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Purpose The purpose of this study is to obtain strong materials with multiwall carbon nanotubes (MWCNTs) doped and investigate laser cut of MWCNTs also find the effect of the laser cutting parameters on composite materials. Design/methodology/approach The laminated composite plates were manufactured by using a vacuum infusion process. The mechanical properties of the composite materials produced were determined according to American Society for Testing and Materials (ASTM) D3039M, ASTM D3171, ASTM D 792 and ASTM D2583. A 130 Watts carbondioxide (CO2) laser cutting machine was used for drilling the two different composite plates with a thickness of 1.6–1.5 mm. Three variables were considered as process parameters including laser power (in three levels of 84.50, 104.00 and 127.40 W), cutting speed (in three levels of 4, 6, 8 mm/s) and 14 mm fixed focal position. Findings The fibers could not be cut due to insufficient melting in the experiments performed using 84.50 and 104.00 W laser power but the cutting was successfully completed when the laser power was 127.40 W. However, as the cutting speed increased, the contact time of the laser beam with the material decreased, so the kerf decreased, but the increased laser power created a thermal effect, causing an increase in hardness around the cutting surface. This increase was lower in MWCNTs doped composites compared to pure composites. It has been found that the addition of nanoparticles to layered glass fiber composite materials played an effective role in the strength of the material and affected the CO2 laser cutting quality. Originality/value This study is a unique study in which the CO2 laser cutting method of MWCNT-doped composite materials was investigated and the machinability without cutting errors, such as delamination, splitting, distortion and burring using the most suitable laser cutting parameters was revealed.

In this study, the holes of glass fiber reinforced polymer (GFRP) and multi-walled carbon nanotubes (MWCNTs) doped GFRP composite materials were drilled using abrasive water jet (AWJ), CO2 laser cutting, orbital drilling, and punching methods; the effects of these methods on hole quality were determined. The hole entry and exit dimensions were obtained equal and in the desired size by orbital drilling; thus, kerf formation was prevented due to the lateral and face milling of the end mill. The surface hardness change was not observed in the hole circles obtained with the orbital drilling and punching methods. However, epoxy hardening was observed in the hole circles obtained by laser cutting due to the heat effect of laser beam. In AWJ method, matrix-fiber integrity was disrupted, and delamination was observed due to the effect of water pressure and kinetic energy; consequently an increase in material thickness was observed and surface hardness decreased. It was determined that MWCNTs additive increased the surface hardness of composites and maintained its hardness and durability in post-cutting measurements. Splintering and burring were not seen in any method, but fiber carbonization was observed in the inner parts of the hole due to thermal effects in laser cutting.

In this study, the effect of adding nanosize additive to glass fiber reinforced composite plates on mechanical properties and surface milling was investigated. In the light of the investigations, with the addition of MWCNTs additive in the composite production, the strength of the material has been changed and the more durable composite materials have been obtained. Slots were opened with different cutting speed and feed rate parameters to the composite layers. Surface roughness of the composite layers and slot size were examined and also abrasions of cutting tools used in cutting process were determined. It was observed that the addition of nanoparticles to the laminated glass fiber composite materials played an effective role in the strength of the material and caused cutting tool wear.

The article presents the results of research on the influence of the length of elements made of carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP) on surface roughness, surface topography, passive forces and cutting torques after circumferential milling with diamond-coated inserts (PCD). The paper also presents the results of research the stiffness of the elements depending on their length. Samples of composite materials were clamped in a vise at the machining center. The length of the element was defined as the unsupported distance between the milled surface and the place of attachment of the composite element. With constant milling parameters, the maximum values and amplitudes of the values of passive forces and cutting torques at variable element lengths were determined. The obtained surface was measured in order to determine the surface roughness parameters and 3D topography. Research have shown that the carbon fiber reinforced plastics is on average one and a half times stiffer than that the glass fiber reinforced plastics. Based on the results obtained, it was found that as the length of the element increases, the passive forces and cutting torques increase and the roughness parameters increase. It has also been shown that for the glass fiber reinforced plastics, above a certain length, the surface roughness clearly deteriorates.

In this study, glass fiber reinforced composite layers which are with and without additives of 0.1 wt.% multi walled carbon nanotubes (MWCNTs) of epoxy were manufactured by vacuum infusion method. Unlike the conventional methods, punching was used in processing and drilling of these materials. The 62 - 64 HRC hard punches made of 1.3343 material with specially designed 90 degrees, 30 degrees, 15 degrees, V, C profiles were used for punching of composites. Additionally, made of 1.2379 material with 62 - 64 HRC hardness, the mold with 0.05, 0.01 and 0.16 mm clearance values was used. Fujifilm prescale and chatillon load cell were used for force measurement that showed the pressure applied by punches with different cutting profiles. Hole diameter, delamination and burring were analyzed by 3d laser scanner. In test values with mold's 0.05 mm clearance, no burr was observed. The cutting surface of MWCNTs doped composite materials was found to be cleaner and material strength was higher.

The aim of this work is to investigate the effect of the hexagonal nano boron nitride (h-BN) doped epoxy on the mechanical performances and machinability behaviors of basalt fiber (BF) composites. The h-BN has used as a dopant with a weight rate of 1 wt. %. The polymer composites were prepared by the vacuum bagging method and specimens were processed with abrasive water jet machining (AWJM) to analyze the machinability of the material. A circular hole with an 8 mm size was machined by abrasive water jet (AWJ) on the composite plate with a thickness of 2.3 ± 0.1 mm using the garnet size of 80 µm as an abrasive. Taper angle and circularity of machined hole, the entry-exit hole diameter, delamination, splintering, burring, thickness, and hardness were measured. Results indicate that cutting speed has a high influence on the taper angle and circularity respectively.

Masonry structures are economical, easy to construct and has important advantages such as the use of natural materials. In Turkey, these structures have been heavily built especially with traditional construction methods and nowadays they are popular as well. Therefore, the reinforcement of masonry structures and seismic safety are of paramount importance. Masonry walls are not naturally stable and cannot be considered as homogeneous structures so it is difficult to predict their behavior under load by using numerical methods. Supportive framework of the mathematical model and the data of the experimental studies are required. In this study, 36 wall blocks were prepared in 900 × 900 × 200 mm using hollow masonry brick, blend brick and aerated concrete and these blocks are reinforced with Carbon Fiber Reinforced Polymer in both directions by using three different methods. For the analysis of retrofit brick walls produced and reinforced with different materials, ASTM E591 test method was used. At the end of the experiment period; shear strength performances of the reinforcement methods of the elements, their deformation and energy dissipation capacities were evaluated. According to results, maximum shear strength performance was observed at the masonry panel strengthened by two face. Maximum load value was 172.63 Kn. Also maximum dissipation capacity was observed at the masonry wall reinforced with CFRP covered diagonally. Maximum energy dissipation capacity was 317.1 J. © 2018 Elsevier Ltd

Materials play a fundamental role in defining the vibrational and acoustic characteristics of structures and their importance is even increasing because of the continuing demand for lightweight products. Carbon Fibre Reinforced Plastics (CRFP) components are becoming more and more popular because of their excellent mechanical properties but are unfortunately almost unable to dissipate energy. This is one of the reasons why their usage is limited to structural components and does not directly affect acoustic and vibrational response, which are among the factors responsible for harshness and comfort. In vehicles, for example, large panels of CFRP are as noisy as metallic panels so that this kind of lightweight structures is only used when a limited mass is of paramount importance, e.g. in racing cars. The chance of incorporating a damping material in the stacking sequence of CF layers that define a composite seems to be a viable solution to ameliorate the vibrational behaviour of composite materials. This configuration permits to cure the damping layers together with the resins, in order to obtain both free and constrained layer solutions. In this paper, the Oberst beam method has been chosen to determine the elastic modulus and loss factor of such materials, as a function of both frequency and temperature. Three nominally identical samples for each configuration have been tested in a temperature controlled environment, according to the Oberst beam test method. The effects of aging have been simulated by an accelerated standard procedure, with cyclically varying temperature and humidity for a total of 792 h (3 cycles x 264 h). The analysis of experimental data has been performed in the frequency domain by a least square fitting procedure, aimed at outperforming the simple half-power point method. An open source version of the fitting technique has also been implemented and can be obtained from the authors under the CC-by license.

The additive manufacturing (AM) of carbon fiber reinforced plastic (CFRP) composites continue to grow due to the attractive strength-to-weight and modulus-to-weight ratios afforded by the composites combined with the ease of processibility achievable through the AM technique. Short fiber design factors such as fiber content effects have been shown to play determinant roles in the mechanical performance of AM fabricated CFRP composites. However, this has only been investigated for tensile and flexural properties, with no investigations to date on compressive properties effects of fiber content. This study examined the axial and transverse compressive properties of AM fabricated CFRP composites by testing CF-ABS with fiber contents from 0%, 10%, 20%, and 30% for samples printed in the axial and transverse build orientations, and for axial tensile in comparison to the axial compression properties. The results were that increasing carbon fiber content for the short-fiber thermoplastic CFRP composites slightly reduced compressive strength and modulus. However, it increased ductility and toughness. The 20% carbon fiber content provided the overall content with the most decent compressive properties for the 0–30% content studied. The AM fabricated composite demonstrates a generally higher compressive property than tensile property because of the higher plastic deformation ability which characterizes compression loaded parts, which were observed from the different failure modes.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2017-02-23, 資料番号: PA1710071000

Las operaciones de taladrado tienen un gran impacto en los tiempos y costes de los procesos de fabricación y montaje de estructuras aeronáuticas, debido al gran volumen de uniones mecánicas que se realizan, la dificultad para mecanizar estos componentes y los altos estándares de calidad requeridos. En esta industria, destaca el uso de materiales compuestos, especialmente, reforzados con fibras de carbono (CFRPs), que poseen excelentes propiedades mecánicas específicas y una buena resistencia a la fatiga y a la corrosión. El mecanismo de arranque de material que se produce en los CFRP, se caracteriza por cortes intermitentes de las fibras y la fluctuación de las fuerzas de corte. Además, las herramientas sufren un desgaste severo causado por la abrasividad y dureza de las fibras de carbono. Por otro lado, en elementos estructurales con elevas y complejas cargas, se requiere el uso de aleaciones de titanio y aluminio, por sus mejores propiedades mecánicas. Este documento se centra en el estudio de las operaciones de taladrado en Ti por su menor maquinabilidad debido a su elevada resistencia y dureza, baja conductividad térmica y afinidad química con la mayoría de los materiales que se utilizan en la fabricación de herramientas. En los procesos de montaje, cuando se requiere la unión de dos o más componentes formados por materiales compuestos y aleaciones metálicas, se denomina apilado híbrido, cuyo mecanizado supone una gran complejidad. Esto se debe a la baja maquinabilidad de los materiales y a las interacciones que se producen durante su taladrado, pudiendo afectar a la calidad y a la integridad superficial del agujero. En esta tesis se analizan, de forma experimental, diversas operaciones de taladrado con herramientas de metal duro y recubrimiento de diamante para los procesos de taladrado automático. En los materiales compuestos CFRP se estudia la influencia de los parámetros de corte en los mecanismos y evolución del desgaste de herramienta, así como en la calidad y control del daño inducido por el mecanizado en el agujero. Este análisis combinado permite optimizar las condiciones de corte y determinar la dependencia de estas variables en avanzados estados de desgaste. En cuanto a los apilados híbridos, en este documento se presenta un estudio sobre la influencia de los niveles de lubricación MQL (Minimum Quantity Lubrication) en los mecanismos de desgaste y la calidad de cada una de las capas que componen un apilado Ti/CFRP/Ti. La mejora de los procesos de taladrado en apilados híbridos y la optimización de los niveles de lubricación MQL permiten realizar mayor cantidad de agujeros en una única operación de taladrado (One Shot Drilling, OSD) e introducir técnicas de montaje avanzadas. Drilling operations have a huge impact of time and cost on aircraft structures manufacturing and assembly processes, owing to the big volume of mechanical joints used, the complexity of the machining operation and the quality standards required. In this industry, composite materials are used extensively, mainly, Carbon Fiber Reinforced Plastics (CFRPs), which stand out by their excellent specific mechanical properties and good fatigue and corrosion resistance. The material removal process is characterized by intermittent fracture of the fibers and oscillation of the cutting forces. Furthermore, the drill bits suffer a severe tool wear produced by the abrasiveness and hardness of the carbon fibers. On the other hand, structural elements with very demanding and complex loads are made of titanium and aluminum alloys for their superior mechanical properties. This document focuses on the analysis of Ti drilling due to its high hardness and strength, poor thermal conductivity and chemical affinity with most cutting tool materials, which result in a lower machinability. In assembly processes, components made from composite materials and Ti alloys are usually joined, producing hybrid stacks, which machining imposes an extra complexity. During drilling operations, interactions may occur between these different nature materials that may affect the quality and surface integrity of the hole. In this thesis, multiple drilling operations are analyzed, from an experimental point of view, with diamond coated carbide tools for automatic drilling processes. For CFRP drilling, it was studied the influence of the cutting parameters in tool wear mechanisms and evolution, as well as in the quality and control of the machining induced damage of the hole. This combined analysis allows to optimize cutting conditions and to determine the dependence of these variables under severe tool wear. Regarding hybrid stacks, this document focuses on the analysis of the Minimum Quantity Lubrication (MQL) level influence in tool wear mechanisms and the quality of each layer in a Ti/CFRP/Ti stack. The improvement of hybrid stacks drilling processes and the optimization of the MQL lubrication level, allows to perform more holes in a single drilling operation (One Shot Drilling, OSD) and to introduce advance assembly processes. El proyecto de investigación está financiado por Airbus Defense and Space, a través de Airbus Group Innovation (AGI), con el proyecto "Drilling Processes Improvement for Multi Material CFRP-Al-Ti Stacks". También se ha contado con financiación complementaria por parte del Ministerio de Economía y Competitividad del Gobierno de España, a través de la ayuda para Personal Técnico de Apoyo con referencia PTA2015-10741-I. Programa de Doctorado en Ingeniería Mecánica y de Organización Industrial por la Universidad Carlos III de Madrid Presidente: Eugenio Giner Maravilla.- Secretario: Antonio Díaz Álvarez.- Vocal: Joaquín Barreiro García

In practical application, carbon fiber reinforced plastics (CFRP) structures are easy to appear all sorts of invisible damages. So the damages should be timely located and detected for the safety of CFPR structures. In this paper, an acoustic emission (AE) localization system based on fiber Bragg grating (FBG) sensing network and support vector regression (SVR) is proposed for damage localization. AE signals, which are caused by damage, are acquired by high speed FBG interrogation. According to the Shannon wavelet transform, time differences between AE signals are extracted for localization algorithm based on SVR. According to the SVR model, the coordinate of AE source can be accurately predicted without wave velocity. The FBG system and localization algorithm are verified on a 500 mm×500 mm×2 mm CFRP plate. The experimental results show that the average error of localization system is 2.8 mm and the training time is 0.07 s.

Linear robots, numerically controlled machines and articulated robots are some of the major components in automation. In various applications, these single systems are linked together to become advanced mechatronic systems since they can realize special and general tasks. Unfortunately, the degree of automation in carbon fiber reinforced plastic (CFRP) manufacturing is currently rather low. A lot of research still needs to be done in order to achieve the knowledge necessary to gain a consistent, robust and reliable production chain for CFRP. The most decisive criterion in automation is the tradeoff between speed in production and the attainable layup accuracy. One aspect that affects accuracy is vibration caused by rapid movement and interaction forces. In the case of advanced mechatronic systems, the effect of the dynamic coupling is one key factor in accuracy. Over the last few decades, the field of active vibration suppression has made use of its excellent capability to improve the accuracy of machines. Therefore, the paper presents a comprehensive review of active vibration suppression technology for the improvement of precision in manufacturing. The work is mainly focused on, but not limited to, the production of components made of CFRP. The paper concludes with a discussion of promising approaches to identify a trend for future work.

Dry drilling of thick carbon fiber reinforced polymer (CFRP) laminates requires careful selection of process parameters in order to obtain acceptable borehole surface quality. Complex contact conditions between the drill margin and the borehole surface determine the integrity of the borehole surface depending on the process parameters and temperature-dependent viscoelastic material properties. Temperature rise during dry drilling reduces the elastic modulus of the CFRP and causes thermal expansion of the drill, resulting in considerable contact length at the drill margin and borehole surface interface. Manufacturers need a better understanding of the interaction among contact pressure, sliding velocity, temperature at the interface, and temperature-dependent material properties to develop predictive models for drilling CFRPs. To examine this complex interaction, this study develops a novel, hybrid model that combines a time-based analytical modeling of drilling process with a finite element-based modeling of temperature rise. Drilling experiments were performed in which thrust force, torque, and temperature were measured as a function of feed, and these measurements were used to identify unknown hybrid model parameters. The results revealed that a significant change in friction conditions occurs when increased temperatures at the margin and borehole surface interface approach and exceed the glass transition temperature of the CFRP laminate at a large feed rate. These findings show the benefit of increasing feed during dry drilling, which is nonetheless limited by the temperature-dependent material properties of the work material. Publisher's Version

In this study, β-cyclodextrin was covalently bonded on carbon fibers and its influence through host-guest complex formation was analyzed. Since cyclodextrins act as host molecules for aromatic compounds, complex formations can be performed in carbon fiber reinforced epoxy resins, between the carbon fiber surface and the aromatic compounds of the surrounding plastic. This interface design leads to improved adhesion between fiber and plastic. An increase of the interfacial shear strength from 12 MPa to 38 MPa was detected. It was possible to increase the interfacial shear strength even further, to 41 MPa, through a prior complex formation with one of the plastics components. In addition to the micromechanical analysis, energy-dispersive x-ray spectroscopy and contact angle measurements were performed to confirm the covalent coating of cyclodextrin on the carbon fiber surface., Materials science, Materials chemistry, Carbon fiber, Cyclodextrin, Pull-out tests, Improved interfacial shear strength, Carbon fiber reinforced plastics, Interface design.

At the German Aerospace Center (DLR), Center for Lightweight Production Technology (ZLP) Augsburg automation solutions for manufacturing processes of extensive fiber composite components are developed. One challenge in this context is the automated preforming process of complex, double-curved geometries. Here, dry fiber cut pieces are transferred from a flat to a three-dimensional state. In order to fix the single layers of the stacking, the fiber package is being compacted and the powder binder system is activated using thermal energy. In addition, double-curved component geometries inhere particularly high requirements on the preforming process, since the fiber materials must not only be deformed, but also be draped. With the state of the art, the production of double-curved components can only be carried out manually, due to the high process complexity. Therefore scientists at the ZLP Augsburg developed an integrated preform manufacturing process, beginning at single cut piece handling till supply of the finished preform. Focus was set on a diaphragm based preforming mechanism that can be directly controlled regarding its forming behavior on the preform to ensure an adequate preforming of the carbon fiber semi-finished product. This paper focuses the challenges of automated production processes for complex, double-curved component geometries and presents one automation solution developed at ZLP Augsburg.

Fiber reinforced polymers (FRPs) show advantageous physical-mechanical, thermal, and dielectric characteristics, making them promising candidates for weight reduction in structural applications. However, machinability is often difficult because of the specificity of their structure. This paper highlights the latest advances in CFRP drilling. Key papers are analyzed with respect to workpiece materials, geometrical tool features, and input variables (such as variation in process parameters). The influence of tool geometry and process parameters on workpiece delamination and hole quality/integrity represents the primary focus of this review. In addition, some new data are presented and discussed.

For the development of a robot based laser cutting process of automotive 3D parts consisting of carbon fibre reinforced plastics (CFRP), investigations with a newly developed fibre guided nanosecond pulsed laser with an average power of P L = 1.5 kW were conducted. In order to investigate the best combination of quality and process time 2 different optical fibres were used, with diameters of d f = 400 μm and d f = 600 μm. The main differences between the two setups are the resulting focal diameter and the maximum available pulse energy up to E P = 80 mJ. In a first instance, a comparable investigation was performed with both fibres for a constant pulse overlap. For each fibre the minimum required line energy was investigated and cuts were performed, distributed over the complete parameter range of the laser source. The influences of the fibre diameter on the quality and efficiency of the cutting process are summarized and discussed.

Potentials of integrating new technologies, particularly carbon fiber reinforced plastics, are not fully considered conventional reengineering processes. This paper firstly addresses the benefit by integration of functions, reduction of weight and fuel consumption, substitution of rare materials and customer individuality. Consequently, these aspects have been evaluated in three case studies, comprising representative cultural goods (eg. pipe organs), components of sport-aircraft (eg. ultralight helicopters) and urban-transport (eg. multifunctional stroller-bicycle trailer). Therefore, the following methods have been applied: functional analysis, reverse engineering and measuring technologies.

Two-dimensional finite element simulations and experiments are presented to examine the ultrasonic wave propagation behavior in the corner section of CFRP (carbon fiber reinforced plastics) laminate structures. The numerical model consists of a right-angle corner section of CFRP laminate immersed in water and subjected to the ultrasonic wave incidence from its inner or outer side. The anisotropic stiffness constants of the unidirectional CFRP are identified experimentally and used to model the curved laminate structure. A commercial finite element analysis code is used to compute the reflection waveforms in the pulse-echo mode, and the effect of the laminate stacking sequence and the wave incidence direction is examined. It is shown that the reflection waveforms for the wave incidence from the outer side of the corner qualitatively resemble those for the plane laminate except that the echo signals of the former are substantially weaker. The numerical simulations are shown to well reproduce the qualitative features of experimental reflection measurements performed for the corner sections of 16-ply CFRP laminate. Experimental results indicate that the porosity content of the corner section can be estimated by the amplitude ratio of the surface and the back-wall echoes when a curvature-dependent calibration relation is properly used.

The production rates of carbon fiber reinforced plastic (CFRP) parts are rising constantly which in turn drives research to bring a higher level of automation to the manufacturing processes of CFRP. Resin transfer molding (RTM), which is seen as a production method for high volumes, has been accelerated to a high degree. However, complex net-shape preforms are necessary for this process, which are widely manually manufactured. To face these challenges a new concept for the manufacturing of carbon fiber preforms with a form-flexible gripping, draping and joining end-effector is presented and discussed. Furthermore, this paper investigates the application of this concept, describes the initial build-up of a demonstrator, focusing on material selection and heating technology, and discusses test results with the prototype. This prototype already validates the feasibility of the proposed concept on the basis of a generic preform geometry. After a summary, this paper discusses future in-depth research concerning the concept and its application in more complex geometries.

The accuracy of reliability analysis of structures made up of CFRP composites rely on the quantification of the uncertainties associated with composite material properties. This study focuses on the experimental characterisation of random field models for the material uncertainties. As a first step, a number of experimental tests on identical samples have been conducted as per ASTM standards. Assuming second order random fields to be appropriate for modelling the uncertain variations along the spatial extent in the macro-scale, statistical tests have been carried out to examine the suitability of some commonly used models for the probability density function for the various mechanical properties of the material. The spatial correlations observed from experimental tests have been compared with some of the commonly used correlation functions and suitable empirical models have been proposed. Finally, the importance of appropriate modelling of the parameters has been highlighted through a numerical example. � 2014 Elsevier Ltd.

In high-speed precision machining, thermal deformation caused by temperature rise affects the accuracy stability of the machine tool to a significant extent. In order to reduce the thermal deformation of ball screws and improve the accuracy, a new adaptive method based on carbon fiber reinforced plastics (CFRP) was proposed in this study and the thermal deformation of ball screws was determined. By using the sequential coupling method, the thermal&ndash, structural coupling analysis of a ball screw was conducted based on the finite element method (FEM). The analysis results were verified through a comparison with the experimental results. Based on the verification, an FE model of the improved ball screw was established to study its thermal characteristics. The key design parameters of the improved ball screw were optimized based on the Kriging model and genetic algorithm (GA). The thermal reduction effect of the improved ball screw was validated through the experimental results. The results indicate that the adaptive method proposed in this research is effective in reducing the thermal deformation of ball screws.

Carbon fiber reinforced plastics (CFRP) show high potential for use in lightweight applications not only in aircraft design, but also in the automotive or wind energy industry. However, processing of CFRP is complex and expensive due to their outstanding mechanical properties. One possibility to manufacture CFRP structures flexibly at acceptable process speeds is high-power laser cutting. Though showing various advantages such as contactless energy transfer, this process is connected to potentially hazardous emission of respirable dust and organic gases. Moreover, the emitted particles may be fibrous, thus requiring particular attention. Here, a systematic analysis of the hazardous substances emitted during laser cutting of CFRP with thermoplastic and thermosetting matrix is presented. The objective is to evaluate emission rates for the total particulate and gaseous fractions as well as for different organic key components. Furthermore, the influence of the laser process conditions shall be assessed, and first proposals to handle the emissions adequately are made.

The present work intends to provide a numerical tool for the efficient design of the multidirectional carbon fiber reinforced plastic (CFRP) material using finite element simulation software ABAQUS ® . A 3D model has been established for simulation of the tensile test composite specimen which enables to understand the mechanical strength and strain at failure of the composite materials. 15 ply CFRP specimens with various stacking sequences were analyzed for their strength and displacement. Exhaustive parametric studies reveal the dependency of reinforcing material and ply orientation on the strength and stiffness of composite materials. Carbon fibers with cross ply lamination were found to be stiffer than angle ply glass fiber lamination. A fairly good comparison was obtained between the predicted results with available experimental and theoretical data in open literature

A hybrid structural health monitoring (SHM) system, consisting of a piezoelectric transducer and fiber optic sensors (FOS) for generating and monitoring Lamb waves, was investigated to determine their potential for damage detection and localization in composite aerospace structures. As part of this study, the proposed hybrid SHM system, together with an in-house developed algorithm, was evaluated to detect and localize two types of damage: a through thickness damage (hole of 2 mm in diameter) and a surface damage (2 mm diameter bore hole with a depth of 0.65 mm) located on the backside of the plate. The experiments were performed using an aircraft representative composite plate skin, manufactured from carbon fiber reinforced polymer (CFRP).

Aluminium alloys provide many benefits and challenges for use in marine environment. Attention on lightweight hulls leads to power saving, better handling and easy transportation. The stiffness and mass of the structure or member is responsible for its natural vibration. The hull panels and stiffeners vibrate at different frequencies when their stiffness is reduced by formation of a crack or any structural problems. If there is a monitoring system on board and by using a sensor detecting the modified vibrations, the maintenance crew senses the spot where urgent repair is needed. Application of composite laminates is convenient in view of portability and simplicity in procedure such as hand lay-up. In this study, the edge-cracked aluminium plates were repaired with one-sided composite patches and their temperature were varied to both low and high temperature levels. Dynamic fracture toughness was determined using Charpy impact test. Three different types of materials were used for composite patching: GFRP (glass-fibre-reinforced plastic), CFRP (carbon-fibre-reinforced plastic) and Kevlar. For each temperature level, two lay-ups were used, viz. three layered and five layered. Aluminium specimens with edge cracks of two different lengths, keeping the width of the crack constant, were prepared. Impact tests were performed for the prepared specimens at different temperatures. The fracture toughness of aluminium strips reinforced with patches was determined and compared with the energy absorbed during the impact of the corresponding specimen without the patch. It was observed that the specimen with patches gave a higher fracture toughness value when compared with that without the patch; corresponding observation on aluminium has been made along with patch at these temperatures. The patch using Kevlar was found to be the best among the three composites. Followed by these experiments, simulations using FRANC 2D software were carried out for finding stress intensity factor at different crack lengths with and without patches. The research has a spin-off application in the selection of materials used for patching and hence in the maintenance of LPG (liquefied petroleum gas) and LNG (liquefied natural gas) storage tanks under cryogenic conditions. � 2013 Copyright Taylor and Francis Group, LLC.

This paper presents the results of 15 experimental tests on rectangular slender reinforced concrete (RC) beams. The results reveal limitations in existing theoretical formulations to estimate the failure moment capacity and mode of failure. An improved theoretical formulation is proposed here to predict the critical buckling moment including effects related to nonlinearity and cracking of concrete. Also, following the trends in steel design, an improved measure of slenderness ratio is proposed. Based on a study of 72 test results, it is shown that there is an interaction between flexural tension and instability modes of failure in moderately slender beams. To avoid lateral instability failure, it is suggested that the slenderness ratio be limited to unity. A 'moment reduction factor' is also proposed to account for slenderness effects in RC beams. � 2011 Elsevier Ltd.

The steel caging technique is used to strengthen RC columns all over the world, as it has been shown to be effective, economical and easy to apply. Most studies carried out to date on this strengthening technique have focussed on isolated sections of columns subjected to axial loads. This paper deals with an experimental study on the behaviour of RC columns strengthened by steel caging under combined bending and axial loads. Full-size specimens were laboratory tested and the beam-column joint was also simulated. Two different types of element were used to solve the strengthening in the zone nearest to the joint. These were: (1) capitals welded to the steel cage in contact with the beam and (2) steel tubes joining the cage on both sides of the joint. The results obtained show that the technique described considerably increases the resistance and ductility of columns strengthened in this way. The results are compared with those that could be obtained with the proposal of Eurocode No. 4 and also with the results of two other similar studies. © 2010 Elsevier Ltd. All rights reserved., The authors wish to express their gratitude for the financial support received from the Spanish Ministry of Science and Technology under Research Project MAT 2003-08075. Also to the Generalitat Valenciana for its financial support within the GVPRE/2008/153 Project. Mr. Garzon-Roca is grateful to the Generalitat Valenciana for the scholarship awarded to him to complete his doctorate studies. Thanks are also due to Ester Gimenez, Salvador Ivorra, and Francisco J. Pallares for their invaluable assistance from the beginning of the Project.

A theoretical analysis has been carried out to study the efficient microwave processing of discrete food sample ceramic composite attached with ceramic (Al2O3 and SiC) plates. Continuous food sample with a specific thickness corresponding to smaller power absorption is replaced by two discrete samples and processed with ceramic composite. The effective power and temperature distribution are found to be function of discrete food sample ratios, type of microwave incidence and ceramic layer thickness. The effect of ceramic material on various discrete sample ratios have been studied via effective average power vs. thickness of ceramic (Al2O3 or SiC) intermediate for one side and both sides microwave incidence. It is found that power absorption is enhanced significantly for beef sample due to specific thickness of ceramic composite corresponding to one side microwave incidence. The power enhancement is lesser and the temperature difference or thermal runaway is larger for bread samples as compared to beef samples. The enhancement of heat absorption is larger for one side incidence as compared to both sides incidence with identical total intensity of microwave incidence. The role of discrete samples with ceramic composites is significant for highly lossy substances (beef) whereas the composites do not play significant role on optimal processing of low lossy substances (bread). � 2008 Elsevier Ltd. All rights reserved.

Dry sliding wear behavior of 8090Al alloy and its composites reinforced with 8, 12 and 18 vol% SiC particles was studied in as-extruded and peak-aged conditions using a pin-on-disc machine. Tests were done at room temperature in air under loads of 10, 20 and 50 N at a constant sliding speed of 1 m s-1. The unreinforced alloy and composites show mild wear upto 20 N. Transition from mild to severe wear takes place beyond 20 N. Composites exhibit better wear resistance compared to the unreinforced alloy in as-extruded condition. Effect of heat treatment (artificial ageing) on wear behavior has also been studied. The unreinforced alloy exhibits better wear resistance at all the three loads used here in peak-aged condition compared to the as-extruded condition. Composites on the other hand, show better wear resistance upto 20 N, however, they show lower wear resistance in peak-aged condition compared to as-extruded condition beyond 20 N. This can be attributed to higher surface and subsurface deformation in peak-aged condition at higher load. � 2008 Elsevier B.V. All rights reserved.

Injection molded polymer composite gears are being used in many power and motion transmission applications. In order to widen the utilization of reinforced polymers for precision motion transmission and noise less applications, the quality or accuracy of molded gears should be increased. Since the injection molded gear quality is significantly influenced by the material shrinkage behaviour, there is a need to understand the influence of fiber orientation on part shrinkage behaviour and hence the gear quality. Unreinforced and 20% short glass fiber reinforced Nylon 6/6 spur gears were injection molded in the laboratory and computer aided simulations of gear manufacturing was also carried out. Results of the mold flow simulation of gear manufacturing were correlated with the actual fiber orientation and measured metrological parameters of the molded gears. Actual orientation of the fibers near the tooth profile, weld line region and injection points of molded gears were observed using optical microscope. Fiber alignment along the tooth profile restricts shrinkage and induces anisotropic shrinkage, which significantly decreases the deviation of involute profile parameter from the design value. Fibers embedded in the molded skin surface increases the gear tooth profile form and lead form deviations. Non-alignment of fibers across the gear tooth section increases the tooth thickness, tooth-to-tooth spacing and radial runout deviations from design values. � 2007 Elsevier Ltd. All rights reserved.

Masonry is one of the conventional materials that is being used throughout the world due to its accessibility, functionality and cost but they fail in earthquakes mainly due to their low tensile and shear resistance. The objective of this investigation is to study the effectiveness of GFRP composite retrofitting on the behaviour of masonry wallettes and shear triplets that are cast with low stiffness table moulded bricks and high stiffness cement mortar through experimental and finite element study. Experiments were conducted on masonry wallettes under compression in different orientations and triplets under shear. Finite element models for the analysis of wallettes and shear triplets is developed using the FE software ABAQUS and validated with the experimental data. The concepts of macromodeling with smeared crack concrete model for masonry wallettes and micromodeling with the elastic properties of brick and mortar for shear triplets are used for the analysis. The changes in deformational capacity and ultimate load resistance are calculated for varying thickness and fiber orientations of GFRP composites. Based on this study, it is concluded that the strength and axial stiffness of the wallettes under compression and strength of shear triplets is increased due to external bonding of GFRP composites. The comparison of finite element and experimental results proved that macromodeling can be used to study behaviour of masonry wallettes retrofitted with GFRP composites and micromodeling is feasible for the analysis of small scale specimens such as triplets. � 2007 Elsevier Ltd. All rights reserved.

High strength fibers are extensively employed in many different composite applications. This article is concerned with the rate dependency of mechanical behavior of these fibers, namely S2 Glass®, Kevlar 29®, and Spectra 900® fibers at low loading rates. Also studied is bonding behavior of these fibers with the most used thermoset composite matrix materials, which are epoxy and polyester resins. With this regard, several tensile and single fiber pull-out tests were carried out by employing a 5 kN Instron testing machine. The experiments were conducted at loading rates ranging from 1 to 250 mm/min. Based on the results obtained in this research work, the tensile strength is increasing from 1 to 100 mm/min loading rate and fiber matrix bonding strengths are decreasing by enhancing loading rate. This implies that certain mechanical properties of some polymer matrix composites could be rate dependent, even at low loading rates.

Glass fiber reinforced vinyl ester polymer composites filled with clay particles were synthesized by a hand lay-up technique with the addition of methy ethyl ketone peroxide (MEKP), cobalt napthalate and benzoyl peroxide. Mechanical and thermal properties of vinyl ester-glass fiber composite and clay particles dispersed vinyl-glass fiber hybrids were investigated in the present work. The hybridization effect of nanoclay dispersion in vinyl ester-fiber composite was discussed. Enhanced mechanical, thermal and vibration properties were observed in nanoclay dispersed composites over vinyl ester-glass fiber composite. � SAGE Publications 2008.

The Cu-W bulk nanocomposites of different compositions were successfully synthesized by high-energy ball milling of elemental powders. The nanocrystalline nature of the Cu-W composite powder is confirmed by X-ray diffraction analysis, transmission electron microscopy, and atomic force microscopy. The Cu-W nanocomposite powder could be sintered at 300-400 �C below the sintering temperature of the un-milled Cu-W powders. The Cu-W nanocomposites showed superior densification and hardness than that of un-milled Cu-W composites. The nanocomposites also have three times higher hardness to resistivity ratio in comparison to Oxygen free high conductivity copper. Copyright � 2007 American Scientific Publishers All rights reserved.

Fast curing of carbon fiber reinforced plastics (CFRPs) is limited by the degradation of the resin under high temperatures and by the development of internal strains. The authors counter these problems by adding nanoparticles to the matrix of CFRPs. In the presented work various volume fractions of nanosized aluminum oxide particles are integrated into the epoxy resin RTM6. To demonstrate the increased heat flow within the CFRP component, thermal conductivity tests are presented. Results show increasing values as the filler content is raised.With increasing filler content the reaction speed is also accelerated. This effect is analyzed by differential scanning calorimetry. It is shown that the particle surface has a catalytic effect on the curing of the epoxy resin. The results of the author also show that the added nanoparticles not only change the material composition, but also modify the network of the epoxy resin. In a series of experiments it is demonstrated how nanoparticles decrease the chemical shrinkage. The results show a reduction of the shrinkage higher than the volume fraction of the nanoparticles, which can be explained by the formation of interphases. Thermal mechanical analysis also confirms a decreased thermal shrinkage due to the integration of nanoparticles. Finally, the inspection of L-shaped CFRPs samples with different filler contents show the ability of nanofillers to decrease the spring-in.In summary, the integration of aluminum oxide decreases the thermal as well as the chemical shrinkage, increases the thermal conductivity and accelerates the chemical reaction.Overall, these changes in curing behavior lead to an increased dimensional stability of the CFRPs. Thus, nanoparticles may be one way of overcoming the disadvantages of fast curing cycles.

Application of short fiber reinforced thermoplastic materials are limited to functionally less important components due to heterogeneous characteristics of material and incomplete understanding of failure mechanisms involved. Reinforcement not only affects mechanical and electrical properties but also the failure mechanisms. Gears used in power/motion transmission may fail in many ways. This paper discusses the various types of failures exhibited by unreinforced and fiber reinforced Nylon 66 gears. Injection molded unreinforced, glass reinforced and carbon reinforced Nylon 66 spur gears were tested in a power absorption type gear test rig. Failed gears were observed under optical and scanning electron microscope to understand the damage mechanism. Different types of failures such as gear tooth wear, cracking at the tooth surface, tooth root cracking and severe tooth shape deformation were observed. Material compositions and applied torque decides the type of failure mechanism. Low interfacial strength between fibers and matrix in the reinforced gears causes fiber pullout. Reinforced gears exhibited longer life compared with the unreinforced gears due to superior mechanical strength and thermal resistance.

A finite element study is carried out for assessing the elastic displacement response of a typical CFRP payload fairing due to separation impulse. Different stacking sequences for the CFRP laminates are considered and their influence on the displacement response studied. Lanczos method is used for eigenvalue analysis and mode superposition method for the response study. The effect of the elastic response on the radial gap is also studied.A finite element study is carried out for assessing the elastic displacement response of a typical CFRP payload fairing due to separation impulse. Different stacking sequences for the CFRP laminates are considered and their influence on the displacement response studied. Lanczos method is used for eigenvalue analysis and mode superposition method for the response study. The effect of the elastic response on the radial gap is also studied.

Cyclostationarity is an inherent characteristic of many communication signals, which can be exploited for performing various signal processing tasks. Determining the cyclic statistics of a signal of interest is often necessary in the design of signal processing systems exploiting this cyclostationary behaviour. This work investigates the second order cyclic statistics of various signalling schemes employed in ultra wideband impulse radio systems. Analytical expressions are derived for the cyclic autocorrelation and spectral correlation density functions. Publisher's Version Q2 WOS:000260000200004

Cataloged from PDF version of article. Carbon fiber reinforced polymers (CFRP) have emerged as the material of choice to satisfy increasing demand for lighter aircrafts. Machinability characteristics of CFRPs are quite different than those of metals; therefore, special tool designs have been developed for CFRP machining. The double helix end mill design compresses the upper and lower sides of the laminate using opposite helix angles that eliminate delamination. A mechanistic force model for double helix tools is developed based on milling force data obtained on flat end mills. The proposed model can be used to improve double helix tool designs and to optimize milling process parameters. 2013 CIRP.

Cataloged from PDF version of article. Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-toweight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates. © 2012 Elsevier B.V. All rights reserved.

This thesis presents a technique used to stochastically estimate the location of hidden discontinuities in carbon fiber composite materials. Composites pose a challenge to signal processing because speckle noise, as a result of reflections from impregnated laminas, masks useful information and impedes detection of hidden discontinuities. Although digital signal processing techniques have been exploited to lessen speckle noise and help to localize discontinuities, uncertainty in ultrasonic wave propagation and broadband frequency based inspections of composites still make it a difficult task. The technique proposed in this thesis estimates the location of hidden discontinuities stochastically in one- and two-dimensions based on statistical data of A-Scans and C-Scans. Multiple experiments have been performed on carbon fiber reinforced plastics including artificial delaminations and porosity at different depths in the thickness of material. A probabilistic approach, which precisely localizes discontinuities in high and low amplitude signals, has been used to present this method. Compared to conventional techniques the proposed technique offers a more reliable package, with the ability to detect discontinuities in signals with lower intensities by utilizing the repetitive amplitudes in multiple sensor observations obtained from one-dimensional A-Scans or two-dimensional C-Scan data sets. The thesis presents the methodology encompassing the proposed technique and the implementation of a system to process real ultrasonic signals and images for effective discontinuity detection and localization.

Stitching is used to reduce dry-core (incomplete infusion of T-joint core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Microscopic inspection, ultrasonic c-scan, pulsed thermography, vibrothermography, and laser spot thermography are used to investigate the internal flaws in a stitched T-joint carbon fiber-reinforced polymer (CFRP) matrix composites. Then, a new microlaser line thermography is proposed. Microcomputed tomography (microCT) is used to validate the infrared results. A comparison between microlaser line thermography and microCT is performed. It was concluded that microlaser line thermography can detect the internal submillimeter defects. However, the depth and size of the defects can affect the detection results. The microporosities with a diameter of less than 54 mu m are not detected in the microlaser line thermography results. Microlaser line thermography can detect the microporosity (a diameter of 0.162 mm) from a depth of 90 mu m. However, it cannot detect the internal microporosity (a diameter of 0.216 mm) from a depth of 0.18 mm. The potential causes are given. Finally, a comparative study is conducted.

Densification behavior of alpha silicon carbide (SiC) during vacuum hot pressing was studied up to 1900C with sintering additives based on AlN and Y2O3 in different proportions. Near theoretical density was obtained with a total sintering additive content of 4 vol.. The microstructure of SiC sintered with AlNY2O3 revealed fine equiaxed grains against the additional elongated grains exhibited by SiC sintered with AlN alone. The SiC having high density exhibited very good strength, elastic modulus, high thermal conductivity, low coefficient of thermal expansion and excellent polishability for telescope mirror applications. � 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

This paper deals with the formulation of a nine-noded piezolaminated degenerated shell finite element for modeling and analysis of multilayer composite general shell structures with bonded/embedded distributed piezoelectric sensors and actuators. The distributed PZT sensors and actuators used in the composite smart structures are relatively thin and could have arbitrary variation of curvatures and thicknesses. They cannot be modeled with shell elements based on curvilinear shell theories which would need the specification of constant shell curvatures and thicknesses. Modeling them with piezo finite elements available in popular commercial codes like ABAQUS, ANSYS, MARC, etc, would need relatively greater computational effort as they are based on solid element formulation. In view of these, the present proposed degenerated piezoelectric shell element would be a better choice giving good computational accuracy and efficiency. The main advantage of a degenerate shell element is that it is not based on any shell theories and is applicable over a wide range of curvatures and thicknesses. This element is developed by using the degenerate solid approach based on Reissner-Mindlin assumptions which allow the shear deformation and rotary inertia effect to be considered and the 3D field is reduced to a 2D field in terms of mid-surface nodal variables. Uniformly reduced integration is carried out to overcome membrane locking and shear locking and the numerical integration is carried out in all three directions to obtain accurate results. The present element has 45 elastic degrees of freedom and 10 electric degrees of freedom per piezoelectric layer in the element. The potential induced due to bending deformation is more accurately represented by assuming quadratic variation of the electric potential through the thickness of each piezoelectric layer. This is achieved by interpolating using nodal mid-plane electric potentials and one electric degree of freedom representing the potential difference between the top and bottom surfaces of the piezoelectric layer. Few case studies of composite general shells with piezoelectric sensors and actuators have been considered by modeling them with the above elements and the active vibration control performance has been studied using linear quadratic Gaussian (LQG) control. � 2008 IOP Publishing Ltd.

Pin-connected precast concrete structures are widely used in some European countries of moderate seismicity. However, this structural system is not earthquake resistant because it does not have enough lateral stiffness or lateral-load resistance. Lack of a rigid diaphragm at the roof level imposes severe forces to connections., It is difficult to strengthen such buildings with conventional strengthening techniques because buildings must be unoccupied before retrofitting, which building owners do not like. To overcome this difficulty, employment of external shear walls and a diaphragm roof level are proposed in this study., A typical pin-connected precast concrete frame and a strengthened structure with the proposed method were tested under-imposed, reversed, cyclic drift of constant rate. The experimental study showed that the proposed method increased lateral stiffness, lateral-load resistance, and seismic energy dissipation and provided a diaphragm effect for the structure.