Publications
236 results found
Fujita Y, Noda S, Takahashi J, et al., 2024, Predicting failure in injection-moulded short-fibre subcomponents under varied environmental conditions through fracture mechanics, Composites Part B: Engineering, Vol: 275, ISSN: 1359-8368
Injection-moulded short-fibre composites are lightweight materials suitable for high-volume applications; however, current simulation methods (based on failure initiation criteria) to design components using these materials cannot yet accurately predict failure. This work presents a methodology to predict failure of injection-moulded short-glass-fibre reinforced thermoplastic (IM-SFRP) composite subcomponents, based on experimentally measured properties. The material's fracture toughness was characterised by Compact Tension tests for different fibre orientations and environmental conditions. These fracture toughnesses were used as the input for cohesive zone modelling in Finite Element simulations of subcomponents representative of automotive applications, coupled with fibre orientation fields predicted by an injection-moulding process simulation. These coupled simulations presented excellent agreement with the experimental results for subcomponents both in terms of (i) the peak load (highlighting the importance of accounting for the finite fracture toughness of the material to accurately predict the ultimate failure of the subcomponents), and (ii) the pre- and post-peak sequence of failure events (verified using fractographic analyses). This work also verified the applicability of temperature-moisture equivalence, not only for material characterisation using coupons including the material's fracture toughness, but also for the mechanical response of subcomponents until final failure. The methodology demonstrated in this paper contributes to designing safer and more efficient damage-tolerant IM-SFRP components.
Kazemi ME, Medeau V, Chen Y, et al., 2024, Ballistic performance of bio-inspired hybrid interleaved composite structures suitable for aerospace applications, Composites Part A: Applied Science and Manufacturing, Vol: 179, ISSN: 1359-835X
We investigate the ballistic performance of an aircraft engine containment casing demonstrator, made of composite materials with a novel bio-inspired hybrid interleaved design, under high-velocity impact (HVI) at a specific angle. Firstly, we apply a bio-inspired (BI) helicoidal design to develop a large-scale monolithic laminate concept made of carbon fibre-reinforced polymer (CFRP). Then, we hybridise the developed BI laminate concept with interleaved blocks of Zylon fibre (PBO)-reinforced polymer to develop a large-scale BI hybrid interleaved laminate concept. We then further hybridise the developed BI hybrid concept with titanium (Ti) foils (located at the impact face) so that in total we have three large-scale laminate concepts. We manufacture 6 large-scale laminates from each concept with dimensions of 225 × 225 mm and a target areal weight of 0.95 g/cm2. We then test them (perpendicularly) under HVI ranging from 150 to 300 m/s to obtain the ballistic limit and energy dissipation. Secondly, after selecting the best-performing developed laminate concept, we scale it up to develop industrial demonstrator panels with a target areal weight of 1.5 g/cm2 and dimensions of 550 × 360 mm. We test the panels under HVI at an angle of 55° with a larger and heavier projectile, to more closely represent a fan blade-off event onto the engine casing. The results of the large-scale laminate concept tests show that the BI hybrid interleaved CFRP/PBO concept outperformed the rest of the concepts with 54% and 34% improvement in energy dissipation compared to that of quasi-isotropic (QI) and the BI monolithic CFRP, respectively. Our results show that small-scale designs for HVI-resistant CFRP-based laminates cannot be simply assumed to exhibit an equivalent performance for industrial applications with thicker laminates, heavier projectiles and impacts at an angle.
Nguyen S, Anthony DB, Katafiasz T, et al., 2024, Manufacture and characterisation of a structural supercapacitor demonstrator, Composites Science and Technology, Vol: 245, ISSN: 0266-3538
Structural power composites, a class of multifunctional materials, may facilitate lightweighting and accelerate widespread electrification of sustainable transportation. In the example considered in this paper, structural power composite fuselage components could provide power to open aircraft doors in an emergency and thus reduce or eliminate the mass and volume needed for supercapacitors currently mounted on the doors. To demonstrate this concept, an 80 cm long multifunctional composite C-section beam was designed and manufactured, which powered the opening and closing of a desktop-scale composite aircraft door. Twelve structural supercapacitor cells were made, each 30 cm × 15 cm × 0.5 mm, and two stacks of four cells were integrated into the web of the beam by interleaving and encasing them with low-temperature-cure woven carbon fibre/epoxy prepreg. This article culminates by considering the engineering challenges that need to be addressed to realise structural power composite components, particularly in an aerospace context.
Kazemi ME, Medeau V, Greenhalgh E, et al., 2023, Bio-inspired interleaved hybrids: Novel solutions for improving the high-velocity impact response of carbon fibre-reinforced polymers (CFRP), Composites Part B: Engineering, Vol: 264, Pages: 1-11, ISSN: 1359-8368
We propose a novel design methodology consisting of bio-inspired (BI) and interleaved layups to develop hybrid carbon fibre-reinforced polymer (CFRP) composite structures for improved high-velocity impact (HVI) performance. Firstly, we apply a BI helicoidal design method consisting of various pitch angles (considering both thick- and thin-ply CFRP) to develop BI monolithic CFRP laminates. Secondly, we apply the interleaving design method to develop BI hybrid CFRP-based laminates interleaved with blocks of BI Zylon fibre-reinforced polymers through the thickness. We evaluate their response and compare it with traditional quasi-isotropic (QI) hybrid bulk layups. In addition to hybridising with Zylon, we apply titanium (Ti) foils to both the monolithic and hybrid CFRP-based laminates to investigate and compare their response. For all our hybrids, we kept the ratio of the hybridising material(s) to be less than 50% to ensure suitable in-plane mechanical properties and aimed at a target areal weight of 0.95 g/cm2. We also manufactured QI thick- and thin-ply monolithic CFRP laminates as baselines. We tested all laminates at 170 and 210 m/s and studied their response and failure modes. Our results show that the average energy dissipation of the QI monolithic thin-ply baseline improved by up to 22% by changing the layup from QI to BI, and by about 118% by changing the baseline QI layup to BI hybrid interleaved. Post-mortem analysis reveals that there are additional failure mechanisms activated in the BI hybrid interleaved layup with respect to the baseline.
Garulli T, Katafiasz TJ, Greenhalgh ES, et al., 2023, A novel bio-inspired microstructure for improved compressive performance of multidirectional CFRP laminates, COMPOSITES PART B-ENGINEERING, Vol: 264, ISSN: 1359-8368
Kazemi ME, Medeau V, Mencattelli L, et al., 2023, Novel zone-based hybrid laminate structures for high-velocity impact (HVI) in carbon fibre-reinforced polymer (CFRP) composites, Composites Science and Technology, Vol: 241, Pages: 1-10, ISSN: 0266-3538
We propose novel zone-based hybrid laminate concepts for improving the high-velocity impact (HVI) response of baseline carbon fibre-reinforced polymer (CFRP) composites while maintaining similar areal weights and retaining substantial in-plane mechanical properties by requiring that about 80% (by mass) of the baseline CFRP is kept in the hybrid concepts. We identify three zones along the thickness of the laminate according to their role during HVI and implemented tailored materials in these zones to improve the HVI response. We studied a wide range of materials, including: fibre reinforcements of carbon (thin- and thick-plies), glass, Zylon and ultra-high molecular weight polyethylene (UHMWPE); a shape memory alloy/carbon fabric; and ceramic, alumina and titanium sheets. All laminate concepts have similar areal weights for a meaningful comparison. After defining the various concepts, we manufactured and measured their specific dissipated energy under HVI, and finally carried out post-mortem analysis (including C-scan and microscopy). The results show up to 95% improvement in energy dissipation over the baseline quasi-isotropic (QI) CFRP configuration.
Asfaw HD, Kucernak A, Greenhalgh ES, et al., 2023, Electrochemical performance of supercapacitor electrodes based on carbon aerogel-reinforced spread tow carbon fiber fabrics, Composites Science and Technology, Vol: 238, ISSN: 0266-3538
Fabric-based supercapacitor electrodes were fabricated by embedding spread tow carbon fiber fabrics, in monolithic, bicontinuous carbon aerogels (CAG). The incorporation of CAG, at less than 30 wt%, increased the specific surface area of the CAG-CF fabric to above 230 m2 g−1 and the pore volume to about 0.35 cm3 g−1, orders of magnitude higher than that for the as-received carbon fibres. The presence of the CAG not only improves the electrochemical performance of the composite electrodes but may enhance the mechanical response due to the high stiffness of the aerogel structure. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance measurements were performed on symmetric supercapacitor cells consisting of two CAG-reinforced fabrics in an ionic liquid electrolyte. The specific capacitance of the symmetric supercapacitor was determined to be in the range 3–5 F g−1, considerably higher than that for the plain carbon fibers. Since optimum structural electrolytes are not yet available, this value was normalized to the total mass of both electrodes to place an upper bound on future structural supercapacitors using this spread tow CAG-CF system. The maximum specific energy and specific power, normalized to the total mass of the electrodes, were around 2.64 W h kg−1 and 0.44 kW kg−1, respectively. These performance metrics demonstrate that the thin CAG-modified spread tow fabrics are promising electrodes for future use in structural supercapacitors. In principle, in future devices, the reduced ply thickness offers both improved mechanical properties and shorter ion diffusion distance, as well as opportunities to fabricate higher voltage multicell assemblies within a given component geometry.
Valkova M, Nguyen S, Senokos E, et al., 2023, Current collector design strategies: The route to realising scale-up of structural power composites, Composites Science and Technology, Vol: 236, Pages: 1-9, ISSN: 0266-3538
Multifunctional structural power composites, which combine mechanical load-bearing and electrochemical energy storage, will transform electric vehicle design. This work focuses on structural supercapacitors, based on carbon aerogel-modified carbon fibre electrodes with copper current collectors. In common with many structural power embodiments, scale-up of these devices is currently limited by large internal resistances and the mass associated with current collection. There is a trade-off between the overall resistive power loss and the additional mass for the current collector material. However, in these devices, mechanical integrity is provided by the structural electrodes, allowing a range of collector designs to be considered. Using finite element simulations, these current collection strategies are explored quantitatively across a range of design space variables. The key conductivity parameters were measured experimentally, using the best existing materials, to inform direct current conduction simulations of the electrode/current collector assembly. For the present device configuration, the performance trade-off is governed by the area of the current collector. The most effective near-term strategy for power loss mitigation lies in reducing the contact resistance; however, improvements can also be obtained by modifying the collector geometry. The findings of this paper can be generalised to other structural power composites and monofunctional energy storage devices, which are relevant in many mass-sensitive electrochemical applications.
Senokos E, Anthony DB, Rubio N, et al., 2023, Robust single‐walled carbon nanotube‐infiltrated carbon fiber electrodes for structural supercapacitors: from reductive dissolution to high performance devices, Advanced Functional Materials, Vol: 33, Pages: 1-11, ISSN: 1616-301X
Multifunctional electrodes for structural supercapacitors are prepared by vacuum infiltration of single-walled carbon nanotubes (SWCNTs) into woven carbon fibers (CFs); the use of reductive charging chemistry to form nanotubide solutions ensured a high degree of individualization. The route is highly versatile, as shown by comparing four different commercial nanotube feedstocks. In film form, the pure nanotubide networks (“buckypapers”) are highly conductive (up to 2000 S cm−1) with high surface area (>1000 m2 g−1) and great electrochemical performance (capacitance of 101 F g−1, energy density of 27.5 Wh kg−1 and power density of 135 kW kg−1). Uniformly integrating these SWCNT networks throughout the CF fabrics significantly increased electrical conductivity (up to 318 S cm−1), surface area (up to 196 m2 g−1), and in-plane shear properties, all simultaneously. The CNT-infiltrated CFs electrodes exhibited intrinsically high specific energy (2.6–4.2 Wh kg−1) and power (6.0–8.7 kW kg−1) densities in pure 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) electrolyte. Multifunctional structural supercapacitors based on CNT-coated CFs offer a substantial increase in capacitive performance while maintaining the tensile mechanical properties of the as-received CF-based composite. This non-damaging approach to modify CFs with highly graphitic, high surface area nanocarbons provides a new route to structural energy storage systems.
Anthony DB, Nguyen SN, Qian H, et al., 2023, Silica aerogel infused hierarchical glass fiber polymer composites, Composites Communications, Vol: 39, Pages: 1-7, ISSN: 2452-2139
Hierarchical systems can address the matrix-dominated failures of structural fiber polymer composites. Here, a new synergistic hierarchical structure combines conventional structural glass fibers with a bi-continuous silica-based aerogel matrix; both pure-silica and organically-modified silicate aerogels are demonstrated. When infused with an epoxy matrix, this type of hierarchical architecture showed a marked improvement in mechanical properties: without any loss in modulus, both the compressive strength and the interlaminar shear strength increased by up to 27%, relative to the equivalent glass-fiber reinforced epoxy composite baseline. The bi-continuous network modification strategy uses industrially-relevant infusion techniques, at or near room temperature, and retains a similar final composite density (within 2%). The strategy presented here provides a versatile and readily applicable means to improve state-of-the art continuous fiber reinforced composite systems in compression and offers an opportunity to develop a new generation of composite materials.
Mohsin MAA, Iannucci L, Greenhalgh E, 2023, Delamination of novel carbon fibre-based non-crimp fabric-reinforced thermoplastic composites in mode I: experimental and fractographic analysis, Polymers, Vol: 15, Pages: 1-14, ISSN: 2073-4360
Delamination, a form of composite failure, is a significant concern in laminated composites. The increasing use of out-of-autoclave manufacturing techniques for automotive applications, such as compression moulding and thermoforming, has led to increased interest in understanding the delamination resistance of carbon-fibre-reinforced thermoplastic (CFRTP) composites compared to traditional carbon-fibre-reinforced thermosetting (CFRTS) composites. This study evaluated the mode I (opening) interlaminar fracture toughness of two non-crimp fabric (NCF) biaxial (0/90°) carbon/thermoplastic composite systems: T700/polyamide 6.6 and T700/polyphenylene sulphide. The mode I delamination resistance was determined using the double cantilever beam (DCB) specimen. The results were analysed and the Mode I interlaminar fracture toughness was compared. Additionally, the fractographic analysis (microstructure characterisation) was conducted using a scanning electron microscope (SEM) to examine the failure surface of the specimens.
Greenhalgh ES, Nguyen S, Valkova M, et al., 2023, A critical review of structural supercapacitors and outlook on future research challenges, Composites Science and Technology, Vol: 235, Pages: 1-19, ISSN: 0266-3538
Structural composites and electrochemical energy storage underpin electrification of transportation, but advances in electric vehicles are shackled by parasitic battery mass. The emergence of structural power composites, multifunctional materials that simultaneously carry structural loads whilst storing electrical energy, promises dramatic improvements in effective performance Here, we assess the literature on structural supercapacitors, not only providing a comprehensive and critical review of the constituent (i.e., structural electrode, structural electrolyte and structural separator) developments, but also considering manufacture, characterisation, scale-up, modelling and design/demonstration. We provide a rigorous analysis of the multifunctional performance data reported in the literature, providing the reader with a detailed comparison between the different structural supercapacitor developments. We conclude with insights into the future research and adoption challenges for structural supercapacitors. There are several significant hurdles which must be addressed to mature this technology. These include development of a processable structural electrolyte; optimisation of current collection to facilitate device scale-up; identification of load-transmitting encapsulation solutions; standard protocols for characterisation and ranking of structural supercapacitors and; predictive multiphysics models for structural supercapacitors. Through addressing such issues, these emerging multifunctional materials will deliver a novel lightweighting strategy that can contribute to managing the ongoing climate crisis.
Fujita Y, Noda S, Takahashi J, et al., 2023, Initiation and propagation fracture toughness of injection-moulded short fibre composites under different environmental conditions, Composites Science and Technology, Vol: 233, Pages: 1-16, ISSN: 0266-3538
Injection-moulded short-fibre composites combine lightweight and manufacturability; however, their fracture behaviour and how it is affected by the microstructure and environmental conditions are yet to be fully characterised. The initiation and propagation fracture toughnesses of injection-moulded short glass-fibre reinforced polyamide 6.6 composites were characterised through compact tension testing under the combined effect of fibre orientation, moisture level and temperature. Full R-curves were calculated using either an FE-based compliance calibration method, or the J-integral method based on full-field measurements from Digital Image Correlation; both data reduction methods provided consistent propagation values for the fracture toughness, although only the J-integral method can characterise the initiation toughness and the shape of R-curves reliably. This work revealed that the material became tougher with increasing fibre orientation along the loading direction, increasing moisture content, and/or increasing temperature; the corresponding increase in toughness was related to changes in failure and toughening mechanisms, identified through fractography. FE simulations of the compact tension tests have demonstrated the need to consider both initiation and propagation values of fracture toughness to accurately predict the response of notched specimens. The thorough characterisation of fracture toughness presented in this paper can contribute to design safer and more efficient damage-tolerant IM-SFRP components.
Anthony D, Woodgate C, Shaw C, et al., 2023, Hierarchical solutions to compressive problems in fibre-reinforced composites, ECCM20 - The 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab), Pages: 1512-1517
Currently, the useable compressive properties of a composite are restricted by set design limits well below the expected intrinsic performance of the materials contained within. The next generation of high-performance fibre-reinforced polymer composites will need to address the challenge of improving the absolute performance of composites in compression. This task requires a rethink of the whole system; not only to address practical limitations of current materials, but their combination, interface, and their architecture. The mechanisms involved do not simply act over the nano-, macro-, or meso-level independently, but are mutually related at the system level, complicating the approach.
Almousa H, De Luca H, Anthony D, et al., 2023, Robust continuous production of carbon nanotube-grafted structural fibres: a route to hierarchical fibre reinforced composites, ECCM20 - The 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab), Pages: 1451-1456
Growth of carbon nanotubes (CNTs) onto the fibre surface by direct chemical vapour deposition (CVD) offers a convenient means to integrate synthesis with assembly. This method delivers the nanostructures where they have the greatest influence on fibre-matrix interface or interphase. However, CVD is usually limited to small batches of short fibre lengths, and can damage the primary properties. Here, we describe a robust process to produce carbon nanotube-grafted-fibres continuously at tow level with a uniform coverage of short (sub-500 nm length), 10-20 nm diameter CNTs. Different CNT growth conditions, such as temperature [650-950 °C], duration [0.72-50 min], line speed [0.6-10 m/h], potential difference [0-1000 V], and reactive gas flow/compositions were investigated. Following optimisation, the fabrication of an entirely “fuzzy” fibre reinforced hierarchical composite was achieved.
Yu B, Katafiasz TJ, Nguyen S, et al., 2023, Characterising and predicting the relationship between translaminar fracture toughness and pull-out length distributions under distinct temperatures, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 381, ISSN: 1364-503X
The translaminar fracture toughness reflects the damage tolerance of a fibre-reinforced composite under longitudinal tension, which often governs the final failure of structures. One of the main energy-dissipation mechanisms that contributes to the translaminar toughness of composites is the fibre pull-out process. The present study aims to quantify and model the statistical distribution of fibre pull-out lengths formed on the translaminar fracture surface of composites, for the first time in the literature; this is done under different temperatures, so that the relationship between pull-out length distributions, micromechanical properties and the translaminar fracture toughness can be established. The fracture surfaces of cross-ply compact tension specimens tested under three different temperatures have been scanned through X-ray computed tomography to quantify the extent of fibre pull-out on the fracture surfaces; the distribution of pull-out lengths showed alarger average and larger variability with an increase in temperature, which also lead to an increase in translaminar fracture toughness. A similar trend has been captured by the proposed analytical model, which predicts the pull-out length distribution based on the analysis of quasi-fractal idealizations of the fracture surface, yielding an overall accuracy of more than 85%.This article is part of the theme issue 'Ageing and durability of composite materials'.
Fujita Y, Noda S, Kimura S, et al., 2023, FAILURE PREDICTION OF INJECTION-MOULDED SHORT-FIBRE COMPOSITES: CHARACTERISATION AND PREDICTION FROM COUPONS TO COMPONENTS
Injection-moulded short-fibre composites are lightweight materials suitable for high-volume applications; however, current simulation methods for these materials cannot yet predict failure accurately. This work proposes a methodology to predict failure of injection-moulded short-glass-fibre reinforced PA66 composite components, based on experimentally measured properties. The material's fracture toughness was characterized for different fibre orientations and environmental conditions, and these values were used as the input for cohesive zone modelling in Finite Element analyses of the subcomponents, coupled with the fibre orientations predicted by an injection-moulding process simulation. The coupled process/structural simulations using cohesive zone modelling presented excellent agreement with the experimental data of the subcomponent tests, highlighting the importance of accounting for the finite fracture toughness of the material to accurately predict the ultimate failure of injection-moulded short-fibre reinforced PA66 composite components.
Almousa HA, De Luca H, Anthony DB, et al., 2023, FAILURE OF CARBON NANOTUBE-GRAFTED CARBON FIBRE REINFORCED COMPOSITES BY SINGLE FIBRE PULL-OUT
Continuous production of carbon nanotube-grafted-carbon fibres (CNT-g-CFs) was performed in an open chemical vapour deposition reactor, and the resultant fibres were used in single-fibre pull-out tests to determine their interfacial properties with epoxy, nanoengineered epoxy, and polypropylene matrices. At a single CNT-g-CF level, the presence of uniform carbon nanotube (CNT) coverage, sub-550 nm length, has been shown to increase the interfacial shear strength (IFSS) by 26% (98.4 ± 7.2 MPa) when compared to the baseline unsized carbon fibre (77.9 ± 5.1 MPa) embedded in a commercial epoxy. The IFSS increased when combining CNT-g-CF with a 2 wt.% multiwall carbon nanotube loaded epoxy matrix to 32% (102.8 ± 6.7 MPa) compared to the same baseline. In a polypropylene matrix, the presence of uniform CNT coverage on the carbon fibre surface also led to an increase in IFSS by 39% (11.2 ± 2.1 MPa) when compared to the unsized carbon fibre/polypropylene baseline (8.1 ± 1.5 MPa).
De Luca HG, Anthony DB, Almousa HA, et al., 2023, CARBON NANOTUBE-GRAFTED QUARTZ FIBERS AS PIEZORESISTIVE REINFORCEMENT ELEMENTS
The mechanical properties of fiber-reinforced composites depend on the properties of the fiber/matrix interface where stress concentrations dominate. Grafting of carbon nanotubes to produce a “hairy” or “fuzzy” carbon fiber creates hierarchical reinforcements, combining two different reinforcement length scales, in this instance micrometer and nanometer. This approach improves the interaction between fibers and polymer matrices, and can enhance thermal and electrical functionality of the final composite. Generally, hairy fiber production is limited to batch processes due to harsh synthesis conditions (e.g. high temperature, inert environment) inherent to chemical vapor deposition, and have only recently been scaled-up to continuous production. The development of hierarchical assemblies, which are the combination of reinforcements at different length scales for instance nanoscale and microscale, have shown promise as multifunctional and structural state-of-the-art materials. The concept of using carbon nano-reinforcements with macroscopic fibers (quartz in this occasion) can directly address the limitations of current composites architectures, e.g. catastrophic failure, limited fire retardancy properties, and poor electro-thermal performances. Continuous production of such hierarchical materials, as a result of research carried out at Imperial College London and the University of Vienna, allows nano-engineered composites to finally meet industry implementation prerequisites. These methods are also compatible with commercial fiber production lines, which is a significant step forward towards the creation of a new class of high performance composite materials. Carbon nanotube-grafted-quartz fibers with uniform 200 nm long carbon nanotubes improved interfacial shear strength of 12% over a commercially sized counterpart (pull-out tests) in an epoxy matrix. Quartz fiber reinforced composites are normally electrically insulating, yet the carbon nano
Garulli T, Katafiasz TJ, Greenhalgh ES, et al., 2023, BIO-INSPIRED MULTIDIRECTIONAL LAMINATES FOR IMPROVED COMPRESSIVE PERFORMANCE
In this study, we developed a novel microstructure inspired by the deep-sea glass sponge Monoraphis chuni to enhance longitudinal compressive performance of multidirectional carbon fibre reinforced polymer laminates. The microstructure features alternating stiff and soft regions, similar to those observed in the sponge's anchoring spicula. To create this microstructure, we utilized a unique manufacturing process. We then assessed the performance of the microstructure through small-scale notched compression tests, comparing it to an industrially-relevant baseline laminate. Our findings demonstrated a statistically significant increase in failure load and average ligament specific stress at failure compared to the baseline, as well as the ability to delay damage initiation and arrest damage propagation. Our research provides valuable insights for the design of lightweight structures under compression.
Whitehouse AD, Yang Y, Médeau V, et al., 2023, A DAMAGE TOLERANT BIO-INSPIRED INTEGRATED COMPOSITE STIFFENER VIA AFP
Stiffened composite panels are vulnerable to rapid debonding of the stiffeners, which has resulted in the development of conservative certification requirements. In this work, inspired by the branch-trunk attachment of trees, an embedded composite stiffener is developed in the pursuit of damage tolerant panels. Improved damage tolerance can pave the way for more ambitious certification requirements, which will allow for more efficient aircraft designs to be realised. Automated Fibre Placement (AFP) is increasingly utilised by industry; in this work, stiffened panels are developed which can be preformed in a single AFP process. This paper presents the results of this manufacturing endeavour, the use of a foam core and curved hat stiffener geometry is validated as an AFP manufacturing route for composite stiffened panels. Preliminary experimental results, using a notched compression configuration, of the bio-inspired embedded concept are presented. Initial stable crack growth and prevention of debonding ahead of the notch tip are demonstrated. Finally, a numerical parametric study is presented for a modified notched compression specimen design to be used in an upcoming comprehensive experimental study of the concept.
Kazemi ME, Médeau V, Greenhalgh E, et al., 2023, BIO-INSPIRED INTERLEAVED COMPOSITE STRUCTURES FOR HIGH-VELOCITY IMPACT APPLICATIONS
We propose a novel design for improving the high-velocity impact (HVI) performance of hybrid carbon fibre-reinforced polymer (CFRP) composite structures. Our novel design consists of a non-conventional bio-inspired hybrid interleaved layup that significantly enhances damage diffusion and energy dissipation in CFRP composite structures. In our design, we retain more than 50% mass of the structure as CFRP to keep in-plane mechanical properties substantial and also aim to maintain the areal weight (compared to the monolithic CFRP baseline). We applied this design methodology to develop laminate concepts made of thin- and thick-ply CFRPs, hybridised with aramid fibre-reinforced polymer (AFRP) for one of the concepts, and also titanium foils for another concept. We tested the laminate concepts under HVI from 150 to 300 m/s and investigated their response in terms of energy dissipation, ballistic limit and failure modes. The results demonstrate a strong increase in ballistic limit and specific energy dissipation for the developed laminate concepts. The bio-inspired monolithic thin- and thick-ply CFRP laminate concepts exhibit about 15% improvement in specific energy dissipation compared to their QI monolithic baselines. Implementing interleaved blocks of AFRP into the bio-inspired monolithic CFRP laminate concepts shows an improvement in specific energy dissipation by up to 54% for the thick-ply and by up to 135% for the thin-ply, compared to their monolithic QI baselines.
Katafiasz TJ, Garulli T, Greenhalgh ES, et al., 2023, COMPRESSIVE FAILURE OF BORON-CARBON FIBRE HYBRID COMPOSITES: A DETAILED EXPERIMENTAL STUDY
Hybridising carbon fibre reinforced polymers (CFRP) with boron fibres offers the potential of improving the compressive response of CFRP. In this work, a small compressive translaminar fracture specimen was designed, manufactured and tested in a scanning electron microscope environment to obtain detailed information on how the presence of the boron fibres affects the typical kinkband formation and propagation within CFRP. It is shown that the boron fibres successfully stop propagating kinkbands in CFRP, and that, as the kinkband approaches a boron fibre, a large split tends to form which protects the subsequent CFRP material.
Whitehouse A, Medeau V, Mencattelli L, et al., 2022, A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite joints, ECCM20 - The 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab)
In this work, we designed metal-CFRP joints with a profiled adherend termination to improve the mechanical performance. We have applied several profiles to the edge of titanium adherends which were adhesively bonded to CFRP substrates. We conducted finite element modelling and experimental 4PB (4-Point-Bend) testing to investigate how the geometry of the adherend edge profile effects the mechanical performance of the joint. This work shows that profiling of the metal adherend can result in increases of at least 27% in the peak load, and of at least 272% in the energy dissipated up to critical failure normalised by the mechanical energy.
Medeau V, Kazemi ME, Greenhalgh E, et al., 2022, Helicoidal layups and interleaved hybrids: a novel design methodology for impact-resistant composite structures, ECCM20 - The 20th European Conference on Composite Materials
Kazemi M, Medeau V, Greenhalgh E, et al., 2022, Implementing structural fuses in CFRP components via microstructurally-engineered crack paths, 20th European Conference on Composite Materials, ECCM20. 26-30 June, 2022, Lausanne, Switzerland, Publisher: Composite Construction Laboratory (CCLab)
This study aims to develop and implement actual carbon fibre-reinforced polymer (CFRP) solutions for realising structural fuses in real components. To this end, we have developed various concepts for structural fuses, applied to generic idealised components and aimed at engaging different in-plane and through-the-thickness damage propagation mechanisms. Micro-cut patterns (MCPs) / crack path combinations have been engraved on thin-ply CFRP prepregs (by using a laser cut machine) for manufacturing CFRP specimens. Afterwards, we have carried out a series of experimental studies to evaluate the fracture properties of various MCPs under three-point bending (3PB). Then, 3PB results were used to refine and down-select ourconcepts, for use in our generic idealised component design to test them under indentation test using a cantilever beam rig. The test results demonstrated that MCPs can provide significant control over the fracture locus and path, additionally allowing the failure initiation load and energy dissipation to be tailored.
Latham KG, Edathil AA, Rezaei B, et al., 2022, Challenges and opportunities in free-standing supercapacitors research, APL Materials, Vol: 10, Pages: 1-14, ISSN: 2166-532X
The design of commercial supercapacitors has remained largely unchanged since the 1970s, comprising powdered electrodes housed in rigid metal cylinders or pouches. To power the next generation of integrated technologies, an evolution in supercapacitor materials and design is needed to create multifunctional materials that allow energy storage while imparting additional material properties (e.g., flexibility and strength). Conductive free-standing electrodes produced from fibers or 3D printed materials offer this opportunity as their intrinsic mechanical properties can be transferred to the supercapacitor. Additionally, their conductive nature allows for the removal of binders, conductive agents, and current collectors from the supercapacitor devices, lowering their economic and environmental cost. In this Perspective, we summarize the recent progress on free-standing supercapacitors from new methods to create free-standing electrodes to novel applications for these devices, together with a detailed discussion and analysis on their electrochemical performance and physicochemical and mechanical properties. Furthermore, the potential directions and prospects of future research in developing free-standing supercapacitors are proposed.
Abdullah SIBS, Iannucci L, Greenhalgh ES, et al., 2022, Impact on Vectran/Epoxy composites: Experimental and numerical analysis, AERONAUTICAL JOURNAL, ISSN: 0001-9240
Ishfaq A, Nguyen S, Greenhalgh ES, et al., 2022, Multifunctional design, feasibility and requirements for structural power composites in future electric air taxis, Journal of Composite Materials, Vol: 57, Pages: 817-828, ISSN: 0021-9983
This study investigates the viability of implementing multifunctional structural power composites in a four-seater air taxi, the CityAirbus. For a given specific energy of the power source, the cruise endurance can be approximately doubled by using structural power composites as opposed to conventional batteries. Replacing all the eligible composite mass and batteries with structural power composites can reduce the CityAirbus weight by 25%. To achieve the current design performance, the minimum required elastic modulus, strength, specific energy and power for the structural power composite are 54 GPa, 203 MPa, 74 Wh/kg and 376 W/kg, respectively: current state-of-the-art structural power composites are now approaching this level of performance. Hence, structural power composites are considered feasible for adoption in the urban air mobility sector and have the potential to improve endurance and facilitate commercialization. This paper also discusses several key challenges that must be addressed to realize the adoption of structural power composites in future electric air taxis.
Garulli T, Greenhalgh E, Pinho S, 2022, A novel bio-inspired microstructure for progressive compressive failure in multidirectional composite laminates, 20th European Conference on Composite Materials, ECCM 2022, Publisher: Composite Construction Laboratory (CCLab)
n this study we take inspiration from biological materials to design a modified microstructure for laminated multidirectional (MD) carbon fiber reinforced polymers (CFRP), with the objective of mitigating their compressive failure behavior. We introduce soft inclusions in the form of thin longitudinal strips of foam in 0° load bearing layers, aiming at arresting kinkband propagation. We conceived a bespoke stacking sequence and developed a tailored procedure for manufacturing the microstructure. We then performed in-situ tests on small scale notched specimens from a baseline laminate and a modified one. Results are presented and discussed.
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