Carbon Fiber Research Articles

Influence of custom dynamic orthoses on tibiotalar joint reaction force and contact Stress: A cadaveric study

Post-traumatic osteoarthritis (PTOA) often develops following tibial pilon fractures. Evidence suggesting PTOA development is driven by elevated articular contact stress from residual malreduction has led surgeons to strive for precise articular reduction, typically at the cost of extended operative time. Post-operative bracing using carbon fiber custom dynamic orthoses (CDOs) offers another means to decrease tibiotalar joint reaction force (JRF) and contact stress. The purpose of this cadaveric study was to measure how CDO stiffness influences ankle JRF and contact stress over the stance phase of gait.A servohydraulic load frame was used to test five cadaver ankles, with axial loading (240–330 N) and pneumatic actuation of the Achilles tendon (50–436 N) serving to quasi-statically model multiple points in the stance phase of gait. Three CDO rotational stiffness conditions were tested: (1) No CDO–0 Nm/deg, (2) low stiffness CDO–1.8 Nm/deg, and (3) moderate stiffness CDO–2.3 Nm/deg. JRF and contact stresses were measured using a piezoresistive pressure sensor inserted into the tibiotalar joint. An insole plantar pressure sensor placed between the cadaveric foot and CDO footplate measured limb/device interactions via the plantar center of pressure (COP).As limb loading progressed through stance, the plantar COP progressed from hindfoot to forefoot, as it would in normal gait. Both CDOs demonstrated decreases in JRF, reaching as high as 32% for the low CDO and 26% for the moderate CDO, with associated decreases in contact stress. This suggests that post-operative bracing could lessen PTOA risk after pilon fractures.

Strain-insensitive fiber sensors bioinspired by spider silk with a multilevel helical structure

The emergence of wearable electronics has greatly stimulated the exploration of fibers due to their inherent wearing comfort. However, the manufacturing of conductive fibers with both exceptional mechanical strength and stable conductive properties remains a formidable challenge. Inspired by the helical structure of spider silk, we propose a strain-insensitive conductive fiber with a multilevel helical structure by helically arranging carbon fibers on the surface of helical polyurethane nanofibers, which is further employed in the fabrication of fiber sensors. The resulting fibers demonstrate outstanding strain stability with a resistance change rate (ΔR/R0) of less than 0.09 when the strain reaches 100% and a resistance change rate below 0.3 at the 200% strain level, significantly outperforming previous reports. Through experimental investigations and computational analysis, we elucidate that the underlying mechanism of the superior conductive performance and stability is attributed to the redundant helical structures and polyurethane nanofiber core layer contraction. Moreover, the fiber devices fabricated on the basis of our strain-insensitive conductive fibers exhibit distinguished performance in various health-related physiological signal monitoring tasks, such as respiration heat monitoring, voice recording, and electrochemical detection of sweat constituents.

Highly protective and functional strengthening strategies for 3D printed continuous carbon fiber reinforced polymer composites: manufacturing and properties

Carbon fiber-reinforced polymer (CFRP) composites have gradually emerged as a crucial material in the aerospace industry. However, inadequate impact resistance and thermal stability limit survival in extreme environments. Inspired by the specific functions of multiple layers of tissue, from bird feathers to the musculoskeletal system. We propose low-cost composite strengthening strategies and efficient novel three-dimensional graphene aerogel manufacturing methods. A novel graphene aerogel/carbon fiber reinforced polymer (GAC) composite prepared by in-situ laser-induced graphene (LIG) layers on the surface of 3D-printed CFRP. GAC composites enhance CFRP's impact protection, thermal insulation, and electromagnetic shielding capabilities. For protection, GAC composites reduce low-velocity impact damage by 26.2%. The graphene layer can increase the thermal buffering capacity of the material four times, and the long-term service temperature can be increased by 40% compared to traditional CFRP. For functionality, the composites enable electromagnetic interference (EMI) shielding effectiveness of up to 50.2 dB. Furthermore, it can achieve surface heating above 400 °C and rapid de-icing through electrothermal effects. The simple and efficient processing method of GAC composites and tunable functionalities holds promise for the development of highly protective and intelligent aircraft skins.

Reliability-based multi-objective optimization design of composite patch repair structure using artificial neural networks

Due to the parameter differences and the existence of random factors, the performance of composite repair structure shows a large dispersion. In order to obtain stronger, lighter and more reliable repair structure, multi-objective optimization design of carbon fiber reinforced polymers (CFRP) laminate repair structure is investigated by combining the reliability theory, artificial neural networks and the genetic algorithm. First, a 3D simulation model of the composite laminate patch repair structures is established using the 3D Hashin criterion and the cohesive region model. Then, the Latin Hypercube sampling (LHS) method is used to realize the random sampling, and the strength proxy model of the repair structure is established by using Back-propagation artificial neural network, further a multi-objective optimization model with tensile strength, reliability and weight as objective functions is built considering the design parameters and the random parameters. Finally, NSGAⅡalgorithm is used to solve the multi-objective optimization problem, and a set of solutions on the Pareto front surface are obtained, also the optimal design parameters of the composite repair structure meets the requirements is obtained.

Electrical energy and overpressure characterization of aeronautical fasteners submitted to a lightning current waveform

Understanding and controlling sparking in fasteners and jointed structures is crucial for flight safety, particularly in fuel tanks. This study investigates the relationship between dissipated electrical energy and pressure buildup within fastener cavities during lightning strikes. Experiments were performed on fasteners installed in aluminum and Carbon Fiber Reinforced Polymer (CFRP) samples, with lightning current waveforms ranging from 1 kA to 10 kA. A sensitivity analysis evaluated the influence of key parameters, such as current peak, clearance fit, sample material, polarity, and fastener coating on pressure rise and energy dissipation. Electrical energy up to 80J and pressure levels reaching 600 bar– unprecedented compared to prior studies – were observed. The pressure-energy relationship showed an approximately linear trend, while pressure exhibited a non-linear dependence on clearance fit. Fastener coating and sample material were found to significantly influence the results, with pressure variations reaching up to a factor of 10 in some cases.

A Novel Small-scale H-type Darrieus Vertical Axis Wind Turbine Manufactured of Carbon Fiber Reinforced Composites

A Novel Small-scale H-type Darrieus Vertical Axis Wind Turbine Manufactured of Carbon Fiber Reinforced Composites

Fabrication of polydopamine doped helical/chiral porous carbon fiber (HPCFs@PDA) and N-doped carbon layers (HPCFs@NCLs) for their application as wave absorber with ultrawide EAB

A new class of wave absorbing materials HPCFst@PDA and HPCFst@NCLs (where HPCFs describes helical/chiral porous carbon fiber, t refers to carbonization 700, 800 °C, PDA ascribed to poly (dopamine), and NCLs corresponds to nitrogen doped carbon layers) with helical/chiral, hierarchical, multi-layered structural morphology containing different heterostructures was triumphantly constructed through single-step carbonization of HPCFst. The HPCFst biomass fiber was go through self-polymerization of dopamine and we get HPCFs700@PDA, HPCFs800@PDA as an intermediate product. Finally, the PDA doped HPCFs biomass (HPCFs700@PDA, HPCFs800@PDA) was effectively transformed into NCLs from inside toward outside (HPCFs700@NCLs, HPCFs800@NCLs) through carbonization. Notably, HPCFs exhibit helical/chiral, hierarchical porous morphology with hetero-interfaces (such as dipole interfaces) that improve dielectric loss, while PDA and NCLs ameliorate wave absorber conductivity, through generation of polarization centers, heterointerfaces and resulting in considerable dielectric loss. Moreover, HPCFs with such unique structural morphology provide additional loss mechanism through cross-polarization that improve dissipation/attenuation of microwave. The microwave absorption mechanism of HPCFst@PDA(1–3), HPCFst@NCLs(1–3) (where 1, 2, 3 refer to filler content 27.50, 30.00, 32.50%wt PDA derived absorber and 20.00, 22.50, 25.00%wt NCLs filler) and their structure active relationship are further elucidated. Evidently, HPCFs700@PDA2 gained reflection loss (RL) of −51.60 dB at 13.60 GHz, across the broad spectrum of frequencies (EAB, RL ≤ −10 dB) covers 6.70 GHz (11.30–18.00 GHz) at 2.70 mm thickness. The EAB ameliorate to the value of 7.20 GHz (10.70–18.00 GHz) at thickness of 2.80 mm. While HPCFs700@NCLs2 RL was improved to −63.00 dB at 2.40 mm thickness with EAB 5.10 GHz (11.40–16.50) at 13.30 GHz frequency. Likewise, HPCFs800@PDA2 RL elevates to the value of −53.40 dB with adequate EAB covering 12.80–18.00 GHz (5.20 GHz) at higher values of 14.40 GHz and 2.10 mm thickness. For HPCFs800@NCLs2, the RL is as high as −65.40 dB at 9.90 GHz, with an effective thickness of 3.20 mm covering 7.50–11.20 GHz (3.20 GHz) EAB. At matching thickness of 2.00 mm the EAB covers 13.80–18.00 (4.20 GHz). Their top-notch microwave absorption capabilities with widened EAB at lower matching thickness demonstrate potentially promising prospects of HPCFst@PDA and HPCFst@NCLs as wave absorbing materials.

Comparative applicability of strength of materials approach to laminated composites with glass and carbon fibre prepregs

Comparative applicability of strength of materials approach to laminated composites with glass and carbon fibre prepregs

Linear viscoelasticity of anisotropic carbon fibers reinforced thermoplastics: From micromechanics to dynamic torsion experiments

The link between experimental characterization and the constitutive behavior of an anisotropic linear viscoelastic unidirectional carbon fiber-reinforced thermoplastic composite is explored using micromechanics modeling. Dynamic torsion tests were conducted at 1 Hz over a wide temperature range, from the glassy to the rubbery states of the polymeric matrix, on both the pure matrix and the composite, for various cutting angles relative to the fibers. A two-step modeling procedure in the frequency domain is presented to predict and validate the effective behavior of the composite. The first step involves FFT-based homogenization, which maps the microstructure and constituent behaviors to effective transversely isotropic viscoelastic properties. The second step consists of finite element simulations using the effective behavior calculated from homogenization as input to replicate the experiments. A comparison between experimental results and model predictions across the entire temperature range is performed. The modeling predictions show good accuracy at low temperatures, where the matrix is in the glassy state. At high temperatures, where the matrix is in the rubbery state, the predicted behavior becomes too soft. As the phase contrast increases and the ratio of matrix bulk modulus to shear modulus rises significantly, the impact of fiber arrangement on the effective properties becomes more pronounced.

Combination of in-/and ex-situ damage detection methods to investigate the forming behavior of fiber-metal-laminates

In this study, the forming behavior of fiber-metal laminates (FML) is investigated by a combination of different (in- and ex-situ) measurement techniques. Using FML-samples consisting of aluminum and carbon fiber reinforced polyamide-6, deep-drawing tests were employed at high temperatures. It can be concluded a conventional approach based on the forming limit curve (FLC) is not suitable to predict the failure initiated in the multi-material setup as principal strains cannot differentiate the strain in aluminum and CFRP and lack sensitivity to detect other relevant failure modes, such as debonding as well as debonding in between layers. To better understand the failure behavior due to forming of FML, an experimental setup, that based on the Nakajima-test, was developed, using in-situ acoustic emission testing, 3D digital image correlation as well as ex-situ X-ray computed tomography. The combined results from all methods helped to gain a deeper insight into how thermoplastic FML behave during deep drawing at elevated temperatures especially focusing on evolving damage inside the hybrid material

Establishing interphase with “rigid-flexible coupling” crosslinking network by supramolecular structure to improve interfacial properties of high modulus carbon fiber reinforced polymer composites

Establishing interphase with “rigid-flexible coupling” crosslinking network by supramolecular structure to improve interfacial properties of high modulus carbon fiber reinforced polymer composites

Evaluating the moisture absorption percentage in the adhesive layers of carbon fiber reinforced plastic joints via electromagnetic induction testing and diffusion analysis

In this study, we propose a method that combines moisture absorption analysis and electromagnetic induction testing (EIT) to detect weak bonds formed in the adhesive layers of carbon fiber reinforced plastic (CFRP) joints due to moisture absorption. Although EIT is effective for assessing CFRP joint adhesive moisture absorption, early detection of weak bonds is challenging. Our method addresses this by combining calculations of moisture absorption percentage via the diffusion equation and EIT-based measurements. First, we conducted diffusion analysis using the finite difference method (FDM). The moisture absorption percentage calculated via the FDM was validated by comparing it with the results of the moisture absorption tests of the CFRP adhesive joints, and good agreement was observed. Second, EIT was applied to the CFRP adhesive joints, and the experimental results indicated that the moisture absorption percentage of the CFRP joint adhesive layer can be qualitatively evaluated using EIT. Finally, the moisture absorption of the CFRP joint adhesive layer was quantitatively evaluated by combining the results of EIT on the CFRP joints with those of the numerical analysis. Therefore, the proposed method enables the previously difficult quantitative evaluation of the initial moisture absorption percentage of CFRP joint adhesive layers and is effective for the early detection of weak bonds created by moisture absorption in CFRP joints.

Research on damage repair and high-velocity impact characteristics of thermoplastic composites

Low-velocity impact (LVI) can result in imperceptible damage to carbon fiber reinforced thermoplastic composites (CFRTP) laminates during service, leading to a reduction in structural strength. The thermal repair of damaged CFRTP laminates is conducted using the repairability of thermoplastic resin at high temperatures. However, the high-velocity impact characteristics of CFRTP laminates following thermal repair remain uncertain. This study examines CFRTP laminates made of two different materials (CF/PEEK and CF/PPS) with varying levels of low-velocity impact damage, and investigates the thermal repair process. A comparative experimental analysis examined the high-speed impact characteristics of CFRTP laminates under varying conditions. The results indicate that CF/PEEK laminates consistently exhibit superior compressive properties and impact resistance compared to CF/PPS laminates under similar conditions. Following damage from low-velocity impact, the compressive properties and high-velocity impact resistance of CFRTP laminates decrease, with CF/PPS laminates typically showing a lower performance retention rate. However, the thermal repair process proposed in this study significantly enhances the performance of CF/PPS laminates. Moreover, the degree of performance healing in CF/PPS laminates is consistently higher than that in CF/PEEK laminates, which is closely related to the semi-crystalline nature of PEEK resin.

Experimental and numerical study of corrugated anchors for CFRP plates

Carbon fibre reinforced polymer (CFRP) plates are promising materials for cables and prestress tendons in structural engineering for the excellent tensile performance, light in weight and anti-corrosion character. Anchoring has always been the main challenge of this high-performance material due to its anisotropy and brittleness. Corrugated anchors are high-efficiency friction-based anchorage devices. Nevertheless, premature failure of the CFRP plates can still be observed with this type of anchors, and the anchor efficiency for the corrugated anchors needs further improvement. This paper proposes a novel configuration of corrugated anchors. Experimental tests are then carried out to investigate the influence of the pre-tensioning bolt load and adhesive layer. Consequently, numerical analysis is conducted to reveal the anchoring mechanism. The results indicate the traditional corrugated anchors lead to non-uniform stress distribution in the CFRP plate, and with the proposed configuration the anchor efficiency can be increased up to 100%.

Ultra-high strength and flame retardant carbon aerogel composites with efficient electromagnetic interference shielding and superior thermal insulation via nano-repairing route

Carbon aerogel composites (CAs) have received numerous attention for protection of aircraft due to their unique properties. However, the shrinkage mismatch between rigid fibers and carbon sources during carbonization dramatically weakens the performance of CAs, and no significant breakthroughs have been made. We propose a vacuum impregnation assisted nano-repairing (VINR) strategy to fabricate crack-free carbon fiber reinforced carbon aerogel (Cf/CA) composites with high strength, electromagnetic interference shielding and thermal insulation. The cross-confined, overlapping nano-CA particles greatly limits the shrinkage of the carbon source, conferring excellent mechanical properties to Cf/CA, and its compressive strength and modulus reaches 3.93 MPa and 69.96 MPa in XY direction and 2.03 MPa and 40.67 MPa in Z direction, respectively, at 5% strain. In addition, Cf/CA exhibits significant thermal insulation (0.054 W/(m·K) at 25 °C under air condition) and superior electromagnetic interference shielding properties (EMI SE is ∼48.52 dB at a thickness of ∼2 mm). Herein, the structurally optimized Cf/CA provides a promising solution for multi-effect protection for critical electronic devices of aircraft in special service environments.

Tailoring magnesium potassium phosphate cement-based adhesive for the improved bonding performance of CFRP/concrete interface

Magnesium potassium phosphate cement (MKPC) with rapid hardening and early high strength can be used as inorganic adhesive for externally bonded carbon fiber reinforced polymer (CFRP). This study aims to tailor MKPC as inorganic adhesive with good infiltration and bonding strength for CFRP-reinforced concrete. The influences of water-to-binder (w/b) ratios and particle sizes of potassium dihydrogen phosphate (PDP) on the fresh properties, hydration kinetics, pore structure, and strength development of MKPC were studied. The bonding strength of CFRP/concrete with MKPC-based adhesive was evaluated by double-shear tests. Results showed that a lower w/b ratio and a finer PDP enhanced the strength of MKPC due to a refined microstructure. The bonding strength of CFRP/concrete was dependent on the rheological characteristics and strength of MKPC. The use of a coarse PDP in MKPC was beneficial to enhance the bonding strength of CFRP/concrete. MKPC with coarse PDP and a w/b ratio of 0.2 resulted in the greatest bonding strength, corresponding to a 20% enhancement compared to epoxy resin. The superior bonding performance of MKPC was ascribed to its higher strength, a better infiltration for CFRP, and a larger MPC/concrete interfacial transition zone (ITZ).

Cotton fiber-derived ultrafine activated carbon fiber for supercapacitor electrode: The effect of fibrillation

Activated carbon fiber (ACF) is a fibrous activated carbon (AC) characterized by high specific surface area (SSA), abundant micropore structure, and excellent machinability, making it an ideal electrode material. This work provided a theoretical basis for the sustainable and large-scale production of high-performance ACF from natural cellulose through fibrillation treatment, papermaking techniques, and CO2 activation. The effect of fiber fibrillation degree on ACF's structure and electrochemical performance was investigated in detail. The results indicated that with the increase of cotton fiber fibrillation, the SSA and beating degree increased gradually, and the air permeability of cotton paper decreased rapidly. The pore volume, SSA, and specific capacitance of ACF all displayed a trend of increasing first and then reducing slowly. Among them, 40°SR ACF had the largest SSA (1267 m2/g) and specific capacitance (0.5 A/g, 129.9 F/g), which were 1.47 and 1.45 times higher than those of ACF without fibrillation treatment. In addition, compared with coconut shell-based AC prepared under the same activation conditions, ACF had a more developed microporous structure, higher SSA, and specific capacitance, making it a preferred raw material for fabricating supercapacitor electrodes. This paper provides a theoretical basis for the application of natural fibers in supercapacitors.

Seismic performance enhancement of underground structure influenced by CFRP wrapping schemes

The seismic failure mechanism of underground structures showing structural collapse is attributed to the deformation incompatibility between the central columns and the sidewalls, especially the insufficient deformation capacity of the central columns. Therefore, the approaches to improve the seismic performance of underground structures mainly aim at avoiding the damage of central columns. This paper presents a comparative study on the seismic performance of underground structures with the central columns retrofitted with different numbers of Carbon Fiber Reinforced Plastics (CFRP) layers. Seismic capacity of the CFRP retrofitting reinforced concrete (RC) columns was explored in detail through experimental and numerical approaches. Then numerical models were built and verified to simulate the behaviors of the CFRP retrofitting RC columns, and the seismic performance of the CFRP retrofitting underground structures was numerically simulated. Based on the numerical results, the damage of the CFRP retrofitting underground structures was calculated, and damage classification illustrated that the seismic performance of underground structures was enhanced remarkably. Finally, parametric studies were conducted to discuss about how the number of CFRP layers and the earthquake intensity affect the earthquake-induced damage of underground structures. Conclusions from this study could be referenced for seismic retrofitting of existing underground structures.

A methodology for selection of solid desiccants in energy recovery ventilators

Controlling indoor humidity levels is essential for maintaining acceptable indoor air quality in buildings. The use of energy recovery ventilators (ERVs) is an energy-efficient way to regulate indoor air humidity. Fixed-bed regenerators and rotary wheels are widely used ERVs because of their high sensible and latent effectiveness. These ERVs are made of desiccant-coated substrates, which enable them to transfer moisture between the supply and exhaust air streams. However, the moisture transfer ability of ERVs depends on the physiochemical and sorption properties of desiccants. Extensive, full-scale experiments are required to determine the best desiccant material for these systems. This paper presents a simplified method of selecting suitable desiccant materials for ERVs. The methodology involves important characterization methods, literature correlations for performance prediction, and cost-effective testing methods prior to full-scale testing, and full-scale test methods are discussed in detail. Furthermore, the performance of a few newly derived materials is evaluated and compared with that of conventional desiccants such as silica gel and molecular sieves. The highest latent effectiveness was obtained for composite of super absorbent polymer (SAP) with potassium formate (SAP-HCO2K-50 %), all-polymer porous solid desiccant (APPSD) and metal organic framework (MOF)–MIL–101 (Cr), followed by activated carbon fibre felt (ACF) Silica sol-LiCl30, SAP, silica gel, MOF–303, and molecular sieve. Researchers and manufacturers would benefit from the proposed methodology and presented data in developing new desiccant materials for ERV applications.

Manufacturing of Thermoset Polyimide Composites by Laser Sintering

Selective Laser Sintering (SLS) is an additive manufacturing technique that builds 3D models layer by layer using a laser to selectively melt cross sections in powdered polymeric materials, following sequential slices of the computer-aided design (CAD) model. SLS generally uses thermoplastic polymeric powders such as polyamides. The resultant 3D-printed objects are often weaker in their strength compared to traditionally processed materials, due to their higher porosity. This paper described the process development of using melt-processable imide oligomers terminated with reactive 4-phenylethynylphthalic anhydride (4-PEPA) to conduct laser sintering (LS). The first successful 3D-printing of high temperature RTM370 thermoset polyimide carbon fiber composite was further post-cured to promote additional crosslinking for achieving higher temperature (Tg = 370°C) capability. Another novel imide oligomer, RTM385-SLS, formulated with a complex melt viscosity [h*] of ~104-105 poise is also suitable for LS. RTM385-SLS resin powder was mixed with 20-25% of hexagonal boron nitride (h-BN) and subjected to LS to print out “Green” specimens which could be further post-cured to afford a thermally conductive but electrically insulating composites with high Tg of 385°C. The cured composite specimens were then subjected to mechanical testing, thermal conductivity and porosity evaluation as well as SEM characterization.