Tesi sul tema "Ductility"
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1
Mohamed, Z. M. E. Q. "Hot ductility of steels". Thesis, City University London, 1988. http://openaccess.city.ac.uk/8348/.
Testo completoAbstract (sommario):
The hot tensile test has been used for a variety of steels, to investigate the influence of such factors as inclusions, precipitation, phase transformation and grain size on hot ductility. Tests were performed in the temperature range 700-1000 °C and at a strain .4 _2 1 rates of (10 —10 S ), generally to simulate the conditions experienced during the straightening operation in the continuous casting process in which transverse cracks propagate. Two zones of reduced ductility can be identified. The Y-a transformation zone which has been shown to produce a significant ductility trough due to strain concentration in the softer ferrite films surrounding the V grains, cating voiding around he MnS inclusions which link to give intergranular failure, and factors which alter the A3 temperature, such as carbon content, have been shown to produce a change in the temperature at which the ductility trough occurs. The second zone of reduced hot ductility was observed in the austenite region, due to the retardation of dynamic recrystallisation associated with the presence of fine carbides, nitrides and/or inclusions precipitates at the austenite grain boundaries, which allows intergranular cracks to develop. The depth and width of this ductility trough is primarily dependent on the size and amount of precipitates present. The influence of MnS inclusions in reducing hot ductility has been noted above and below the Ae3 temperature. Above the Ae3 , inclusions act in a similar way to fine precipitation preventing dynamic recrystallisation and below the Ae3 , they offer more sites for micro-voiding to occur. Although grain size refinement improves ductility, it does so as long as similarity in precipitate volume fraction and size exist. Improved hot ductility has been achieved by adding Ca to the steel which reduces the amount of l9nS inclusions precipitated during cooling from solution temperature at the austenite grain boundaries.
2
Abu, Shousha R. I. "Hot ductility of steels". Thesis, City University London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305120.
Testo completo
3
Wassouf, Mohamad. "Bond and ductility of concrete reinforced with various steel bars surface and ductility conditions". Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6272/.
Testo completoAbstract (sommario):
Reinforced concrete is a wide field for researches and studies in civil engineering subject. It is due to the fact that reinforced concrete is the most widely used material for the infrastructure in the world. Reinforced concrete consists of two main materials: reinforcing steel and concrete, each of those two materials has its own effect on the performance of the structure. In this thesis, the change in RC performance due to different steel properties and specifications will be investigated. The study focuses on the bond interaction between steel and concrete and the flexural behaviour of RC beams. Pull-out forces have been exerted on the reinforcing bars in RC blocks to examine the impact of steel properties on the bond strength and failure mode of the blocks. In addition to that, flexural tests have been conducted on simply supported RC beams to investigate how reinforcement properties can affect the ductility of reinforced concrete. Comparison of results of the previous two tests with codes and analytical models have been carried out to verify the outcome of this research.
4
Crowther, David Neville. "The hot ductility of steels". Thesis, City, University of London, 1986. http://openaccess.city.ac.uk/19368/.
Testo completoAbstract (sommario):
Hot tensile tests have been performed on a variety of plain carbon and micro-alloyed steels, in order to determine the influence of such factors as phase transformation, grain size and precipitation on hot ductility. The γ-∝ phase transformation has been shown to produce a significant ductility trough in the high temperature tensile behaviour of plain C steels, and factors which alter the A3 temperature, such as cooling rate and C content, have been shown to produce a change in the temperature at which the ductility trough occurs. This ductility trough is due to strain concentration in the ferrite films surrounding the grains, leading to intergranular failure. It has also been shown that an increase in grain size can increase the depth and width of this ductility trough. For plain C steels with a C content of 0.35% or above, and for some micro-alloyed steels, a ductility trough may also be present in the single phase austenite region. For the plain C steel, this is. believed to be due to the increase in activation energy for deformation associated with increasing C contents. In microalloyed steels, the trough is due to the retardation of dynamic recrystallization associated with the presence of fine carbide and/or nitride precipitates, which allows intergranular cracks to develop. The depth and width of this ductility trough is primarily dependent on the size and amount of precipitates present, although it has been shown that grain size has a secondary effect. In C-Mn-Nb-Al steels, factors which tend to reduce hot ductility by reducing precipitate size and/or increasing the amount of precipitate present include the reheating of tensile samples cast 'in-situ', the introduction of temperature oscillations during COOling from solution temperature, and the presence of large amounts of'dynamic' precipitates formed during tensile testing. In C-Mn-V-Al steels, 'dynamic' precipitates do not have such an adverse effect. Strain rate was also shown to have an important influence on hot ductility, and decreasing strain rates have been Shown to reduce hot ductility in both plain carbon and micro-alloyed steels.
5
Eon, Kang Shin. "Hot ductility of TWIP steels". Thesis, City University London, 2014. http://openaccess.city.ac.uk/13703/.
Testo completoAbstract (sommario):
TWIP (Twining Induced Plasticity) steel is very promising AHSS (Advanced High Strength Steel) grade owing to its superior toughness and ductility. Recently it has attracted the interest of the automotive and steelmaking industries, as the need for reducing weight to provide better fuel efficiency is of paramount importance with the gradual depletion of fuel resources. A high Al, TWIP steel is being commercially developed as Al has been found very well in delaying fraction in deep drawn products. However these steels are difficult to continuous cast and cracking can occur at the slab surface. Therefore it becomes very important to gain an understanding of the cause of this cracking, in order to prevent their occurrence. To assess the likelihood of the cracking in these high Al TWIP steel slabs (1~1.5%Al, 0.6%C, 18%Mn), conventional hot tensile tests were performed to simulate the continuous casting process. A variety of TWIP steels were tested in order to determine the influence of such factors as chemical composition, cooling rate and thermal cycle on hot ductility. Using a cooling rate of 60oC/min after heating to 1250oC, ductility was generally <40% RA (Reduction of Area) indicating that these high Al TWIP steels it will be difficult to cast without transverse cracking occurring. The 1.5%Al containing steels had worse ductility than the low Al containing steels (0.02%Al) because of the presence of large amounts of AlN precipitated at the austenite grain boundaries. Reducing the Al and N level improved ductility. Higher strength Nb/V high Al containing TWIP steels were also examined although ductility was likely to be worse than the simpler microalloying free TWIP steels as was confirmed. Increasing the cooling rate from 60 to 180oC/min after melting caused the ductility to further deteriorate and high N levels produced only a small reduction in the ductility, probably because ductility is so poor. Increasing the S level from 0.003 to 0.01% caused the ductility to deteriorate in TWIP steels free of microalloying. Increasing the S level to 0.023% caused no further deterioration in ductility even though the MnS volume fraction increased. The worse ductility in the higher S steels was not caused by a simple increase in the sulphide volume fraction but more a consequence of the change from coarse hexagonal plate AlN, which are mainly within the matrix and so have little influence on the hot ductility, to very long dendritic rod precipitates, which are situated at the dendritic or close to the austenite grain boundaries. This dendritic precipitation was rarely observed in the low S steel. The MnS inclusions appeared to act as nucleation sites for the precipitation of AlN and when there was few inclusions precipitation of AlN was mainly confined to the matrix. The ductility of Nb containing high Al, TWIP steels was very poor in the as-cast condition. Adding B and Ti still gave rise to extremely poor ductility when a cooling rate of 60 oC/min was used but reducing it to 12oC/min caused the ductility to improve so that RA values were now close to the 35~40% RA value required to avoid transverse cracking. To improve ductility B and Ti additions were examined. 0.04%Ti and 0.002%B are required to ensure good hot ductility in high Al, TWIP steels. Sufficient Ti is needed to remove all the N as TiN so preventing AlN precipitating as films over the austenite grain surfaces. B is also needed as it can segregate to the boundaries and strengthen them. A SIMS technique confirmed that B had indeed segregated to the boundaries. The slower cooling rate 10~15oC/min compared to 60oC/min will result in the optimum segregation of B as well as coarsening the TiN precipitates so they are no longer effective in reducing the ductility. Following all these recommendations, i.e. a low S level, slow secondary cooling rate, a Ti level above the stoichiometric for TiN and a boron addition of 0.002%, transverse cracking was avoided commercially in these very difficult to cast high strength TWIP steels.
6
Occhiuzzi, Antonio. "Seismic ductility of base isolated structures". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/35011.
Testo completo
7
Henriques, José Alexandre Gouveia. "Ductility requirements in shear bolted connections". Master's thesis, Departamento de Engenharia Civil, 2007. http://hdl.handle.net/10316/15762.
Testo completo
8
Soesianawati, M. T. "Limited ductility design of reinforced concrete columns". Thesis, University of Canterbury. Department of Civil Engineering, 1986. http://hdl.handle.net/10092/3643.
Testo completoAbstract (sommario):
This report describes an experimental and analytical investigation
of the strength and ductility of reinforced concrete columns.
Four columns of square cross-section were tested under axial
compression loading and cyclic lateral loading applied at mid-height which
simulated seismic loading.
The main variable investigated was the quantity of transverse
confining steel used, which ranged between 17 to 46 percent of the NZS
3101:1982 recommended quantity for ductile detailing.
The experimental results are reported in the form of lateral loaddisplacement
and lateral load-curvatures hysteresis loops, curvature
profiles, transverse steel strain distributions and concrete compressive
strains.
The results are discussed and compared with the analytical predictions.
A modified equation for the quantity of confining reinforcement in
rectangular columns is recommended. Conclusions are made regarding the
ductility available from columns containing substantially less transverse
confining reinforcement than recommended by the New Zealand concrete
design code.
9
Lobato, de Sousa Monteiro de Morais Miguel Nuno. "Ductility of beams prestressed with FRP tendons". Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614171.
Testo completo
10
Wolff, Ira M. "Ductility in high chromium super-ferritic alloys". Doctoral thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/22200.
Testo completoAbstract (sommario):
Includes reprints of author's related articles.Bibliography: pages 187-201.
The competition between microfracture and plastic flow has been studied in relation to the thermomechanical processing parameters and minor element chemistry of wrought super-ferritic alloys based on a composition of Fe-40wt% Cr. These alloys have been developed for corrosion-resistant applications, specifically by micro-alloying with platinum group metals to induce cathodic modification, but their use has been hampered by inadequate toughness at ambient temperatures. Brittle cleavage of the alloys is a consequence of the high resistance to plastic flow required to accommodate local stresses, such as those found ahead of a loaded crack. Once initiated, a crack propagates in a brittle manner with minimal ductility. The impact toughness therefore relies on the ability of the alloys to withstand crack initiation. The frequency of the crack initiation events is related to the distribution of secondary phases within the matrix and at the grain boundaries. A direct means of improving the toughness and the ductility is accordingly via annealing cycles and minor alloying additions to control the precipitation of second phases. The ductility is enhanced by raising the mobile dislocation density, and this may be achieved by pre-straining recrystallised material, or increasing the number of dislocation sources in the otherwise source-poor material. The generation of mobile dislocations by prismatic punching at second phase particles in response to local or tessellated stresses was found to increase the ductility and the impact toughness of the alloy. The addition of nickel also increases the brittle fracture resistance by promoting stress accommodation at the crack tip, a result which can, in principle, be explained on the basis of enhanced dislocation dynamics. The tendency of the alloys to form a stable recovered substructure was identified as a critical parameter for both the mechanical and corrosion properties. The low-angle dislocation sub-arrays contribute to overall strain-hardening, but destabilise the passivity of the alloys in acid media. In practice, rationalisation of the microstructural parameters has enabled the practicable fabrication of tough, corrosion-resistant alloys, suitable for commercial development.
11
POZZA, LUCA. "Ductility and behaviour factor of wood structural systems - Theoretical and experimental development of a high ductility wood-concrete shearwall system". Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3422988.
Testo completoAbstract (sommario):
This dissertation focuses on the seismic behavior, ductility and dissipative capacity of modern timber buildings. A number of innovations in the field of timber structures are reported with special regard to the modeling techniques suitable for timber joints and to the characterization of the seismic behavior of modern timber systems.
A preliminary overview on the seismic-resistant timber building technology and on their evolution from the past to nowadays is reported in the introduction of this thesis work. A review of the state of art about the available seismic codes is also reported and the main lack and incongruence with the current constructive practice are pointed out.
The basic terms and concepts used in structural modeling and nonlinear analysis of timber structure are provided in the first part of this dissertation. The specific behavior of wood joints under cyclic actions and therefore under earthquakes is described with emphasis to the pinching effect and strength and stiffness degrading. A literature review on the main numerical models proposed to reproduce the hysteretic load-slip curve of single fasteners, joints and whole wooden elements is presented and discussed. A proposal for a new wood joint numerical model that can be easily implemented into a standard commercial Finite Element code is reported. The reliability of such new developed model to reproduce the fasteners hysteresis behavior is presented and critically discussed in comparison with experimental results.
The second part of this thesis work is based on the evidence that the growing spread of the use of timber structures has led to the development of numerous innovative construction systems but at the same time a lack of code provisions for seismic timber structure still remains, in particular concerning the ductility (or behavior) factor q to be used for the design of different timber systems. This part of dissertation analyzes the definitions of the q-factor given in the scientific literature and its relevance in the design of seismic resistant structures. The traditional methods for estimating the q-factor are investigated and an innovative procedure for expeditious q-factor estimation is presented. The theoretical aspects of this new analytical-experimental procedure are reported and the main advantages and limitations are critically discussed.
The seismic behavior of the Cross Laminated Timber structure is in deep studied in the third part of this dissertation. Such building system is largely spreading in the constructive practice but no design guidelines are provided in the seismic codes yet, especially for what concerning the definition of their sound behavior factor. Aim of this part of dissertation is to define the influence of some significant building characteristics, such as building technology, storeys number, slenderness, design criteria etc.., on the q-factor value. Such influences were studied referring to a numbers of building configuration and by means of nonlinear analyses carried out using specific hysteretic spring lamp-mass models. Based on such numerical assessment a proposal for an analytical formulation suitable to calculate the q-factor of CrossLam buildings has been developed and is presented. The validation and the applicability limits of the proposed formulation are presented and critically discussed.
The final part of the dissertation investigates from the structural efficacy of newly developed construction technology which uses an external concrete shelter made of precast R.C. slabs to improve the performance of standard platform-frame shear walls. The idea consists of external plating made of thin reinforced concrete slabs screwed to the wooden frame of the walls. The concrete slab acts as a diaphragm against the horizontal forces. The structural response of this shearwalls under monotonic and cyclic loading conditions has been assessed by means of experimental tests. The tests outcomes are presented and compared with those from code provisions. Fulfillment of the requirements given by current codes as regards the attribution to the Higher Ductility Class is also verified. The influence of concrete skin on the seismic response of the shearwalls is also evaluated by means of numerical analysis and the assured “q” ductility factor is estimated.In questo lavoro di tesi si analizzano il comportamento sismico, la duttilità e la capacità dissipativa dei moderni edifici con struttura di legno. Le principali innovazioni sviluppate in questa tesi di dottorato riguardano le tecniche di modellazione dei sistemi di connessione usati nelle strutture lignee e la caratterizzazione sismica dei moderni edifici in legno. L’introduzione della tesi evidenzia le caratteristiche che rendono le strutture in legno idonee per l’impiego in zona sismica e riporta una analisi storica delle principali tipologie di edifici sismo-resistenti a struttura in legno e la loro evoluzione dal passato ai giorni nostri. L’introduzione riporta inoltre un’analisi critica dello stato normativo Europeo ed Extraeuropeo sulle progettazione sismica degli edifici a struttura in legno evidenziando le principali lacune e incongruenze con la pratica costruttiva corrente. Il lavoro di tesi sviluppato affronta sostanzialmente quattro argomenti dettagliati in parti indipendenti. Le prime due sono di carattere generale e riguardano tutte le strutture in legno mentre le rimanenti sono specifiche di sistemi costruttivi innovativi e non ancora completamente caratterizzati sismicamente. La prima parte della tesi è dedicata alla descrizione del comportamento isteretico che caratterizza le connessioni utilizzate nelle strutture in legno e dei modelli numerici disponibili in letteratura per una riproduzione fedele di tale comportamento evidenziandone le potenzialità, i limiti di applicazione e l’efficienza numerica. Viene inoltre proposto un modello isteretico innovativo per riprodurre il comportamento delle connessioni tipicamente utilizzate nelle strutture in legno riproducibile anche mediante codici agli elementi finiti di tipo commerciale e non specificatamente orientati alla ricerca. Questa prima parte della tesi si conclude con la validazione e la descrizione dei principali vantaggi e limiti di applicazione della modello numerico proposto. La seconda parte della tesi riguarda la definizione del fattore di struttura q dei sistemi costruttivi in legno innovati e di recente diffusione che non sono annoverati nelle normative sismiche. In questa parte della tesi vengono descritti i metodi tradizionali utilizzati per la stima del fattore di struttura evidenziandone i vantaggi e i principali limiti. Viene proposta una procedura innovativa di tipo misto analitico-sperimentale che consente una valutazione speditiva del valore del fattore di comportamento q.. Questa parte del lavoro di tesi si conclude riportando la validazione della procedura proposta nonché gli aspetti teorici i limiti di applicabilità. La terza parte della tesi approfondisse lo studio sul sistema costruttivo a parete massiccia del tipo CrossLam. Preliminarmente viene riportatolo lo stato dell’arte sull’attività di ricerca sinora svolta su tale sistema costruttivo. L’obiettivo di questa parte del lavoro di tesi consiste nella definizione dell’effetto di determinate caratteristiche dell’edificio come il numero di piani, la snellezza, la composizione delle pareti, i criteri di progetto ecc. sul valore del fattore di struttura da utilizzare nella progettazione sismica dell’edificio stesso. Tale correlazione viene studiata mediante una serie di simulazioni numeriche su diverse configurazioni di edifici. I risultati ottenuti sono stati sintetizzati in una nuova formulazione analitica per la definizione del fattore di struttura q a partire dalle specifiche caratteristiche dell’edificio. Infine si riporta la validazione di tale formulazione analitica e si descrivono i principali vantaggi e limitazioni. L’ultima parte di questo lavoro di tesi consiste nello sviluppo teorico e sperimentale di un nuovo sistema costruttivo misto legno-calcestruzzo ad alta duttilità e performance anti-sismiche. Il sistema sviluppato consiste nell’applicazione di un rivestimento esterno in lastre di calcestruzzo alle tradizionali pareti di taglio a telaio. La riposta strutturale, la duttilità e il comportamento isteretico è stato verificato mediante dei test sperimentali condotti su differenti configurazioni di pareti. Infine sono state condotte delle simulazioni numeriche, con modelli numerici appositamente sviluppati e tarati sulla base dei test sperimentali, mediane le quali è stato possibile stimare il valore del fattore di struttura q da utilizzare per il progetto sismico di questo nuovo sistema costruttivo.
12
Gardner, Christopher Andrew. "Ductility capacity of HPS70W net-section tensile members /". Diss., ON-CAMPUS Access For University of Minnesota, Twin Cities Click on "Connect to Digital Dissertations", 2001. http://www.lib.umn.edu/articles/proquest.phtml.
Testo completo
13
Dávila-Sänhdars, Migual Angel. "Ductility of RC beams with FRP reinforcing bars /". Title page, synopsis and contents only, 1998. http://web4.library.adelaide.edu.au/theses/09ENS/09enss127.pdf.
Testo completo
14
Lau, Tak-bun Denvid. "Flexural ductility improvement of FRP-reinforced concrete members". Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38907756.
Testo completo
15
Watson, Soesianawati. "Design of reinforced concrete frames of limited ductility". Thesis, University of Canterbury. Department of Civil Engineering, 1989. http://hdl.handle.net/10092/3745.
Testo completoAbstract (sommario):
An experimental programme was carried out to investigate the flexural strength and ductility.
of reinforced concrete columns under simulated earthquake loading. The main variable
examined was the quantity of transverse reinforcement for concrete confinement. The experimental
results were described and compared with theoretical studies. It was found that
to achieve adequate ductility in columns, the current New Zealand concrete design code
NZS3101:1982 equations for concrete confinement need to be refined. Using design charts
for ductility, which were previously derived from a theory for cyclic moment-curvature behaviour,
a refined design equation to replace the current code equations is proposed.
The inelastic dynamic response of frames of limited ductility was examined, and compared
with the response of ductile frames. The analysis indicated that non-capacity designed
frames, designed for seismic forces corresponding to a limited ductility demand, performed
reasonably well. Although some plastic hinges did develop in the columns, the ductility
demand was acceptable and can be achieved by appropriate detailing. As a result, some
suggestions for the seismic design requirements of frames of limited ductility are presented.
16
Lau, Tak-bun Denvid, e 劉特斌. "Flexural ductility improvement of FRP-reinforced concrete members". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B38907756.
Testo completo
17
Du, Yingang. "Effect of reinforcement corrosion on structural concrete ductility". Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368516.
Testo completoAbstract (sommario):
This thesis presents the experimental and analytical results to investigate the effect of corrosion on the mechanical properties of reinforcing bars and concrete beams, with particular reference to their ductility. In the experimental works, specimens were electrochemically corroded, before they were loaded to failure. In the finite element analysis, the corrosion of reinforcement was modelled as either internal pressure or radial expansion around corroded bars. The study indicates that the amount of corrosion to cause cracking at the bar and concrete surfaces almost linearly increased with the bar diameter and ratio of cover to diameter, respectively. No matter whether concrete cover c increased or bar distance S decreased, once the ratio of S / c became less than 2.5, corrosion cracks first propagated internally between the bars and caused delamination. Although corrosion did not alter the shape of force-extension curves substantially, it decreased bar strength and, especially, ductility greatly. Furthermore, although the reductions of strengths were identical, the ductility of bars corroded in concrete decreased more rapidly than that of bare corroded bars. Corrosion decreased beam strength and altered its ductility and failure mode. When the cracking of compressive concrete or the reduction of tensile bar area dominated beam response, corrosion increased beam ductility and caused a beam to fail in a less brittle and even ductile manner. When the deterioration of bond strength or the reduction of steel ductility controlled beam behaviour, however, corrosion decreased beam ductility and led the beam to fail in a less ductile and even brittle manner. There is a concern regarding the ductility of reinforcing bars and under-reinforced beams if the amount of corrosion exceeds 100/0, since bar ultimate strain decreased below the minimum requirements prescribed in the Model Code 90 for situations requiring high ductility.
18
Diao, Hele. "Carbon fibre reinforced polymer composites with enhanced ductility". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/44273.
Testo completoAbstract (sommario):
Carbon fibre reinforced polymers (CFRPs) have high strength and stiffness, low density, long fatigue life in the fibre direction and good corrosion resistance. Nowadays, CFRPs are been used in aeronautics, wind turbine blades, sports goods and civil industry. However, one fundamental limitation of CFRPs is their brittleness (low ductility): CFRPs fail catastrophically at a relatively low strain (1.5% to 1.8%) under the tension with little warning or residual load-carrying capacity. To overcome this weakness, there is considerable interest to enhance the ductility of CFRPs exhibiting increased failure strains under tension and more progressive, graceful failure modes. In this work, three different methods were developed to improve the ductility of unidirectional (UD) CFRPs. The first method was to introduce fibre waviness into UD composites. The fibre alignment angles of the resulting composites and control composites were assessed and it was found that fibre waviness in UD composite did result in a stepwise tensile failure mode and an enhanced strain to failure. The second method was using an air-assisted fibre tow spreading and commingling technology to manufacture continuous intermingled carbon fibre/glass fibre hybrid tows. After defining and quantifying the degree of hybridisation (at the filament level) of two carbon fibre/glass fibre hybrid tows, the one with the higher degree of hybridisation was selected to manufacture intermingled UD hybrid composites. It was found that hybridising of continuous glass and carbon fibres resulted in the composites with an increased failure strain. Moreover, these hybrid composites failed more gradually. The final method investigated for introducing ductility was the introduction of ply cuts into PEEK interleaved UD carbon fibre/PEEK composites, which were manufactured by compression moulding. The resulting cut-ply interleaved carbon fibre/PEEK composite possessed a non-linear tensile stress-strain curve and ductility strain of 0.4%, which is due to shearing of the PEEK interleaves in the overlap regions between the cut carbon fibre plies.
19
Li, Jian Xing. "Ductility and fracture mechanisms of particulate filled thermoplastics". Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1060703053.
Testo completo
20
Fuller, Jonathan. "Pseudo-ductility of thin ply angle-ply laminates". Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683726.
Testo completoAbstract (sommario):
Composite materials usage is limited by the sudden, brittle failure they often exhibit. It has been shown in this work that it is possible to remove this inherent limitation and enlarge the design space by using thin ply angle-ply laminates that exhibit a non-linear 'pseudo-ductile' stress-strain response. Characterisation of the spread tow thin ply carbon-epoxy prepreg material (ply thickness of 0.03 mm) was conducted in order to allow an experimental study of the potential for pseudo-ductility. It has been shown that highly non-linear stress-strain responses can be achieved with angle-ply laminates, whilst suppressing the damage that normally causes their premature failure . Several orientations between 15°- 45° were investigated in a [±e5 ls layup. For all angles, micrographs and X-ray computed tomography showed that delamination and matrix cracking were suppressed, allowing pseudoductile strains to develop. Significant fibre rotations were shown to take place, permitted by matrix plasticity, leading to a stiffening at high strains. Analytical modelling that incorporates matrix plasticity and reorientation of the fibres into classical laminate analysis has been developed. The approach was successfully validated against experimental results, capturing the main characteristics of the stress-strain curve, such as the initial largely linear, 'yield ' and stiffening regions. Further analysis identified a fibre angle (±26°) that exhibited strength in excess of 900 MPa, strain to failure greater than 3.5% and pseudo-ductile strain of 1.2%. Inclusion of unidirectional plies at the mid-plane of the laminate led to experimental pseudo-ductile metal-like tensile stress-strain responses with 700 MPa 'yield' stress and 2.2% pseudo-ductile strain using [±265 /O]8 lam-' inates. Enhancements to the analytical model allowed predictions of other [±θm/On]8. layups, which were validated with experimental tests. Postfailure specimen analysis greatly improved the understanding of the pseudoductile stress-strain behaviour. A gradual failure was identified, caused by multiple fibre fractures in the 0° plies that, in some cases, led to dispersed delaminations at the 0/ -θ interfaces. A preliminary study of the compressive behaviour of thin ply angle-ply laminates has also been conducted, via four-point bending of a honeycomb sandwich beam. Layups of [±266]8 and [±306]8 showed significantly less 11011- linearity than the same configurations loaded in tension. This is likely to be have been due to the relatively low shear 'yield' stress of the material. These tests , however, have shown potential for thin ply angle-ply laminates to exhibit pseudo-ductility under compression.
21
Shitindi, Rowland V. "IMPROVEMENT OF DUCTILITY IN FRP-CONCRETE FLEXURAL MEMBERS". Kyoto University, 1999. http://hdl.handle.net/2433/181308.
Testo completo
22
Jamwal, Ranbir Singh. "Microstructural origins of variability in the tensile ductility of dual phase steels". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39477.
Testo completoAbstract (sommario):
Quantitative relationships among processing parameters, microstructure, and material properties are of considerable interest in the context of development of robust processing routes that optimize the required material properties. As a result, the scientific literature contains a large number of experimental and theoretical studies on microstructure-properties relationships. Fracture sensitive mechanical properties such as ductility, ultimate tensile strength, fatigue life, and fracture toughness depend on the average microstructural parameters as well as the distributions of microstructural parameters and their extrema.Development of quantitative relationships between such material properties and microstructural distributions and extrema has received considerably less attention, particularly in the wrought metals and alloys. Accordingly, an important objective of this research is to perform a systematic investigation in this direction.
The dependence of the fracture-sensitive mechanical properties on the microstructural distributions and extrema often leads to substantial variability in these properties: a set of specimens having the same average chemistry, the same average processing history, and the same average microstructural parameters such as volume fractions of different constituents can exhibit substantially different material properties. The present research (i) is concerned with high strength (~ 1000 MPa) high martensite (>50%) dual phase steel where the martensite is a topologically continuous phase (matrix) containing a dispersion of islands of ferrite, and (ii) focuses on understanding the microstructural origins of the variability in fracture sensitive mechanical properties, in particular variability in the room temperature uniaxial tensile ductility. The research involves quantitative microstructure characterization using stereology and digital image processing and quantitative fractography using scanning electron microscopy (SEM) and fracture profilometry. The analysis of the quantitative fractographic and microstructural data obtained in this research leads to useful guidelines for reducing the variability in the tensile ductility of the dual phase steel under investigation.
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El-wazri, Abdelbaset M. "Effect of thermal history on hot ductility of steel". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0022/MQ50604.pdf.
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Ingram, Gregory O. "Experimental characterization of the effect of inertia on ductility". Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16087.
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El-Wazri, Abdelbaset M. "Effect of thermal history on hot ductility of steel". Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20904.
Testo completoAbstract (sommario):
One of the major quality problems encountered in continuous casting is the formation of transverse cracks, which is partly due to the poor hot ductility of the cast steel. In this work, high temperature tensile testing is used to determine the hot ductility of a Nb-Ti and Ti-B microllayed steels. The influence of reheat treatment on hot ductility of the alloys is studied. In order to accomplish this task, steel specimens were reheated near the incipient melting temperature, and subsequently tensile tested to fracture at a strain rate typical of the unbending operation over a range of temperatures, in order to obtain hot ductility data. The results are compared to those obtained after melting and solidification prior to high temperature tensile testing.As well, tensile specimens were subjected to thermal histories typical of continuously cast billet surface up to the unbending operation, and then subjected to a tensile test to fracture. In other words, physical simulations of the continuous casting procedure were performed. (Abstract shortened by UMI.)
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Davies, Paul. "Ductility and Deformability of FRP Strengthened Reinforced Concrete Structures". Thesis, University of South Wales, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517957.
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Ratkovich, John. "Processing and elevated temperature ductility of Aluminum alloy 7475". Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27223.
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Roberts, R. J. "The elasticity, ductility and fracture toughness of pharmaceutical powders". Thesis, University of Bradford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320442.
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Chuang, Eugene (Eugene Yu) 1975. "Ductility enhancement of high performance cementitious composites and structures". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/33272.
Testo completoAbstract (sommario):
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references (p. 280-287).
High performance cementitious composites (HP2C) are a new generation of fiber reinforced cementitious composites (FRCC) with substantial improvements in mechanical behavior. The most important development in these HP2C materials may be the nearly elasto-plastic ductile behavior, which allows safe exploitation of the tensile and shear capacity in structural elements. This thesis presents a comprehensive investigation into the ductility enhancement of HP2C structures. Beginning at the micromechanical level, sources of ductility are examined and micro-to-macro relations are derived from homogenization theory and fracture mechanics. These micro-to-macro relations form the basis for a novel 3-D two-phase material model, which captures macroscopically observed behavior. Currently existing models which describe the mechanical behavior of FRCC are often micromechanical in nature. However, this macroscopic approach permits one to model the mechanical behavior of HP2C in a continuous fashion, i.e. through the various states of cracking in HP2C, while capturing - through the two-phase composite structure of the model - the micromechanical sources of energy dissipation in the fiber reinforced composite.
(cont.) The 3-D model is implemented in a finite element program to simulate the behavior of two HP2C applications: a flexural girder and a shear girder, which have recently been tested by the FHWA. It is shown how the two-phase model aptly and accurately predicts the structural behavior of HP2C. Next, a sensitivity analysis of the HP2C model parameters elucidates how changes in HP2C mechanical behavior, observed at material level, manifest themselves at the structural level. By setting limits on the permanent composite matrix strain, which accounts for cracking in HP2C, one can set service limits on HP2C structures.Hence, a comprehensive (micromechanical, macroscopic, and structural) method for the assessment of the ductility enhancement of HP2C structures is presented. A significant scientific benefit of this research is the HP2C model which links micromechanical processes to macroscopic behavior and ultimately to structural behavior. This research also provides a design tool, that is the finite element application, which can be used to predict the behavior of HP2C structures and suggest improvements in HP2C structural and material design.
by Eugene Chuang.
Sc.D.
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Azizi, Abdul R. "Modelling moment redistribution in continuous reinforced concrete beams". Thesis, Durham University, 1996. http://etheses.dur.ac.uk/1578/.
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Kim, SangHun Aboutaha Riyad S. "Ductility of carbon fiber-reinforced polymer (CFRP) strengthened reinforced concrete". Related Electronic Resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2003. http://wwwlib.umi.com/cr/syr/main.
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Fielding, Lucy Chandra Devi. "Understanding toughness and ductility in novel steels with mixed microstructures". Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245654.
Testo completoAbstract (sommario):
The purpose of the work presented in this thesis was to explore and understand the mechanisms governing toughness, ductility and ballistic performance in a class of nanostructured carbide-free bainite-austenite steels, sometimes known as ‘superbainite’. The mechanical properties of these alloys have been extensively reported, but their interpretation is not clear. The thesis begins with an introduction to both the relevant nanostructures and some of the difficulties involved in explaining observed properties, alongside a summary of the role of mixed- microstructures in alloy development. An overview of the debate regarding the mechanism of bainite formation is pre- sented in Chapter 2, in the form of a literature survey encompassing the period of explicit recognition of the bainite microstructure. Of note is the role played by the displacive theory of formation in the development of the alloy structures investigated in this thesis. A characterisation of a commonly available bainitic alloy forms the basis for Chapter 4. Observations confirm the nanoscale nature of the structure, although additional phases are found to be present, namely: cementite and martensite. This is explained as resulting from relatively low alloying additions and chem- ical segregation effects, which are modelled using thermodynamic and kinetic approaches. Chapters 5 and 6 contain a comprehensive study of the response of this alloy to the stress concentration present at the notch root of a Charpy impact sample. The work provides evidence of notch root embrittlement due to stress-induced martensite transformation. Results from synchrotron and laboratory X-ray experiments in particular reveal that machining, as well as applied stress, can initiate the austenite-martensite transformation, and methods to mitigate this effect are suggested. An innovative approach is harnessed in Chapter 7, in order to identify exper- imentally the volume fraction at which three-dimensional connectivity (‘percolation’) of austenite is lost in a superbainitic steel. Hydrogen thermal desorption techniques are applied to this problem, inspired by the tendency of such alloys to undergo tensile failure with limited or zero necking. The striking result sheds light on the importance of austenite morphology in restricting the diffusion of hydrogen into a mixed structure. The final set of experimental work is directed towards understanding the damage mechanisms that occur during projectile penetration of a coarser bainitic armour- plate alloy. The formation of adiabatic shear bands is found to be a dominant factor governing the ballistic failure of the plate. The sheared material undergoes severe high-temperature deformation, but does not change phase upon cooling, leading to the proposal of certain methods that could be implemented to improve ballistic resistance of the steel. The totality of the research presented herein is summarised in Chapter 9, which draws attention to new areas of interest that have arisen from the current work, proposing several future directions of investigation. The broader issue of understanding, common to all studies performed thus far, is that of the causes, effects, and extent, of stress-induced transformation to martensite experienced by the retained austenite that is a key feature of superbainite and similar steels.
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Ewen, Kristian A. J. "Ductility in FRP rods for concrete reinforcement by interfacial shearing". Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/10798.
Testo completoAbstract (sommario):
Non-corrosive reinforcement of concrete provides great potential for reducing life cycle costs (LCC) of highway infrastructure (bridge decks and columns, light-standards, dividers) and concrete structures near water (piers, retaining walls, platforms). This is especially important in areas where salts are common (cold weather road salting, coastal regions) and is achieved by extending the life of structures and the period between major repairs. Costs of infrastructure rehabilitation due to corrosion of reinforcement are estimated to be $1.2 billion dollars in Ontario in the next few years, and up to 40% of all annual infrastructure costs in the province of Quebec. Efforts to reduce the frequency of repair and replacement of ageing structures include using epoxy coating of the reinforcing bar (rebar), cathodic protection, alternate types of steel and fibre reinforced polymer (FRP) rebar. Of these, FRP rebar appears to be the most promising. The limitation of FRP rebar is the low maximum strain and linear behaviour up to failure. Prior attempts at increasing the ductility and producing non-linear behaviour have had limited success. Maximum strain remains limited to that of the highest strain fibres available. Pseudo-ductility has been achieved by combining multiple fibre types having different material properties. The work described in this thesis focussed on non-traditional methods for achieving ductility in FRP rebars by taking advantage of the frictional interface of two materials. Two methods were tested. The first employed a solid inner-core with an over-wrap cut at regular intervals and relied on the rebar pulling out of the concrete at sustained load. Rods were tested in concrete beams under bending loads. Sustained load was achieved for significant pull-out. The second method combined continuous fibres with discontinuous meso-rods wherein the continuous fibres provide initial stiffness and maximum strength and the discontinuous meso-rods provide high-ductility via fibre pull-out. A concept model using aligned short steel fibres was manufactured and tested. Load-displacement behaviour showed substantial local elongation. Prototype models using carbon fibres were manufactured and tested. Specimens showed evidence of fibre pull-out. Future specimens should employ an intermediate material with a controlled and repeatable shear strength for the interface.
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Zaina, Mazen Said Civil & Environmental Engineering Faculty of Engineering UNSW. "Strength and ductility of fibre reinforced high strength concrete columns". Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2005. http://handle.unsw.edu.au/1959.4/22054.
Testo completoAbstract (sommario):
The main structural objectives in column design are strength and ductility. For higher strength concretes these design objectives are offset by generally poor concrete ductility and early spalling of the concrete cover. When fibres are added to the concrete the post peak characteristics are enhanced, both in tension and in compression. Most of the available experimental data, on fibre reinforced concrete and fibre reinforced high strength concrete columns, suggest that an improvement in both ductility and load carrying capacity due to the inclusion of the fibres. In this thesis the ductility and strength of fibre reinforced high strength concrete are investigated to evaluate the effect of the different parameters on the performance of columns. The investigation includes both experimental and the numerical approaches with 56 high strength fibre reinforced concrete columns being tested. The concrete strength ranged between 80 and 100 MPa and the columns were reinforced with 1, 2 or 2.6 percent, by weight, of end hooked steel fibres. The effect of corrugated Polypropylene fibres on the column performance was also examined. No early spalling of the cover was observed in any of the steel fibre reinforced column tested in this study. A numerical model was developed for analysis of fibre and non-fibre reinforced eccentrically loaded columns. The column is modelled as finite layers of reinforced concrete. Two types of layers are used, one to represent the hinged zone and the second the unloading portion of the column. As the concrete in the hinged layers goes beyond the peak for the stress verus strain in the concrete the section will continue to deform leading to a localised region within a column. The numerical model is compared with the test data and generally shows good correlation. Using the developed model, the parameters that affect ductility in fibre-reinforced high strength concrete columns are investigated and evaluated. A design model relating column ductility with confining pressure is proposed that includes the effects of the longitudinal reinforcement ratio, the loading eccentricity and the fibre properties and content and design recommendations are given.
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Mostofinejad, Davood. "Ductility and moment redistribution in continuous FRP reinforced concrete beams". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ26859.pdf.
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Zahn, Franz August. "Design of reinforced concrete bridge columns for strength and ductility". Thesis, University of Canterbury. Department of Civil Engineering, 1985. http://hdl.handle.net/10092/2872.
Testo completoAbstract (sommario):
Methods for the design of reinforced concrete bridge columns and
piers for strength and ductility are considered. The investigations cover
the following areas.
An experimental investigation of the influence of reinforcing steel
grade and amount of confining steel on the stress-strain behaviour of
confined concrete is presented. The results are discussed and compared
with theoretical models. Special attention is given to the possibility
of fracture of the confining steel.
An extensive experimental investigation into the ductile performance
of a range of reinforced concrete columns is presented. The columns were
subjected to constant axial load and cyclic lateral displacements. The
test units included four square columns with the lateral load applied
in the direction of a cross section diagonal, six circular hollow columns
with different wall thickness to diameter ratios, and four columns with
transverse reinforcement from Grade 380 steel. The available strength and
ductility of the columns is discussed and compared with the performance
of columns tested previously at the University of Canterbury, and with
theoretical predictions using monotonic as well as cyclic moment-curvature
analyses. The main variables for the solid columns were the influence of
biaxial bending, the use of Grade 380 transverse steel for confinement,
and the spacing between transverse bars along the column axis. The
circular hollow columns were unconfined on the inside face of the tube
wall, and the main variables were the influence of the axial load level
and the wall thickness.
The implications of the column test results, including the results
of other investigations, for the design of reinforced concrete columns
for strength and ductility are discussed and, where appropriate, used to
calibrate theoretical models. In particular, the influence of cyclic
loading on the strength deterioration of reinforced concrete columns with
high axial loads is emphasized. More realistic definitions of the ideal
flexural strength, of the flexural overstrength and of the yield curvature
are suggested and, together with a set of criteria for the ultimate limit
state, used to establish design charts for the available strength and
ductility of reinforced concrete columns. A cyclic moment-curvature
analysis was used for this purpose, incorporating cyclic stress-strain
models for the concrete and for the steel, thus taking into account the
cyclic strength deterioration observed for columns with high axial loads.
Finally, a rational step-by-step design procedure is presented that
will make less complex the task of considering the great number of
variables involved in the seismic design of reinforced concrete columns
for both strength and ductility.
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Cowley, Andrew. "Hot ductility and its relationship to transverse cracking in steels". Thesis, City University London, 2004. http://openaccess.city.ac.uk/8416/.
Testo completoAbstract (sommario):
The influence of the Ara on the hot ductility of steels was examined. Tensile samples were heated to 1603K, cooled at 60Kmin" and tested in the temperature range 1323-873K at a strain rate of 3x10-3S-1. The Ara was altered by variations in C, (0.1 to 0.15%C), Mn, (0.6 to 1.4%Mn), Si (0.1 to 0.5%Si) and P, (0.001 to 0.025%P). Elements that raise the Ara e. g. Si and P were found to lead to recovery in ductility at slightly higher temperatures at the low temperature end of the trough. However, reducing C levels to <0.1C had the most pronounced influence on hot ductility since ductility was then observed to recover just below the Ae3 and the trough was very narrow. The lower C level allowed large amounts of deformation-induced ferrite (equilibrium amounts) to form, ferrite having excellent ductility. mThe influence of both S in solution and elongated sulphides on hot ductility was also examined. Although elongated sulphides encouraged ferrite formation, this was a relatively minor improvement. In these steels, low C levels (<0.1%) i. e. high Ae3 temperatures, ensured ductility recovered rapidly just below the Ae3 obscuring the effect of S. Similar behaviour was noted with as-cast steel, increasing the S level from 0.004 to 0.019% had little influence on the hot ductility. Increasing the cooling rate after solidification, from conventional continuous casting to that pertaining to thin slab casting, results in worse ductility. This can be ascribed to finer precipitation and/or a finer inclusion distribution at the y grain boundaries. A model was devised for predicting the hot ductility curve for simple plain C-Mn steels. However, this model has limited application and further development is needed to take into account the influence of grain boundary sliding on the reduction of area values. Columnar grains were found to be very detrimental to hot ductility and to avoid transverse cracking, it is suggested magnetic stirring be used in the mould to break up the columnar structure.
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Zouzou, Ammar. "The ultimate strength and ductility of structural concrete corner joints". Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1408.
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Li, Tieqiang. "The analysis and ductility requirements of semi-rigid composite frames". Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239925.
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Raffoul, Samar. "Development of confined rubberised concrete for high ductility structural applications". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/20030/.
Testo completoAbstract (sommario):
The global environmental and economic implications of the disposal of waste tyres have prompted research exploring valuable outlets for their components. Concrete is an inherently brittle material and can benefit from tyre rubber properties to achieve higher ductility and energy dissipation for special applications in locations of high deformation demands, such as coupling beams. Despite the prospective benefits, the use of rubber as partial mineral aggregate replacement negatively affects concrete workability and strength. Recent research has shown that the external confinement of RuC can benefit from its high lateral expansion and mitigate the drawbacks of RuC, leading to high strength. Nevertheless, the majority of this research is limited to low rubber contents, which restricts the deformability potential of confined rubberised concrete (CRuC). This research aims to advance the understanding on unconfined and FRP-confined RuC, developed with high rubber contents and optimised mix parameters, leading the way for new high-strength high-deformability concrete elements. More than forty RuC mixes were investigated experimentally to develop an understanding of the effect of rubber and various concrete mix parameters on RuC fresh properties and short-term compressive strength. An “optimum” RuC mix with adequate workability and strength at all rubber contents was developed for further study. The influence of rubber (content and type) on the stress-strain behaviour of the optimised RuC mix was investigated in a second parametric study involving more than 60 cylinders. The addition of rubber to concrete led to high lateral strains and premature failure, particularly at high rubber contents, which can be exploited to activate external confinement. The mix with high rubber content (60% total aggregate replacement) was identified as most suitable for study to maximise the deformability in RuC. The use of Aramid or Carbon FRP sheets as external confinement to high rubber contents RuC was examined experimentally under monotonic and cyclic uniaxial compression. This led to the development of constitutive models to accurately predict the performance of confined rubberised concrete (CRuC) subject to monotonic or cyclic loading. CRuC led to unprecedented axial strains (>6%) and compressive strength above 90 MPa, indicating high potential for its use in a variety of structural applications.
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Shrestha, Umesh Shahu. "Modified Composite Application to Improve Strength and Ductility ofStructural Components". University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418403567.
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Sjöström, Julia, e Helena Åkesson. "Investigation of Ductility Dip at 1000˚C in Alloy 617". Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209823.
Testo completoAbstract (sommario):
Alloy 617 displays a ductility dip during straining at exactly 1000˚C, leading to brittle fracture. A sudden decrease in ductility appearing during Gleeble hot ductility tests of Ni-based superalloys is a well-known phenomenon, while its cause is unknown. Many mechanisms have been established as possible contributors to the issue, and in later years not one, but the simultaneous presence of several of these mechanisms were confirmed as the cause. The ductility dip leads to solid state cracking and a specific solid state cracking phenomenon known as ductility dip cracking is specifically common in Ni-based superalloys. Ductility dip cracking is identified by intergranular cracks and the occurrence of specific precipitates, among other things. This work investigates the possibility that the decreased ductility is due to ductility dip cracking. Furthermore, other possible explanations are investigated. Visual examination was conducted through LOM, SEM and chemical analysis using EDS technique. Combined with thermodynamic calculations, the existence of Cr-rich M23C6 carbides, Ti(N,C) and Mo-rich particles, most likely M3B2, were confirmed. Further, it is established that the ductility dip is related to the lack of dynamic recrystallization at 1000˚C. It is not confirmed that the ductility dip in alloy 617 is due to ductility dip cracking.Nickelbaslegeringen 617 uppvisar en minskning i duktilitet under Gleeble-dragprovning vid exakt 1000˚C vilket leder till sprött brott. En plötslig sänkning av duktiliteten vid varmdragning av Ni-baserade superlegeringar är ett välkänt fenomen, dock är orsaken inte fastställd. Många mekanismer har bekräftats som bidrag till problemet och under de senaste åren har den simultana närvaron av fler av dessa mekanismer bekräftats som orsaken. Sänkningen i duktilitet leder till sprickbildning i fast fas och en specifik typ av sprickbildning känd som ”ductility dip cracking” är speciellt förekommande i Ni-bas legeringar. Denna identifieras bland annat genom intergranulära sprickor och närvaron av specifika utskiljningar. Detta arbete undersöker möjligheten att duktilitetssänkningen beror på ”ductility dip cracking”. Dessutom undersöks fler tänkbara förklaringar. Visuell granskning genomfördes via LOM och SEM och analys av sammansättningar via EDS-analys. I kombination med termodynamiska simuleringar blev förekomsten av Cr-rika M23C6 karbider, Ti(N,C) och Mo-rika partiklar, troligtvis M3B2, bekräftad. Fortsatt är det bekräftat att duktilitetssänkningen är relaterat till avsaknaden av rekristallisation vid 1000˚C. Det är inte bekräftat i detta arbete att duktilitetssänkningen i legering 617 beror av ”ductility dip cracking”.
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Mostofinejad, Davood Carleton University Dissertation Engineering Civil and Environmental. "Ductility and moment redistribution in continuous FRP reinfoced concrete beams". Ottawa, 1997.
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Hervillard, Thomas P. C. "Effectiveness of polymer fibers for improving the ductility of masonry structures". Online access for everyone, 2005. http://www.dissertations.wsu.edu/Thesis/Fall2005/T%5FHervillard%5F110705.pdf.
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Ho, Yin Bon. "Enhancing the ductility of non-seismically designed reinforced concrete shear walls /". View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202006%20HO.
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Norouzi, Siavash. "A Micromechanical Model for Numerical Study of Rock Dilation and Ductility". Thesis, New Mexico Institute of Mining and Technology, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10688951.
Testo completoAbstract (sommario):
The newly implemented micromechanical model in the CA2 computer program was studied in this work. The purpose was to address some of the issues in the numerical studies involving the Bonded Particle Model (BPM) including unrealistically low qu/σ t ratios, overall dilation behavior, and the post-failure response of rocks. The plasticity model allows both tensile and shear softening of the filling material at the contact points of the particles. It is shown that for a more ductile material, there is less scatter of micro-cracking at the peak load. Furthermore, the ductility parameter appears to be a good tool in controlling the ratio of compressive to uniaxial tensile strength of rock. While the ductility of the filling at the contact points of the particles has a drastic effect on the macroscopic post-peak rock behavior in the direct tensile testing, its role in dictating the post-peak rock behavior in compression is negligible and needs further study. The combined effect of ductility and initial micro-cracking on rock strength characteristics was studied as well. The numerical results suggest that the ratio of Brazilian to direct tensile strength of the simulated material is affected by the initial micro-crack intensity; this ratio is around 1 for a material with no initial micro-cracks but it gradually increases as the initial micro-crack intensity is increased. In terms of the overall dilation behavior, it is shown that the macro-dilation angle can be controlled by means of the micro-dilation angle in a positive correlation provided that the average grain size is sufficiently small or when a joint is involved. As the grain size increases, the resulted macro-asperities suppress the functionality of the micro-dilation angle and consequently, the macro-dilation angle cannot be controlled. Further, it is shown that the genesis pressure can help to govern the overall dilation behavior. This parameter is also able to control the post-peak behavior of a bonded particle system. It is shown that high values of the genesis pressure yield to more brittle BPM system with greater dilation angles and steeper post-peak curves.
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Whittaker, Jarrod Talbott. "Ductility and Use of Titanium Alloy and Stainless Steel Aerospace Fasteners". Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5796.
Testo completoAbstract (sommario):
The main purpose of this thesis is to investigate the ductility and application of titanium alloys, like titanium 6Al-4V, when used in aerospace fasteners compared to more conventional stainless steel aerospace fasteners such as A286. There have been concerns raised about the safe usability of titanium 6-4 in the aerospace industry due to its lack of strain hardening. However, there is a lack of data pertaining to this concern of safe usage which this thesis aims to address. Tensile tests were conducted to find the ductility indexes of these fasteners which quantify the amount of plastic to elastic elongation. From the tests conducted it was found that the two materials yield and tensile strengths were very similar, though the ductility index of A286 is on average ten times greater than that of titanium 6-4. This thesis includes joint diagram examples that analyze typical joints using both materials. It was found from joint diagram examples that the lower ductility index of the titanium alloy will only be detrimental to use at higher preloads. However, the titanium alloy can be used safely in place of A286 in most loading situations just with narrower safety margins in these controlled examples.
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Rahgozar, Mohammad Ali. "Ductility and strength demands in building structures subjected to earthquake forces". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0006/NQ32349.pdf.
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Randelius, Mats. "Influence of microstructure on fatigue and ductility properties of tool steels". Licentiate thesis, Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4624.
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Li, Xiaohui [Verfasser]. "Enhanced ductility of Mg alloys containing rare earth elements / Xiaohui Li". Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2013. http://d-nb.info/1037333403/34.
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