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1
Bradley, Luke R. "Mechanical testing and modelling of carbon-carbon composites for aircraft disc brakes". Thesis, University of Bath, 2003. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426204.
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Rubin, Ariel. "Strenghtening of reinforced concrete bridge decks with carbon fiber composites". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19320.
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Fox, Bronwyn Louise. "The manufacture, characterization and aging of novel high temperature carbon fibre composites". View thesis entry in Australian Digital Theses Program, 2001. http://thesis.anu.edu.au/public/adt-ANU20011207.114246/index.html.
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Scudder, Lawrence Philip. "Characteristics and testing of carbon fibre reinforced polymer composites using laser generated ultrasound". Thesis, University of Warwick, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283488.
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Wanner, Svenja. "Systematic approach on conducting fatigue testing of unidirectional continuous carbon fibre composites". Thesis, KTH, Lättkonstruktioner, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-261694.
Testo completoAbstract (sommario):
High fuel saving potentials, increased load carrying capacities and therefore competitive advantages force the heavy goods vehicle industry to enhance the efforts towards comprehensive lightweight designs. Facing this challenge, the material evaluation in terms of simulations and physical testing of composite materials is required for the design against fatigue failure due to road introduced vibrations. Eliminating fatigue testing issues in order to gain acceptable and reproducible results, a future-oriented systematic approach on conducting constant amplitude tension-tension fatigue testing on a unidirectional composite material is presented. Following the material characterisation of the carbon/epoxy material in terms of tensile and shear properties as well as fibre volume fraction, several combinations of tab configurations and specimen geometries have been tested with regard to their suitability for fatigue testing. Finally, the unidirectional material was successfully tested under tension-tension fatigue and first elaborated test data were assessed. In conclusion, the usage of straight aluminium tabs completely clamped inside the grips and bonded to the straight-sided specimen with 3M DP420 adhesive, using ventilation during the test is the recommended test procedure.Lastbilsindustrin tvingas öka ansträngningarna för omfattande viktbesparingar med lättviktskonstruktioner då dessa har konkurrenskraftiga fördelar med potential att minska bränsleförbrukningen samt öka den lastbärande kapaciteten. Genom att ta sig an denna utmaning kommer materialkarakterisering, provning och simulering av kompositmaterial vara av stor betydelse för att kunna konstruera produkter utsatta för cykliska laster från väginducerade vibrationer. Vid utmattningsprovning är det viktigt att kunna generera acceptabla och reproducerbara resultat. I denna rapport presenteras hur man kan undvika och eliminera problem vid utmattningsprovning, samt ett systematiskt tillvägagångsätt vid genomförande av utmattningsprovning med konstant amplitud för belastningen drag-drag på ett kompositmaterial med enkelriktad fiberorientering. Ett kolfiber/epoximaterial är karakteriserat och flertal kombinationer av tab-konfiguration och provstavsgeometri har testats, med avseende på lämplighet för utmattningsprovning. Slutligen har kolfiber/epoximaterialet provats med framgång under cyklisk drag-drag belastning i fiberriktningen. Slutsatsen för utmattningsprovning är att använda sig av raka aluminium tabbar helt fastklämda inuti greppen. Tabbarna limmas fast på provstaven med 3M DP420 lim. Ventilation är också rekommenderat under provning för att undvika en ökning av temperatur i provstaven.
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Drivas, Thanos. "Manufacturing Three-dimensional Carbon-fibre Preforms for Aerospace Composites". Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31577.
Testo completoAbstract (sommario):
Carbon fibre reinforced polymer matrix composites (CF PMCs) are increasingly used in state-of-the-art aerospace applications. Aerospace manufacturers favour components made of CF PMCs over those made of traditional metallic alloys because of their light weight and corrosion resistance, which lead to significant improvements in fuel consump- tion, increased payload capability, and reduced maintenance and inspection costs. How- ever, manufacturing of CF PMC components is performed differently than traditional material in all stages – design, prototyping and production – and therefore, many com- mercial manufacturers have only recently begun producing components with CF PMCs.
The first half of this thesis was written as a contribution to the CRIAQ COMP-501 project, which focusses on investigating the cost-effective procurement of airframe com- ponents that are manufactured from final-thickness, net-shaped, and through-thickness reinforced CF preforms. Reinforcement preforms were assembled from commercial 2D woven fabric using stacks of various configurations of structural through-thickness CF stitch. The contribution herein provides the results obtained from investigations into the mechanical behaviour of the relevant reinforcements, when subjected to pre-infusion op- erations typical to RTM VARTM; mechanical behaviour in compaction, shear (draping) and bending (forming).
The second half of this thesis presents the major developments which were made to an alternative process for producing thick 3D preforms with great versatility, a process originally proposed as a candidate for supplying preforms to the COMP-501 project. This process interfaces a proprietary kinematic drape optimization (CAD) software with proprietary automated dry fibre placement assembly (CAM) machinery to produce vari- able or final-thickness reinforcements which are highly-drapable and can lay steered tow yarns.
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Bass, Roger Wesley. "Synthesis and Characterization of Self-Healing Poly (Carbonate Urethane) Carbon-Nanotube Composites". Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/2999.
Testo completoAbstract (sommario):
Synthesis of high molar mass polycarbonate polyurethanes using a novel polyol is described. The resulting elastomers demonstrate excellent mechanical properties as well as the capability to re-heal after rupture without the addition of additives or imbedded healing agents. The self-healing functionality is shown to greatly improve with the addition of up to 1% single and multi-walled carbon nanotubes. The interface of the carbon nanotubes and self-healing polymer are probed using Raman techniques and provide an insight into how the self-healing actions are improved with the addition of carbon nanotubes.
Synthesis of polycarbonate polyurethanes and carbon nanotube composites using a novel casting method is described and compared to the more traditional solution casting method. The dispersion of the carbon nanotubes is evaluated as well as the effect of effective dispersion on the composites through tensile testing, rheometry and hardness testing. Although complete agglomeration avoidance could not be achieved, significant size decrease was observed. Over 200% improvement in tensile strength is shown with conventional solution casting method which is further improved by the described novel solution casting method.
Contact angle measurements on our novel self-healing poly (carbonate urethane) and CNTs composites show that surface energies are drastically changed when CNTs are used. The most revealing finding is that f×svp increases in CNT composite materials from ~30% of the surface energy on average for the samples tested, to ~80%. We have shown that surface free energies increase most likely as a result of exposing hydrogen bonding sites typically found within the bulk in polyurethanes. Our polyurethane differs from traditional polyurethanes in that it has both novel soft segments made from a novel polycarbonate polyol discussed in chapter 2 and relatively soft ¡§hard¡¦ segments resulting from the use of H12MDI, all leading to increased ability to hydrogen bond within the material. The availability of the hydrogen bonding sites is demonstrated by FTIR absorbance bands for associated and unassociated hydrogen bonding sites, which do not seem to be accessible to a large until the PCPU¡¦s surface is disrupted. Once disrupted, the exposed hydrogen bonding sites are able to bond with other bonding sites of adjacent ruptured surfaces. This would explain why our material is non-blocking, e.g. won¡¦t stick to itself, until the surface is ruptured. It would also explain why any two ruptured surfaces of our material will reheal, even if they were not attached previously.
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Etheridge, George Alexander. "Investigation of progressive damage and failure in IM7 carbon fiber/5250-4 bismaleimide resin matrix composite laminates". Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/19669.
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Haberle, Jurgen. "Strength and failure mechanisms of unidirectional carbon fibre-reinforced plastics under axial compression". Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/11390.
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Thompson, Luke Francis. "Through-thickness compression testing and theory of carbon fibre composite materials". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/throughthickness-compression-testing-and-theory-of-carbon-fibre-composite-materials(02ad7cfa-b779-4e69-9361-3c5bb44c6114).html.
Testo completoAbstract (sommario):
This study investigates the through-thickness behaviour of carbon/epoxy laminates. A through-thickness compression test regime was conducted utilising three specimen designs, which are waisted, hollow cylindrical and cubic specimens. An assessment and comparison of each specimen is given regarding their advantages and disadvantages in characterising the through-thickness response of [+45/-45/90/0]s quasi-isotropic AS4/8552 carbon/epoxy laminates. A finite element (FE) study of the three specimens is presented which results in specimen geometries that provided a macroscopically uniform stress response throughout the gauge length whilst also minimising other features such as stress concentrations. Further to the final geometries being presented, the method of manufacture for the laminate and machining processes for each of the specimens is given. A mesoscopic FE study is presented relating to the free-edge effects induced by through-thickness loading in quasi-isotropic laminates. The results presented show that free-edge effects will be present in the test specimens and will have a larger overall impact on the hollow cylindrical specimen. The free-edge effects also increase the stress concentrations present in the corners of the waisted and cubic specimens. Characteristic stress strain curves are presented for each specimen with strain data taken from post yield strain gauges attached to the specimens. The extracted initial Young's modulus Ez and Poisson's ratios vzx and vzy show a small variation between specimens. The strength values for the three specimens vary greatly with the waisted specimen being the strongest and cylindrical specimen the weakest, indicating that the chosen specimen geometry dominates failure. The experimental data will be used for test case 12 in the Second World Wide Failure Exercise (WWFE-II). A study is presented to predict the effective elastic properties of Z-pinned laminates. The materials under consideration are UD and [0/90]s cross-ply AS4/3501-6 carbon/epoxy laminates. Estimates on the effective properties are provided by two FE approaches and two analytical bounding approaches; namely Voigt and Reuss bounds and Walpole's bounding theory. The two FE approaches are based on extreme assumptions about the in-plane fibre volume fraction in the presence of Z-pins and provide a tight range of values in which the real result should lie. Furthermore, whilst the bounding methods are simple and in the case of Young's moduli produce very wide bounds the selection of the suitable bound result can lead to a good estimate in comparison with the FE data. Typically the best bounding method result for each elastic property is within 10% of the FE predictions.
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Hull, Brandon Tristan. "Examination of Mechanical Stretching to Increase Alignment in Carbon Nanotube Composites". Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/52629.
Testo completoAbstract (sommario):
Individual carbon nanotubes have been theoretically and experimentally proven to be the strongest and stiffest materials discovered to date with tensile strengths ranging from 1-5 TPa and elastic modulus values as high as 150 GPa. In this work, the recent development of continuous sheets of CNTs, produced by Nanocomp Technologies Inc ., are investigated for their potential as reinforcement in polymer matrix composite (PMC) materials. The potential of these nanotube-based PMC materials have been reported by researchers at Florida State University (FSU). Through the use of mechanical stretching procedures to increase the alignment of the nanotubes within the CNT sheets, the tensile strength and Young's modulus of the composites in the FSU study averaged 3081 MPa and 350 GPa, respectively. These values are for composites fabricated from 40% stretched CNT sheets and are 48% and 107% improvements over composites fabricated from the pristine, unstretched CNT sheets. However, the test specimens used in the FSU study consisted of a single CNT ply and each coupon was individually stretched and cured for testing. Therefore, the process used to generate the coupons which exhibited these high mechanical properties would be difficult to scale to a usable size for aerospace structural components. In the current study, a scalable process has been developed in which 2-ply, 3" x 3" panels of CNT and resin composites are fabricated. An apparatus and methodology for mechanically stretching the CNT sheets used in these composite panels has also been developed. After initial testing was conducted with the CNT composites and the coupons exhibited significant elongation at failure, along with the absence of a linear elastic region, conventional test standards for material testing were deemed impractical. For this reason, new mechanical testing methodologies have been developed to determine the mechanical properties of specific strength and specific modulus of CNT-polymer composites.
In order to obtain the maximum benefits of a fiber in any matrix in terms of stiffness and strength, it is preferable to align the high strength and stiffness fibers in the direction of loading. Given that these CNT sheets essentially consist of billions of short, discontinuous CNTs of 2-3mmin length, the process of mechanical stretching is used in an attempt to align these tubes in the direction of the applied tensile load. Here we have explored methodologies for stretching, fabricating, and mechanical testing. Having identified a process which seems viable, an examination into the effect of the mechanical stretching to increase the alignment of the nanotubes within the CNT sheets, and thus to increase the material properties of the 2-ply composites constructed from them, is conducted. In order to correlate the enhancements in the mechanical properties with the increased alignment of the CNTs, polarized Raman spectroscopy techniques have been used. Lastly, Scanning Electron Microscopy (SEM) is used to examine the effect of stretching on the pristine CNT sheet, as well as examine the fracture surfaces of failed test coupons to better characterize the failure modes.
In this report, polarized Raman spectroscopy has been used to confirm the enhancedalignment of nanotubes within the CNT sheets through the used of a nematic order parameter. Unstretched sheets exhibit an order parameter of 0.07 and 0.09 for untreated and Acetone treated sheets, respectively. Upon stretching the untreated sheets to 45%, the order parameter increases to 0.1409 and, when stretched to 30%, Acetone treated sheets have an order parameter of 0.1518.
During the mechanical testing of 2-ply composites fabricated from stretched CNT sheets, the effect of this increased alignment is made apparent. Untreated CNT sheets are used to fabricate 2-ply composites after being stretched and are compared to baseline values of panels fabricated using sheets which are not stretched. In the panels fabricated with PEI resin and 43% stretched, untreated CNT sheets, a 137% increase in average specific strength and a 44% increase in average specific modulus over the baseline panel is observed. For panels fabricated with BMI and 33% stretched, untreated CNT sheets, a 169% increase in average specific strength and 105% increase in average specific modulus is observed when compared to the baseline panel. These increases are evidence for the potential of mechanical stretching to align the nanotubes within the CNT sheets and bolster the mechanical properties of resulting CNT-polymer composites.Master of Science
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Richardson, Sarah. "In-Situ Testing of a Carbon/Epoxy IsoTruss Reinforced Concrete Foundation Pile". Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1280.pdf.
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Lyons, Kevin Mark. "Tensile testing and stabilization/carbonization studies of polyacrylonitrile/carbon nanotube composite fibers". Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45915.
Testo completoAbstract (sommario):
This study focuses on the processing, structure and properties of polyacrylonitrile (PAN)/ carbon nanotube (CNT) composite carbon fibers. Small diameter PAN/CNT based carbon fibers have been processed using sheath-core and islands-in-a-sea (INS) fiber spinning technology. These methods resulted in carbon fibers with diameters of ~3.5 μm and ~1 μm (for sheath-core and INS respectively). Poly (methyl methacrylate) has been used as the sheath or the sea component, which has been removed prior to carbonization. These fibers have been stabilized and carbonized using a batch process. The effect of stabilization has been characterized by Fourier Transform Infrared Spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). A non-isothermal extent of cyclization (Mcyc) from the DSC kinetics study was developed in order to obtain an unbiased method for determining the optimal stabilization condition. The results of Mcyc were found to be in good agreement with the experimental FTIR and WAXD observations. The carbon fiber fracture surfaces have been examined using SEM. Various test parameters that affect the tensile properties of the precursor fiber (both PAN and PAN/CNT), as well as carbon fiber have been studied. In an attempt to validate single filament tests, fiber tow testing has also been done using standard test methods. Batch processed carbon fibers obtained via sheath-core geometry exhibited tensile strengths as high as 6.5 GPa, while fibers processed by islands-in-a-sea geometry exhibited strength values as high as 7.7 GPa.
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Poudel, Anish. "AN INTELLIGENT SYSTEMS APPROACH FOR DETECTING DEFECTS IN AIRCRAFT COMPOSITES BY USING AIR-COUPLED ULTRASONIC TESTING". OpenSIUC, 2011. https://opensiuc.lib.siu.edu/theses/594.
Testo completoAbstract (sommario):
Circular air-coupled ultrasonic testing (ACUT) setup for the inspection of commercial carbon-carbon composite aircraft brake disks was developed in Intelligent Measurement and Evaluation Laboratory (IMEL) at Southern Illinois University Carbondale (SIUC). The developed test setup utilizes Airstar single channel air-coupled equipment and has only manual A-scan and B-scan capability. The developed ACUT technique is unique compared to the commercial C-scan ultrasonic systems and is proficient, fast, economically feasible, and easy to implement method particularly for the inspection of carbon-carbon (C/C) composites aircraft brake disks. Prior to conducting air-coupled measurements, wobble analysis was carried out. This was important because significant wobbling in the test setup can lead to the interference of the reflected and the incident beam which would result to inaccurate ultrasonic measurements. The measured deviation due to wobbling, surface profile of the disk, design, and experimental error were relatively small. Therefore, these errors were neglected while performing ACUT measurements. For ACUT measurements, several through-transmitted amplitude signals were recorded within the C/C brake disks manually. The images were then reconstructed using Matlab based on the through-transmitted amplitude signals. Finally, a comparison was drawn between the reconstructed images and the C-scan images of the C/C brake disks obtained from the commercial Airstar C-scan ACUT system. Like commercial C-scan ACUT image results, reconstructed images were also able to detect all defects in the commercial C/C brake disks which served for the system verification and validation. In addition, defect, non-defect, and suspected areas within the C/C brake disks were quantified with air-coupled measurement. For this, light microscopy was conducted for every sample made from each C/C brake disks at lower magnification of 10X. It was concluded that it is very difficult to assess the crack or delamination situation based on a 2D micrograph of one depth. Also, it was concluded that an internal porosity and micro-cracks may not be only factors that can be related to defects. Finally, an intelligent systems approach, specifically, fuzzy logic and artificial neural network (ANN) methodologies were implemented for the automatic defect detection in commercial C/C aircraft brake disks by using air-coupled ultrasonic results. For this, a multi-layer perceptron (MLP) with two hidden layers and a scaled conjugate gradient back-propagation (BP) learning algorithm was used for the ANN training. The network training process was performed in an off-line mode using the ANN toolbox in Matlab. The network training was repeated until a steady state was reached, where there was no further change in the synaptic weights. The ANN provided plausible results in detecting the defect areas for different C/C brake disks. It was also demonstrated that the system was able to learn the rules without knowing any algorithm for automatic defect detection.
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Sheats, Matthew Reed. "Rehabilitation of reinforced concrete pier caps using carbon fiber reinforced composites". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19490.
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Khwaja, Moinuddin. "Carbon nanotube sheet for structural health monitoring and thermal conductivity in laminated composites". University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1562842660883351.
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Lee, Tuan Kuan 1976. "Shear strength of reinforced concrete T-beams strengthened using carbon fibre reinforced polymer (CFRP) laminates". Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/6647.
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Aschy, Ameni. "Imagerie ultrasonore de strucutres composites hétérogènes". Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1008.
Testo completoAbstract (sommario):
Ce travail de thèse a pour objectif de développer une méthodologie visant à imager les défauts dans les structures composites moyennant les ultrasons multiéléments. Plus précisément, la motivation essentielle réside dans la difficulté d’application des méthodes ultrasonores conventionnelles pour le contrôle de structures composites épaisses et hétérogènes. En effet, l’application de ces méthodes est d’autant plus difficile en présence d’anisotropie structurelle où les paramètres vitesse et atténuation changent de façon importante en fonction du trajet ultrasonore considéré. Cela pourrait même se compliquer en présence de dispersion fréquentielle des propriétés viscoélastiques du matériau composite. Les méthodes d’imagerie étudiées sont appliquées dans le cas de structures composites hétérogènes de forte épaisseur. Dans un premier temps, les paramètres vitesse et atténuation des ondes élastiques de volume se propageant dans le composite sous différentes incidences ont été déterminées.Ce travail a également permis de remonter aux caractéristiques viscoélastiques par méthode inverse.Les différents paramètres trouvés par méthodes directe et inverse sont ensuite intégrés au modèle direct de calcul de trajets ultrasonores pour corriger les effets d’anisotropie dans l’imagerie Total Focusing Method (TFM) et Plane Wave Imaging (PWI) et étudier ainsi les possibilités d’amélioration de la détection et de la caractérisation des défauts pouvant exister au sein des structures composites étudiées. Enfin, il est important de souligner que ce même travail discute de la nécessité de connaître le tenseur d’élasticité pour une prise en compte optimale de l’anisotropie. À cet effet, une comparaison avec un modèle simplifié mettant en jeu les vitesses de groupe est proposéeThis work aims to develop a methodology to image defects in composite structures by using Phased Array ultrasonic techniques. More specifically, the essential motivation lies in the difficulty of applying conventional ultrasonic methods for the control of thick and heterogeneous composite structures. Indeed, the application of these methods is more difficult in the presence of structural anisotropy where the velocity and the attenuation parameters change significantly depending on the ultrasound considered path. This could be more complicated in the presence of the viscoelastic properties frequency dispersion of the composite material. The studied imaging methods are applied in the case of heterogeneous and thick composite structures. First, the velocity and attenuation parameters of the elastic volume waves propagating in the composite under different incidences is determined. This work also allowed to go back to the viscoelastic characteristics by inverse method. The various parameters found by direct and inverse methods are then integrated into the direct ultrasound path calculation model to correct the anisotropy effects in the Total Focusing Method (TFM) and Plane Wave Imaging (PWI) imagery and thus to study the possibilities of improvement of the detection and characterization of defects that may exist within the studied composite structures. Finally, it is important to emphasize that this same work discusses the need of the tensor of elasticity for an optimal characterization of the anisotropy. For this purpose, a comparison with a simplified model involving group velocity is proposed
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Livingston-Peters, Ann E. "AN INVESTIGATION INTO THE PROPERTIES AND FABRICATION METHODS OF THERMOPLASTIC COMPOSITES". DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1224.
Testo completoAbstract (sommario):
As applications for thermoplastic composites increase, the understanding of their properties become more important. Fabrication methods for thermoplastic composites continually improve to match designs specifications. These advanced thermoplastics have begun to show an improvement in mechanical properties over those found in thermoset composites commonly used in industry. Polyaryletherketones (PEK) have high service temperatures, good mechanical properties, and improved processing capabilities compared to thermoplastics used in the past making them important to the aerospace industry. The wide range of types of PEK make them suitable for a variety of applications, but selection of specific chemistries, processing parameters, and composite stack-ups determine the mechanical properties produced. Differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) were used to determine crystallinity and chemical properties of several polyaryletherketones. Tensile, compressive, and Mode I interlaminar fracture toughness tests were conducted to analyze mechanical properties of these advanced thermoplastics. Several fabrication processes were also tested to determine optimal consolidation and aesthetic appearance of structural members. All testing was conducted at The Boeing Company in Seattle, Washington. Because all testing and conclusions are proprietary a general synopsis of the experience will be presented.
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Warraich, Daud Sana Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Ultrasonic stochastic localization of hidden discontinuities in composites using multimodal probability beliefs". Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2009. http://handle.unsw.edu.au/1959.4/43719.
Testo completoAbstract (sommario):
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.
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Warnock, Corinne Marie. "Process Development for Compression Molding of Hybrid Continuous and Chopped Carbon Fiber Prepreg for Production of Functionally Graded Composite Structures". DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1518.
Testo completoAbstract (sommario):
Composite materials offer a high strength-to-weight ratio and directional load bearing capabilities. Compression molding of composite materials yields a superior surface finish and good dimensional stability between component lots with faster processing compared to traditional manufacturing methods. This experimental compression molding capability was developed for the ME composites lab using unidirectional carbon fiber prepreg composites. A direct comparison was drawn between autoclave and compression molding methods to validate compression molding as an alternative manufacturing method in that lab. A method of manufacturing chopped fiber from existing unidirectional prepreg materials was developed and evaluated using destructive testing methods. The results from testing both the continuous and chopped fiber were incorporated into the design of a functionally graded hybrid continuous and chopped carbon fiber component, the manufacture of which resulted in zero waste prepreg material.
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Lavoie, J. André. "Scaling Effects on Damage Development, Strength, and Stress-Rupture Life on Laminated Composites in Tension". Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30510.
Testo completoAbstract (sommario):
The damage development and strength of ply-level scaled carbon/epoxy composite laminates having stacking sequence of [+Tn/-Tn/902n]s where constraint ply angle, T, was 0, 15, 30, 45, 60, and 75 degrees, and size was scaled as n=1,2,3, and 4, is reported in Part I. X-radiography was used to monitor damage developments. First-ply failure stress, and tensile strength were recorded. First-ply failure of the midplane 90 deg. plies depended on the stiffness of constraint plies, and size. All 24 cases were predicted using Zhang's shear-lag model and data generated from cross-ply tests. Laminate strength was controlled by the initiation of a triangular-shaped local delamination of the surface angle plies. This delamination was predicted using O'Brien's strain energy release rate model for delamination of surface angle plies. For each ply angle, the smallest laminate was used to predict delamination (and strength) of the other sizes.
The in-situ tensile strength of the 0 deg. plies within different cross-ply, and quasi-isotropic laminates of varying size and stacking sequence is reported in Part II. No size effect was observed in the strength of 0 deg. plies for those lay-ups having failure confined to the gauge section. Laminates exhibiting a size-strength relationship, had grip region failures for the larger sizes. A statistically significant set of 3-point bend tests of unidirectional beams were used to provide parameters for a Weibull model, to re-examine relationship between ultimate strength of 0 deg. plies and specimen volume. The maximum stress in the 0 deg. plies in bending, and the tensile strength of the 0 deg. plies (from valid tests only) was the same. Weibull theory predicted loss of strength which was not observed in the experiments. An effort to model the durability and life of quasi-isotropic E-glass/913 epoxy composite laminates under steady load and in an acidic environment is reported in Part III. Stress-rupture tests of unidirectional coupons immersed in a weak hydrochloric acid solution was conducted to determine their stress-life response. Creep tests were conducted on unidirectional coupons parallel and transverse to the fibers, and on ±45°. layups to characterize the lamina stress- and time-dependent compliances. These data were used in a composite stress-rupture life model, based on the critical element modeling philosophy of Reifsnider, to predict the life of two ply-level thickness-scaled quasi-isotropic laminates.Ph. D.
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Welter, John T. "Oblique angle pulse-echo ultrasound characterization of barely visible impact damage in polymer matrix composites". University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1575295152635788.
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Renner, Axel, Uwe Marschner e Wolf-Joachim Fischer. "A new imaging approach for in situ and ex situ inspections of conductive fiber–reinforced composites by magnetic induction tomography". Sage, 2014. https://tud.qucosa.de/id/qucosa%3A35619.
Testo completoAbstract (sommario):
Fiber-reinforced plastics for industrial applications face constantly increasing demands regarding efficiency, reliability, and economy. Furthermore, it was shown that fiber-reinforced plastics with tailored reinforcements are superior to metallic or monolithic materials. However, a trustworthy description of the load-specific failure behavior and damage evolution of composite structures can hardly be given, because these processes are very complex and are still not entirely understood. Among other things, several research groups have shown that material damages like fiber fracture, delamination, matrix cracking, or flaws can be discovered by analyzing the electrical properties of conductive composites, for example, carbon fiber–reinforced plastics. Furthermore, it was shown that this method could be used for structural health monitoring or nondestructive evaluation. Within this study, magnetic induction tomography, which is a new imaging approach, is introduced in the topic of nondestructive evaluation of carbon fiber–reinforced plastics. This non-contacting imaging method gains the inner spatial distribution of conductivity of a specimen and depicts material inhomogeneity, like damages, not only in two-dimensional images but also in three-dimensional images. Numerical and experimental investigations are presented, which give a first impression of the performance of this technique. It is demonstrated that magnetic induction tomography is a promising approach for nondestructive evaluation. Potentially, it can be used for fabrication quality control of conductive fiber–reinforced plastics and as a structural health monitoring system using an integrated or superficially applied magnetic induction tomography setup.
25
Yang, Kao Z. "MENs Doped Adhesive and Influence on Fracture Toughness". FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2487.
Testo completoAbstract (sommario):
Composites are in high demand; however, fasteners are often required for joining process and can reduce their advantages. One solution is adhesive bonding, but uncertainty exists regarding long term durability and the ability to interrogate bonds noninvasively. One potential solution to qualify bond integrity over its service life is to dope an adhesive with magneto-electric nanoparticles (MENs). MENs can yield output magnetic signatures that are influenced by bond quality and damage state. In this study, adhesives have been doped with MENs prior to bonding at 1% volume concentration. For optimum implementation, this health monitoring system should be evaluated for effects of the MENs on the mechanical properties. Lap-shear testing was conducted to assess changes in the bond strength from addition of the nanoparticles. End-notched flexure (ENF) tests were also conducted for fracture mechanism evaluation. Results showed an increase of 12% in shear strength as a function of MENs loading concentration. In addition, a feasibility study of output magnetic signature as a function of elevated temperature and humidity were evaluated for MENs doped and un-doped adhesives. Results gave an order of magnitude change in magnetic signal as a function of exposure time.
26
Zulu, Andrew Wisdom. "Thick Composite Properties and Testing Methods". Thesis, KTH, Lättkonstruktioner, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-243885.
Testo completoAbstract (sommario):
In most application to date reinforced carbon fiber composites have been used in relatively smaller thickness, less than 10mm thick and essentially for carrying in-plane loads. As a result, design and testing procedures were developed which reflected the need to understand the in-plane response of the material. recently, engineers and designers have begun to use reinforced carbon fiber composites in thicker sections, where an understanding of the through-thickness response is of para-mount importance in designing reliable structures, particularly where the through-thickness strength has a controlling influence on the overall structural strength of the component. In this thesis tests will be done on carbon fiber non-crimp fabric (NCF) which will be loaded in compression and shear and elastic moduli and strength will be evaluated. In characterizing the through-thickness mechanical properties of a composite, the objective is to produce a state of stress in the test specimen which is uniform and will repeatedly measure the true properties with accuracy. In this study, specimens were machined from two blocks of thick (~20 mm) laminates of glass/epoxy and NCF carbon fiber infused with vinylester and tested in compression, and shear.
27
Gratton, Michel. "Comportement d'un composite 3D carb/carb : méso-modélisation pour la prévision de la réponse sous choc". Cachan, Ecole normale supérieure, 1998. http://www.theses.fr/1998DENS0004.
Testo completoAbstract (sommario):
Ce travail, mené en collaboration avec l'aérospatiale Les Mureaux et le centre d'études de Gramat, concerne la modélisation de matériaux composites tridirectionnels carbone/carbone sous sollicitations fortement dynamiques. Pour ce type de sollicitations, la notion de matériau homogène équivalent est inadaptée. L'objet de ce travail est de tester l'aptitude d'une modélisation a l'échelle des constituants mésoscopique (torons de fibres et blocs de matrice), a reproduire la réponse du matériau sous choc. Le matériau est tout d'abord identifie a l'échelle de ses méso-constituants. A cette fin, divers essais quasi-statiques sont réalisés et une modélisation sans effet de vitesse du comportement des constituants est alors proposée. Elle prend en compte des mécanismes d'endommagement, de compaction et d'anélasticité. Une technique de changement d'échelle, basée sur les développements asymptotiques adaptée aux matériaux périodiques, est utilisée. Associée à une analyse de sensibilité et à une hiérarchisation des mécanismes non-linéaires, elle permet de déterminer les paramètres locaux du modèle a partir des réponses globales du matériau. Afin de tester le méso-modèle ainsi identifie, une partie des informations est exploitée dans un logiciel de dynamique simplifie. Ce dernier permet de simuler les essais d'impact plaque/plaque suivant une direction de torons. Des essais de compression dynamique et des essais d'écaillage (réalisés par le ceg) sont ainsi bien reproduits. Les simulations montrent des modes distincts de propagation d'ondes dans les torons et dans la matrice ainsi que des phénomènes de transferts de charges. Des essais i pulsionnels, mal reproduits par simulation, ouvrent de nombreuses perspectives, notamment sur la nécessite de compléter la modélisation du comportement des méso-constituants par une sensibilité a la vitesse de déformation.
28
Bale, Jefri Semuel. "The damage observation of composite using non destructive testing (NDT) method". Thesis, Paris 10, 2014. http://www.theses.fr/2015PA100067/document.
Testo completoAbstract (sommario):
L'objectif de ce travail de thèse est d'étudier le comportement de l'endommagement des matériaux composites sous chargement statique et fatigue par contrôle non destructif (C.N.D) thermographie et soutenu par émission acoustique et la tomographie (CT scan). Pour cela, ce unidirectionnels composite à fibres de verre (GFRP) et discontinue composite à fibres de carbone (DCFC) ont été utilisés comme les éprouvettes qui ont fourni par PSA peugeot citröen, France. Une série d'essais mécaniques a été réalisée pour déterminer le comportement de l'endommagement sous chargement statique et fatigue. Pendant tout des essais mécanique, la thermographie a été utilisé pour l'observation en temps réel pour suivre l'évolution des températures sur la surface de l'éprouvette et supporté par émission acoustique dans certaines conditions. Cette étude a utilisé une forme rectangulaire et se compose d'éprouvettes trouées et non trouées au centre de l'éprouvette. La vitesse de déplacement constante est appliquée pour observer l'effet sur le comportement de l'endommagement sous chargement de traction statique. Sous les essais de fatigue, le paramètre constant de la fréquence et de l'amplitude de stress a été étudiée pour chaque niveau de charge pour avoir les propriétés de fatigue et l'évolution de l'endommagement de l'éprouvette. La tomographie a été utilisée pour confirmer l'apparition de l'endommagement et l'etat du matériau après l'essai de fatigue. L'analyse des résultats de l'expérimentation et de l'observation NDT montré le bon accord entre les résultats mechnical et NDT thermographie avec prise en charge par l'observation de l'émission acoustique en détecter l'apparition et la propagation de l'endommagement de GFRP PRV et DCFC sous chargement de statique en traction. Les essais en fatigue montrent que la dissipation thermique est liée à l'évolution de l'endommagement et également thermographie et peut être utilisé avec succès pour déterminer la limite d'endurance (HCFS) et la courbe de Wöhler du matériau composite. Les résultats par CT scan ont mesurée avec succès les endommagements et l'état du matériau après essai de fatigue du matériau compositeThe aim of this study is to investigate the damage behaviour of composite material in static and fatigue condition with non destructive testing (NDT) thermography method and supported by acoustic emission and also computed tomography (CT) scan. Thermography and acoustic emission are used in real-time monitoring techniques during the test. On the other hand, NDT observation of tomography is used for a post-failure analysis. In order to achive this, continuous glass fiber composite (GFRP) and discontinuous carbon fiber composite (DCFC) have been used as the test specimens which supplied by PSA Company, France. A series of mechanical testing was carried out to determine the damage behaviour under static and fatigue loading. During all the mechanical testing, thermography was used in real-time observation to follow the temperature change on specimen surface and supported by acoustic emission in certain condition. This study used rectangular shape and consist of specimen with and without circular notches (hole) at the center. The constant displacement rate is applied to observe the effect on damage behaviour under tensile static loading. Under fatigue testing, the constant parameter of frequency and amplitude of stress was explored for each load level to have the fatigue properties and damage evolution of specimen. The tomography was used to confirm the appearance of damage and material condition after fatigue testing. The analysis from the experiment results and NDT observation shown the good agreement between mechnical results and NDT thermography with supported by acoustic emission observation in detect the appearance and propagation of damage for GFRP and DCFC under static loading. Fatigue testing shows that thermal dissipation is related to the damage evolution and also thermography and can be successfully used to determine high cycle fatigue strength (HCFS) and S-N curve of fiber composite material. From post failure analysis, CT scan analysis successfully measured and evaluated damage and material condition after fatigue test for fiber composite material. v
29
Parris, Donald R. "Electrical characterization of carbon black filled rubber". Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/91055.
Testo completoAbstract (sommario):
DC resistance and AC conductance and capacitance have been measured under various conditions in an effort to electrically characterize and make electrical-mechanical correlations for 15 carbon black filled rubber samples.
Resistance, conductance and capacitance have been monitored as functions of uniaxial compressive stress, time, temperature, and mechanical and thermal history. Capacitance and conductance have also been monitored as functions of frequency under various degrees of compressive loading and before and after specific heat treatments.
A direct relationship has been found between sample • conductance and capacitance under any thermal and/or mechanical condition. This is in agreement with previous theories of conduction network formation and percolation. Various conduction mechanisms have been enumerated and an equivalent circuit of a network of lumped R-C "microelements'' has been qualitatively described. Stress, relaxation, frequency, and temperature dependences of the macroscopic parameters measured ( conductivity and capacitance) are discussed in terms of this model.M.S.
30
Walls, Joshua C. "High Temperature Compression Testing of an Advanced Carbon-Carbon Composite in an Oxidizing Atmosphere". Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/WallsJC2002.pdf.
Testo completo
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Leão, Rodrigo Junqueira. "Simulação da propagação de ondas ultrassônicas longitudinais em materiais estruturais aeroespaciais". [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263960.
Testo completoAbstract (sommario):
Orientador: Auteliano Antunes dos Santos JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Materiais compósitos são cada vez mais utilizados na indústria aeroespacial, por apresentarem baixa relação entre massa específica e resistência mecânica. Para a realização de ensaios não destrutivos utilizando o ultrassom, faz-se necessário conhecer a velocidade com que o som se propaga através desses materiais. Nem sempre é possível desenvolver protótipos reais durante o desenvolvimento de um projeto, por limitações construtivas e de custo; modelos virtuais são, pois, necessários. O objetivo deste trabalho é desenvolver modelos virtuais para avaliar a propagação de ondas em compósitos e compará-los com resultados experimentais. Uma liga de alumínio é usada inicialmente, de forma a calibrar o modelo e configurar alguns parâmetros de simulação. O material composto analisado é um laminado unidirecional, fabricado a partir de 97 camadas de material pré-impregnado (AS4/8552) da Hexcel¿. Utiliza-se o método dos elementos finitos para simular a geração, propagação e recepção de ondas ultrassônicas no modelo. O foco do estudo são ondas longitudinais de volume, embora a geração de ondas longitudinais criticamente refratadas (Lcr) também seja demonstrada. A razão é que o estudo é parte de uma pesquisa sobre o desenvolvimento de técnicas ultrassônicas para a medição de tensões em compósitos, utilizando Acustoelasticidade. A fim de permitir a medição da velocidade da onda ultrassônica em diferentes orientações, foi fabricado um corpo de prova em formato de prisma de base poligonal de 24 lados. O modelo numérico desenvolvido considera o caso ideal, onde as lâminas são perfeitamente coladas umas nas outras e não há problemas como delaminação ou vazios. Um modelo simplificado de cada lâmina foi admitido, de modo a utilizar uma malha menos refinada nas simulações e reduzir o gasto computacional. A fração volumétrica de reforço e matriz foi mantida. Um pulso de 1 MHz foi inserido no modelo e as discretizações no tempo e no espaço foram escolhidas de forma coerente. Simulações para o caso de 0º e 90º foram feitas e um modelo para os outros ângulos de orientação foi proposto. Os resultados mostram-se satisfatórios e indicam que, no futuro, o modelo simplificado adotado poderá ser estendido, levando em conta não conformidades e uma distribuição mais heterogênea das fibras, permitindo o desenvolvimento de ferramentas de inspeção aperfeiçoadas
Abstract: The use of composite materials in the aerospace industry is increasing due to its low ratio between density and mechanical strength. To perform non-destructive testing using ultrasound, it is necessary to know the sound velocity in these materials. It is not always possible to manufacture physical prototypes during the development of a project because of time, construction limitation and cost; virtual models are therefore needed. The objective of this work is to develop virtual models to evaluate the wave propagation in composites and compare them with experimental results. Initially, an aluminum alloy is used in order to calibrate the model and configure some simulation parameters. The composite material analyzed is a unidirectional laminate, made from 97 layers of prepreg material (AS4/8552) from Hexcel¿. We use the finite element method to simulate the generation, propagation and reception of ultrasonic waves in the model. The focus of this study is the generation of longitudinal bulk waves, although the generation of Critically Refracted Longitudinal (Lcr) waves is also demonstrated. The reason is that the study is part of an ongoing research project on the development of ultrasonic techniques for measuring residual stress in composites, using acoustoelasticity. To enable the measurement of the ultrasonic wave velocity in different orientations, we manufactured a specimen in a prismatic shape (24-sided polygonal base). The numerical model consists of the ideal case, where the different materials are completely attached to each other and there are no problems such as delamination or voids. A simplified model of each layer was admitted, to use a less refined mesh in the simulations and reduce the computational cost. The volume fraction of reinforcement and matrix was maintained. A pulse of 1 MHz was inserted into the model and the discretization both in time and space was chosen consistently. Simulations for the case of 0° and 90° were made and a model for the other orientations was proposed. The results prove to be satisfactory and indicate that in the future, the simplified model adopted could be extended, taking into account nonconformities and a more heterogeneous distribution of the fibers, allowing the development of improved inspection tools
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Kuhn, Eric. "Contrôle non destructif d'un matériau excité par une onde acoustique ou thermique, observation par thermographie". Thesis, Paris 10, 2013. http://www.theses.fr/2013PA100177/document.
Testo completoAbstract (sommario):
Afin de pouvoir détecter un défaut dans un composite, plusieurs méthodes de contrôle non destructif ont été développées. Le but de ce travail est de localiser un délaminage dans un stratifié carbone / époxyde en utilisant deux méthodes : la thermosonique et la thermographie. La première méthode consiste en une excitation par ultrasons et une détection par caméra IR. Pour la seconde technique, le matériau est irradié par une onde thermique et la détection est aussi réalisée par une caméra IR. Afin de comparer les résultats obtenus, des tests par immersion ultrasons C-scan ont été réalisés sur les échantillons. Cette méthode permet d'obtenir une cartographie du délaminage présent dans le stratifié. Un algorithme de comparaison entre la détection du délaminage faite par les ultrasons C-scan et les deux méthodes a permis de révéler les différences de forme du défaut détecté. Différents traitements d'images ont été appliqués aux images IR obtenues : des analyses temporelles et des analyses spatiales/temporelles. L'étude de l'évolution instantanée ainsi que l'évolution globale de la température se sont révélées prometteuses pour la thermosonique. L'image la plus décorrélée obtenus par l'analyse en composante principales donne un résultat tout aussi satisfaisant pour cette méthode. Pour la méthode sans contact, la thermographie, l'étude de la phase a permis de révéler la forme du délaminage avec la même précision que la thermosonique.Une comparaison de ces deux méthodes a été réalisée afin de mettre en évidence leurs avantages et leurs inconvénientsTo detect a defect in a composite, several methods of non destructive testing have been developped. The aim of this work is to find a delamination in polymer matrix laminates thanks to two methods : thermosonics and thermography. The first method consists of an ultrasonic excitation and a detection by an IR camera. For the second technique, the plate is irradiated with a thermal wave and the detection is also performed by an IR camera. To compare the results, ultrasonic immersion tests were performed on the samples. This method provides a map of the delamination in the laminate. An algorithm for comparing the detection of delamination made by the ultrasonic C-scan and both methods revealed differences in the shape of the detected defect. Several image processing have been applied to the IR images recorded : temporal analysis and spatial / temporal analysis. The study of the instant evolution and the global evolution of the temperature are promissing for thermosonics. The most uncorrelated image obtained by principal component analysis gives is satisfactory for this method. For thermography, the non contact method, the phase study revealed the shape of delamination with the same precision as thermosonics.A comparison between the two methods was realised to highlight their advantages and their drawbacks
33
Clarke, Andrew Bryson. "Mechanical properties and process conversion of a novel form of unidirectional carbon fibre/epoxy rod". Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267007.
Testo completo
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Pierce, Matthew Ryan. "Microvascular Heat Transfer Analysis in Carbon Fiber Composite Materials". University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1280944914.
Testo completo
35
Nicolas, Matthew James. "Structural analysis and testing of a carbon-composite wing using fiber Bragg gratings". Thesis, Mississippi State University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1536133.
Testo completoAbstract (sommario):
The objective of this study was to determine the deflected wing shape and the out-of-plane loads of a large-scale carbon-composite wing of an ultralight aerial vehicle using Fiber Bragg Grating (FBG) technology. The composite wing was instrumented with an optical fiber on its top and bottom surfaces positioned over the main spar, resulting in approximately 780 strain sensors bonded to the wings. The strain data from the FBGs was compared to that obtained from four conventional strain gages, and was used to obtain the out-of-plane loads as well as the wing shape at various load levels using NASA-developed real-time load and displacement algorithms. The composite wing measured 5.5 meters and was fabricated from laminated carbon uniaxial and biaxial prepreg fabric with varying laminate ply patterns and wall thickness dimensions. A three-tier whiffletree system was used to load the wing in a manner consistent with an in-flight loading condition.
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FARINA, LUIS C. "Caracterizacao viscoelastica por meio de ensaios de fluencia e ruptura por fluencia de compositos polimericos de matriz de resina epoxidica e fibra de carbono". reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9391.
Testo completoAbstract (sommario):
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Pearce, Garth Morgan Kendall Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "High strain-rate behaviour of bolted joints in carbon fibre composite structures". Awarded by:University of New South Wales. Mechanical & Manufacturing Engineering, 2009. http://handle.unsw.edu.au/1959.4/44593.
Testo completoAbstract (sommario):
An investigation is presented into the behaviour of carbon fibre composite joints subjected to dynamic loading rates in the range of 0.1 m/s to 10 m/s. The research is focused on the response of single fastener joints and more complex structural arrangements involving multiple fasteners and complex loads. Fasteners play a crucial role in the joining of aerospace components due to their ease of installation and inspection and their resistance to creep and environmental degradation. A consequence of the operating environment of aircraft is that many critical load cases involve impact and crash. These loading events are characterised by high loading rates, high kinetic energy and possibly loads well above the static design case. The properties of composite materials change with loading rate, so it is likely that the behaviour of bolted composite joints may also vary significantly. Dynamic behaviour of bolted joints is an area of research that has been given little attention to date. The few available papers on the topic are limited to the investigation of ideal bearing loads and include some contradictory results. The research developed a detailed understanding of the behaviour of bolted joints in composite structures through a combined numerical and experimental investigation. A set of quasi-static and dynamic single fastener joint tests was conducted to develop an understanding of the complex failure mechanisms present in bolted composite joints. Simple structural tests were developed to investigate the interaction of multiple bolts in a joint. High speed camera footage, full-field strain measurement and CT scanning techniques were all used to develop an understanding of the changes in the failure process with increased loading rate. Finite element analyses used implicit and explicit dynamic algorithms to model the tests. The finite element analysis contributed to the understanding of the experimental results as well as providing a predictive tool to minimise the need for further testing. A method of incorporating detailed information about bolt failure into large scale structural models was investigated and developed. The original contributions of this thesis involve novel dynamic joint testing including dynamic pull-through and structural tests. CT Scanning was utilised in a novel way to investigate the complex failure modes within a bolted joint. Novel finite element techniques were developed for modelling bolted joints at both a detailed level and a simplified level for structural analyses. These contributions significantly improve the current understanding of bolted joint failure, both quasi-statically and dynamically, and will allow for more efficient design of bolted composite structures for crash and impact loads.
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LEBRAO, GUILHERME W. "Viabilidade de fabricação de tubo para prótese de membro inferior em compósito híbrido epoxi carbono-vidro". reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11498.
Testo completoAbstract (sommario):
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Wong, Sidney. "Carbon Nanotube (CNT) Coated E-Glass Fibre Sensor for Structural Health Monitoring of Composite Materials". DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2108.
Testo completoAbstract (sommario):
Composite materials are extensively used as an advanced engineering material, particularly in aerospace, automotive, and buildings industries due to its superior properties such as high strength to weight ratios and resistance to corrosion. As composite materials are rapidly replacing traditional materials in aircraft manufacturing, improved methods of identifying damage and critical failure is in development. One of the most commonly used procedures utilizes a health monitoring system that relies on transducers to monitor transmitted waves generated by ultrasonics. By replacing this method with a nanotechnology-based one, it is possible to efficiently detect damage without the time-extensive process of scanning the structure. This research investigated the development of a nanomaterial-based sensor for health monitoring of composite structures. To develop the sensor, carbon nanotube/epoxy mixture (2%wt CNT) was coated on a strand of E-glass fibre to be adhered onto a fiberglass composite specimen. The selection of E-glass fibre and fibreglass plate was largely due to its electrical insulating properties to demonstrate that the carbon nanotube is driving the sensing capabilities through its highly conductive nature. In addition, by adhering the coated E-glass fiber to a fibreglass coupon, the homogeneity and material properties were approximately maintained. Tensile testing of the specimen conducted through a Lloyd LD50 tensile testing machine provided data on the actual strain which was correlated with the experimental differential resistances measured by a multimeter, both at the same specified tensile loading conditions. With two sets of data, the experimental resistance data was calibrated with the actual strain data collected. Ultimately, the experimental sensors created a sample of gauge factors which represents 91.24% probability of replicating the observed range of gauge factors by using the same manufacturing procedures, providing a valid alternative and consistent method to detecting composite damage.
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Kelly, Gordon. "Joining of Carbon Fibre Reinforced Plastics for Automotive Applications". Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3819.
Testo completoAbstract (sommario):
The introduction of carbon-fibre reinforced plastics in loadbearing automotive structures provides a great potential toreduce vehicle weight and fuel consumption. To enable themanufacture and assembly of composite structural parts,reliable and cost-effective joining technologies must bedeveloped. This thesis addresses several aspects of joining andload introduction in carbon-fibre reinforced plastics based onnon-crimp fabric reinforcement.
The bearing strength of carbon fibre/epoxy laminates wasinvestigated considering the effects of bolt-hole clearance.The laminate failure modes and ultimate bearing strength werefound to be significantly dependent upon the laminate stackingsequence, geometry and lateral clamping load. Significantreduction in bearing strength at 4% hole deformation was foundfor both pin-loaded and clamped laminates. The ultimatestrength of the joints was found to be independent of theinitial bolt-hole clearance.
The behaviour of hybrid (bolted/bonded) joints wasinvestigated both numerically and experimentally. Athree-dimensional non-linear finite element model was developedto predict the load transfer distribution in the joints. Theeffect of the joint geometry and adhesive material propertieson the load transfer was determined through a parameter study.An experimental investigation was undertaken to determine thestrength, failure mechanisms and fatigue life of hybrid joints.The joints were shown to have greater strength, stiffness andfatigue life in comparison to adhesive bonded joints. However,the benefits were only observed in joint designs which allowedfor load sharing between the adhesive and the bolt.
The effect of the environment on the durability of bondedand hybrid joints was investigated. The strength and fatiguelife of the joints was found to decrease significantly withincreased ageing time. Hybrid joints demonstrated increasedfatigue life in comparison to adhesive bonded joints afterageing in a cyclic freeze/thaw environment.
The strength and failure mechanisms of composite laminatessubject to localised transverse loading were investigatedconsidering the effect of the specimen size, stacking sequenceand material system. Damage was found to initiate in thelaminates at low load levels, typically 20-30% of the ultimatefailure load. The dominant initial failure mode wasintralaminar shear failure, which occurred in sub-surfaceplies. Two different macromechanical failure modes wereidentified, fastener pull-through failure and global collapseof the laminate. The damage patterns and ultimate failure modewere found to depend upon the laminate stacking sequence andresin system. Finite element analysis was used to analyse thestress distribution within the laminates and predict first-plyfailure.
Keywords:Composite, laminate, bearing strength,joining, load introduction, hybrid joint, finite elementanalysis, mechanical testing.
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Audette, Scott. "Mechanical Properties of Aerospace Composite Parts Made from Stitched Multilayer 3D Carbon Fibre Preforms". Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31691.
Testo completoAbstract (sommario):
Producing composite parts using low-cost processes such as resin transfer moulding
(RTM) has received much interest in the aerospace industry. RTM manufactured components
require near net shape preforms which closely fit mould cavities. To reduce labour
costs associated with composite production, automated preforming processes must be
utilized. However, obtaining reproducible high quality preforms is required for manufacturing
consistent high quality parts. Stitched multilayer 3D non crimp fabric preforms
are well suited for automation and an investigation into quality and performance of
components manufactured from these preforms is required.
This thesis provides an initial evaluation of quality and mechanical properties of components
made from stitched multilayer 3D non crimp fabric preforms using RTM. Similar
sized flat plates of varying fibre volume fractions were manufactured to evaluate flexural
modulus and strength, short beam shear strength and drop weight impact resistance of
the material. Also, integral reinforced panels (IRPs) featuring a reinforcing section joined
to a flat plate of varying laminating sequences were manufactured to evaluate debonding
strength between sections. Optical microscopy was performed on component samples to
determine quality based on void content and was found to be within acceptable limits
for production composites. Flexural moduli were found to be comparable with theoretical
expected values, however flexural strength was limited by the presence of transverse
stitches. Short beam shear strength results showed high consistency between specimens,
however were lower than comparable values found in literature. Impact specimens showed
consistency among specimens, with greater damage resistance than comparable values
found in literature. Determining debonding strength proved difficult as different failure
modes were observed between IRPs, however, initial baseline values were acquired.
42
Yao, Shulong. "Highly Stretchable Miniature Strain Sensor for Large Dynamic Strain Measurement". Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849674/.
Testo completoAbstract (sommario):
This thesis aims to develop a new type of highly stretchable strain sensor to measure large deformation of a specimen subjected to dynamic loading. The sensor was based on the piezo-resistive response of carbon nanotube(CNT)/polydimethysiloxane (PDMS) composites thin films, some nickel particles were added into the sensor composite to improve the sensor performance. The piezo-resistive response of CNT composite gives high frequency response in strain measurement, while the ultra-soft PDMS matrix provides high flexibility and ductility for large strain measuring large strain (up to 26%) with an excellent linearity and a fast frequency response under quasi-static test, the delay time for high strain rate test is just 30 μs. This stretchable strain sensor is also able to exhibit much higher sensitivities, with a gauge factor of as high as 80, than conventional foil strain gauges.
43
Warner, Wyatt Young. "Characterization of Local Void Content in Carbon Fiber Reinforced Plastic Parts Utilizing Observation of In Situ Fluorescent Dye Within Epoxy". BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7772.
Testo completoAbstract (sommario):
Experimentation exploring the movement of voids within carbon fiber reinforced plastics was performed using fluorescent dye infused into the laminates observed through a transparent mold under ultraviolet light. In situ photography was used as an inspection method for void content during Resin Transfer Molding for these laminates. This in situ inspection method for determining the void content of composite laminates was compared to more common ex-situ quality inspection methods i.e. ultrasonic inspection and cross-section microscopy. Results for localized and total void count in each of these methods were directly compared to test samples and linear correlations between the three test methods were sought. Test coupons were then cut from these laminates and were used to calculate the interlaminar shear strength at certain locations throughout the laminates. Although this research did not adequately observe correlations between results obtained from ultrasonic C-scans, cross-sectional microscopy and in situ photography of the surface, it was seen that the fluid dynamics of the thermosetting epoxy used in this experimentation correlated to results obtained from previous experimentation performed by students at Brigham Young University using vegetable oil as a substitute for resin.
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Chebbi, Houssem. "Méthode des coordonnées curvilignes pour la modélisation électromagnétique des matériaux complexes : application au contrôle non destructif par courants de Foucault des matériaux composites The fast computation of eddy current distribution and probe response in homogenized composite material based on semi-analytical approach Investigation of layer interface model of multi-layer structure using semi-analytical and FEM analysis for eddy current pulsed thermography". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST004.
Testo completoAbstract (sommario):
Ce travail de thèse de doctorat, effectué au sein de Laboratoire de Simulation et Modélisation Électromagnétique (LSME) du CEA List, s’intègre dans le cadre du projet européen « NDTonAir » financé sous l'action « H2020-MSCA-ITN-2016- GRANT 722134 ». Le principal objectif est le développement d’un outil de simulation rapide et précis dédié au contrôle non destructif par courants de Foucault des matériaux composites homogénéisés. Comme cas d’application, on s’intéresse particulièrement à l’orientation des fibres d’une part, et d’autre part, à des défauts de type délaminage et ondulation des fibres qui se manifestent par une déformation géométrique locale des interfaces. Les méthodes semi-analytiques existantes dans la littérature, basées sur le formalisme des Dyades de Green, sont limitées jusqu’au là à des structures planes multicouches. Pour introduire des variations locales de géométrie aux interfaces, nous proposons une approche innovante basée sur un changement de coordonnées adapté au profil de la pièce et des interfaces. On propose un modèle numérique performant basé sur le formalisme covariant des équations de Maxwell. Ce formalisme unificateur englobe l'anisotropie du spécimen et les déformations locales des interfaces. La méthode de coordonnées curvilignes est usuellement utilisée pour résoudre des problèmes de diffraction sur des surfaces rugueuses dans le domaine des hautes fréquences (diffraction sur des réseaux). Ce travail de thèse s’inspire des méthodes de Fourier modale et propose de nouveaux outils adaptés au domaine des courants de Foucault. L’extension de la méthode des coordonnées curvilignes au domaine du contrôle des composites par courants de Foucault constitue l’innovation de ce travail. Deux modèles numériques ont été développés pour le calcul de l’interaction du champ émis par un capteur à courants de Foucault avec un matériau composite multicouches. Le modèle numérique développé pour le contrôle des composites plans exploite les structures particulières des matrices creuses pour réduire le temps de calcul sans limitation de nombre de modes utilisés pour la représentation du champ. Dans le cas des profils curvilignes des interfaces, le modèle permet de traiter des interfaces parallèles et quelques cas particuliers des profils non parallèles. Ce cas général présente quelques limitations qui nécessitent le développement des outils numériques complémentaires. Enfin, plusieurs configurations de contrôle ont été envisagées et les résultats numériques produits par les modèles ont été confrontés à des données de simulation par éléments finis. Quelques expérimentations ont été effectuées dans des laboratoires partenaires étrangers pour accroître notre expérience sur la validation expérimentaleThis doctoral thesis work, carried out within the Laboratory of Simulation and Modeling for Electromagnetics (LSME) of CEA List, is part of the “NDTonAir” European project funded under the action “H2020-MSCA-ITN -2016- GRANT 722134”. The main goal of the project is the development of a fast and accurate simulation tool for the non-destructive eddy current testing of homogenized composite materials. As an application case, we are particularly interested in the orientation of the fibers on the one hand, and on the other hand, in defects as delamination which are manifested by a local geometrical deformation of the interfaces. The semi-analytical methods existing in the literature, based on Green's Dyad formalism, have been limited so far to multilayered and planar structures. To introduce local variations in geometry at the interfaces, we propose an innovative approach based on a change of coordinates adapted to the profile of the local perturbation. We propose a powerful numerical model based on the covariant formalism of Maxwell's equations. This unifying formalism takes in the anisotropy of specimen and the local deformations of the interfaces. The curvilinear coordinate method is usually used to solve diffraction problems on rough interfaces in the high frequency domain (diffraction on gratings). This thesis work is inspired by Fourier Modal Methods and proposes new tools which have been adapted to the field of eddy currents. The extension of the curvilinear coordinate method to the field of eddy currents non-destructive testing technique of composites constitutes the innovation of this work. Two numerical models have been developed to calculate the interaction of the field emitted by an eddy current probe with a multilayered composite material. The numerical model developed for the evaluation of planar composite exploits the particular structures of sparse matrices to reduce the computation time without limiting the number of modes used for the modal expansion of the field. In the case of the curvilinear profiles of the interfaces, the model makes it possible to treat parallel interfaces and some particular cases of non-parallel profiles. The general case of non-identical profiles presents some limitations which require the development of complementary numerical tools. Finally, several testing configurations were considered and the numerical results produced by the models were compared to finite element simulated data. Some experiments were carried out in foreign partner laboratories to increase our experience on experimental validation
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Blake, Aaron Joseph. "From 2D to 3D: On the Development of Flexible and Conformal Li-ion Batteries via Additive Manufacturing". Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1480761406535228.
Testo completo
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Walls, Joshua C. "High temperature compression testing of an advanced carbon-carbon composite in an oxidating atmosphere /". 2002. http://www.library.umaine.edu/theses/theses.asp?Cmd=abstract&ID=MEE2002-006.
Testo completo
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Okai, Smart K. "Determination of residual stresses in a carbon-fibre reinforced polymer using the incremental hole-drilling technique". Thesis, 2017. http://hdl.handle.net/10539/22997.
Testo completoAbstract (sommario):
A Research Report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering(Mechanical Engineering
30 January 2017An extensive variety of experimental techniques exist to determining residual stresses, but few of these techniques is suitable, however, for finding the residual stresses that exist in orthotropic or anisotropic layered materials, such as carbon-fibre reinforced polymers (CFRP). Among these techniques, particularly among the relaxation techniques, the incremental hole-drilling technique (IHD) has shown to be a suitable technique to be developed for this purpose. This technique was standardized for the case of linear elastic isotropic materials, such as the metallic alloys in general. However, its reliable application to anisotropic and layered materials, such as CFRP materials, needs to be better studied. In particular, accurate calculation methods to determine the residual stresses in these materials based on the measured in-depth strain relaxation curves need to be developed. In this work, existing calculation methods and already proposed theoretical approaches to determine residual stresses in composite laminates by the incremental hole-drilling technique are reviewed. The selected residual stress calculation method is implemented using MATLAB. For these calculations, specific calibration coefficients have to be numerically determined by the finite element method, using the ANSYS software. The developed MATLAB scripts are then validated using an experimental procedure previously developed. This experimental procedure was performed using CFRP specimens, with the stacking sequence [0o, 90o]5s and, therefore, this composite laminate was selected as case study in this work. Some discrepancies between the calculated stresses using the MATLAB scripts and those imposed during the experimental calibration procedure are observed. The errors found could be explained considering the limitations inherent to the incremental hole-drilling technique and the theoretical approach followed. However, the obtained results showed that the incremental hole-drilling can be considered a promising technique for residual stress measurement in composite laminates.
MT2017
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Koski, William C. "Design, analysis, and validation of composite c-channel beams". Thesis, 2012. http://hdl.handle.net/1957/34292.
Testo completoAbstract (sommario):
A lightweight carbon fiber reinforced polymer (CFRP) c-channel beam was previously designed using analytical theory and finite element analysis and subsequently manufactured through a pultrusion process. Physical testing revealed the prototype did not meet the bending and torsional stiffness of the beam model. An investigation revealed that the manufactured prototype had lower fiber content than designed, compacted geometry, an altered ply layup, missing plies, and ply folds. Incorporating these changes into the beam model significantly improved model-experiment agreement.
Using what was learned from the initial prototype, several new beam designs were modeled that compare the cost per weight-savings of different composite materials. The results of these models show that fiberglass is not a viable alternative to CFRP when designing for equivalent stiffness. Standard modulus carbon was shown
to have slightly lower cost per-weight savings than intermediate modulus carbon, although intermediate modulus carbon saves more weight overall. Core materials, despite potential weight savings, were ruled out as they do not have the crush resistance to handle the likely clamp loads of any attaching bolts. Despite determining the ideal materials, the manufactured cost per weight-savings of the best CFRP beam design was about double the desired target.Graduation date: 2013
Access restricted to the OSU Community at author's request from Oct. 5, 2012 - Oct. 5, 2014
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Almuhammadi, Khaled H. "Electrical Impedance Characterization for Damage Detection in Carbon Fiber-Reinforced Polymer (CFRP) Laminated Composites". Diss., 2018. http://hdl.handle.net/10754/629851.
Testo completoAbstract (sommario):
The use of modern carbon fiber-reinforced polymer (CFRP) composite materials is becoming increasingly widespread recently. However, the failure modes of such composite structures are extremely complex and, unlike metals, they may suffer significant degradation with barely visible surface damage. Since the damage may cause serious decrease in material strength and lead to catastrophic failure, the development of reliable structural health monitoring techniques is indispensable and has a tremendous impact on the life-cycle cost spent for inspection and repair.
Such techniques that are based on the change in the electrical properties of materials are promising and viable approach for maintaining the structural integrity. They are low-cost, fast, effective, and have high potential to be applicable on real structures where they can be monitored online and real-time. The topic of this PhD dissertation is mainly focused on a number of key developments and milestones towards monitoring damage in CFRP laminated composites and making electrical-based methods practical on real structures.
One of the major components of these methods is the electrode, which is the interface between the external hardware and the monitored structure. We develop a novel method for surface preparation of composite laminates for better electrode quality using pulsed laser irradiation. Further, we provide a new insight on the anisotropic behavior of the contact impedance for the electrodes on CFRP laminated composites. Another major component for achieving reliable monitoring techniques is the in-depth understanding of impedance response of these materials when subjected to an alternating electrical excitation, information that is only partially available in the literature. For more efficient electrical signal-based inspections, we investigate the electrical impedance spectroscopy response at various frequencies of laminates chosen to be representative of classical layups employed in composite structures. Finally, we use different electrodes configurations on CFRP plates applied to one side mimicking the case of real structures that is undergoing a quasi-static indentation representative of the impact load. We investigate the coupling between the electrical measurements and the type of mechanical degradation using an in-house built electro-mechanical system that measures the change in impedance and phase angle in-situ and real-time.
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Chuang, Chih-Lan Jasmine. "Application of digital image correlation in material parameter estimation and vibration analysis of carbon fiber composite and aluminum plates". Thesis, 2012. http://hdl.handle.net/1957/30170.
Testo completoAbstract (sommario):
Identifying material parameters in composite plates is a necessary first step in a variety of structural applications. For example, understanding the material parameters of carbon fiber composite is important in investigating sensor and actuator placement on micro-air-vehicle wings for control and wing morphing purposes. Knowing the material parameters can also help examine the health of composite structures and detect wear or defects. Traditional testing methods for finding material parameters such as stiffness and damping require multiple types of experiments such as tensile tests and shaker tests. These tests are not without complications. Methods such as tensile testing can be destructive to the test specimens while use of strain gages and accelerometers can be inappropriate due to the lightweight nature of the structures.
The proposed inverse problem testing methods using digital image correlation via high speed cameras can potentially eliminate the disadvantages of traditional methods as well as determine the required material parameters including stiffness and damping by conducting only one type of experiment. These material parameters include stiffness and damping for both isotropic and orthotropic materials, and ply angle layup specifically for carbon fiber materials. A finite element model based on the Kirchoff-Love thin plate theory is used to produce theoretical data for comparison with experimental data collected using digital image correlation. Shaker experiments are also carried out using digital image correlation to investigate the modal frequencies as validation of the results of the inverse problem.
We apply these techniques first to an aluminum plate for which material parameters are known to test the performance and efficiency of the method. We then apply the method to a composite plates to determine not only these parameters, but also the layup angle. The inverse problem successfully estimates the Young's modulus and damping for the aluminum material. In addition, the vibration analysis produces consistent resonance frequencies for the first two modes for both theoretical and experimental data. However, carbon fiber plates present challenges due to limitations of the Kirchoff-Love plate theory used as the underlining theoretical model for the finite element approximation used in the inverse problem, resulting in a persistent mismatch of resonance frequencies in experimental data.Graduation date: 2012