Tesi sul tema "Hardening-Softening"
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Mshana, S. J. "Rate-dependent constitutive equations of cyclic softening and hardening". Thesis, University of Ottawa (Canada), 1986. http://hdl.handle.net/10393/5422.
Tahar, Benabdellah. "Câ†2 continuous hardening/softening elasto-plasticity model for concrete". Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323061.
Zeng, Xiaohui. "Modeling hardening and softening due to high-angle grain boundaries in crystalline solids /". Göttingen : Cuvillier, 2007. http://d-nb.info/985835710/04.
Mesmar, Sultan. "On the use of viscosity as a regularisation technique for hardening/softening constitutive models". Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341798.
Li, Tianbai. "Stress integration strategies for a new hardening/softening elasto-plasticity model for structural concrete". Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425181.
Conca, Luca. "Mechanical properties of polymer glasses : Mechanical properties of polymer glasses". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1050/document.
This manuscript presents recent extensions to the PFVD model, based on the heterogeneity of theh dynamics of glassy polymers at the scale of a few nanometers et solved by 3D numerical simulation, which aim at providing a unified physical description of the mechanical and dynamical properties of glassy polymers during plastic deformation. Three main topics are treated: Plasticization. Under applied deformation, polymers undergo yield at strains of a few percent and stresses of some 10 MPa.We propose that the elastic energy stored at the scale of dynamical heterogeneities accelerates local dynamics. We observe yield stresses of a few 10 MPa are obtained at a few percent of deformation and that plastification is due to a relatively small amount of local yields. It has been observed that dynamics becomes faster and more homogeneous close to yield and that the average mobility attains a stationary value, linear with the strain rate. We propose that stress-induced acceleration of the dynamics enhances the diffusion of monomers from slow domains to fast ones (facilitation mechanism), accelerating local dynamics. This allows for obtaining the homogeneisation of the dynamics, with the same features observed during experiments. Strain-hardening, in highly entangled and cross-linked polymers. At large strain, stress increases with increasing strain, with a characteristic slope (hardening modulus) of order 10 – 100 MPa well below the glass transition. Analogously to a recent theory, we propose that local deformation orients monomers in the drawing direction and slows dows the dynamics, as a consequence of the intensification of local interactions. The hardening moduli mesured, the effect of reticulation and of strain rate are comparable with experimental data. In addition, strain-hardening is found to have a stabilizing effect over strain localization and shear banding
Kopūstienė, Diana. "Korozijai ir karščiui atsparaus plieno standaus apkrovimo ciklinių deformavimo parametrų nustatymas". Master's thesis, Lithuanian Academic Libraries Network (LABT), 2005. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2005~D_20050613_191225-20900.
Kpodekon, Crescent. "Effet du pré-écrouissage sur la durée de vie d'aciers austénitiques de type 304L". Phd thesis, INSA de Rouen, 2010. http://tel.archives-ouvertes.fr/tel-00581715.
Miyagi, Lowell. "Microstructures and Deformation in Some Fault Rocks From The McConnell Thrust at Mount Yamnuska (Alberta) : Implications for Fluid Flow and Faulting and Cycles of Strain-Hardening and Softening". Oberlin College Honors Theses / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1411739220.
Diao, Hui. "Deformation behaviours of coarse-grained and nanocrystalline Mg-5wt% Al alloys". Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/46870/1/Hui_Diao%27s_Thesis.pdf.
Kuprin, Corinna. "Verformungsverfestigung bei zyklisch inkrementeller Torsion von Reineisen und dem Stahl 42CrMo4N". Doctoral thesis, Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-103890.
Ferritic-pearlitic steel 42CrMo4N and pure iron under different strain paths are compared regarding their flow behaviour. Mainly in cyclic torsion tests with resulting strain increment per cycle shear stresses and strain hardening are analysed. The results show, that the cementite lamellae determine the flow behaviour of the steel 42CrMo4N, whereas the properties of pure iron are governed by the evolving dislocation cell structure. The dependency of flow stress on the strain direction is different for the two materials. Yield surfaces describe strain hardening quantitatively. The procedure for yield point detection and the dependency of subsequent yield surfaces on experimental conditions and strain states is shown. For pure iron isotropic hardening, for steel 42CrMo4N kinematic strain hardening dominates the flow behaviour
KLODA, LUKASZ. "Coupled longitudinal-transversal vibrations of nonlinear planar Timoshenko beams with an axial end spring". Doctoral thesis, Università Politecnica delle Marche, 2020. http://hdl.handle.net/11566/274580.
In the thesis, studies on nonlinear dynamics of a homogeneous and isotropic beam are performed. Partial differential equations of motion of a straight planar beam model are derived, taking into account extensibility and shearing effects, longitudinal, transverse and rotational inertia as well as different curvature definitions. For special boundary conditions (like hinged-simply supported beam with an axial spring) approximate method of multiple time-scales is implemented to catch various dynamic phenomena of the system, wherein free dynamics and forced-damped vibrations are represented by backbone curves and nonlinear frequency response curves, respectively. In the structure axial-transverse oscillations are coupled and the importance of combination of two modes, for instance in internal resonance, is shown. Analytical considerations are supported by numerical model elaborated in commercial software Abaqus_CAE. Initially, the linear behaviour of the beam model in frequency module is tested and then backbone curves and stable frequency response curves with use of transient dynamic explicit module are obtained. Time-dependent simulations with path-following and shooting methods are used and outcomes are compared with analytical results. Apart from sophisticated theoretical approaches, a basic validation tests on the Euler-Bernoulli beam prototype are done. Nonlinear dynamics of kinematically excited prototype with various boundary conditions in axial direction is executed experimentally. Hardening/softening phenomena and jumps between stable solutions are observed in analytical and numerical solutions, as well as in experiments. Study on nonlinear dynamics of a beam ends with conclusions and further developments are suggested.
López, Martínez Juan Ángel. "CHARACTERISATION OF THE TENSILE BEHAVIOUR OF UHPFRC BY MEANS OF FOUR-POINT BENDING TESTS". Doctoral thesis, Universitat Politècnica de València, 2017. http://hdl.handle.net/10251/79740.
El Hormigón de Muy Alto Rendimiento (HMAR) combina los últimos avances tecnológicos en hormigón y se erige como un material prometedor para el futuro. El HMAR ha demostrado su gran capacidad para adaptarse a las cada vez más exigentes demandas sociales y medioambientales. Con un gran abanico de posibilidades en su dosificación para conseguir las propiedades mecánicas deseadas, el HMAR es un material lleno de posibilidades aún sin explorar y sin explotar. Los ingenieros tienen la responsabilidad de esta tarea. Sin embargo, es justo reconocer que no se trata de una tarea fácil y que requiere de un desarrollo previo de códigos de diseño adecuados y ampliamente aceptados por parte de la comunidad científica. La aparición de nuevas tecnologías, el mayor conocimiento sobre la aportación de las fibras así como su industrialización y bajada de precios, las mayores preocupaciones sobre la durabilidad estructural, incremento de la vida útil o la reducción de los costes de mantenimiento, entre otros factores, han derivado en el desarrollo de nuevas tipologías de hormigones cuyo comportamiento mecánico difiere de manera sustancial de los tradicionales hormigones con fibras. Es por ello que tanto la readaptación de las metodologías de caracterización como las metodologías de diseño deben ser reformuladas. Y esto debe hacerse de manera no disruptiva, es decir, manteniendo la línea de los hitos alcanzados en los hormigones con fibras convencionales de manera que queden integrados en metodologías de caracterización y de diseño que los engloben, porque al fin y al cabo, y aunque con nuevas y mejores propiedades mecánicas, los nuevos hormigones siguen siendo hormigones. Así debe ser entendido y así debe quedar reflejado en las nuevas normativas. El presente trabajo se centra en uno de esos nuevos materiales desarrollados con el avance de las nuevas tecnologías como es el HMAR. En especial, este documento se centra en ese aspecto tan fundamental para el desarrollo de nuevos hormigones como es la caracterización mecánica y la tipificación. Este trabajo incluye una revisión del comportamiento mecánico uniaxial a tracción del hormigón y de su evolución con la aparición de las diferentes tecnologías. Además, se revisan y se ponen en cuestión los sistemas tradicionales de caracterización, así como los nuevos sistemas desarrollados en los últimos años para su empleo específico en el HMAR. A lo largo del documento se desarrollan diferentes metodologías para la obtención del comportamiento constitutivo a tracción del HMAR, así como la propuesta de una metdología simplificada de caracterización especialmente diseñada para ser incluida en una norma, todas ellas debidamente validadas. Estas metodologías son de aplicación específica a los resultados experimentales obtenidos mediante un ensayo a cuatro puntos sin entalla, cuya propuesta de estandarización para el HMAR ha sido también desarrollada. Finalmente, se presenta una propuesta de tipificación de acuerdo a los parámetros más relevantes del comportamiento a tracción del HMAR que son necesarios para el diseño y que pueden ser directamente obtenidos del ensayo de caracterización propuesto. Esta clasificación engloba a la clasificación existente para el hormigón armado convencional y los actuales hormigones con fibras, de manera que se presenta la actual definición de hormigón con fibras como un caso particular de estos nuevos hormigones, respetando al máximo la evolución de este material y aunando los logros conseguidos por la comunidad científica.
Dins de les combinacions de les tecnologies més recents en el formigó, el formigó de molt alt rendiment (UHPFRC) sorgeix com un material prometedor per al futur pròxim. L'UHPFRC ha demostrat poder ser un formigó flexible per adaptar-se a les sempre canviants demandes socials i mediambientals. Amb una gran flexibilitat en la seua composició i les seues propietats mecàniques, l`UHPFRC està ple de possibilitats de ser explorades i explotades. Els enginyers han de prendre la responsabilitat d'aquesta tasca. No obstant això, és just reconèixer que això no serà fàcil i requerirà el desenvolupament de normes de disseny fiables i àmpliament acceptades per la comunitat científica. Hi ha una gran preocupació al voltant de la durabilitat, la vida útil de les estructures i la reducció del cost de manteniment, juntament amb el desenvolupament de noves tecnologies de formigó, un millor coneixement de l'efecte de la fibra i un enorme creixement en la indústria de la fibra acompanyat per la reducció del preu de la fibra, han conduït, entre altres factors, al desenvolupament de nous tipus de formigons, el comportament mecànic dels quals es diferencia substancialment dels formigons reforçats amb fibres convencionals. És per això que les metodologies de caracterització actuals i les normes de disseny han de ser revisades i ajustades a aquests nous materials. No obstant això, la revisió del codis de disseny no pot prescindir de les antigues fites aconseguides gràcies a dècades de treball dur. S'ha d'oferir una visió integrada en la qual els nous tipus de formigons integren els ja existents en un grup més ampli, ja que, al cap i la fi i malgrat tenir propietats noves i millorades, els nous tipus de formigons són encara un tipus de formigó. Així es com s'hauria d'entendre i reflectir-se en els nous codis i normes. El treball presentat en aquest document es centra en un d'aquests materials que s'han desenvolupat recentment i que abasta les principals tecnologies avançades en el formigó: el Formigó de Molt Alt Rendiment Reforçat amb Fibres (UHPFRC). Aquest treball se centra específicament en els requisits fonamentals per al desenvolupament i l'ús generalitzat d'aquest, com ara la caracterització i classificació del comportament constitutiu a tracció. Aquest treball inclou una revisió profunda del comportament a tracció uniaxial del formigó i els seus canvis al temps que la tecnologia de les fibres ha evolucionat. A més, els mètodes tradicionals estàndard de caracterització, així com els recentment desenvolupats per al seu ús específic en l'UHPFRC són revisats i qüestionats. Al llarg del document, es mostra el desenvolupament de diferents metodologies per a determinar el comportament constitutiu a tracció uniaxial de l'UHPFRC, juntament amb una proposta de caracterització simplificada especialment desenvolupada per poder ser inclosa en normativa. Totes les metodologies desenvolupades presentades en aquest document han estat comprovades i validades. Aquests mètodes estan dissenyats específicament per a la seva aplicació en els resultats experimentals obtinguts a partir d'un tipus especial d'assaig de flexió a quatre punts, a més també s'inclou una proposta d'estandardització per a l'UHPFRC. Finalment, es presenta una proposta de classificació en funció dels paràmetres més rellevants del comportament a tracció de l'UHPFRC que són necessaris per al disseny i que es poden obtindre directament del mètode d'assaig estàndard suggerit per a la caracterització de l'UHPFRC. La classificació proposada té amb compte la classificació existent per al formigó armat convencional i el reforçat amb fibres. En ella, tant el formigó en massa com el formigó reforçat amb fibres es presenten com un cas particular d'una resposta constitutiva a tracció més general per al formigó. La metodologia estàndard i la classificació proposada estan d'acord amb l'evolució de formigó i unifica l
López Martínez, JÁ. (2017). CHARACTERISATION OF THE TENSILE BEHAVIOUR OF UHPFRC BY MEANS OF FOUR-POINT BENDING TESTS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/79740
TESIS
Alamo, Vargas Valentin. "Transfert énergétique irréversible grâce à un résonateur acoustique à comportement non-linéaire". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSET006/document.
Nowadays, there is a need of new types of technologies for sound reduction because of the growing of different industries. In this context, we have studied the targeted energy transfer using a purely acoustic resonator. These acoustic resonators act, in the linear regime, as a Tuned Masse Damper (TMD) and they are efficient for a narrow frequency band. But, when they are excited with high forces, in the nonlinear regime, they are efficient for a wider frequency band if the nonlinear terms are activated. First, an experimental study about the nonlinear behavior of a modified Helmholtz Resonator was done. Then, the governing equation of such resonators were developed considering the nonlinearities in the restitution force and damping. An approximation of the analytical solution of the governing equation of the acoustical resonator is derived using the multiples scales of time method and the non-smooth time transformation method. In a second part, a study about the coupling between an acoustic mode in low frequencies and a resonator (the one studied in the previous part) with a nonlinear behavior is done. In order to do this, experimental measurements of the coupled system to confirm acoustic attenuation by the resonator in forced and free regime were done. Then, an analytical modelling of the coupled system allowed to derive the expression of the Slow Invariant Manifold (SIM), in order to identify the possible equilibrium points and singular points of the system. Derived analytical models were verified by numerical simulations
Šmíd, Miroslav. "Stanovení zkrácených cyklických deformačních křivek superslitiny Inconel 738LC při zvýšených teplotách". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2008. http://www.nusl.cz/ntk/nusl-228279.
Wassermann, Alice. "Quantification multi-échelles de la dégradation d’un sable traité soumis à des cycles hydriques". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0085.
Soil treatment, especially with hydraulic binders or lime, is a widespread technique to improve the mechanical characteristics of poor-quality soils. After their construction, engineering structures are subjected to environmental solicitations that can potentially alter the effects of the treatment, and thus lead to the degradation of the performance of the treated soil. In this context, the objective of this thesis was to study the impact of the accumulation of hydric cycles on the mechanical behaviour of a cement-treated sand. A multi-scale and multi-physics methodology was set up to understand and quantify the degradation of the macroscopic mechanical behavior of cement-treated sands during drying/wetting cycles.Short-term mechanical characterization of the sand was performed by conducting a triaxial testing campaign. The bonding ratio, η_bondmax, defined according to the stress-dilatancy theory, was introduced to assess the mobilization and the degradation of cementitious bonds during the triaxial tests. In order to characterize the durability of the treated sand, the impact of two types of hydric cycles of different intensity was evaluated. Following the cycles, triaxial tests were performed constituting a database of 130 test results. The bonding ratio monitoring allowed to explicitly quantify the degradation of the cemented specimens as a function of the type and number of cycles. The main effect of the hydric cycles is to alter the cementitious bonds and subsequently to decrease the mechanical performances. This alteration depends on the cement content but also on the intensity of the cycles. Type I cycles lead to a more important degradation than type II cycles. The kinetics of the alteration as well as its extent depend on the cement content.The investigation of the processes occurring at the microscopic scale after 24 cycles of the two types via microscopic observations (SEM and TEM) and physicochemical analyses (XRD and GTA) has highlighted intense mineralogical transformations including carbonation of the cementitious phases to various degrees depending on the intensity of the cycle as well as the formation of ettringite needles in the pore-space. However, in terms of macromechanical behaviour, a stabilization of mechanical performance after a moderate decrease (-20 to -30% of the deviatoric stress) was observed after 12 hydric cycles. This approach has shown that relating mineralogical transformations to durability is not sufficient. It is necessary to evaluate the contribution of each phase to the strength since intense mineralogical transformations are not necessarily associated with strong degradation of the treated soils.A constitutive law to model the observed deviatoric behaviour of treated sand was proposed by combining the Hardening Soil Model for the pre-peak hardening and an inverse sigmoid function for the post-peak softening. This approach showed a satisfactory accuracy to simulate the behaviour and in particular the softening of treated soils under relatively high confining pressures. Under low confining pressures an exponentially decreasing function was however more suitable. In addition, parameters optimization determined the most appropriate values for 5 model parameters (ψ, Rf, m, λ, and ecrit) as a function of cement content. The modeling permitted to complete the experimental study and broughtsome reflexions on the way to simulate the post-peak behaviour.This study allowed a mechanical quantification from macroscopic observations coupled with a physicochemical quantification of the various processes occurring during hydric cycles. A conceptual framework allowing to take into account the effect of cementing in the behaviour of treated soils was proposed
Danka, Labus Zlatanović. "Friction stir spot welding of ultrathin sheets made of aluminium – magnesium alloy". Phd thesis, Univerzitet u Novom Sadu, Fakultet tehničkih nauka u Novom Sadu, 2020. https://www.cris.uns.ac.rs/record.jsf?recordId=114672&source=NDLTD&language=en.
У оквиру ове докторске дисертације испитивано је тачкасто заваривање трењем са мешањем ултратанких лимова дебљине 0.3 mm од легуре АА 5754 – H111 (AlMg3). Утицај геометрије алата и параметара као што су угаона брзина и аксијално оптерећење су детаљно анализирани уз помоћ бројних техника. Установљено је да приликом заваривања ниским угаоним брзинама долази до деформационог ојачавања, док на високим угаоним брзинама долази до термичког омекшавања зоне завара. Код узорка завареног са најмањим бројем обртаја долази до формирања комплексног слоја на међуконтактној површини који изазива деламинацију приликом испитивања механичких особина.
U okviru ove doktorske disertacije ispitivano je tačkasto zavarivanje trenjem sa mešanjem ultratankih limova debljine 0.3 mm od legure AA 5754 – H111 (AlMg3). Uticaj geometrije alata i parametara kao što su ugaona brzina i aksijalno opterećenje su detaljno analizirani uz pomoć brojnih tehnika. Ustanovljeno je da prilikom zavarivanja niskim ugaonim brzinama dolazi do deformacionog ojačavanja, dok na visokim ugaonim brzinama dolazi do termičkog omekšavanja zone zavara. Kod uzorka zavarenog sa najmanjim brojem obrtaja dolazi do formiranja kompleksnog sloja na međukontaktnoj površini koji izaziva delaminaciju prilikom ispitivanja mehaničkih osobina.
Chalmovský, Juraj. "Analýza chování kořene kotvy v jemnozrnných zeminách". Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-392297.
Günther, Ralf-Michael. "Erweiterter Dehnungs-Verfestigungs-Ansatz". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-27196.
Günther, Ralf-Michael. "Erweiterter Dehnungs-Verfestigungs-Ansatz: Phänomenologisches Stoffmodell für duktile Salzgesteine zur Beschreibung primären, sekundären und tertiären Kriechens". Doctoral thesis, TU Bergakademie Freiberg, 2009. https://tubaf.qucosa.de/id/qucosa%3A22710.
Mezquida, Alcaraz Eduardo José. "Numerical Modelling of UHPFRC: from the Material to the Structural Element". Doctoral thesis, Universitat Politècnica de València, 2021. http://hdl.handle.net/10251/167017.
[CA] El principal objectiu de la present tesi es el desenvolupament d'una completa metodologia per al modelat numèric de l'UHPFRC des del nivell material fins arribar als elements estructurals. Es pretén contribuir a l'avanç del coneixement del comportament mecànic de l'UHPFRC per mitjà d'un procediment per al modelat numèric útil per al modelat i disseny estructural que permeta fer que aquest material siga competitiu al mercat de la construcció. En la metodologia de modelat proposta, es considera un comportament constitutiu de l'UHPFRC optimitzat per mitjà d'un procediment directe i fiable amb el qual s'aprofiten els avantatges del material, resultant en un disseny estructural eficient des del punt de vista mecànic i econòmic. És necessari produir SH-UHPFRC per a aconseguir grans propietats mecàniques? És possible generar SS-UHPFRC amb el qual queden reduïts els costs inicials mantenint unes propietats mecàniques i de durabilitat competitives que comporten un disseny estructural efectiu? El desenvolupament d'UHPFRC amb baix enduriment per deformació i de SS-UHPFRC pot reduir les seues propietats mecàniques però, si són adequadament estudiades i controlades, aquests podrien ser optimitzats. La tesi aborda algunes d'aquestes qüestions per mitjà de l'estudi del comportament a tracció de l'UHPFRC que va des de SH-UHPFRC fins SS-UHPFRC. Es pretén dur a terme una proposta de procediment fiable per a caracteritzar el comportament constitutiu a tracció i definir un model numèric d'elements finits fiable per a modelar amb precisió la resposta de provetes i elements estructurals armats d'UHPFRC. Per a definir el procediment directe per a caracteritzar a tracció tant SH-UHPFRC com SS-UHPFRC, s'ha dut a terme una campanya experimental i numèrica en la que s'ha analitzat el resultat d'assajar 227 provetes sense armadura fabricades amb UHPFRC amb quantitats de fibres curtes i llises d'acer de 120-130kg/m3 i 160kg/m3, assajades a flexió per mitjà de l'assaig a quatre punts (4PBT). El desenvolupament i la validació de l'esmentat procés són assegurats per mitjà d'un model no lineal d'elements finits (NLFEM) fiable. La validació numèrica duta a terme ha estat decisiva per a que aquest procediment siga precís, simple i fiable. Utilitzant aquesta campanya experimental, s'ha desenvolupat una aplicació predictiva per a estimar els paràmetres que defineixen el comportament constitutiu a tracció de l'UHPFRC. Aquesta aplicació és simple i directa i evita la possible variabilitat produïda per males interpretacions en l'aplicació del procés. A més a més, també s'ha dut a terme una segon campanya experimental constituïda per bigues d'UHPFRC armades a flexió amb diferents escales: 36 bigues curtes amb 130 i 160kg/m3 de fibres i dos bigues llargues de gran escala. Aquesta campanya s'ha modelat amb el NLFEM ací desenvolupat incloent efectes importants deguts a la interacció de l'UHPFRC amb les barres d'armat. Addicionalment, també s'han modelat amb el NLFEM tirants d'UHPFRC armats a tracció provinents d'una campanya experimental d'altra investigació. El model considera efectes deguts a la retracció, al 3D i comportament tensió stiffening que generen resultats molt precisos quan es comparen amb els resultats experimentals. Per tant, com a resultat de la present tesi doctoral, s'ha obtingut un model d'elements finits capaç de modelar amb precisió elements estructurals d'UHPFRC armats. Els resultats del model comparats amb els resultats experimentals no sols demostren la fiabilitat del NLFEM dut a terme sinó que també la coherència del procediment directe desenvolupat per a caracteritzar el comportament constitutiu a tracció de l'UHPFRC als dos casos, tant per a SH-UHPFRC com SS-UHPFRC, tant en elements estructurals armats a flexió com amb elements estructurals armats a tracció directa. Conseqüentment, s'ha proposat una metodologia completa i efectiva per al modelat numèric de l'UHPFRC des del niv
[EN] The main objective of the present PhD thesis is to develop a complete methodology for the numerical modelling of UHPFRC from the material level to structural elements. It intends to contribute to advanced knowledge of mechanical UHPFRC behaviour to lead to a numerically modelling proposal that is useful for structural modelling and design that allows options for this material to be competitive in the construction market. Optimised UHPFRC material constitutive behaviour, characterised by a direct reliable defined procedure, is considered in the proposed modelling methodology to take advantage of these properties, and to lead to an efficient structural design from the mechanical and economical points of view. Is it necessary to produce SH-UHPFRC to obtain excellent properties? Is it possible to develop SS-UHPFRC that leads to lower initial costs and to maintain competitive mechanical and durability properties that result in an effective structural design? The development of low strain-hardening and SS-UHPFRC would lead to reduce its mechanical properties, but they can be optimised if they are studied and controlled. The thesis addresses some of these questions by studying tensile UHPFRC behaviour to cover a wide range of tensile constitutive behaviours from SH-UHPFRC to SS-UHPFRC. It intends to propose a reliable tensile characterisation process and a reliable finite element model capable of accurately simulating the response of UHPFRC specimens and reinforced structural elements. An extensive experimental and numerical campaign with 227 unreinforced four-point bending test (4PBT) specimens with amounts of smooth-straight (13/0.20) steel fibres of 1.53-1.66% (120-130kg/m3) in volume and with 2.00% (160kg/m3), which represents SS-UHPFRC and SH-UHPFRC tensile behaviours, was carried out to set up a direct tensile characterisation procedure involving SS-UHPFRC and SH-UHPFRC. The direct procedure's development and validity are ensured by a reliable non-linear finite element model (NLFEM). Numerical validation was carried out and is decisive for performing the direct procedure to characterise the tensile behaviour of both SS and SH-UHPFRC herein developed accurately, simply and reliably. With the experimental programme herein, a predictive application for estimating tensile UHPFRC parameters was developed. The prediction offers reliable results. The application is simple and direct, and avoids variability in the characterisation procedure due to possible misinterpretations in its application. In addition, a second experimental programme, which includes reinforced concrete flexural beams on different scales, with 36 UHPFRC reinforced short beams with 130 and 160kg/m3 of steel fibres and two full-scale long beams, was carried out and modelled with the NLFEM herein developed including major effects due to the interaction between UHPFRC and reinforcement bars. Additionally, reinforced UHPFRC tensile bars from a recent experimental campaign performed by other researchers were modelled with the NLFEM. The model considers shrinkage effects, tension stiffening behaviour and 3D effects due to the particularities of the test, which provide very accurate results compared to those obtained with the experimental tests. As a result of this PhD thesis, an accurate NLFEM was obtained to model reinforced UHPFRC structural elements. The results of the model compared to the experimental ones demonstrate not only the reliability of the developed NLFEM, but also the coherence of the developed direct procedure to characterise tensile UHPFRC behaviour in both strain-softening and strain-hardening in reinforced flexural and direct tensile structural elements. Consequently, a complete and effective methodology for numerical UHPFRC modelling from the material level to structural elements is proposed.
Mezquida Alcaraz, EJ. (2021). Numerical Modelling of UHPFRC: from the Material to the Structural Element [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/167017
TESIS
Hsiao, Sheng-Yuan, e 蕭勝元. "Strain Softening and Anneal Hardening in Alloys". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/8q3836.
大同大學
材料工程學系(所)
95
In this study thermomechanical processings were applied to four alloys, including AZ31 and L9 Mg alloys, 6061 Al alloy and Cu-30%Zn alloy, for the strain softening and anneal hardening studies. By using differential scanning calorimetry (DSC), optical microscopy (OM), and elevated temperature compression test. The relationships between microstructure evolution and the behaviors of strain softening and anneal hardening were examinated. The results showed that the elevated temperature strength of alloys is inversely proportional to the applied pre-strain, which leads to the strain softening effect. An anneal treatment, on the other hand, increases the elevated temperature strength of alloys, and the magnitude of anneal hardening was found to be proportional to the magnitude of pre-strain.
Mohan, Nisha. "Extracting Material Response from Simple Mechanical Tests on Hardening-Softening-Hardening Viscoplastic Solids". Thesis, 2014. https://thesis.library.caltech.edu/8235/1/Nisha_Mohan_2014.pdf.
Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches.
A fundamental question that motivates the modeling of foams is ‘how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?’ A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,“Analysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes,” J. Mech.Phys. Solids, 59, pp. 2227–2237, Erratum 60, 1753–1756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like
1) The initial linear elastic response.
2) One or more nonlinear instabilities, yielding, and hardening.
The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.
Wu, Yu-Ting, e 吳昱霆. "Analysis of Collapse Surfaces for Trusses with Hardening and Softening". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/24716981297439472671.
國立臺灣大學
土木工程學研究所
100
There are some severe restrictions in the traditional limit analysis. For the load type, the load space is one-dimensional and monotonic by imposing the restriction of uni-directional proportional loading. On the other hand, only can the constitutive law be perfectly elastic, either rigid-perfectly plastic or elastic-perfectly plastic. However, the load space is usually high dimensional in true situation, and the hardening/softening behavior prevails in almost all engineering structures. To deal with these problems, it is important to loose the above restrictions. The greatest advantage of limit analysis is that it can obtain collapse loads directly without giving loading paths. In the field of limit analysis, the most common approach is applying mathematical programming to calculating the collapse loads of elastoplastic structures, and the problem becomes an optimization problem of maximizing the collapse load. Collapse loads form a collapse surface in high dimensional load space; we deem a collapse surface to be not merely numerical results of optimization, but an equivalent model of yield surfaces once the structure in equilibrium loses its static indeterminancy and forms mechanisms. That is, we observe that each piece of a collapse surface represents a collapse mode of the structure and is corresponding to the yield surfaces of those structural members that form a collapse mechanism.Therefore, by using the relationship between the collapse surface and the yield surface in load space, we define the conditions of mechanism vectors which have mathematical and physical meaning. After searching each mechanism, the model of collapse surface can be constructed, and then we can construct the safety region in load space. Finally, some examples for truss structures with hardening and softening are given to verify this method.
Xiao, Xiong. "Development and application of cavity expansion theory based on bounding surface and kinematic hardening plasticity". Thesis, 2020. http://hdl.handle.net/1959.13/1411293.
In this thesis, the undrained and drained spherical cavity expansions in clays are analysed according to a new viewpoint, in which this boundary problem is treated as the integration of stress-strain following cavity expansion load paths. The widely adopted substepping scheme numerical integration technique is used in developing the undrained and drained solution of cavity expansion problems based on the modified UH model and the original and modified two-surface bubble models. This bounding surface plasticity series model has been proved to have inherent advantages in capturing the overall soil behaviour for clays with different consolidation histories than the other critical state models under the classical plasticity framework, especially for predicting nonlinear soil response at the early stage of cavity expansion for a soil stress state initially located beneath the yield surface for previous consolidation. Since the embedded hardening law of the modified UH model and the original and modified two-surface bubble model are related to the degree of overconsolidation, the influence of consolidation history (OCR) on the expansion responses for spherical cavities in clays under both undrained and drained conditions can be fully demonstrated. In addition, the solution developed in this study will then be used to predict soil behaviour in the compaction grouting test and the pressuremeter test. The advantage of using this method over the conventional interpretation method for the results of the compaction grouting test and pressuremeter test is also outlined. Therefore, the newly developed solution can serve as a useful tool in many geotechnical engineering problems, such as interpreting the results of cone penetration tests, as well as predicting the excess pore-pressure generated during pile installation. Additionally, the solution system developed in this study can be used as a platform to develop the cavity expansion solution, based on another more sophisticated constitutive model, to consider effects such as creep and local consolidation.
Yu, Yu-Sheng, e 余育陞. "A Study on the Strain Softening and Anneal Hardening in Zn-22 wt% Al Alloy". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/36961256043992689091.
大同大學
材料工程學系(所)
93
In this study thermomechanical processings were applied to a Zn-22 wt.% Al alloy to produce fine- and coarse-grained structures for the strain softening and anneal hardening studies. The microstructure, hardness and compression curve of Zn-22 wt.% Al alloy were studied by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), microhardness measurements and compression tester. The results showed the occurrence of a strain softening phenomenon in the Zn-Al alloy in the temperature range from -10℃ to 250℃ and an anneal hardening behavior in the softened Zn-Al alloy upon high temperature annealing. The mechanism of the strain softening behavior was found to be the DRX-induced softening during hot working, which can be facilitated by the formation of ultra-fine β grains with high-angle-boundaries; the mechanism of the anneal hardening behavior, on the other hand, was the annihilation of the ultra-fine β grains by a high temperature grain coarsening treatment to retard the occurrence of the DRX-induced softening and to restore the “normal strength” of the alloy. A composite stress-strain curve model was proposed in this study to resolve the mechanism of strain softening in the Zn-22 wt.% Al alloy. By using this model detailed informations regarding to the deformation and the DRX (i.e. the strain softening behavior) in individual α and β phases were disclosed from the experimental compressive stress-strain curve.
Chan, Yu-Shuo, e 詹育碩. "A Study on the Strain Softening and Anneal Hardening in Pseudo-single- and Dual-phase Zn-Al Alloys". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/51769460161026877329.
大同大學
材料工程學系(所)
94
In this study thermomechanical processings were applied to three Zn-Al alloys, namely the micro-duplex Zn-22 wt.% Al alloy, pseudo-single α phase Zn-95 wt.% Al and pseudo-single β phase Zn-1wt.% Al for the strain softening and anneal hardening studies. The microstructure, hardness and compression S-S curves of these Zn-Al alloys were studied by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), microhardness measurements and compression tester. The results showed the occurrence of a strain softening phenomenon in Zn-Al alloys containing a substantial amount of β phase in the temperature range from -10℃ to 250℃ and an anneal hardening behavior in the strain softened Zn-Al alloys upon high temperature annealing. The mechanism of the strain softening behavior was found to be a DRX-induced softening during hot working, which can be facilitated by the formation of ultra-fine β grains with high-angle-boundaries; the mechanism of the anneal hardening behavior, on the other hand, was found to be the annihilation of the ultra-fine β grains by a high temperature grain coarsening treatment to retard the occurrence of the DRX-induced softening and to restore the “normal strength” of the alloy. A composite stress-strain curve model was proposed in this study to resolve the strain softening and anneal hardening behaviors in the dual-phase Zn-22 wt.% Al alloy. By using this model detailed informations regarding to the deformation, the DRX (i.e. the strain softening) and the grain coarsening (i.e. the anneal hardening) behaviors in the β phase can be disclosed.
Cheng, Y. "Investigation of mechanical behaviours of Eucalyptus nitens timber". Thesis, 2022. https://eprints.utas.edu.au/47524/1/Cheng_whole_thesis.pdf.
Kuprin, Corinna. "Verformungsverfestigung bei zyklisch inkrementeller Torsion von Reineisen und dem Stahl 42CrMo4N". Doctoral thesis, 2012. https://monarch.qucosa.de/id/qucosa%3A19830.
Ferritic-pearlitic steel 42CrMo4N and pure iron under different strain paths are compared regarding their flow behaviour. Mainly in cyclic torsion tests with resulting strain increment per cycle shear stresses and strain hardening are analysed. The results show, that the cementite lamellae determine the flow behaviour of the steel 42CrMo4N, whereas the properties of pure iron are governed by the evolving dislocation cell structure. The dependency of flow stress on the strain direction is different for the two materials. Yield surfaces describe strain hardening quantitatively. The procedure for yield point detection and the dependency of subsequent yield surfaces on experimental conditions and strain states is shown. For pure iron isotropic hardening, for steel 42CrMo4N kinematic strain hardening dominates the flow behaviour.