Browse Topic: Fibers
With performance advances proposed for the Future Vertical Lift suite of aircraft and advancements in the electronic battlefield, it is imperative that advanced materials and concepts be included in the vehicle designs to meet the aggressive weight reduction objectives, structural requirements, and operational environment capabilities. Integrating electromagnetic (EM) shielding during the design process offers an opportunity to make progress towards the performance goals. To this end, efforts must be made to minimize the impact of this shielding to platform weight and structural performance. This article presents work to develop a hybrid multifunctional composite material technology that incorporates copper mesh into a carbon fiber and thermoplastic matrix structural composite material to achieve required levels of EM shielding and high levels of structural efficiency while reducing the overall weight of the system. This article focuses on the design of a representative helicopter tailcone as means of illustrating expected improvements in weight and manufacturing cost. Baselines that include structure fabricated from aluminum and thermoset composite are established and predicted improvements quantified.
Stretch broken carbon fiber (SBCF) offers enhanced formability as compared to continuous carbon fiber (CCF). However, robust, quantitative evaluation of forming defects remains a challenge. This study introduces a unified formability index (UFI) that integrates multiple defect types, including texture anomalies, bridging, wrinkling, thickness variation, spring-back, and resin distribution variation (RDV), into a single weighted score. Each defect is ranked on a scale of 0-5 using normalized metrics with a tunable parameter, α, allowing users to balance defect magnitude and frequency as desired. The full scoring pipeline is demonstrated for texture defects using measured data, while normalized legacy scores from previous work are used for non-texture defects to enable complete formability index computation. Case studies on three laminates illustrate how variations in α affect both texture scoring and the overall formability index and demonstrate the geometry-agnostic nature of the updated ranking and UFI systems. This framework maintains compatibility with existing evaluations while offering improved resolution, consistency, and scalability for assessing laminate quality across complex geometries.
The work done in developing stretch broken carbon fiber technology is described. The objectives of the program include the scale up of the process to demonstrate production feasibility, as well as reducing the maximum filament stretch break length to ~50mm/2” or below, less than half of what was achieved on previous programs. The shorter break length is considered to be critical in order to achieve formability into complex geometries. The new stretch break line at Montana State University, BC3, has been commissioned to achieve the required material characteristics and throughput. To date, 6 tows have been successfully stretch broken simultaneously, representing a significant improvement compared with what was achieved on previous programs. Possible geometries and forming evaluation methods are described. Mechanical testing is to be conducted, including both equivalency testing of continuous vs stretch broken carbon fiber and a later minimal level allowables program. It is expected that there will be no strength reduction when using SBCF in a cured laminate as was the case on the prior programs; this will be verified under the current program with material from the new BC3 stretch break line. Single tow SBCF spools will shortly be available for evaluation by potential prepreg manufacturers and other end users.
The demand for carbon fiber reinforced polymers (CFRPs) is growing, especially for use in high-performance applications. Components manufactured of CFRP are made by layering sheets of carbon fibers within a resin matrix. Due to the fibers’ brittle nature, CFRPs are difficult to shape into complex forms, limiting adoption of the material in applications such as vertical lift systems. To address this limitation, researchers at Montana State University, Bozeman (MSU) are developing a new form of carbon fiber called stretch broken carbon fiber (SBCF). SBCF maintains the strength of continuous carbon fibers, while allowing for fiber slip that is used to create a pseudo-plastic strain response needed in most forming processes. Dome and bulge tests were used for comparing the formability response of IM7 MSU SBCF/977-3 with continuous Hexcel IM7 12K/977-3. Results showed increased formability of the MSU SBCF ones due to their ability to stretch under an applied load.
Advanced structural analysis methods, known as progressive damage and failure analysis tools, are being developed to predict initiation and propagation of damage under repeated loading based on capturing individual and interacting damage modes. This work develops structural fatigue life prediction capability in state-of-the-art emerging progressive damage failure analysis tool CDMat developed at the University of Texas Arlington Advanced Materials and Structures Lab. While JIntegral, implemented in CDMat, appears as the most objective and rigorous approach to predict delamination growth-based fatigue life of composite structures, the key material properties of the J-Integral fatigue model have not been measured with the adequate accuracy. This work addressees a fundamental challenge of eliminating the established and routine assumptions and developed a methodology to determine the key material properties meeting the material input data requirements for the JIntegral based structural fatigue life prediction models. This work generated input data for fatigue crack growth propagation, including optimized input data parameters for the in-situ cohesive law and modeling as-manufactured specimen conditions. In addition, a methodology to account for and characterize the effects of fiber bridging in static tests is presented. It uses a simple standard unidirectional panel for testing, before a component is manufactured, fabricated from the same batch of prepreg to qualify the effects of fiber bridging. Also, this work attempted to determine a minimum conservative initial crack size to streamline the fatigue crack propagation prediction. Fatigue predictions have been demonstrated on a representative composite skin–hat stiffener sub-component section and compared with tests.
This work proposes an experimental and numerical activity aimed at developing methods to evaluate the strength and toughness of Kevlar/Epoxy composite fastened joints used in aeronautical structures and exposed to high energy impacts. Experiments were conducted using an Arcan rig that allowed applying various loading conditions, ranging from pull-through to bearing. A non-linear model of the material based on a bi-phasic decomposition and hybrid meshing technique was built and calibrated. The material model was used to develop a high-fidelity model of the junction to simulate the pull-through test with the Abaqus/Explicit finite element solver. The results of the analysis point out that the implemented progressive damage laws are capable of achieving an appreciable experimental-numerical correlation, both from the qualitative and the quantitative standpoint. Therefore, the combined experimental-numerical approach is promising for developing a validated numerical tool capable of predicting the overall response of different junctions with minimal experimental effort, so to provide data for simulating impact scenarios at the rotorcraft structural scale and designing critical joints.
This paper experimentally investigates direct effects of lightning strikes on flax fiber-reinforced polymers. Highcurrent artificial lightning strikes are conducted on coupon level to evaluate thermo-mechanical damage and to quantify the sufficiency of copper wire mesh as lightning strike protection (LSP). The dataset shall also serve for verification of prospected numerical simulation. The natural fiber flax, as a sustainable source of composite reinforcement, has been demonstrated to be suitable for semi-structural parts of rotorcraft. However, its low electrical and thermal conductivity requires a functional LSP layer for aviation applications. The test panels are investigated regarding their material combination, stacking sequence and level of LSP. Results show that two as well as three layers of 72 g/m2 copper mesh are not sufficient to withstand the standardized lightning current component A waveform of 200 kA. The high induced currents and low capability of energy dissipation leads to electro-explosion of metal and transient mechanical forces from shock waves causing mechanical damage on the test panels. Back surface-velocities increase with higher peak currents and higher level of protection results in lower damage. It is shown that a stacking of copper wire mesh results in less arc root dispersion.
Carbon fiber reinforced epoxy composite stiffened panels are increasingly being used for structural components in large transport rotorcraft. However, problems are arising with high levels of vibration and interior noise due to the increased stiffness-to-density ratio of composites. The current investigation explores the potential of reducing vibrations in carbon/epoxy stiffened panels with the integration of acoustic black holes (ABH), namely features that incorporate a power law thickness taper. The proposed approach involves designing a taper into the thickness of the blade stiffeners as well as the thin plate. Integration of ABHs into the fuselage structure has the potential to reduce broadband vibrations. Multiple parametric studies with either an ABH integrated into the blade stiffener or a grid of ABHs integrated into the plate were conducted, and the tradeoffs between vibration amplitudes, panel mass, and compressive buckling load were examined. Carbon/epoxy panels were fabricated using vacuum-bag-oven processing with out-of-autoclave prepreg and verified to be of good quality. The integrated velocity response, a proxy for the radiated noise from a panel, and compressive buckling were simulated using finite elements. Comparisons were made to experimentally measured data from modal testing and compression buckling testing. Experimental results indicated that when an ABH is integrated into the blade stiffener and 15 ABHs are integrated into the plate in a grid configuration, the panel mass was unchanged, the integrated velocity response decreased by 2.82 dB, and the buckling load increased by 2.9% compared to a baseline non-tapered design.
This white paper discusses the application of carbon fiber roving for rotor magnet retention in high-performance Brushless DC (BLDC) motors, focusing on sectors like Advanced Air Mobility and motorsports. Highlighting the benefits of carbon fiber's tensile strength, thermal characteristics, and electrical resistivity, it compares thermoset and thermoplastic matrices, analyzing their trade-offs. It delves into manufacturing methods, particularly the advantages of in-situ winding of Hexcel® HexTow® IM7 12k carbon fiber directly onto rotors, versus pre-wound sleeves, emphasizing controlled processes for even stress distribution and preventing failure. Key design factors such as operating speed, temperature, and air gap dimensions are considered to optimize carbon fiber's application. Windings' expertise in fabricating high-tolerance carbon fiber wound rotors is showcased, highlighting its potential to enhance motor power output and offering collaboration for innovative retention solutions in BLDC motors.
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This SAE Recommended Practice defines a procedure for the construction and testing of glass to metal lap shears for determining shear strength of sealant adhesives for automotive stationary glass bonding. This procedure can also be used for fiber reinforced plastic (FRP) when used in place of metal.
Carbon fiber reinforced polymer composites (CFRP) are extensively used as structural components in rotorcraft applications. Here, we report considerable improvement in the fatigue life of CFRP through the infiltration of nanoscale silica particles into the epoxy resin matrix (nanoCFRP). Fumed silica nanoparticles were initially added to the epoxy resin to prepare epoxy-silica nanocomposites, which were demonstrated to have superior fracture and fatigue properties. Fractographic analysis indicated presence of various key toughening mechanisms including crack deflection, plastic void growth as well as a hitherto unreported heterogeneity induced mesoscale toughening effect. The epoxy-silica nanocomposite resin was then used as the matrix material to fabricate nanoCFRP. Cyclic flexural bending tests indicate significant fatigue life enhancement for the nanoCFRP. The enhancement is especially pronounced in the high cycle fatigue regime. This enhancement in high cycle fatigue is indicative of transfer of small-scale toughening mechanisms from the silica-epoxy nanocomposite resin to the nanoCFRP system. Such nanoCFRP show promise to improve the fatigue life and reduce the operational/maintenance cost for next generation rotorcraft.
The complex dynamics of rotorcraft structures under varying operational and environmental conditions demand the development of accurate and robust-to-uncertainties structural health monitoring (SHM) approaches. The inherent uncertainty within monitoring data makes it difficult for conventional methods to accurately and robustly detect and quantify damage without the need for a large number of data sets. In addition, due to the time-varying nature of rotorcraft operations, such conventional metrics might still fail even with abundance of data. In this paper, we propose a unified probabilistic damage detection and quantification framework for active-sensing, guided-wave SHM that focuses on monitoring rotorcraft structural "hotspots". The proposed framework involves three stages: The first stage incorporates statistical damage detection based on stochastic non-parametric time series (NP-TS) models of ultrasonic wave propagation signals within a hotspot sensor network configuration. The second stage involves the statistical path selection, where a NP-TS representation is used for the sole purpose of identifying damage-intersecting signal (wave propagation) paths, that is the paths that are most sensitive to damage, in order to use them in the subsequent damage quantification stage. That last stage achieves probabilistic damage quantification, where the results of the NP-TS models are used to train Bayesian Gaussian Process regression and classification models. This unified framework ensures accurate and robust damage detection and quantification in a data-efficient manner since only damage-intersecting paths are selected and used in the analysis. The performance of the proposed framework is compared to that of conventional state-of-the-art damage indices (DIs) in detecting and quantifying simulated damage in two representative coupons: a Carbon Fiber Reinforced Polymer (CFRP) coupon and a stiffened aluminum (Al) panel. It is shown that the proposed framework outperforms conventional DI-based active-sensing guided-wave SHM methods.
Bismaleimide (BMI) resins are commonly used in advanced carbon composites for their high service temperature and excellent mechanical properties. In this study, two different BMI resins were compared: 1) formula RS-8HT, a high-cure temperature resin requiring pressurized consolidation, and 2) formula BMI-2, a lower cure temperature resin compatible with vacuum bag only fabrication. The objective was to identify a suitable high-temperature resin system for hybrid aerospace gear application, however, these materials are applicable to a variety of hot-zone parts. Laminates were fabricated from each resin type and characterized by their fiber volume fraction, compression strength vs. temperature, and glass transition temperature (Tg). Optical microscopy was performed to verify laminate quality. It was found that the carbon/RS-8HT laminates were prone to thermally-induced cracking, especially during post-cure. Carbon/BMI-2 laminates were found to attain a high degree of cure and high Tg from a realtively low temperature cure, without crack development. Additionally, the fiber volume fraction of the carbon/BMI-2 laminates, which were fabricated by a vacuum bag only process, were similar to that of the autoclave-processed carbon/RS-8HT laminates.
EPFL researchers have developed electronic fibers that, when embedded in textiles, can collect a wealth of information about our bodies by measuring subtle and complex fabric deformations. Their technology relies on transmission line theory and offers a host of applications, such as in healthcare and robotics.
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