Tesi: "Polymeric composites"

1

Norpoth, Lawrence R. "Processing parameters for the consolidation of thermoplastic composites". Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/19099.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Corlay, Charlotte. "Thermal and mechanical analysis of polymer matrix composite materials exposed to a concentrated heat source for a short duration". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 236 p, 2007. http://proquest.umi.com/pqdlink?did=1251905081&Fmt=7&clientId=79356&RQT=309&VName=PQD.

Testo completo

Abstract (sommario):

Thesis (M.S.M.E.)--University of Delaware, 2006.
Principal faculty advisors: Suresh G. Advani, Dept. of Mechanical Engineering; and Shridhar Yarlagadda, Shridhar Yarlagadda, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Prystaj, Laurissa Alia. "Effect of carbon filler characteristics on the electrical properties of conductive polymer composites possessing segregated network microstructures". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/31667.

Testo completo

Abstract (sommario):

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Rosario Gerhardt; Committee Member: Gleb Yushin; Committee Member: Hamid Garmestani. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Gli stili APA, Harvard, Vancouver, ISO e altri

4

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

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Podnos, Eugene Grigorievich. "Application of fictitious domain method to analysis of composite materials /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Poole, Eric L. "Durability of polymeric composites after elevated temperature aging /". Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9963.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Potocki, Mark L. "Behavior of composite panels under an applied load and one dimensional heat flux /". Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/7025.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Yang, Heechun. "Modeling the processing science of thermoplastic composite tow prepreg materials". Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/17217.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Bhuyan, Satyam Kumar. "Investigation of tribological properties of biobased polymers and polymeric composites". [Ames, Iowa : Iowa State University], 2008.

Cerca il testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

10

Batra, Saurabh. "Creep rupture and life prediction of polymer composites". Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10381.

Testo completo

Abstract (sommario):

Thesis (M.S.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains xix, 195 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 193-195).

Gli stili APA, Harvard, Vancouver, ISO e altri

11

Gates, Peter. "Polymeric facades : advanced composites for retrofit". Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619213.

Testo completo

Abstract (sommario):

Replacing a building’s façade offers the prospect of improving the whole life performance of the building, in some instances as a favourable alternative to replacing the entire structure. This presents the opportunity to exploit the properties of advanced composite materials for maximum benefit. ‘Upwards and outwards’ retrofit, where extending floor slabs yields extra floor area, is permitted by a lightweight replacement façade, without the need to underpin foundations. For typical medium or high-rise office buildings, the extra let-able space obtained, and reduced heating and maintenance costs, can work to offset the expense of implementation. The specific materials, manufacturing processes, and façade type, most appropriate for such a scheme have been investigated. A unitised façade of sandwich panels with foam cores and pultruded GFRP skins has formed the ‘design platform’ for research conducted. It is paramount to resolve how the connections in such a façade system can meet the many requirements of an integrated building envelope. Structural integrity, enhanced environmental control, sustainability attributes, fire provisions, acoustic control, ease of manufacture, tolerance control, durability, lightness in weight, cost effectiveness and aesthetics must all be addressed simultaneously by any proposed design methodology. Investigating suitable connections through prototype development and review reveals key issues requiring targeted research. The permanent action acting on light, selfsupporting GFRP panels is small, however wind and occupancy loading impart significant imposed actions. Therefore, whilst creep deflection is often a significant consideration for structural GFRP design, quantifying fatigue performance is a higher priority for validating the ideology of polymeric facades. The unidirectional nature of pultrusion reinforcement yields a scenario of principle stresses at the panel interfaces, occurring in the weaker, secondary fibre, direction. As a consequence a fatigue-testing programme is aimed at understanding the performance and characteristics of pultruded angles compatible with ‘long-edge’ panel connections. The long-term performance of fibre-reinforced polymer (FRP) structures must be assessed if FRP is to win acceptance as a mainstream material for use in the construction industry. The environmental durability of wholly polymeric structures is often called in to question. In response, accelerated testing is usually undertaken on artificially aged FRP specimens; lack of genuine naturally aged material has previously hindered research and validation of material related design life. Case study investigation has permitted a full durability appraisal of naturally aged GFRP through laboratory testing campaign. Retrofit of existing buildings as an activity makes up 50% of all building construction in the UK. This project aims to address the shortfall in industry-required design knowledge. The tensile strength of pultruded naturally aged GFRP has been shown to reduce by only 0.65% over 17 years where natural exposure does not include UV irradiation, and by 13.1% where UV irradiation does occur as one element of exposure. The findings expose the degree of inaccuracy and fundamental flaws in existing predictive ageing models. The physical mechanisms of degradation do not match. A procedure to quantify the extent of polymer brittle hardening has been developed and applied as an analytical tool. Mechanical testing campaign has pioneered the use of the RMS (Route Mean Square) procedure to present the performance of connection specimens as a continuous function throughout programmes of fatigue testing. Testing has shown that though a threshold strain for damage accumulation does exist in complex fatigue loading of connections, and for direct tension fatigue loading.

Gli stili APA, Harvard, Vancouver, ISO e altri

12

Sharma, Rajdeep. "Micromechanics of toughening in polymeric composites". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38561.

Testo completo

Abstract (sommario):

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (leaves 195-206).
The macroscopic tensile toughness of glassy homo-polymers is often limited due to either localized crazing followed by failure [e.g., polymethyl-methacrylate (PMMA), polystyrene (PS)], or cavitation-induced brittle failure under high triaxiality [e.g., polycarbonate (PC)]. Judicious choice of polymer composites alleviates the above concerns by spreading the inelastic deformation and damage throughout the material, thereby increasing the macroscopic toughness. This thesis focuses on the micro- and macro-mechanics of two polymer composite systems - ductile/brittle PC/PMMA microlaminates and rubber-toughened PS. Ductile/brittle microlaminates are comprised of alternating layers of ductile polymer (e.g., PC) that inelastically deform by shear yielding, and brittle polymer (e.g., SAN, PMMA) that undergo crazing in tension. The layer thicknesses are typically in the sub-micron to tens of micron range. We have modeled the deformation and axial tensile toughness of PC/PMMA micro-laminates. Experiments indicate that the macroscopic ductility of ductile/brittle polymeric laminates depends on several factors such as the thickness of the brittle and ductile layers, the volume fraction of the ductile component, as well as strain rate.
(cont.) The nominally brittle layer can undergo in-elastic deformation by both crazing and shear-yielding, with the relative contribution of these mechanisms being dependent on the laminate morphology and strain rate. In particular, with decreasing brittle layer thickness, the inelastic behavior of the brittle layer is dominated by shear-yielding. We present a micromechanical model for two-phase ductile/brittle laminates that enables us to capture the macroscopic behavior, as well as the underlying micro-mechanisms of deformation and failure, in particular the synergy between crazing and shear yielding. The finite element implementation of our model considers a two-dimensional and three-dimensional representative volume element (RVE), and incorporates continuum-based physics-inspired descriptions of shear yielding and crazing, along with failure criteria for the ductile and brittle layers. The interface, between the ductile and brittle layers, is assumed to be perfectly bonded. The model is used to probe the effect of laminate parameters, such as the absolute and relative layer thicknesses, and material properties on the behavior during tensile loading. In addition, our modeling approach can be generalized to other laminate systems, such as two-phase brittle-1/brittle-2 and three-phase ductile-I/brittle/ductile-2 laminates, as well as to more complex loading conditions.
(cont.) Results from our studies reveal that the 2D RVE does not adequately capture the effect of volume fraction of the constituents on the laminate toughness. However, the 3D RVE captures the effect of volume fraction based on the extent of craze tunneling through the width of the specimen; at high volume fractions of PC, crazes emanating from the surface do not tunnel through the specimen width significantly, while at low volume fractions of PC, the crazes tunnel through the entire specimen width. The 3D RVE captures the strain-rate effect on toughness based on the greater rate-sensitivity of shear yielding compared to craze initiation, thereby increasing the craze density in the laminate at higher rates. The length-scale effect is captured by the 3D RVE, based on decrease in the craze opening rate and damage confinement by the PC layers. It is well-known that the incorporation of a small volume fraction (10-25 %) of micron-order size, compliant and well-dispersed rubbery particles in (brittle and crazeable) polystyrene (PS) yields considerable dividends in tensile toughness at the expense of reduction in stiffness and yield strength. In commercial rubber-toughened PS, the rubbery particles often have a composite "salami" morphology, consisting of 70-80 % volume fraction of sub-micron PS occlusions dispersed in a topologically, continuous polybutadiene (PB) phase.
(cont.) While it is recognized that these composite particles play the dual role of providing multiple sites for craze initiation in the PS matrix and allow the stabilization of the crazing process through cavitation/fibrillation in the PB-phase within the particle, the precise role of particle morphology, as well as the particle-matrix interface are not well understood or quantified. This work probes the micromechanics and macromechanics of uni-axial tensile deformation and failure in rubber-toughened PS through axi-symmetric finite element representative volume element (RVE) models that can guide the development of blends of optimal toughness. The RVE models reveal the effect on craze morphology and toughness by various factors such as particle compliance, particle morphology, particle fibrillation and particle volume fraction. The principal result of our study is that particle compliance and particle heterogeneity alone cannot account for the macroscopic behavior of HIPS, as well as the experimentally observed craze profile. Fibrillation/cavitation of PB domains within the heterogeneous particle provides the basic key ingredient to account for the micro- and macro-mechanics of HIPS.
by Rajdeep Sharma.
Ph.D.

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Hayes, Brian Steven. "Simulation engineering of polymeric prepreg composite systems /". Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9906.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Such, Georgina School of Chemical Engineering &amp Industrial Chemistry UNSW. "The investigation of novel polymer-photochromic conjugates". Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2005. http://handle.unsw.edu.au/1959.4/32750.

Testo completo

Abstract (sommario):

My research has focussed on the development of a technique to tailor photochromic switching rates by creating a customised local environment for the dye within an otherwise rigid host matrix. Living radical polymerisation offers the potential to design such a system. A living radical initiator based on a spirooxazine compound was used to polymerise a polymer chain of well controlled molecular weight and polydispersity. This technique facilitated the construction of a conjugate with every photochromic moiety convalently attached to a polymer chain with uniform characteristics. The photochromic behaviour of these new polymer-spirooxazine conjugates were investigated in a cross-linked polymer matrix with a Tg of approximately 120??C. It is well known that photochromic switching is susceptible to local environment effects such as rigidity, free volume and polarity.1, 2 The goal of these systems was to create a uniform local environment which would facilitate controlled changes in the photochromic switching rates. The photophysical investigation of these systems demonstrated the success of this technique. The photochromic rates were directly related to the characteristics of the polymer conjugate. It was postulated the conjugates acted as a customised local environment for the photochromic moiety, encapsulating it from the host matrix. Consequently systematic tailoring of the photochromic switching rates was achieved by changes in the characteristics of the attached polymer. To our knowledge this is the first technique to control local environment of a photochromic compound and thus the first example of systematic tuning of photochromic switching rates. Throughout this research, several characteristics of the attached polymer were modified to give a series of rules for the tuning of photochromic switching rates using this technique. The largest variation in switching speed is achieved through variation of Tg. A range of photochromic rates from extremely slow to near solution-like can be easily achieved. The necessary variations in Tg can be achieved easily using living radical polymerisation techniques. The use of different homopolymers, block and random copolymers were all demonstrated successfully in this work. For finer tuning of the photochromic rates, changes in chain length can be used. It was also found the best living radical polymerisation method for this work was ATRP due to the bulky or incompatible halogen which contributed to efficient encapsulation. However this endgroup effect is only important in systems which do not have a low Tg component. The incorporation of such a component overrides all other contributions to the overall behaviour.

Gli stili APA, Harvard, Vancouver, ISO e altri

15

Le, Guilly Marie O. "Development of ionic polymer actuator arrays /". Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/7078.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Liu, Jing. "Carbon nanotube/polymer composites and novel micro- and nano-structured electrospun polymer materials". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/22673.

Testo completo

Abstract (sommario):

Thesis (Ph. D.)--Textile and Fiber Engineering, Georgia Institute of Technology, 2007.
Committee Chair: Kumar, Satish; Committee Member: Carr, Wallace; Committee Member: Graham, Samuel; Committee Member: Griffin, Anselm; Committee Member: Yao, Donggang.

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Ng, Po-king. "Molecular and polymeric metal complexes for electroluminescence applications". Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20979435.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

18

Klug, Jeremy Hager. "High-performance adhesive systems for polymer composite bonding applications /". Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9883.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

19

James, Aaron. "Development of composites materials from waste paper and plastic". Australian Digital Thesis Program, 2006. http://adt.lib.swin.edu.au/public/adt-VSWT20070130.165426/index.html.

Testo completo

Abstract (sommario):

Thesis (PhD) - Swinburne University of Technology, Industrial Research Institute Swinburne - 2006.
A thesis submitted for the degree of Doctor of Philosophy, Industrial Research Institute Swinburne, Swinburne University of Technology - 2006. Typescript. "August 2006". Includes bibliographical references (p. 361-389).

Gli stili APA, Harvard, Vancouver, ISO e altri

20

Green, Keith Jamahl. "Multiscale fiber reinforced composites using a carbon nanofiber/epoxy nanophased matrix processing, properties, and thermochemical behavior /". Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2007m/green.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Kanelidis, Ioannis [Verfasser]. "Polymer-Nanocrystal Composites: Copolymers, Polymeric Particles and Hybrid Systems / Ioannis Kanelidis". Wuppertal : Universitätsbibliothek Wuppertal, 2012. http://d-nb.info/1022590464/34.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Na, Gwang-Seok. "Load-displacement behavior of frame structures composed of fiber reinforced polymeric composite materials". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26699.

Testo completo

Abstract (sommario):

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Dr. Leroy Z. Emkin; Committee Co-Chair: Dr. Abdul-Hamid Zureick; Committee Member: Dr. Dewey H. Hodges; Committee Member: Dr. Kenneth M. Will; Committee Member: Dr. Rami M. Haj-ali. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Zhang, Xiefei. "Studies on Single Wall Carbon Nanotube and Polymer Composite Films and Fibers". Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7610.

Testo completo

Abstract (sommario):

Single wall carbon nanotubes (SWNT) have been extensively studied over the last decade due to their excellent comprehensive properties for a variety of applications. This study is focused on the applications of SWNTs as reinforcement for polymer matrices. Due to van der Waal interactions, SWNTs form bundles of about 30 nm diameters. In order to take full advantage of the SWNT mechanical properties, SWNT must exfoliate or at least disperse in small diameter bundle size. Optical microscopy and SEM only give qualitative information of dispersion. Quantitative characterization through TEM or AFM can be time consuming in order to get statistical result. In this study, simple method is developed to quantitatively estimate the size of SWNT bundle in dispersion based on the geometry controlled electrical percolation behavior. The SWNTs can be dispersed /exfoliated via PVP wrapped SWNT aqueous dispersion assisted by surfactants such as sodium dodycel sulfate. PVA / SWNT composite films prepared through PVP wrapped SWNTs exhibit improved mechanical properties as well as the evidence of load transfer from the polymer matrix to the SWNT as monitored by the Raman spectroscopy. SWNT can also be well dispersed into PVA/DMSO/H2O solution. Gel spinning of PVA/SWNT composite fiber has been successfully carried out with improved mechanical properties. Functionalized tubes can be used to enhance SWNT dispersion and exfoliation. Oxidation in strong acids is one method used for functionalizing nanotubes. SWNTs have been functionalized in nitric acid. The structure and properties of films (buckypaper) processed from nitric acid functionalized tubes have been studied exhibiting high tensile strength and high electrical conductivity. Nitric acid treatment results in selective degradation of the small diameter tubes.

Gli stili APA, Harvard, Vancouver, ISO e altri

24

伍寶琼 e Po-king Ng. "Molecular and polymeric metal complexes for electroluminescence applications". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B29866303.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

25

Megnis, Modris. "Inelastic analysis of fiber reinforced polymeric composites /". Luleå : Luleå tekniska univ, 2002. http://epubl.luth.se/1402-1544/2002/07.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Treviño-Garrido, Margie N. "Aging of polymeric composites : a literature review". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83749.

Testo completo

Abstract (sommario):

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 97-103).
Due to their increased use in today's society, an extensive survey was undertaken in this report to condense what's been, thus far, discovered as to the effects of aging on polymeric composites. Special emphasis was placed on composites with vinyl ester as the matrix reinforced with glass or carbon fibers. Moisture exposure, thermal conditioning, and cyclic loading were the aging mechanisms used to mimic environmental effects. Fatigue, flexural, tensile tests, and scanning electron microscopy were among the many methods used in studies to determine the effects of aging on composites. The deleterious effect of moisture on composite performance was undeniable, with the drop in flexural strength being as high as 48%. Studies found no difference between salt and distilled water aging, although salt water was reported as being more slowly absorbed. Composite materials were observed to experience no further loss of strength beyond the point of saturation. Findings showed that, after aging, composites retained some of their strength, with flexural strength retention reported as high as 66%. Frequently, the glass transition temperatures of the materials changed depending on the aging process. In most cases, Fick's law of diffusion was confirmed as an accurate model for moisture absorption. Temperature fluctuations were always deemed as damaging to composite structures. Due to the haziness still present in current research coupled with the importance of composite applications, the need for additional investigation in this topic is urgently obvious. All in all, future studies are encouraged to tabulate test procedures and results in an effort to minimize the current ambiguities in the aging information accumulated thus far.
by Margie N. Treviño-Garrido.
S.B.

Gli stili APA, Harvard, Vancouver, ISO e altri

27

Fonseca, Beatriz Condesso Macedo Lobo da. "Thermomechanical characterization of shape-memory polymeric composites". Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/21209.

Testo completo

Abstract (sommario):

Mestrado em Engenharia Mecânica
The shape-memory materials are nowadays an important subject in the scienti c community due to their huge technological potential. These materials have the capability of being triggered by an external stimulus and, consequently, change their shape. Considering the recent development of the biomedical industry, this dissertation aims to develop the applicability of shape-memory materials into biomedical devices, enabling a more e cient operability. Therefore, the shape-memory polyurethane was chosen to this end due to their high biocompatibility and proximity between the thermal transition temperature of the material and the human body temperature. However, the thermoplastic polyurethane (TPU), and the shape-memory polymers in general, possesses major drawbacks related to the inferiority of its mechanical performance as compared with shape-memory alloys (SMAs) and its large shape recovery time. In order to pursue the mechanical reinforcement and improvement of the polyurethane properties, it was conducted an experimental study in which polyurethane nanocomposites containing carbon based nanoparticles were produced. It was used carbon nanotubes (CNTs), treated and non-treated, and graphene, as these materials exhibit excellent thermo-mechanical properties reported in the literature. The nanocomposites were produced through mechanical melt mixing and injection moulding and they were incorporated with 0.5 vol.%, 1.0 vol.% and 1.5 vol.% of non-treated CNTs, treated CNTs and non-treated graphene. It was performed the morphological, thermal and mechanical characterization of the nanocomposites. Thermo-mechanical properties, such as glass transition temperature (Tg), melting temperature (Tm), speci c heat capacity (cp), thermal di usivity ( ), elastic modulus (E), tensile strength at break ( b) and elongation at break ("b) were evaluated. In the present dissertation it could be analysed the in uence of the di erent types of nanoparticles and di erent concentrations on the thermo-mechanical properties of the produced nanocomposites. Through this, the best relation regarding the materials and parameters used in this work was determined. It was also possible to draw some conclusions regarding the shape-memory performance of the nanocomposites.
Os materiais com memória de forma são, atualmente, um tema em estudo pela comunidade cientí ca devido ao seu grande potencial tecnológico. Estes materiais possuem a capacidade de reagir a um estímulo externo e, em consequência disso, alterar a sua forma. Tendo em conta a recente expansão na indústria biomédica, este trabalho de dissertação pretende dar resposta à aplicabilidade de materiais com memória de forma em dispositivos biomédicos, permitindo uma operabilidade mais e ciente dos mesmos. Para tal, foi considerado o uso do poliuretano com memória de forma, devido à sua elevada biocompatibilidade e à proximidade entre a temperatura de ativação térmica do material e da temperatura média do corpo humano. No entanto, o poliuretano termoplástico (TPU), e a generalidade dos polímeros com memória de forma, tem desvantagens relacionadas com o seu desempenho mecânico inferior comparativamente com as ligas metálicas com memória de forma e com o elevado tempo de recuperação de forma. Procurando o reforço mecânico e a melhoria das propriedades do poliuretano com memória de forma, foi realizado um trabalho experimental de processamento de nanocompósitos de poliuretano aditivados com nanopartículas de carbono. Para tal, foram usados nanotubos de carbono (CNTs), não tratados e sujeitos a funcionalização, e grafeno, uma vez que estes materiais possuem excelentes propriedades térmicas e mecânicas documentadas na literatura. Foram produzidos através do método de mistura mecânica por fusão e posterior injeção os nanocompósitos aditivados com 0.5 vol.%, 1.0 vol.% e 1.5 vol.% de nanotubos de carbono não tratados, nanotubos de carbono funcionalizados e grafeno não tratado. Foi realizada caracterização morfológica, térmica e mecânica dos nanocompósitos. Propriedades como a temperatura de transição vítrea (Tg), a temperatura de fusão (Tm), o calor especí co (cp), a difusividade térmica ( ), o módulo de elasticidade (E), tensão de rotura ( b) e deformação de rotura ("b) foram avaliadas. Através desta dissertação foi possível avaliar a in uência das diferentes nanopartículas e das diferentes concentrações usadas nas propriedades termo-mecânicas do material e posteriormente determinar uma relação entre os materiais e parâmetros usados. Foi possível ainda estabelecer algumas conclusões relativas à performance da memória de forma dos nanocompósitos.

Gli stili APA, Harvard, Vancouver, ISO e altri

28

Natarajan, Venkatakrishnan. "Fatigue response of fabric reinforced polymeric composites". Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=3237.

Testo completo

Abstract (sommario):

Thesis (M.S.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains x, 87 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 85-87).

Gli stili APA, Harvard, Vancouver, ISO e altri

29

Scott, David William. "Short- and long-term behavior of axially compressed slender doubly symmetric fiber-reinforced polymeric composite members". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19276.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Bozkurt, Emrah Tanoğlu Metin. "Mechanical and thermal properties of non-crimp glass fiber reinforced composites with silicate nanoparticule modified epoxy matrix/". [s.l.]: [s.n.], 2006. http://library.iyte.edu.tr/tezler/master/makinamuh/T000517.pdf.

Testo completo

Abstract (sommario):

Thesis (Master)--İzmir Institute of Technology, İzmir, 2006
Keywords: polymer composites, Nanoparticles, glass fiber, mechanical properties, thermal properties. Includes bibliographical references (leaves 75-79).

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Daga, Vikram Kumar. "Rheology and electrospinning of neat and laponite-filled poly(ethylene oxide) solutions". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file Mb., 133 p, 2006. http://wwwlib.umi.com/dissertations/fullcit?1435916.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

32

Chang, Kaiguo. "Synthesis and characterization of conducting polymer-inorganic composite materials /". View online ; access limited to URI, 2000. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3108646.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

33

Wright, Richard J. "Bolt bearing creep behavior of highly loaded polymer matrix composites at elevated temperatures". Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17362.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

34

Parvatareddy, Hari. "The effect of environmental aging/exposure on the durability of high performance polymeric composites". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06102009-063332/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

35

Abdalla, Mohamed A. "Carbon nanotube/epoxy nanocomposites effect of interfacial chemistry and processing on molecular mobility, cure behavior, morphology and properties /". Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2009r/abdalla.pdf.

Testo completo

Abstract (sommario):

Thesis (Ph. D.)--University of Alabama at Birmingham, 2008.
Additional advisors: Gregg M. Janowksi, Tamara Floyd Smith, Gregory B. Thompson, Uday Vaidya. Description based on contents viewed July 7, 2009; title from PDF t.p. Includes bibliographical references.

Gli stili APA, Harvard, Vancouver, ISO e altri

36

Buehler, Frédéric Ulysse. "Viscoelastic processing and characterization of high-performance polymeric composite systems /". Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/9880.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Faria, Maria Cândida Magalhães de [UNESP]. "Estudo das intempéries nas propriedades mecânicas e viscoelásticas de compósitos PPS/Fibras de carbono e EPOXI/Fibras de carbono de uso aeronaútico". Universidade Estadual Paulista (UNESP), 2012. http://hdl.handle.net/11449/103726.

Testo completo

Abstract (sommario):

Made available in DSpace on 2014-06-11T19:32:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-10-03Bitstream added on 2014-06-13T21:04:59Z : No. of bitstreams: 1 faria_mcm_dr_guara.pdf: 2691005 bytes, checksum: a507bf57757d62ae4ad112e4aeb41c2e (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Durante o século XX os materiais compósitos estruturais receberam especial atenção dos pesquisadores, o que levou a uma rápida evolução tecnológica acarretando uma intensa procura e posterior obtenção de materiais com características mecânicas cada vez mais elevadas, principalmente no que diz respeito ao módulo de elasticidade e a resistência mecânica. Dessa forma, os materiais tradicionalmente aplicados em engenharia aeroespacial, como o aço e o alumínio entre outros, vêm sendo substituídos por uma nova classe de materiais denominada materiais compósitos, em particular os de matrizes poliméricas reforçadas com fibras contínuas, em resposta à impossibilidade de aumento de resistência e tenacidade nos materiais homogêneos associado a redução de massa específica. Entretanto, devido às aeronaves operarem em uma grande variedade de condições ambientais tais como: ar frio e seco, em condições quentes e úmidas e diferentes gradientes de temperatura, estas condições adversas sempre devem ser consideradas na utilização de materiais aeronáuticos. Portanto, torna-se extremamente importante a avaliação da resistência às intempéries por parte dos materiais a serem selecionados para aplicações estruturais, principalmente em estruturas primárias. Dentro desse contexto, o objetivo do presente trabalho foi avaliar a influência da temperatura e umidade em laminados de aplicação aeronáutica (PPS/fibras de carbono e epóxi/fibras de carbono), a partir da exposição desses materiais a ambientes agressivos (câmaras higrotérmica, de ciclagem térmica e de choque térmico) e, posteriormente, estudar a degradação das suas propriedades mecânicas por meio de ensaios de tração, compressão e cisalhamento interlaminar e das suas propriedades térmicas utilizando-se das técnicas de...
During the 20th century the structural composites received special attention of the researchers leading to the very fast technological development of such materials. This way, occurred the preparation of materials with good mechanical properties, mainly concerning high mechanical strength and stiffness. So, the materials usually applied in aeronautical engineering, as steel and aluminium among others, have been substituted by a new class of materials, named composite materials, particularly polymeric matrix reinforced with continuous fibers answering the difficulty in increasing of mechanical strength and toughness in the homogeneous materials. Therefore, because the aircraft are always operating under different environment conditions such as dry and cold air, warm and wet conditions and large cyclical variations of temperature, these conditions have to be taken into consideration in the utilization of the aeronautical materials. However, it is extremely important the evaluation of the resistance of the materials to the intemperate weather to be selected for structural applications, mainly as primary structures. In this context the aim of this work was the evaluation the influence of intemperate weather in the laminates of aeronautical application (PPS/carbon fiber and epoxy/carbon fiber), submitting these materials to aggressive environment and study the degradation of their mechanical properties by tensile, compression and interlaminar shear tests as well as thermal properties by DMA and TMA. From these found results, it was observed that for PPS/carbon fiber laminates no one used conditioning generate significant differences in the glass transition temperature nor on the mechanical performance of its composite, qualifying this laminate for aeronautical application when its necessary this kind of requirements... (Complete abstract click electronic access below)

Gli stili APA, Harvard, Vancouver, ISO e altri

38

Milanese, Andressa Cecília [UNESP]. "Processamento e caracterização de compósito fibra de sisal/resina epóxi via RTM". Universidade Estadual Paulista (UNESP), 2012. http://hdl.handle.net/11449/115652.

Testo completo

Abstract (sommario):

Made available in DSpace on 2015-03-03T11:52:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-11-26Bitstream added on 2015-03-03T12:07:17Z : No. of bitstreams: 1 000706554.pdf: 2183734 bytes, checksum: 9c69fb93433a041adafed9efedc0ee91 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O desenvolvimento de compósitos formados por matrizes poliméricas e reforçados com fibras naturais ganhou notável interesse na pesquisa, a partir da década de 90. A elevada demanda por compósitos, aliada à regulamentação das leis ambientais, tornou indispensável o aperfeiçoamento e o desenvolvimento de técnicas de processamento menos poluentes, com a utilização de matérias-primas provenientes de fontes naturais e, consequentemente, com menor custo envolvido. Esta pesquisa dá continuidade aos estudos do mestrado e se fundamenta no desenvolvimento do compósito polimérico com matriz de resina epóxi reforçado por fibras naturais de sisal, para uso como material de reforço em estruturas de madeira cuja integridade esteja afetada. Diante do exposto, esta pesquisa envolve o desenvolvimento e o estudo do comportamento do compósito sisal/epóxi processado via moldagem por transferência de resina (RTM). A caracterização das matérias-primas empregadas na preparação do compósito ocorreu pela determinação da massa específica, da porosidade do tecido, das análises térmicas por meio das técnicas de termogravimetria (TGA), calorimetria exploratória diferencial (DSC) e análise dinâmico-mecânica (DMA), pelas resistências à tração e à flexão e também pelo estudo da permeabilidade do tecido de sisal. Em sequência, o trabalho apresenta o processamento e as caracterizações térmicas, físicas e mecânicas de laminados planos do compósito de matriz epóxi reforçada com duas camadas do tecido plain-weave de sisal, processados via RTM. Os laminados obtidos foram ensaiados em tração, flexão, ultrassom (C-Scan), TGA, DSC, DMA, além da determinação da massa específica. As análises termogravimétricas indicaram que a temperatura inicial de degradação do compósito é de 182ºC. A Tg – temperatura de transição vítrea, determinada por DSC e por DMA, é de 49,0oC e 45,2oC...
Polymeric composites reinforced with natural fibers has obtained considerable interest in the research area, when from the 90’s, the high demand by composites and with the environmental laws regulation become indispensable the improvement and development of processing techniques with less pollutants, that involves the use of raw materials from natural sources and, therefore, with low cost. The objective of this work is continue a research line beginning in the master’s studies, that is based on the polymeric composite development using epoxy resin reinforced with natural sisal fibers, to apply as reinforcement to restore timber structures, whose integrity was affected. So, this research proposes to develop the sisal/epoxy composite, processed by resin transfer molding (RTM) and to characterize the raw materials, regarding to density, thermal analysis techniques using thermogravimetry (TGA/DTG), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), mechanical tests as tensile and flexural and permeability of the woven sisal fabric. Subsequently, the epoxy/two layers of woven plain-weave sisal laminated composite was scanned by ultrasound and characterized with respect of thermal analysis, physical and mechanical characterizations. Thermogravimetry analysis suggests that the onset degradation temperature of composite is 182°C. The glass transition temperature (Tg), determined from DSC and DMA, is 49.0°C and 45.2°C, respectively. The mechanical tests showed values of 36 MPa for tensile strength, 75 MPa for flexural strength, 2.19 GPa for tensile modulus and 3.86 GPa for flexural ...

Gli stili APA, Harvard, Vancouver, ISO e altri

39

Hillermeier, Roman Werner. "Development engineering of advanced polymeric composite systems /". Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/9919.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

40

Bocchieri, Robert Thomas. "Time-dependent deformation of a nonlinear viscoelastic rubber-toughened fiber composite with growing damage /". Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008280.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

41

Robinette, Eric Jason Palmese Giuseppe R. "Toughening vinyl ester matrix composites by tailoring nanoscale and mesoscale interfaces /". Philadelphia, Pa. : Drexel University, 2005. http://hdl.handle.net/1860/1125.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

42

Meure, Samuel James School of Chemical Engineering &amp Industrial Chemistry UNSW. "Development and characterisation of polypyrrole composites". Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2006. http://handle.unsw.edu.au/1959.4/24341.

Testo completo

Abstract (sommario):

The development and characterisation of new PPy composites has been carried out using direct addition of polypyrrole (PPy) powders to polymeric substrates and in situ polymerisation in order to develop workable composites with conductivities similar to that of oxidised PPy. Precipitation, dispersion and emulsion polymerisation techniques were used in the development of PPy fillers. Electron microscopy, differential light scattering (DLS), nitrogen adsorption surface area analysis and conductivity measurements were used to determine the physical properties of PPy powders produced with ferric chloride oxidant. Powders possessing approximately 380-1400nm effective particle diameters, 8-50m2 surface areas and 0.001-1S/cm conductivities were produced. Physically mixed composites were produced by adding PPy powders to Surlyn ionomer, styrene ethylene butylene styrene triblock copolymers (SEBS) and nitrile butadiene rubber (NBR) hosts. Changes in physical properties (including tensile strength and electrical conductivity) of PPy and carbon black filled composites were also studied and compared. In situ polymerisation-based composite development of PPy composites with higher conductivities than obtained using physical mixing techniques (<10-4S/cm) was carried out. Sequential treatments with monomer and oxidant were used to test the combination of polymer host (including those described above) and reaction media (including tetrahydrofuran, diethyl ether and acetonitrile). Examination of PPy penetration and content (using optical microscopy and gravimetric analysis) showed a diethyl ether reaction media and SEBS host were suitable for further PPy Abstract composite development. The simultaneous diffusion polymerisation (SDP) technique, which involves treating opposite sides of host sheets with separate monomer and oxidant solutions, was employed to form PPy- SEBS composites. The layered morphology of SDP-formed composites was characterised by techniques including X-ray imaging, Raman mapping and electron probe microchemical analysis; and a PPy growth mechanism proposed. Optimisation of PPy composite properties was carried out using a central composite factorial design (varying reagent concentrations, reaction temperatures and reaction times) with conductivities of approximately 1S/cm achieved, Properties of PPy composites formed using physical mixing and SDP techniques were compared. Preliminary investigations (using electron and atomic force microscopy) were carried out to develop core-shell PPy composites that possess a continuous PPy component rather than the layered morphology associated with reductions in tensile strength.

Gli stili APA, Harvard, Vancouver, ISO e altri

43

Senan, Anish Sen. "Determination of the Viscoelastic Properties of General Anisotropic Materials". Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/SenanAS2003.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

44

Bauer, Bernhard. "Aluminium-modified polymeric precursors to Si³N⁴?SiC ceramics". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670051.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

45

Miller, Charles Andrew. "MODELING OF THERMAL DEGRADATION OF PHYSICALLY HETEROGENEOUS POLYMERIC SOLIDS". Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291219.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

46

Basson, Nicolaas Christiaan. "The effect of molecular composition on the properties of polyolefin-wood composites". Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80222.

Testo completo

Abstract (sommario):

Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Polymer composites, and in particular wood-polymer composites have become commercially and environmentally important materials. Studies in polyolefin-wood composites have mostly focused on polypropylene (PP) and polyethylene (PE). To our knowledge, no study has been undertaken on advancing impact polypropylene copolymer (IPPC)-wood composites as a suitable alternative to using PP and PE. IPPC have proven to be a suitable alternative to PP at low temperatures to improve impact resistance for manufactured polymer products, and could be a great addition to improved properties for wood polymer composites. This study shows that the physical properties of IPPC-wood composites can be markedly improved when compatibilizer(s) are used to improve the distribution of the wood within the matrix, as well as improving the interaction between the wood and the polymer matrix.. The use of different compatibilizers, vi polypropylene-graft-maleic anhydride (PPgMA) and poly(ethylene-co-vinyl alcohol) (EvOH) results in different physical properties. Using simple admixtures of the PPgMA and EvOH in IPPC-wood composites result in a large spread of results, while pre-reacting the PPgMA and EvOH to form a joint compatibilizer gives reproducible results w.r.t the physical testing. A study of the fundamental interactions of the compatibilizer(s) with the molecular components of the IPPCs was undertaken. The IPPCs used were fractionated by preparative temperature rising elution fractionation, and the fractions were mixed with the compatibilizers. To this end, fluorescence microscopy was utilized to study the interaction. The results clearly indicate that the interaction of the PPgMA with the fractions differ from that of the EvOH. These differences can be explained in terms of the chemical composition distribution within the IPPC fractions. Atomic force microscopy (AFM) was used to study adhesive forces between compatibilizer, polymer and cellulose and lignin. Successful coating of AFM tips with PPgMA and EvOH was achieved. Whilst interactions based on chemical force microscopy (CFM) could not be quantified, the AFM results in conjunction with fluorescence spectroscopy provided meaningful insight in the way that compatibilizers interact with both the wood and the impact copolymers used in this study.
AFRIKAANSE OPSOMMING: Polimeer saamgestelde material, en meer spesifiek hout-polimeer saamgestelde material het die afgelope tyd belangrike produkte geword, beide kommersieel en in verband met omgewingvriendelikheid. Navorsing op die gebied van poli(olefien)-hout komposiete het tot op hede meestal gefokus op die grbruik van poli(propileen) (PP) en poli(etileen) (PE). Sover dit on kennis strek is daar nog geen studie gedoen om die gebied van impak polipropileen kopolimere (IPPK)-hout komposiete uit te bou nie. IPPKs is ‘n geskikte alternatief vir PP in veral laetemperatuur aanwendings. Die gebruik van IPPKs as matriks vir die hout komposiete kan ‘n groot staqp vorentoe beteken. Hierdie studie wys dat die fisiese eienskappe van iPPK-hout komposiete merkwaardig verbeter kan word waneer versoeningmateriale gebruik word om die verspreiding van die hout in die polimeermatriks sowel as die interaksie tussen die hout en polimeer te verbeter. Die gebruik van verskillende versoenings material, t.w poli(propileen-ent-maleinsuur anhidried) (PPeMA) en pol(etlieen-ko-viniel alkohol) (EVOH). Deur gebruik te maak van eenvoudige mengsels van PPeMA en EVOH in IPPK-hout composite het ‘n geweldige wye verpreiding van resultate tot gevolg gehad, terwyl ‘n voorafgaande reaksie tussen die PPeMA en die EVOH om ‘n saamgestelde versoeningmateriaal te maak tot gevolg gehad het dat reproduseerbare resultate verkry kon word. ‘n Studie van die fundamentele interaksies van die versoeningsmateriale met die molkulêre komponente van die IPPKs is uitgevoer. Die IPPKs is gefraksioneer deur preparatiewe temperatuur-stygende uitloog frakasionering en die fraksies is gemeng met die versoeningmateriale. Fluoressensie mikroskopie is gebruik om hierdie interaksies te bestudeer. Die resultate dui duidelik daarop dat die interaksie van die PPeMA met die fraksies verskil met die van die EVOH. Die verskille kan verduidelik word aan die hand van die chemiese samestelling verspreiding van die IPPK fraksies. Atoomkrag mikroskopie (AKM) is gebruik om die adhesive-kragte tussen die versoeningmateriale, polimere, sellulose en lignien. AKM tippe is suksesvol bedek met PPeMA en EVOH, onderskeidelik. Alhoewel interaksies gebaseer op chemiese krag mikroskopie (CKM) nie gekwantifiseer kon word nie, lewer hierdie resultate tesame met die fluoressensie spektroskopie unieke insig in die manier wat versoeningmateriale met beide die hout en die polimeer reageer.

Gli stili APA, Harvard, Vancouver, ISO e altri

47

Olea, Mejia Oscar Fernando. "Micro and nano composites composed of a polymer matrix and a metal disperse phase". Thesis, University of North Texas, 2007. https://digital.library.unt.edu/ark:/67531/metadc5135/.

Testo completo

Abstract (sommario):

Low density polyethylene (LDPE) and Hytrel (a thermoplastic elastomer) were used as polymeric matrices in polymer + metal composites. The concentration of micrometric (Al, Ag and Ni) as well as nanometric particles (Al and Ag) was varied from 0 to 10 %. Composites were prepared by blending followed by injection molding. The resulting samples were analyzed by scanning electron microscopy (SEM) and focused ion beam (FIB) in order to determine their microstructure. Certain mechanical properties of the composites were also determined. Static and dynamic friction was measured. The scratch resistance of the specimens was determined. A study of the wear mechanisms in the samples was performed. The Al micro- and nanoparticles as well as Ni microparticles are well dispersed throughout the material while Ag micro and nanoparticles tend to form agglomerates. Generally the presence of microcomposites affects negatively the mechanical properties. For the nanoparticles, composites with a higher elastic modulus than that of the neat materials are achievable. For both micro- and nanocomposites it is feasible to lower the friction values with respective to the neat polymers. The addition of metal particles to polymers also improves the scratch resistance of the composites, particularly so for microcomposites. The inclusion of Ag and Ni particles causes an increase in the wear loss volume while Al can reduce the wear for both polymeric matrices.

Gli stili APA, Harvard, Vancouver, ISO e altri

48

Jack, David Abram. "Advanced analysis of short-fiber polymer composite material behavior". Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4363.

Testo completo

Abstract (sommario):

Thesis (Ph. D.) University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 2, 2007) Includes bibliographical references.

Gli stili APA, Harvard, Vancouver, ISO e altri

49

Nguyen, Felix Nhanchau. "Improvement of mechanical properties of polymeric composites : experimental methods and new systems /". Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9907.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

50

Salin, Irene. "Scale-up studies for thermo-oxidative stability of polymeric composites /". Thesis, Connect to this title online; UW restricted, 1994. http://hdl.handle.net/1773/9871.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Tesi sul tema "Polymeric composites"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili