Article

New Carbon Fiber Tow-Spread Technology and Applications to Advanced Composite Materials

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Abstract

The new tow spreading technology (FUKUI method) to obtain the continuously wide and thin reinforcing fiber tow was developed. By the use of this method, thin prepreg sheet less than 0.05 mm in thickness can be produced at the processing speed of 10 m/min or higher. And also, we developed the weaving process of the spread fiber tow, and it succeeded in manufacturing the woven fabric of 80 g/m2 or less in fiber weight with spread fiber tow from 12K carbon fiber. Then, the various mechanical tests were conducted on the quasi-isotropic laminated composites consist of the thin prepreg sheet with spreading technology. As a result, the dramatic differences in the mechanical properties (tensile, compression, and fatigue) were clarified. Particularly, the thin layer (Thickness is 0.05 mm or less) laminated composites were superior to the conventional layer (Thickness is approx. 0.13 mm and more) laminated composites.

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... The state of the art is to use 3k tows for woven fabrics and conventional 12k tows for unidirectional (UD) tapes. A recent method for achieving ultra-lightweight composite material is referred to as spread-tow technology [1,2], whereby a conventional 12k CF tow (i.e. comprising 12,000 filaments) is thinned by increasing the tow width from 5 mm to 25 mm, thereby reducing the weight per unit area by approximately 500%. . ...
... Fig. 1 shows a schematic diagram of the technology used for tow spreading. The mechanism involved is referred to as pneumatic spreading and has been previously described in the literature [1,2]. In Fig. 1, the original (conventional/un-spread) CF tow is threaded though a spreading system that is provided with an air duct and a vacuum that sucks the air downward through the air duct which is controlled in position by guide rolls. ...
... Fig. 2 shows the experimental setting of spreading process used in this work. Multiples of CF spread tows creels were produced (5 m/min for each tow) and subsequently used on a loom specially designed for the warp insertion of spread tows [1]. ...
Conference Paper
This paper reports a study of a method for achieving ultra-light weight thermoplastic composites referred to as tow-spreading technology, whereby a conventional 12k carbon fibre (CF) tow is thinned by increasing the tow width from 5mm to ca 25mm, thereby reducing the weight per unit area by ca 500%. Using the tow-spreading technology, sheets of unidirectional and/or woven fabric may be produced. Thermoplastic film of Polyphenylene sulphide (PPS) was used to stabilise and impregnate the spread tow fabric, converting it into a partially consolidated prepreg; woven 12k CF spread tow/PPS (50/50 wt. %). A consolidated laminate was then made from the prepreg, and for comparison, a second laminate was produced from a conventional woven prepreg of 3k CF/PPS (60/40 wt. %). The spread tow laminate exhibited better fibre packing, lower level of crimp, lower void content and improved mechanical properties.
... The state of the art is to use 3k tows for woven fabrics and conventional 12k tows for unidirectional (UD) tapes. A recent method for achieving ultra-lightweight composite material is referred to as spread-tow technology [1,2], whereby a conventional 12k CF tow (i.e. comprising 12,000 filaments) is thinned by increasing the tow width from 5 mm to 25 mm, thereby reducing the weight per unit area by approximately 500%. . ...
... Fig. 1 shows a schematic diagram of the technology used for tow spreading. The mechanism involved is referred to as pneumatic spreading and has been previously described in the literature [1,2]. In Fig. 1, the original (conventional/un-spread) CF tow is threaded though a spreading system that is provided with an air duct and a vacuum that sucks the air downward through the air duct which is controlled in position by guide rolls. ...
... Fig. 2 shows the experimental setting of spreading process used in this work. Multiples of CF spread tows creels were produced (5 m/min for each tow) and subsequently used on a loom specially designed for the warp insertion of spread tows [1]. ...
... comprising 3000 filaments) tows for woven fabrics and conventional 12k tows for UD tapes. A recent method for achieving lightweight composite material is referred to as spread-tow technology [2,3], whereby conventional tow (typically 12k CF) is thinned by increasing the tow width from 5mm to 25mm, thereby reducing the weight per unit area by ca 500%, consequently the thinner the ply the better the composite mechanical properties [4][5][6][7]. ...
... Tow-Spreading Technology Figure 1 shows a schematic diagram of the spreading method used for CF tow-spreading. The mechanism involved is referred to as pneumatic spreading and is well described in the literature [1,2]. Multiples of CF spread-tow creels were produced and subsequently assembled into a UD sheet of spread-tows (see Figure 2). ...
... Although the failure behavior of laminated composites and their structures has been carefully studied, the mechanisms are difficult to predict accurately since they depend on many geometrical and structural properties, such as stacking sequence, material, ply thickness, component geometry, and loading conditions, among others [2,3]. Spread-tow thin-ply prepreg, herein called 'thinpreg', was introduced by Kawabe et al. [4][5][6][7][8], focuses on stable and gentle opening of dry tows so that even flatter fiber plies can be produced and subsequently pre-impregnated with a resin, as is commonly done for conventional thickness prepregs. This technique allows the production of ultra-thin prepreg (up to 7× thinner than traditional prepreg) while suppressing issues associated with fiber arrangement and ply uniformity. ...
Article
Thin-ply carbon fiber laminates have exhibited superior mechanical properties and damage resistance when compared to standard thickness plies and enable greater flexibility in laminate design. However, the increased ply count in thin-ply laminates also increases the number of ply-ply interfaces, thereby increasing the number of relatively weak and delamination-prone interlaminar regions. In this study, we report the first experimental realization of aligned carbon nanotube interlaminar reinforcement of thin-ply unidirectional prepreg-based carbon fiber laminates, in a hierarchical architecture termed ‘nanostitching’. We synthesize a baseline effective standard thickness laminate using multiple thin plies of the same orientation to create a ply block, and we find an ~15% improvement in the interlaminar shear strength via short beam shear (SBS) testing for thin-ply nanostitched samples when compared to the baseline. This demonstrates a synergetic strength effect of nanostitching (~5% increase) and thin-ply lamination (~10% increase). Synchrotron-based computed tomography of post mortem SBS specimens suggests a different trajectory and mode of damage accumulation in nanostitched thin-ply laminates, notably the complete suppression of delaminations in the nanostitched region. Finite element predictions of damage progression highlight the complementary nature of positive thin-ply and nanostitching effects that are consistent with an ~15% improvement in Mode I and II interlaminar fracture toughness due to the aligned carbon nanotubes at the thin-ply interfaces.
... The wide use of carbon fiber has led to the development of technologies making it possible to increase the operational characteristics of composite materials on their basis [14,15]. One of such technologies is making straightened (flattened) tows (spread tows) from which different fabrics and tapes (prepregs) are produced [16,17]. ...
Article
A mathematical model and a technique for evaluating the technological process parameters to obtain superthin prepregs by flattening carbon tows impregnated with an epoxy binder have been developed. It is recommended to simultaneously roll 25-50 carbon tows containing 400-600 monofilaments by rolls 50-100 mm in diameter, which is conceptually and technically consistent with possibilities of the existing equipment. The preferred viscosity range of the binder within which superthin prepregs with a thickness of 1-10 monofilament diameters are obtained has been identified. The results found significantly expand the design and technological potentialities of creating superthin skins made of carbon-fiber-reinforced plastics in comparison with the existing ones Keywords: flattening, rolling, carbon-fiber-reinforced plastic, technological parameters, ultrathin prepregs
... Any technology capable of reducing the ply thickness can substantially improve the laminate performance by delaying the matrix cracking, increasing the strength and reducing the weight. Recently, thin-ply technology (Spread-tow technology) has gained more attention due to its potential to achieve ultra-thin ply as low as 20 μm [1][2][3][4]. The effect of ply thickness and stacking ultra-thin plies is to increase transverse strength by suppressing transverse cracking known as size effect [5][6][7]. ...
Article
A micromechanical model is used to investigate ply thickness effect on damage evolution of thin-ply carbon fiber reinforced laminate under transverse tensile load. Representative volume element (RVE) for 90° lamina are constructed and sandwiched between two homogenized zero degree plies. Four different thicknesses for 90° RVEs including 30, 60, 90, and 120 μm are considered for analysis. The three dimensional (3D) computational micromechanics are combined with augmented finite element method (AFEM) to provide high-fidelity results of damage evolution. Random arrangement for fibers and normal distribution for interface toughness and strength are considered within RVEs. Damage evolution in different RVEs under tensile loading are discussed and compared. The results show that decreasing 90° lamina thickness alters damage progression mechanism and suppresses cracking within matrix loading. A detailed comparative discussion on the influence and importance of material parameters as well as voids/defects on the process of cracking are given.
... Ply thinning is expected to increase transverse strength of lamina constrained by surrounding plies (so-called in situ effect [1]) and delay matrix cracking and delamination. Spread tow technology is a current method to achieve ultra-thin ply as low as 20 lm [2][3][4]. This technique offers cost-effective production of thin plies without damage caused during the process. ...
Article
In this work, failure mechanisms and damage evolution in low-thickness composite laminates are numerically simulated. The effect of thinning ply on the strength and damage evolution of composite laminates is investigated. Micromechanical modeling is performed to study damage initiation and propagation mechanisms and ply thickness or in situ effect in thin-ply carbon fiber-reinforced laminate under transverse tension loading. Two different sets of models are examined. The first set of the thin-ply laminate models contains a representative volume element (RVE) of 90° lamina constrained between two homogenized 0° plies. Thicknesses of models with embedded 90° lamina were 30, 60, 90 and 120 μm. In the second set, two models with 30 and 90 μm of 90° thin ply as the outer layers with embedded homogenized 0° layer are considered. Micromechanical analysis is combined with augmented finite element method to provide high-fidelity results of damage evolution. Random fibers’ arrangement and interface toughness and strength normal distribution are considered to capture the composite stochastic behavior. It is shown that the damage initiation and propagation locations are affected by the thickness of 90° lamina and distributions of fracture properties within the RVE.
... Ply thicknesses of less than 50 µm can nowadays be mass-produced, and record thicknesses of around 20 − 25 µm, or ∼ 4 − 5 times the average fiber's diameter, have been achieved. In its current form the technique, sometimes referred to as "FUKUI method", was firstly 15 proposed towards the end of the 1990s [4] and perfected in the subsequent decade [5,6]. ...
Preprint
Full-text available
The effects of crack shielding, finite thickness of the composite and fiber content on fiber/matrix debond growth in thin unidirectional composites are investigated analyzing Representative Volume Elements (RVEs) of different ordered microstructures. Debond growth is characterized by estimation of the Energy Release Rates (ERRs) in Mode I and Mode II using the Virtual Crack Closure Technique (VCCT) and the J-integral. It is found that increasing fiber content, a larger distance between debonds in the loading direction and the presence of a free surface close to the debond have all a strong enhancing effect on the ERR. The presence of fully bonded fibers in the composite thickness direction has instead a constraining effect, and it is shown to be very localized. An explanation of these observations is proposed based on mechanical considerations.
... Since the development of the spread tow technology or "FUKUI method" [1], significant efforts have been directed toward the characterization of thin-ply laminates [2,3,4,5,6,7,8,9,10,11] and their application to mission-critical structures in the aerospace sector [12]. 5 At the lamina level, the use of thin-plies leads to more regular and homogeneous microstructures [6,9]. ...
Preprint
Full-text available
Models of Representative Volume Elements (RVEs) of cross-ply laminates with different geometric configurations and damage states are studied. Debond growth is characterized by the estimation of the Mode I and Mode II Energy Release Rate (ERR) using the Virtual Crack Closure Technique (VCCT). It is found that the presence of the 0° /90° interface and the thickness of the 0° layer have no effect, apart from laminates with ultra-thin 90° plies where it is however modest. The present analysis supports the claim that debond growth is not affected by the ply-thickness effect.
... Un gain économique : L'étalement des fibres de carbone pour la fabrication de plis fins est aussi une innovation économique puisque cette méthode permet d'utiliser des fils de plus de 12 000 filaments (fils de titre élevé plus abordables) pour fabriquer des plis plus fins et plus légers que les tissus de faible grammage généralement fabriqués à partir de fil de 1K ou 3K extrêmement onéreux, [22], [23]. ...
Thesis
L’industrie aéronautique travaille sur l’amélioration des systèmes propulsifs parl’introduction de composites dans la fabrication des aubes de soufflante afin d’alléger lastructure et ainsi de réduire la consommation en carburant des avions. Ces pièces réaliséesen tissage 3D présentent généralement des irrégularités de surface. Une manière d’optimisercet aspect est d’ajouter un pli additionnel de surface : nos travaux de thèse portent sur ledéveloppement de ce pli sous la forme d’un renfort « Non Crimp Fabric » (NCF) biaxial extrafinen fibre de carbone de module intermédiaire (IM), inférieur à 100 g/m², régulier et ayant unebonne déformabilité. Lors de nos travaux de thèse, nous avons utilisé la méthode des plans d’expériencepour améliorer la technologie d’étalement afin de répondre aux exigences demandées. Nousavons pu définir la configuration optimale d’étalement permettant d’atteindre la cible d’un pliinférieur à 50 g/m² en fibre de carbone IM. Pour réaliser un NCF extra-fin, après étalement,les plis sont assemblés par couture afin d’assurer la tenue du renfort. La combinaison decouture choisie (armure, tension, longueur, jauge …) conditionne l’aspect du NCF et sacapacité à être manipulée et déformée. Nous avons donc optimisé les paramètres de coutureafin d’obtenir les propriétés souhaitées. Après avoir optimisé l’étalement des fibres et l’assemblage des plis, nous avons réalisé et caractérisé les renforts NCF extra-fins pour valider leurs propriétés. Nous sommesfinalement parvenus à mettre au point un renfort NCF en fibre de carbone IM, inférieur à50 g/m² par pli ayant un taux de couverture supérieur à 98 % et une bonne capacité à sedéformer.
... methods based upon vacuum, compressed air, vibration or form of deflection [1]. First mentioned methods put a heavy emphasis on spreading for subsequent through thickness impregnation [2][3][4][5]. ...
Conference Paper
Full-text available
For composites manufacturing processes such as automated fibre placement, filament winding or pultrusion, roving behaviour is crucial. Understanding and controlling these processes is only possible if material changes induced by guidance to the processing area are fully understood. Fibre placement system manufacturers such as Coriolis Composites use a creel to store and feed material to a placement head. Material deflection take place in the creel system as well as in the placement head itself, which unintentionally can impact the material prior to being processed. In this work, a two-stage-approach is presented to address the topic of roving spreading properties for future application in guidance optimization. In the first phase, a manual spreading test rig was set up. It consists of three rollers whose position form an isosceles triangle on a rigid composition of aluminium profiles. The specimen used for the experiments were pre-cut, clamped to weights, measured in dimensions and applied to the setup. Through geometrical alterations in the setup, changes in spreading behaviour were observed and put into context with an existing spreading model developed by Wilson [1]. As a result, the lateral changes in width were studied in manifolds of three back-and-forth motions until equilibrium of spreading was achieved. In the second phase, a configuration of five acetal rollers was set up on an automated spreading test rig. The used material was taken off continuously from a spool fixed on a mandrel. The roving was then initially measured in its cross-sectional dimensions by means of light sectioning sensor, then guided through the configuration of rollers and finally profiled again. An emphasis in this phase was put on the systematics to acquire profiling data and influences corrupting the experiments.
Article
In this article, the effects of ply thickness on the impact damage mechanisms in CFRP laminates are discussed based on the experimental observations. Quasi-isotropic CFRP laminates were manufactured using 38 µm thick thin-ply prepregs. Impact damage inside the laminates was evaluated by using ultrasonic scanning and sectional fractography. Compression after impact strength was also evaluated. Thin-ply laminates showed 23% higher strength than standard-ply laminates. Transverse cracks decreased drastically in thin-ply laminates, and localized delamination was largely extended. Based on the discussions in our previous study and the literature, the specific ply thickness without drastic crack propagation appears to be less than or equal to 40 µm. Therefore, the thin laminates showed few and localized transverse cracks and delamination was largely propagated in the midplane.
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In order to examine the effect of ply thickness on the crack initiation and propagation in the 90 degrees layer in [0 degrees/90(n)degrees/0 degrees] laminates, we conducted numerical simulations using two-dimensional mesoscopic numerical models. We found that the stress increase in the thin layer with 40 mm thickness was restricted in the vicinity of the adjacent layers, leading to restriction of crack penetration through the 90 degrees layer. In addition, we confirmed the effect of stiffness of adjacent layers. In the case where the 90 degrees layer was sandwiched between 45 degrees layers, which had lower stiffness than the 0 degrees layers, crack propagation in the 90 degrees layer was faster than that observed with the 0 degrees adjacent layers. Thus, the crack propagation behavior in the 90 degrees layer was significantly influenced by the change in the stiffness caused by the orientation angle of the adjacent layers.
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Textile reinforced composites are extensively used in thermal protection engineering because of their outstanding mechanical and physical properties. Spread tow woven pierced composites (STWPs) are composed of fiber rods, a spread tow and a matrix with small air pores. In the experiment, the STWPs displayed improved thermal conductivities compared with traditional woven composites. Thermal conductivities in the in-plane and out-of-plane directions have increments of 18.7% and 16.7%, respectively. This is mainly attributed to the influence of the fiber volume fraction. Herein, three numerical models were constructed to predict the thermal conductivities of the matrix, spread tow and fiber rods, and as the input parameter of the mesoscale model. The curvature of the interlaced tow in the mesoscale model was defined considering that the spread tow is extremely light and thin. The predicted results are in accordance with the experimental results, with only 8.13% and 8.94% errors in the in-plane and out-of-plane directions, respectively, indicating that the numerical models are accurate and effective. In addition, the thermal conductivities of STWPs decrease with the increase of porosity, but increase with the increment in fiber volume fraction and interphase thermal conductance. This work can provide effective guidance for the thermal design of STWPs.
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It is generally known that the crack initiation strain is increased with decreasing of ply thickness of 90° layer. However, the mechanism has not been well clarified in the case of very thin thickness as thin as 40μm. A systematic detailed experimental observation was made on the damage growth behavior in 90° layer of cross-ply CFRP laminates. As a result of observation, the damage mode and the damage growth behavior were different depending on the ply thickness of 90° layer. It was clarified that crack extension was restrained and its speed became slower as ply thickness thinner. Moreover, it was shown that crack opening displacement became smaller as ply thickness became thinner, and the energy release rate at the crack tip became smaller based on FEM calculations.
Article
The effects of crack shielding, finite thickness of the composite and fiber content on fiber/matrix debond growth in thin unidirectional composites are investigated analyzing Representative Volume Elements (RVEs) of different ordered microstructures. Debond growth is characterized by estimation of the Energy Release Rates (ERRs) in Mode I and Mode II using the Virtual Crack Closure Technique (VCCT) and the J-integral. It is found that increasing fiber content, a larger distance between debonds in the loading direction and the presence of a free surface close to the debond have all a strong enhancing effect on the ERR. The presence of fully bonded fibers in the composite thickness direction has instead a constraining effect, and it is shown to be very localized. An explanation of these observations is proposed based on mechanical considerations.
Thesis
Full-text available
At the end of the second decade of the XXI century, the transportation industry at large faces several challenges that will shape its evolution in the next decade and beyond. The first such challenge is the increasing public awareness and governmental action on climate change, which are increasing the pressure on the industrial sectors responsible for the greatest share of emissions, the transportation industry being one of them, to reduce their environmental footprint. The second big challenge lies instead in the renewed push towards price reduction, due to increased competition (as for example, in the market for low-Earth orbit launchers, the entry of private entities) and innovative business models (like ride-sharing and ride-hailing in the automotive sector or low-cost carriers in civil aviation). A viable and effective technical solution strategy to these challenges is the reduction of vehicles’ structural mass, while keeping the payload mass constant. By reducing consumption, a reduced weight leads to reduced emissions in fossil-fuels powered vehicles and to increased autonomy in electrical ones. By reducing the quantity of materials required in structures, a weight reduction strategy favors in general a reduction of production costs and thus lower prices. Transportation is however a sector where safety is a paramount concern, and structures must satisfy strict requirements and validation procedures to guarantee their integrity and reliability during service life. This represents a significant constraint which limits the scope of the weight reduction approach. In the last twenty years, the development of a novel type of Fiber-Reinforced Polymer Composite (FRPC) laminates, called thin-ply laminates, proposes a solution to these competing requirements (weight with respect to structural integrity) by providing at the same time weight reduction and increased strength. Several experimental investigations have shown, in fact, that thin-ply laminates are capable of delaying, and even suppress, the onset of transverse cracking. Transverse cracks are a kind of sub-critical damage in FRPC laminates and occur early in the failure process, causing the degradation of elastic properties and favoring other, often more critical, modes of damage (delaminations, fiber breaks). Delay and suppression of transverse cracks were already linked, at the end of the 1970’s, to the use of thinner plies inside a laminate. However, thin-plies available today on the market are at least 10 times thinner than those studied in the 1970’s. This characteristic changes the length scale of the problem, from millimeters to micrometers. At the microscale, transverse cracks are formed by several fiber/matrix interface cracks (or debonds) coalescing together. Understanding the mechanisms of transverse cracking delay and suppression in thin-ply laminates requires detailed knowledge regarding onset of transverse cracking at the microscale, and thus the study of the mechanisms that favor or prevent debond initiation and growth. The main objective of the present work is to investigate the influence of the microstructure on debond growth along the fiber arc direction. To this end, models of 2-dimensional Representative Volume Elements (RVEs) of Uni-Directional (UD) composites and crossply laminates are developed. The Representative Volume Elements are characterized by different configurations of fibers and different damage states. Debond initiation is studied through the analysis of the distribution of stresses at the fiber/matrix interface in the absence of damage. Debond growth on the other hand is characterized using the approach of Linear Elastic Fracture Mechanics (LEFM), specifically through the evaluation of the Mode I, Mode II and total Energy Release Rate (ERR). Displacement and stress fields are evaluated by means of the Finite Element Method (FEM) using the commercial solver Abaqus. The components of the Energy Release Rate are then evaluated using the Virtual Crack Closure Technique (VCCT), implemented in a custom Python routine. The elastic solution of the debonding problem presents two different regimes: the open crack and the closed crack behaviour. In the latter, debond faces are in contact in a region of finite size at the debond tip; in the latter, the debond is everywhere open and no contact exists between the faces. In the open crack regime, it is known that stress and displacement fields at the debond tip present an oscillating singularity. A convergence analysis of the VCCT in the context of the FEM solution is thus required to guarantee the validity of results and represents the first step of the work presented in this thesis. It is found that the total ERR does not depend on the size of elements at the debond tip, while the values of Mode I and Mode II ERR depend on element size in the open crack or mixed mode case. It is furthermore shown that Mode I and Mode II ERR do not converge, i.e. their asymptotic behavior for decreasing element size is not bounded. Thus, error reduction between successive iterations cannot be used to validate the solution and comparison with another method is required. Results obtained with the Boundary Element Method (BEM), available in the literature, are selected to this end. Debond growth under remote tensile loading is then studied in Representative Volume Elements of: UD composites of varying thickness, measured in terms of number of rows of fibers, from extremely thin (one fiber row) to thick ones; cross-ply laminates with a central 90◦ ply of varying thickness, measured as well in terms of number of rows of fibers, from extremely thin (one fiber row) to thick ones; thick UD composites (modelled as infinite along the through-the-thickness direction). Different damage configurations are also considered, corresponding to different stages of transverse crack onset: non-interacting isolated debonds; interacting debonds distributed along the loading direction; debonds on consecutive fibers along the through-the-thickness direction. Among the most relevant results, it is found that neither the 90◦ ply thickness nor the 0◦ ply thickness influences debond ERR in cross-ply laminates, differently from what is observed for transverse cracks with the so-called ply-thickness and ply-block effects. On the other hand, debond interaction along the loading direction is shown to influence significantly the Energy Release Rate, but this interaction possesses a characteristic distance (in terms of number of undamaged fibers) that defines the region of influence between debonds. Finally, an estimation of debond size at initiation and of debond maximum size is proposed based on arguments from stress analysis (for initiation) and on Griffith’s criterion from LEFM (for propagation). For a debond in a cross-ply laminate, its maximum size is estimated to lie in the range 40◦ − 60◦ , which is in strong agreement with previous results from microscopic observations available in the literature.
Article
Thin carbon-fiber prepregs can improve the designability of the number and the angle of layup at a constant laminate thickness, and meet the requirements of the load bearing capacity of the thin-walled structure. In this work, experiments based on the MIL17 method were performed to investigate the performance of carbon-fiber laminates manufactured from thin prepregs, and compare to those of conventional prepregs. Besides the performance advantages of thin prepregs and conventional prepregs hybrid laminates were explored. It is shown that longitudinal compression properties, tensile properties and mechanical joint properties of the thin unidirectional plates have been improved to some extent. The initial damage strength of the longitudinal tensile of thin laminates is increased by 30%, which indicates that the thin prepregs can delay the generation of initial damage in laminates. It is worth noting that the basic mechanical properties of the hybrid laminates are obviously improved and the longitudinal tensile/compressive strength is approximately increased 50%. In addition, these performance improvements are accompanied by changes in failure modes. The failure modes of thin specimens, especially hybrid specimens, tend to be brittle failure. The results of present study have certain guiding significance for the engineering application of thin prepregs in thin-walled structures.
Article
In this paper, a systematic and detailed observation was made of the crack extension behavior of thin 90° layers of cross-ply carbon fiber reinforced plastics (CFRP) laminates. The effect of ply thickness on the crack propagation mechanism was discussed with respect to the energy release rate of the intralaminar transverse crack, calculated using finite element analysis. In a laminate with a 40 μm-thick-ply, the crack gradually extended with increasing strain. Conversely, extreme crack extension was found at around 1.0% strain in a laminate with a standard thick ply. Based on the numerical analysis, the crack suppression effect is verified using a thin ply; the effect is apparently caused by a decrease in the energy release rate at the crack tip in the thin layer.
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