bipolar plates. Graphite composite plates with three different designs, i.e., parallel in series, interdigitated, and bio-inspired, were fabricated using the SLS process. The performance of these SLS fabricated plates was studied experimentally within a fuel cell assembly under various operating conditions. The effect of temperature, relative humidity, and pressure on fuel cell performance was investigated. In the tests conducted in this study, the best fuel cell performance was achieved with a temperature of 65–75°C, relative humidity of 100%, and back pressure of 2 atm. The performance of fuel cell operating over an extended time was also studied, with the result showing that the SLS fabricated graphite composite plates provided a relatively steady fuel cell output power.

Fabrication of Graphite Composite Bipolar Plate for Miniature PEMFCs by Micro Planing with Multi-Cutter

This study explores the feasibility of using a novel process, micro planing with multi-cutter, to fabricate graphite composite bipolar plates of proton exchange membrane fuel cells (PEMFCs). Through the use of multi-cutter, this study succeeds in machining micro flow channels with dimensions of 0.2 mm×0.23 mm×0.4 mm (channel width × rib width × depth size) on graphite composite bipolar plate (21 mm × 80 mm × 1.5 mm), in a reaction area of 10 mm × 60 mm. The graphite composite plates fabricated by multi-cutter are tested for cell performance under varying back-pressures. Results show that the cell performance increase with the rising back-pressures and can be promoted apparently by decreasing the size of flow channels.

CNTs nanostructuring effect on the properties of graphite composite bipolar plate

Intent of present investigation is to improve the properties of graphite–polymer composite bipolar plate by nanostructuring. This involves the incorporation of different vol.% of multiwall carbon nanotubes (MWNTs) in graphite–polymer composite bipolar plate. It has been found that by inclusion of 1 vol.% of MWNTs in graphite composite plate, the electrical and thermal conductivity of nanocomposite increased by 100%. The thermal conductivity of nanocomposite plate increases from 1 W/m K to 13 W/m K in through-plane and in-plane from 25 W/m K to 50 W/m K at 1 vol.% of MWNTs. This significant enhancement is due to the orientation of MWNTs in all the directions of composite, positive synergistic effect of MWNTs and heat transfer along the axis directions. However, bending strength of nanocomposite increases by 25% and maximum augmentation is in case of 1 vol.% of MWNTs. The improvement in conductivity of nanocomposite plate is due to an increase in the electron transfer ability within the composite plate which influences the I– V performance of ultimate fuel cell. These observations confirm that the optimal content of MWNTs is 1 vol.%, in graphite–polymer composite.

Durability and characterization studies of polymer electrolyte membrane fuel cell’s coated aluminum bipolar plates and membrane electrode assembly

Coated aluminum bipolar plates demonstrate better mechanical strength, ease of manufacturability, and lower interfacial contact resistance (ICR) than graphite composite plates in polymer electrolyte membrane (PEM) fuel cell applications. In this study, coated aluminum and graphite composite bipolar plates were installed in separate single PEM fuel cells and tested under normal operating conditions and cyclic loading. After 1000 h of operation, samples of both the bipolar plates and the membrane electrode assembly (MEA) were collected from both the cathode and the anode sides of the cell and characterized to examine the stability and integrity of the plate coating and evaluate possible changes of the ionic conductivity of the membrane due any electrochemical reaction with the coating material. Scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis were performed on the land and valley surfaces of the reactant flow fields at both the anode and the cathode sides of the bipolar plates. The measurements were superimposed on the reference to identify possible zones of anomalies for the purpose of conducting focused studies in these locations. The X-ray diffraction (XRD) analysis of samples scraped from the anode and cathode electrodes of the MEA showed the tendency for catalyst growth that could result in power degradation. Samples of the by-product water produced during the single fuel cell operation were also collected and tested for the existence of chromium, nickel, carbon, iron, sulfur and aluminum using mass spectroscopy techniques. The EDX measurements indicated the possibility of dissociation and dissolution of nickel chrome that was used as the binder for the carbide-based corrosion-resistant coating with the aluminum substrate.

Structural Health Monitoring of Fiber-reinforced Composite Plates for Low-velocity Impact Damage using Ultrasonic Lamb Wave Tomography

The feasibility of imaging low-velocity impact damage in thin multi-layered composite plates using Lamb wave tomography is explored. Low-velocity impact damages (6-20 J) are induced by the drop-weight method on graphite fiber epoxy matrix composite laminates of cross-ply and quasi-isotropic lay-up and the damage assessment is carried out by conventional C-scans and ultrasonic Lamb wave tomography. Lamb wave based tomography based on modified cross-hole sensor configuration is used to image the damage as a function of impact energy for graphite composite plates. The reconstructed tomograms are able to capture the lateral extent of the damage even for impact energies as low as 11 J in a 2 mm graphite epoxy quasi-isotropic lay-up sample that can be classified as barely visible impact damage.

Effect of Collector Plate Resistance on Fuel Cell Stack Performance

The electrical resistance of the collector plate (both bulk and surface resistance) plays a major role in fuel cell stack performance. Energy Partners (EP) has developed molded graphite composite plates with enhanced electrical conductivity, as an alternative to expensive machined graphite. By optimizing collector plate materials, compounding and molding processes, the resistance of the molded collector/backing layer sandwich was reduced by about 12 mΩcm2. This resulted in an improvement in performance of more than 50 mV per cell at 1 A/cm2 in a 10-cell stack with 300 cm2 active area.

A focused-field eddy current sensor for nondestructive testing

An original structure of an eddy current sensor meant for nondestructive testing of electrically conducting materials is presented. The basic physical principles of the sensors are recalled, and the fact that it is generally impossible to design a sensor with good spatial resolution and good range detection is discussed. An original idea is proposed, which consists of exploiting the good directivity of large cup sensors associated with a particular set of measurements in order to extract relevant information about the small part of the eddy currents induced in the target, below the center of the sensor. This method is illustrated by scanning graphite composite plates containing small defects. The comparison of the results obtained with actual sensors and the authors' focused-field sensor demonstrates the efficiency of the structure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Separation of conductivity and distance measurements for eddy current nondestructive inspection of graphite composite materials

We deal with the study of a process based on the principle of eddy current sensors for the nondestructive evaluation of graphite composite plates. This research has been carried out in the Laboratoire d'Electricite Signaux et Robotique by the team working on data-collecting sensors for robotics in collaboration with Aerospatiale. Eddy current sensors are characterized by their impedance, which varies when a conducting material is approached in their sensitive area. For a given sensor, the output signal depends directly on the electrical and geometrical properties of the object. In the case discussed here, the interesting data are the distance between the sensor and the object, and its local conductivity. In order to invert the relationships between the sensor signal and the properties of the material, an external parametrical model has been developed. A scanning of the surface with a sensor designed for good spatial resolution measurements gives two accurate maps of the useful data

Friction and wear behavior of graphite fiber‐reinforced composites

AbstractFriction and wear behavior of continuous graphite fiber composites was studied for different fiber orientations against the sliding direction. The effect of fiber orientation on friction and wear of the composite and on deformation of the counterface was investigated experimentally. A pin on disk type testing machine was built and employed to generate friction and wear data. A graphite fiber composite plate was produced by the bleeder ply molding in an autoclave and machined into rectangular pin specimens with specific fiber orientations, i.e., normal, transverse, and longitudinal directions. Three different wear conditions were employed for two different periods of time, 24 and 48 hours. The wear track of the worn specimens and the metal counterface was examined and a scanning electron microscope (SEM) to observe the damaged fibers on the sliding surface of the specimen and wear film generation on the counterface. A wear mechanism of the continuous graphite fiber composite during sliding wear is proposed based on the experimental results.

40072 A model for ultrasound transmission through graphite composite plates containing delaminations : Margetan, F.J.; Gray, T.A.; Thompson, R.B.; Newberry, B.P. Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22–26 Jun. 1987. Vol. 7B, pp. 1083–1092. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988

40072 A model for ultrasound transmission through graphite composite plates containing delaminations : Margetan, F.J.; Gray, T.A.; Thompson, R.B.; Newberry, B.P. Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22–26 Jun. 1987. Vol. 7B, pp. 1083–1092. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988