Design, Manufacturing and Applications of Composites - Twelfth Joint Canada-Japan Workshop on Composites
In-Situ Monitoring of Strain Distribution of FRP by Rayleigh Scattering-Based Optical Fiber Sensors and Their Applications
Recently composites have been applied to many engineering fields such as automotives and then cost reduction and improvement of efficiency of the manfacturing process has been considered as key technologies in near future. For the purposes, in-situ and internal monitoring of composites during molding process is very effective. Many smart sensors have been devloped for monitoring flow front of impregnated resin, degree of cure, complex stifness and process-induced strain. Amog these sensors, optical fiber sensors are considered to be promising sensors due to easy embedment, multi-functionality and life-time usability. For example, Fresnel-based sensors can measure degree of cure precisely and FBG ( Fiber Bragg Grating) sensors can be used for measuring strain with high accuracy and stability while these sensors have sensing point and cannot be used for measuring distribution. On the other hand, optical fiber distribution sensors can measure strain and temperature distribution along fiber length. B-OTDR (Brillouin Optical Time Domain Reflectometry) was used for measuring strain distribution of composites during molding. However the typical spacing resolution is a few sub-meters and then the application was limitted to large-scale structures.
A Multifaceted Approach for Process Characterization of Polymer-matrix Composites
During processing of advanced polymer-matrix composites, the matrix undergoes several phase transitions and possible phase separations. As curing progresses, a thermosetbased matrix changes from a high viscosity liquid to a viscoelastic rubber and eventually a hypo-elastic glass. Such progression of behaviour combined with the multiscale nature of composites is manifested as a complex and dynamic response at the laminate-level. As the need for process simulation of composites has become more apparent in recent years, so has the need to develop effective process characterization methods. A comprehensive review of characterization methods is presented in this study. Attention is given to the resin thermal expansion and cure shrinkage. Methods including Digital Image Correlation (DIC), Thermomechanical Analysis (TMA) and Digital Microscopy (DM) are discussed and compared. It is shown that a single approach cannot be used to characterize the response of material across all phases. It is also shown that by using a combination of these methods, a comprehensive understanding of material behaviour can be achieved. The effectiveness of such an approach is demonstrated by a cross-comparison of experimental results for the AS4/8552 prepreg system.
Influence of Up- and Down-Cutting Process on Interlaminar Shear Strength of CFRP Plates (abstract only)
Surface damage often occurs in the vicinity of the surface layers of a CFRP plate during the trimming process. Since the surface damage degrades with an increasing feed rate of a milling machine, trimming quality issues cannot be neglected in high-cycle manufacturing processes. We previously reported that damages on the cutting surfaces of the specimen reduce its interlaminar shear strength. In this study, we investigate the influence of up- and down cutting process on interlaminar shear strength of CFRP plates. We prepared the specimens processed at three kinds of cutting speeds respectively using up- and down cutting, and interlaminar shear tests with the specimens were performed.
Hybrid-fiber Reinforced Thermoplastic Rivet
A lightweight anti-corrosive rivet is proposed using a fiber reinforced thermoplastic (FRTP) for the joining of carbon fiber reinforced plastic (CFRP). The FRTP rivet was fabricated via the braiding technique, where Glass fiber/PA66 commingled yarns were wrapped around straightly aligned Carbon fiber/PA66 commingled yarns. Using a pultrusion method, the braided yarn was consolidated into a FRTP rod, which was then cut to an appropriate length for use as a FRTP rivet. Quasi-isotropic CFRP laminates were joined by this rivet through a thermal forming process. Single-lap joint specimens were subjected to tensile tests, and compared with a bolted joint. The results revealed that, for the same joint strength, FRTP-rivet replacement of the metallic joint yields a reduction in the weight of the joint.
Fastening Composite Structures Using Carbon Fiber/Polyetherimide Rivets
To reduce aircraft weight, composite materials are used for their high specific properties. Joining these composite components brings new challenges, since the matrix cannot support the high located loads during the deformation of a metallic rivet, traditionally used to joint metallic structures. Mechanical fastening using titanium bolts is the most used joining method in the aerospace industry. However, this solution presents many drawbacks with regards to its weight, lightning strike hazard, risk of water penetration and cost. To overcome these problems, an innovative assembly technology using carbon fiber/thermoplastic composite rivets was developed. It was previously demonstrated with Carbon/Polyamide (C/PA) rivets. These rivets are heated, using Joule effect, above the melting temperature of the thermoplastic resin. They are then molded in situ, i.e, into the laminates to be joined. The materials similarity eliminates the galvanic corrosion and the electromagnetic shielding issues. To ensure a constant quality for an industrial application, the riveting technique is automated. The riveting parameters are controlled to ensure the joint quality and repeatability. Carbon fiber/polyetherimide (C/PEI) blanks manufactured using pultrusion were used to join carbon/epoxy laminates. The mechanical testing showed that the mechanical properties of the composite riveted joint with C/PEI rivets are higher than those riveted with C/PA rivets. With these advantages, the technology could be applied in the next generation of aircraft structures.
Optimm Design of Airfoil Stiffeners of CFRP Wing for a Small UAV
In recent years，a UAV for emergency assistance of disaster and observation has attracted strong attention especially in Japan. A wing of large UAVs has usually the same structure as typical manned aircraft. On the other hand, in case of small UAV, more simple structure composed of CFRP spars and skins are often introduced due to the easy and low cost manufacturing. However in order to operate small UAVs in tough environment such as typhoon, more strong and stiffened skin structures are necessary and then ribs should be introduced to withstand the large lift force and moment. This design increase manufacturing cost of the UAVs calculation. In the present paper, idea of designing light and high-strength wings by introducing airfoil stiffeners integrated into a CFRP skin. In this design, a number of the parts of the wing can be reduced comparing to traditional wing structures. Optimization of number, size and placement of the airfoil stiffeners were conducted by CFD and FEM analysis.
Stochastic Nonlinear Analysis of Composites by First-Order Perturbation Based Homogenization Method
With the broaden applications of fibrous composites in engineering fields, a variety of numerical methods for predicting their mechanical properties and behaviours are presented. In this paper, a stochastic homogenization method based on the first-order perturbation technique with the help of finite element method is developed to calculate not only macroscopic properties but also microscopic strain of composite materials under given macroscopic strain condition considering uncertainties in many physical parameters of constituent materials. Afterward, a stochastic prediction algorithm of damage propagation was introduced. In this nonlinear analysis, the characteristic displacements of the model are updated when damage occurs. For demonstration, a numerical example was carried out using fibre/matrix interphase composite model. The results show that the developed method is useful to predict the stochastic damage propagation of composite materials.
Stress Propagation in a Viscoelastic Composite Structure Subject to Large Deformations
Large deformations occur in practice for aircraft wings of high aspect ratio that are very flexible. The deformations and associated stress increase concerns of an in-flight, catastrophic failure. For composite aircraft wings composed of polymer resins, viscoelastic effects occur. These time-dependent effects include energy dissipation and stress memory. The time dependency must be considered when designing high aspect ratio wings for a given operation life. A novel theory is proposed to assess the stress propagation through, and over the life, of a viscoelastic structure. The theory combines the time component with the conventional three-dimensional spatial components via a Riemann manifold. The manifold includes multiple time-like dimensions to account for the initial and long term behaviour of the viscoelastic material. Following the work of Green and Adkins, a metric tensor is introduced to find the strain of the structure and the corresponding stress, in response to the applied distributed loads. The stress is modelled as a wave that propagates across the manifold. The wave at any point on the Riemann manifold represents the state of a viscoelastic structure at a given time and position. The theory is demonstrated for a viscoelastic cantilever wing subject to distributed loads.
Estimation of R-curve for Mode II Interlaminar Fracture Toughness by Using CFRP Laminates with Fibre Discontinuities
When CFRP plates of structures with complicated geometry are fabricated by using prepregs, fiber discontinuities remain in the laminates since some slits or cuts are introduced in prepregs before lamination. The CFRP laminates with fibre discontinuities show tensile failure at much lower stress due to crack originated from the discontinuities. Previous studies have shown that the stress at which crack propagation from fiber discontinuity occurs can be predicted by using mode II interlaminar fracture toughness ô€œ©ô€¯‚ô€¯‚. The present study aims to reverse this methodology in order to estimate the R curve of mode II interlaminar fracture toughness from tensile test of CFRP laminates with fiber discontinuity. In the technique we suggest here there is no need to perform stabilized ENF tests that require a variety of controls. Tensile tests for CFRP laminates that contain fiber discontinuous dispersed at an arbitrary interval are carried out. Relations between the obtained fracture stress and the interval are converted into that between critical energy release rate (CERR) in mode II and crack extension that can be compared with R-curve obtained by ENF tests. As a result, although mismatch are found in the initial region of R-curve a.k.a. ô€œ©ô€¯‚ô€¯‚ô€®¼ , CERR matched with R-curve during crack propagation, which is the region where the change of ô€œ©ô€¯‚ô€¯‚ converges as ô€œ©ô€¯‚ô€¯‚ô€¯‹.
Fatigue Modeling for Intra-laminar Damage of Composite Materials Based on Continuum Damage Mechanics
The aim of this study is to model intra-laminar fatigue damage of composite materials based on continuum damage mechanics. In this study, the fatigue model is defined as a damage evolution law in which the intra-laminar damage progresses with increasing number of cycles of cyclic loading. This paper presents a method which combines fatigue damage analysis with a cycle jump algorithm. Fatigue damage analysis are conducted and the results of the simulation are compared with experimental data for the validation of the fatigue model.
Progressive Failure Prediction of a Bonded Composite Component
Virtual numerical testing has been used increasingly in many industries for various designs and/or damage assessments required by life management processes. Aided by representative verification tests, the developed numerical models can effectively screen and assess specific testing tasks and results, which greatly reduce overall cost and also guide practical decision making. However, challenges remain in development of high-fidelity, riskbased damage and failure prediction approaches for fibre-reinforced composites due to the complex nature of damage evolution and process-dependent properties of composite structures. This work is one of the first steps towards development of virtual testing tools for composite failure prediction. A three-dimensional (3D) finite element model was developed using ABAQUS. Three-dimensional continuum shell elements integrated with the cohesive zone technique were employed to predict damage and failure of a bonded composite structure. This bonded structure consisted of a laminated skin and a stiffener. This work used a damage mechanics, fracture mechanic–based approach to study progressive failure behaviour of a bonded composite structure subjected to a tensile loading condition. Good correlation in static strength was obtained between the experimental and numerical results with less than 1% difference.
Evaluation of Damage Development and Damping Characteristics for Woven Composites Under Tensile Loading
In this paper, mechanical characteristics of stiffness, damage development and damping property for woven composites of carbon-fiber/epoxy, aramid-fiber/epoxy, polyarylate-fiber/epoxy had been investigated. Three fiber-types of specimens were prepared for the tensile test, and the In-situ observation of damage mode at cross section of the specimens was carried out with CCD microscope under 20%, 40%, 60%, and 80% loading of the tensile strength. And, the damping ratio of each specimen along with the tensile loading was also estimated. As the results of In-situ observation of damage development, the delamination was observed under 40% and 60% loading in polyarylate FRP and aramid FRP, respectively. The damping ratio in case of polyarylate FRP had decreased 7.6%, however, the damping ratio was much higher than that of aramid FRP. In case of CFRP, the damping ratio was much lower than those of aramid FRP and polyarylate FRP. The phenomena were caused by effects of mechanical properties of fibers and the damage development.
An Estimation of Material Damping Properties for Polyarylate Woven Fabric Composites
It was identified that PFRP has had high damping properties in the vibration test. However it has not been clarified where the energy is dissipated. Polyarylate fiber plain woven fabric composites was analyzed by finite element method. Numerical results and strain energy distribution of PFRP was compared with one of GFRP. Damping ratio of PFRP is larger than one of GFRP. High dissipated strain energy of PFRP composites was in polyarylate fiber bundle part. It is recognized that much energy is dissipated in polyarylate fiber bundle part. This result agrees with consideration that longitudinal strain occurred in polyarylate fiber bundle in vibration test.
Large Deformation Behavior of Angle-Plied CFRP Laminates by Inserting PA Mesh as Interlayer
When angle-plied CFRP laminates which do not contain 0° fibers are loaded in tension, intralaminar matrix cracks are developed in all plies and followed by interlaminar delamination, and then this leads to rupture of laminates at relatively low strain. Some studies found that greater fracture strain can be achieved by using thin plies since matrix crack is suppressed by the constraint effect. However using thin plies is costly because stacking number increases. The present study applies polyamide (PA) mesh which can improve interlaminar fracture toughness by inserting them between plies. This study aims greater fracture strain in angle-plied laminates by suppressing interlaminar delamination between plies by inserting PA mesh. Damage behavior in two kinds of angle-plied CFRP laminates such as [452/-452]S and [452/PA/-452]S are evaluated by tensile tests. It is found that by inserting PA mesh strength and maximum strain improved compared to the laminates without PA mesh. An X-ray observation for the specimen just before tensile rupture reveals that interlaminar delamination is not induced though there are many intralaminar matrix cracks in the laminates with PA mesh. From these experimental results, it is assumed that even if matrix cracking occurred, it does not progress to interlaminar delamination by inserting PA mesh and these phenomena lead to greater fracture strain due to accumulation of damage.
Development of TiB2/Steel Composites with High Termal Conductivity
Die-cast process is important for mass-production of the aluminum, magnesium and zinc alloy used in industrial parts such as automobile. In order to improve the life-time of die, the improvement of the thermal conductivity is required because of the degradation of the thermal stress. In this study, the improvement of the thermal conductivity is attempted by using steel matrix composites with titanium diboride (TiB2). Staring powders were 40CrMoV5 steel alloy (ISO standard) and TiB2. The powders were mixed by V shape type ball milling in ethanol. 4vol.%, 8vol.%, 20vol.%TiB2 containing 40CrMoV5 steel alloy composites was prepared by spark plasma sintering under the conditions of 1273 K, 10 min. in temperature keeping time, and 50MPa in applied pressure. The composites with low content of TiB2, has lower thermal conductivity for theoretical value because of the reaction of TiB2 with Fe and C. As increasing TiB2 content, many TiB2 remains in composites because of the improvement of chemical stability aggregation of TiB2, and the thermal conductivity increased. Although the relative density of 20vol. %TiB2 / 40CrMoV5 steel alloy composites were about 92.6%, the thermal conductivity of the composites with 8 vol. % TiB2 was 35.0W/mK, which is better than 40CrMoV5 monolithic alloy. As increasing TiB2 content, the tensile strength decreased but elongation increase.
Effect of Tailored Fiber Placement Parameters on Carbon Fiber/Epoxy Composite
The recent emergence of fiber placement manufacturing processes such as tailored fiber placement (TFP) is giving new avenues to the design of parts with tailored properties and net shape fabrication. However, this design flexibility is usually at the expanse of the inplane mechanical properties. In this study, the impact of the number of plies and the stitching material on the in-plane mechanical properties is investigated. Carbon fiber preforms were fabricated by TFP and were impregnated by RTM to produce composite plates. Image analysis from computer tomography was used to determine the through-the-thickness profile of fiber volume fractions. Tensile tests with digital image correlation (DIC) and interlaminar shear strength tests were performed on the specimens. It was found that there is a significant variation of the fiber volume fraction thru the thickness of the specimens. The stitching material and the number of layers had low impact on the tensile properties. Kevlar® stiches have given better results than polyester and Nomex® in terms of interlaminar shear strength.
Evaluation of Breakdown Current Density of Carbon Nanotube Sheets and Their Composites for Lightning Strike Protection
A combination of the high electrical conductivity, excellent mechanical properties and low density of carbon nanotubes (CNTs) suggests the potential of CNT-based materials to replace existing lightning strike protection technologies based on metal meshes. This study focuses on the development of a screening test method using the current carrying capacity (CCC) to evaluate CNT-based films and their composites. The method simultaneously provides breakdown current density (J ) and breakdown temperature. The testing setup consists of bowtie shaped coupons connected to a power source and carrying electricity until degradation of the sample causes a current drop. Normalization of J values to the volumetric mass density (specific J ) enables consideration of the potential weight savings with each material. The higher specific J of CNT-based films in comparison to existing standard materials based on metallic meshes suggests the advantage of CNT-based films for future development of a lighter protective layer against lightning strikes.
Fabrication and Testing of Electrically Conductive Layerwise-Hybrid CFRP for Lightning Strike Application
Multi-functional composites have gained interest among researchers in these recent years, especially in aeronautic application where the materials are required to be light weight and display high specific strengths. This study aims to propose the method of fabricating hybrid laminates of carbon fiber reinforced plastics (CFRP) with two systems of resins: carbon fiber reinforced with polyaniline-base resin (CF/PANI) and carbon fiber with epoxy resin (CF/epoxy). Each system of laminates was fabricated layerwise using hand lay-up method. The CF/PANI and CF/Epoxy laminates were fused with adhesive film. The coupon specimens were characterized for their bending properties, interlaminar shear strength (ILSS) and electrical conductivity. Simulated lightning strike tests were also conducted to investigate the damage behavior.
Research of Aramid/CF Hybrid Composite Material
It is desirable to reduce the weight of automotive materials by replacing metals with composite materials, because it is effective in reducing CO2 emissions, improving fuel efficiency, and extending the cruising distance. Therefore, research on carbon fiber composites has been actively carried out recently. In this research, the practical running tests on rally car are carried out for the material adaptation to mass production vehicles. Carbon fiber reinforced thermoplastic have been applied to floor guard, and the test run have been carried out. The problem is impact resistance. In this study, hybrid composites of aramid knit and carbon fiber fabric were fabricated to improve impact resistance, and impact resistance was investigated by drop impact test. As a surface layer of carbon fiber nonwoven fabric, impact resistance was compared between when carbon fiber woven fabric was distributed and when aramid knit was distributed. Experimental results suggest that when aramid is applied to the surface layer, both the maximum load and the absorption energy are improved. It was also suggested that the use of both aramid knit and carbon fiber cloth significantly improved the absorption energy due to the shift in the timing of breakage.
Development of Commingled Yarn for Textile Thermoplastic Composites
Recently, continuous fiber reinforced thermoplastic composite (FRTP) is paid attention. However, using continuous fiber and thermoplastic resin makes the impregnation difficult because of the high melt viscosity. According to this reason, intermediate material is important for molding FRTP, so commingled yarn set resin fiber nearby reinforcement fiber was developed by our team. We have improved commingled yarn, we developed “pre-impregnated commingled yarn (PCY)â€. PCY is the new intermediate material which resin fiber of commingled yarn was already melted but a portion of matrix was impregnated. If all matrix was impregnated, it would become impregnated tape and it would too hard to use for textile but PCY whose a portion of matrix was impregnated easily to use for textile compare to impregnated tape. The purpose of this research is to investigate the impregnation property, textile workability and mechanical property of composite made from commingled yarn and PCY. Finnaly, we established the producing method of the intermediate material, “PCYâ€, which has both high impregnation property and textile workability
Energy Absorption Properties of Braided Glass Fiber Rod-Reinforced Carboard Panels
This paper investigates the quasi-static compression properties of cardboard panels reinforced with braided glass fiber rods manufactured using a tubular braiding machine. Compression tests are performed on glass fiber rods without any cardboard material first, and the specific energy absorption of rods with and without a taper angle is compared. Braided rods with a taper show much better progressive crushing than those without and have a specific energy absorption that is approximately 1.5 times larger. The rods are then inserted in a single layer of cardboard 3 cm × 3 cm and cases involving one, four, and five rods are investigated. The cardboard is observed to constrain the rods from excessive splaying, causing greater levels of fiber fragmentation which consumes more energy compared with rods without cardboard. Compression testing is also performed on panels made from two layers of cardboard, reinforced with longer rods. The crushing results of single-layer panels show more progressive crushing than those of two-layer panels where the longer rods become inclined from the direction of applied load due to deformation of the surrounding cardboard resulting in reduced crushing performance.
Estimation of Mechanical Characterization of Woven CFRTP Under Tensile Loading Based on Acoustic Emission
The demand of carbon fiber-reinforced thermoplastic (CFRTP) materials is increasing, however, much less work has been done on CFRTP which contains matrix having high formability such as polyamide. We evaluated the mechanical characterization of damage development in CFRTP by conventional tows and spread tows. The quasi-static tensile tests were carried out with using DIC (digital image correlation) system to estimate the full field strain and AE (acoustic emission) sensors for measurement of the acoustic emission features. The CFRTP specimens were also investigated with optical microscope to clarify the difference of damage. The fiber debonding and delamination were shown in CF (with spread tows)/PA composites and the damage in weft yarn covered a wide range of test specimens. It is suggested that the mechanical characterization of damage is affected by fiber opening. This may also be explained by AE events. In weft yarn of CF (with conventional tows)/PA composites, we can observe transverse cracks and cracks which propagate in parallel with loading direction. From these results, the damage development of woven composites is sensitive to the form of fiber bundles and the properties of the matrix.
Non-destructive Thermographic Inspection of Multilayer Dry Fiber Reinforcement Stacks for Polymer Composites
This paper discusses thermographic techniques for the inspection of dry multilayer fibre reinforcement stacks used in the manufacturing of polymer-matrix composites (PMCs) using liquid moulding (LM) processes. The aim is to identify defects in thick multilayer stacks of dry textile reinforcements before resin injection and the manufacturing of the composites. Inspecting dry preforms is not aimed at replacing the final inspection of PMC parts, but it can avoid wasteful manufacturing of PMC parts from preforms that are defective prior to injection. Defects sought in this paper cannot be detected using visual inspection. Tests were conducted on textile stacks only, and on stacks laid on a metal mould and vacuumed. Different devices, techniques and heat sources were used. The first technique used a hand-help camera. Stacks featured 2 to 4 reinforcement layers with defects of different widths, types and orientations. Defects were identified. Detection was influenced by the orthotropic fibre thermal conductivity, textile architecture, relative orientations of defects and yarns, and number of layers. In the second technique, optical excitation thermography and advanced image processing were used for inspecting stacks featuring different textile structures, thicknesses and defects. The performance of different techniques was rated through signal-to-noise ratio analysis. Monitoring modalities most suitable to industrial manufacturing were identified. In the last part of the work, stacks were positioned on a mould and inspected either on a heated mould or by heating from the front of the stack, under vacuum but without moulding ancillaries beyond the vacuum, using a number of different heat sources. The potential of the technique in an industrial setting is demonstrated; additional work remains in terms of image analysis in order to automate the technique and generalize its use.
Real-time Optimization of Cure Process of Thick FRP Plates
In the manufacture of large and complex-shaped FRP structuers, the temperature distribution overall the product may become nonuniform and then the uneven distiribution of degree-of-cure is generated. Since this unevenness influences on the quality of FRP products and requires, a lage number of manufacturing trials are necessary to explore optimum molding conditions. The trail-and-error method is one of factors increasing the manufacturing cost of FRP. Therefore, a more efficient method to obtain the optimum molding condition is required.
Achieving Structural Health Monitoring Using Additive Manufacturing
Additive Manufacturing (AM) is a process which produces components by continuously adding layers of material to produce a product. Initially, AM was used to produce prototypes. However, AM is now commonly used to create functional components. A significant amount of research has been focused on the investigation of the mechanical properties these products. Structural health monitoring (SHM) is a technique, which combines sensors with advanced engineering structures. SHM is commonly used in the aerospace and construction industries to monitor structural integrity. Many researchers have focused on AM and SHM technologies individually, but few have investigated the possibility of combining these two technologies. This study reports on a proof-of-concept work that demonstrates the feasibility of achieving SHM using AM. AM components embedded with thin conductive graphene-layers were produced using dual-extrusion 3D printers. The specimens were then deformed using a tensile test frame equipped with extensometers to measure the mechanical strain. The resistance changes of the conductive layer (SHM-sensor) were also measured during the tests. Later, the strains from the extensometer were used to calibrate the resistance changes of the SHM-sensor to obtain their gage factors. This work develops a method for integrating SHM within advanced AM structures.
The Essentials of the Training Kit to Improve Trimming Skills in the Autoclaved CFRP Products (abstract only)
Carbon fiber reinforced polymer (CFRP) products are utilized in the aerospace industry to provide high specific stiffness/strength. Tacit knowledge of experts acquired from their experiences and insights is required to produce the complex shaped and high quality products. The CFRP products are manufactured in a similar manner to the traditional Japanese crafts such as bows, fabrics, and plates. Due to prolongation of acquiring the skills of experts, reduction in manufacturing cost, enhancement of functionality in manufacturing machines, and the change in work values of young generation, we face the serious problem on the development of human resources; i.e., the number of experts in a company decreases, leading to the deterioration of Japanese manufacturing competitiveness. Therefore, it is significantly important to prepare educational guidance to learn the skills of experts. Also, the educational scheme to expand the number of experts needs to be organized through joint efforts between industry and academia. The educational scheme for composite processing needs to be established to expand the number of experts and to overcome the difficulty of quality control. In this paper, we propose the educational aid for the trimming and hole-making operation of autoclave technology to effectively improve the skill of workers. Trimming by power tools such as grinders and sanders is crucial to satisfying the required shapes and dimensions of CFRP products. The training aid for trimming translated from the skill of an expert is prepared and analyzed to identify the relationship between work and skill.
Evaluation of Influence of Molding Conditions on Process-Induced Strain of Reinforcements of GFRP by FEM Analysis and In-Situ Strain Measurement
FRP(Fiber Reinforced Plastic) is a composite material for glass or carbon reinforcements with resin. In the heat forming method of FRP, residual stress occurs due to discrepancy of different thermal expansion. Since it is known that process-induced residual stress influences behavior of matrix cracks generated in operation, accurate estimation of the residual stress is an important issure for FRP manufacturing. For thermoset-based FRP, the residual stress may result from curing shrinkage as well as thermal deformantion. However, the residual stress caused by cure reaction has been hardly studied and then the effect of molding temperature pattern on the residual stress has not been cleared. In the present syudy, FEM analysis was performed to evaluate the molding processinduced strain occurred in reinforcement fibers on the assumption of viscoelastic properties of resin depending on the degree of cure. In addition, model specimens of glass optical-fiber reinforced polymers were manufactured for in-situ evaluation of process-induced strain by embedded FBG (Fiber Bragg grating) sensors.
Improving Filament Winding Productivity by Multiple Feeds
We Murata Machinery, Ltd. have developed a new filament winding machine (MFW) with multiple fees for carbon fiber. It performed a high productivity. In the MFW, 180 carbon fiber bundles are wound simultaneously on a liner for high pressure vessels. The MFW produces non-crimp structure with continuous carbon fiber automatically. Furthermore, the continuous CFRP pipe production system is also developing by applying MFW concept. The system is able to produce various fiber orientation angle constitutions. It is expected to produce non-crimp preforms for automotive parts which required high productivity.
Additive Manufacturing Bio-based Filaments Reinforced with Cellulose Nanocrystals
Additive Manufacturing (AM), commonly known as 3D printing, is a manufacturing technique that is attracting broad attention due to its advantages, tailorability, and low cost. Among the many different types of AM processes, extrusion based systems are commonly used due to its low initial equipment and material costs. Bio-based Polylactic Acid (PLA) is one of the most commonly used materials in this market. However, mechanical properties and final tolerances of 3D printed PLA based parts are in need of improvement for applications that require high strength, stiffness and structural stability. Addition of filler materials such as organic particles can provide the required property improvements. Cellulose Nanocrystals (CNC) are novel bio-based nano-fibers with excellent mechanical properties. These particles have high potential to improve mechanical and thermo-mechanical properties of PLA. The present work investigates production and use of PLA/CNC composite filaments as an attractive option for 3D printing. PLA/CNC filaments were produced via twin-screw extrusion and fed into extrusion-based printers to form 3D printed components. The investigation shows an increase in mechanical properties from plain 3D printed PLA to a CNC reinforced PLA.
Effect of Silane-induced Interphase on Mechanical Properties of GFRP
Silane-treated glass fiber affects not only the interfacial strength due to silane bound to glass fiber surface but also the properties of resin near the interface between fiber and resin, that is, denatured resin interphase. Using epoxy resin for composites, the resin made denatured area induced by silane treatment for glass fiber. This phenomenon was similar to that produced with vinyl ester resin. The thickness of denatured area depended only on amount of silane on glass fiber, irrespective of amount of chemical-bonded silane on fiber, that is, silane fixation. To confirm the mechanical effect of resin interphase, the mechanical stability of interface and matrix resin has been evaluated after molding of composites. Microdroplet test has been used to determine the interfacial shear strength. Bending test has been employed using unidirectional epoxy resin composites with silane-treated glass fiber. Interfacial shear strength significantly depend on silane fixation, while bending strength seems to be indirectly reflected from interfacial reinforcement. This difference was interpreted in terms of brittleness of denatured resin area near interface of glass fiber using a result of whitening along glass fiber at breakage of GFRP.
4D printing is a manufacturing process which combines 3D printing with reconfiguration of the structure into a more complex shape. The normal 4D printing would involve the deposition of polymeric materials with special properties to make flat layers. These flat layers are then subjected to some activation mechanism such as heat, light, water absorption etc. The materials in the flat layers then react to the activation mechanism to change the shape of the structure. Most of the materials used in 4D printing have low mechanical properties. 4D printing of composites (4DPC) is similar to the 4D printing mentioned above, except that the materials are regular composite materials that have been used to make structures such as airframes. These materials are light, stiff and strong. Flat layers of the composite are laid using Automated Fiber Placement. The layers have different orientations to make unsymmetric laminates. Upon curing, the interaction of layers of different orientations will make the structure to be curved. This technique can be used to make structures of different curvatures, without the need to use complex molds (as such it can be termed as moldless composite manufacturing). This paper presents the mechanical behavior of composite springs that are made using 4D printing method.
Damage Behavior of CFRP/Titanium Mesh Laminates Under Three-point Bending Loading
Fiber Metal Laminates (FML), which is molded by alternately laminating FRP and metal layers, attract attention as hybrid composites material that show excellent fatigue resistance and damage tolerance. However, there is a problem that interfacial debonding between FRP and metal layers tend to occur due to such as an out-of-plane loading. In this research, we introduce mesh-shaped metal layers in FML in order to suppress the interfacial debonding because adjacent FRP layer can stick together through the meshes. The damage behavior such as FRP/metal interfacial debonding is evaluated by observing the cross section during three-point bending tests. CFRP / titanium mesh laminates are molded as a flat plate or a curved plate with a radius of curvature of 50mm by using an autoclave or a hot press. The impregnation of resin depends on the thickness of titanium mesh used, and some voids are found inside. By three point bending tests and cross-sectional observations, it is indicated that the maximum load and absorbed energy are improved and the interfacial debonding was suppressed in the flat specimen. These can be assumed as an effect of adopting the mesh structure for metal layers. Improvement of absorbed energy and suppression of interfacial debonding are also observed in the curved plates.
Compressive Mechanical Property of Braided CFRTP Pipe at Elevated Temperatures
Carbon fiber reinforced thermoplastics (CFRTP) pipe can be used for fabrications such as frame materials of vehicle and truss of aerospace. Mechanical properties of CFRTPs decreased as the temperature increases. Therefore, the mechanical properties of CFRT Ps pipes at elevated temperatures must be examined. In this study, carbon fiber (CF) and polyamide (PA) were used. B raided CFRTP pipe was developed using open molding method with braiding technology. The compression test for the braided CFRTP pipe was conducted at elevated temperature s from 40 o C to 120 o C. The compressive mechanical property of the braided CFRTP pipe was me a sured and assessed. Results showed that b raided CFRTP pipe compressed at the temperatures lower than 60 o C was broken with ‘fiber break’ around pipe surface in the circumstance direction . Braided CFRTP pipe compressed at the temperatures equal and over 60 o C was fractured in the ‘kink- band’ type.
Initial Fracture of Carbon Fabric Reinforced Polyamide Composite
In this study, 10 types of condition were investigated. 2 types polyurethane dispersion (PUD) were applied as surface treatment of washed and non-washed carbon plain woven fabric reinforced thermosetting and thermoplastic composites. To investigate the effects of surface treatment on the mechanical properties, Dynamic mechanical analysis was employed to investigate the interfacial interaction properties. Static tensile test was used to study the mechanical properties of composites. The acoustic emission from various composites was recorded in order to investigate the initial fracture and failure mechanism.
Solvent-Case D Printing and Secondary Metallic Infiltration for Highly Dense Metallic Structures (abstract only)
Three-dimensional (3D) printing is referred to create objects by adding material layer-bylayer rather than traditionally removing material from a part. In this study, we developed a method to fabricate metal 3D microstructures consisting of 3D printing at room temperature and two following processes: sintering and copper infiltration. 3D structures such as scaffolds and planetary gears with the filament diameter of 250 μm are printed using a steel micro powders/polylatic acid (PLA) composite at a printing speed of 10 mm/s. The ink concentration is up to 98.28 wt%. Filament porosity of copper infiltrated samples is under 0.3%. After sintering, copper is infiltrated into the sintered sample to obtain steel and copper alloy 3D structures. The Young’s modulus of the fabricated structures is up to 195 GPa and its electrical conductivity is 1.42 × 106 S/m, which are almost the same as those of the bulk material
Evaluation of Resin Impregnation Behavior in Thick FRP with Corner During VaRTM Process
Vacuum assisted resin transfer molding (VaRTM) method is a manufacturing method for FRP, which is capable of producing relatively high quality parts at low cost. However, since resin impregnation behavior in the fibre preform during VaRTM process is still not understood exactly, there is a possibility of voids being remained after cure. The purpose of this study is to evaluate resin impregnation behavior in thick FRP with corner, which is said to be likely to contain voids, by focusing out-of-plane flow in the fibre preform attributed to distribution media (DM). However, our previous experiments show that when DM is placed on top of fibre preform, the flow front along the bottom surface becomes quite complicated, and thus the quantitative evaluation of resin impregnation behavior is of great difficulty. Therefore at first we evaluated the effect of permeability of DM (KDM) and the number of plies on the flow front shape by using a flat tool. It was found that when KDM is low or number of plies is small, the flow front along the bottom surface becomes relatively linear, while with higher KDM or larger number of plies, the flow front along the top surface becomes complicated. We evaluate resin impregnation behavior in thick FRP with corner by using mentioned DM with appropriately low KDM.
Effect of Molding Condition on Mechanical Properties of FRP by RTM (abstract only)
In general, it is considered that mechanical properties of CFRP should be the same if reinforcing fiber and matrix resin, reinforcements and surface treatment were the same whatever molding method was. However, it was revealed that mechanical properties were influenced by molding method. In recent study, propagation of microscopic damage was different depending on the molding method, and microscopic damage of FRP by RTM was likely to occur compared to FRP by hand-lay-up. It was said that difference in interface properties formed by molding method was caused. On the other hand, thermosetting resin composite material have high heat resistance, but long molding time was needed due to the chemical reaction. Therefore, HP-RTM (High Pressure Resin Transfer Molding) using fast cure type resin has been adopted. HP-RTM is a molding method that enables to shorten the molding time by using fast cure type resin pour into the molding die in a high pressure condition. However, the resin is transferred under the condition of high pressure and high speed in HP-RTM, interface property might be declined. The purpose of this study was to restrain microscopic damage by improving interface properties in RTM method. Also, effect of molding pressure by HP-RTM was revealed. After carbon fiber reinforced composite material was molded by changing pressure of HP-RTM, tensile test and observation of microscopic damage were carried out to observe propagation of microscopic damage.
Influence of Needle Punch Density on Mechanical Properties of Jute/Glass Hybrid Composites
Glass fiber reinforced plastics (GFRP) have been used for in wide range and approximately 70 years passed. Hand lay-up method is the most primitive molding method. This method can utilize the property of unsaturated polyester resin curing at normal temperature and normal pressure with solventless liquid resin. Fabricate the Jute/Glass hybrid composite with needle punch density 1, 2, 3, 77 and without needle punch. Flexural test and the short-beam test was conducted. Density2 compression from Jute side was 103MPa, 56% higher than without needle punch (61MPa). Interlaminate fracture occurred the only specimen on without needle punch compression from Glass side.
Production of Flax Polypropylene (Flax/PP) Injection Moldable Pellets for Automotive Applications Using Pultrusion (abstract only)
The aim of this research project was to demonstrate the use of pultrusion technology to make flax and polypropylene (flax/PP) injection moldable pellets for automotive applications. Rods of 3/16 inches in diameter were pultruded using multi-die vacuumassisted pultrusion system. The fiber volume fraction of the rods was 50% and the void content was below 3%. The rods could be pelletized into different lengths based on request and it can be pelletized in the range of 3 to 25 mm. The impregnation quality in pultruded rods was characterized by optical microscopy and void content measurements. During pultrusion of flax/PP the fiber bundles attained great degree of fiber collimation. Due to the low shear involved in the pultrusion process, fairly little fiber damage was observed. The pellets were successfully used during injection molding of dogbone coupons.
Investigation of Preheating Conditions for Various Base Material in Hybrid Molding (abstract only)
The strength of carbon fiber reinforced plastic increases with an increasing fiber length. However, it is significantly difficult to mold complex 3-dimensional shaped products using continuous fibers. The hybrid molding method where complex-shaped products with high strength are processed in short time is proposed. The hybrid molding method addressed in this study is one of the insert molding technology. Parts requireing high strength is processed by press molding where long or continuous fibers are utilized while complexshaped parts are integrally molded by injection molding using short fibers. The main issue of the method is the occurrence of delamination between a pressed part and injected part. It was reported from the previous study that bonding strength of hybrid molded products was improved by preheating base materials employed in press molding. However, the influence of preheating to the quality of products depending on the reinforcements of the base material is not clarified. The ultimate goal of this study is to find optimum molding conditions of each base material. This paper discusses the differences in mechanical properties between two kinds of pre-heated base materials, nonwoven fabric and woven fabric through threepoint bending test and cross-sectional observation.
Stiffness Reduction Resulting from Matrix Cracking in FRP Laminates
Fiber Reinforced Polymer laminates (FRP) have properties, which are highly dependent on the ply fiber orientations and which can be designed for optimum laminate performance. The purpose of this study is to investigate effect of matrix cracking on the mechanical properties of FRP laminates with various off-axis angles. Carbon and glass fiber reinforced polymer laminates (CFRP and GFRP) are tested. FRP prepregs are cured by using autoclave method to form laminates with layups [m/ n]s. The laminates are then loaded monotonically and cyclically to obtain their mechanical properties and the effect of matrix cracks on the properties. One of the main effects is reduction of laminates’ stiffness. In order to obtain higher crack densities in specimens, artificial cracks method was introduced in this study. The measured stiffness reduction as a function of the crack density is compared to an analytical prediction for cracked angle-ply laminates based on a variational stress analysis. The experimental results for stiffness reduction agree well with the analytical results. Understanding the behavior of damaged laminates with simple configurations used in this study is of high importance for prediction of damage effects on laminates with more complex configuration, e.g. with quasi-isotropic layups.
Flame Attack on Protected Carbon/epoxy Laminates—Small-scale Material Screening for Potential Use as Aircraft Powerplant Firewalls (abstract only)
Carbon/epoxy composites are found in primary and secondary aircraft structures and their use has extended aircraft powerplants’ “coldâ€ zone. When found in designated fire zones, they need to act as firewalls where appropriate protective methods need to be incorporated. Hence, aircraft-powerplant certification guidelines require large-scale fire tests to determine material integrity. Such tests can translate in expensive and lengthy campaigns that could be mitigated with a preliminary small-scale test campaign. A smallscale rapid screening method is presented. Virgin and protected carbon/epoxy specimens, with a similar configuration to those found in powerplant firewalls, were exposed to a 1100 °C flame for 15 minutes. Backside temperature and mass loss values are compared. This method adequately rates the fire performance of several protection methods.
Bending Formability on Molded Continuous FRTP Pipe (abstract only)
In the field of engineering, it’s widely known that continuous fiber textile thermoplastic composite pipe which could be freely bend-processed in every dimensional way are demanded. By replacing metal complex shaped parts into CFRTP bend-formed items, it can improve vehicle efficiency and performance by reducing its weight. For example, CFRTP coil spring for suspension parts is one of the ultimate target for pipe bend-forming (360°bend). These techniques can also be applied for other vehicle parts like stabilizer and door beam members. As the cross-sectional shape of the pipe is made in hollow, a big reduction of weight can be expected. From the recent researches, it’s been found out that bend curvature will be formed by changing fiber orientation angles on both inner and outer side of the pipe. To prevent wrinkling, inner side of the pipe needs to be tensioned during bending process. Previously, the appropriate bending temperature for bend-forming was investigated. In this research, two types of reinforcement, Filament Winding (FW) and braiding were compared for bend-forming. The best bend-formability for reinforcement has been specified by searching flexibility from their fiber orientation angle change after bendforming. Also bend-forming with inserting axial yarn inside the pipe was challenged for another topic.
Development of Bending Process for Composite Pipe During Molding Process (abstract only)
Fiber reinforced composite materials are utilized in automotive applications as a substitute of steels because of high specific stiffness and strength. If it is achieved that a fiber reinforced composite material is bent during pultrusion molding, it is expected that the utilization of fiber reinforced composite materials will be expanded. Therefore, the bending process during the pultrusion process was examined using braided fabric. Continuous fibers with the thermoplastic resin are used to construct the braided composite pipe for pultrusion. Focusing on the continuous processing of roll forming, a bending machine was introduced after the pultrusion process of a composite pipe. In the previous study, a bending machine that can bend a composite material pipe by three-point bending was devised. When bending was performed with a three-point bending machine, the cross-section of FRP pipe could not be maintained to be an original circular shape because of no core material. Therefore, in order to overcome the problem, a new bending machine which made aluminum molding die with the passage of outlet part shape R and bending by passing the composite material pipe through the molding die was proposed. Furthermore, in order to prevent flattening of the cross-section after bending process, bending was carried out with the core material inserted in the composite material pipe, and the effect of inserting was also examined.
Modelling D Interlock Fabrics Using Elliptic Yarn Section with Quadrant-parametric Equations (abstract only)
3D interlock woven fabrics provide multiple possibilities of fiber architecture. The selected architecture directly influences the cross-section shape of the yarns. Elliptic equations are commonly used to represent the yarns in 3D woven fabrics modeling software. This conventional definition limits the architecture resemblance to the actual fabric. This study presents a generalized approach to model yarns by dividing their crosssection shape in quarters. The influence of this approach on the fabric thickness is analyzed. A specific superellipse equation is used in this study. The analyzed 3D woven fabrics are non-crimp fabrics (NCS). The results of this study allow to confirm that quadrant definition of the cross-section helps to model precisely the interaction between yarns, thus having a fabric thickness close to the reality.
Metal-to-thermoplastic Adhesion Improvement in a Resistance Welded Composite Joint (abstract only)
Thermoplastic composites can be resistance welded. This method requires the inclusion of a porous electrically conductive element between the two composites to be joined. By applying a current to it, it will heat by joule effect and melt the composites matrix. By maintaining pressure on the joint it will consolidate during cooling. These joints are very resistant to fatigue and shear. However it has been observed that the rupture of these joints is mainly between the conductive element made of stainless steel and the thermoplastic matrix with a composite of poly(phenylene sulfide) (PPS) reinforced with carbon fibers. In order to improve these welded joints, the silane is used as a coupling agent between the two materials. It is a bivalent molecule with a silanol part (-Si-OH) that can be grafted to the oxides of the steel and an amine part. Grafting silanes onto the steel increases its adhesion with organic materials. The application of silane layer on the steel has already made it possible to increase the apparent shear strength of welded joints by more than 30%. The optimization of the steel treatment and the modification of the PPS matrix could then significantly improve the mechanical performance of such joints.
The Effect of Molding Condition on Properties of Pultruded Carbon Fiber Reinforced Polymer Composites
Pultrusion is the one of technologies to fabricate the high performance polymer composites. In order to produce high quality pultruded profiles, there are variables such as fiber impregnation, resin viscosity, pulling speed and molding temperature that have to be considered and molding temperature one of variable is discussed in this research. The effect of molding temperature at zone number eight (exit die) on the mechanical properties and degree of polymerization of the composites were evaluated. The result of this study, the molding temperature zone number eight (exit die) for pultrusion process is 200ºC is the optimum condition for this study. It could be improve the mechanical properties and degree of polymerization of composites.
Building a Model to Understand the High Performance Fiber Fuzz Created by Yarn and Pulley Interactions During Textile Processing (abstract only)
Thanks to their great specific rigidities and resistances, composite materials tend to progressively replace metal in the design of high-performance structures. As an example, the last generation of airliners (Airbus A350, Boeing 787, and Bombardier CSeries) now includes up to 50% in mass of composite materials. Carbon fibers are often chosen to design parts that undergo heavy loads. These fibers are usually shipped as tows, consisting of hundreds to thousands clustered single filaments. May it be for coating, storage, braiding or weaving process, carbon tows often needs to be driven through a series of pulleys. Such a process may induce strong material loss due to filament rupture and therefore induce unwanted costs. In order to understand the cause of this rupture, carbon fiber tows behavior have been investigated through experimental and numerical analyses. Filament scale explicit dynamic calculations have been conducted and compared to experimental measurements gathered on a specifically designed test bed. The experimental and numerical data obtained is used to determine the prominent factor inducing the fiber degradation.