Spelling suggestions: "subject:"fiber composites"" "subject:"fiber komposites""
31 |
[pt] ANÁLISE EXPERIMENTAL DA ADERÊNCIA ENTRE O CONCRETO E COMPÓSITOS COM TECIDO DE FIBRAS DE CARBONO / [en] EXPERIMENTAL ANALISYS ON BOND BETWEEN CONCRETE AND CARBON FIBER COMPOSITES FABRICJULIANA MARTINELLI MENEGHEL 02 January 2006 (has links)
[pt] É descrito neste trabalho um programa experimental sobre a
aderência entre os
compósitos com tecido de fibras de carbono e o concreto.
Este programa
experimental consistiu em ensaios de tração-compressão de
corpos-de-prova
compostos de dois blocos de concreto (móvel e fixo)
colados por tiras de tecido
de fibra de carbono coladas nos lados opostos desses
blocos. Foram ensaiados
nove corpos-de-prova, com três resistências à compressão
aos 28 dias de 20,5
MPa, 28,7 MPa e 38,1 MPa e duas larguras do tecido iguais
a 50 mm e 100 mm.
Todos os corpos-de-prova foram concretados, instrumentados
e ensaiados no
Laboratório de Estruturas e Materiais da PUC-Rio. O
objetivo deste trabalho foi
estudar a influência da resistência do concreto e da
largura do tecido de fibra de
carbono sobre a resistência de aderência do sistema. Os
resultados mostraram
que a resistência de aderência pode ser considerada
independente da resistência
do concreto e da largura do tecido. Foi obtido, neste
estudo, um valor
característico de 1,45 MPa para a resistência de aderência. / [en] An experimental study on the bond between carbon fiber
fabric composites and
concrete is described in this work. This experimental
program consisted of
tension-compression tests of specimens with two concrete
blocks (movable and
fixed) jointed by carbon fiber fabric strips bonded on two
opposite sides of these
blocks. Nine specimens, with three concrete compressive
strength of 20,5MPa ,
28,7MPa and 38,1MPa at 28 days and two fabric width of 50
mm and 100
mm, were tested. All specimens had the same geometrical
characteristics. All the
specimens were cast, instrumented and tested in the
Structural and Materials
Laboratory at PUC-Rio. The objective of this work was to
study the influence of
concrete strength and the width of the fabric on the bond
strength of the system.
The results showed that the ultimate bond strength may be
considered
independent of concrete strength and of the width of the
fabric. A characteristic
value of 1.45 MPa was found for the bond strength.
|
32 |
Fracture Toughness of Carbon Fiber Composite MaterialRea, Allison 14 December 2022 (has links)
No description available.
|
33 |
Experimental Evaluation and Simulations of Fiber Orientation in Injection Molding of Polymers Containing Short Glass FibersVelez-Garcia, Gregorio Manuel 22 May 2012 (has links)
Injection molded short fiber reinforced composites have generated commercial interest in the manufacturing of lightweight parts used in semi-structural applications. Predicting these materials’ fiber orientation with quantitative accuracy is crucial for technological advancement, but the task is difficult because of the effect of inter-particle interactions at high concentrations of fiber found in parts of commercial interest.
A complete sample preparation procedure was developed to obtain optical micrographs with optimal definition of elliptical and non-elliptical footprint borders. Two novel aspects in this procedure were the use of tridimensional markers to identify specific locations for analysis and the use of controlled-etching to produce small shadows where fibers recede into the matrix. These images were used to measure fiber orientation with a customized image analysis tool. This tool contains several modifications that we introduced in the method of ellipses which allow us to determine tridimensional fiber orientation and to obtain measurements in regions with fast changes in orientation. The tool uses the location of the shadow to eliminate the ambiguity problem in orientation and characterizes non-elliptical footprints to obtain the orientation in small sampling areas.
Cavitywise measurements in two thin center-gated disks showed the existence of an asymmetric profile of orientation at the gate and an orientation profile that washed out gradually at the entry region until disappearing at about 32 gap widths. This data was used to assess the prediction of cavitywise orientation using a delay model for fiber orientation with model parameters obtained from rheometrical experiments. Model predictions combining slip correction and experimentally determined orientation at the gate are in agreement with experimental data for the core layers near the end-of-fill region.
Radialwise measurements of orientation at the shell, transition and core layer, and microtextural description of the advancing front are included in this dissertation. The analysis and assessment of the radial evolution of fiber orientation and advancing front based on comparing the experimental data with simulation results are under ongoing investigation. / Ph. D.
|
34 |
The role of flexibility on propulsive performance of flapping finsKancharala, Ashok Kumar 02 September 2015 (has links)
The versatility of the fish to adapt to diverse swimming requirements has attracted the attention of researchers in studying bioinspired propulsion for developing efficient underwater robotics. The tail/caudal fin is a major source of thrust generation and is believed that the fish modulates its fin stiffness to optimize the propulsive performance. Inspired by the stiffness modulation of fish fins, the objective of this research is to predict and evaluate the effect of flexibility on propulsive performance of flapping fins. The stiffness of the fins vary along their length and optimization studies have been performed to predict the stiffness profiles that maximize performance. Experiments performed on the real fish caudal fins to measure the stiffness variation along their length validate the theoretical optimal stiffness profiles and provide an insight about the evolution of fish fins for optimal performance. Along with the fin stiffness, the stiffness of the joint (caudal peduncle) connecting the fish body to the tail plays a major role in the generation of thrust. The numerical and experimental investigation has shown that there exists an optimal combination of fin and joint stiffness for each operating condition, thus providing the motivation for active stiffness control during locomotion to optimize efficiency.
Inspired by nature's ability to modulate stiffness and shape for different operating conditions, an investigation has been carried out on active control of flapping foils for thrust tailoring using Macro Fiber Composites (MFCs). It has been observed that the performance can be enhanced by controlling the deformation, and distributed actuation along fin produces maximum performance through proper selection of the phase difference between heaving and voltage. Flapping fins produce forces which are oscillatory in nature causing center of mass (COM) oscillations of the attached bodies posing problems of control and maneuverability. Optimization studies have revealed that flexibility of the fin plays a major role in reducing the COM oscillations along with the other operating parameters. Based on these studies, the design principles and guidelines that control the performance have been proposed which aid in the development of aerial and underwater robotic vehicles. Additionally, these studies provide some insight in to how fish might modulate its stiffness based on the requirements. / Ph. D.
|
35 |
Synthesis and Characterization of High Performance Polymers for Gas Separation and Water Purification Membranes and as Interfacial Agents for Thermplastic Carbon Fiber CompositesJoseph, Ronald Matthew 03 July 2018 (has links)
This dissertation focuses on the synthesis and characterization of high performance polymers, specifically polybenzimidazoles (PBIs) for gas separation applications and polyimides (PI) for water purification and as interfacial agents for thermoplastic carbon fiber composites.
Two methods for improving the gas transport properties (for H2/CO2 separation) of a tetraaminodiphenylsulfone (TADPS)-based polybenzimidazole were investigated. Low molecular weight poly(propylene carbonate) (PPC) and poly(ethylene oxide) (PEO) were incorporated as sacrificial additives that could be removed via a controlled heat treatment protocol. PBI films containing 7 and 11 wt% PPC (blend) and 13 wt% PEO (graft) were fabricated and the gas transport properties and mechanical properties after heat treatment were measured and compared to the PBI homopolymer. After heat treatment, the 7 wt% PPC blend exhibited the highest performance while retaining the toughness exhibited by the PBI homopolymer.
Novel sulfonated polyimides and their monomers were synthesized for use as interfacial agents and water purification membranes. Polyimides are high performance polymers that have high thermal, mechanical, and chemical stability. The objective was to assess structure-property relationships of novel sulfonated polyimides prepared by direct polymerization of the diamine monomers. A series of sulfonated polyimides was synthesized using an ester-acid polymerization method with varying degrees of sulfonation (20%, 30%, and 50% disulfonated and 50% and 100% monosulfonated polyimides). The results showed that the toughness of the polyimides in the fully hydrated state was much better than current commercial cation exchange membranes.
A 100% disulfonated polyimide (sPI) and poly(amic acid) salt (PAAS) using the same monomers used for the synthesis of Ultem® were utilized as suspending agents for the fabrication of coated sub-micron polyetherimide (PEI) particles. Sub-micron particles were obtained using 1 wt% PAAS and 4 wt% sPI to coat the PEI. The PEI particles were coupled onto ozone treated carbon fibers using a silane coupling agent. SEM images showed a significant amount of particle coating on the treated carbon fibers compared to the non-silane treated carbon fibers. / PHD
|
36 |
Manufacturing and Testing of Composite Hybrid Leaf Spring for Automotive ApplicationsHimal Agrawal (7043354) 12 August 2019 (has links)
Leaf
springs are a part of the suspension system attached between the axle and the
chassis of the vehicle to support weight and provide shock absorbing capacity
of the vehicle. For more than half a century the leaf springs are being made of
steel which increases the weight of the vehicle and is prone to rusting and
failure. The current study explores the feasibility of composite leaf spring to
reduce weight by designing, manufacturing and testing the leaf spring for the
required load cases. An off the shelf leaf spring of Ford F-150 is chosen for making
of composite hybrid spring prototype. The composite hybrid prototype was made
by replacing all the leaves with glass fiber unidirectional laminate except the
first leaf. Fatigue tests are then done on steel and composite hybrid leaf
spring to observe the failure locations and mechanism if any. High frequency
fatigue tests were then done on composite beams with varying aspect ratio in a displacement-controlled
mode to observe fatigue location and mechanism of just glass fiber composite
laminate. It was observed that specimens with low aspect ratio failed from
crack propagation initiated from stress concentrations at the loading tip in
3-point cyclic flexure test and shear forces played a dominant role in
propagation of crack. Specimens with high aspect ratio under the same loading did
not fail in cyclic loading and preserved the same stiffness as before the
cyclic loading. The preliminary fatigue results for high aspect ratio composite
beams predict a promising future for multi-leaf composite springs.
|
37 |
[en] EXPERIMENTAL INVESTIGATION OF THE BOND STRENGTH BETWEEN CFC-CONCRETE UNDER IMPACT LOADING / [pt] VERIFICAÇÃO EXPERIMENTAL DA ADERÊNCIA CFC-CONCRETO COM CARREGAMENTO DE IMPACTOANTONIO ROGERIO PELLISSARI 10 April 2008 (has links)
[pt] Neste trabalho realizou-se uma investigação experimental
sobre os efeitos de forças de impacto sobre a resistência
de aderência entre compósitos de fibras de carbono e o
concreto. O programa experimental consistiu de ensaios de
flexão de corpos-de-prova constituídos de dois blocos de
concreto unidos por uma rótula na região superior
(comprimida) e por tiras de compósito de fibras de
carbono coladas nas faces inferiores dos blocos. Foram
ensaiados 23 corpos-deprova, com resistências à compressão
do concreto variando de 25 MPa a 35 MPa. A principal
variável foi a taxa de carregamento ( expressa em termos de
tensão de aderência), variou entre 6,06 MPa/s (estático) a
3.690.485 MPa/s (dinâmico). Os resultados mostraram que a
resistência de aderência aumenta com o aumento da taxa de
carregamento. / [en] An experimental investigation on the effects of impact
loads on the bond
strength between carbon fiber composite and concrete is
described in this work.
The objective was to investigate the influence of loading
rate on the bond
strength. Concrete-fiber specimens were tested under
loading rates varying from
a minimum of 6,06 MPa/s (static) to a maximum of 3.690.485
MPa/s. In
addition, twenty tree concrete prisms were tested under
different loading rates in
order to investigate the effects of the loading rate on the
tensile strength of
concrete and carbon fiber separately. The results show that
the bond strength
increase with the increase of the loading rates.
|
38 |
[en] STRUCTURAL RELIABILITY ANALYSIS APPLICATION TO THE DESIGN OF CARBON FIBRES REINFORCED POLYMER SHEAR STRENGTHENING OF REINFORCED CONCRETE BEAMS / [pt] ANÁLISE DE CONFIABILIDADE DE ESTRUTURAS APLICADA AO PROJETO DE REFORÇO À FORÇA CORTANTE DE VIGAS EM CONCRETO ARMADO COM COMPÓSITOS DE FIBRAS DE CARBONOMARCELA TORNO DE AZEREDO LOPES 06 December 2007 (has links)
[pt] A análise de confiabilidade aplicada ao projeto de
estruturas é uma
ferramenta que permite avaliar a probabilidade de falha da
estrutura para um
certo modo de comportamento e a sensibilidade deste
projeto em relação às
variáveis consideradas. Neste trabalho a análise de
confiabilidade é aplicada
ao projeto de reforço à força cortante com compósitos de
fibras de carbono de
vigas em concreto armado. Inicialmente, modelos e
prescrições normativas
para verificar a capacidade resistente do reforço à força
cortante são
implementados em MathCad. Os resultados teóricos são
comparados com os
obtidos de programas experimentais realizados por diversos
pesquisadores.
Posteriormente, um programa de confiabilidade de
estruturas é implementado
em liguagem C onde é utilizado o método FORM First Order
Reliability
Method. Este programa permite: avaliar a confiabilidade à
força cortante de
seções de vigas de concreto armado reforçadas ou não e
dimensionar a taxa
geométrica de reforço para um valor estabelecido de índice
de confiabilidade
de referência e este valor segue recomendações do Eurocode
EN1990 (2001).
As taxas geométricas de reforço são dimensionadas por dois
enfoques: o semiprobabilístico,
prática corrente de projetos, e o probabilístico, projeto
baseado
em confiabilidade. Os resultados obtidos são comparados.
No enfoque
probabilístico, as taxas geométricas de reforço são
calculadas estabelecendo
que o valor do índice de confiabilidade equivalente,
avaliado utilizando
formulação de sistemas em série, seja maior ou igual ao
valor do índice de
confiabilidade de referência. Os valores dos índices de
confiabilidade,
considerando ou não a formulação de sistemas em série, das
probabilidades
de falha e dos fatores de importância das variáveis
aleatórias são obtidos para
a seção sem e com reforço. As coordenadas dos pontos de
projeto e os
coeficientes parciais de segurança são obtidos para a
seção reforçada. / [en] Structural reliability analysis provides a prediction of
the structural
probability of failure against some behavior mode and the
design sensibility with
respect to the random variables evaluated at the design
point. In this research
the reliability analysis is applied to design the carbon
fibres reinforced polymer
shear strengthening of reinforced concrete beams. First,
models and code
recommendations, available in literature, to verify the
shear strengthening are
implemented in MathCad. Further, a structural reliability-
based software, using
the First Order Reliability Method (FORM), is implemented
in C programming
language. This software provides the evaluation of the
shear reliability of
reinforced concrete beams cross-sections, either
strengthened or not by CFRP,
and the shear reinforcement ratio for a target reliability
index. The target
reliability index is established as defined by Eurocode EN
1990 (2001). The
random variables probabilistic models are based upon
code`s recommendations
available in specialized literature. The shear
reinforcement ratio is designed by
two approaches: semi-probabilistic, as the current design
practice, and the
probabilistic, reliability-based design. The results are
compared. In the
probabilistic approach, the shear reinforcement ratio
design aims to obtain a
series system reliability index value larger than a
predefined target value. The
reliability index values, their corresponding failure
probabilities and the
percentages of total uncertainty associated to which
random variable arise from
reliability-based design, developed for either
strengthened or not reinforced
concrete beams cross-sections. For the strengthened cross-
sections, the
design point and the partial safety factors are also
obtained.
|
39 |
Desenvolvimento de uma metodologia computacional para determinar coeficientes efetivos de compósitos inteligentes / Development of a computational methodology for determining effective coefficients of the smart compositesMedeiros, Ricardo de 15 February 2012 (has links)
O presente trabalho visa empregar uma metodologia numérica para determinar as propriedades macro mecânica de compósitos ativos (AFC - Active Fiber Composite ou MFC - Macro Fiber Composite), combinando o conceito de Volume Elementar Representativo (VER) com o Método dos Elementos Finitos (MEF). Inicialmente, apresenta-se a fundamentação teórica associada à abordagem numérica empregada. Posteriormente, os modelos numéricos desenvolvidos são aplicados na determinação dos coeficientes efetivos de materiais compósitos inteligentes transversalmente isotrópicos com fibras piezelétricas de seção com forma circular e quadrada, respectivamente. Finalmente, os resultados numéricos obtidos pela metodologia proposta são, então, comparados com resultados da literatura. Constata-se que os resultados obtidos são muito semelhantes aos resultados relatados pela literatura para arranjo quadrático e hexagonal com fibra de geometria circular, sendo que neste caso, compararam-se os resultados numéricos com analíticos obtidos através do Método de Homogeneização Assintótica. Em seguida, a metodologia é aplicada para determinação dos coeficientes efetivos para arranjo quadrático e hexagonal com fibra de geometria quadrada. Empregando diferentes frações volumétricas de fibras, os resultados via MEF foram comparados aos resultados analíticos obtidos através do Método dos Campos Uniformes (Uniform Field Method). Após a avaliação das limitações e potencialidades da metodologia, de forma direta, através de resultados analíticos, realizou-se a avaliação da mesma de forma indireta. Para tal, foram realizadas análises dinâmicas visando comparar as Funções de Resposta em Frequência (FRF) experimentais com as obtidas computacionalmente. Dessa forma, utilizou-se uma viga de alumínio estrutural engastada-livre, onde foram colados duas pastilhas piezelétricas, sendo uma para realizar a excitação da estrutura e, a outra para fazer a aquisição dos dados. Os modelos computacionais via MEF empregaram para o domínio das pastilhas, as propriedades efetivas determinadas através da metodologia desenvolvida. Os resultados obtidos demonstraram mais uma vez as potencialidades da metodologia proposta. Assim, conclui-se que a metodologia numérica não é somente uma boa alternativa para o cálculo de coeficientes efetivos de compósitos inteligentes, mas também uma ferramenta para o projeto de estruturas inteligentes monitoradas por materiais piezelétricos. / This work presents the development a numerical methodology to determine the mechanical properties of active macro composites (AFC - Active Fiber Composite, or MFC - Macro Fiber Composite), combining the concept of Representative Elementary Volume (REV) with the Finite Element Method (FEM). In the first instance, the theoretical framework associated with the numerical approach employed is presented. Later, numerical models based on unit cell are applied to predict the effective material coefficients of the transversely isotropic piezoelectric composite with circular cross section fibers. Finally, numerical results obtained by the proposed methodology are compared to other methods reported in the literature. It appears that the results are very similar to the literature results for square and hexagonal arrangement of fibers with circular geometry, in which case, it was compared numerical with analytical results calculated by Asymptotic Homogenization Method (AHM). After that, the methodology is applied to determine the effective coefficients for square and hexagonal array with square fiber geometry. Employing different fiber volume fractions, it follows that the results obtained by the proposed methodology were compared to analytical results calculated by the Uniform Field Method (UFM). After assessing the potential and limitations of the methodology, either directly, through analytical results, the evaluation took place in the indirect approach. Then, dynamic analyses were performed in order to compare the Frequency Response Functions (FRFs) determined by experimental tests with computational results. Thus, it was used a cantilever beam aluminum structure, which were bonded two piezoelectric patches, one to carry the excitement of the structure and the second to perform the data acquisition. The effective properties determined by the proposed methodology were applied for the dominium established by the piezoelectric patches. The results showed, again, the potential of the proposed methodology. Therefore, the numerical methodology is not only a good alternative for the calculation of effective coefficients of smart composite, but also a tool for the design of smart structures monitored by piezoelectric materials.
|
40 |
Desenvolvimento de uma metodologia computacional para determinar coeficientes efetivos de compósitos inteligentes / Development of a computational methodology for determining effective coefficients of the smart compositesRicardo de Medeiros 15 February 2012 (has links)
O presente trabalho visa empregar uma metodologia numérica para determinar as propriedades macro mecânica de compósitos ativos (AFC - Active Fiber Composite ou MFC - Macro Fiber Composite), combinando o conceito de Volume Elementar Representativo (VER) com o Método dos Elementos Finitos (MEF). Inicialmente, apresenta-se a fundamentação teórica associada à abordagem numérica empregada. Posteriormente, os modelos numéricos desenvolvidos são aplicados na determinação dos coeficientes efetivos de materiais compósitos inteligentes transversalmente isotrópicos com fibras piezelétricas de seção com forma circular e quadrada, respectivamente. Finalmente, os resultados numéricos obtidos pela metodologia proposta são, então, comparados com resultados da literatura. Constata-se que os resultados obtidos são muito semelhantes aos resultados relatados pela literatura para arranjo quadrático e hexagonal com fibra de geometria circular, sendo que neste caso, compararam-se os resultados numéricos com analíticos obtidos através do Método de Homogeneização Assintótica. Em seguida, a metodologia é aplicada para determinação dos coeficientes efetivos para arranjo quadrático e hexagonal com fibra de geometria quadrada. Empregando diferentes frações volumétricas de fibras, os resultados via MEF foram comparados aos resultados analíticos obtidos através do Método dos Campos Uniformes (Uniform Field Method). Após a avaliação das limitações e potencialidades da metodologia, de forma direta, através de resultados analíticos, realizou-se a avaliação da mesma de forma indireta. Para tal, foram realizadas análises dinâmicas visando comparar as Funções de Resposta em Frequência (FRF) experimentais com as obtidas computacionalmente. Dessa forma, utilizou-se uma viga de alumínio estrutural engastada-livre, onde foram colados duas pastilhas piezelétricas, sendo uma para realizar a excitação da estrutura e, a outra para fazer a aquisição dos dados. Os modelos computacionais via MEF empregaram para o domínio das pastilhas, as propriedades efetivas determinadas através da metodologia desenvolvida. Os resultados obtidos demonstraram mais uma vez as potencialidades da metodologia proposta. Assim, conclui-se que a metodologia numérica não é somente uma boa alternativa para o cálculo de coeficientes efetivos de compósitos inteligentes, mas também uma ferramenta para o projeto de estruturas inteligentes monitoradas por materiais piezelétricos. / This work presents the development a numerical methodology to determine the mechanical properties of active macro composites (AFC - Active Fiber Composite, or MFC - Macro Fiber Composite), combining the concept of Representative Elementary Volume (REV) with the Finite Element Method (FEM). In the first instance, the theoretical framework associated with the numerical approach employed is presented. Later, numerical models based on unit cell are applied to predict the effective material coefficients of the transversely isotropic piezoelectric composite with circular cross section fibers. Finally, numerical results obtained by the proposed methodology are compared to other methods reported in the literature. It appears that the results are very similar to the literature results for square and hexagonal arrangement of fibers with circular geometry, in which case, it was compared numerical with analytical results calculated by Asymptotic Homogenization Method (AHM). After that, the methodology is applied to determine the effective coefficients for square and hexagonal array with square fiber geometry. Employing different fiber volume fractions, it follows that the results obtained by the proposed methodology were compared to analytical results calculated by the Uniform Field Method (UFM). After assessing the potential and limitations of the methodology, either directly, through analytical results, the evaluation took place in the indirect approach. Then, dynamic analyses were performed in order to compare the Frequency Response Functions (FRFs) determined by experimental tests with computational results. Thus, it was used a cantilever beam aluminum structure, which were bonded two piezoelectric patches, one to carry the excitement of the structure and the second to perform the data acquisition. The effective properties determined by the proposed methodology were applied for the dominium established by the piezoelectric patches. The results showed, again, the potential of the proposed methodology. Therefore, the numerical methodology is not only a good alternative for the calculation of effective coefficients of smart composite, but also a tool for the design of smart structures monitored by piezoelectric materials.
|
Page generated in 0.1096 seconds