Carbon Composite Plates Research Articles

Impact of cryogenic environment on piezoelectric transducers used in SHM applications

A high number of actors of the space industry, including ESA (European Space Agency) and CNES (French national space agency), are engaged in a program aiming at developing future European reusable space launchers. In this context, PYTHEAS Technology has developed an embedded Non-Destructive Testing (eNDT) solution to ensure that strategic structural elements of the launcher are free of damage before a new launch, performing Structural Health Monitoring (SHM). The sensors used for this application are subject to severe temperature variations, including cryogenic temperatures. Cryogenic conditions are present in other fields requiring SHM solutions, such as liquid hydrogen reservoirs, increasing the importance of this study. Results of experimental tests are presented, where piezoelectric transducers are glued with two types of glue on samples of aluminum plates and carbon composite plates. A reference measurement is carried out before plunging the plates in a climatic chamber, down to -196°C. Pulse-echo and admittance measurements are performed during the temperature decrease and after the temperature rise. The admittance measurements show no deterioration of the samples after being immersed in liquid nitrogen: the transducers, wires, glue, and samples themselves have resisted to the temperature cycle. The pulse-echo signals’ time and frequency analysis show a linear attenuation of the signals relative to temperature. A difference in signal intensity and wave behavior has also been observed relative to the sample’s material: composite or aluminum. No difference regarding the type of glue is witnessed. These results pave the way for damage detection in harsh environments, since the system’s performance is maintained through a whole temperature cycle in cryogenic conditions.

Air-coupled transducer tilted C-scan for delamination introduced during the manufacturing process in CFRP plates

ABSTRACT Carbon fibre reinforced polymers (CFRPs) have gained attention as viable substitutes for conventional metals and alloys in weight-sensitive applications like aerospace, primarily because of their outstanding strength-to-weight characteristics. Nevertheless, these materials are susceptible to intricate and challenging-to-anticipate sub-surface impairments, such as delamination after certain impacts. Non-destructive ultrasonic testing (NDT) is a widely employed technique for examining workpieces’ properties. Nonetheless, conventional ultrasonic testing faces significant constraints due to the necessity of physically coupling ultrasonic transducers to the test medium, typically involving substances like liquid and gel, which could cause unnecessary corrosion and pollution on composite materials. This study proposed a tilted non-contact C-scan detection on carbon composite plates with internal delamination based on air-coupled transducers (ACT). By introducing a tilted C-scan method, the subtle pre-fabricated internal impurities can be detected.

Comparing the efficiency of strengthening timber beams reinforced with carbon composite rods and plates

This study reports the results of experiments comparing the effect of structural reinforcement for timber beams strengthened with different carbon composite materials. Samples of one series were strengthened by gluing a carbon fiber plate from the outside to the face of the beam. The samples of the other series were strengthened by laterally gluing two carbon fiber rods inside the beam. According to the bending research program, the ultimate loads and deflections were determined for both series. As a result of the analysis of the results and comparison with unreinforced samples from the control series, the effect of beam reinforcement and the model of their destruction were determined. Studies have shown that the effect of external reinforcement with a plate was 86.7 % according to the criterion of full failure load, 20.5 % according to the criterion of ultimate load, 13.4 % according to the criterion of ultimate deflection. The effect of rod reinforcement was 48.6 %, 18.6 %, and 4.1 %, respectively. The theoretical analysis of the results showed a convergence of up to 8.2 % with the experimental results. External reinforcement with a plate compared to lateral gluing of rods showed better results due to the placement of the plate in the zone of maximum tensile stresses. This arrangement more effectively limited the spread of ultimate stresses and the development of cracks. The reinforcement parameters of the samples (materials, placement, percentage of reinforcement) were selected under the condition of the same theoretically predicted bearing capacity after reinforcement. However, comparative experimental studies have revealed differences in the processes of deformation and destruction of reinforced beams. The results will contribute to making rational project decisions and for choosing a relevant technique of strengthening timber beams with carbon composite materials

New superstructural thermoplastics and carbon composite materials based on them

New superconstructional polyarylates with glass transition temperatures from 216 to 280°C and polyethersulfones with glass transition temperatures from 230 to 255°C have been developed. On the basis of these polymers, industrial polysulfone PSFF-30, PSF-150, polyethersulfone E-3010, polyetherimide Ultem 1000, PEEK and PEKK, and two types of carbon fabrics, thermoplastic prepregs and consolidated carbon composite plates were obtained, and their mechanical properties under compression and three-point bending were determined.

Experimental research on tungsten alloy spherical fragments penetrating into carbon fiber target plate

A ballistic projectile launching device was used to study the penetration behaviors of tungsten alloy spherical fragments of various diameters into carbon fiber composite target plates of different thicknesses. Based on the ballistic test results, we obtained the relationship between ultimate penetration velocity, target plate thickness, and fragment diameter as well as the relationship between the fragment penetration energy and fragment incident velocity. Using dimensional analysis, we obtained a formula relating the incident fragment velocity and the fragment penetration energy, which showed good agreement with the experimental values. We also analyzed the main fracture mode and the energy absorption mechanism of the carbon composite target plate under high-velocity impacts of tungsten alloy spheres and investigated the experimental damage modes of the target plate at different fragment velocities during the ballistic impact.

Experimental and Numerical Modal Analysis of the Carbon Composite Plate Damaged by Cut

The given paper is closely connected with the experimental and numerical modal analysis of the carbon composite plate damaged by cut. In relation to the tested carbon composite, modal analysis was performed by help of special measuring device Pulse 12. The mentioned device was supplied by company BrĂźel & Kjear and the experimental measurements were carried out using damaged and undamaged plate sample which were prepared from the mentioned material hereinbefore. The investigated and analyzed plates of carbon composite were made of six layers of carbon fibres and they were arranged under the angle 90º (it is like fabric material made off carbon fibres). The layers arranged in the given way were joined by epoxide resin MGS 285. The experimental measurement of eigenfrequencies of carbon composite plates was carried out using the undamaged and damaged sample with proportions 78 mm x 78 mm while ten measurements were performed for each one specified site of the sample. In relation to the damaged plate sample, there was cut in length of 20 mm in the centre border. The finite element method in the software system ADINA v.8.6.2 was used for numerical analysis of the eigenfrequencies.

Condition monitoring with defect localisation in a two-dimensional structure based on linear discriminant and nearest neighbour classification of strain features

ABSTRACTA method for condition monitoring and localization of defects in mass-produced structural members using supervised learning is presented. An example for the effectiveness of the developed method comprises cantilevered carbon composite plate. In a numerical finite element model, the plate is partitioned into zones and a point mass is put on several locations within each zone. Point mass is treated as a pseudo-defect locally modifying structural properties of the plate. For each act of mass application, strain values are recorded and serve as defect-sensitive feature. Two variables of classification are tested – two different supervised learning algorithms (linear discriminant and non-linear k-nearest neighbours) and a limited number of strain data points per class which is varied in the range of 2 to 9 points. Several query points are simulated and subjected to classification in terms of belonging to particular zones of the partitioned plate. This step can be treated as a defect localization. It is shown that only 2 strain readings per class are sufficient for defect localization. The methodology is experimentally validated on a cantilevered carbon composite prepreg of the same dimensions and properties.

Effect of angle orientation lay-up on uniaxial tensile test specimen of Fiber carbon composite manufactured by using resin transfer moulding with vacuum bagging

The main objective of performing uniaxial tensile test is to determine the maximum uniaxial load that a laminate specimen could withstand. The tensile test was carried out to obtain the maximum load and to study effect of the angle-ply laminated composite plates. Specimen is fabricated by using resin transfer moulding with vacuum bagging. Carbon/Epoxy composite with [+45/-45], [0/90] and [0/90 45/-45 combination] lamination schemes were built. The test set was done by using ASTM Standard D3039 with 12 layers of composite laminate. Geometry specimen is 250 mm x 25 mm x 2.75 mm. Fiber carbon composite plates under uniaxial tensile loading for several lamination schemes were modelled by using ACP tool. The tensile strength obtained in ANSYS and compared with experimental value. Based on the result, it can be seen that highest tensile strength on specimen with 0/90 orientation angle lay-up.

Effect of fiber tension on the deformation of a carbon composite plate for space radio telescopes

This study examined the influence of fiber tension on the deformation of carbon composite plates used as the specular surface components of space radio telescopes. Applying the standard equations of composite theory, we developed an analytical model for the stress–strain state of carbon composite plates, considering the fiber tension and thermal stresses. The results of experiments performed on square plates fabricated from the carbon composites were in good agreement with the predictions from the proposed model. The fiber tension of the carbon composite was analyzed for different composite structures. Our results indicated that high fiber tension levels in the carbon composite reduced the degree of deformation in the composite structure.

An investigation into the use of additive manufacture for the production of metallic bipolar plates for polymer electrolyte fuel cell stacks

The bipolar plate is of critical importance to the efficient and long lasting operation of a polymer electrolyte fuel cell (PEMFC) stack. With advances in membrane electrode assembly design, greater attention has been focused on the bipolar plate and the important role it plays. Although carbon composite plates are a likely candidate for the mass introduction of fuel cells, it is metallic plates made from thin strip materials which could deliver significant advantages in terms of part cost, electrical performance and size. However, there are some disadvantages. Firstly, interfacial stability of the metal interconnect is difficult to achieve. Secondly, and the issue addressed here, is the difficultly and cost in developing new plate designs when there are very significant tooling costs associated with manufacture. The use of selective laser melting (SLM: an additive manufacturing technique) was explored to produce metallic bipolar plates for PEMFC as a route to inexpensively test several plate designs without committing to tooling. Crucial to this was proving that, electrically, bipolar plates fabricated by SLM behave similarly to those produced by conventional manufacturing techniques. This research presents the development of a small stack to compare the short term performance of metallic plates made by machining against those made by SLM. Experimental results demonstrate that the cell performance in this case was unaffected by the manufacturing method used and it is therefore concluded that additive manufacturing could be a very useful tool to aid the rapid development of metallic bipolar plate designs.

Experimental Investigation on Modal Response of Woven Fabric Carbon Composite Plate Reinforced with Particles of Micro Rubber Blended Epoxy Matrix under Free Vibration Condition

Vibration damping is proving important for improved vibration control and dynamic stability in advanced engineering systems like aerospace systems, automobiles and in ship building industry. In the present investigation, vibration characteristics of woven fabric carbon composite plate reinforced with micro rubber particle blended into epoxy matrix is studied for enhancing the vibration damping performance. Test Specimens are fabricated in the form of hand layup method. CTBN rubber particle size of 5μm is selected and added to the epoxy matrix for fabricating carbon/epoxy composite plates. Rubber particles of 3% & 15 % by weight were considered as blended percentage in epoxy matrix and compared with 0% addition of rubber particles for understanding and analyzing the vibration characteristics and its difference in damping performance. Vibration damping and modal responses of various kinds of prepared plates were studied and compared. Among tested samples, carbon/epoxy composite plate with 15 wt % micro rubber particle by weight showed very good damping performance.

A matched-pair comparison of two different locking plates for valgus-producing medial open-wedge high tibial osteotomy: peek–carbon composite plate versus titanium plate

The first purpose of this study was to compare the clinical and radiographic outcome of two different locking plates used for valgus-producing medial open-wedge high tibial osteotomy (HTO). The second purpose was to histologically evaluate peek-carbon wear for biocompatibility. Twenty-six consecutive patients undergoing open-wedge HTO using the first-generation PEEKPower HTO-Plate® (Group I) were matched with 26 patients after open-wedge HTO with the TomoFix™ plate (Group II). Clinical scores (visual analogue scale for pain, WOMAC, Lysholm score) were obtained preoperatively and at a minimum follow-up of 24 months postoperatively. Fixation stability was evaluated radiographically by comparing the medial proximal tibial angle (MPTA) and tibial slope 2 days after open-wedge HTO and after implant removal. Tissue samples of Group I were collected at the time of implant removal for histologic evaluation. Implant-related complications occurred in 15 % (n = 4) of Group I and 0 % of Group II. Out of them, 3 implant replacements were excluded from statistical analyses. After a final median follow-up of 25 months (range 24-31), the clinical scores in both groups showed significant improvements compared to preoperatively (visual analogue scale, WOMAC, Lysholm score; p < 0.001), without significant group differences (visual analogue scale, n.s.; WOMAC, n.s.; Lysholm score, n.s.). No significant differences between baseline and follow-up measurements for MPTA and tibial slope were observed within each group (MPTA: Gr. I, n.s.; Gr. II, n.s.; tibial slope: Gr. I, n.s.; Gr. II, n.s.) or between the two groups (MPTA, n.s.; tibial slope, n.s.). In histologic samples, CF PEEK abrasion did not induce inflammation or tissue necrosis. The first-generation PEEKPower HTO-Plate® provided a higher rate of implant-related complications compared to the TomoFix™ plate at a minimum follow-up of 24 months after valgus-producing open-wedge HTO. Therefore, it is not recommended to use the first-generation PEEKPower HTO-Plate® in the clinical practice. III.

Robust inverse identification of piezoelectric and dielectric effective behaviors of a bonded patch to a composite plate

Piezoelectric and dielectric behaviors of a piezoceramic patch adhesively centered on a carbon composite plate are identified using a robust multi-objective optimization procedure. For this purpose, the patch piezoelectric stress coupling and blocked dielectric constants are automatically evaluated for a wide frequency range and for the different identifiable behaviors. Latters' symmetry conditions are coded in the design plans serving for response surface methodology-based sensitivity analysis and meta-modeling. The identified constants result from the measured and computed open-circuit frequencies deviations minimization by a genetic algorithm that uses meta-model estimated frequencies. Present investigations show that the bonded piezoceramic patch has effective three-dimensional (3D) orthotropic piezoelectric and dielectric behaviors. Besides, the sensitivity analysis indicates that four constants, from eight, dominate the 3D orthotropic behavior, and that the analyses can be reduced to the electromechanically coupled modes only; therefore, in this case, and if only the dominated parameters are optimized while the others keep their nominal values, the resulting piezoelectric and dielectric behaviors are found to be transverse-isotropic. These results can help designing piezoceramics smart composites for various applications like noise, vibration, shape, and health control.

Inspection on SiC coated carbon–carbon composite with subsurface defects using pulsed thermography

An investigation on SiC coated carbon–carbon (C/C) composite plates has been undertaken by pulsed thermography. The heat transfer model has been built and the finite element method (FEM) is applied to solve the thermal model. The simulation results show that defects with DA/DP smaller than one can hardly be detected by an infrared camera with the sensitivity of 0.02°C. Certificated experiments were performed on the built pulsed thermography system. The thermal wave signals have been processed by subtracting background image method (SBIM), pulsed phase thermography (PPT), and temperature–time logarithm fitting method (TtLFM). The limit DA/DP of defects in SiC coated C/C composite plates with the thickness of 6mm that can be detected by pulsed thermography with the presented signal analysis algorithms has been obtained.

Preparation and characterization of carbon composite plates using Ni-PTFE composite nano-plating

Graphite particles (100 and 40μm) were coated with Ni (18–38wt.%) and PTFE fine particles (0.3μm; 8wt.%) via electroless Ni-PTFE composite nano-plating. The conductivity of C/Ni-PTFE with 100μm and 40μm graphite particles increased concomitantly with the Ni content and reached about 300Sm−1 and 210Sm−1 at 38wt.% Ni, respectively. The particles were pressed into be plates under a pressure of 10–500kgcm−2 and the plates were then subjected to heat treatment at 350°C. The surface of C/Ni-PTFE plates contained infinitely many gaps of 0.01–20μm; these gaps are useful as a pathway for reacting gases. The current density (43mAcm−2 at 300mV) of C/Ni-PTFE electrode with 100μm graphite particles was about 2.4 times higher than that of C/Ni-PTFE electrode with 40μm graphite particles, which might be attributed to the improvement of total conductivity.

Multi-scale damage state estimation in composites using nonlocal elastic kernel: An experimental validation

In recent years early detection of structural damage (detecting incubation of damage) has received great attention in the structural health monitoring field. However, extraction of lower scale information to quantify the degree of damage is a challenging task, especially when the detection is based on macro-scale acoustic wave signals. All materials exhibit dependence on the intrinsic length scale. An attempt is made in this paper to extract lower scale feature from the macro-scale wave signal using nonlocal elasticity theory. The Christoffel solution has been modified using nonlocal parameters. The dispersion curves are generated for anisotropic solids using perturbation parameter through nonlocal theory. Dispersion curves are sensitive to initiation of damage in anisotropic solids at the intrinsic-length scale. In this paper detection of initiation of damage in a 4 mm carbon composite plate is demonstrated by employing nonlocal perturbation parameter and formulating a new Nonlocal Damage Index (NDI). The nonlocal theory is used to demonstrate the early prediction of failure of the system and to show progressive evolution of the damage.

Modelling of machinability parameters of carbon–carbon composite—a response surface approach

This paper reports the experimental investigations on the electric discharge machining of carbon–carbon composite plate using copper electrodes of negative polarity. The relevance of this study is that it establishes empirical relations, as a function of machining variables, relevant to analyse the machinablity of carbon–carbon composite. The machinability parameters (response functions) considered are relative circularity of hole represented by the ratio of standard deviations, overcut, electrode wear rate (EWR) and material removal rate (MRR) while machining variables are pulse current, pulse on time and gap voltage. Experiments are conducted on the basis of Response surface methodology (RSM) technique. Empirical models correlating process variables and their interactions with the said response functions have been established. The models developed reveal that pulse current is the most significant machining parameter on the response functions followed by gap voltage and pulse on time. These models can be used for selecting the values of process variables to get the desired values of the response parameters.

Impact damage detection in carbon fibre composites using HTS SQUIDs and neural networks

A neural network-based data analysis tool, developed to speed the damage detection process for the NDE of impact damaged carbon fibre composites, is discussed. A feature extraction method utilising a gradient threshold search function and a feed forward neural network for pattern recognition were used to develop the system. Impact damaged carbon composite sample plates were scanned with an eddy current-based NDE setup using HTS SQUID gradiometers and double-D excitation coils. Detection of damage sites in data affected by noise spikes caused by environmental disturbances is demonstrated. Finally, a possible design for a future entirely automated scanning system is also introduced.

Impact damage with compressive preload and post-impact compression of carbon composite plates

This paper examines the effect on laminated composites of in-plane compression followed by impact damage, and the coupling between the two, on compression-after-impact (CAI) performance. It is found that preload can actually raise the CAI strength if the load approaches the initial buckling value, since the plate loses stiffness and the impact-induced force is reduced and so is the consequent damage. However, as the preload approaches the CAI strength the induced delamination can propagate catastrophically during the impact, but at a preload value below the CAI strength. The coupling between impact and preload is simulated using the equations of motion, and the same dynamic solver is then used to capture the snap-through when a plate is loaded beyond its initial buckling load. A special ‘dynamic relaxation’ routine is shown to be robust and reliable when handling these ‘snap-through’ problems which can be formidable challenges to conventional static incremental loading.

An experimental study of the failure modes of reinforced concrete beams strengthened with prestressed carbon composite plates

Concrete structures deteriorate for various reasons and upgrading has been achieved for over 20 years by bonding steel plates using epoxy resins. Disadvantages of this method include transporting, handling and installing heavy plates and corrosion of the plates. The use of composite materials overcomes these problems and provides equally satisfactory solutions. The rehabilitation of concrete structures represents a large demand for efficient strengthening methods and composite materials are well suited to this application. Further advantages are gained by prestressing the plate before bonding to the concrete. The benefits of external prestressing using polymeric composite materials have been investigated only relatively recently and further work in this field is needed in order to understand the behaviour of members prestressed with composite materials, thereby allowing full advantage to be gained from the ease with which composites can be handled and applied, and from their excellent duarability. This artcile is concerned specifically with the failure modes of reinforced concrete beams prestressed in this way. Reinforced concrete beams of 1.0 and 4.5 m lengths were tested in four point bending after strengthening them with externally bonded carbon fibre reinforced polymer plates. The plates were bonded without prestress and with prestress levels ranging from 25% to 50% of the plate strength. The non-prestressed beams failed by separation of the plate from the beam, associated with concrete fracture in the cover to the internal rebars, while most of the prestressed beams failed by plate fracture. The plate prestress prevented cracking of the adhesive layer, a phenomenon associated with shear cracking in the concrete. The bonded plates failed progressively by longitudinal splitting and interlaminar fracture, rather than suddenly without warning. Under a shear span-beam depth ratio of 3.40, plate separation was initiated by a shear displacement in the concrete: a high prestress was required to enable the ultimate plate strain to be reached before the shear displacement reached its critical value.