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Dissertations / Theses on the topic 'Flexure'
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1
Vasquez, Daniel James. "Flexure-based nanomagnetic actuators." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1383481101&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Gojuri, Arun. "Stability of End Notched Flexure Specimen." Thesis, Högskolan i Skövde, Institutionen för teknik och samhälle, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-4487.
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This paper deals with two-dimensional Finite Element Analysis of the End Notched Flexure (ENF) specimen. The specimen is known to be unstable if the crack length is shorter than some critical crack length acr. A geometric linear two-dimensional Finite Element (FE) analysis of the ENF specimen is performed to evaluate acr for isotropic and orthotropic elastic materials, respectively. Moreover, the Mode II Energy Release Rate (ERR) JII and the compliance of the specimen are calculated. The influence of anisotropy is studied. Comparisons are made with the results from beam theory. This work is an extension of previous work.
3
Bildsten, Erika Margit. "Analysis of novel flexure-based joint." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74423.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 53).
As robots and other actuated mechanisms get smaller, so must their moving parts. A novel flexure-based joint was developed for Squishbot1 by a team at MIT, which can be made small (sub-cm), or much larger. Here, pseudo-rigid-body modeling is used in conjunction with the geometry of the joint mechanism in order to create analytic models of the forces at play in the joint, so as to better enable their design and use. Two mechanisms are analyzed: one in which the flexure is pinned to the moving legs, and one in which it is fixed. Systems of equations are generated for fixed flexure and pinned flexure joints, which are provided for the reader to use in order to develop their own mechanisms, and optimize them to their own applications. The fixed flexure, no leg contact model is tested for a particular configuration, and less than 3% error is found between the experimental and model data. The advancement of small (sub-cm) actuated mechanisms will push forward the development of small robots, and expand the terrains and applications in which robots can work.
by Erika Margit Bildsten.
S.B.
4
Barnett, D. N. "Convection, elasticity and flexure inside terrestrial planets." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596394.
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In this dissertation, the large-scale geophysical behaviour of the Earth, Venus and Mars are compared, using data collected by the Magellan spaceprobe (for Venus) and the Viking and Mars Global Surveyor (MGS) probes (for Mars). Neither Venus nor Mars show evidence of plate tectonics operating at the present day. On Venus, the lack of water means the frictional resistance at faults and the viscous drag on the base of the moving lithospheric plates are too high to be overcome by the driving forces for plate tectonics. The high elastic thickness of Mars results in a large frictional resistance to fault motion, although the faults themselves are probably no stronger than those on the Earth, and means large compressive stresses are required to initiate subduction. The likely high viscosity of the martian mantle, a consequence of its probable dryness and low temperature, may also result in large drag forces on the base of the lithosphere. Plate tectonics may have operated in the past on both planets, providing a possible explanation for the rapid resurfacing of Venus required by the crater counts and the linear magnetic anomalies recently discovered on Mars.
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Chen, Jay-San. "Standardisation of flexure testing of engineering ceramics." Thesis, University of Warwick, 2000. http://wrap.warwick.ac.uk/67042/.
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With the increase in usage of engineering ceramics, a new industrial standard is required in order to evaluate its properties and to perform a fair and just trade. The thesis investigates the faults and omissions of existing work and judges today's requirements thereby constructing a framework with which today's and future standards in flexure testing can be based. The draft standard presented in this thesis covers the three major testing methods for determining the biaxial flexural strength (modulus of rupture) of engineering ceramics. The ring-on-ring, ball-on-ring, and 4-Ball test fixtures were all adopted as standard, since it is known that each of these systems is suited for a particular application and each has different advantages and disadvantages. The three major biaxial test methods prescribed in this draft standard have been devised so that more consistent and accurate test results can be obtained. However, the uncertainty of measurement in flexure testing always exists and needs to be estimated. The estimation of uncertainty in flexure testing in this study is based on the methodology provided in the ISO Guide to the expression of uncertainty in measurement. The results of the estimation showed that the uncertainty in measurement for the biaxial flexure test standard proposed in this thesis is very low compared to the inherent variability of the strength of ceramic materials. It was also found that the applied load, thickness of the disc plate, and random effects are the three major components contributing to the overall uncertainty. The total uncertainty of measurement in biaxial flexure testing can be significantly minimised by the reduction of the uncertainty contributed from these components, especially from random effects.
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D'Arrigo, Paolo. "Control of flexure in large astronomical spectographs." Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244064.
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Bry, Madeleine. "Flexure of the lithosphere at foreland basins." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439115.
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Hunter, Johnny. "Flexure and rheology of Pacific oceanic lithosphere." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:fee30488-1a30-48ae-b47e-b6dbc4e3d4d6.
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The idea of a rigid lithosphere that supports loads through flexural isostasy was first postulated in the late 19th century. Since then, there has been much effort to investigate the spatial and temporal variation of the lithosphere's flexural rigidity, and to understand how these variations are linked to its rheology. In this thesis, flexural modelling is used to first re-assess the variation in the rigidity of oceanic lithosphere with its age at the time of loading, and then to constrain mantle rheology by testing the predictions of laboratory-derived flow laws. A broken elastic plate model was used to model trench-normal, ensemble-averaged profiles of satellite-derived gravity at the trench-outer rise system of circum-Pacific subduction zones, where an inverse procedure was used to find the best-fit Te and loading conditions. The results show a first-order increase in Te with plate age, which is best fit by the depth to the 400 ± 35 °C plate-cooling isotherm. Fits to the observed gravity are significantly improved by an elastic plate that weakens landward of the outer rise, which suggests that bending-induced plate weakening is a ubiquitous feature of circum-Pacific subduction zones. Two methods were used to constrain mantle rheology. In the first, the Te derived by modelling flexural observations was compared to the Te predicted by laboratory-derived yield strength envelopes. In the second, flexural observations were modelled using elastic-plastic plates with laboratory-derived, depth-dependent yield strength. The results show that flow laws for low-temperature plasticity of dry olivine provide a good fit to the observations at circum-Pacific subduction zones, but are much too strong to fit observations of flexure in the Hawaiian Islands region. We suggest that this discrepancy can be explained by differences in the timescale of loading combined with moderate thermal rejuvenation of the Hawaiian lithosphere.
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Meyyappan, Karumbu Nathan. "Failure prediction of wire bonds due to flexure." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1737.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Haddad, David. "Lithospheric flexure and the evolution of Australian basins." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302396.
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Shilpiekandula, Vijay 1979. "Flexure-based nanopositioning systems : integrated design and control." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57892.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 209-219).
This thesis deals with the design and control of flexure-based mechanisms for applications requiring multi-degree-of-freedom positioning and alignment. Example applications include positioning a probe or sample in atomic force microscopy, alignment of tool and sample in stamping processes, and fine-positioning of wafer steppers in semiconductor manufacturing. Such applications necessitate nanopositioning systems that satisfy critical functional requirements, such as load-capacity, bandwidth, resolution, and range. Therefore, a systematic approach for design and control is an important tool for research and development for flexure-based nanopositioning systems. In this thesis, a novel methodology is presented for generating flexure-based topologies that can meet performance requirements, such as those dictating structural strength or dynamical behavior. We present performance metrics that allow for the generation of topologies that are tuned for a desired level of structural strength or modal separation. The topology generation is aimed as a valuable addition to the design toolkit, facilitating novel designs that could not have been conceived otherwise. The parameters within any particular topology could be adjusted at a subsequent phase through a detailed shape and size optimization. The thesis also proposes a controller generation approach. Unlike existing controller parameterizations, a novel parameterization formulated in this thesis allows for directly tuning the sensitivity transfer function of the closed-loop system. Tuning sensitivity is critical in mitigating the effects of disturbances affecting the system, as well as those arising from cross-coupling and parasitic error motions. Further, an integrated methodology for design and control is presented. This methodology uses the design topology generation approach and controller generation approach proposed in the thesis. The key distinction of our design for control approach is that the design is iterated over topologies and not just parameters within a selected topology. A simple one-degree-of-freedom positioning system example is worked out to detail the steps of the proposed integrated design and control methodology. A novel design topology that is ideally suited for achieving a desired design and control performance is derived using this methodology. Finally, the hardware design and control of a novel flexure-based nanopositioner implementation for scanning probe microscopy are presented to illustrate the effectiveness of the approaches discussed in this thesis.
by Vijay Shilpiekandula.
Ph.D.
12
Dorosh, Mark Norman. "Damage growth in bending of composite beams." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28376.
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A study has been made of glass fibre reinforced plastic beams in three-point bending. In recent years, the importance of flexural loading in composites has manifested itself in the form of composite leaf springs, helicopter rotors, and other applications. This study is directed at the initiation, growth, characterization and measurement of damage in unidirectional and cross-ply composite beams.
Beams were tested in three-point static and cyclic bending. Following damage initiation, either by a machined notch or by repeated cycling, damage growth has been characterized by two damage parameters: a damage depth encompassing a number of broken fibres on the tensile surface at the central load point, and a damage length or delamination parallel to the beam longitudinal axis.
A model was developed to predict the compliance, or deflection under applied load, as a function of beam properties and damage dimensions. The model is able to predict the compliance of damaged beams with reasonable accuracy. From fracture mechanics concepts it is shown that the two damage dimensions, depth and length, are related. It is concluded that the increase in compliance, a result of the growing damage dimensions, is related to the growth of the damage depth; the damage length follows from the relation between damage parameters and the compliance follows from the compliance model.
The damage state can thus be determined by compliance measurements if the relevant material properties and loading conditions are known. However, in service, compliance measurements may not be practical. Therefore a section of this study is devoted to an alternative damage measurement technique, namely acoustic emission monitoring. Damage initiation, compliance, damage length and damage depth were measured with AE monitoring techniques.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Sarzynski, Melanie Diane. "Carbon foam characterization: sandwich flexure, tensile and shear response." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/55.
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The focus of this research is characterizing a new material system composed of carbon and graphite foams, which has potential in a wide variety of applications encompassing aerospace, military, offshore, power production and other commercial industries. The benefits of this new material include low cost, light weight, fire-resistance, good energy absorption, and thermal insulation or conduction as desired. The objective of this research is to explore the bulk material properties and failure modes of the carbon foam through experimental and computational analysis in order to provide a better understanding and assessment of the material for successful design in future applications. Experiments are conducted according to ASTM standards to determine the mechanical properties and failure modes of the carbon foam. Sandwich beams composed of open cell carbon foam cores and carbon-epoxy laminate face sheets are tested in the flexure condition using a four point setup. The primary failure mode is shear cracks developing in the carbon foam core at a critical axial strain value of 2,262 με. In addition to flexure, the carbon foam is loaded under tensile and shear loads to determine the respective material moduli. Computational analysis is undertaken to further investigate the carbon foam's failure modes and material characteristics in the sandwich beam configuration. Initial estimates are found using classical laminated plate theory and a linear finite element model. Poor results were obtained due to violation of assumptions used in both cases. Thus, an additional computational analysis incorporating three dimensional strain-displacement relationships into the finite element analysis is used. Also, a failure behavior pattern for the carbon foam core is included to simulate the unique failure progression of the carbon foam on a microstructure level. Results indicate that displacements, strains and stresses from the flexure experiments are closely predicted by this two parameter progressive damage model. The final computational model consisted of a bond line (interface) study to determine the source of the damage initiation, and it is concluded that damage initiates in the carbon foam, not at the bond line.
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Reeves, Eric E. "Structural reliability of ultra-high performance concrete in flexure." Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1177090784.
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Awtar, Shorya 1977. "Synthesis and analysis of parallel Kinematic XY flexure mechanisms." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17945.
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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2004.Includes bibliographical references (p. 193-198).
This thesis presents a family of XY flexure mechanisms with large ranges of motion, first-order decoupled degrees of freedom, and small parasitic error motions. Synthesis is based on an systematic and symmetric layout of constraints that are realized by means of common flexure building blocks. An analytical formulation incorporating geometric non-linearities is used in deriving the characteristics of these flexure building blocks. Of concern are issues related to qualification and quantification of undesirable motions, mobility, stiffness variation within the range of motion, determination of center of stiffness, and sensitivity to manufacturing and assembly tolerances. Based on the properties of the building blocks, the performances characteristics of the resulting XY flexure mechanisms are discussed and the influence of symmetry in reducing error motions is analytically illustrated. To verify the design theory, a 300mm x 300mm prototype stage was fabricated, assembled and tested at the National Institute of Standards and Technology (NIST). Measurements using laser interferometry, autocollimation and capacitance gauges indicate levels of performance much better than the capabilities of the current state of the art of precision flexure stages. The prototype flexure stage has a 5mm x 5mm range of motion, with cross-axis errors of the order of one part in one thousand, and motion stage yaw errors of the order of a few arc seconds.
by Shorya Awtar.
Sc.D.
16
Lees, J. M. "Flexure of concrete beams pre-tensioned with aramid FRPs." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/273030.
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Mertz, David Hunter. "Lift-off performance in flexure pivot pad and hybrid bearings." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3197.
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Razak, Hashim Abdul. "Time dependent effects in reinforced concrete sections subjected to flexure." Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/1003/.
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RAMIREZ, JORGE DUENAS. "BLOCK-FLEXURE TOPPLING MECHANISM: CASE NW SLOPE TINTAYA´S MINE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9597@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Esta tese apresenta o fenômeno de ruptura por tombamento bloco-flexural, que acontece na zona NW da mina Tintaya. O objetivo do presente estudo é contribuir o conhecimento de este tipo de fenômeno de ruptura, quantificando as características do maciço rochoso com as técnicas da mecânica das rochas. O trabalho inicia-se por uma caracterização geral da zona de estudo, com especial relevo das propriedades geomecánicas das descontinuidades presentes, pelo que foram desenvolvidos mapeamentos das caras de bancada e a amostragem da rocha intacta, esta data permitiu estabelecer correlações dos parâmetros geomecânicos e fazer a análise cinemática da zona de estudo. Após de fazer a caracterização e avaliação das características das descontinuidades, foi definido o tombamento bloco-flexural, pelo jeito das descontinuidades presentes no maciço, já que este tipo de ruptura é mais complexo do que os outros tipos de tombamento, porque é uma combinação de tombamento e deslizamento dos blocos. Em vez da ruptura flexural de colunas contínuas, neste caso o tombamento é resultado de deslocamentos acumulados das juntas transversais. Com o objetivo de fazer uma análise numérica, obtou-se por um modelo contínuo- equivalente que inclui os efeitos de orientação e espaçamento das juntas é o modelo de plasticidade de Cosserat. O contínuo de Cosserat, conhecido também como contínuo micropolar acrescenta os graus de liberdade de rotação ao contínuo convencional. Pelo que foi analisado este tipo de ruptura através de uma modelagem computacional com um programa de elementos finitos feito na PUC-Rio, assim, tornar possível a modelagem computacional com a teoria do continuo de Cosserat.
This thesis presents the block - flexural toppling failure phenomenon, which happens at NW zone of the Tintaya´s mine. The objective of the present study is to contribute the knowledge of this type of phenomenon of failure, quantifying the characteristics of rock mass with the techniques of the rock mechanics. The work begins for a general characterization of the zone, with special relief of the geomechanical properties of the discontinuities, which were developed the window sampling (bench face mapping) and sampling of the intact rock, this information allowed to establish correlations of the geomechanical parameters and make feasible kinematics analysis from the zone of study. After doing the rock mass characterization and evaluation of the characteristics of the discontinuities, the block - flexural toppling failure was defined, on those long column rocks crossed by numerous huge subhorizontal joints. The block-flexural type failure is a complex phenomenon compared with other types of toppling failure, because it is a combination of pure toppling and sliding. With the intention of numerical analysis, I have been proposed analyzing this rupture for a continuum - equivalent model of Cosserat, that includes the orientation and the discontinuity´s spacing. This model is known also as continuum micropolar, which adds the degrees of freedom of rotation to a conventional continuum. It was analyzed this type of failure through a computational modeling with a program of finite elements made in the PUC-Rio, so, the computational modeling possible with the theory of continuum of Cosserat.
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Ljubicic, Dean M. "Design and analysis of a monolithic flexure atomic force microscope." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45201.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 175-178).
This thesis details the design, manufacture, and testing of a sub-nanometer accuracy atomic force microscope. It was made to be integrated into the Sub-Atomic Measuring Machine (SAMM) in collaboration with the University of North Carolina at Charlotte (UNCC). The microscope uses a tuning fork sensor to gauge its proximity to the sample surface. The sensor is fixed to a stage that is guided to move in one degree of freedom by a monolithic flexure. A piezoelectric actuator drives the moving stage while three capacitance sensors provide a non-contact direct measurement of the displacement. A decoupling flexure prohibits the error motions of the actuator from propagating into the moving stage. A digital control system uses closed loop control to regulate the vertical displacement of the stage. The positioning system demonstrated a 450 Hz -3db closed loop bandwidth and 0.249 RMS noise positioning. A new probe named after its inventor Dr. Terunobu Akiyama is implemented in a feedback control system that adjusts the displacement of the stage in order to maintain a constant gap between the probe and the sample. The system displayed an 8.3 nm RMS positioning noise when set to measure a stationary block of aluminum. The dynamics of the feedback control loop indicate that the system can operate at 27 Hz upon application of a proportional controller. Advanced methods to self excite the tuning fork sensor at resonance by use of a phase locked loop are explored. Follow-up work to integrate the atomic force microscope into the SAMM stage, diminish the electrical noise in the tuning fork, and to implement the phase locked loop circuit are suggested.
by Dean Marko Ljubicic.
S.M.
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Delgado-Velázquez, Iván. "Nonlinear vibration of a cantilever beam /." Online version of thesis, 2007. http://hdl.handle.net/1850/3930.
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Luty, Mark. "Precision balances for measurement of mass and air density." Thesis, Brunel University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363465.
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Nallagula, Sandeep. "Behavior and Flexure Analysis of Balsa Wood Core Sandwich Composites: Experimental, Analytical and Finite Element Approaches." ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/371.
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The load-deflection behavior of a US Army Corps of Engineers available sandwich plates in three-point bending with glass phenolic facings and balsa wood core is being investigated under room and elevated temperatures. Test data on bending rigidity, critical interfacial failure (skin-to-core interface) and shear stress are collected and analyzed. The load-deflection curves plots up to the point of failure initiation are being studied. The effects of the span and the radius of the loading nose on the bending modulus and strength are examined systematically. Theoretical calculations from a modified beam theory of sandwich structure are applied and the effect of the shearing rigidity of the core is studied, and the propensity with respect to the span is also investigated. A finite element model is developed to study the flexural and stress analysis. Based on the results, this thesis proposes a desirable analytical approach that correlates theory with experiment as defined below.
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Lavu, Srikanth. "Failure analysis and performance modelling of a MEMS flexure electrothermal actuator." Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2053.
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Reliability is a major challenge for the successful exploitation of MEMS technology. ' This thesis presents a systematic taxonomy of typical failure modes and effects in MEMS. The failures are classified according to their occurrence: manufacturing, operation, environmental effect and package related effect. To prioritise these failures, a systematic proactive Failure Mode and Effect Analysis (FMEA) is presented as a tool to be used concurrently in the design phase. The FMEA is successfully applied on a MEMS flexure electrothermal actuator. The FMEA study identified the key issues affecting the reliability of the considered actuators and provided val,uable recommendations to improve their functional performance, efficiency and reliability. Particular emphasis is put on the failure modes of the micro electrothermal flexure actuator and the corresponding failure mechanisms are presented. A high-level functional behavioural modelling methodology for fast and flexible modelling of multiphysical MEMS functional behaviour is presented using the VHDL-AMS language. In particular a high level behavioural model is described for the functional displacement of the electrothermal flexure actuator. Moreover, using the same approach a theoretical study of the performance is presented in the case of the electrothermal flexure actuator at low pressure and high temperature ambient conditions. Practical testing of the effects of low ambient pressures and high ambient temperatures on the performance and reliability of the thermal actuators has been performed. The test results are compared successfully with the results of the thermal actuators high level performance model to assess the validity and accuracy ofthe models.
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Dryburgh, Gillian. "Bifurcation and vibration of a surface-coated elastic block under flexure." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/2023/.
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The behaviour of a surface-coated rectangular, non-linearly elastic block subject to (plane-strain) flexure is investigated in this thesis. We consider a rectangular block of incompressible, isotropic elastic material coated with a thin elastic film on part of its boundary. Initially, the bulk material undergoes a non-homogeneous deformation and the equilibrium of the coated body is examined on the basis of the elastic surface coating theory derived by Steigmann and Ogden (1997a). Incremental displacements are then superimposed on the finitely deformed configuration in order to study possible bifurcation of the deformed block. Numerical bifurcation results pertaining to two particular strain-energy functions (for the bulk material) and a general energy function (for the coating material) are subsequently obtained. These results allow the influence of the surface coating on the bifurcation behaviour of the block to be determined and assessed with reference to corresponding results for an uncoated block. Next, use is made of the dynamic equivalent of the static surface coating theory, developed by Ogden and Steigmann (1999), to establish incremental equations of motion for the coated block. Corresponding incremental governing equations for an uncoated, pre-flexed block then emerge as a special case. The resulting frequency equations are solved numerically, again on specialization of the form of strain-energy function. The numerical vibration results then provide evidence of the effect of surface coating on the dynamic behaviour of the considered coated block relative to the uncoated case. Finally, we turn our attention to the (non-linear) shear responses of bonded elastic bodies. We examine the plane-strain problem of a rectangular compressible isotropic elastic block bonded to two rigid parallel plates. The deformation behaviour of the block is described by applying minimum energy and maximum complementary energy principles to obtain upper and lower bounds on the shear stress-strain relationship. Although maximum and minimum principles are not generally justifiable in non-linear elasticity we show that under certain conditions they are applicable and, for a particular form of strain-energy function, derive explicit energy bounds which we illustrate graphically.
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Matloff, Laura Yu. "Design and optimization of x-y-[t̳h̳e̳t̳a̳]z̳, cylindrical flexure stage." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83727.
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Thesis (S.B.)--Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013.Cataloged from PDF version of thesis. In title on title page, double-underscored "t̳h̳e̳t̳a̳" appears as Greek letter. In title on title page, double underscored "z̳" appears as subscript.
Includes bibliographical references (pages 63-64).
Cylindrical flexures (CFs) are composed of curved beams whose length is defined by a radius, R, and a sweep angle, [phi], [1]. The curved nature of the beams results in additional kinematics, requiring additional design rules beyond those used for straight-beam flexures. The curvature also adds additional parameters that allow for adjustments, suggesting that CFs may meet requirements that cannot be met with straight-beams. CFs have the potential to further open the flexure design space. In this study, cylindrical flexure design rules and models were used to optimize an x-y-[theta]z stage design for a Dip-pen nanolithography (DPN) application. DPN a nanometer-scale fabrication technology that uses an atomic force microscope (AFM) cantilevered tip to place chemical compounds on a substrate. The flexure designed aids in alignment of the tip relative to the machine, increasing accuracy and repeatability. The first step to design a flexure system is applying CF design rules to create a system that best fits functional requirements. Several different system configurations were considered, since reaching an optimal design is a highly iterative process. Once the best configuration was determined, element parameters were optimized using CF design rules. The optimized design was then corroborated using finite element analysis (FEA). The CF design rules greatly informed the design, reducing time spent on FEA by quickly narrowing in on successful designs. The finalized flexure design was fabricated using a waterjet machine and placed in a testing apparatus designed to measure predicted stiffnesses and verify functionality. The CF model predicted the final measurements quite closely, although there were variability in the measurements and simplifications in the model. In K[theta]z, the error was as small as 0.3%, while the other stiffnesses had errors around 30%, except for Kx, which is twice as stiff than the model. This could be due to the simplification of more complicated tip boundary condition effects in the model or error in measurement of the fabricated flexure. Although the model did not predict the final stiffness values exactly, it was critical in reducing time spent optimizing the system by quickly determining key parameters. The process of design and optimization shed light on advantages and disadvantages of using cylindrical flexures for an x-y-[theta]z stage in general, and demonstrated the usability of CF rules. Observations from this research augmented the design guidelines, which will help others design CFs for other functional requirements.
by Laura Yu Matloff.
S.B.
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Moon, Daniel K. (Daniel Kyeongtaek) 1978. "Flexure based mounts for sensitive payloads : a management and engineering study." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8537.
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Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 51-52).
With the cooperation of the Los Alamos National Laboratory and the Massachusetts Institute of Technology, an investigative and design study was performed to examine the history of the W80- 0 Area Aft Mount, understand its performance, and explore potential new designs. Simultaneously, professional and technical enhancement of the author was achieved. The historical organization of LANL influences the design space for this project, and understanding those relationships provides insight into concept generation and selection. In addition, the current organizational structure within the laboratory as well as with its customers provides additional constraints that must be managed technically. The new design concepts attempt to simulate the nonlinear load vs. displacement characteristics of the previously employed B3223 cellular silicone Pad Mount. New concepts separate the spring and damping characteristics of the cellular silicone into separate component parts. This uncoupled method should allow the new designs increased variability and control with respect to matching original Aft Area Mount performance in shock mitigation and deflection limiting.
by Daniel K. Moon.
S.M.and S.B.
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Hopkins, Jonathan B. (Jonathan Brigham). "Design of parallel flexure systems via Freedom and Constraint Topologies (FACT)." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39879.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 391-393).
The aim of this thesis was to generate the knowledge required to represent the possible freedom topologies (motions of a mechanism) and the possible constraint topologies (flexural elements that guide the mechanism) in a form that designers can use to design parallel flexure systems. The framework that links these topologies enables designers to create three-dimensional, multi-axis flexure systems by using "Freedom and Constraint Topologies" (FACT). FACT embodies every possible design solution for parallel flexure systems. This information enables designers to consider every possible design and then select the design that is best suited for a specific application. FACT was created to improve the design processes for small-scale flexure systems and precision machines. For instance, there is a need to create multi-axis nanopositioners for emerging three-dimensional nano-scale research/manufacturing.
(cont.) Through this work the following contributions were made: (1) twenty six unique matching pairs of freedom and constraint spaces were identified; (2) it was proven that these spaces embody all possible solutions; (3) a design process was created to guide a designer from design requirements, to freedom spaces, to constraint spaces, to mechanism designs; (4) a sub-process was created to guide designers in the selection of redundant constraints that help satisfy stiffness and symmetry requirements without altering the mechanism's kinematics; (5) mathematical expressions were created to represent the freedom and constraint spaces in a form that enables computers to identify and manipulate them. In this thesis, three case studies are provided to demonstrate the FACT design process for mechanisms of varying complexity: (1) a compliant spherical ball joint, (2) a compliant probe for a five axis STM, and (3) a compliant rotary flexure are designed. The second case study demonstrates the sub-process for selecting redundant constraints.
by Jonathan Brigham Hopkins.
S.M.
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Segado, Martin Alan. "Design of planar-flexure-based contacts for high-repeatability kinematic couplings." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40484.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 29).
This research assesses the effects of planar flexural elements on the repeatability of a high-precision kinematic coupling. Few devices exist that are capable of passive, repeatable nanoscale fixturing; this research facilitates the design of such devices by providing a more complete understanding of how flexural elements affect their performance. Improvements in coupling technology are expected to decrease production and assembly costs in a variety of industries where repeatable fixturing is required (e.g. the semiconductor, automotive, and tooling and machinery industries), and have the potential to improve the quality of research in a wide range of fields by increasing the speed and accuracy of manufacturing processes and metrology systems. Flexures serve to improve the performance of ball-and-flat contacts by preventing motion of the flats in the direction perpendicular to the contacts while allowing motion in tangential directions, thus reducing the effects of friction and wear at the interface. Flexural elements have been used to reduce hysteresis and prevent overconstraint in kinematic couplings but the use of planar flexures as friction and wear reducing devices has not been previously studied.
(cont.) A kinematic coupling that uses planar flexures was designed, constructed and tested. This coupling showed similar repeatability to a rigid coupling used as a control when the ball-and-flat contacts of both were free of wear; however, the flexure-based coupling performed much better than the control coupling after the contacts had been roughened by material failures resulting from repeated loading.
by Martin Alan Segado.
S.B.
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Malan, Andreas Dawid. "Critical normal traffic loading for flexure of bridges according to TMH7." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80013.
Full textAbstract:
Thesis (MScEng)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Different types of live loading due to traffic may act on bridges. The focus of this study is on normal traffic loading according to the South African specification of TMH7. Heavy vehicles are not included in normal traffic loading. TMH7 represents the code of practice for the design of highway bridges and culverts in South Africa. The aim of the study is to provide an insight into the flexural analysis of skew bridges, under the effects of normal traffic loading. The need for the study arose since the specification of TMH7 does not explicitly specify application patterns for normal traffic loading. Only the intensity of normal traffic loading is specified and it should be applied to yield the most adverse effects. For these reasons, a set of so-called standard application patterns are investigated and developed through the course of this study. The envelope of the values from the standard application patterns are compared to the most adverse application pattern for flexural effects in certain design regions of the bridge deck. Flexure, as in the context of this study, translates into the bending and twisting of the bridge deck under loads. A number of numerical experiments are performed for typical single span and multi-span continuous carriageways, where the standard application patterns are compared to the most adverse application patterns. The results from the numerical experiments are documented and compared as the angle of skew of the bridge deck increases in plan-view. For this purpose, the development of effective and specialized software was necessary. It was found that the set of standard application patterns can be used as a preliminary approximation for the most adverse effects of normal traffic loading, for specific flexural resultants in certain design regions of a bridge deck. However, for a large number of secondary flexural effects, the set of standard application patterns did not represent a good approximation for the most adverse values.
AFRIKAANSE OPSOMMING: Verskillende tipes lewendige belasting, as gevolg van verkeer, kan op brûe inwerk. Die fokus van die studie is op normale verkeers-belasting volgens die Suid-Afrikaanse spesifikasie van TMH7. Swaar-voertuie word nie ingesluit by normale verkeers-belasting nie. TMH7 verteenwoordig die kode vir die ontwerp van padbrûe en duikers in Suid-Afrika. Die doel van die studie is om insig te verskaf in die buig-analise van skewe brûe, as gevolg van die werking van normale verkeers-belasting. Die rede vir hierdie studie ontstaan aangesien die spesifikasie van TMH7 nie eksplisiet aanwendingspatrone vir normale verkeers-belasting voorskryf nie. Slegs die intensiteit van normale verkeersbelasting word voorgeskryf en dit moet aangewend word om die negatiefste effekte te verkry. Vir hierdie redes word 'n versameling van sogenaamde standaard aanwendings-patrone deur die loop van die studie ondersoek en ontwikkel. Die omhullings-kurwe van die waardes wat deur die standaard patrone gelewer word, word vergelyk met die waarde van die aanwendings-patroon wat die negatiefste buig-effek in sekere ontwerp-areas van die brugdek veroorsaak. Buig-effekte, soos van toepassing op hierdie studie, verwys na buig en wring van die brugdek as gevolg van belastings. 'n Aantal numeriese eksperimente, vir enkel-span sowel as multi-span deurlopende brugdekke, word uitgevoer en die standaard aanwendings-patrone word vergelyk met die aanwendings-patrone wat die negatiefste waardes lewer. Die resultate van die numeriese eksperimente word gedokumenteer en vergelyk soos die hoek van skeefheid van die brugdek in plan-aansig toeneem. Vir hierdie doel is die ontwikkeling van effektiewe en gespesialiseerde sagteware dus nodig. Daar is gevind dat die standaard aanwendings-patrone, vir spesifieke buig-resultante in sekere ontwerp-areas van die brugdek, as 'n voorlopige benadering vir die negatiefste effekte van normale verkeers-belasting gebruik kan word. Dit was egter verder gevind dat vir 'n groot aantal sekondêre buig-effkte, die versameling standaard aanwendings-patrone nie as 'n goeie benadering vir die negatiefste waardes dien nie.
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Wallace, Michelle Hall. "Application of numerical techniques to faulting and flexure of the lithosphere." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185776.
Full textAbstract:
This research investigates problems of faulting and flexure of the lithosphere using the finite element technique. I examined two aspects of faulting, the nucleation and growth of dip slip faults in a stable craton in Chapter 2, and the rupture of the Loma Prieta earthquake in Chapter 3. Linear elastic fracture mechanics and the shear fracture energy criteria are used in conjunction with the finite element method to evaluate the stability of fault rupture. I investigated fault nucleation and growth under conditions of variable dip and shear fracture energy. Strain required for fault growth varied with respect to shear fracture energy gradient and rupture direction but not with dip. Rupture upward required more than twice the initial strain to cause fault growth, as compared to rupture downward, and would result in very large earthquakes. Rupture downward in models associated with the higher G(c) gradient resulted in stable growth of the fault. I suggest that fault nucleation and growth is a stable process which would preferentially occur by rupturing downward under stable conditions. In Chapter 3, I model the rupture of the Loma Prieta Fault, a moderately dipping reverse fault which is subparallel to the San Andreas Fault. Rupture initiated at 18 km and propagated updip in an oblique slip motion to 8-5 km depth. A similar technique as outlined above is used to investigate controls on the rupture propagation and the genetic relationship of the Loma Prieta and San Andreas faults. Low stress in the upper crust caused by a low strength material or the presence of other faults is responsible for stopping rupture. An evaluation of the stress at the intersection of the two faults indicates that the Loma Prieta Fault in the upper crust is still closer to the point of failure than the San Andreas Fault. Thus, rupture of the Loma Prieta did not significantly increase the seismic hazard of the San Andreas in that region. In Chapter 4, I analyze the problem of buckling a faulted elastic plate. I studied the effect of changes in fault depth, spacing and dip on the buckling stress, wavelength and effective Young's modulus. Modeling results show that as the fault depth increases both the buckling stress and wavelength decrease. Similarly, the effective Young's modulus is a decreasing function of depth. As fault spacing was increased, the effect of the faults on the buckling stress and wavelength was minimized. Fault dip appears to have no significant effect on buckling response. The buckling response of a thick, faulted lithosphere is not equivalent to that of a thinner elastic plate.
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Joshi, Angela. "THE INTERACTION OF FLEXURE AND COMPRESSION IN REGULAR AND OFFSET EXTERIOR COLUMNS." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/theses/2558.
Full textAbstract:
When a structural element is acted upon by axial compressive force simultaneously with bending, the design must consider the effect of combined bending and compression. Hence, the structure should be designed with the consideration of bending moment in order to provide the enough design strength to the member. The main objective of this thesis is to compare the effect of interaction of flexural moment and axial compressive force on the regular column of the steel moment frame with the same column when cantilever section is introduced into the frame as the loading is kept constant in all three cases. In this work, STAAD is used to determine the required variables such as axial forces, bending moments and deformations in all the cases, and those values are used in approximate second order analysis for the further analysis of special steel moment frame. The calculated values are then plugged into the design interaction equation for combined flexure and compression as given by AISC Steel Construction Manual (2011) to check the criticality of the moment frame. The result of the analysis indicates that the regular frame model has higher demand of capacity ratio in design of columns than the one with cantilever projection.
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Ali, Alameer. "Behaviour of Prestressed Ultra-High Performance Concrete I-Beams Subjected to Shear and Flexure." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24280.
Full textAbstract:
Ultra-high performance concrete (UHPC) is a new type of concrete developed by selecting the
particle sizes and gradation in the nano- and micro-scales targeting the highest possible packing.
The resulting concrete with very high density is called UHPC. UHPC has very low permeability
and hence it is very highly durable compared to traditional or high performance concrete (HPC).
Micro reinforcement of UHPC by random distributed steel-synthetic fibers results in superior
mechanical properties such as very high compressive and tensile strengths, high ductility, and
high fatigue resistance. The material selection and early age curing processes, use of fiber
reinforcement, and very high quality in production resulted in a very high initial cost of UHPC
structures. In order to enable the mass production and cost effective use of the material,
performance based design and optimization of UHPC structural members are required. This
study is part of an NRC Canada research project to develop innovative, cost effective, and
sustainable bridge structural systems using UHPC and other innovative materials. In this study,
the estimation of shear and flexural capacities using the available approaches of international
design guidelines of UHPC structures are comprehensively compared to a proposed truss
models, linear and nonlinear finite element models. Several design trials intended to allow for an
optimized use of the materials and a maximum load capacity was conducted for simply
supported beams with one or two external loads, and having rectangular or I cross sections.
Linear and non-linear finite element models are developed and their results were compared to the
available international design recommendations. Truss models are proposed to simplify the stress
analysis in the shear zone of the prestressed UHPC beams.
It is found that prestressed UHPC I-beam section gives the highest possible load capacity with
minimum use of materials. The study shows that for the case of no stirrups, massive flexure and
shear cracks initiate and propagate suddenly where a diagonal shear crack is fully developed and
sudden collapse may expected. The proposed truss model gives very good match to nonlinear
finite element analysis results for almost all the truss members. The results are significantly
improved when additional struts are considered for both cases of beams with or without shear
reinforcement. The study shows the importance of future experimental investigatinons to
calibrate the proposed models.
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Moorhouse, Kevin Michael. "Determination of a Whiplash Injury Severity Estimator (WISE Index) for Occupants in a Motor Vehicle Accident." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36814.
Full textAbstract:
The diagnosis of a whiplash injury is a very subjective process. A claim of this type of injury is usually made on the basis of pain, which may or may not be accompanied by clinical signs of trauma. This study was aimed at providing a more objective, quantitative approach to identifying the potential for whiplash injury in a directfront-or-rear-end automobile collision.
The Whiplash Injury Severity Estimator (WISE Index) was created using data obtained from Dr. Schneck's personal library of case files, including the collisionacceleration of the vehicle, and the height, weight, and sex of the occupant. Some extrapolated data was also used representing the low and high ranges of height, weight, and collision acceleration to increase the range of the WISE Index. Data was analyzed by the Dynaman computer program in conjunction with the Articulated Total Body Model, to calculate the response of the body to external forces and impacts. The dynamic response of the occupant, combined with preexisting medical statistics provided the information necessary to perform a regression analysis in MINITAB and thus construct the WISE Indices shown below.
Male WISE Index (R² = 0.993)
£ = 0.2643 ± 0.4071 |(accel,g)| -0.01428(PI)
1.1g<=accel<=5g; 22.4<=PI<=25.0
Female WISE Index (R² = 0.978)
£ = 0.6214 ± 0.3429 |(accel,g)| -0.02929(PI)
0.8g<=accel<=5g; 22.3<=PI<=31.0
Acceleration: Use the negative sign if it is a rear-end collision and the positive sign if it is a head-on collision.
£ : A negative value means that potential injury results from backward head rotation, as in a rear-end collision. A positive value means that potential injury results from forward head rotation, as in a head-on collision.
|£ | < 1 = " Safe "
|£ | > 1 = " Dangerous "
The WISE Index allows one to predict the potential for a whiplash injury, as well as the intensity of the injury, based solely on collision acceleration, height, weight, and sex of the occupant. It is anticipated that this work and future efforts in this area will provide the information base necessary for anyone to effectively evaluate the validity of an alleged whiplash injury.
Master of Science
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Al-Ghothani, Ali M. "A unified approach to the dynamics of bending and extension of moderately thick laminated composite plates /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487266691094416.
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Rimpel, Aaron Michael. "Analysis of flexure pivot tilting pad gas bearings with different damper configurations." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3011.
Full text
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Sim, Kyu-Ho. "Rotordynamic and thermal analyses of compliant flexure pivot tilting pad gas bearings." Thesis, [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1575.
Full text
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Solmaz, Taylan. "Evaluation Of Performance Based Displacement Limits For Reinforced Concrete Columns Under Flexure." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612323/index.pdf.
Full textAbstract:
Reinforced concrete frame buildings are the most common type of constructions in Turkey which are exposed to various types of forces during their lifetime. Seismic performance of reinforced concrete frame buildings is dominated by columns which can be classified as primary members of these structures. When current codes are considered, all of them contain several provisions in order to implement reliable seismic performances of reinforced concrete columns. In order to evaluate the accuracy of these provisions, analytical and parametric studies are carried out for flexure critical reinforced concrete columns. In these studies, total numbers of 30 flexure critical columns are extracted from PEER database (2005) and analytically investigated. Once the seismic responses obtained from analytical investigations are close enough to experimental seismic responses, performance based displacement limits are pointed out according to TEC (2007), FEMA 356 (2000), Eurocode 8 (2003), and ASCE/SEI 41 Update (2009). In addition to this, total numbers of 144 flexure critical columns are generated in parametric studies to present the effects of various parameters such as column geometry, concrete strength, axial load ratio, transverse reinforcement ratio, and yielding strength of longitudinal reinforcement on performance based displacement limits. Performance based displacement limits proposed by TEC (2007), FEMA 356 (2000), Eurocode 8 (2003), and ASCE/SEI 41 Update (2009) are found very conservative compared to limits obtained from both experimental and analytical behavior. On the other hand, performance based displacement limits given in Eurocode 8 (2003) and ASCE/SEI 41 Update (2009) predict the experimental behavior more accurate than TEC (2007) and FEMA 356 (2000). Improvements on these limits are proposed.
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Larsen, Jeffrey James. "Continuum structural representation of flexure and tension stiffened one-dimensional spacecraft architectures." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/larsen/LarsenJ0509.pdf.
Full textAbstract:
Spacecraft designs are a result of system properties and design variables that ensure the spacecraft will operate to mission objectives. The focus of this effort is a set of global system variables for frequency, length, total mass and the ratio between the payload mass and the support structure mass. These properties will be explored to observe the behavior of the system and develop relationships that govern the trade-offs between the variables and assist mission planners in future spacecraft design. These variables will be observed in one-dimensional structures where the dominating dimension is many times larger than the other two dimensions and the system is comprised of a support and a payload member. To observe the interaction between the payload and the support, the system was varied for different system variables and observed through ABAQUS finite element software. Attempts were made to predict the system frequency through mathematical approaches. The finite element work was able to generate several approximate relationships between the system variables and the fundamental natural frequency of the system. From these relationships an approximate equation was developed for the frequency for a fixed mass ratio and load ratio as a function of the length, bending stiffness, and total mass of the system. Additional work into the changes to the system as the number of connect points is increased shows the system converging towards a frequency solution which results in a minimized dependence on the connection points. These results were then compared to those of several derived analytical models to determine if a closed-form solution could be used to predict system behavior over the same range of structural characteristics. This closed form solution proved to correlate well to analytical predictions only for the case where the support structure dominates the total system mass, and thus the structural system performs like a beam under compression. Further work is necessary to accurately predict the system frequency through an analytical approach. These insights promise to aid mission designers in objectively evaluating new structural architectures based on structural performance rather than on an unbalanced adherence to heritage or in some cases personal preference.
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Dirksen, Frank [Verfasser]. "Non-intuitive Design of Compliant Mechanisms Possessing Optimized Flexure Hinges / Frank Dirksen." Hamburg : Helmut-Schmidt-Universität, Bibliothek, 2014. http://d-nb.info/1046797948/34.
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Filmer, Paul Edward. "Flexure of the oceanic lithosphere in the vicinity of the Marquesas Islands." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/52955.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992.Includes bibliographical references (p. 225-234).
by Paul Edward Filmer.
Ph.D.
42
Pollard, Lloyd Wayne 1936. "Design of a flexure mount for optics in dynamic and cryogenic environments." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276741.
Full textAbstract:
The design of the flexure mount recently submitted to NASA Ames for the structural support of the primary mirror of the Space Infrared Telescope Facility (SIRTF) is presented. The flexure system must passively accommodate the differential thermal contraction between the glass mirror and the aluminum structure of the telescope during cryogenic cooldown. Further, it must support the one meter diameter, 116 kilogram (258 pound) primary mirror during a severe launch to orbit. Procedures used to establish the required radial compliance using computer programs NASTRAN and FRINGE are discussed. The parametric design program developed to study early concepts is presented. Methods of combining modal responses resulting from a displacement response spectrum analysis are discussed, and a combination scheme called MRSS, Modified Root of Sum of Squares, is presented. Modal combination schemes using MRSS, SRSS, and ABS are compared to the results of a Modal Frequency Response analysis.
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Jawdhari, Akram Rasheed. "BEHAVIOR OF RC BEAMS STRENGTHENED IN FLEXURE WITH SPLICED CFRP ROD PANELS." UKnowledge, 2016. http://uknowledge.uky.edu/ce_etds/37.
Full textAbstract:
FRP laminates and fabrics, used as an externally bonded reinforcement (EBR) to strengthen or repair concrete members, have proven to be an economical retrofitting method. However, when used to strengthen long-span members or members with limited access, the labor and equipment demands may negate the benefits of using continuous EBR FRP. Recently, CFRP rod panels (CRPs) have been developed and deployed to overcome the aforementioned limitations. Each CRP is made of several small diameter CFRP rods placed at discrete spacing. To fulfill the strengthening length, CRP’s are spliced together and made continuous by means of overlaps (or finger joints).
In this doctoral dissertation, the effectiveness of spliced CRPs as flexural strengthening reinforcement for RC members was investigated by experimental, analytical and numerical methods. The experimental research includes laboratory tests on (1) RC beams under four-point bending and (2) double-lap shear concrete specimens. The first set of tests examines the behavior of concrete members strengthened with spliced CRPs. Several beams were fabricated and tested, including: (a) unstrengthened, (b) strengthened with spliced CRPs, (c) strengthened with full-length CRPs, and (d) strengthened with full-length and spliced CFRP laminates. The double-lap shear tests serve to characterize the development length and bond strength of two commonly used CRPs. Several small-scale CRPs, with variable bond lengths, were tested to arrive to an accurate estimation of development length and bond strength. Several other specimens were additionally tested to preliminarily examine the effects of bond width and rod spacing.
A 3D nonlinear finite element simulation was utilized to further study the response of CRP strengthened RC beams, by extracting essential data, that couldn’t be measured in the experimental tests. Additionally, analytical tools were added to investigate the behavior of tested bond and beam specimens. The first tool complements the double-lap shear tests, and provides mathematical terms for important characteristics of the CRP/concrete bond interface. The second tool investigates concrete cover separation failure, which was observed in the beam testing, for RC beams strengthened with full-length and spliced CRPs.
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Jordan, Tom A. R. M. "Gravity anomalies, flexure, and the long-term rigidity of the continental lithosphere." Thesis, University of Oxford, 2007. http://ora.ox.ac.uk/objects/uuid:9f803b42-522e-442b-9849-bb8e6c2a5494.
Full textAbstract:
The cause and distribution of spatial variations in the mechanical properties of the continental lithosphere are fundamental questions for modern geology. In this study variations in long-term lithospheric rigidity have been investigated. These investigations used profile- and grid-based flexural models of the lithosphere’s response to geologically imposed topographic, or buried, loads. These models were constrained by topographic and gravity data allowing recovery of best fitting rigidity values. In Oman a Cretaceous ophiolite acts as a significant load on the continental crust. Flexural models along profiles orthogonal to the ophiolite strike show that the observed gravity data can be best modelled by an elastic beam with standard thickness (Te) of 30 km. Along strike there is shown to be significant variation in the foreland shape and the observed gravity signal. This, it is proposed, relates to the complex tectonic processes which occurred as the ophiolite was obducted. The Himalayan foreland has been the focus of controversy over the recovered long-term rigidity of the continents, with recovered Te values ranging from 40 to over 90 km. Both profile- and grid-based techniques show that Te is high (>70 km) in the foreland region. Across the India-Eurasia collisional system as a whole Te values are variable. Beneath the Tibetan plateau recovered values are generally low (<10 km), while the plateau margins are marked by regions of higher rigidity. Recovered Te values across the Arabia-Eurasia collisional system range from over 60 km in the foreland region to close to zero beneath the high Zagros mountains. In the eastern part of the foreland, flexural models match the gravity data; however, they disagree with sediment thickness data for the material infilling the foreland. This discrepancy is interpreted in terms of de-coupling of the flexural lithosphere from the shallower crustal levels, caused by the presence of significant salt deposits in this region. Application of grid-based techniques to South America, North America and Europe recover a broad range of Te values from ∼0 to over 90 km. The low Te values are explained in active orogenic belts in terms of current processes acting to weaken the lithosphere, and in the continental interiors as the relics of past orogenic events. High Te values in the continental interiors correlate with ancient cratonic cores which have undergone little deformation since their formation in the Archean. This study shows that Te variations have a critical influence on the development of large compressional orogenic belts. In the Himalayan and Andean orogens there is a correlation between the over-thrusting of the orogenic belt and high Te foreland regions. Where lower Te regions are seen, less over thrusting is apparent, and in the case of the India-Eurasia collisional system out-flow of lower crustal material may be occurring.
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Al-Obaidi, Salam. "Behavior of Reinforced Concrete Beams Retrofitted in Flexure Using CFRP-NSM Technique." PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2294.
Full textAbstract:
A variety of retrofitting methods are used to upgrade existing structures. For example, steel plates and Fiber Reinforced Polymer (FRP) jackets are externally bonded to members to increase their capacity in flexure and shear. However, due to the issue of corrosion these strengthening systems may lose their efficiency with time. FRP materials have been used to strengthen many structural components of different shapes and types. FRP jackets, FRP Strips, and FRP rods have commonly been used to rehabilitate existing structural components. The many advantages of using FRP as strengthening materials have made this material an attractive alternative: advantages such as lightweight, high strength, and ease of setting up. Among the many applications using FRP, Near Surface Mounted -- Fiber Reinforced polymer (NSM-FRP) is a promising technique used to strengthen concrete members. However, de-bonding issues have to be overcome to make this technique efficient and reliable. The NSM-FRP technique consists of making a groove along the surface of the concrete member to be retrofitted with depth less than the cover of the member. After cleaning the groove, epoxy paste is used to fill two-thirds of the groove's depth. The FRP element is then mounted in the groove. Finally, the groove is filled with epoxy and the excessive epoxy is leveled with surface of the concrete. This technique makes the FRP material completely covered by epoxy in the cover of the concrete. This method can be used for strengthening both the positive and negative moment regions of girders and slabs. Groove size, paste, concrete, and rods properties are the main variables that control the efficiency of the NSM-FRP rods. The main objective of this research project is to determine the behavior of reinforced concrete beams that are strengthened with NSM-CFRP reinforcement bars. In this research project, the bond characteristics of NSM-CFRP reinforcement bars are first determined from pullout tests. Then, NSM-CFRP rods are installed in reinforced concrete beams and the beams are tested. Loads, strains, and deflections are measured and theoretical and measured capacities are compared. Finally, the reliability and efficiency of using NSM-CFRP rods technique in retrofitting existing structures is observed.
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Hamai, Lamine. "Étude thermomécanique de la zone de transition mer-continent de la marge algérienne : implication géodynamique." Thesis, Nice, 2016. http://www.theses.fr/2016NICE4021/document.
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Comprendre comment s’initie une subduction au niveau d’une marge passive est un problème géodynamique majeur, mais il reste très débattu en raison des forces nécessaires pour provoquer la flexion de la plaque plongeante, et dépasser la résistance frictionnelle de la lithosphère pour localiser cette subduction. Formant la bordure sud de la Méditerranée Occidentale, la marge algérienne subit des conditions aux limites en compression en raison de la convergence Afrique-Eurasie à un taux de moins de 1 cm/an. Ce contexte favorise l’inversion de cette marge nord-africaine et possiblement le début d’une subduction. En effet, des données géophysiques récentes acquises dans le bassin algérien (campagnes de MARADJA, 2003, 2005 (MARge Active d’el Djazaïr) et SPIRAL 2009 (Sismique Profonde et Investigations Régionales en ALgérie) ont montré des indices de déformation compressive récente. Nous avons utilisé les profils SPIRAL afin de calculer l’état isostatique de la lithosphère au voisinage de la limite océan-continent. Ceci nous a permis d'imager un Moho trop profond dans le domaine océanique, et plus superficiel dans le domaine continental, de part et d'autre d'une limite située vers le pied de pente de cette marge, donc un déséquilibre isostatique général de la marge. Nos résultats indiquent que la marge algérienne montre les mêmes anomalies isostatiques qu’au niveau d'une marge active, avec une zone de découplage océan/continent située en pied de marge. Ces anomalies peuvent être interprétées par un mécanisme de flexure des deux lithosphères en présence, que l’on peut simuler ensuite par une modélisation en éléments finis d’une plaque mince élastiqueUnderstanding how subduction initiates at a passive margin is a major geodynamic question, which remains debatted because of the forces necessary to overcome bending and frictional resistance of the lithosphere and initiate this subduction. Along the southern shore of the Western Mediterranean Sea, the Algerian margin undergoes ~NS compression due to the African-Eurasian convergence at a rate of less than ~ 1 cm / year. This setting causes tectonic inversion of this North African passive margin and possibly incipient subduction. Indeed, recent geophysical marine data acquired in the Algerian Basin (MARADJA, 2003, 2005MARge Active d’el Djazaïr) and SPIRAL 2009 (Deep Seismic and Regional Investigations in Algeria campaigns) showed evidence of recent compressive deformation. We used SPIRAL wide-angle seismic profiles to determine the state of isostatic equilibrium at the vicinity of the continent-ocean boundary. This allowed us to image a too deep Moho in the oceanic part, and a too shallow one in the continental domain, with a boundary between both domains located at the margin toe. These results indicate that the Algerian margin display the same isostatic anomalies as an active margin. This isostatic disiquilibrium may be simulated by the flexural bending of two lithospheric plates that can be modelled by a finite element procedure. This modeling shows larger vertical deflection in the central part of the study area (6-7 km) compared to the earsternmost and westernmost profiles (3 km)
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Peng, Jun, and 彭軍. "Effects of strain gradient on maximun concrete stress and flexural capacity of normal-strength RC members." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43085787.
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Peng, Jun, and 彭军. "Strain gradient effects on flexural strength and ductility design of normal-strength RC beams and columns." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48329630.
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The stress-strain characteristics of concrete developed in flexure is very important for flexural strength design of reinforced concrete (RC) members. In current RC design codes, the stress-strain curve of concrete developed in flexure is obtained by scaling down the uni-axial stress-strain curve to account for the strain gradient effect. Therefore, the maximum concrete stress that can be developed under flexure is smaller than its uni-axial strength, and the use of which always underestimates the flexural strength of RC beams and columns even though the safety factors for materials are taken as unity. Furthermore, the value of strength underestimation was different for RC beams and columns, which indicates that the extent of strain gradient will affect the maximum concrete stress and stress-strain curve developed under flexure.
To investigate the maximum concrete stress, 29 column specimens were fabricated and tested in this study. They were divided into 9 groups, each of which was poured from the same batch of concrete and contained specimens with identical cross-section properties. In each group, one specimen was tested under concentric load while the rest was/were subjected to eccentric or horizontal load. To study the strain gradient effects, the ratio of the maximum concrete compressive stress developed in the eccentrically/horizontally loaded specimens to the maximum uni-axial compressive stress developed in the counterpart concentrically loaded specimens, denoted by k3, is determined based on axial force and moment equilibriums. Subsequently, the concrete stress block parameters and the equivalent rectangular concrete stress block parameters are determined. It is found that the ratios of the maximum and equivalent concrete stress to uni-axial cylinder strength, denoted respectively by k3 and , depend significantly on strain gradient, while that of the depth of stress block to neutral axis depth, denoted by , remains relatively constant with strain gradient. Design equations are proposed to relate and with strain gradient for strength calculation, whose applicability is verified by comparing the strengths of RC beams and columns tested by various researchers with their theoretical strengths predicted by the proposed parameters and those evaluated based on provisions of RC codes.
Based on the test results, the stress-strain curve of normal-strength concrete (NSC) developed under strain gradient is derived using least-square method by minimising the errors between the theoretical axial load and moment and the respective measured values. Two formulas are developed to derive the flexural stress-strain curve, whose applicability is verified by comparing the predicted strength with those measured by other researchers.
Lastly, the application of the proposed stress-block parameters and stress-strain curve of NSC will be illustrated by developing some charts for flexural strength design of NSC beams and columns. The application will further be extended to develop strength-ductility charts for NSC beams and columns, which enable simultaneous design of strength and ductility. By adopting the proposed design charts, the flexural strength design, as well as that of the plastic hinge forming mechanism during extreme events, will be more accurate. The resulting design will be safer, more environmentally friendly and cost effective.published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy
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Fuchs, John Peter. "Numerical and experimental investigation of the bending response of thin-walled composite cylinders." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40109.
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A numerical and experimental investigation of the bending behavior of six eight-ply graphite-epoxy circular cylinders is presented. Bending is induced by applying a known end-rotation to each end of the cylinder, analogous to a beam in bending. The cylinders have a nominal radius of 6 inches, a length-to-radius ratio of 2 and 5, and a radius-to-thickness ratio of approximately 160. A [±45/0/90]S quasi-isotropic layup and two orthotropic layups, [±45/02]S and [±45/902]s, are studied. A geometrically nonlinear special-purpose analysis, based on Donnell's nonlinear shell equations, is developed to study the prebuckling responses and gain insight into the effects of non-ideal boundary conditions and initial geometric imperfections. A geometrically nonlinear finite element analysis is utilized to compare with the prebuckling solutions of the special-purpose analysis and to study the buckling and postbuckling responses of both geonletrically perfect and imperfect cylinders.
The imperfect cylinder geometries are represented by an analytical approximation of the measured shape imperfections. Extensive experimental data are obtained from quasistatic tests of the cylinders using a test fixture specifically designed for the present investigation.
A description of the test fixture is included. The experimental data are compared to predictions for both perfect and imperfect cylinder geometries. Prebuckling results are presented in the form of displacement and strain profiles. Buckling end-rotations, moments. and strains are reported, and predicted mode shapes are presented. Observed and predicted moment vs. end-rotation relations, deflection patterns. and strain profiles are illustrated for the postbuckling responses. It is found that a geometrically nonlinear boundary layer behavior characterizes the prebuckling responses. The boundary layer behavior is sensitive to laminate orthotropy, cylinder geometry, initial geometric imperfections, applied end-rotation, and non-ideal boundary conditions. Buckling end-rotations, strains, and moments are influenced by laminate orthotropy and initial geometric imperfections.
Measured buckling results correlate well with predictions for the geometrically imperfect specimens. The postbuckling analyses predict equilibrium paths with a number of scallop-shaped branches that correspond to unique deflection patterns. The observed postbuckling deflection patterns and measured strain profiles show striking similarities to the predictions in some cases. Ultimate failure of the cylinders is attributed to an interlaminar shear failure mode along the nodal lines of the postbuckling deflection patterns.Ph. D.
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Peng, Jun. "Effects of strain gradient on maximun concrete stress and flexural capacity of normal-strength RC members." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43085787.
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