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Dissertations / Theses on the topic 'Composite materials. Stress waves'

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Published: 4 June 2021
Last updated: 6 February 2022

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1

Tasdemirci, Alper. "Experimental and modeling studies of stress wave propagation in multilayer composite materials." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 11.67 Mb., 261 p, 2006. http://wwwlib.umi.com/dissertations/fullcit/3200525.

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2

Madhav, Arun. "Statistical methods applied to acousto-ultrasonic technique." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45791.

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The growth in the extent of applications of composite materials, particularly in commercial products, has been dramatic and carries an implied mandate for effective methods for material quality evaluation. The cost of composite materials dictates that non-destructive test methods be used. At the same time, the nature of composites limits the use of conventional techniques such as radiography , eddy-current or ultrasonics. Recently, a new technique known as the Acousto-Ultrasonic (AU) technique, has been developed and appears to hold promise as a method for the evaluation of composite material quality.

Implementation of the AU method is examined using the zeroth moment method developed by Henneke et.al. A new parameter termed as Acousto Ultrasonic Factor (AUF) has been defined for this purpose. The behavior of the AUF response to specimens of known quality is investigated statistically. It is found that the transformed/actual readings follow a Beta distribution and that specimens of different quality are readily distinguishable using the statistical analysis of the AUF response. Reasonable future steps for translating these findings into efficient quality evaluation methods have been suggested.Master of Science

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Jain, Jayesh R. "Homogenization Based Damage Models for Monotonic and Cyclic Loading in 3D Composite Materials." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1230431496.

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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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Seale, Michael David. "Propagation of guided acoustic waves in composite media." W&M ScholarWorks, 1996. https://scholarworks.wm.edu/etd/1539623884.

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Composite materials are being more widely used today by aerospace, automotive, and a number of other commercial industries because of their advantages over conventional metals. Composites are finding applications ranging from bicycle frames to the proposed High-Speed Civil Transport (HSCT). Determining the response to a variety of damage mechanisms is necessary for a complete understanding of the total use environment of composite structures. The objective of the research presented here is to provide a method of quantifying the amount of damage in composite materials for a number of different damage scenarios. Components which have non-visible damage, but have degraded performance, are of interest. at this level of damage, the safety margin designed into the structure may be compromised.;Nondestructive Evaluation (NDE) is a field of measurement physics where energy is imparted to a material and information is obtained from observing how the energy interacts with the system. Many different forms of energy can be used to obtain useful information from these measurements: acoustic, thermal, x-ray, optical, and electromagnetic. Among the many various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating these composite materials. as a material is damaged, the elastic parameters of the structure change. Since the Lamb wave velocity depends on these properties, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Additionally, Lamb wave measurements are beneficial because they can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material.;Presented in this study are the results involving the investigation of a variety of damage mechanisms (fatigue, thermal, and thermal-mechanical) using the Lamb wave technique. Two fatigue studies were conducted which showed that the change in modulus and change in velocity of the Lamb wave squared follow the same general trend. The Lamb wave velocity was also observed to decrease with increasing crack density. For the thermal damage study, the results showed that the velocity of the lowest order symmetric Lamb mode dropped significantly for extended thermal damage. When the experimental results were compared to model calculations, good agreement was observed for both fatigue and thermal damage. Finally, for thermal-mechanical damage, it was found that the Lamb wave technique was also able to predict a local defect in a specimen, which was later found to have a large delamination zone.;The Lamb wave velocity is a quantitative measurement and it has been shown by this work to be an effective tool in monitoring different types of damage in composites. Since the Lamb wave velocity depends on a variety of material properties, an ideal technique exists to monitor composites as damage is incurred. With the continued development of damage assessment techniques such as the Lamb wave method, the safety of such structures can be assured.
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6

Li, Rufeng. "Nonlinear viscoelastic stress and fracture analyses of laminated composites /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9978.

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7

Choi, John O. "Dynamic stress intensity factors in orthotropic materials." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12409.

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8

Fung, Kin-Hung. "Phononic band gap of locally resonant sonic materials with finite thickness /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202004%20FUNG.

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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 73-74). Also available in electronic version. Access restricted to campus users.
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9

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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Kiernan, Michael T. "An acousto-ultrasonic system for the evaluation of composite materials." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/76441.

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A presentation is given of an acousto-ultrasonic system for the evaluation of composite materials. First, a brief statement will be made on the acousto-ultrasonic technique and its relative worth compared to other nondestructive testing techniques as applied to composite materials. The following two chapters describe the system instrumentation and system software, respectively. Next, comments are given regarding the implementation of the system for research on graphite/epoxy laminates, with additional remarks concerning efforts to evaluate aluminum/graphite tubes with the system. This includes physical descriptions of the composite systems. Subsequently, results are presented comparing parameters and forms of presentation which can be employed to relate results. Finally, conclusions are made on the application of the acousto-ultrasonic system to nondestructive testing of composite materials, with specific results on its application to graphite/epoxy plates. More specifically, comments are made on the variation of SWF factors with azimuthal angle on the graphite/epoxy plates, the identification of specific frequency peaks, and the relationships these may have to certain modes of vibration and material properties. For example, a low frequency mode was found to vary in a manner reminiscent of Ex and to show characteristics of an extensional Lamb wave. In general, results are presented and discussed in order to show how the system can be implemented to gain physical information on composite materials, such as the property of anisotropy.
Master of Science
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11

Lee, Seung-Woo. "Computational electromagnetic approaches for the analysis of rough surface scattering and artificial composite materials /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/5997.

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Fruhmann, Richard Konrad. "Stress and damage assessment in woven composite materials by means of thermoelastic stress analysis." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72146/.

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The work described in this thesis considers the application of thermoelastic stress analysis (TSA) to assess stresses and damage in woven composite materials. Woven composite materials oer high specic strength and stiness, while being well suited to low cost manufacturing techniques. This makes them a cost eective material for weight critical structural applications. The weave, however, introduces stress concentrations at the meso-scale which are critical to damage initiation. Experimental techniques are therefore required to assess the severity of stress concentrations and damage. TSA is an infrared (IR) technique which uses the thermoelastic eect to obtain measurements related to the stresses within a material. The non-contacting nature of TSA make it ideal for studying components with non-uniform stress elds. In this work, a new IR detector system for TSA is introduced which provides radiometric calibration, high frame rates and a motion compensation routine, essential for studying the thermoelastic response at small scales. This has enabled TSA to be conducted at the scale of the individual yarns in woven composites. A simple model has been used to predict the thermoelastic response from individual yarns. This has revealed that careful determination of the material properties is critical for accurate predictions, and that the use of literature values, as has been done in the past, can lead to misleading results. Thus it is shown that the response from a woven composite originates from the yarns, rather than a surface resin layer, and that the non-uniform strain eld manifests itself strongly in the TSA data. The work then investigates the development of fatigue damage in woven composites. This has shown that damage can initiate at stress levels as low as 10% of the ultimate failure stress in single ply composites. Using the high resolution optics and motion compensation it has been possible to follow the development of matrix cracks in individual yarns. A signature pattern in the TSA data is dened that enables the matrix cracks to be clearly identied. For TSA to be applied as a tool for non-destructive testing of in-service structures, it is essential that simple procedures are developed and that the equipment is portable. To facilitate the more widespread uptake of TSA, the feasibility of using a simplied means of introducing a load into a component was investigated. It was demonstrated that a single transient excitation can be used to obtain a TSA measurement. The work described in this thesis thereby demonstrates that TSA can be applied to study stresses and damage in inhomogenous materials. The feasibility of using a simplied loading methodology is proven. The study thereby represents a signicant step towards an improved understanding of TSA and increasing its application range.
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Chow, Wai Tuck. "Calculation of stress intensity factors for an interfacial crack." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/21286.

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Zhao, Huyue. "Stress Analysis of Tapered Sandwich Panels with Isotropic or Laminated Composite Facings." Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/ZhaoH2002.pdf.

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Owens, Anthony Taylor Tippur Hareesh V. "Development of a split Hopkinson tension bar for testing stress-strain response of particulate composites under high rates of loading." Auburn, Ala., 2007. http://repo.lib.auburn.edu/Send%2002-04-08/OWENS_ANTHONY_54.pdf.

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Treiber, Martin Paul. "Characterization of cement-based multiphase materials using ultrasonic wave attenuation." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26588.

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Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Jacobs, Laurence J.; Committee Member: Kim, Jin-Yeon; Committee Member: Qu, Jianmin. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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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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18

Wei, Bo-Siou. "Thermoelastic stress analysis techniques for mixed mode fracture and stochastic fatigue of composite materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24818.

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Thesis (Ph.D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Rami Haj-Ali; Committee Member: Arash Yavari; Committee Member: Bruce R. Ellingwood; Committee Member: Kenneth M. Will; Committee Member: Richard W. Neu.
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Tong, Y. "The low velocity impact fatigue and stress relaxation behaviour of composite materials." Thesis, Swansea University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639251.

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The low velocity impact, tension-tension fatigue and stress relaxation behaviour of glass fibre and natural fibre composites were investigated. For glass fibre composites, two fibre architectures ([±45o]4 and [0/90o]2s) and two matrix resins (polyvinyl-ester and polyester) were used. Non-woven randomly oriented hemp fibre mat was used as reinforcement of natural fibre composites. The effects of low velocity impact on residual tensile properties, fatigue life and modulus degradation behaviour during cyclic loading were investigated. Damage mechanisms of the composites during impact and fatigue loading were discussed. It was found that modulus degradation behaviour of composites was strongly dependent on the reinforcing fibres and their architecture. Multistage modulus degradation behaviour with gradual reduction in modulus was observed during fatigue loading of [±45o]4 glass fibre composites. For hemp fibre composites, however, no decrease in modulus was observed before final fatigue failure. Low velocity impact did not significantly change the modulus degradation behaviour of composites during fatigue loading. Since the normalized S-N curves for undamaged and impacted samples superimposed, the fatigue life of impact damaged composites could be predicted from knowledge of the S-N curve of non-impacted composites and the static residual strength of impact damaged composites. Stress relaxation curves of [±45o]4 and [0/90o]2s glass fibre composites were compared, and the effects of initial stress, impact damage, fatigue loading and the combination of impact and fatigue were investigated. Mechanisms of stress relaxation of composites were discussed. Stress relaxation curves of the glass fibre composites could be modelled by a simple logarithmic equation. Stress relaxation tests were found useful to characterise the loading history of composites.
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Garza, Rodriguez Carlos. "Deep-hole drilling measurements of residual and assembly stress in composite materials." Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720824.

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Hopkinson, David P. "Development of stress gradient enhanced piezoelectric composite unimorph actuators." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16372.

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Shady, Ebraheen Hassan E. H. Gowayed Yasser. "Stress mapping of textile composite materials and its application in interfacial shear behavior." Auburn, Ala., 2005. http://hdl.handle.net/10415/1272.

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Dutta, Monojit. "Residual stress measurement in engineering materials and structures using neutron diffraction." Thesis, Open University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301945.

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Al-Ramahi, Nawres. "Numerical stress analysis in hybrid adhesive joint with non-linear materials." Licentiate thesis, Luleå tekniska universitet, Materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67293.

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This thesis presents systematic numerical study of stresses in the adhesive of a single-lap joint subjected to various loading scenarios (mechanical and thermal loading). The main objective of this work is to improve understanding of the main material and geometrical parameters determining performance of adhesive joint for the future analysis of failure initiation and development in these structures. The first part of the thesis deals with development of a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates). The model takes into account the nonlinearity of materials (adherend and adhesive) with geometrical nonlinearity also accounted for. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criteria and it allows separation of edge and end effects. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters is carefully examined by analyzing peel and shear stress distributions in the adhesive layer. Discussion and conclusions with respect to the magnitude of the stress concentration at the ends of the joint overlap as well as overall level of stresses within overlap are presented. Recommendations concerning use of nonlinear material model are given. The rest of the work is related to the various methods of manufacturing of joint (curing) and application of thermo-mechanical loading suitable to these scenarios. The appropriate sequences of application of thermal and mechanical loads for the analysis of the residual thermal stresses developed due to manufacturing of joints at elevated temperature required to cure polymer (adhesive/composite) are proposed. It is shown that the most common approach used in many studies of simple superposition of thermal and mechanical stresses works well only for linear materials and produces wrong results if material is non-linear. The model and simulation technique presented in the current thesis rectifies this issue and accurate stress distributions are obtained. Based on the analysis of these stress distributions the following conclusions can be made: joint processing at elevated temperature causes high stresses inside the adhesive layer; the residual thermal stresses will reduce the peel stress concentration at the ends of overlap joint and the shear stress within the overlap, moreover, this effect is more pronounced for the case of the one-step joint manufacturing in comparison with two-step processing technique. This study has generated a lot of results for better understand of behavior of adhesive joints and it will help in design of stronger, more durable adhesive single-lap joints in the future.
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Bruhschwein, Taylor John. "Identification of Delamination Defects in CFRP Materials through Lamb Wave Responses." Thesis, North Dakota State University, 2014. https://hdl.handle.net/10365/27328.

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Delamination is currently a largely undetectable form of damage in composite laminate materials. This thesis will develop a method to more easily detect delamination damage within composite materials. Using finite element analysis modeling and lab testing, a new method from interpreting the results obtained from existing structural health monitoring techniques is developed. Lamb waves were introduced and recorded through an actuator and sensors made of piezoelectric material. The data was then analyzed through a novel data reduction method using the Fast Fourier Transform (FFT). Using the data from FFT, the idea of covariance of energy change was developed. By comparing the covariance of energy change in beams with differing delamination size, thickness and depth, correlations were able to be developed. With these correlations, the severity and of damage was able to be detected.
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Shinall, Brian Darnell. "Using surface plasmon resonance spectroscopy to characterize thin composite films." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/10157.

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Sepasdar, Reza. "A Deep Learning Approach to Predict Full-Field Stress Distribution in Composite Materials." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103427.

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This thesis proposes a deep learning approach to predict stress at various stages of mechanical loading in 2-D representations of fiber-reinforced composites. More specifically, the full-field stress distribution at elastic and at an early stage of damage initiation is predicted based on the microstructural geometry. The required data set for the purposes of training and validation are generated via high-fidelity simulations of several randomly generated microstructural representations with complex geometries. Two deep learning approaches are employed and their performances are compared: fully convolutional generator and Pix2Pix translation. It is shown that both the utilized approaches can well predict the stress distributions at the designated loading stages with high accuracy.
M.S.
Fiber-reinforced composites are material types with excellent mechanical performance. They form the major material in the construction of space shuttles, aircraft, fancy cars, etc., the structures that are designed to be lightweight and at the same time extremely stiff and strong. Due to the broad application, especially in the sensitives industries, fiber-reinforced composites have always been a subject of meticulous research studies. The research studies to better understand the mechanical behavior of these composites has to be conducted on the micro-scale. Since the experimental studies on micro-scale are expensive and extremely limited, numerical simulations are normally adopted. Numerical simulations, however, are complex, time-consuming, and highly computationally expensive even when run on powerful supercomputers. Hence, this research aims to leverage artificial intelligence to reduce the complexity and computational cost associated with the existing high-fidelity simulation techniques. We propose a robust deep learning framework that can be used as a replacement for the conventional numerical simulations to predict important mechanical attributes of the fiber-reinforced composite materials on the micro-scale. The proposed framework is shown to have high accuracy in predicting complex phenomena including stress distributions at various stages of mechanical loading.
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Amini, Niaki Sina. "A three-phase integrated flow-stress framework for process modelling of composite materials." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63081.

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An accurate and efficient predictive tool for process modelling of fibre-reinforced polymeric composite materials is highly desirable because of high production cost and substantial risk involved in their manufacturing. Process modelling of composite materials is complex due to multitude of physical and chemical processes such as flow of resin and gaseous volatiles through the fibre-bed, thermochemical changes, and stress development. These phenomena are usually simulated sequentially in a so-called “integrated sub-model” framework. In the sequential method, (i) mapping of the results from one state to another is performed in a tedious and inefficient process, (ii) the concurrent occurrence of resin flow and stress development is ignored, (iii) the history of pressure during the flow regime of processing is relinquished, and (iv) the local spatial and temporal variations in resin gelation is not captured. Incorporating the main steps of process modeling into a unified module that captures the various phenomena in a continuous manner would help overcome the foregoing drawbacks of the sequential approach. In this thesis, a new methodology is presented to integrate the simulation of resin and gas flow and stress development into a unified computational modelling framework. The governing equations are developed for the general case of a composite system that initially is regarded as a three-phase liquid-gas-solid system and, as a consequence of curing, the resin undergoes a transition from a fluid-like state into an elastic solid forming a solid cured composite material. The employed constitutive equations provide a continuous representation of the evolving material behaviour while maintaining consistency with the formulations that are typically used to represent the material at each of the two processing extremes. The model is implemented in a 2D plane strain displacement-velocity-pressure (u-v-P) finite element code developed in MATLAB. Various numerical examples are presented to demonstrate the capability of the Integrated Flow-Stress (IFS) model to predict the flow-compaction and stress development throughout the curing process of thermoset composite materials. The interactive effects of resin flow, gas flow, and stress development are investigated and comparisons are made with the predicted results obtained from the application of the stress model alone.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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MOUANE, KHALID. "Polyimide thin-ply composite." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-70118.

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Mechanical performance of composite structures is influenced by the accumulation of damage from the manufacturing process and throughout the whole service life. For instance, an aircraft is subjected to a combination of mechanical loading and the thermo-oxidative environment from the take-off to the landing. Therefore, this degree project consists of studying the damage initiation and evolution in carbon fibre reinforced polyimide composites and assesses the thickness effect of the laminated composites. After manufacturing, the level of residual thermal stresses occurring at room temperature lead to the occurrence of microcracks in bundles of the quasi-isotropic composites. Further cooling to cryogenic temperature creates new cracks were appearing. This reinforces the conclusion that cracks are created due to thermal stresses. Comparison between a baseline composite made of carbon fibre T650 8-harness satin weave with thermosetting polyimide resin (ply thickness= 190µm) and thin-ply textile laminate made of Textreme carbon fibre IMS65 (ply thickness=83µm) with the same resin shows that the ply thickness has a significant effect on suppressing or delaying the occurrence and the propagation of microcracks after mechanical loading. It is assumed that there are some edge effects leading to different damage state in 90° and ±45° layers.
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Kamf, Tobias. "High speed flywheel design : Using advanced composite materials." Thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-181256.

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This thesis is a part of a larger project that focuses on the development of a highspeed, high energy flywheel using both high-tech composites and levitating magneticbearings alongside a custom made, permanent magnetized generator built into theflywheel itself. The goal of the project is then to integrate this flywheel into anelectrical vehicle.The main focus of this thesis is the composite material. The composite is to be usedas a shell around the flywheel rotor. This composite shell fills two purposes. The firstis to act as the main energy carrying material, storing above 75% of the total energy inthe flywheel. The second purpose it to strengthen the machine, holding it together.This so that higher speeds than normally possible can be achieved, with the goal beingset to 30 000rpm.In order to be able to design the composite shell correctly a method of calculating theload stresses had to be developed. This was done by the creation of a Matlabprogram, named Spin2Win, capable of calculating the stresses inside a compositemetal hybrid flywheel. Using said Matlab code, combined with modelling andsimulations from SolidWorks, a fully-fledged flywheel was designed complete withdrawings and material specifications.The composite analysis surprisingly shows that the best combination of compositematerials is a mixture of both high strength carbon fibres alongside softer glass fibrescoupled with the weight of the central core. This allowed for control of the radialstresses which was shown to otherwise be the limiting factor when designing rotatingcomposite materials.One of the most interesting, and perhaps even unique, parts of the design is that theelectrical machine has been integrated into the flywheel’s composite shell. Having thetwo entities working together in order to control the radial stresses in thecomposite, by utilizing the weight of the permanent magnets.
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Vuppala, Archana. "Thermal and thermal stress analyses of the state-changing tooling." abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1460787.

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32

Caliskan, Ari Garo. "Micromechanics-based approach to predict strength and stiffness of composite materials." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-09052009-041025/.

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33

Lhotellier, Frederic C. "Matrix-fiber stress transfer in composite materials elasto-plastic model with an interphase layer." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/40934.

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The matrix-fiber stress transfer in glass/epoxy composite materials was studied using analytical and experimental methods. The mathematical model that was developed calculates the stress fields in the fiber, interphase, and neighboring matrix near a fiber break. This scheme takes into account the elastic-plastic behavior of both the matrix and the interphase, and it includes the treatment of stress concentration near the discontinuities of the fibers. The radius of the fibers and the mechanical properties of the matrix were varied in order to validate the mathematical model. The computed values for the lengths of debonding, plastic deformation, and elastic deformation in the matrix near the fiber tip were confirmed by measurements taken under polarized light on loaded and unloaded single fiber samples. The fiber-fiber interaction was studied experimentally using dog-bone samples that contained seven fibers forming an hexagonal pattern.


Master of Science
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34

Call, Russell Kent. "Parameter establishment and verification of a fabrication stress model and a thermo-kinetic cure model for filament wound structures." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08142009-040256/.

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35

Asmar, Ghazi H. "Stress analysis of anisotropic plates containing rectangular cuts /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9901214.

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36

Jongchansitto, Pawarut. "Mechanical analysis of 2D composite granular materials : thermomechanical experiments and numerical simulations." Thesis, Clermont-Ferrand 2, 2015. http://www.theses.fr/2015CLF22592/document.

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L'objectif de la thèse est d'analyser le comportement mécanique de matériaux granulaires composites bidimensionels en terme de textures granulaires en utilisant deux approches : étude expérimentale par "thermoelastic stress analysis" et étude numérique par dynamique moléculaire. Les systèmes granulaires composites sont préparés à l'aide de cylindres en polyoxyméthylène (POM) et polyéthylène haute densité (PEHD), présentant un rapport de rigidité de 4 entre eux. Différents rapports de diamètres et de nombres de particules sont considérés. Les résultats expérimentaux et numériques sont en bon accord à l'échelle macroscopique. En particulier, le réseau fort (qui est ici caractérisé par des contraintes hydrostatiques supérieures à la valeur moyenne) contient moins de 50% des particules, et présente une distribution décroissance exponentielle quel que soit le type de particules considéré pour l'analyse (particules souples, particules rigides, toutes les particules). De plus, la distribution des contacts entre particules rigides (contacts POM-POM) est anisotrope et tend à s'organiser dans le sens de la direction du chargement extérieur appliqué, tandis que les autres types de contact agissent principalement pour maintenir le système en équilibre
The main objective of our dissertation is to analyze the mechanical behavior of two-dimensional composite granular materials through the granular textures. Thermoelatic stress analysis experiments and molecular dynamics simulations are used for this purpose. The composite granular systems are prepared from polyoxymethylene (POM) and high-density polyethylene (HDPE) cylinders with a stiffness ratio of about 4 between them. Different configurations in terms of ratios of diameter size and ratio of particle numbers are systematically investigated. Experimental and numerical results are good correlated at the macroscopic scale. In particular the strong network, which is here characterized by hydrostatic stresses higher than the mean value, consists of less than 50% of all particles, and exhibits an exponential decay whatever the type of particles considered for the analysis (soft, stiff, or both types). In addition, the contact distributions between stiff particles (POM-POM contacts) is anisotropic with an effort to arrange parallel to the direction of the external applied load, whereas the other types of contacts just act to sustain the granular system in equilibrium
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37

Hsu, Sheng-yuan. "On the prediction of compressive strength and propagation stress of aligned fiber-matrix composites /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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38

Joven, Pineda Ronald Vicente. "Characterization and modeling of shear stress during manufacturing and thermal properties of structural composite materials." Diss., Wichita State University, 2013. http://hdl.handle.net/10057/6383.

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39

Katepalli, Nagababu Lankarani Hamid M. "Parametric study of stress concentration in bolted lap joints between particulate metal matrix composite materials." Diss., A link to this thesis in SOAR, 2006. http://soar.wichita.edu/dspace/handle/10057/660.

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Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.
"December 2006. Title from PDF title page (viewed on August 17, 2007). Thesis adviser: H.M. Lankarani. Includes bibliographic references (leaves 84-86).
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40

Joven, Ronald. "Characterization and modeling of shear stress during manufacturing and thermal properties of structural composite materials." Diss., Wichita State University, 2013. http://hdl.handle.net/10057/6383.

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An experimental methodology is presented to determine tool-part frictional interaction of composite parts and the structural integrity of sandwich structures when subjected to temperatures and pressures similar to those of autoclave processing. This methodology includes the development of a testing rig that mimics the deformation mismatch between tools and parts, and quantifies shear stress—that is, tool-part friction or shear stress of sandwich structures. Discrete and continuous friction characterization was performed to validate this testing methodology, and a semiempirical mathematical model was obtained to predict the tool-part frictional interaction as a function of different manufacturing variables including temperature, pressure, and part length. Moreover, a characterization of the shear strength of sandwich structures is presented where results indicate a strength decrease when temperature and pressure increase following an inverse-exponential trend for both cases. Furthermore, an alternative methodology to measure thermal properties of composite materials by radiation known as light flash analysis (LFA) is used to characterize diffusivity, conductivity, and specific heat of composite materials tested at typical manufacturing temperatures. Accordingly, this research portrays the mathematical considerations required for the testing of anisotropic materials. Thermal properties of cured composite samples with three different fabric weaves and two resin formulations were obtained, and results indicate that conductivity, diffusivity, and density are strongly influenced by testing temperature, fiber configuration, and fiber volume fraction.
Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering
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41

Zamorovskii, Vlad. "Composite materials filled with ferromagnetic microwire inclusions demonstrating microwave response to temperature and tensile stress." Thesis, University of Plymouth, 2017. http://hdl.handle.net/10026.1/9488.

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Amorphous and polycrystalline microwires cast from ferromagnetic Fe-based or Co-based alloys in glass envelope demonstrate unique magneto-anisotropic and high frequency impedance properties that make them very attractive for sensor applications. Magnetic anisotropies of different types result from the inverse magnetostriction effect (positive or negative) at the interface between the glass shell and the metal core, in the presence of the residual stresses induced during the Taylor-Ulitovski casting method. Therefore, the glass shell is not just isolation, but also is one of most important factors that defines the physical properties of microwires. In particular, magnetic anisotropy allows high frequency impedance to be tuned by external stimuli such as magnetic field, tensile stress, or temperature. In the project, these effects are explored for the creation of low density microwire inclusions that might introduce tuneable microwave properties to polymer composite materials. The project aims to study high frequency impedance effects in ferromagnetic wires in the presence of tensile stress, temperature, and magnetic field. The integration of microwave equipment with mechanical and thermal measurement facilities is a very challenging task. In the project, we develop new experimental techniques allowing comprehensive study of composite materials with electromagnetic functionalities. The wire surface impedance recovered from such measurements can then be used to model the microwave response from wire-filled composites in free space. The obtained results significantly expand the horizon of potential applications of ferromagnetic wires for structural health monitoring.
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42

Mikucka, Vita. "Dynamic problems for interface cracks under harmonic loading." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=228606.

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This thesis is devoted to solution of the two-dimensional elastodynamic problem for a cracked bimaterial loaded by harmonic waves. The system of boundary integral equations for displacements and tractions at the interface is obtained from Somigliana identity with the allowance for the contact interaction of the opposite crack faces. Full expressions of the integral kernels derived by the consecutive differentiation of the Green's displacement tensor are given. Due to the contact that takes place between the faces of the crack under the applied external loading, the resulting process is a steady-state periodic, but not a harmonic one. Thus, components of the stress-strain state are expanded into exponential Fourier series. The collocation method with a piecewise constant approximation on each linear continuous boundary element is used for the numerical solution. The problem is solved using the iterative algorithm. The solution is refined during the iteration process until the distribution of physical values satisfies the imposed constraints. The results are obtained for the interface crack subject to normal tension-compression, normal shear, or oblique tension-compression waves with different values of the angle of the wave incidence and the wide range of the dimensionless wave number. The distributions of the normal and tangential components of the contact forces and displacement discontinuities on the surface of the crack are investigated. The stress intensity factors are computed and analyzed for various values of the wave frequency, the friction coefficient, and material properties. The maximal stress intensity factors at the trailing crack tip differ from the SIF values at the leading crack tip showing non-symmetry of solution with respect the space and time variables. It is concluded that the crack closure and friction effect change the solution both qualitatively and quantitatively, as the difference between comparable results can achieve 30-50%.
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43

Angelides, Michael. "Stress compatible finite elements for bimaterial interface problems." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63808.

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44

Nair, Aravind R. "Characterization of thermo-mechanical and long-term behaviors of multi-layered composite materials." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1821.

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45

Ju, Jaehyung. "Design of a novel conduction heating based stress-thermal cycling apparatus for composite materials and its utilization to characterize composite microcrack damage thresholds." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4213.

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The objective of this research was to determine the effect of thermal cycling combined with mechanical loading on the development of microcracks in M40J/PMR-II- 50, the second generation aerospace application material. The objective was pursued by finding the critical controlling parameters for microcrack formation from mechanical stress-thermal cycling test. Three different in-plane strains (0%, 0.175~0.350%, and 0.325~0.650%) were applied to the composites by clamping composite specimens (M40J/PMR-II-50, [0,90]s, a unitape cross-ply) on the radial sides of half cylinders having two different radii (78.74mm and 37.96mm). Three different thermal loading experiments, 1) 23oC to –196oC to 250oC, 2) 23oC to 250oC, and 3) 23oC to -196oC, were performed as a function of mechanical inplane strain levels, heating rates, and number of thermal cycles. The apparatus generated cracks related to the in-plane stresses (or strains) on plies. The design and analysis concept of the synergistic stress-thermal cycling experiment was simplified to obtain main and interaction factors by applying 2k factorial design from the various factors affecting microcrack density of M40J/PMR-II-50. Observations indicate that the higher temperature portion of the cycle under load causes fiber/matrix interface failure. Subsequent exposure to higher stresses in the cryogenic temperature region results in composite matrix microcracking due to the additional stresses associated with the fiber-matrix thermal expansion mismatch.
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46

Rousseau, Carl Q. "Stresses and deformations in angle-ply composite tubes." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/51901.

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The objective of this study was to investigate, both experimentally and analytically, the stresses and deformations in angle-ply composite tubes subjected to axisymmetric thermal loading. For the theoretical portion, a generalized plane strain elasticity analysis was developed. The analysis included mechanical and thermal loading and temperature-dependent material properties. Using the elasticity analysis and a temperature range of 116 K to 450 K, stress levels were found to be high for the specific designs considered, compared to material failure levels. In addition, the use of temperature-dependent material properties was found to have a significant effect on the predicted stresses and deformations. The elasticity analysis was also used to study the effect of including a thin metallic coating on a graphite-epoxy tube. The stresses in the coatings were found to be quite high, exceeding the yield stress of aluminum. An important finding in the analytical studies was the fact that even tubes with a balanced-symmetric lamination sequence exhibited shear deformation or twist. The radial location of an off-axis ply was found to influence its effect on the overall torsional tube response. For the experimental portion, an apparatus was developed to measure torsional and axial response in the temperature range of 140 K to 360 K. Eighteen specimens were tested, combining three material systems, eight lamination sequences, and three off-axis ply orientation angles. For the twist response, agreement between analysis and experiment was found to be good. The axial response of the tubes tested was found to be greater than predicted by a factor of three. As a result of the study, it is recommended that the thermally-induced axial deformations be investigated further, both experimentally and analytically.
Master of Science
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47

Kiernan, Michael T. "A physical model for the acousto-ultrasonic method." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54214.

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A basic physical explanation, a model, and comments on NDE application of the acoustoultrasonic method for composite materials are presented. The basis of this work is a set of experiments where a sending and a receiving piezoelectric transducer were both oriented normal to the surface, at different points, on aluminum plates, various composite plates, and a tapered aluminum plate. Chapter one introduces the purpose and basic idea of the dissertation, while supporting its need. Also, general comments on the AU method are offered. The second chapter offers a literature review of areas pertinent to the dissertation, such as composite materials, wave propagation, ultrasonics, and the AU method. Special emphasis is given to theory which is used later on and past experimental results that are important to the physical understanding of the AU method. The third chapter describes the experimental set-up, procedure, and the ensuing analysis. In the fourth chapter, the experimental results are presented in both a quantitative and qualitative manner. Chapter five furnishes a physical understanding of experimental results based on elasticity solutions, Lamb wave theory, and through-the-thickness-transverse·resonance (TTTR). Computer results are presented for sake of comparison. The sixth chapter discusses modeling and applications of the AU method for composite materials and the seventh chapter states general conclusions. The unique offering of this work is the physical model of the AU method for composite materials, something which has been much needed and sorely lacking. This physical understanding is possible due to the extensive set of experimental measurements, also reported in this dissertation.
Ph. D.
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48

Mahieux, Celine Agnès. "Stress rupture of unidirectional polymer matrix composites in bending at elevated temperatures." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/45398.

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A new method for stress-rupture experiments in bending has been developed and used to characterize unidirectional polymer matrix composites. The method. which makes use of very simple fixtures, led to coherent results. These results have been modeled using the large deflection of buckled bars theory (elastica) and it is possible to predict with good accuracy the strain at each point of the specimen if the end-to-end distance is known. The failure process has been experimentally characterized. The formation and propagation of microbuckles leads to a compressive failure. Based on the elastica and the classical lamination theory, a model for the distribution of the Young's modulus along the length of the specimen has been established. Three different micromechanical models have been applied to analyze the time-to-failure versus strain behavior at two temperatures - one below and one above the glass transition. The first micromechanical model considers the nucleation of the microbuckles as the main cause of failure. In addition, the stiffness and stress distributions at any time before failure are calculated based upon the rotation of the fibers in the damaged region. The second and last models, respectively based upon a Paris Law and energy considerations relate the time-to-failure to the propagation of the main microbuckle. For this last model, a good correlation between experimental and theoretical data has been obtained. Finally the influence of the temperature on these models has been studied.


Master of Science
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49

Tsai, Ming-Yi. "Application of localized hybrid methods of stress analysis to some problems in the mechanics of composites." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39697.

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50

Shaabin, Maram. "The effect of inhibitor and initiator concentration on degree of conversion, flexural strength and polymerization shrinkage." Connect to resource online, 2009. http://hdl.handle.net/1805/2113.

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Thesis (M.A.)--Indiana University School of Dentistry, 2009.
Title from PDF t. p. (viewed Mar. 30, 2010) Advisor(s): Gabriel Tien-Min Chu, Chair of the Research Committee, Melvin R. Lund, Bruce A. Matis, Carlos Gonzalez-Cabezas, Michael A. Cochran. Curriculum vitae. Includes abstract. Includes bibliographical references (leaves 79-87).
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