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Dissertations / Theses on the topic 'Structural analysis (Engineering) Composite materials'
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1
Phillips, John L. "Structural analysis and optimum design of geodesically stiffened composite panels." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040802/.
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2
Anders, William S. "Structural acoustic analysis of shape memory alloy hybrid composite panels." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-11012008-063243/.
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3
Hou, An. "Strength of composite lattice structures." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12475.
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4
Stone, Daniel Paul. "The influence of ply orientation on the open-hole tension strength of composite laminates." Online access for everyone, 2008. http://www.dissertations.wsu.edu/Thesis/Spring2008/d_stone_042208.pdf.
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5
Kang, Paul J. (Paul Ji Hwan) 1974. "A technical and economic analysis of structural composite use in automotive body-in-white applications." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/34697.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering; and, (S.M.)--Massachusetts Institute of Technology, Technology and Policy Program, 1998.Science Library copy in pages.
Includes bibliographical references (leaves 163-170).
by Paul J. Kang.
S.M.
6
Singh, Mukti Nath. "Efficient reliability estimation approach for analysis and optimization of composite structures." Master's thesis, Mississippi State : Mississippi State University, 2002. http://library.msstate.edu/etd/show.asp?etd=etd-11072002-103328.
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7
Rantis, Theofanis D. "Probability-based stability analysis of a laminated composite plate under combined in-plane loads." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07292009-090358/.
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8
Salehian, Armaghan. "Identifying the location of a sudden damage in composite laminates using wavelet approach." Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0711103-155908.
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9
Odi, A. R. A. "Bonded Repair of Composite Structures; A Finite Element Approach." Thesis, Department of Materials and Medical Sciences, 2009. http://hdl.handle.net/1826/3893.
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This thesis addresses the issues surrounding the application of the finite element
method to analyse composite structure repairs with an emphasis on aircraft
applications. A comprehensive literature survey has been carried out for this purpose
and the results are presented.
A preliminary study and a comparative study of different modelling approaches have
been completed. These studies aim to explore and identify the problems in modelling
repairso n simplec ompositep anelsw ith speciala ttention given to adhesivem odelling.
Three modelling approaches have been considered: Siener's model which is an
extension of the traditional plane strain 2D model used for adhesively bonded joints,
Bait's model which is a promising new approach and a full 3D model. These studies
have shown that these methods are complementary providing a different insight into
bonded repairs. They have also highlighted the need for a new modelling approach
which will provide an overall view of bonded repairs.
Improved modelling approachesh ave been developedf or externallyb onded patch and
flush repairs. These models enable the study of adhesive failure as well as composite
adherendf ailures.T hesea pproachesh aveb eena ppliedt o real repairs and the predicted
results compared to experimental data. Four case studies have been conducted:
external bonded patch repairs to composite plates, a scarf joint for bonded repairs, a
flat panel repaired with a scarfed patch and a repaired curved panel.
These case studies have shown that bonded repairs to composite structures can be
analyseds uccessfullyu sing PC-basedc ommercialf inite elementc odes.
10
Odi, A. Randolph A. "Bonded repair of composite structures : a finite element approach." Thesis, Cranfield University, 1998. http://dspace.lib.cranfield.ac.uk/handle/1826/3893.
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This thesis addresses the issues surrounding the application of the finite element method to analyse composite structure repairs with an emphasis on aircraft applications. A comprehensive literature survey has been carried out for this purpose and the results are presented. A preliminary study and a comparative study of different modelling approaches have been completed. These studies aim to explore and identify the problems in modelling repairso n simplec ompositep anelsw ith speciala ttention given to adhesivem odelling. Three modelling approaches have been considered: Siener's model which is an extension of the traditional plane strain 2D model used for adhesively bonded joints, Bait's model which is a promising new approach and a full 3D model. These studies have shown that these methods are complementary providing a different insight into bonded repairs. They have also highlighted the need for a new modelling approach which will provide an overall view of bonded repairs. Improved modelling approachesh ave been developedf or externallyb onded patch and flush repairs. These models enable the study of adhesive failure as well as composite adherendf ailures.T hesea pproachesh aveb eena ppliedt o real repairs and the predicted results compared to experimental data. Four case studies have been conducted: external bonded patch repairs to composite plates, a scarf joint for bonded repairs, a flat panel repaired with a scarfed patch and a repaired curved panel. These case studies have shown that bonded repairs to composite structures can be analyseds uccessfullyu sing PC-basedc ommercialf inite elementc odes.
11
Kim, Joun S. "A Comparison Study of Composite Laminated Plates With Holes Under Tension." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1895.
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A Comparison Study of Composite Laminated Plates with Holes under Tension
A study was conducted to quantify the accuracy of numerical approximations to deem sufficiency in validating structural composite design, thus minimizing, or even eliminating the need for experimental test. Error values for stress and strain were compared between Finite Element Analysis (FEA) and analytical (Classical Laminated Plate Theory), and FEA and experimental tensile test for two composite plate designs under tension: a cross-ply composite plate design of [(0/90)4]s, and a quasi-isotropic layup design of [02/+45/-45/902]s, each with a single, centered hole of 1/8” diameter, and 1/4" diameter (four sets total). The intent of adding variability to the ply sequences and hole configurations was to gauge the sensitivity and confidence of the FEA results and to study whether introducing enough variability would, indeed, produce greater discrepancies between numerical and experimental results, thus necessitating a physical test. A shell element numerical approximation method through ABAQUS was used for the FEA.
Mitsubishi Rayon Carbon Fiber and Composites (formerly Newport Composites) unidirectional pre-preg NCT301-2G150/108 was utilized for manufacturing—which was conducted and tested to conform to ASTM D3039/D3039M standards.
A global seed size of 0.020, or a node count on the order of magnitude of 30,000 nodes per substrate, was utilized for its sub-3% error with efficiency in run-time.
The average error rate for FEA strain from analytical strain at a point load of 1000lbf was 2%, while the FEA-to-experimental strains averaged an error of 4%; FEA-to-analytical and FEA-to-tensile test stress values at 1000lbf point load both averaged an error value of 6%. Suffice to say, many of these strain values were accurate up to ten-thousandths and hundred-thousandths of an in/in, and the larger stress/strain errors between FEA and test may have been attributed to the natural variables introduced from conducting a tensile test: strain gauge application methods, tolerance stacks from load cells and strain gauge readings.
Despite the variables, it was determined that numerical analysis could, indeed, replace experimental testing. It was observed through this thesis that a denser, more intricate mesh design could provide a greater level of accuracy for numerical solutions, which proves the notion that if lower error rates were necessitated, continued research with a more powerful processor should be able to provide the granularity and accuracy in output that would further minimize error rates between FEA and experimental. Additionally, design margins and factors of safety would generally cover the error rates expected from numerical analysis.
Future work may involve utilizing different types of pre-preg and further varied hole dimensions to better understand how the FEA correlates with analytical and tensile test results. Other load types, such as bending, may also provide insight into how these materials behave under loading, thus furthering the conversation of whether numerical approximations may one day replace testing all together.
12
Kahle, Matthew Gilbert. "Partially restrained composite connections : design and analysis of a prototype structure." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/20830.
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Chandrashekhara, K. "Geometric and material nonlinear analysis of laminated composite plates and shells." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54739.
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An inelastic material model for laminated composite plates and shells is formulated and incorporated into a finite element model that accounts for both geometric nonlinearity and transverse shear stresses. The elasto-plastic material behavior is incorporated using the flow theory of plasticity. In particular, the modified version of Hill's initial yield criterion is used in which anisotropic parameters of plasticity are introduced with isotropic strain hardening. The shear deformation is accounted for using an extension of the Sanders shell theory and the geometric nonlinearity is considered in the sense of the von Karman strains. A doubly curved isoparametric rectangular element is used to model the shell equations. The layered element approach is adopted for the treatment of plastic behavior through the thickness. A wide range of numerical examples is presented for both static and dynamic analysis to demonstrate the validity and efficiency of the present approach. The results for combined nonlinearity are also presented. The results for isotropic results are in good agreement with those available in the literature. The variety of results presented here based on realistic material properties of more commonly used advanced laminated composite plates and shells should serve as references for future investigations.Ph. D.
14
Liu, Albert Darien. "THE EFFECT OF SENSOR MASS, SENSOR LOCATION, AND DELAMINATION LOCATION OF DIFFERENT COMPOSITE STRUCTURES UNDER DYNAMIC LOADING." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/917.
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This study investigated the effect of sensor mass, sensor location, and delamination location of different composite structures under dynamic loading. The study pertains to research of the use of accelerometers and dynamic response as a cost-effective and reliable method of structural health monitoring in composite structures. The composite structures in this research included carbon fiber plates, carbon fiber-foam sandwich panels, and carbon-fiber honeycomb sandwich panels. The composite structures were manufactured with the use of a Tetrahedron MTP-8 heat press. All work was conducted in the Cal Poly Aerospace Structures/Composites Laboratory. Initial delaminations were placed at several locations along the specimen, including the bending mode node line locations. The free vibration of the composite structure was forced through a harmonic horizontal vibration test using an Unholtz-Dickie shake system. A sinusoidal sweep input was considered for the test. The dynamic response of the composite test specimens were measured using piezoelectric accelerometers. Measurements were taken along horizontal and vertical locations on the surfaces of the composite structures. Square inch grids were marked on the surfaces to create a meshed grid system. Accelerometer measurements were taken at the center of the grids. The VIP Sensors 1011A piezoelectric accelerometer was used to measure vibration response. The measurements were then compared to response measurements taken from a PCB Piezotronics 353B04 single access accelerometer to determine the effects of sensor mass. Deviations in bending mode natural frequency and differences in mode shape amplitude became the criteria for evaluating the effect of sensor mass, sensor location, and delamination location. Changes in damping of the time response were also studied. The experimental results were compared to numerical models created using a finite element method. The experimental results and numerical values were shown to be in good agreement. The sensor mass greatly affected the accuracy and precision of vibration response measurements in the composites structures. The smaller weight and area of the VIP accelerometer helped to minimize the decrease in accuracy and precision due to sensor mass. The effect of sensor location was found to be coupled with the effect of sensor mass and the bending mode shape. The sensor location did not affect the vibration response measurements when the sensor mass was minimized. Off-center horizontal sensor placement showed the possibility of measuring vibration torsion modes. The effect of delamination changed the bending mode shape of the composite structure, which corresponded to a change in natural frequency. The greatest effect of the delamination was seen at the bending mode node lines, where the bending mode shape was most significantly affected. The effect of delamination was also dependent on the location of the delamination and the composite structure type. The results of this study provided considerations for future research of an active structural health monitoring system of composite structures using dynamic response measurements. The considerations included sensor mass reduction, sensor placement at constraints and bond areas and the presence of damping material.
15
Geyer, Susanna Elizabeth. "Advanced low order orthotropic finite element formulations." Diss., Pretoria : [s.n.], 2001. http://upetd.up.ac.za/thesis/available/etd-03062006-114313/.
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Lo, Patrick Kar-Leung. "Comparison of theory and experiment for flexural-torsional buckling of laminated composite columns." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/50051.
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Vlasov’s one-dimensional structural theory for thin-walled open section bars was originally developed and used for metallic elements. The theory was recently extended to laminated bars fabricated from advanced composite materials. The purpose of this research is to provide a study and assessment of the extended theory. The focus is on flexural and torsional-flexural buckling of thin-walled, open section, laminated composite columns. Buckling loads are computed from the theory using a linear bifurcation analysis, and are compared to available experimental data. Also, a geometrically nonlinear beam column analysis by the finite element method is developed from the theory. Results from the nonlinear compression response analysis are compared to limited available test data. The merits of the theory and its implementation are discussed.Master of Science
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17
Ball, Jeffrey Craig. "Design and analysis of multifunctional composite structures for nano-satellites." Thesis, Cape Peninsula University of Technology, 2017. http://hdl.handle.net/20.500.11838/2572.
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Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2017.The aim of this thesis is to investigate the applications of multifunctional compos- ite (MFC) technology to nano-satellite structures and to produce a working concept design, which can be implemented on future Cube-Satellites (CubeSats). MFC tech- nologies can be used to optimise the performance of the satellite structure in terms of mass, volume and the protection it provides. The optimisation of the structure will allow further room for other sub-systems to be expanded and greater payload allowance. An extensive literature view of existing applications of MFC materials has been conducted, along with the analysis of a MFC CubeSat structural design account- ing for the environmental conditions in space and well-known design practices used in the space industry. Numerical analysis data has been supported by empirical analysis that was done where possible on the concept material and structure. The ndings indicate that the MFC technology shows an improvement over the conventional alu- minium structures that are currently being used. Improvements in rigidity, mass and internal volume were observed. Additional functions that the MFC structure o ers include electrical circuitry and connections through the material itself, as well as an increase electromagnetic shielding capability through the use of carbon- bre composite materials. Empirical data collected on the MFC samples also show good support for the numerical analysis results. The main conclusion to be drawn from this work is that multifunctional composite materials can indeed be used for nano-satellite structures and in the same light, can be tailor-made to the speci c mission requirements of the satellite. The technology is in its infancy still and has vast room for improvement and technological development beyond this work and well into the future. Further improvements and additional functions can be added through the inclusion of various other materials.
18
Turgut, Tahir. "Manufacturing And Structural Analysis Of A Lightweight Sandwich Composite Uav Wing." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608774/index.pdf.
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This thesis work deals with manufacturing a lightweight composite unmanned aerial vehicle (UAV) wing, material characterization of the composites used in the UAV wing, and preliminary structural analysis of the UAV wing.
Manufacturing is performed at the composite laboratory founded in the Department of Aerospace Engineering, and with hand lay-up and vacuum bagging method at room temperature the wing is produced. This study encloses the detailed manufacturing process of the UAV wing from the mold manufacturing up to the final wing configuration supported with sketches and pictures.
Structural analysis of the composite wing performed in this study is based on the material properties determined by coupon tests and micromechanics approaches. Contrary to the metallic materials, the actual material properties of composites are generally not available in the material handbooks, because the elastic properties of composite materials are dependent on the manufacturing process. In this study, the mechanical properties, i.e. Young&rsquos Modulus, are determined utilizing three different methods. Firstly, longitudinal tensile testing of the coupon specimens is performed to obtain the elastic properties. Secondly, mechanics of materials approach is used to determine the elastic properties. Additionally, an approximate method, that can be used in a preliminary study, is employed. The elastic properties determined by the tests and other approaches are compared to each other. One of the aims of this study is to establish an equivalent material model based on test and micromechanics approach, and use the equivalent model in the structural analysis by finite element method. To achieve this, composite structure of the wing is modeled in detail with full composite material descriptions of the surfaces of the wing structure, and comparisons are made with the results obtained by utilizing equivalent elastic constants. The analyses revealed that all three approaches have consistent, and close results
especially in terms of deflections and natural frequencies. Stress values obtained are also comparable as well. For a case study on level flight conditions, spanwise wing loading distribution is obtained using a program of ESDU, and the wing is analyzed with the distributed loading. Reasonable results are obtained, and the results compared with the tip loading case. Another issue dealt in this study is analyzing the front spar of the wing separately. The analysis of the front spar is performed using transformed section method and finite element analysis. In the results, it is found that both methods calculates the deflections very close to each other. Close stress results are found when solid elements are used in the finite element analysis, whereas, the results were deviating when shell elements are used in the analysis.
19
Davis, Dan M. "Finite Element Modeling of Ballistic Impact on a Glass Fiber Composite Armor." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/815.
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Finite Element Modeling of Ballistic Impact on a Glass Fiber Composite Armor
Dan Davis
Experiments measuring the ballistic performance of a commercially available fiberglass armor plate were used to guide the development of constitutive laws for a finite element model of the impact. The test samples are commercially available armor panels, made from E-glass fiber reinforced polyester rated to NIJ level III. Quasi-static tensile tests were used to establish material properties of the test panels. These properties were then used to create models in the explicit finite element code LSDYNA.
Ballistic impact testing of the panels was conducted using a compressed gas gun firing spherical steel projectiles oriented normal to the test panel surface. The V50 ballistic limit of these panels was found to be approximately 560 m/s. Tuning parameters in the finite element models were adjusted to match the experimentally measured penetration depths and ballistic limits. Models were created in LSDYNA by adjusting the available material library types 3 and 59 for the target, and material type 15 for the projectile. Type 3 models are isotropic, and resulted in shear punch-out type failures of the plate that poorly replicated the test results. Type 59 takes orthotropic properties into consideration, and can analyze delamination when used with solid elements. Results with model type 59 were significantly better than those using type 3, however, this model was found to vastly underestimate the impact resistance of the plate. With significant adjustments to the material properties in the type 59 model, the LSDYNA simulations were found to better replicate the experimentally observed response of the panels. However, these deformations are questionable since they required quite unrealistic adjustments to the material properties.
20
Rajagopal, Anurag. "Advancements in rotor blade cross-sectional analysis using the variational-asymptotic method." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51877.
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Rotor (helicopter/wind turbine) blades are typically slender structures that can be modeled as beams. Beam modeling, however, involves a substantial mathematical formulation that ultimately helps save computational costs. A beam theory for rotor blades must account for (i) initial twist and/or curvature, (ii) inclusion of composite materials, (iii) large displacements and rotations; and be capable of offering significant computational savings compared to a non-linear 3D FEA (Finite Element Analysis). The mathematical foundation of the current effort is the Variational Asymptotic Method (VAM), which is used to rigorously reduce the 3D problem into a 1D or beam problem, i.e., perform a cross-sectional analysis, without any ad hoc assumptions regarding the deformation. Since its inception, the VAM based cross-sectional analysis problem has been in a constant state of flux to expand its horizons and increase its potency; and this is precisely the target at which the objectives of this work are aimed. The problems addressed are the stress-strain-displacement recovery for spanwise non-uniform beams, analytical verification studies for the initial curvature effect, higher fidelity stress-strain-displacement recovery, oblique cross-sectional analysis, modeling of thin-walled beams considering the interaction of small parameters and the analysis of plates of variable thickness. The following are the chief conclusions that can be drawn from this work:
1. In accurately determining the stress, strain and displacement of a spanwise non-uniform beam, an analysis which accounts for the tilting of the normal and the subsequent modification of the stress-traction boundary conditions is required.
2. Asymptotic expansion of the metric tensor of the undeformed state and its powers are needed to capture the stiffnesses of curved beams in tune with elasticity theory. Further improvements in the stiffness matrix can be achieved by a partial transformation to the Generalized Timoshenko theory.
3. For the planar deformation of curved laminated strip-beams, closed-form analytical expressions can be generated for the stiffness matrix and recovery; further certain beam stiffnesses can be extracted not only by a direct 3D to 1D dimensional reduction, but a sequential dimensional reduction, the intermediate being a plate theory.
4. Evaluation of the second-order warping allows for a higher fidelity extraction of stress, strain and displacement with negligible additional computational costs.
5. The definition of a cross section has been expanded to include surfaces which need not be perpendicular to the reference line.
6. Analysis of thin-walled rotor blade segments using asymptotic methods should consider a small parameter associated with the wall thickness; further the analysis procedure can be initiated from a laminated shell theory instead of 3D.
7. Structural analysis of plates of variable thickness involves an 8×8 plate stiffness matrix and 3D recovery which explicitly depend on the parameters describing the thickness, in contrast to the simplistic and erroneous approach of replacing the thickness by its variation.
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Pérez, Galmés Magdalena. "Analysis and development of experimental characterization methodologies of mode II fracture toughness on CFRP bonded joints." Doctoral thesis, Universitat de Girona, 2018. http://hdl.handle.net/10803/664508.
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Adhesives have been shown to be an excellent solution for joining fibre reinforced polymer (FRP) components thanks to their capacity to redistribute loads, reduces stress concentrations and contribute to overall weight saving in the structure. The most relevant mechanical property in adhesive bonded joints design is the shear (mode II) fracture toughness of the adhesive.
The application of the existing mode II delamination standards to adhesive joints entails some major limitations that result in severe under/over estimations of the adhesive properties and, in many cases, can even prevent results from being obtained from tests.
The main objective of the present thesis is to develop robust tools for the determination of shear (mode II) facture toughness in adhesive joints. This includes studying data reduction methods as well as the test geometriesEls adhesius han demostrat ser una magnífica solució per unir components de polímers reforçats amb fibres (FRP) gràcies a la seva capacitat per redistribuir càrregues, reduir les concentracions de tensions i contribuir a l’estalvi general de pes en l’estructura. La propietat mecànica més rellevant en el disseny d’unions adhesives és la tenacitat a la fractura a tallant (mode II) de l’adhesiu. L’aplicació dels actuals assajos estandaritzats a les unions adhesives pot derivar en estimacions errònies, per sota o per sobre, de les propietats adhesives i, en molts casos, evitar que l’assaig es pugui realitzar satisfactòriament. L’objectiu principal d’aquesta tesi és el desenvolupament d’eines robustes per a la determinació de la tenacitat a la fractura a tallant (mode II) d’unions adhesives. S’estudia l’aplicabilitat dels mètodes d’assaig de deslaminació en mode II existents a les unions adhesives estructurals. Això inclou l’estudi dels mètodes de reducció de dades i de les geometries d’assaig
22
Swindeman, Michael James. "A Regularized Extended Finite Element Method for Modeling the Coupled Cracking and Delamination of Composite Materials." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1324605778.
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Sakarya, Arzu. "Multidisciplinary Design Of An Unmanned Aerial Vehicle Wing." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613606/index.pdf.
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In this thesis, the structural design, structural analysis and producibility analysis of an unmanned aerial vehicle wing were performed. Three different wing models, made of different materials, were designed. The wings were aluminum wing model and composite wing modelsmade of prepreg and wet lay-up. All wings have the same aerodynamic geometry and structural configuration under the same flight conditions. The structural designs of three wings were done by using Unigraphics NX. The finite element modeling of the wings were built by using MSC Patran package program. After the application of the loads on models, structural analyses were performed by MSC Nastran. Finally, the producibility analysis of prepreg wing model was conducted by using FiberSIM package program. The prepreg wing model was selected as optimum design with studies conducted in the study considering weight, producibility, cruise and gust stress and displacement conditions.
24
Nezamian, Abolghasem 1968. "Bond strength of concrete plugs embedded in tubular steel piles." Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/5601.
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Avachat, Siddharth. "Experimental and numerical analyses of dynamic deformation and failure in marine structures subjected to underwater impulsive loads." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44904.
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The need to protect marine structures from the high-intensity impulsive loads created by underwater explosions has stimulated renewed interest in the mechanical response of sandwich structures. The objective of this combined numerical and experimental study is to analyze the dynamic response of composite sandwich structures and develop material-structure-property relations and design criteria for improving the blast-resistance of marine structures. Configurations analyzed include polymer foam core structures with planar geometries. A novel experimental facility to generate high-intensity underwater impulsive loads and carry out in-situ measurements of dynamic deformations in marine structures is developed. Experiments are supported by fully dynamic finite-element simulations which account for the effects of fluid-structure interaction, and the constitutive and damage response of E-glass/polyester composites and PVC foams.
Results indicate that the core-density has a significant influence on dynamic deformations and failure modes. Polymeric foams experience considerable rate-effects and exhibit extensive shear cracking and collapse under high-magnitude multi-axial underwater impulsive loads. In structures with identical masses, low-density foam cores consistently outperform high-density foam cores, undergoing lesser deflections and transmitting smaller impulses. Calculations reveal a significant difference between the response of air-backed and water-backed structures. Water-backed structures undergo much greater damage and consequently need to absorb a much larger amount of energy than air-backed structures. The impulses transmitted through water-backed structures have significant implications for structural design. The thickness of the facesheets is varied under the conditions of constant material properties and core dimensions. The results reveal an optimal thickness of the facesheets which maximizes energy absorption in the core and minimizes the overall deflection of the structure.
26
Rodriguez, George IV. "Finite Element Modeling of Delamination Damage in Carbon Fiber Laminates Subject to Low-Velocity Impact and Comparison with Experimental Impact Tests Using Nondestructive Vibrothermography Evaluation." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1583.
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Carbon fiber reinforced composites are utilized in many design applications where high strength, low weight, and/or high stiffness are required. While composite materials can provide high strength and stiffness-to-weight ratios, they are also more complicated to analyze due to their inhomogeneous nature. One important failure mode of composite structures is delamination. This failure mode is common when composite laminates are subject to impact loading.
Various finite element methods for analyzing delamination exist. In this research, a modeling strategy based on contact tiebreak definitions in LS-DYNA®was used. A finite element model of a low-velocity impact event was created to predict delamination in a composite laminate. The resulting delamination relative size and shape was found to partially agree with analytical and experimental results for similar impact events, while the force-time plot agreed well with experimental results. A small difference in contact time in the simulation compared to experimental testing is likely due to the omission of composite failure modes other than delamination.
Experimental impact testing and subsequent vibrothermography analysis showed delamination damage in locations shown in previous research. This confirmed the validity of vibrothermography as a nondestructive evaluation technique for analyzing post-impact delamination.
27
Wang, Yaou. "Failure mechanism and reliability prediction for bonded layered structure due to cracks initiating at the interface." Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1236645979.
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Faulk, Joanna (Joanna E. ). "Composite materials in dynamic shipboard structural mounts." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68837.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 18).
The purpose of this thesis is to investigate the viability of replacing traditional metal structural and machinery mounts with padding made of composite material. The two types of padding or isolation materials are represented by steel and CFRP (carbon fiber reinforced polymer). Machinery and instruments in ships are often mounted for two main reasons: they create unwanted vibrations and they need to be isolated from shock and external vibration. In order to analyze this problem, the machinery or instrument plus its padding are modeled as a mass-spring-damper system. The results show that CFRP generally works better for vibration isolation, while steel works better for shock isolation.
by Joanna Faulk.
S.B.
29
Ahmad, Mansur. "Analysis of Calcutta bamboo for structural composite materials." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/28742.
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Land use issues have dramatically changed the timber supply outlook for our nation's forest products industry. Since demand for wood products shows no sign of abating, alternative products must be developed. Bamboo is a very promising alternative raw material for the manufacture of structural composite products. It is fast growing, economical, renewable and abundant throughout the world. Bamboo has physical and mechanical properties that are comparable to many commercial timber species, and thus, may easily be processed using existing technology from the wood-based composites industry. Bamboo can be cultivated in the U.S., and thus has the potential to relieve some of the harvesting pressure from our nation's forestlands. However, the use of specific bamboo species for structural composite products will require a thorough investigation of the material as well as its interaction with other components. Thus, the primary objective of this dissertation is to determine the properties of Calcutta bamboo and its interaction with adhesives. The properties investigated were relative density, dimensional stability, equilibrium moisture content, bending strength and stiffness, tensile strength, pH, buffer capacity, wettability and the adhesive penetration. In addition to this, a prototype bamboo parallel strip lumber (BPSL) was manufactured and tested for its physical and mechanical properties. The relationships among the properties of Calcutta bamboo and the prototype bamboo composite were also investigated. As the result of these investigations, it is concluded that Calcutta bamboo is technically a suitable raw material for structural composite products. This result may also be applicable for the utilization of other bamboo species, thus aiding companies in decisions regarding investment in bamboo plantations and manufacturing facilities in the U.S, Malaysia and other parts of the world. The primary benefits from this research may be the development of new products to serve growing markets, and thereby relieving some of the pressure to harvest forestlands.Ph. D.
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Johnson, Wayne Michael. "Structural acoustic optimization of a composite cylindrical shell." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-06072004-131213/unrestricted/johnson%5Fwayne%5Fm%5F200405%5Fphd.pdf.
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Sambasivam, Shamala. "Thermoelastic stress analysis of laminated composite materials." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72144/.
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In this work thermoelastic stress analysis (TSA) is used to obtain quantitative stress/ strain data from a variety of multi-directional laminated composites. In order to in- terpret the thermoelastic signal correctly the source of the thermoeleastic response has been investigated in detail. In this thesis four possible routines to extract quantitative stress/strain information from thermoelastic data have been explored. A set of carefully selected glass/epoxy composite specimens with designated stacking sequences provided a scheme to identify the source and nature of the thermoelastic response. All of the material properties of the composite laminate were obtained experimentally, to aid an accurate assessment of each routine. The variation in the stress experienced by the laminate in the surface resin layer and ply by ply there after leads to large variations in the temperature change through the thickness. The thermoelastic measurements from dierent laminates revealed a local non-adiabatic condition within the layered medium. Therefore, the implication of applied loading frequency on the heat conduction properties of the laminates was studied. Based on the experimental observation from a representa- tive specimen, numerical models have been developed to understand the nature of the heat transfer in the glass/ epoxy material considered in this work. An analysis of the eect of holes in a variety of laminated components is presented to provide stress concen- tration factors (SCF's) based on TSA data. The conventional, orthotropic surface ply model most often used for thermoelastic stress analysis of composite material is revisited in order to elucidate the invariant nature of the equation. This is an important base for the analysis of structures which are better notated in coordinate system other than Cartesian, or as ratio of thermoelastic measurements in two dierent coordinate systems. The nature of the thermoelastic response in the presence of the in-plane stress gradient is investigated with the aid of numerical and analytical models. An introductory work for quantifying the SCF's around pin-loaded holes in laminated composite based on TSA measurements is also presented. The work presented in this thesis provides a step forward in the application of TSA to the composite materials in a quantitative manner.
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Kabche, Jean Paul. "Structural Testing and Analysis of Hybrrid Composite/Metal Joints for High-Speed Marine Structures." Fogler Library, University of Maine, 2006. http://www.library.umaine.edu/theses/pdf/kabchejp2006.pdf.
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Mewer, Richard C. "Analysis and Structural Health Monitoring of Composite Plates with Piezoelectric Sensors and Actuators." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/MewerRC2003.pdf.
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Chandrasekaran, Ganesh. "Dynamic analysis of a composite moving beam." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1526.
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Thesis (M.S.)--West Virginia University, 2000.Title from document title page. Document formatted into pages; contains xi, 159 p. : ill. Includes abstract. Includes bibliographical references (p. 156-159).
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Lee, Jin Woo. "Multi-level Decoupled Optimization of Wind Turbine Structures Using Coefficients of Approximating Functions as Design Variables." University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1501003238831086.
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Johnson, Shane Miguel. "Infrared thermography and thermoelastic stress analysis of composite materials and structural systems." Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-07072006-161614/.
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Pinfold, Martyn Keith. "Composite mechanical properties for use in structural analysis." Thesis, University of Warwick, 1995. http://wrap.warwick.ac.uk/3995/.
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In order to be able to undertake an analysis of a component the designer will need to know the properties of the material being used. The aim of this work is help the design engineer such that the mechanical properties of continuous glass fibre reinforced composite material can be determined and used in the design analysis of components manufactured from this material. The literature survey has shown that for the material considered here, then given the constituent properties, the fibre arrangement and the fibre volume fraction, the composite mechanical properties may be determined mathematically by the use of micromechanical equations. The micromechanical prediction of the mechanical properties of uni-directional, random and woven fibre reinforced composites has been examined. The variation of these mechanical properties that may occur in a composite component due to the manufacturing process has been highlighted as being of importance. This has been studied to determine whether such a variation is significant by analysing examples of composite components and plates. The results from these analyses have been correlated with experimental results and investigated to study the importance of such variations in properties. Many micromechanical equations have been found in the literature for the prediction of the mechanical properties of continuous fibre reinforced composite materials. An accuracy of the predicted properties to within 10% of the experimental data was concluded to be acceptable and good enough for initial design purposes as design engineers are not usually able to design to such tight tolerances. This work has shown that further development of the micromechanical theories is not the most important problem concerning the prediction of the mechanical properties. These properties can currently be predicted with acceptable accuracy from the micromechanical equations already available in the literature. However, the design engineer is unlikely to have knowledge of the micromechanical equations necessary to determine the required properties. It is only by undertaking a large literature survey that the designer would be able to find this information. Many of the micromechanical equations require the use of an empirical factor. The knowledge of a value for such a factor is again something that would not be readily available to the designer. Rather than concentrating upon improving the micromechanical predictions, this work shows that effort should be made to understand the influence of other factors upon the mechanical properties of composite materials. In particular, the behaviour and flow of the material during the manufacturing process has been highlighted as being of importance as it can cause a significant variation in the properties. Thus, analyses of composite components cannot assume that the mechanical properties are constant throughout, and it is therefore necessary to first model the manufacturing process to determine the mechanical properties before undertaking a structural analysis.
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Grall, Bruno. "Structural analysis of geodesically stiffened composite panels with variable stiffener distribution." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-12232009-020522/.
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Kenik, Douglas J. "Advanced techniques for constituent-based progressive failure analysis of composite structures." Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1939245921&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Kuang, Kevin. "Optical fibre sensors for process and structural health monitoring of advanced composite materials." Thesis, University of Liverpool, 2001. http://livrepository.liverpool.ac.uk/1194/.
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The concept of smart structures with integrated optical fibre sensors capable of performing real-time structural health-monitoring has attracted much attention in recent years due to the potential safety and economic benefits they offer. In addition, optical fibres have also been employed as in-situ sensors to monitor the fabrication cycle of polymer composites. The aim of the present research study is to explore the concept of smart composite structures for damage detection and strain monitoring using optical fibre technology. The first part of this thesis summarises a study of the use of two types of optical fibre systems for realtime health-monitoring of advanced composite structures based on a conventional multi-mode optical fibre and a Bragg grating sensor. These sensors have either been embedded or surface-bonded to the host material for health assessment of the structure. The second part of the thesis outlines an investigation which has been carried out to assess the potential of an intensity-based optical fibre sensing system to monitor the chemo-rheological changes which take place during the processing of a thermoplastic composite. The study has demonstrated the potential of the system and has shown that this technique offers a cost-effective means of monitoring the processing cycle of a polymer composite material. Regarding the health-monitoring aspect of the research, intensity-based optical fibre sensors have been embedded in a thermoplastic composite and a fibre-metal laminate system based on the same composite constituent. Impact tests and quasi-static three-point bend tests have been conducted to investigate the ability of these optical fibres to detect damage induced by these loading types. The embedded UAT-type optical fibre was found to be sensitive to impact energies as low as 1 Joule. The hard-clad EMT-type optical fibre on the other hand was shown to be capable of surviving extensive sub-perforation-type impact damage and could be used for detecting ballistic damage in aircraft combat situations. In the three-point bend tests, embedded UAT-type optical fibres were observed to be sensitive to flexural failure and were shown to be capable of detecting damage in the host material. Fibre Bragg grating sensors were embedded in a number of thermosetting composites and a thermoplastic fibre-metal laminate to examine their potential for strain monitoring and damage detection. Uniaxial tests have demonstrated that specimens exhibiting a single peak spectrum show excellent linearity. In contrast, specimens with multiple-peak spectra were shown to exhibit strain anomalies. In impact tests, the specimens were impacted repeatedly and, although in each case the spectrum underwent a significant change in shape, the sensor showed excellent survivability. Postimpact fatigue tests have demonstrated that the linearity of the FBG was maintained. The results also highlighted the potential of the sensor to detect impact event and damage propagation. In addition, the study has demonstrated the ability of fibre Bragg gratings to measure post-processing residual strains within a multi-material structure. Multi-mode optical fibres were used as sensors in an intensity-based optical fibre system to obtain real-time information during the processing of thermoplastic-based glass fibre-reinforced polypropylene (GFPP). The technique used to monitor the melting and solidification process in this study is based on monitoring the modulation of the refractive index of the polymer matrix. The intensity modulation of the signal was monitored during the composite processing cycle. Differential scanning calorimetry (DSC) was performed to provide a reference to evaluate the validity of the optical fibre data. The results have demonstrated the potential of this method in achieving a repeatable and accurate indication of the melting and recrystallisation temperatures within the semicrystalline matrix.
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Oehlers, Deric John. "Mechanisms in composite structures /." Title page, abstract and table of contents only, 2004. http://web4.library.adelaide.edu.au/theses/09END/09endo285.pdf.
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Farhat, Ali Y. "Vibrational analysis of composite double layer skeletal structures." Thesis, University of Surrey, 1992. http://epubs.surrey.ac.uk/624/.
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Ganapathy, Visvanathan 1957. "Structural analysis of stretched membrane reflector modules using advanced composites." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276569.
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The concept of achieving low cost (≈ $20/m²) and ultra low weight (5 kg/m²) for heliostats is explored theoretically and experimentally. The objective of this work is to significantly improve the cost and performance of the structure under concern, without sacrificing strength and efficiency. The focus is on an innovative design of stretched-membrane heliostats. A reflective membrane of thin film is supported by a taut fishnet structural membrane consisting of graphite fiber-polymer matrix composite. The reflective and structural membranes are attached to a ring frame made of wood. The nonlinear problem of stress-strain analysis is formulated and solved using the finite-element code NASTRAN. The analysis is done for loads which include the initial stretching of the film and structural membrane and the pressure load due to wind. The scope of the present work is limited to analyzing the structural deformation behavior of flat-plate heliostats and partial extension to parabolic and semi-hemispherical dish reflectors.
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Alvarez-Valencia, Daniel. "Structural Performance of Wood Plastic Composite Sheet Piling." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/AlvarezValenciaD2009.pdf.
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Boettcher, Dennis N. "A Resistance Based Structural Health Monitoring System for Composite Structure Applications." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/843.
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This research effort explored the possibility of using interwoven conductive and nonconductive fibers in a composite laminate for structural health monitoring (SHM). Traditional SHM systems utilize fiber optics, piezoelectrics, or detect defects by nondestructive test methods by use of sonar graphs or x-rays. However, these approaches are often expensive, time consuming and complicated.
The primary objective of this research was to apply a resistance based method of structural health monitoring to a composite structure to determine structural integrity and presence of defects.
The conductive properties of fiber such as carbon, copper, or constantan - a copper-nickel alloy - can be utilized as sensors within the structure. This allows the structure to provide feedback via electrical signals to a user which are essential for evaluating the health of the structure. In this research, the conductive fiber was made from constantan wire which was embedded within a composite laminate; whereas prepreg fiberglass, a nonconductive material, serves as the main structural element of the laminate. A composite laminate was constructed from four layers of TenCate 7781 “E” fiberglass and BT250E-1 resin prepreg. Integrating the constantan within the composite laminate provides a sensory element which supplies measurements of structural behavior. Thus, with fiberglass, epoxy, and a constantan conductive element, a three-part composite laminate is developed.
Test specimens used in this research were fabricated using a composite air press with the recommended manufacturer cure cycle. A TenCate BT250E-1 Resin System and 7781 "E" impregnated glass-fiber/epoxy weave was used. A constantan wire of 0.01” gauge diameter was integrated into the composite structure. The composite laminate specimen with the integrated SHM system was tested under tensile and flexural loads employing test standards specified by ASTM D3039 and D7264, respectively. These test methods were modified to determine the behavior of the laminate in the elastic range only. A tension and flexural delamination test case was also developed to investigate the sensitivity of the SHM system to inherent defects. Moreover, material characteristic tests were completed to validate manufacturer provided material characteristics. The specimens were tested while varying the constantan configurations, such as the sensor length and orientation. A variety of techniques to integrate the sensor were also investigated. Two different measurement methods were used to determine strain. Strain measurements were made with Instron Bluehill 2 software and correlated to strain obtained by the structural health monitoring system with the use of a data acquisition code written to interact with a micro-ohm-meter.
The experimental results showed good agreement between measurements made by the two different methods of measurement. Observations discovered that varying the length of the sensor element improved sensitivity, but resulted in different prediction models when compared to cases with less sensor length. The predictions are based on the gauge factor, which was determined for the each test case. This value provides the essential relationship between resistance and strain. Experiments proved that the measured gauge factor depended greatly on the sensor length and orientation. The correlation was of sufficient accuracy to predict strain values in a composite laminate without the use of any added tools or equipment besides the ohm-meter.
Analytical solutions to the loading cases were developed to validate results obtained during experiments. The solutions were in good agreement with the experimental results.
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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.
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Emery, Trystan Ross. "Identification of damage in composite materials using thermoelastic stress analysis." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/51292/.
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A quantitative damage assessment methodology for composite materials has been achieved using Thermoelastic Stress Analysis (TSA). The TSA technique provides fullfield data which is collected in a non-contacting and real time manner. The damage assessment methodology proposed requires a means of calibrating and temperature correcting the thermoelastic signal; these are developed and presented in this thesis. The thermoelastic theory for calibrating thermoelastic data from orthotropic bodies has traditionally been based on a stress formulation. There are difficulties in calibrating orthotropic materials in this manner and an alternative calibration routine has been devised and validated. The calibration routine provides the thermoelastic theory as a function of strain and permits a simplified calibration route as the laminate strains are the basis and can be measured in a straightforward manner. During damage propagation in laminated structures the specimen heats. The increase in temperature has a significant effect on the thermoelastic data and necessitates that the thermoelastic data be corrected to remove the effect of temperature from the data. A routine is developed that enables the correction of the thermoelastic data in a point-bypoint manner. By combining the strain calibration and temperature correction procedures a damage assessment methodology has been devised. The application of the methodology is demonstrated on glass / epoxy laminate specimens that are fatigue damaged and the damage state assessed using this method; the extent and type of damage is verified qualitatively using visual inspection methods. The work described is applicable to any orthotropic material. The effect of fatigue damage is assessed by periodically collecting thermoelastic data during the specimen life. This data is analysed using damage metrics based on the calibrated strain obtained from the TSA. The wider application of the TSA damage assessment methodology is considered by assessing the ability to locate subsurface damage. A complementary IR technique is used in conjunction with TSA known as Pulse Phase Thermography (PPT). Initial studies demonstrate the ability to resolve the spatial extents of subsurface damage. The purpose of this step is to guide TSA to areas of concern that can subsequently be assessed using the damage metrics to characterise the effect of damage on the residual life of the component. The strain calibration and temperature correction methods that enable TSA to be applied quantitatively to damaged composite materials have not been accomplished prior to this work. They provide novel methods by which TSA data can be assessed, and their application is not restricted to damage studies alone. The ability to temperature correct TSA data has been shown to be of vital importance if thermoelastic data is to be compared in a quantitative fashion. The strain calibration procedure presented will enable thermoelastic studies to be reported quantitatively and expand the application of TSA particularly in validation studies. The damage assessment methodology presented represents a step forward in the application of TSA to the damage assessment of composite materials.
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Taylor, Joshua Michael. "Nonlinear analysis of steel frames with partially restrained composite connections and full or partially composite girders." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19272.
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Tenek, Lazarus. "Finite-element natural-mode analysis of arbitrary composite shells." Thesis, University of Westminster, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339247.
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Subramaniam, C. "Chemorhelogical Modeling Of Amine-Cured Multifunctional Epoxy Resin Systems Used As Matrices In Aerospace Composites." Thesis, Indian Institute of Science, 1994. http://hdl.handle.net/2005/127.
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High performance multifunctional epoxy resin systems are becoming increasingly important as matrix materials for the advanced composites used in aerospace, electronics, automotive and other industries. In a composite based on epoxy resin systems, a three-dimensional network of the matrix is formed around the reinforcing fibre as a result of the chemical reaction between the resin and the curing agent. This chemical process, known as curing, is an important event to he considered in the production of composite components made up of these resin systems. Two process parameters namely viscosity and chemical conversion are of paramount significance in the production of composite materials Curing studies of the resin systems based on these two parameters, would therefore assume great importance in deciding the performance reliability of the end product.
The objectives of the present investigation are
1. to study the cure kinetics of three thermoset resin systems, viz.,
i) epoxy novolac (EPIT)/ diamino diphenyl methane{DDM), ii) trigylcidyl para- ammo phenol (TGPAP)/toluene diamine (TDA) and iii) tetraglycidyl diamino diphenyl methane (TGDDM)/pyridine diamine(PDA) using the cure kinetic models based on chemical conversion (α), Theological conversion (β) and viscosity.
2.to develop a correlation between a and viscosity (η) and modify an existing autocatalytic model based on α, to the viscosity domain and
3.to investigate the cure behaviour of these systems in terms of the TTT cure diagram and its associated models.
EPN/DDM, TGPAP/PDA and TGDDM/PDA resin systems were chosen for the studies to represent a range of functionalities, The cure was monitored using differential scanning calorimetry (DSC), fourier transform infrared (FTIR) and dynamic mechanical analysis (DMA) techniques by following the changes in enthalpy, functional groups and rheology, respectively.
The kinetic parameters namely, order of reaction and activation energy were estimated from dynamic DSC data using the methods of Freeman-Carroll and Ellerstein using nth rate expression. Barton, Kissinger and Osawa methods were employed to find out the activation energy from the peak/equal conversion at different heating rates. Isothermal DSC data were also analyzed using nth order model and it was observed that the data could be fitted satisfactorily only for higher temperatures The results obtained from the analysis of both dynamic and isothermal DSC data using nth order model clearly indicate that this model is inadequate for describing the cure behavior. The isothermal DSC data was analyzed by the autocatalytic models of Hone and Kamal Good correlation was observed with Hum and Kamal models up to 60-70%, 25% and 45% conversions for EPN/DDM, TGPAP/TDA and TCDDM/PDA systems respectively. However, the parameters m and n in Kamal model were found to be temperature dependent for EPN/DDM and TCPAP/TDA systems. The limited applicability of the autocatalytic models IK attributed to the counter-effect offered by the intra-molecular bonding taking place.
The primary amine and epoxy groups conversions obtained from FTIR were analyzed using autocatalytic model and the kinetic parameters were calculated. The reactivity ratio of the primary amine and the secondary amine with epoxy was found to be dependent on temperature in agreement with the recent findings reported m the literature.
The existing models that relate the cure kinetics and the rheological changes, are dual Arrhenius nth order model and autocatalytic model The nth order kinetic model was used to evaluate the kinetic parameters using the viscosity data at different cure temperatures under isothermal conditions As the storage modulus, G' is proportional to the chemical cross links and becomes significant only after the g<4 point, it was used to follow the changes in conversion known as rheoconversion after the gel point The rheoconversion was found by normalizing the G' data with G1^, the storage modulus of the fully cured resin It was used to study the cuie kinetics using an autocatalytic model The kinetic parameters such as rate constant, acceptation and retardation parameters were evaluated and that temperature dependence was established.
While the existing models relate viscosity and conversion only up to gel point the new proposed model, termed VISCON model takes into account the changes up to vitrification. The relation so developed is used to modify the autocatalytic cure model based on chemical conversion. The parameters appearing in this model were evaluated using Levenberg-Marquardt error minimization algorithm. The kinetic parameters obtained are comparable with the values estimated using the DSC data.
All the models cited above represent the microkinetic aspects. The models based on the information of TTT cure diagrams, however, represent the macrokinetic aspects of the cure, as they are based on the cure stages such as gelation and vitrification TTT diagram relates the cure characteristics like cure temperature, cure time, Ta and, indirectly, chemical conversion Hence the ultimate properties of the composite could he predicted and established with the help of the models based on TTT cure diagrams The changes in the storage modulus, G1 and loss modulus, G", were followed to identify the gel and vitrification points of the resin systems at different cure temperatures Gel point and vitrification point were used to generate gelation and vitrification hues in the construction of TTT cure diagrams for EPN/DDM, TGPAP/TDA and TGDDM/PDA resin systems Theoretical TTT diagrams were generated and IBO-T, contours were established using the TTT diagram-based models The cure schedule for the resin systems investigated could be determined from the TTT diagram and the respective rheological data.