Dissertations / Theses on the topic 'Fracture toughness'
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1
Chung, Wai-Nang. "Fracture toughness and creep fracture studies of polyethylenes." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46720.
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Daming, Duan. "Fracture toughness and term fracture behaviour of polyethylenes." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243909.
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Hayes, D. A. "The fracture toughness of dental amalgams." Thesis, Open University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317412.
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SAKAIDA, Yoshihisa, and Keisuke TANAKA. "Evaluation of Fracture Toughness of Porous Ceramics." The Japan Society of Mechanical Engineers, 2003. http://hdl.handle.net/2237/9181.
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Sieurin, Henrik. "Fracture toughness properties of duplex stainless steels." Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3964.
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Kuhl, Adam. "A technique to measure interfacial fracture toughness." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16626.
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Westphal, Mark Emil. "Fracture toughness of coral graphite cast iron." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/16892.
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Tinston, S. F. "Fracture toughness of mechanised pipeline girth welds." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381698.
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Smith, Matthew S. "Bone fracture toughness of estrogen deficient rabbits." Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=3094.
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Thesis (M.S.)--West Virginia University, 2003.Title from document title page. Document formatted into pages; contains x, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 91-96).
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de, Faria Teixeira Rita. "Translaminar fracture toughness of CFRP : from the toughness of individual plies to the toughness of the laminate." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/26112.
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The translaminar fracture toughness of fibre reinforced polymers (FRP) is important for characterising the failure resistance of composite structures. Measuring the translaminar fracture toughness for any possible layup is not feasible. Therefore, it is of interest to relate the translaminar toughness of a laminate to that of its plies. Numerous studies have measured the translaminar fracture toughness of composite laminates and of individual plies. However, any attempts to relate the two have so far been very limited, and restricted to initiation values. This work presents experimental and analytical research on Compact Tension (CT) tests on several T800s/M21 carbon-epoxy laminates with different combinations of 0° , ±45 and 90° plies, and with various ply thicknesses. Post-mortem techniques, such as X-ray, optical and scanning electron microscopy, were used to determine the damage extent in each specimen. Acoustic emission (AE) was also used to sequence the occurrence of the failure mechanisms. Failure mechanisms found in the multidirectional laminates included a combination of the failure mechanisms found on bidirectional laminates ( /90° ) made of its constituent plies. Ply splitting, fibre bridging and fibre pull-out were the main features characterizing the fracture surfaces. Assuming that the damage can be represented as a single crack, the resistance curve (R-curve) for each layup was extracted from these tests. From each laminate R-curve, three distinct fracture toughness values were obtained for each layup: non-linearity onset, initiation and propagation. The R-curves were used to define a trilinear cohesive law for each layup, and the specimens were then successfully simulated using a cohesive approach in a Finite Element (FE) model. On the one hand, there was good agreement supporting the representation of translaminar damage as a cohesive crack. On the other hand, damage was considerably diffuse when the laminate included substantial ply-blocking, thus suggesting that a single equivalent crack may, in some cases, neglect some important aspects of translaminar damage (as well as delamination). Four analytical predictive models were used to predict the translaminar toughness of the laminates from that of the constituent plies. The assumption of translaminar fracture toughness additivity by means of a rule of mixtures correlated best with the experimental results. The experimental results for a mode I crack propagation in a 45° ply were shown to corroborate a simple analytical model which relates the critical energy release rate of a 45° ply to those of 0 and 90 plies. Thickness size effects were investigated by using different 0 ply thicknesses, by means of 0° ply-blocks and using two grades of the same material system. Since it was found that excessive ply-blocking can lead to significantly diffuse damage, a second study with thin-ply TR50s/K51 carbon-epoxy system was conducted, leading to the first translaminar fracture characterisation of a 0° CFRP ply for a range of thicknesses from 0.03 mm to 0.12 mm. The toughness of the 0° plies was confirmed to be significantly dependent on the thickness, even for ranges of thicknesses where delamination does not play a significant role.
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Kasturi, Krishna Kumar. "Microcracking Fracture Toughness for Graphite Epoxy Composite Laminates Using Finite Fracture Mechanics." ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/427.
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Graphite/epoxy composite laminates are widely used in the aerospace industry. However the industry cannot take full advantage of the superior strength and stiffness of composite materials until their failure mechanisms can be thoroughly understood by engineers. Recognizing the importance of such understanding, the current study was undertaken to determine the microcracking fracture toughness in composite laminates using the energy release rate criteria. Three materials of specific interest in the aerospace industry – IM7/977-2, IM7/5555 and IM7/5276-1 – were analyzed. To evaluate the microcracking fracture toughness, displacement controlled static tensile tests were performed. Microcrack density (the number of microcracks per unit length) was measured as a function of applied stress. The data were analyzed to obtain the microcracking fracture toughness (Gm) for each material system. The value of Gm can be used to predict the microcracking behavior of composite laminates made from the corresponding material.
12
To, Theany. "Fracture toughness and fracture surface energy of inorganic and non-metallic glasses." Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S013/document.
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La ténacité et l’énergie de surface de fracture de verres, de vitrocéramiques et de composites à matrice en verre ont été étudiées. Tout d'abord, un test de flexion bi-axiale (configuration anneau/anneau) a été réalisé sur des verres de silice et des verre-à-vitres avec différentes conditions de surface afin d’identifier la relation entre le défaut de surface, la résistance et la ténacité du verre. Ensuite, trois méthodes d’expérimentation ont été mises en œuvre, principalement la méthode de poutre de flexion à pré-entaille droit (SEPB), la méthode de la poutre entaillée en chevron (CNB) et la méthode de la poutre avec indentations Vickers (VIF), afin de déterminer la ténacité de quatre verres produits industriellement et de déterminer les avantages et les inconvénients des différents méthodes sélectionnées. La méthode qui est apparue la plus fiable et auto-cohérente, la méthode SEPB (Single Edge Precrack Beam), a été appliquée à la détermination de la ténacité de nombreux verres et vitrocéramiques, afin d’étudier l’influence de la composition et de la microstructure sur les caractéristiques de fissuration (KIC et énergie de fissuration, γ). Enfin, l’influence de la température et de l'environnement sur la ténacité a été étudiée à l'aide de la méthode SEPB. Deux verres d'oxyde ont été testés à des températures élevées et avec une vitesse de charge de 10 MPa∙√m/s, une température de transition de 1,11Tg a été trouvée. Quatre autres verres d'oxyde ont été testés en environnement inerte et les mêmes valeurs de ténacité ont été obtenues à partir de deux vitesses de charge (100 fois) différentesFracture toughness and fracture surface energy of commercial and laboratory glasses, glass-ceramics and glass matrix composites have been studied. First, bi-axial bending test (RoR configuration) was performed on fused silica and window float glasses with different surface conditions to identify the relationship between the surface flaw, the strength and fracture toughness. After, three experiment methods, mainly single-edge precracked beam (SEPB), chevron-notched beam (CNB) and Vickers indentation fracture (VIF) were performed to determine the fracture toughness of four commercial known glasses and to determine the advantages and inconveniences of the different selected methods. The method that is appeared as the most reliable and self-consistent, the SEPB (Single Edge Precrack Beam) method, was applied to determine the toughness of the large amount of glasses and glass-ceramics, to study the influence of the composition and the microstructure on the characteristics of cracking (KIC and fracture energy, γ). Last but not least, the influence of the temperature and environment on the fracture toughness was studied by means of the SEPB method. Two oxide glasses were tested in elevated temperatures and with the loading rate of 10 MPa∙√m/s, a transition temperature of 1.11Tg was found. Four other oxide glasses were tested in the inert environment and the same fracture toughness values were obtained from (100 times) two different cross-head speeds
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Yang, Kao Z. "MENs Doped Adhesive and Influence on Fracture Toughness." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2487.
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Composites are in high demand; however, fasteners are often required for joining process and can reduce their advantages. One solution is adhesive bonding, but uncertainty exists regarding long term durability and the ability to interrogate bonds noninvasively. One potential solution to qualify bond integrity over its service life is to dope an adhesive with magneto-electric nanoparticles (MENs). MENs can yield output magnetic signatures that are influenced by bond quality and damage state. In this study, adhesives have been doped with MENs prior to bonding at 1% volume concentration. For optimum implementation, this health monitoring system should be evaluated for effects of the MENs on the mechanical properties. Lap-shear testing was conducted to assess changes in the bond strength from addition of the nanoparticles. End-notched flexure (ENF) tests were also conducted for fracture mechanism evaluation. Results showed an increase of 12% in shear strength as a function of MENs loading concentration. In addition, a feasibility study of output magnetic signature as a function of elevated temperature and humidity were evaluated for MENs doped and un-doped adhesives. Results gave an order of magnitude change in magnetic signal as a function of exposure time.
14
Cretegny, Laurent. "Fracture toughness behavior of weldments at elevated temperature." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19957.
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Bernard, Marie. "The development of a new fracture toughness procedure /." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74059.
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Ma, Wei. "Fracture toughness characterization of thin Ti/SiC composites." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/9324.
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Titanium based alloys reinforced uniaxially with silicon carbide fibres (Ti/SiC)
are advanced and innovative materials for aerospace vehicles. To avoid
potential problems, these new materials should be extensively tested and
analyzed before application.
This research focuses on experimental fracture toughness study on 0.5 mm
thick Ti/SiC composite materials for aerospace applications. The fracture
toughness tests are mainly based on BS 7448 with some modifications for
transversely isotropic behaviour of the composite materials.
By loading on specimens in the direction perpendicular to the fibre axis, three
critical values of fracture toughness parameters characterizing fracture
resistance of material, plane strain fracture toughness [Plane strain fracture toughness
}, critical crack tip
opening displacement [Critical crack tip opening displacement
] and critical J-integral [Critical at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
]are measured for two
kinds of titanium alloy specimens and three kinds of Ti/SiC composites
specimens.
The values of [Provisional value of Plane strain fracture toughness
] obtained from the fracture toughness tests are not valid [Plane strain fracture toughness
]
for these materials, since the thickness of specimens is insufficient to satisfy the
minimum thickness criterion; however, the results could be used as particular
critical fracture toughness parameter for 0.5 mm thick structures of the materials.
The valid values of [Critical J at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
] and [Critical crack tip opening displacement
] could be used as fracture toughness
parameters for all thickness of structures of the materials. The results also show
that: fracture toughness of the titanium alloys decreases dramatically after being
unidirectional reinforced with SiC fibre, which is mainly triggered by poor
fibre/matrix bonding condition. Moreover, Ti-Al3-V2.5 reinforced with 25%
volume fraction SiC fibre performs better than the other two composites in
fracture resistance.
17
Ratcliffe, J. G. A. "The interfacial fracture toughness characterisation of sandwich structures." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399287.
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Li, Zhongtao 1971. "High fracture toughness and high modules silicone resins." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8301.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000.Includes bibliographical references (leaves 159-163).
Rigid silicone resins, generally referred to as polyalkylsilsesquioxanes, are an important class of hybrid thermosetting polymers with both inorganic and organic characteristics. They have superior thermal stability, heat resistance, fire resistance, and still can be easily processed. Silicone resins recently have attracted much interest as low dielectric constant materials replacing silicon dioxide as interlevel dielectrics. Unfortunately, poor mechanical properties, such as brittleness and low strength, limit their broader acceptance and applications. Efforts to toughen them date back to the 1970's, but little success has been achieved until now. Conventional polymer toughening techniques, such as incorporating second phase particles directly into the resins, typically do not work. Neither does decreasing the crosslink density of the resin network, which can compromise modulus and other properties. High fracture toughness and modulus addition cure rigid silicone resins are obtained in this study by a combination of intrinsic toughening and extrinsic toughening techniques. The addition cure silicone resin comprises two components: polyphenylsilsesquioxane oligomers containing silicon vinyls and low molecular weight silane crosslinkers containing silicone hydrides. The resin is cured by hydrosilylation between the two. Intrinsic toughening improves the plasticity and rigidity of the resin by choices of crosslinkers and polyphenylsilsesquioxane oligomers. The characteristics of molecular structure of the crosslinker and polyphenylsilsesquioxane oligomers that contribute to high fracture toughness and modulus are identified.
(cont.) Extrinsic toughening with rubber particles and rigid inorganic fillers further utilized the improved plastic deformation capability from intrinsic toughening This approach not only increases the fracture toughness from 0.3MPam⁰ç⁵ to as high as 1.44 MPam⁰ç⁵, but also the modulus from 1.03GPa to 1.90GPa.
by Zhongtao Li.
Ph.D.
19
Whitehead, Richard Donaldson. "Assessment of fracture toughness for polyethersulphone injection mouldings." Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/848561/.
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This project assessed fracture toughness (K[IC] and G[IC]) for thin-section injection-moulded PES and for which there are no standard fracture-mechanics tests. Standard methods of testing are based on thick specimens that are easily available for metals but unusual for injection mouldings. Tests were, therefore, made which adapted the standard Mode-I (crack-opening) tests to the thin sections of injection-moulded discs. Then the question of the tests' validity arose. Were the elastic assumptions being met? If both critical Mode-I stress-intensity factor and strain-energy release rate were found then a Young's modulus value could be derived. If this derived modulus when compared to the directly measured Young's modulus was found to be identical then the assumption of linear elasticity would be upheld. Two different styles of fracture-mechanics test were investigated: ones with explosive fracturing and one with controlled crack growth. In explosive fracture-mechanics tests, the fracturing of the testpiece was so rapid that the minimum data was collected, so many such tests had to be aggregated to sample the range of notch-depth possible. This was true for both the three-point-bend (TPB) and tensile tests made on single-edge-notched (SEN) bars cut from the discs. However, when the derived modulus for the explosive tests was compared with Young's modulus it was found to be smaller, so these tests did not uphold the assumptions of elasticity. The reason for this failure was found to be that the notch did not act like the sharp propagating crack required for successful tests. In the controlled crack-growth test sequence, a crack was grown across the diameter of an injection-moulded disc and measurements were made, as the crack progressed, of the crack's position, corresponding loading and work done. From this sequence of measurements, independent values of stress-intensity factor and strain-energy release rate, under quasistatic conditions, were calculated that produced values of derived modulus which were, at least, equal to the Young's modulus, thus upholding the elastic integrity of the test. Moreover, initial surges of crack-growth (similar to explosive fracturing) were shown by linear regression analysis to give larger stress-intensity factors and to be significantly different from the data collected only during controlled crack-growth. Thus, the use of controlled crack-growth is Justified as a more reliable method of fracture-mechanics testing. Yield stress measurements were also made and with the valid stress-intensity factor predicted plastic zone sizes entirely compatible with yielded regions observed as crazes whose lengths were reported by Hine.
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Kamat, Samir V. "Fracture toughness of particulate-reinforced aluminum-matrix composites /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487592050230594.
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Sacks, Natasha. "The fracture toughness of ultrafine WC-Co Alloys." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/20181.
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Bibliography: pages 147-152.This thesis examines the fracture toughness behaviour of a series of cemented carbides having carbide grain sizes between 0.35f.Lm and 4f.Lm, cobalt contents ranging from 6 to 15wt%, and vanadium carbide contents from 0 to 0.8wt%. A series of twenty-four ultrafine WC-Co alloys were sintered from powders produced through three different production routes, namely, the spray conversion process and two variations of the conventional powder production methods. A further twelve WC-Co alloys with three different carbide grain size distributions were produced through conventional powder metallurgy processes. Two different fracture toughness test methods have been used to determine the toughness measurements, namely, the Palmqvist Indentation test and the Short Rod test. A Terra Tek Fractometer machine was used to automatically determine the Short Rod toughness values. The Palmqvist testing was carried out on a Vickers hardness machine using indenting loads of 20, 30 and 50kg. The Palmqvist crack lengths were measured by summing the individual crack lengths emanating from the corners of the hardness indentation. These crack lengths were used in a formula developed by Shetty et al., to calculate the Palmqvist fracture toughness. The influence of annealing at 800°C and 900°C on the Palmqvist crack lengths has also been assessed. Microstructural parameters have been determined using ASTM procedures and microscopy techniques and the influence of these parameters on the fracture toughness has also been assessed.
22
McCarroll, Catherine Anne. "High rate fracture toughness measurement of laminated composites." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9037.
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The aim of this research is to understand and analyse the behaviour of specimens used to measure fracture toughness in laminated composites when loaded at high displacement rates. Finite element (FE) analysis is used as a tool to investigate dynamic behaviour of rapidly loaded mode I intralaminar specimens and to investigate of the data reduction strategy. Finally, using knowledge from current literature and experience gathered from the FE analysis, an experimental test procedure for the measurement of intra-laminar fracture toughness at high loading rates is designed and evaluated. To gain confidence in the dynamic FE modelling the behaviour of a mode I interlaminar double-cantilever beam specimen loaded at high rates was analysed. The findings were compared to experimental observations and a data reduction strategy from the published literature was assessed. FE modelling was then used to investigate the behaviour of an intralaminar compact tension (CT) test performed at high rates and a data reduction strategy was developed which does not require the measurement of the applied load. A CT specimen for measurement of interlaminar fracture toughness at high loading rates was also developed which can be analysed using the same data reduction strategy. Experiments were carried out at displacement rates between 0.2 mm/min and 15 m/s to determine the effects of test velocity and crack growth velocity on inter- and intralaminar fracture toughness. Results from the dynamic experimental tests were filtered to remove the noise in the data. Critical energy release rates were calculated using the filtered and unfiltered data and the results were used to assess the accuracy of the filtering procedure. Results are then presented in terms of the trend of critical energy release rate, GIc, with test velocity and average crack speed. The findings are discussed with reference to micrographs of the fracture surfaces of specimens at each test speed. The intralaminar specimens showed a possible decrease in GIc with test speed and average crack speed, but the range of values fell within the scatter in the results. The interlaminar test results suggest interlaminar GIc is constant with test. The increase in interlaminar GIc with crack speed was also within the range of the scatter in the results.
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Kimu, Hyonmin. "Design of Bioactive Materials with High Fracture Toughness." Kyoto University, 1997. http://hdl.handle.net/2433/202290.
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Rys, Tomasz. "Mixed mode fracture toughness of stitched laminated composites." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006994.
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Marnock, Patrick J. (Patrick Joseph). "Development of a Simplified Fracture Toughness Tool for Polymers." Thesis, University of North Texas, 1997. https://digital.library.unt.edu/ark:/67531/metadc278473/.
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This thesis presents research toward the development of a simple inexpensive fracture toughness tool for polymeric materials. Experiments were conducted to test the specimen configuration and the fracture toughness tool against an established ASTM standard for polymer fracture toughness, D5045, and a commonly used four-point bend method. The materials used in this study were polycarbonate and high density polyethylene. Reductions in both the production time and the variability resulting from the preparation of the specimens were addressed through the use of specially designed fixtures. The effects from the razor cut depths used in the chevron notch were compared to the fracture toughness values obtained in order to determine the effect upon the validity of the fracture toughness.
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Browne, David J. "Fracture characteristics of coarse grained ceramics." Thesis, University of Newcastle Upon Tyne, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254026.
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Dhansay, Nur Mohamed. "Fracture mechanics based fatigue and fracture toughness evaluation of SLM Ti-6Al-4V." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24326.
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The focus of this research project was to determine experimentally the fatigue and fracture toughness characteristic, from a fracture mechanics perspective, of Ti-6Al-4V titanium alloy manufactured by Selective Laser Melting (SLM). Three build orientations are considered where a fatigue crack is grown parallel and two are grown perpendicular to the build orientation. The project then endeavours to generate a fracture mechanics based Paris equation from the fatigue crack growth rate results and together with the fracture toughness, fatigue life predictions may be determined based on crack propagation lifetimes. SLM is an Additive Manufacturing (AM) technique whereby an object is fabricated in a layerwise manner via the use of lasers, directly from a 3D CAD model. This process allows for the manufacture of complex designs in its net or near net shape form, which is not possible with conventional manufacturing techniques. There are minimal amounts of material wastage and it potentially eliminates post manufacture machining and processing costs. Ti- 6Al-4V is used in many applications where high strength at low density is required at moderate temperatures. Corrosion resistance qualities of the alloy are also considered for many applications. Some of the applications where this alloy is used include turbine engine components, aircraft structural components, aerospace fasteners, high-performance automotive parts, marine applications, medical implant devices and sports equipment. Due to the large use of the alloy in industry and with the potential benefits of manufacturing by SLM, there is a great need for investigating SLM Ti-6Al-4V as a viable alternative to conventional casting, forging and machining. There is limited literature covering the fatigue crack growth rate and fracture toughness of SLM Ti-6Al-4V and the effect of build orientation on these characteristics. However, it is clear, from the limited available literature that fatigue crack growth rate behaviour is affected by build orientation, and so this project investigates the effect of these orientations, and aims to contribute to understanding why these orientation effects occur. Since there is even less literature available on the fracture toughness of SLM Ti-6Al-4V with respect to build orientation, this project also endeavours to characterise orientation effects on fracture toughness, if any, and compares these with those of conventionally manufacture Ti-6Al-4V.
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Wu, Shang-Xian. "Fracture analyses and toughness : measurement of specimens with deep and shallow cracks." Thesis, The University of Sydney, 1990. https://hdl.handle.net/2123/26383.
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Slip—line field analyses and finite element analyses have been conducted for three— and four-point bend specimens with deep and shallow cracks. The results show that under large scale yielding the stress and strain fields ahead of deep and shallow cracks are quite different and there is no single—parameter characteristics in these fields. Specially, the maximum hydrostatic stress is substantially lower ahead of shallow cracks than ahead of deep cracks and this strongly affects the fracture behaviour of specimens with shallow cracks. A preliminary crack length requirement for valid J—characterization of crack tip fields is suggested. The slip—line field solutions are used to develop test methods of J1C and CTOD suitable for specimens with shallow cracks as well as with deep cracks. With these methods experimental studies of fracture toughness and fracture mechanism in specimens with deep and shallow cracks for a free—cutting steel and CS 1030 plain carbon steel are carried out. The results reveal a phenomenon of ductile-brittle fracture transition due to increasing crack length in CS 1030 steel. The RKR critical stress model for cleavage fracture in conjunction with the finite element analyses of crack tip stress fields successfully explains that the ductile-brittle transition is due to the increase in the maximum tensile stress ahead of crack tip from below the critical stress to above it. The model also predicts values of CTOD of cleavage fracture in agreement with experimental results. A Rice-Johnson type model for void growth and coalescence is developed for three-point bend specimens with deep and shallow cracks and gives a qualitative explanation of the dependence of CTOD for ductile fracture on the hydrostatic stress as observed in experiment conducted in the free-cutting steel.
29
Horvath, Andrew T. "Chemical Methods for Improving the Fracture Toughness of Paper." Doctoral thesis, KTH, Fiberteknologi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4752.
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Paper is a network material composed of a great number of fibers that interact with each other through fiber joints. In order to make a clear statement regarding observed changes being made in paper, it is vital to determine the structural level of paper that is being affected by chemical modifications. Polyelectrolytes having a wide range in molecular properties have been synthesized to investigate the adsorption behavior of cationic polyelectrolytes to cellulosic fibers. The interaction with the porous cell wall of cellulosic fibers is governed by the molecular properties of the polyelectrolyte. More specifically, polyelectrolytes having a low charge density are able to penetrate into the fiber cell wall, while high charge density polyelectrolytes are restricted to the exterior fiber surface. The molecular mass also influences the extent to which adsorption occurs within the cell wall, although this is typically only pronounced for low charge density polyelectrolytes. High charge density polyelectrolytes are generally restricted to the fiber surface due to strong Coulombic interactions between charged groups along the molecular backbone, which create a stiff molecular conformation. These results were confirmed by fluorescent labeling techniques, which allow the polyelectrolytes to be tracked inside the cell wall by confocal laser scanning microscopy. This approach was also used to demonstrate the effect of an electrolyte, which screens the Coulombic interactions and facilitates penetration into the cell wall. However, a considerable difference in the adsorption behavior of polyelectrolytes having similar molecular mass is still observed at high electrolyte concentration, where the electrostatic contributions are negligible. These differences are a consequence of a diffusion process that occurs on a longer times scale. Although polyelectrolyte adsorption to cellulosic fibers reaches a pseudo-equilibrium at short times, a driving force into the cell wall exists due to the bulk charge of the fiber. The time scale of this diffusion process depends on the polyelectrolyte properties, and was observed to persist for over 3 months. As the extent to which these polyelectrolytes penetrate into the cell wall has been ascertained, and the fibers can be crosslinked to different degrees in the cell wall or at the surface. Cationic acetal dextran was prepared as a model crosslinking agent, as the molecular mass, charge density and degree of acetal substitution can readily be controlled during synthesis. A considerable effect on the tensile properties and fracture toughness was observed for crosslinked paper, which could be attributed to either the fibers or the fiber joints. Crosslinking acted to stiffen the fibers and the fiber joints, which influenced the transfer of applied stresses through the paper structure. Changes in the material behavior at high relative humidity could be improved by crosslinking the fibers at the correct the structural level.QC 20100811
30
Watring, Dillon S. "Development of Novel, Microscale Fracture Toughness Testing for Adhesives." FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3474.
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The purpose of this thesis was to develop microscale fracture toughness tests to be performed in situ based off previously used macroscale fracture toughness tests. The thesis also was to use these tests to perform in situ analysis and imaging of reinforced adhesives during crack propagation. Two different fracture toughness tests were developed for this thesis through developing fixtures and sample geometry. A microscale double cantilever beam (DCB) test was developed for mode I fracture (opening mode). A microscale end notch flexure (ENF) test was developed for mode II fracture (sliding mode).
Three different types of materials were used as a reinforcing agent and tested using the micro-DCB and micro-ENF tests. Magnetoelectric nanoparticles (MENs) doped adhesive showed a 12% increase in mode II toughness and 33% increase in total fracture energy for micro-DCB. Similarly, the graphene foam (GrF) doped adhesive showed an approximate 34% increase in mode II toughness and a 71% increase in total fracture energy for mode I. In situ imaging provided real time imaging of crack propagation for all three reinforcing agents that allowed for a novel analysis of the crack propagation and general fracture.
31
Bateman, Joseph A. "High temperature fracture toughness of Cr-Mo-V welds." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/15025.
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Smith, Kevin. "Fracture Toughness of a Hyperelastic Material During Surgical Cutting." Honors in the Major Thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1564.
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Despite being one of the most important organs of vertebrates, the material properties of skin are also one of the most poorly understood. In the field of designing medical devices and surgical tools there are significant advantages to having a model that describes the interaction of forces between a blade tip and skin during surgical cutting. In general, skin can best be described as a composite layer consisting of a viscoelastic dermis with interwoven collagen and elastin fibers beneath a superficial epidermis. The purpose of this research is to study the fracture toughness of porcine skin during practical cutting applications, the behavior of skin under quasistatic loads, and viscoelastic behavior of skin during stress relaxation. To fully describe the mechanics of skin in this model tensile test are conducted to determine the material properties of skin. The fracture toughness of the material is calculated by measuring the energy release rate of the material during required during cutting with Number 11 scalpel blade with a tip radius of 12 [micro]m . These results are then compared to a finite element analysis with a debonding interface and a Mooney-Rivlin hyperelastic material model with viscoelastic relaxation in an effort to predict the loads required by tools during surgical applications. The main outcome of this research is the development of a testing protocol and material model of skin that can be used in finite element simulations of uniaxial loads and surgical cutting.B.S.M.E.
Bachelors
Engineering and Computer Science
Mechanical and Aerospace Engineering
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Roberts, R. J. "The elasticity, ductility and fracture toughness of pharmaceutical powders." Thesis, University of Bradford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320442.
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Li, Yan. "Prediction of material fracture toughness as function of microstructure." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52999.
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Microstructure determines fracture toughness of materials through the activation of different fracture mechanisms. To tailor the fracture toughness through microstructure design, it is important to establish relations between microstructure and fracture toughness. To this end, systematic characterization of microstructures, explicit tracking of crack propagation process and realistic representation of deformation and fracture at different length scales are required. A cohesive finite element method (CFEM) based multiscale framework is proposed for analyzing the effect of microstructural heterogeneity, phase morphology, texture, constituent behavior and interfacial bonding strength on fracture toughness. The approach uses the J-integral to calculate the initiation/propagation fracture toughness, allowing explicit representation of realistic microstructures and fundamental fracture mechanisms.
Both brittle and ductile materials can be analyzed using this framework. For two-phase Al₂O₃/TiB₂ ceramics, the propagation fracture toughness is improved through fine microstructure size scale, rounded reinforcement morphology and appropriately balanced interphase bonding strength and compliance. These microstructure characteristics can promote interface debonding and discourage particle cracking induced catastrophic failure. Based on the CFEM results, a semi-empirical model is developed to establish a quantitative relation between the propagation toughness and statistical measures of microstructure, fracture mechanisms, constituent and interfacial properties. The analytical model provides deeper insights into the fracture process as it quantitatively predicts the proportion of each fracture mechanism in the heterogeneous microstructure. Based on the study on brittle materials, the semi-analytical model is extended to ductile materials such as AZ31 Mg alloy and Ti-6Al-4V alloy. The fracture resistance in these materials not only depends on the crack surfaces formed during the failure process, but also largely determined by the bulk plastic energy dissipation. The CFEM simulation permits surface energy release rate to be quantified through explicit tracking of crack propagation in the microstructure. The plastic energy dissipation rate is evaluated as the difference between the predicted J value and the surface energy release rate. This method allows competition between material deformation and fracture as well as competition between transgranular and intergranular fracture to be quantified. The methodology developed in this thesis is potentially useful for both the selection of materials and tailoring of microstructure to improve fracture resistance.
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Rothwell, Glynn. "Fracture toughness determination using constraint enhanced sub-sized specimens." Thesis, Liverpool John Moores University, 2003. http://researchonline.ljmu.ac.uk/4971/.
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Prakash, Sunil. "Modeling the Constraint Effects on Fracture Toughness of Materials." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1259271280.
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Strebel, Jeffrey Jerome. "The measurement and origin of fracture toughness in polyethylene." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1056650936.
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Velpuri, Seshagirirao V. "Fracture Toughness Testing of Plastics under Various Environmental Conditions." Thesis, University of North Texas, 1997. https://digital.library.unt.edu/ark:/67531/metadc278346/.
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The primary objective of this study is to test the applicability to plastics of a fracture toughness testing tool developed for metals. The intent is to study pre-test conditioning of several plastic materials and the effect of the depth of the razor notch cut in the chevron notched fracture toughness test specimens. The study includes the careful preparation of samples followed by conditioning in various environments. Samples were subjected to laboratory air for a specific duration or to a controlled temperature-humidity condition as per the ASTM D1870. Some of the samples were subjected to vacuum conditioning under standard test specifications. Testing was conducted using the conventional three-point bend test as per ASTM D5045-95. ASTM E1304, which sets a standard for short rod and bar testing of metals and ceramics provides some basis for conducting chevron notched four-point bend tests to duplicate the toughness tool. Correlation of these results with the ASTM test samples is determined. The four-point bend test involves less specimen machining as well as time to perform the fracture toughness tests. This study of fracture toughness testing has potential for quality control as well as the fracture property determination.
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Swadener, John Gregory. "Primary fracture toughness mechanisms of a glass/epoxy interface /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Kalarikkal, Sujith G. "Fracture toughness of graphite/epoxy laminates at cryogenic conditions." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006960.
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Winfield, P. H. "Toughness development in fibre reinforced metals." Thesis, Cranfield University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259794.
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Naidu, Thevashen. "A fracture mechanics study of the fracture toughness testing techniques applied to brittle materials." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/4960.
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Includes bibliographical references.This dissertation describes an investigation into the application of fracture mechanics to brittle materials, with particular emphasis on the fracture toughness testing techniques used on these materials.
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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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Ayatollahi, Majid Reza. "Geometry and constraint effects in mixed mode fracture." Thesis, University of Bristol, 1998. http://hdl.handle.net/1983/fa0c832a-e66f-478a-a572-746f8ab21352.
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Shin, Dong-Woo. "Microstructure-property relationships of SiC fibre-reinforced borosilicate glass." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282096.
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Zhang, Zhuyao. "Microstructure and continuous cooling transformation of C-Mn-Ni and C-Mn-Ni-Mo weld metals." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386602.
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Ingham, Edward John. "The development of impact toughness and resistance to slow crack growth in modified polyvinyl chloride and polyethylene pipe grade polymers." Thesis, Manchester Metropolitan University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271274.
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Kiiru, Beatrice Maiwa. "Effect of curing on the fracture toughness of composite materials." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19124/.
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This thesis studies the effect of the degree of cure of a prefabricated part on the fracture toughness of co-cured composite part. A novel resin system, Airstone 780E/785H, that is used in the manufacture of wind turbine blades, is under consideration.
Chemical characterization of the resin tells us its curing behavior while thermal characterization analyses the material’s response to temperature variations. From these experimental findings,an optimized heat transfer model that can identify the degree of cure and the temperature distribution at any given time during the manufacturing process is implemented.
For mechanical characterization, test laminates, 3 co-cured each to different degrees of cure (α) and one control laminate that was not co-cured, are manufactured through VARTM. From these, DCB test coupons are prepared and the fracture toughness is tested in accordance with the ASTM D5528-13 standards.
Samples with α ranging from 0.725 - 0.942 were realized. It was found that a decrease in α of the prefab corresponded to an improvement in fracture toughness. When α approached 1 the fracture toughness was worse than that of the control test specimen.
The degree of cure is proportional to the degree of crosslinks formed in the resin system. Lower α have a relatively low degree of crosslinks formed at the interface. While at high values of α, a high level of crosslinking is achieved making it hard to form new ones. This in turn leads to the poorer fracture toughness properties of these samples.
From a manufacturing perspective, use of co-curing is shown to be advantageous on the basis of process time. Curing time is reduced since we don’t have to wait for complete cure to be achieved during sample preparation.
A more detailed consideration of this problem is recommended. A model that could replicate and possibly predict the influence of the degree of cure on the fracture toughness would allow the possibility of finding an optimum α for this resin system.
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Nevalainen, Markku J. "The effect of speciment and flaw dimensions on fracture toughness /." Espoo : Technical Research Centre of Finland, 1997. http://www.vtt.fi/inf/pdf/publications/1997/P314.pdf.
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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.