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High strain-rate behaviour of polymers using blast-wave and impact loading methodsAhmad, Sahrim Haji January 1988 (has links)
No description available.
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Development of a strain energy storage mechanism using tension elements to enhance golf club performance /Whitezell, Marc A., January 2006 (has links) (PDF)
Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (p. 107-109).
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Dynamic interactions of electromagnetic and mechanical fields in electrically conductive anisotropic compositesBarakati, Amir 01 December 2012 (has links)
Recent advances in manufacturing of multifunctional materials have provided opportunities to develop structures that possess superior mechanical properties with other concurrent capabilities such as sensing, self-healing, electromagnetic and heat functionality. The idea is to fabricate components that can integrate multiple capabilities in order to develop lighter and more efficient structures. In this regard, due to their combined structural and electrical functionalities, electrically conductive carbon fiber reinforced polymer (CFRP) matrix composites have been used in a wide variety of applications in most of which they are exposed to unwanted impact-like mechanical loads. Experimental data have suggested that the application of an electromagnetic field at the moment of the impact can significantly reduce the damage in CFRP composites. However, the observations still need to be investigated carefully for practical applications. Furthermore, as the nature of the interactions between the electro-magneto-thermo-mechanical fields is very complicated, no analytical solutions can be found in the literature for the problem.
In the present thesis, the effects of coupling between the electromagnetic and mechanical fields in electrically conductive anisotropic composite plates are studied. In particular, carbon fiber polymer matrix (CFRP) composites subjected to an impact-like mechanical load, pulsed electric current, and immersed in the magnetic field of constant magnitude are considered. The analysis is based on simultaneous solving of the system of nonlinear partial differential equations, including equations of motion and Maxwell's equations. Physics-based hypotheses for electro-magneto-mechanical coupling in transversely isotropic composite plates and dimension reduction solution procedures for the nonlinear system of the governing equations have been used to reduce the three-dimensional system to a two-dimensional (2D) form. A numerical solution procedure for the resulting 2D nonlinear mixed system of hyperbolic and parabolic partial differential equations has been developed, which consists of a sequential application of time and spatial integrations and quasilinearization. Extensive computational analysis of the response of the CFRP composite plates subjected to concurrent applications of different electromagnetic and mechanical loads has been conducted. The results of this work verify the results of the previous experimental studies on the subject and yield some suggestions for the characteristics of the electromagnetic load to create an optimum impact response of the composite.
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Measurements of Drag Torque and Lift Off Speed and Identification of Stiffness and Damping in a Metal Mesh Foil BearingChirathadam, Thomas A. 2009 December 1900 (has links)
Metal mesh foil bearings (MMFBs) are a promising low cost gas bearing technology
for support of high speed oil-free microturbomachinery. Elimination of complex oil
lubrication and sealing system by installing MMFBs in oil free rotating machinery offer
distinctive advantages such as reduced system overall weight, enhanced reliability at
high rotational speeds and extreme temperatures, and extended maintenance intervals
compared to conventional turbo machines. MMFBs for oil-free turbomachinery must
demonstrate adequate load capacity, reliable rotordynamic performance, and low
frictional losses in a high temperature environment.
The thesis presents the measurements of MMFB break-away torque, rotor lift off and
touchdown speeds, temperature at increasing static load conditions, and identified
stiffness and equivalent viscous damping coefficients. The experiments, conducted in a
test rig driven by an automotive turbocharger turbine, demonstrate the airborne operation
(hydrodynamic gas film) of the floating test MMFB with little frictional loses at
increasing loads. The measured drag torque peaks when the rotor starts and stops, and
drops significantly once the bearing is airborne. The estimated rotor speed for lift-off
increases linearly with increasing applied loads. During continuous operation, the
MMFB temperature measured at one end of the back surface of the top foil increases
both with rotor speed and static load. Nonetheless, the temperature rise is only nominal
ensuring reliable bearing performance. Application of a sacrificial layer of solid
lubricant on the top foil surface aids to reduce the rotor break-away torque. The
measurements give confidence on this simple bearing technology for ready application
into oil-free turbomachinery.
Impact loads delivered (with a soft tip) to the test bearing, while resting on the
(stationary) drive shaft, evidence a system with large damping and a structural stiffness
that increases with frequency (max. 200 Hz). The system equivalent viscous damping
ratio decreases from ~ 0.7 to 0.2 as the frequency increases. In general, the viscous
damping in a metal mesh structure is of structural type and inversely proportional to the
frequency and amplitude of bearing motion relative to the shaft. Impact load tests,
conducted while the shaft rotates at 50 krpm, show that the bearing direct stiffness is
lower (~25% at 200 Hz) than the bearing structural stiffness identified from impact load
tests without shaft rotation. However, the identified equivalent viscous damping
coefficients from tests with and without shaft rotation are nearly identical.
The orbits of bearing motion relative to the rotating shaft show subsynchronous
motion amplitudes and also backward synchronous whirl. The subsynchronous vibration
amplitudes are locked at a frequency, nearly identical to a rotor natural frequency. A
backward synchronous whirl occurs while the rotor speed is between any two natural
frequencies, arising due to bearing stiffness asymmetry.
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Failure analysis on laminate structures of windsurfing boards using thin film modelling techniquesSchwarzer, Norbert, Heuer-Schwarzer, Peggy 08 February 2006 (has links) (PDF)
Within this paper recently developed mathematical tools for the modelling of contact problems on thin film structures [1] for multilayers and gradient coatings are adapted to allow the investigation of laminate structures of transversal isotropy.
Applying series approaches using Bessel and Sinus functions complete three dimensional solutions can be found for relatively complex laminate structures allowing to model quasistatic contact, impact and bending loads. Worked into a small computer program the approach can be used to model laminate structures with up to 100 different layers on an ordinary personal computer in an acceptable calculation time.
The new tool is applied to analyse a variety of load problems typically occurring in windsurfing and leading to damage of the boards consisting of a laminated shell and an polymer foam core.
[1] N. Schwarzer: „Modelling of the mechanics of thin films using analytical linear elastic approaches“, habilitation thesis of the TU-Chemnitz 2004, department “Physics of solid bodies”, http://archiv.tu-chemnitz.de/pub/2004/0077
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[en] BEHAVIOR OF REINFORCED CONCRETE BEAMS STRENGTHENED WITH CFC UNDER IMPACT LOADING / [pt] COMPORTAMENTO DE VIGAS DE CONCRETO ARMADO REFORÇADAS COM CFC SUJEITAS A CARGA DE IMPACTOROBERTO MACHADO DOS SANTOS 20 February 2009 (has links)
[pt] Este trabalho tem como objetivo o estudo experimental do
comportamento
de vigas de concreto armado reforçadas a flexão com CFC
sujeitas a carga de
impacto. As variáveis adotadas foram a taxa de carregamento
e a taxa de
reforço. Todas as vigas foram dimensionadas para resistirem
ao mesmo
carregamento, de forma que a ruptura fosse governada pelo
escoamento do aço
da armadura longitudinal de tração. O programa experimental
consistiu no
ensaio de dezoito vigas biapoiadas de concreto armado.
Todas as vigas foram
construÃdas com a mesma seção transversal, vão e
resistência de concreto,
diferindo somente na armadura longitudinal de tração. Foram
confeccionados
três tipos de vigas, sendo que as vigas com maior taxa de
aço de armadura
longitudinal de tração não receberam reforço, enquanto que
as demais foram
reforçadas com CFC de forma a suportar a mesma carga última
das vigas sem
reforço. Foram realizados ensaios estáticos e dinâmicos.
Para a aplicação da
carga de impacto utilizou-se um martelo, que liberado de
diferentes alturas de
queda, forneceu diferentes taxa de carregamento e,
consequentemente, diferentes
taxas de deformação nas vigas ensaiadas. Os resultados
mostraram que as vigas
com reforço de CFC possuem menor capacidade de
desaceleração do movimento
de queda do martelo. Verificou-se que quanto maior a altura
de queda do martelo
maior é a força máxima de reação das vigas, apresentando um
crescimento
praticamente linear com o aumento da taxa de carregamento. / [en] An experimental study on the behavior of reinforced
concrete beams
strengthened in flexure with CFC under impact load was
carried out in this
work. The main objective was to investigate the effects of
the loading rate on the
strength of the beams. The variables were the loading rate
and the ratio of fiber
to steel reinforcement cross sections. All beams were
design to resist the same
load, in a way that the failure should be governed by the
yielding of the
longitudinal tension steel reinforcement. The experimental
program consisted of
the test of eighteen simply supported beams. All the beams
had the same cross
section, span and concrete strength. The only difference
was the amount of
longitudinal tension steel and fiber reinforcements. Static
and dynamic testing
had been carried through. A hammer was used for the impact
load application,
which was released from different heights, giving different
loads rates and,
consequently, different deformation rates in the tested
beams. The results
showed that the beams with reinforcement of CFC had less
capacity of
movement deceleration of hammer fall. It was observed that
the higher the
height of the hammer the higher was the maximum force of
reaction of the
beams, showing practically a linear growth with the
increase of the loading rate.
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Failure analysis on laminate structures of windsurfing boards using thin film modelling techniquesSchwarzer, Norbert, Heuer-Schwarzer, Peggy 08 February 2006 (has links)
Within this paper recently developed mathematical tools for the modelling of contact problems on thin film structures [1] for multilayers and gradient coatings are adapted to allow the investigation of laminate structures of transversal isotropy.
Applying series approaches using Bessel and Sinus functions complete three dimensional solutions can be found for relatively complex laminate structures allowing to model quasistatic contact, impact and bending loads. Worked into a small computer program the approach can be used to model laminate structures with up to 100 different layers on an ordinary personal computer in an acceptable calculation time.
The new tool is applied to analyse a variety of load problems typically occurring in windsurfing and leading to damage of the boards consisting of a laminated shell and an polymer foam core.
[1] N. Schwarzer: „Modelling of the mechanics of thin films using analytical linear elastic approaches“, habilitation thesis of the TU-Chemnitz 2004, department “Physics of solid bodies”, http://archiv.tu-chemnitz.de/pub/2004/0077
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Vliv hyperkinetické zátěže na vybrané mechanické změny axiálního systému člověka. / Influence of Hyperkinetic Load on Selected Mechanical Changes of Human Axial System.Panská, Šárka January 2019 (has links)
Title: Influence of Hyperkinetic Load on Selected Mechanical Changes of Human Axial System. Objectives: The main aim of this thesis is to determine the influence of hyperkinetic load on the change of selected mechanical properties of the rhythmic gymnastic axial system based on the sophisticated use of the Transfer Vibration through Spine (TVS) method. Methods: The following experimental methods were used to identify changes in rheological properties of AS and to assess load intensity: 1) TVS method; 2) software for evaluating and analyzing vibration tests of heterogeneous systems; 3) kinematic and dynamic motion analysis using: 2D motion video recording, QUALISYS 3D motion analysis system, KISTLER, to analyze dynamic human-surroundings interactions. Results: Pilot studies and the main experimental part of the thesis have shown that the use of the TVS method can identify both short-term and longitudinal changes of AS mechanical properties. Due to the hyperkinetic load, the selected mechanical properties of the rhythmic AS are changed. The gymnastic apparatus reacts to the training load by reducing the rheological parameters, especially the damping coefficient b and the viscosity µ. After regeneration, which is on the following day, the parameters return to the default values. The impact load...
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Fallviktsförsök på skjuvarmerade betongbalkarAtterling, Louise, Widmark, My January 2022 (has links)
Standards and regulations for dimensioning of load-bearing structures are based on the response of load-bearing structures subjected to loads without variation in time. In the event of an accidental load, e.g. a collision or explosion, causes the load to have a rapid variation in the time resulting in a dynamic response. Previous studies have shown that structures that respond in a certain way under static load have shown a completely different behavior under dynamic influence and therefore it is of interest to study the dynamic response of structures.By testing concrete beams with varying amounts of shear reinforcement subjected to impact loading, the purpose of this report is to analyze how the beams responds in terms of crack width and vibrations when they are exposed to a dynamic load. For comparison, reference tests have also been performed on beams subjected to a quasi-static load.The result of the project shows that the shear reinforcement comes into play as the beams with a larger amount of reinforcement have more capacity to hold the flexural shear cracks together. There is also an indication that the dynamic flexural shear capacity could be lower than static shear capacity as the shear cracks had an increased inclination during dynamic loading for some of the beams. This results in a decreased flexural shear capacity as only one stirrup carried the load across the shear crack.Measured signal shows that beams failing respond when impacted by the similar to a plastic collision, while beams responding with a flexure dominated mode without going to failure instead answer similar to an elastic collision. Furthermore, there is indication that the natural frequencies change significantly due to both flexural cracks and flexural shear cracks.
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Etude du comportement dynamique d'un massif en sol renforcé par géotextile alvéolaire M3S® / Study of the dynamic behaviour of a soil mass reinforced with M3S® cellular geotextileSoude, Maxime Charles 11 October 2011 (has links)
Depuis 2007, la société Sol-Solution avec le partenariat du laboratoire LaMI de l’Université Blaise Pascal de Clermont-Ferrand a entrepris des recherches pour étudier le comportement mécanique d’un ouvrage en sol renforcé par une structure alvéolaire M3S® et soumis à une sollicitation dynamique. Dans le cadre de ce travail de recherche, les sollicitations de type choc ont plus particulièrement été étudiées. Ce mémoire est structuré en 3 parties : la première partie rappelle les caractéristiques principales du comportement mécanique ainsi que les principes généraux de conception d’un ouvrage en sol renforcé par géotextiles M3S®. Une étude bibliographique s’intéresse ensuite à la caractérisation des 3 sollicitations dynamiques retenues (séisme, explosion, choc) et aux méthodes existantes permettant leur prise en compte dans la conception d’ouvrage ; la seconde partie présente l’approche numérique préliminaire qui a conduit au développement de deux modèles numériques d’impacts sur des structures en sol renforcé par géocellulaires. Les résultats ont permis d’identifier les paramètres mécaniques les plus influents des différents matériaux constitutifs ; la dernière partie s’appuie sur les résultats précédents ainsi que sur les lois de similitudes pour concevoir une expérimentation d’un impact sur deux massifs alvéolaires à échelle géométrique 1/10e. L’influence sur la réponse de deux types de renforcement au comportement mécanique différent a été étudiée. Les résultats expérimentaux ont ensuite permis un développement des deux modèles numériques préliminaires. Enfin, les perspectives d’utilisation de cet outil numérique ainsi que les applications industrielles sont présentées. / Since 2007, Sol Solution company with the help of the Clermont-Ferrand Blaise Pascal University’s LaMI laboratory, performed a study on the mechanical behaviour under dynamic load of a structure reinforced by the M3S (c) geocell system. In the context of that PhD, impact solicitations have been studied. This memory is divided in three parts : First part focuses on the main mechanical behaviour characteristics and general rules of reinforced soil with M3S(c) geocells design. Then, the bibliographical approach focuses on the 3 dynamic loads chosen (seism, blast, impact) and on the way they are taking in account on work design ; Second part shows the preliminary numerical approach which lead to the development of two numerical impact model on soil reinforced geocell structure. Results allows us to identify the most influent mechanical parameters of the different materials ; Last part groups numerical and similitude laws that allow to design a 1/10th low-scale impact experiment on two structures. Two different reinforcement were tested, plastic and paper. Experimental results allowed to improve two preliminary numerical models. Finally, discussion about that numerical tool and engineering applications are performed.
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