Carbon Fiber Composite Panels Research Articles

Preparation, Cure, Characterization, and Mechanical Properties of Reactive Flame-Retardant Cyanate Ester/Epoxy Resin Blends and their Carbon Fiber Reinforced Composites

This study explores the formulation space of flame retardant thermoset polymers, specifically involving blends of epoxy and cyanate ester (EP/CE) and a reactive phosphorus-based flame retardant, poly (m-phenylene methylphosphonate) (PMP). Two CE monomers were investigated, each blended with the same epoxy monomer (DGEBA) in a 1:1 wt ratio. The impact of phosphorus concentration on the neat (neat meaning no fibers were present) resin blends was characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The flammability and mechanical characteristics were assessed using micro-combustion calorimetry (MCC) and dynamic mechanical analysis (DMA). Carbon fiber composite panels were successfully fabricated using a wet layup process and autoclave curing with a fiber volume fraction (Vf) of approximately 0.5. DMA testing of the cured composite laminates pinpointed that the average Tg of the EP/CE blend was reduced with PMP addition by up to 39 °C at a phosphorous level of 3 wt%. Cone calorimetry tests confirmed the effectiveness of the flame retardant by reducing the peak Heat Release Rate (HRR) by approximately 27 %. The integration of PMP into EP/CE only marginally reduced the 3-point flexural strength (6–15 %) and modulus (7–13 %) relative to baseline samples.

Low velocity impact and compression after impact of thin and thick laminated carbon fiber composite panels

This study explores the impact behavior of thin and thick composite panels, yielding insights into their behavior under increasing impact energies. Thin composite specimens demonstrated limited surface damage tolerance, while thicker panels remained visually intact but suffered internal damage, adversely affecting their compressive load capacity. The study shows a robust correlation between impact energy and key measurements, including dent depth, bottom surface matrix splitting, and internal delaminations. Moreover, the research identified a consistent pattern in damage initiation, showing that the onset of matrix splitting and delamination remained relatively constant regardless of increasing impact energy, emphasizing the predictability of damage initiation. Compression after impact study showed distinctive responses between thin and thick composites. Thin composites exhibited global buckling before final failure, with a gradual reduction in peak load-carrying capability as damage escalated. In contrast, thick composites suffered substantial damage and delamination at higher impact energies, leading to significant losses, up to 60%, in residual compressive load capacity. The study introduces a simplified quasi-static model to capture delamination effects on panel responses to low-velocity impacts. This study contributes significantly to understanding composite materials’ impact behavior, providing essential knowledge for practical applications and future research endeavors.

Low-velocity impact performance of integrally-3D printed continuous carbon fibre composite sandwich panels

Sandwich panels are heavily used in industrial sectors where specific mechanical properties are of utmost importance due to their high weight-stiffness ratio and energy absorption capacity. Lightweight sandwich cores with bio-inspired topologies have been used as an advanced alternative to conventional bulk cores to improve performance. Nowadays, sandwich structures comprised of core and skins are typically manufactured with two different processes and are afterwards adhesively joined together. Here, with a less time-consuming and more efficient assembly procedure in mind, an integrally 3D-printing strategy is proposed. This investigation analyses the low-velocity impact and quasi-static perforation performance of sandwich core designs inspired by the beetle's forewing trabecular structure. It was found that the core material was responsible of the rate dependence observed in the force–displacement curves. More complex finite element models than those employed here are necessary to capture all the fracture modes observed experimentally.

Innovativeness in tradition: a comparative study of traditional leather armor scales and modern materials

In medieval Korea, armors made of various materials were developed. Among these, the leather armors were lighter and cheaper than the iron armors and were easy to make. For these reasons, there was a movement toward replacing two-thirds of suits of iron armor with leather armor made of pig or cow skin. As a follow-up to a previous study in which the basic physical properties of a leather scale specimen were investigated, in this study, we focused on the protective performance of this material through a comparison with materials such as steel and polycarbonate. In particular, the superiority of the leather was verified through a quantitative comparison with a modern carbon fiber composite. As part of this study, armor that copied the shape of traditional myeonpigap was produced. Carbon fiber composite panels were used to coat this armor in order to satisfy the requirements for the armor to be light, wearable, and provide effective anti-stab protection at the same time.

In-situ integration and performance verification of large-scale PZT network for composite aerospace structure

Piezoelectric transducer (PZT) based structural health monitoring (SHM) technology has been proved to be effective in increasing safety and reliability of composite aircraft structures. However, the attachment of PZT network to the host structure is considered as a weak link when facing the long term durability requirement of aerospace SHM, which should be overcome for aerospace SHM. In this paper, a surface-mounted co-curing method is creatively proposed to realize in-situ integration of large-scale PZT network and composite structure. By jointly controlling curing temperature and pressure, the proposed method can realize integration of large-scale PZT network and structural surface with high reliability and performance consistency. Compared with the conventional integration methods, the proposed method does not affect the manufacturing process or reduce the mechanical property of structure, and can be easily implemented whenever the host structure is available. To evaluate the effectiveness of the proposed integration method, a large-scale PZT network with an overall dimension of 1100 mm × 600 mm is integrated with a carbon fiber composite panel of wing box. The integration caused influence on functional integrity is first assessed by performing electro-mechanical impedance based theoretical analysis and experimental investigation. Then guided wave signals of the integrated large-scale PZT network are also acquired and analyzed, which proves the good signal repeatability and consistency of the network. At last, the SHM performance of the network is verified by conducting impact damages on the composite panel and performing damage monitoring, experimental results show that accurate monitoring is realized.

Improving the reliability of a visual inspection of damaged aircraft structural components made of composite materials

The given article represents the study of the influence of color, surface finish and shape of dents on the reliability of 3D surface dents visual inspection, which are formed due to damage to epoxy composite materials reinforced with carbon fiber resulted from impacts. This article provides an analysis of the influence of surface color of aircraft structural components made of composite materials on the reliability of a visual inspection. The test results are given. Using these values, it is possible to determine the cross-section profiles of surface defects caused by impacts with energy within the range from 5 J to 80 J. The new designs of aircraft, which have been put into service thus far, feature 50 % and more composite materials of the airframe mass and use monolithic carbon fiber composite panels for the fuselage skin. Carbon fiber composite is particularly sensitive to the post-impact compressive strength reduction, and the operating aircraft environment is characterized by an array of sources of impact damages. Samples of the surface appearance of real composite structures of the aircraft on impact is the confidential information. Currently available literature concerning impact damage to composite materials, focuses on impact testing using hemispherical impact elements of typical diameters Ø 15mm, Ø 20 mm or Ø 25 mm. Testing information regarding larger diameter samples is not provided. There is no published research into impact damages to monolithic, fully finished carbon fiber composites.

Low velocity impact and compressive response after impact of thin carbon fiber composite panels

Impact damage of laminated composite structures continues to be a challenging problem. The complexity of damage morphology, the sequence of damage events, and multiple damage modes pose significant challenges when it comes to design for damage tolerance. In an effort to reduce some of the complexity, a systematic experimental study was conducted to understand the sequence of damage during impact of a thin composite plate. Two configurations of carbon fiber reinforced epoxy composite panels were impacted with increasing impact energies. Digital image correlation (DIC), using high speed camera, was performed to measure plate deflection and strain evolution during the impact event. Detailed post impact measurement and imaging were conducted to quantify the extent of damage and delamination. Compression after impact (CAI) tests were conducted to ascertain the post impact compressive load carrying capability of the panel. The results of the experiments indicate a sequence of damage from back surface splitting, delamination and then impact surface compressive failure. Correlations were also found between impact energies, panel configuration and damage type and morphology. The data thus generated is useful for validating computational models for impact damage and CAI. An approach to performing such validation is also provided in this study.

Investigation of carbon nanotube reinforcement to polyurethane adhesive for improving impact performance of carbon fiber composite sandwich panels

In this study, the development of a polyurethane adhesive by using carbon nanotubes (CNT) to enhance the low-velocity impact behavior of aluminum honeycomb sandwich composite structures was investigated. The interaction of CNT and polyurethane for the impact behavior of sandwich composite panels is the main originality of this paper. The fabrication of carbon fiber reinforced composite (CFRC) sandwich structures was conducted using different polyurethane (PU) adhesives and different honeycomb cell sizes. CFRC sandwich structures were fabricated with multi-walled carbon nanotube (MWCNT) added and neat PU adhesives, 6.78 and 10.39 mm honeycomb cell sizes, and carbon fiber prepregs. Neat and nanotube added PU adhesives with MWCNT at reinforcement of 0.1% and 0.2% by weight percent were prepared. Sandwich composite panels were manufactured using the hot pressing method. Specimens of 100 × 100 mm were cut from the sandwich panels, and low-velocity impact tests were conducted at 100 J initial impact energy according to ASTM D7136 standard. After experiments, load-deflection curves, load-time, and energy-time histories were acquired. The absorbed energy values at maximum load were evaluated as a function of MWCNT content and honeycomb cell size. Specimens were sectioned from the impacted region and scanned using scanning electron and optical microscopes to analyze the damaged area. Specimens with MWCNT reinforced adhesives carried higher maximum loads compared to neat ones. CFRC sandwich structures with MWCNT added PU adhesives exhibited a 6% higher impact resistance at 100 J energy levels. Experimental results demonstrated that an increase in MWCNT loading and a decrease in PU adhesive cell size increased the maximum load values in CFRC sandwich panels. Among the nanotube added adhesives, 0.1 wt percent showed the best impact performance.

CFRP-patching enhancement on open-hole CFRP panel with micro/nanofillers-modified adhesive interface: Experimental and numerical simulation

Carbon-fiber composite (CFRP) patching has been widely used to strengthen the open-hole structure, but limited by low adhesive bonding properties. Thus, micro/nanofillers-modified adhesive interfaces are designed to maximize the CFRP-patching capability. Both experiment and numerical studies into flexural behaviors of CFRP-patched open-hole CFRP panel with the modified adhesive interfaces are conducted. Carbon nanotube (CNT) and hierarchical Aramid-Pulp micro/nanofibers (AP) are used as micro/nanofillers to propose CNT-interface, AP-interface and AP-RPCCNT-interface. Here, CNT-modified Resin Pre-Coating (RPCCNT) is proposed as a simple and effective technique for stronger adhesive bonding. The patched open-hole panels with different adhesive interfaces are manufactured and tested under the three-point bending. The flexural behaviors of intact panel, open-hole panel, patched open-hole panel with different adhesive interfaces are compared. It is found that the patched open-hole panels with AP-interface and AP-RPCCNT interface show 41.00% and 55.88% higher maximum flexural load than intact panel. The interfacial enhancements are mainly attributed to the formed CNT-bridging, AP-bridging and across-layer CNT-bridging at the micro-scale. Structural failure and possible interfacial failure mechanisms are revealed by experimental and simulated results, predicted by the validated finite element model. Finally, numerical studies on the related influence parameters are conducted for further understandings.

Preparation and sound transmission loss analysis of carbon fiber composite sandwich panel

Preparation and sound transmission loss analysis of carbon fiber composite sandwich panel

High-force dynamic mechanical analysis of composite sandwich panels for aerospace structures

High-force dynamic mechanical analysis (DMA) has enabled the non-destructive evaluation of thermo-mechanical properties for highly stiff structures over a range of loading frequencies, allowing for additional insight not provided by commonly used static and impact test procedures. In this study, carbon fiber composite sandwich panels with both aluminum and aramid honeycomb cores are characterized based on application conditions in the airframe structure of a high-performance two passenger aircraft. The relative stiffness and damping ability across critical flight frequencies (1 – 100 Hz) for different panel cores are compared. It is found that the damping of the composite sandwich panels is dependent on the applied static load as well as the core material used. Temperature sweeps are also conducted and found to be capable of detecting differences in the glass transition temperature of the composite face sheet matrix material based on post-curing procedures of the manufactured panels.

Investigation on the shear behaviors of carbon fiber composite sandwich panels with the X-core

In-plane shear response of an all-composite X-core sandwich panel was investigated experimentally, numerically and analytically in this paper. The shear experiments of the X-core sandwich panels with three different relative densities were performed and the delamination on the joint and web was the dominant failure mode. Finite element analysis were conducted to further investigate the large deformation and progressive failure of the X-core sandwich panels under in-plane shear loading. The numerical models can correctly simulate the initiation and extension of the delamination and the predictions for the shear response were in good agreement with experiments. A theoretical model based on a modified Reddy zig-zag laminated beams theory and a spring model for the joint were employed to forecast the shear mechanical properties. The analytical results indicated the member shear deformation and joint stiffness had significant effects on the shear modulus and had a reasonable agreement with the experimental results.

Chassis Influence on the Exposure Assessment of a Compact EV during WPT Recharging Operations

In this study, the external magnetic field emitted by a wireless power transfer (WPT) system and the internal electric field induced in human body models during recharging operations of a compact electric vehicle (EV) are evaluated. The magneticfield is calculated with a hybrid scheme coupling the boundary element method with the surface impedance boundary conditions in order to fit the multiscale open-boundary characteristics of the problem. A commercial software is then used to perform numerical dosimetry. Specifically, two realistic anatomical models, both in a driving position and in a standing posture, are considered, and the chassis of the EV is modeled either as a currently employed aluminum alloy and as a futuristic carbon fiber composite panel. Aligned and misaligned coil configurations of the WPT system are considered as well. The analysis of the obtained results shows that the International Commission on Non-Ionizing Radiation Protection (ICNIRP) reference levels are exceeded in the driving position, especially for the carbon fiber chassis, whereas the system is compliant with the basic restrictions, at least for the considered scenarios.

Modal response and vibration attenuation of carbon fiber composite sandwich cylindrical panels made of bi-directional corrugated strip cores

To explore desirable structures with both higher fundamental frequency and better vibration suppression, we designed and fabricated carbon fiber composite bi-directional corrugated sandwich cylindrical panels (BCSCPs) by a hot press molding and post-assembly approach. Modal response and vibration attenuation performance of such structures were investigated experimentally and numerically. Furthermore, the free and forced vibration responses of simple laminated cylindrical panels (SLCPs), axial corrugated sandwich cylindrical panels (ACSCPs) and circular corrugated sandwich cylindrical panels (CCSCPs) with almost the same relative density were investigated and compared with that of BCSCPs. The results indicated that the numerical models were reasonable to estimate the vibration properties of BCSCPs, and the vibration attenuation performance can be improved by suitably increasing the thickness of face sheet and bi-direction corrugated core. Besides, it was revealed that the BCSCPs, ACSCPs and CCSCPs all had comparatively better vibration attenuation performance than that of the SLCPs, and the present BCSCPs generally had higher natural frequencies than those of the ACSCPs and CCSCPs with almost the same weight, which may provide some references for further engineering application of such kinds of composite sandwich structures.

あと施工プレート定着型せん断補強鉄筋と炭素繊維複合パネルの併用による RC 橋脚の耐震補強工法に関する研究

あと施工プレート定着型せん断補強鉄筋と炭素繊維複合パネルの併用による RC 橋脚の耐震補強工法に関する研究

Joint Scanning Laser Thermography Defect Detection Method for Carbon Fiber Reinforced Polymer

In this paper, a new inspection method, joint scanning laser thermography (JSLT) as well as its data reconstruction and processing algorithm, is proposed. The new inspection method is utilized to detect and characterize the flat-bottom holes (FBH) in carbon fiber composites by using joint laser scanning scheme. By analyzing the nature of the thermal image sequences sampled under such a scanning scheme, a quick and simple reconstruction method is developed to characterize the buried depth of defects based on 1D heat conduction model. The processed thermal images are expected to get higher temporal resolution and spatial resolution. It can inspect larger area within shorter acquisition time than the pulse thermography. Thus, the study solves the dilemma between the inspection speed and the inspection capacity. Later, a joint laser scanning thermography test is set up to test the algorithm on a carbon fiber composite panel with defects buried at different depth. The experimental results show that the reconstructed data almost behave as those under pulse excitation. The tendency of temperature to change in the logarithmic domain over time is similar to the curve in the TSR method. But, unlike the pulse thermography data, the defect detection rate of PCA based on reconstructed data is higher than that of fast Fourier transform (FFT) amplitude image, independent component analysis (ICA) and FFT phase image. The JSLT system is used to detect FBHs and the diameter-depth ratio reached 3.33.

Modeling and Measuring the Shielding Effectiveness of Carbon Fiber Composites

We provide a model able to predict the shielding effectiveness (SE) of carbon fiber composite (CFC) panels made of stacked layers of conducting fibers. This model permits us to obtain simple formulas in which the only parameters needed are the sheet square resistance and the effective panel thickness. These tools let us predict a minimum SE, which always increases with the frequency and therefore constituting the worst case, from an electromagnetic shielding perspective. Consequently, the measurement of minimum SE requirements can be simply measured with a micro-ohmmeter using an specific experimental setup which is also described here. Additionally, this method allows to measure very high SE falling far beyond the dynamic range of the values measurable with the most commonly used standard, the ASTM D4935. After describing the modeling technique and the different test setups used, across-validation between theoretical and experimental results is made for four different samples of CFC; two designed to test the modeling assumptions and two which are representative of the ones nowadays used in a real aircraft.

Experimental electrical characterisation of carbon fibre composites for use in future aircraft applications

This study presents experimental testing of samples from two uni-directional carbon fibre composite (CFC) manufactured panels to determine the factors that influence the electrical properties of CFCs and to also determine the temperature coefficient of resistance. The CFC panels were manufactured by two different techniques to compare the impact of the manufacturing process on the electrical properties. Various electrical conductivity measurement methods were evaluated to determine the most consistent and accurate technique. The influence of sample geometry on the measured electrical conductivity was also investigated. Thermal imaging was used to image resistive losses and illustrate the current paths through the fibres within the CFC test samples. Finally, the effects of increasing temperature on the CFC samples are presented, illustrating that CFCs have a negative temperature coefficient.

Phase-Locked Restored Pseudo Heat Flux Thermography for Detecting Delamination Inside Carbon Fiber Reinforced Composites

Thermogram reconstruction methods based on one-dimensional models are widely used in data processing for thermography inspections. However, the surface temperature variances caused by thermal diffusion will be compatible with those caused by delamination whose normalized aspect (diameter-to-depth) ratio is close to 1 when the defect itself is very thin, about 0.15 mm in this research. This phenomenon makes the detection capacity of these methods reduced at such defects with small aspect ratios. The paper proposes a new reconstruction method, phase-locked restored pseudo heat flux (RPHF), for thermography inspection using square-wave optical stimulations. The theoretical analysis shows the independence of the method upon the effect of thermal diffusion blur at defect-free areas. Square-wave thermography tests are conducted on a carbon fiber composite panel with artificial delimitations buried up to 4 mm deep. The method is implemented on a private computer to deconvolute the RPHF kernel from the transformed thermogram data. The data are separated into two sets with a one-period phase shift to each other sequentially; a phase-locked substation is applied between the sets. The global signal-to-noise ratios obtained with the proposed method are compared to those obtained with Busse's lock-in phase images and those with thermographic signal reconstruction. The phase-locked RPHF gives the best global signal-to-noise ratios for normalized aspect ratio at 1.1 when sufficient heat is applied. It's concluded that the thermal diffusion effect at defect-free areas should be considered in thermography inspection for defects with a normalized aspect ratio at 1.1.

Damage detection and location in woven fabric CFRP laminate panels

The need for multifunctional carbon fibre composite laminates has emerged to improve the reliability and safety of carbon fibre composite components and decrease costs. The development of an electrical selfsensing system for woven fabric carbon fibre composite laminate panels which can detect and locate damage due to impact events is presented. The electrical sensing system uses a four probe electrical resistance method. Two different sensing mats are investigated, the main difference between them are the surface area of the electrodes and the distance between the electrodes. To investigate the damage sensitivity of the sensing system for woven fabric carbon fibre composite laminate panels, panels are produced with various thicknesses from 0.84 to 3.5 mm and are impacted at energies from 1 to 10 J to generate barely visible impact damage. Damage is detected using global electrical resistance changes, the changes in electrical resistance vary depending on carbon fibre volume fraction, spacing distance between the sensing electrodes in the sensing mats, the surface area of the electrodes, damage size, and damage type; it is found that the thicker the panel, the less sensitive the electrical resistance system is. The effect of the surface area of the sensing electrodes is high on the electrical resistance baseline, where the baseline increases by up to 55% when the surface area of the sensing electrodes increases from 100 mm2 to 400 mm2; while spacing distance between electrodes has a greater effect on damage sensitivity of the electrical resistance sensing system than the surface area of the sensing electrodes.