Dissertations / Theses: 'Aluminum alloys – Fracture'

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Lee, Jonghee. "Fracture analysis of a propagating crack in a ductile material /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/7081.

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Zafari, Farzad. "Experimental and numberical study of elastic-plastic mixed-mode fracture /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/7034.

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3

Pouillier, Édouard. "Hydrogen-induced Intergranular Fracture of Aluminum-Magnesium Alloys." Paris, ENMP, 2011. http://www.theses.fr/2011ENMP0095.

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Les alliages d'aluminium de la famille 5XXX (Al-Mg) sont utilisés dans la fabrication de pièces de structure en raison de leurs bonnes propriétés mécaniques, de soudabilité et de résistance à la corrosion. Toutefois, dans des conditions d'utilisation sévères, une synergie entre la déformation plastique et les réactions de corrosion se produit et entraîne une fissuration intergranulaire, par corrosion sous contrainte (CSC), voire par fragilisation par l'hydrogène (FPH). La ductilité passe de 50% à quelques %, montrant une fissuration fragile. La compréhension des mécanismes qui régissent ce type de fissuration nécessite la détermination de l'importance respective des principaux facteurs (notamment mécaniques et chimiques). Cette étude se concentre sur le rôle de la plasticité cristalline dans le cas de la fragilisation par l'hydrogène. Pour ce faire, des éprouvettes préalablement fragilisées en surface par l'hydrogène (via un chargement cathodique) ont été sollicitées en traction. Ces essais ont été menés in situ dans le microscope électronique à balayage. Les résultats de corrélation d'image ont montré que les fissures s'amorcent dans des régions faiblement déformées adjacentes à des régions fortement déformées, là où les contraintes intergranulaires les plus élevées sont attendues. Par ailleurs, la cartographie des orientations cristallines des surfaces observées au cours des essais a servi de base à un maillage réaliste de la structure, qui a permis de calculer les champs de contraintes et de déformation locaux à l'aide d'un modèle de plasticité cristalline. Le modèle a été validé par la confrontation des prédictions à la mesure des champs de déformation et aux courbes de chargement macroscopique. Les contraintes ainsi estimées par simulation numérique ont permit d'établir un critère de rupture. Ce critère de rupture a ensuite été incorporé dans la simulation de microstructure quasi-2D grâce à un modèle de zone cohésive. Les résultats obtenus en accord avec les observations ont mis en avant la nécessité de développer une méthodologie permettant de prendre en compte les effets de la microstructure situés sous les surfaces étudiées. Ces microstructures ont été caractérisées à l'aide de plusieurs techniques d'analyse 3D de la morphologie microstructurale des agrégats polycristallins (EBSD par couches successives et par microtomographie rayons X des joints de grains à l'aide de diffusion de gallium). Les résultats des simulations avec les microstructures réelles en 3D dans le domaine élastique sont cohérant avec ceux obtenus en 2D pour des agrégats composés de 40 grains
Aluminium alloys that are strengthened by alloying elements in solid solution may present a particular sensitivity to intergranular stress corrosion cracking as a result of intergranular dissolution. In Al-5Mg alloys such as AA5083, precipitation of the β-phase (Al3Mg2) at grain boundaries strongly favours intergranular fracture. Previous experimental studies revealed that local plasticity seems to play a significant role in crack initiation. Nevertheless, the exact role of crystal plasticity in the vicinity of grain boundaries is not well understood. The main goal of this doctoral thesis is two-fold: (i) to study the role of the local stress and strain fields on the mechanism of intergranular stress corrosion cracking and, based on such understanding, (ii) to develop a micro-mechanics based model to predict the onset of grain boundary cracking, through a suitably defined failure criterion, and the subsequent intergranular crack propagation. An experimental procedure based on in-situ tensile tests within the chamber of an scanning electron microscope was developed to measure the evolution of local strain fields at various microstructural scales and of lattice orientation using digital image correlation and electron backscatter diffraction (EBSD) techniques, respectively. Digital image correlation techniques were used in particular over areas comprising just a few grains up to mesoscopic regions of the polycrystal to quantify the deformation and strain fields required in the multi-scale study of intergranular fracture. From these observations, it was established that interfaces between two grains which have undergone little amount of deformation but lying within a neighbourhood of significantly deformed grains are the first to develop micro-cracks. In addition, X-Ray tomography and serial EBSD sectioning analyses revealed that cracked grain boundaries were perpendicular to the applied tensile load, where maximum tensile tractions are expected. To determine the role of local stresses and local plasticity on the mechanisms of intergranular fracture, a dislocation mechanics based crystal plasticity model was employed to describe the constitutive behaviour of each grain in the finite element model of the in-situ experiments. The model parameters were calibrated as a function of the solid solution magnesium content in the aluminium alloy. Measured EBSD maps were relied upon to define the orientation of the discrete grain regions of the in-situ specimens in the corresponding multi-scale finite element (FE) models. From the FE results, a range of threshold values of the normal grain boundary tractions needed to initiate intergranular cracks was identified. This finding is in close agreement with the predictions from an analytical solution of a simplified model of intergranular cracking based on an extension of Eshelby's theory for inclusions. Finally, a cohesive zone model calibrated with the critical grain boundary tractions and typical surface energies was added to the FE model of the polycrystal. A comparison between the experimental and numerical results reveals a good agreement with the observed experimental cracking pattern

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Lyons, Jed S. "Microstructural influences on fracture toughness in A357 cast aluminum alloys." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/16689.

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Deshpande, Nishkamraj U. "Characterization of fracture path and its relationship with microstructure and fracture toughness of aluminum alloy 7050." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/20210.

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Jordon, James Brian. "EXPERIMENTS AND MODELING OF FATIGUE AND FRACTURE OF ALUMINUM ALLOYS." MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11062008-110529/.

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In this work, understanding the microstructural effects of monotonic and cyclic failure of wrought 7075-T651 and cast A356 aluminum alloys were examined. In particular, the structure-property relations were quantified for the plasticity/damage model and two fatigue crack models. Several types of experiments were employed to adapt an internal state variable plasticity and damage model to the wrought alloy. The damage model was originally developed for cast alloys and thus, the model was modified to account for void nucleation, growth, and coalescence for a wrought alloy. In addition, fatigue experiments were employed to determine structure-property relations for the cast alloy. Based on microstructural analysis of the fracture surfaces, modifications to the microstructurally-based MultiStage fatigue model were implemented. Additionally, experimental fatigue crack results were used to calibrate FASTRAN, a fatigue life prediction code, to small fatigue-crack-growth behavior. Lastly, a set of experiments were employed to explore the damage history effect associated with cast and wrought alloys and to provide motivation for monotonic and fatigue modeling efforts.

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Vasudevan, Satish. "AN INVESTIGATION OF QUASI-STATIC BEHAVIOR, HIGH CYCLE FATIGUE AND FINAL FRACTURE BEHAVIOR OFALUMINUM ALLOY 2024 AND ALUMINUM ALLOY 2219." Akron, OH : University of Akron, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1193668130.

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Thesis (M.S.)--University of Akron, Dept. of Mechanical Engineering, 2007.
"December, 2007." Title from electronic thesis title page (viewed 02/23/2008) Advisor, T. S. Srivatsan; Faculty readers, Craig Menzemer, Amit Prakash; Department Chair, Celal Batur; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

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Dadkhah, Mahyar Sh. "Analysis of ductile fracture under biaxial loading using moiré interferometry /." Thesis, Connect to this title online; UW restricted, 1988. http://hdl.handle.net/1773/7026.

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Hilty, Eric. "Influence of Welding and Heat Treatment on Aluminum Alloys." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1396877051.

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Balasundaram, Arunkumar. "Effect of stress state and strain on particle cracking damage evolution in 5086 wrought al-alloy." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/14809.

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11

Crepeau, Paul Noles. "The effect of processing and microstructure on the mechanical properties of aluminum alloy 339-T5." Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/20193.

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Lam, Paul W. "Crack curving in a ductile pressurized fuselage /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/7143.

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13

Hamilton, Benjamin Carter. "Creep crack growth behavior of aluminum alloy 2519-T87." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/20500.

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14

Valiveti, Dakshina M. "INTEGRATED MULTISCALE CHARACTERIZATION AND MODELING OF DUCTILE FRACTURE IN HETEROGENEOUS ALUMINUM ALLOYS." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1253035787.

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15

Cernyar, Jeffery. "Fatigue and fracture behavior of a 2124 aluminum alloy reinforced with silicon carbide whiskers." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20053.

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Wong, Yat Khin. "A phenomenological and mechanistic study of fatigue under complex loading histories." University of Western Australia. School of Mechanical Engineering, 2003. http://theses.library.uwa.edu.au/adt-WU2003.0017.

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[Truncated abstract. Please see pdf format for complete text.] Over the years much work has been done on studying sequence effects under multilevel loading. Yet, the underlying fatigue mechanisms responsible for such interactions are not fully understood. The study of fatigue under complex loading histories begins by investigating strain interaction effects arising from simple 2-step loading sequences. Fatigue for all investigations were conducted under uniaxial push-pull mode in strain-control. Fatigue is traditionally classified as either low or high cycle fatigue (LCF and HCF respectively). The boundary for LCF and HCF is not well-defined even though the fatigue life of LCF is typically dominated by crack “initiation”, while for HCF, fatigue life is usually dominated by stable crack growth. The terms LCF and HCF, apart from referring to the low and high number of fatigue cycles required for failure, also bear little physical meaning in terms of describing the state of fatigue imposed. As a result, conventional definitions of the two distinct regimes of fatigue are challenged and a new method of classifying the boundary between the two regimes of fatigue is proposed. New definitions are proposed and the terms plastically dominant fatigue (PDF) and elastically dominant fatigue (EDF) are introduced as suitable replacements for LCF and HCF respectively. PDF refers to the condition of a material undergoing significant reverse plasticity during cyclic loading, while for EDF, minimal reverse plasticity is experienced. Systematic testing of three materials, 316 L stainless steel, 6061-T6 aluminium alloy and 4340 high strength steel, was performed to fully investigate the cycle ratio trends and “damage” accumulation behaviour which resulted from a variety of loading conditions. Results from this study were carried over to investigate more complex multilevel loading sequences and possible mechanisms for interaction effects observed both under 2-step and multi-step sequences were proposed. Results showed that atypical cycle ratio trends could result from loading sequences which involve combinations of strain amplitudes from different fatigue regimes (i.e. PDF or EDF). Mean strain effects on fatigue life were also studied. The objective of this study was to identify regimes of fatigue which are significantly influenced by mean strains. Results indicated that mean strains affected EDF but not PDF. 2-step tests, similar to those performed in earlier studies were conducted to investigate the effects of mean strain on variable amplitude loading. Again, atypical cycle ratio trends were observed for loading sequences involving combinations of PDF and EDF. It is understood that fatigue crack growth interaction behaviour and mean stress effects are two dominant mechanisms which can be used to explain cycle ratio trends observed. The significance and importance of proper PDF/EDF definition and specification are also stressed. The study of fracture mechanics is an important component of any fatigue research. Fatigue crack growth in 4140 high strength steel CT specimens, under conditions of plane stress and plane strain were studied. In this investigation, the effects of R and overload ratios were also studied for both plane stress and plane strain conditions. Results indicate that differences in the point of crack “initiation” under both plane stress and plane strain conditions decrease with increasing load range, while the extent of crack retardation as a result of overloading, is greater under plane stress than plane strain conditions. The extent of crack growth retardation increases with decreasing R ratios and increasing overload ratios. The final phase of this project involves the proposal of two practical models used to predict cumulative “damage” and fatigue crack propagation in metals. The cumulative “damage” model proposed takes the form of a power law and the exponent which governs “damage” accumulation can easily be calculated by knowing the failure life, Nf, for a given strain or load level. Predictions for the “damage” model performed better when compared to other popular cumulative “damage” models. The second model proposed predicts fatigue crack growth behaviour from known monotonic and smooth specimen fatigue data. There are several benefits of having a model that can predict fatigue crack growth from monotonic and smooth specimen fatigue data: a) traditionally, engineers had to rely on expensive and time-consuming crack propagation tests to evaluate and select materials for maximum fatigue resistance, and b) monotonic and smooth specimen fatigue data are readily available. The crack propagation model is proposed to alleviate the material selection process by providing engineers a means to rapidly eliminate and narrow down selections for possible material candidates.

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17

Rider, Andrew Chemistry Faculty of Science UNSW. "Surface Properties Influencing the Fracture Toughness of Aluminium-Epoxy Joints." Awarded by:University of New South Wales. School of Chemistry, 1998. http://handle.unsw.edu.au/1959.4/17804.

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This thesis systematically investigates the properties of the aluminium adherend which influence the fracture toughness of aluminium-epoxy adhesive joints in humid environments. The fracture energy of the adhesive joint exposed to a humid environment in comparison with the fracture energy in a dry environment provides a measure of the joint durability. A 500C and 95% relative humidity environment is used to simulate aging of an adhesive joint over several years under normal service conditions. Initially, surface roughness is found to have a significant influence on the fracture toughness of the adhesive joint in humid conditions. A direct correlation between the bond durability and the angle of deliberately machined micro-roughness in the aluminium surface is determined. Consequently a model is developed which initially has the capacity to describe the bond durability performance. The preparation of aluminium surfaces involves the use of a novel ultramilling tool to produce well defined and controlled surface topography. This work represents the first time surface angles of features in the 1????m to 10????m range have been systematically varied and a direct relationship with bond durability has been determined. The use of surface analytical tools aids in elucidating mechanisms involved in the failure of the adhesive joint and contributes to the development of the stress based diffusion model. Examination of the aluminium oxide hydration level reveals this property has a negligible effect on the fracture toughness of the aluminium-epoxy joints exposed to humid environments. This information confirms the dominant role of the physical properties of the aluminium surface in determining the adhesive joint durability. This is the first occasion that planer oxide films grown in an RF plasma have had their hydration state adjusted in a controlled manner and their properties subsequently assessed in terms of bond durability properties. Further alteration of the aluminium surface chemistry is achieved through the application of an organo-silane coupling agent and a series of novel organo-phosphonate compounds. This work further develops the stress based diffusion model developed in conjunction with the micro-machining studies. The components of surface roughness and the ability of interfacial bonds to co-operatively share load are essential for the maintenance of fracture toughness of adhesive joints exposed to humid conditions. The ability of the silane coupling agent to share load through a chemically cross-linked film is a significant property which provides the superior fracture toughness in comparison with the phosphonate treated joints. Although the organo-phosphonate treated aluminium provides hydrolytically more stable bonds than the silane coupling agent, the film is not cross-linked via primary chemical bonds and the reduced load sharing capacity of interfacial bonds increases the bond degradation rate. The stress based diffusion model evolving from the initial work in the thesis can be used to predict the performance of more complex systems based on a thorough characterisation of the aluminium surface chemistry and topography. The stress based diffusion model essentially describes the concept of the production of micro-cavities at the epoxy-aluminium interface under mode 1 load, as a result of the distribution of strong and weak adhesive bonds. Alternatively, micro-cavities may result from an inhomogeneous stress distribution. In areas where the adhesive bonds are weak, or the local stresses are high, the interfacial load produces larger micro-cavities which provide a path of low resistance for water to diffuse along the bond-line. The water then degrades the adhesive bond either through the displacement of interfacial epoxy bonds or the hydration of the oxide to form a weak barrier layer through which fracture can occur. Alternatively, the water can hydrolyse the adhesive in the interfacial region, leading to cohesive failure of the epoxy resin. The bond durability performance of a series of complex hydrated oxide films used to pre-treat the aluminium adherend provides support for the stress based diffusion model. Whilst surface area is an important property of the aluminium adherend in producing durable bonding, the best durability achievable, between an epoxy adhesive and aluminium substrate, requires a component of surface roughness which enhances the load sharing capability in the interfacial bonding region. This component of durability performance is predicted by the model. In more specific terms, a boiling water treatment of the aluminium adherend indicates a direct correlation between bond durability, surface area and topography. The characterisation of film properties indicates that the film chemistry does not change as a function of treatment conditions, however, the film topography and surface area does. The overall bond durability performance is linked to both of these properties. The detailed examination of the hydrated oxide film, produced by the boiling water treatment of aluminium, is the first time the bond durability performance has been related to the film topography. It is also the first occasion that the mechanism of film growth has been examined over such a large treatment time. The combination of surface analysis and bond durability measurements is invaluable in confirming the properties, predicted by the stress based diffusion model, which are responsible in forming fracture resistant adhesive bonds in humid conditions. The bond durability of high surface area and low surface area hydrated oxide films indicates that surface area is an important property. However, this study confirms that the absence of the preferred surface topography limits the ultimate bond durability performance attainable. The fracture toughness measurements performed on aluminium adherends pre-treated with a low surface area film also supports the mechanism of load sharing of interfacial adhesive bonds and its contribution to the overall bond durability. The role performed by the individual molecules and particles in an oxide film is similar to the load sharing performed by the silane coupling agent molecules. Further support for the stress based diffusion model is provided by films produced on aluminium immersed in nickel salt solutions. The topography of these film alters as a function of treatment time and this is directly related to fracture toughness in humid environments. This work provides the first instance where such films have been characterised in detail and their properties related to bond durability performance. The study is also the first time that the growth mechanism of the film produced on the aluminium substrate has been examined in detail. The film growth mechanism supports the film growth model proposed for the hydrated oxide film produced by the boiling water treatment. The major findings presented in this thesis are summarised as the direct correlation between surface profile angle, the importance of co-operative load sharing of interfacial adhesive bonds and the relative insignificance of surface oxide hydration in the formation of durable aluminium-epoxy adhesion. This information is used to develop a stress based diffusion model which has the capacity to describe the fracture toughness of a range of aluminium-epoxy adhesive joint systems in humid environments. The stress based diffusion model is also capable of predicting the relative performance of the bond systems examined in the final chapters of the thesis, where complex interfacial oxide films are involved in the formation of adhesive bonds.

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18

Hinton, Kimberly D. "Extended heat treatment effects on the fracture toughness of cast aluminum alloy A357." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/17361.

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Agarwal, Himanshu. "Effect of loading condition, stress state and strain on three-dimensional damage evolution in 6061 wrought Al-alloy." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/14798.

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20

Paquet, Daniel. "Adaptive Multi-level Model for Multi-scale Ductile Fracture Analysis in Heterogeneous Aluminum Alloys." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1324565883.

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21

Blandford, Robert. "Characterization of fatigue crack propagation in AA 7075-T651." Master's thesis, Mississippi State : Mississippi State University, 2001. http://library.msstate.edu/etd/show.asp?etd=etd-04092001-152127.

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22

Athasniya, Mohit. "Extrinsic Influence of Environment on Tensile Response, Impact Toughness and Fracture Behavior of Four Metals: Ferrous Versus Non Ferrous." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1444242002.

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23

Dighe, Manish D. "Quantitative characterization of damage evolution in an Al-Si-Mg base cast alloy." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/20219.

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Lados, Diana Aida. "Fatigue crack growth mechanisms in Al-Si-Mg alloys." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0204104-125758.

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Thesis (Ph. D.)--Worcester Polytechnic Institute.
Keywords: Microstructure; Elastic-Plastic Fracture Mechanics; Crack closure; A356; J-integral; Conventionally cast and SSM Al-Si-Mg alloys; Residual stress; Heat treatment; Fatigue crack growth mechanisms; Threshold stress intensity factor; Plastic zone; Paris law; Fracture toughness; Roughness. Includes bibliographical references.

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Drury, William James. "Quantitative microstructural and fractographic characterization of AE-Li/FP metal matrix composite." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/19958.

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Dighe, Manish Deepak. "Development of digital image processing based methodology to study, quantify and correlate the microstructure and three dimensional fracture surface morphology of aluminum alloy 7050." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/21013.

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Hu, Chao. "Locally enhanced voronoi cell finite element model (LE-VCFEM) for ductile fracture in heterogeneous cast aluminum alloys." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1199209208.

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Mekky, Waleed Nicholson P. S. "Fracture toughness of the nickel-alumina laminates by digital image-correlation technique." *McMaster only, 2005.

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Tucker, Matthew Taylor. "Structure-property stress state dependent relationships under varying strain rates." Diss., Mississippi State : Mississippi State University, 2009. http://library.msstate.edu/etd/show.asp?etd=etd-04022009-091044.

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Godbole, Chinmay. "The Influence of Reinforcement on Microstructure, Hardness, Tensile Deformation, Cyclic Fatigue and Final Fracture behavior of two Magnesium Alloys." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1321633235.

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Matthews, Stephen John. "Cavitation erosion of aluminium alloys, aluminium alloy/ceramic composites and ceramics." Thesis, Coventry University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317927.

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Zhemchuzhnikova, Daria. "Influence of the extreme grain size reduction on plastic deformation instability in an AlMg and AlMgScZr alloys." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0324/document.

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L'élaboration de nouveaux alliages maintient un fort intérêt pour le phénomène d’instabilité plastique, ou l'effet Portevin-Le Chatelier (PLC), provoqué par l'interaction des dislocations avec des atomes de soluté. Par ailleurs, l'effet PLC attire l'intérêt comme un exemple remarquable d'auto-organisation dans les systèmes dynamiques. Il est associé à des motifs complexes de séries de chutes de contrainte liées à la nucléation et au mouvement des bandes de déformation dans le matériau déformé, et nécessite une compréhension de l'auto-organisation des dislocations. La déformation plastique des alliages Al-Mg est sujette à l'instabilité dans une large gamme de conditions expérimentales. Pour cette raison, les alliages Al-Mg binaires ont longtemps servi d'objets modèles pour l'étude de l'effet PLC. En même temps, l'utilisation pratique des alliages binaires Al-Mg est limitée en raison d’une faible résistance mécanique. Une amélioration significative de leurs propriétés peut être atteinte en ajoutant des solutés supplémentaires, conduisant en particulier à la formation de précipités. En outre, une forte réduction de la taille de grains du polycristal pourrait être une technique clé pour produire des matériaux à haute résistance et ténacité. Cependant, il existe très peu d'information, souvent contradictoire, sur l'instabilité PLC dans les alliages Al-Mg à grains fins et contenant des précipités. Le but de l'étude de cette thèse a été d'étudier les caractéristiques spécifiques de l'effet PLC dans les alliages à base AlMg, avec et sans nanoparticules, à gros grains et à grains fins, ces derniers obtenus par une méthode de déformation plastique sévère. Grâce à l’application de méthodes d’extensométrie locale, notamment de la technique de corrélation d’images, ces études ont révélé une persistance non habituelle de la propagation des bandes de déformation dans les alliages comprenant des précipités et/ou des grains fins. Ce mode dynamique est observé dans un large intervalle de vitesses de déformation, tandis qu’il n’apparait qu’à haute vitesse dans des alliages modèles AlMg. Par ailleurs, l’analyse des distributions statistiques des amplitudes des chutes de contrainte a révélé une tendance vers une statistique en loi puissance, caractéristique du mode de propagation. Ce phénomène est attribué à une modification du couplage spatial entre les dislocations, due à la concentration de contraintes internes. La combinaison de ces études avec l’analyse de l’émission acoustique a mis en évidence une influence de la microstructure sur la compétition entre un facteur aléatoire et la synchronisation des dislocations. Enfin, l’étude par corrélation d’images a permis d’observer une interrelation entre l’instabilité PLC et la formation de la striction
The elaboration of new alloys sustains a strong interest to the phenomenon of unstable plastic flow, or the Portevin–Le Chatelier (PLC) effect, caused by interaction of dislocations with solute atoms. Moreover, this effect attracts interest as a rich example of self-organization in dynamical systems. It is associated with complex patterns of stress serrations related to nucleation and motion of deformation bands in the deforming material, and requires understanding of self-organization of dislocations. Plastic deformation of Al-Mg alloys is prone to instability in a wide range of experimental conditions. For this reason, binary Al-Mg alloys served for a long time as model objects for investigation of the PLC effect. At the same time, the practical use of binary Al-Mg alloys is limited because of their low strength. A significant improvement of their properties can be achieved by additional alloying, in particular, leading to precipitation. Further, extensive grain refinement could be a key technique used to produce tough and high- strength materials. However, there exists very limited and often contradictory information on the PLC instability in fine-grained Al-Mg alloys containing precipitates. The objective of the present thesis was to investigate specific features of the PLC effect in AlMg-based alloys with and without nanoscale particles, both in coarse-grained and fine-grained states, the latter obtained by severe plastic deformation. Using local extensometry methods, particularly the image correlation technique, these studies revealed an unusual persistence of the propagation of deformation bands in alloys with precipitates and/or fine grains. This dynamic mode is observed in a wide range of strain rates, whereas it only appears at high strain rate in model Al-Mg alloys. Moreover, the analysis of statistical distributions of stress drop amplitudes revealed a tendency to power law statistics characteristic of the propagation mode. This phenomenon was attributed to a modification of the spatial coupling between dislocations due to the concentration of internal stresses. The combination of these studies with the acoustic emission analysis uncovered an influence of the microstructure on the competition between a random factor and the dislocation synchronization. Finally, the study by the image correlation made it possible to observe an interrelation between the PLC instability and the neck formation

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Neely, Jared A. "Correlation of Stress Intensity Range with Deviation of the Crack Front from the Primary Crack Plane in both Hand and Die Forged Aluminum 7085-T7452." University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1557162451907811.

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34

Cai, Huasu. "The toughness of high strength aluminium alloys." Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315472.

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Nascimento, Denise Ferreira Laurito. "Estudo do comportamento em fadiga de baixo ciclo e fadiga sob cargas multiaxiais das ligas de alumínio AA6005, AA6063 e AA6351." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-21052015-153422/.

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O uso das ligas de alumínio em aplicações estruturais tem crescido consideravelmente nas últimas décadas. Nos transportes, a baixa massa específica do alumínio resulta em uma alta razão resistência/ peso, favorecendo a fabricação de aviões, trens e automóveis. Com a crescente preocupação em reduzir a emissão de gases poluentes, vem tornando-se promissora a alternativa de reduzir o peso dos veículos substituindo peças convencionalmente produzidas com outros materiais por peças de alumínio. As ligas tratáveis termicamente da série 6xxx são frequentemente escolhidas para estas aplicações. Assim, para que o emprego dessas ligas seja otimizado, é importante um estudo mais detalhado de suas propriedades mecânicas, principalmente sob solicitações cíclicas. Neste trabalho foram estudadas ligas de Al-Si-Mg que são amplamente utilizadas nas indústrias automotivas, em especial na fabricação de componentes de carroçarias para caminhões e ônibus. Foi realizado o estudo do comportamento em fadiga de baixo ciclo e fadiga multiaxial das ligas AA6005 T6, AA6063 T6 e AA6351 T6, fornecidas pela CBA (Companhia Brasileira de Alumínio) visando caracterizar e comparar essas ligas em sua microestrutura, propriedades de tração e fadiga. As propriedades básicas de fadiga foram determinadas por meio do método ε-N (fadiga de baixo ciclo) e os ensaios foram realizados com controle de deformação total, onda triangular e taxa de deformação 0,005 seg-1. As análises dos laços de histerese elasto-plástica permitiram inferir sobre aspectos microestruturais relacionados às propriedades mecânicas das ligas estudadas. O comportamento em fadiga multiaxial foi avaliado por meio de carregamentos combinados axial-torcional em fase e fora de fase. Para ajustar os dados experimentais obtidos, foram testados alguns dos modelos encontrados na literatura. Os cálculos baseados no modelo de plano crítico, proposto por Fatemi e Socie, apresentaram resultados satisfatórios. Também foram realizadas análises microestruturais e fractográficas para as três ligas. As superfícies de fratura dos ensaios de fadiga multiaxial mostraram resultados diferentes de acordo com o carregamento adotado. A avaliação comparativa das três ligas estudadas fornece subsídios para fundamentar a seleção de materiais para a fabricação de componentes estruturais para o setor automotivo.
The use of aluminum alloys in structural applications has grown considerably in recent decades. In transportation, the low density of aluminum results in a high strength-to weight ratio, proving attractive for production of aircrafts, trains and automobiles. With a growing concern for the reduction of pollutant gas emissions, aluminum alloys are becoming a promising alternative to diminish vehicle weight through the replacement of conventionally produced parts made from other heavier materials for aluminum parts. The heat treatable alloys from the 6xxx series are often chosen for these applications. Therefore, to optimize the employment of these alloys, a detailed study of their mechanical properties, primary under cyclic solicitations is necessary For the present study Al-Mg-Si alloys were chosen, which are widely used in automotive industries, particularly in the manufacturing of components for trucks and bus bodies. The low-cycle fatigue behavior and multiaxial fatigue of the three following aluminum alloys: AA6005 T6, AA6063 T6 and AA6351 T6, provided by CBA (Brazilian Aluminum Company), were assessed, with the aim of characterizing and comparing these alloys in their microstructure, tensile properties and fatigue. The basic properties of fatigue were studied by ε-N method (low cycle fatigue) and the experiments were performed with total strain control, triangular waveform and with a constant deformation rate of 5.0x10-3 s-1. The analyses of hysteresis loops elasto-plastic provided insight about microstructural aspects, related to mechanical properties of the studied alloys. Multiaxial fatigue behavior was assessed in combined axial-torsion loading in phase and out of phase. To adjust the experimental data, some models found in the literature were tested. Calculations based on critical plane model, proposed by Fatemi Socie, presented satisfactory results. Furthermore, microstructure analyses and fractography were performed for these three alloys. The fracture surface of multiaxial fatigue assays demonstrated different results according to the adopted loading. Comparative evaluation of the three studied alloys provides support for the selection of materials for manufacturing structural components of the automotive sector.

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36

Owen, Nigel. "The fracture behaviour of an aluminium lithium alloy." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47559.

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37

Harrison, M. "Fracture studies in aluminium alloys : An investigation of the effect of manganese-bearing and zirconium-bearing dispersoids on the fatigue properties of peak aged Al-Zn-Mg alloys." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376914.

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38

Warrington, David. "Studies on the hot cracking behaviour of aluminium alloys." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316958.

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39

Zhang, Y. H. "Small fatigue crack growth in high strength aluminium alloys." Thesis, Open University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314821.

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40

Jones, S. P. "Stress-corrosion and exfoliation of high strength aluminium alloys." Thesis, Cranfield University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.352939.

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41

Haskel, Tatiane. "Efeito do tratamento térmico de solubilização na microestrutura e nas propriedades mecânicas da liga de alumínio A356." Universidade do Estado de Santa Catarina, 2009. http://tede.udesc.br/handle/handle/1742.

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This work examines the effects of solution heat treatment on the microstructure and mechanical properties of A356 aluminum alloy. Tensile bars were molten to tensile tests and solution treatment in several conditions of time and temperature were performed. The A356 alloy with different weight percentage of magnesium and with its respective as-casting specimens were also analysed to evaluate the heat treatment. To evaluate the results tensile tests, alloy hardness and matrix microhardness, and metallographic analysis and fractographs were performed. The microstructural analysis allowed to evaluate the evolution of microstructural transformation. Results changes were attained to alloy with less percentage of Mg (0,15wt. %). However, to the alloy with higher percentage of Mg (0,3wt. %) the results indicated increase in all properties analysed, increasing the time and the temperature of solution. Only to the temperature of 570°C, a property drop of ultimate tensile strength and elongation were observed. The best properties were obtained to 10 hours of the solution in 540°C, as a result of a better distribution and coalescence of the Si particles. The fractographs showed changes on the fracture mode in function of increase in the solution time and temperature, evidencing the increase of the ductility observed through mechanical tests. The kind of alloy fracture and the matrix fracture mode and Si particles were evidenced in fracture surfaces.
Este trabalho avalia os efeitos do tratamento térmico de solubilização sobre a microestrutura e as propriedades mecânicas da liga de alumínio A356. Foram fundidos corpos de prova para ensaios de tração e realizados tratamentos de solubilização em diversas condições de tempo e temperatura. A liga A356, com diferentes percentuais em peso de magnésio e com suas respectivas amostras brutas de fundição, também foram analisadas para avaliação dos efeitos do tratamento térmico. Para avaliação dos resultados foram realizados ensaios de resistência à tração, de dureza da liga e microdureza da matriz e, análises de metalografias e fractografias. As análises microestruturais permitiram avaliar a evolução da transformação microestrutural. Variações nos resultados foram obtidos, para liga com menor teor de Mg (0,15% em peso). Porém, para liga com maior teor de Mg (0,3% em peso) os resultados indicaram aumento em todas as propriedades analisadas, com o aumento do tempo como da temperatura de solubilização. Apenas para temperatura de 570°C uma queda nas propriedades de máxima resistência e alongamento foram observadas. As melhores propriedades foram obtidas com 10 horas de solubilização a 540°C, como resultado de uma melhor distribuição e coalescimento das partículas de Si. As fractografias mostraram alterações no modo de fratura, em função do incremento no tempo e na temperatura de solubilização, evidenciando o aumento de ductilidade observada através dos ensaios mecânicos. O tipo de fratura da liga, e o modo de fratura da matriz e das partículas de Si também foram evidenciados pelas superfícies de fratura.

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42

Milan, Marcelo Tadeu. "Fatigue crack growth resistance and fracture toughness of selectively reinforced aluminium alloys." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251924.

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The main aim of this work was to investigate the fatigue crack growth resistance and fracture toughness of selectively reinforced Al alloys. In such bimaterials, the crack growth resistance is affected by the failure mechanism, the direction of crack approach to the interface and by the conflict between the elastic-plastic mismatch and residual stresses. When the crack approaches the interface from the composite side, in the A12124 based bimaterials, the fatigue crack growth rate is reduced below "composite only" values by the compressive residual stress, although the elastic-plastic mismatch was expected to cause the opposite effect. In the A16061 based bimaterials, although some crack deceleration is also observed, fatigue crack growth rates are above the "composite only" values presumably because these bimaterials have lower compressive residual stress and higher plastic mismatch near the interface. After crossing the interface, the crack driving force is affected by closure mechanisms developed on the composite side of the crack wake. Conversely, when the crack grows from the Al alloy side, for both A12124 and A16061 based bimaterials, the crack growth rate is mainly reduced by the elastic-plastic mismatch. After crossing the interface, the crack driving force is well described by the thermal residual stresses, unless a crack tip deflection reduces the Mode I near tip stresses. In a fracture toughness test, when the pre-crack tip is in the composite side of the A12124 based bimaterials, KQ(5%) values are increased above "composite only" values presumably due to the compressive residual stresses and despite the amplification of the crack driving force from the elastic-plastic mismatch. In the A16061 based bimaterials, due to the higher plastic mismatch and lower compressive residual stresses, KQ(5%) values are below "composite only" values. Additionally, for all bimaterials, KQ(5%) values increase if the pre-crack tip is closer to the interface. When the crack propagates, it extends to the interface, bifurcates and arrests. The load then had to be increased to promote the onset of plastic collapse. The crack tip blunting and deflection mechanism increases the toughness attained at the onset of plastic collapse of the bimaterials above "Al alloy only" values. Conversely, if the pre-crack tip is in the Al alloy side, the final failure is deduced to occur when damage accumulated on the composite side links to the pre-crack tip. When the pre-crack tip is at 2.0mm from the interface, for the A12124 based bimaterials, KQ(5%) values are in general lower than the "A12124 only" value due to the tensile residual stresses. For the A16061 based bimaterials, KQ(5%) values are as high as the "A16061 only" value presumably due to the higher plastic mismatch and lower tensile residual stress of such bimaterials. Additionally, for all bimaterials, KQ(5%) values increase if the precrack tip is at 0.5mm from the interface. If the pre-crack tip is at 2.0mm from the interface, Kerit and Scrit values of the bimaterial are higher than the "Al alloy only" value and this is deduced to be due to the increase in the elastic-plastic mismatch shielding and by delayed critical particle damage within the composite side. At 0.5mm from the interface, Keritt and Scrit values are reduced and this is deduced to be because both the near tip tensile residual stress is higher and critical particle damage occurs earlier on the composite side; moreover, the unreinforced Al alloy layer is thinner and the damage on the composite side is deduced to link more easily to the pre-crack tip. For a constant particle size, there is an optimum particle volume fraction in which both Kerit and Scrit values are maximised with respect to a specific pre-crack tip position.

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McMahon, Martin Andrew. "The microstructure and corrosion properties of laser processed aluminium alloys." Thesis, University of Liverpool, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284591.

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44

Rutgers, Lyndal Materials Science &amp Engineering Faculty of Science UNSW. "Development and fracture behaviour of graded alumina/epoxy joins." Awarded by:University of New South Wales. School of Materials Science and Engineering, 2005. http://handle.unsw.edu.au/1959.4/26004.

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Introduction of a composition gradient at a join between two materials of different elastic properties should reduce the stress concentrating effect of the interfacial discontinuity. A crack oriented perpendicular to this elasticity gradient will experience mode-mixity, and possible subsequent crack deflection. Explicit analytical solutions for the stress state at the tip of an angled crack in a graded material of a given finite geometry do not exist, and ongoing crack path development in such a gradient has not been characterised. An infiltration processing technique is developed which allows two materials to be joined through a region of graded composition, of tailored width and composition profile. Composition discontinuities at layer interfaces in a stepped gradient can be tolerated due to the resulting interpenetrating network structured (INS) microstructure. Firing stresses were found to be a limitation of the processing technique, overcome by limiting the steepness of the elastic gradient. Alumina and epoxy resin graded composites were produced and tested under monotonic loading, resulting in stable crack path evolution. Stress-field asymmetry at the tip of a crack oriented perpendicular to an elastic gradient was demonstrated, followed by subsequent crack deflection. Stress intensity factor and deflection angle increase with increasing gradient steepness. Rising R-curve behaviour was demonstrated for all compositions of the INS composite, with initiation and plateau toughness decreasing with increasing epoxy content. Evidence of crack bridging by intact ligaments of the epoxy phase in the crack wake explains this behaviour. Crack deflection towards the epoxy region was anticipated and demonstrated for all gradient configurations. An increase in relative crack depth was seen to increase mode-mixity at the crack-tip and subsequent crack deflection, up to a relative depth of ~0.5. No conclusive evidence was found for the influence of crack bridging on crack deflection. Toughness was shown to increase with the inclusion of a microstructural gradient. Measured toughness within graded samples was shown to be controlled by both the local composition and the volume of bridging ligaments in the crack wake. The optimum gradient should ??? extend over the widest region practical, ??? encompass the widest composition range possible, and ??? demonstrate extrinsic crack extension toughening.

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Rogers, Janette Louise. "Corrosion inhibition of aluminium alloys by molybdenum and tungsten sulphido species." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303656.

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46

Green, Andrew Morgan. "Environmentally-assisted crack growth in aluminium alloy 7475." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359748.

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47

O'Dwyer, John Gerard. "Creep performance of SiCp reinforced aluminium alloy 2618A." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313719.

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Kelly, D. J. "Exfoliation and stress corrosion cracking of the aluminium-lithium alloy 8090." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302803.

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Cheung, C. M. S. "The R-curve approach for the fracture assessment of an aluminium alloy bridge." Thesis, Swansea University, 2001. https://cronfa.swan.ac.uk/Record/cronfa42424.

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A result of fatigue testing on a full scale aluminium alloy bridge, which is used by the military for temporary crossings, showed an unexpected increase in fracture resistance, compared with its plane strain K[IC]. This increase was due to a combination of low constraint and large stable crack extension in the bridge components. Previous work had attributed the increase to the loss of constraint alone, but the present work shows stable cracking is equally important. The effect of stable cracking in the bridge alloy was first examined experimentally in large 25mm thick 3PB specimens which were analysed numerically using the finite element method. The numerical 2-D results provided a concave J[R]-curve showing that dJ[R]/da rises increasingly with crack extension. This increase is associated with the transition from flat to slant fracture in the experimental test pieces, due to the loss of plane strain constraint. Fracture assessment using the R-curve approach showed that long cracks, both in large fracture mechanics specimens and the bridge girder, are stable because, although for a given load, G=J[R], dG/dadJ[R]/da when G=J[R]. The J[R]-curve for low constraint geometries should be indexed by the T-stress. The fatigue crack growth rate for the bridge alloy, taken from different sources, was compared. The Paris law index was nearly 4 for large CT and tension specimens, but only about 2 from fatigue tests on a full-scale bridge. For a large tension specimen, the corresponding K[IC] at the change in index was delayed from 35 (the plane strain K[IC] value) to 48MPa√m, because of the effect of low constraint. A simple model based on the J[R]-curve (at initiation) was developed for predicting crack extension under high cyclic load (K[max] > K[IC]), but with limited success.

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Kayes, A. P. "The influence of chemical pre-treatment on the occurrence of filiform corrosion in aluminium alloys." Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323842.

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Dissertations / Theses on the topic 'Aluminum alloys – Fracture'

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