Carbon Composite Samples Research Articles

Embedding Fiber Bragg Grating Sensors in Carbon Composite Structures for Accurate Strain Measurement

Fiber Bragg Grating (FBG) sensors written by femtosecond laser pulses in polyamide-coated low bending loss optical fibers are succesfully embedded in carbon composite structures, following laminating and light resin moulding processes which optimize the size of each ply to address aesthetic, drapability and structural requirements of the final components. The sensors are interrogated by a tunable laser operating at around 1.55 μm and their response to temperature and strain variations is characterized in a thermally controlled chamber and by bending tests using suspended calibrated loads and a laser scanning system. Experimental results are in good agreement with simulations, confirming that the embedding process effectively overcomes potential issues related to FBG spectral distortion, birefringence and losses. In particular the effects of the composite material non homogeneity and FBG birefringence are investigated to evaluate their impact on the monitoring capabilities. A bi-material mechanical beam model is proposed to characterize the orthotropic laminates, pointing out better accuracy in estimating the applied load with respect to the classical homogeneous beam model. A comparative analysis, performed on different instrumented carbon composite samples and supported by theory, points out the repeatability of the FBG sensors embedding process and the effectiveness of the technology for real time accurate strain measurement. Based on such measurements damages and/or changes in local stiffness can be effectively detected, allowing for structural health monitoring of composite structures for applications in specific industrial fields like automotive and aerospace.

Defects studies of BiI3-Polymer composites with carbon fillers to achieve better charge transportation for direct X-ray detectors

Wide bandgap heavy semiconductor materials capable of detecting X-rays at room-temperature without cryogenic cooling have great advantages that include portability and wide-area deployment with major applications include medical imaging, spectroscopy, and astrophysics. BiI3 being a wide band gap material, is explored as a prospective material for X-ray and gamma ray detection. However, thick samples of Bismuth tri-iodide (BiI3) are more prone to defects, which trap the photo-generated charge carriers thereby limiting the charge collection efficiency. Here, we report the defects and charge transportation properties of BiI3-polymer (Polystyrene and Polymethyl-methacrylate) composite pellets of thickness 1.5 mm, upon irradiation with X-rays at tube voltage 60 kV. The defects in the samples have been studied using photoluminescence and the lifetime calculation has been done using Time Resolved Photoluminescence Spectroscopy. In order enhance the transport properties, defect engineering in the samples have been done by embedding carbon based conductive fillers into BiI3-polymer composites using hot compression method leading to decrease in the deep defect density. The mobility-lifetime product (μτ) of the charge carriers in composite samples has been calculated to be 6.53 × 10−1 cm2/V, using modified Hetch equation which is enhanced from 10−4 cm2/V for pristine BiI3 and from 10−2 cm2/V for CdZnTe and perovskites-based detectors. Also, the charge collection has been achieved up to 90% at a bias of 0.8 V for BiI3-polystyrene/super carbon composite samples. The results indicate that defects have been mitigated in the stable BiI3-polymer/filler composite pellets, making them a promising material for room temperature X-ray detection and imaging applications.

Determination of interlayer crack resistance of stitched thin-sheet epoxy carbon composites using wedge delamination (wedging) technique

The local indices of the crack resistance of a thin-sheet reinforced polymeric carbon composite (CCM) stitched with glass and aramid threads with a double lockstitch were determined by wedging in the framework of linear elastic fracture mechanics under loading mode I using standard samples in the form of a double cantilever beam (DCB). Different number of stitches and stitching lines were used for different directions of crack propagation relative to the laying of the reinforcing fabric and stitches. It is shown that regardless of the type of stitching thread and the crack propagation direction, the average and normalized (relative to non-stitched samples) values of the local crack resistance parameters of stitched CCM samples mostly depend on the crack propagation area and on the density (pitch) of stitching responsible for a pronounced locality and anisotropy of the crack resistance. The highest resistance to crack propagation is observed in the areas of interweaving of the stitching threads as a result of additional energy consumption for deformation and breaking of stitching threads, and the lowest one is characteristic of the areas between stitches along the stitch or step between lines, both in the longitudinal and perpendicular directions of the crack propagation relative to the laying of the fabric and stitching lines. When evaluating the specific average values of the parameters of the local crack resistance of CCM samples related to one line of stitching with a longitudinal crack propagation or to one stitch when a crack propagates across the stitching lines, the effect of increased local crack resistance in the areas of interlacing of threads turns out to be significantly weaker, whereas this decrease in stitch areas and between the stitching lines is significantly more pronounced. For more accurate assessment of the crack resistance of a thin-sheet stitched CCM, it is advisable to determine and use specific local parameters taking into account scale effects.

RESEARCHES OF THE POSSIBILITY OF ASSESSING DAMAGE TO THREE-LAYER STRUCTURES BY IMPACT DAMAGE BY METHOD OF COMPUTED X-RAY TOMOGRAPHY

This article describes the results of researches on the assessment of the applicability of the method of computer X-ray tomography for monitoring the internal structure of three-layer structures with carbon composite cladding and aluminum honeycomb, a general description of the method is given. It has been experimentally shown that the method of computed X-ray tomography allows one to evaluate the porosity of carbon composite plating, to identify stratifications resulting from impact. Comparative results of the non-destructive testing of a three-layer carbon composite sample made by autoclave molding from a unidirectional carbon tape and an adhesive epoxy matrix and aluminum honeycomb before and after impact are presented. It was revealed that for the upper lining of a carbon composite, the maximum number of macrodefects of the type stratification occurs directly in the impact zone and adjacent local areas, and leads to a change in the geometry of the skin and honeycomb aggregate, as well as a multiple increase in porosity in comparison with the results of the preimpact test. It should be noted that in the lower skin the porosity due to impact increases slightly, evenly distributed over the volume of the skin, which indicates the occurrence of cracking in the polymer matrix of the carbon composite.Thus, the method of computer x-ray tomography is an effective tool for controlling the damage of three-layer structures by impact.

Facile synthesis of carbon-based nanoporous adsorbent exhibiting high ammonia uptake under low pressure range

We synthesized a nanoporous composite of an activated carbon and organic acids, exhibiting a high ammonia uptake under low pressure (9.5-mmHg). It was prepared by impregnation of organic acids (succinic-, itaconic-, benzoic-, or adipic-acid) into an activated carbon. Among thus prepared organic acid/activated carbon composite samples, the activated carbon impregnating succinic acid (13.3 wt%) showed the best ammonia adsorption capacity under the low pressure: 108 cm 3 g −1 (STP) under 9.5 mmHg at 298 K. This amount is slightly higher than that of the previous best-recording ammonia adsorbent. We also investigated the ammonia-breakthrough property of the adsorbent under a very low concentration (100 ppm in argon balance, flow rate of feed gas = 400 mL min −1 ) at 298 K. The breakthrough amount was 1.89 mmol g −1 . The present adsorbent shows high potential in the application fields of purification of land-fill gas and bio-gas which contain very low concentration of ammonia species. • Organic-acid impregnated nanoporous carbon for NH 3 adsorption was synthesized. • This adsorbent shows high NH 3 adsorption capacity under very low pressure. • This adsorbent can be properly used for NH 3 removal from land-fill/bio-gas.

Comparison of Tensile and Impact Absorption properties of Bio-Inspired Helicoidal stacked with Cross-Ply Stacked Carbon Fiber Laminate

Herrigbone structures are identified on the chitins of the Mantis shrimp. Bio-inspired helicoidal arrangement of composite layers can mimic these herringbone structures. First, the carbon composite samples are fabricated using the hand lay-up method, followed by a curing process using a hot press system. The impact absorption properties of these samples will be analyzed through a series of impact tests. The samples will also be tested for its tensile properties to compare the effect of plies arranged in helicoidal [0,45,90], [0,30,60,90] and Cross-ply orientations to form the laminate structure. The results showed that helicoidal samples have higher penetration tolerance and toughness as compared to Cross-ply samples during impact tests. It is found that the specimen with helicoidal stacking sequence has better debonding resistance and improved damage tolerance. The 6-ply helicoidal samples exhibits higher tensile strength as compared to 6-ply Cross-ply samples due to better fiber to matrix adhesion for helicoidal structure in the direction of pulling force.

Manufacturing and Testing of Carbon Composite Samples Intended for Aviation

Abstract The paper presents the manufacturing technology and quality control of samples made of composite materials intended, inter alia, for aircraft elements. The samples are made from carbon fiber reinforced prepreg in a polymer matrix which is commonly used in the aerospace industry. The authors described the dimensional requirements for samples made of composite materials for strength testing, and the main stages of production which have a direct impact on the quality of composite samples. Also presented is the technological process of producing flat carbon composite panels for composite samples, cutting the produced panels with a CNC plotter, cutting the samples on a conventional milling machine, and surface treatment of the samples on a surface grinder. The machining parameters that were experientially found to be optimal for the milling and grinding of carbon samples are specified as well. Finally, the method of quality control of the ready composite samples is described and solutions are presented to improve the production of high-quality samples.

Surface temperature of carbon composite samples during thermal degradation

An infrared camera and a Fourier transform infrared spectrometer were used simultaneously to observe the radiation from the surface of carbon composite samples during thermal degradation experiments. Surface temperatures were estimated from radiation measurements conducted during cone calorimeter tests. Infrared spectra and images were post-processed involving a subtraction method between successive images, to withdraw the high incident flux from the cone calorimeter partly reflected by the sample. The surface intensities were first evaluated as a function of time. Then, an identification step was implemented linking the rise in intensity between two time steps with the increase in sample temperature. Corrections were introduced for the reflection of the incident radiation from the heater and for the true emissivity of the material. Both experimental devices – camera and spectrometer – showed temperature evolutions in a good agreement. The sharp temperature increase of the sample and the auto-ignition of the pyrolysis gases on the surface were observed and evaluated for various incident fluxes from the cone between 20 and 65 kW/m2. Measurements carried out with a short time step down to 0.2 s further allowed an evaluation of the supplementary flux due to the auto-ignition with a peak up to 20 kW/m2 for an incident flux of 35 kW/m2 on a carbon composite sample with surface 50 mm × 300 mm and thickness 5 mm.

Crash Test of Carbon Composite

Composite structures are now increasingly used for their properties in all areas of industrial production where high specific strength is demanded. They gradually replace metal parts and components not only because they are lighter, but above all for their comparable and in many ways even better mechanical properties. Knowledge of behavior of simple synergies between the fibres and the matrix allows the prediction of behavior of complex components and their application in practice. The subject of this article is a description of an experiment and numerical model, that compares the mechanical properties of carbon fiber composite with the values obtained using analytical models. Carbon composite samples were studied in laboratory conditions through Barrier test (ie. Crash test).

A procedure for locating acoustic-emission signals during static testing of carbon composite samples

The results of static tests of specimens that were made from carbon fiber reinforced plastic with a honeycomb filler according to acoustic emission (AE) and strain-gauge measurement are given. When using the two-lag method, the stable locations of AE signals are obtained, which indicates the development of fatigue cracks. The dependences between the main informative parameters of AE signals and features of the destruction of a material are analyzed. According to strain-gauge measurement data, the values of the failure stress are determined.

X-ray tensor tomography(a)(a)The authors declare no competing financial interests.

Here we introduce a new concept for x-ray computed tomography that yields information about the local micro-morphology and its orientation in each voxel of the reconstructed 3D tomogram. Contrary to conventional x-ray CT, which only reconstructs a single scalar value for each point in the 3D image, our approach provides a full scattering tensor with multiple independent structural parameters in each volume element. In the application example shown in this study, we highlight that our method can visualize sub-pixel fiber orientations in a carbon composite sample, hence demonstrating its value for non-destructive testing applications. Moreover, as the method is based on the use of a conventional x-ray tube, we believe that it will also have a great impact in the wider range of material science investigations and in future medical diagnostics.

Effects of Carbon Phase Deposition in Silica Gel Pores on NO2 Reactive Adsorption at Ambient Conditions on Carbon/Silica Composites

Silica-carbon composite samples containing various carbon contents deposited within a silica gel matrix were synthesized. The composites were evaluated as nitrogen dioxide adsorbents at ambient conditions in either wet (70% RH) or dry air streams. The surface chemistry and textural features of the initial and exposed samples were characterized using nitrogen adsorption, potentiometric titration, thermal analysis, and FT-IR. The deposition of the carbon phase significantly increased the amount of NO2 adsorbed in comparison with that adsorbed on the silica gel. With an increase in the amount of carbon an increase in the performance was found. The positive effect was especially noticed when water was present in the system. An oxidation of the surface and release of NO was observed. The acidification/oxidation of the surface is more pronounced in moist conditions, and it is linked to the formation of nitric acid adsorbed in the pore system. The carbon phase besides providing some level of hydrophobicity also brings phenolic groups to the system, on which immobilization of NO2 takes place via nitrification reactions.

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.

Effect of Two-Stage Process on the Preparation and Characterization of Porous Carbon Composite from Rice Husk by Phosphoric Acid Activation

Activated carbon composite prepared from rice husk using phosphoric acid activation has been studied through precarbonization of the precursor followed by chemical activation. This method can produce carbons with micro- and mesoporous structure. The ratio of chemical activating agent to precarbonized carbon was fixed at 4.2. The surface area, pore volume, and pore size distribution of carbon composite samples activated at three different temperatures (700, 800, and 900 °C) were measured using nitrogen adsorption isotherms at 77 K. The pore-opening and pore-widening effects occurred simultaneously during the process, as evidenced by scanning electron micrographs. The X-ray diffraction curve revealed the evolution of crystallites of carbon and silica during activation at higher temperature. The FTIR spectrum also provided evidence for the presence of silica in the carbon composite. The proper choice of the preparation conditions had an influence on the micropore and mesopore volumes of the activated carbon composite, which were 0.1187 and 0.2684 cm3/g, respectively. The production yield was observed to decrease with increasing activation temperature.

SEM analysis of ablated carbon felt–Carbon composite samples

Ablated carbon felt–carbon composite samples were analysed using scanning electron microscopy (SEM). Results indicate processing-induced microstructure change in preoxidized and intermediate strength PAN carbon fibres. Structural features were analysed accordingly.

A one-step process for fabrication of carbon-carbon composites

A one-step preparation of carbon-fiber-carbon-matrix composites has been developed, using a new aromatic diacetylene oligomer as a precursor for the matrix. The oligomer gives 95% carbon yield at 650°C, which permits a major simplification in the current method used for fabrication of carbon-carbon composites. The one-step process includes conventional hot pressing in an inert atmosphere. The carbon composite samples demonstrated good mechanical properties. Scanning electron microscopy showed good wetting of the fibers by the carbon matrix at fracture surfaces.