To see the other types of publications on this topic, follow the link: Fatigue of bearing alloys.
Dissertations / Theses on the topic 'Fatigue of bearing alloys'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Fatigue of bearing alloys.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Busby, A. K. "Structure-property relations in some bearing alloys." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376887.
Full text
2
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.
Full text
3
Szost, Blanka Angelika. "Hydrogen trapping in bearing steels : mechanisms and alloy design." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244934.
Full textAbstract:
Hydrogen embrittlement is a problem that offers challenges both to technology and to the theory of metallurgy. In the presence of a hydrogen rich environment, applications such as rolling bearings display a significant decrease in alloy strength and accelerated failure due to rolling contact fatigue. In spite of these problems being well recognised, there is little understanding as to which mechanisms are present in hydrogen induced bearing failure. The objective of this thesis are twofold. First, a novel alloy combining the excellent hardness of bearing steels, and resistance to hydrogen embrittlement, is proposed. Second, a new technique to identify the nature of hydrogen embrittlement in bearing steels is suggested. The new alloy was a successful result of computer aided alloy design; thermodynamic and kinetic modelling were employed to design a composition and heat treatment combining (1) fine cementite providing a strong and ductile microstructure, and (2) nano-sized vanadium carbide precipitates acting as hydrogen traps. A novel technique is proposed to visualise the migration of hydrogen to indentation-induced cracks. The observations employing this technique strongly suggest that hydrogen enhanced localised plasticity prevails in bearing steels. While proposing a hydrogen tolerant bearing steel grade, and a new technique to visualize hydrogen damage, this thesis is expected to aid in increasing the reliability of bearings operating in hydrogen rich environments.
4
Josi, Georg. "Fatigue of bearing-type shear splices." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40066.pdf.
Full text
5
Dudgeon, Helen D. "Fatigue of aluminium-lithium alloys." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276536.
Full text
6
Hunt, Anthony W. "Fatigue of commercial aluminium alloys." Thesis, Aston University, 1986. http://publications.aston.ac.uk/11901/.
Full textAbstract:
Fatigue crack propagation has been observed for a number of commercial aluminium alloys. Comparable data was obtained for a variety of crack and specimen geometries over a range of crack lengths for a given alloy. Where crack propagation only was of interest the initiation event has been excluded by pre-cracking the specimen using a fin of material adjacent to the crack face. By this method a controlled defect size is introduced in to the specimen. By modification of the D.C. potential drop method it has been shown possible to measure the growth of cracking from 0.12mm by this method. Crack growth from defects greater than 0.6mm have been shown to give conventional crack propagation deduced by principle of similitude. Fatigue fracture surface analysis has been conducted for cracking from both free surfaces and from blunt notches. A `quasi cleavage' feature has been identified and is shown to be prominent when the fatigue stress intensity range is below 10 MNm-3/2.
7
Yang, Xiaofan. "Corrosion and passivation of molybdenum-bearing alloys." Thesis, University of Surrey, 1995. http://epubs.surrey.ac.uk/843256/.
Full textAbstract:
Molybdenum-bearing alloys are widely used in industry because of their excellent corrosion resistance. However, the role of molybdenum in passivation is a subject which has been a matter for discussion and controversy for many years. In the previous work carried out in this laboratory, Professor Castle and Dr Qiu suggested that molybdenum oxide might provide the nuclei for formation of the passive film. This hypothesis is the basis of the present work. In order to find out the evidence for the existence of the molybdenum oxide nuclei, furthermore, to establish a model of passivation for the molybdenum-bearing alloys, the passivation of molybdenum-bearing alloys are investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), especially in-situ AFM, in conjunction with SEM and TEM. During the passivation study, it was found that the chemical composition on anodically polarised surfaces varied with potential. For 516 alloy, the peak value of molybdenum in the surface is at the low potential of the passive region close to the Flade potential. Therefore, molybdenum exerts its greatest function in this potential region. A further AFM study at this potential revealed, surprisingly, that a platelet layer formed on the passivation surface. The dendritic structure on the surface of the platelets presented under the high resolution of STM, which shows the crystallization property of the platelets. These platelets are mainly composed of chromium and molybdenum oxides and they are only found in the passivation of the molybdenum-bearing alloy, so the formation of the platelets may be associated with molybdenum nucleation in passivation. The in-situ AFM studies provide the evidence for the formation and disappearance of the platelets during the passivation of molybdenum-bearing alloys, i.e. the platelets form at the early stage of passivation and they gradually merge into the passive film if they are not disturbed by the environment. Based on the above finding, the role of molybdenum in passivation is proposed as following: molybdenum oxide precipitated on the surface seeds chromium oxide to form platelets at the early stage of passivation and the formed platelet layer prohibits the dissolution of the passive species from the metal. By this way, molybdenum facilitates the formation of the passive film on alloys. Using Fe-Cr-Mo duplex stainless steels, the corrosion of molybdenum-bearing alloys are studied in HCl and the kinetics of the corrosion are traced by in-situ AFM. During corrosion, it was observed that the ferritic phase in duplex stainless steel dissolves more rapidly than the austenitic phase and the dissolution occurs on the austenite preferentially along grain boundaries, sub-grain boundaries and the planes with high energy. By switching the electrochemical condition from active dissolution to passivation and then changing it back, it is found that under the passivation condition after the active dissolution, the corrosion changes from selective dissolution of the crystallographic feature to general corrosion. This situation persists even though the electrochemical condition changes back to the active condition from the passivation condition. Since AFM is a new technique and this is one of the first attempts at applying it to a corrosion study, an in-depth explanation of the images obtained from a corroded rough surface is an important topic on which so far little work has been reported. In this study, therefore, the artifacts and the reality of the structure in AFM images obtained in the corrosion study are discussed.
8
Mohin, Ma. "Fatigue crack growth assessment and fatigue resistance enhancement of aluminium alloys." Thesis, University of Hertfordshire, 2018. http://hdl.handle.net/2299/20824.
Full textAbstract:
Fatigue damage of aluminium alloys is one of the key concerns in transport industries, particularly in the aerospace industry. The purpose of the project is to develop new knowledge and techniques against fatigue failure for these industries through a systematic investigation of fatigue resistance and crack growth behaviours of aluminium alloys. Fatigue and fracture mechanics have been investigated analytically, numerically and experimentally in this project. Overload transient effect on fatigue crack growth has been examined by considering various parameters including crack closure, overload ratio (OLR), load ratio (R ratio), baseline stress intensity factor range, (∆K)_BL and geometry. It was found that crack closure can be correlated qualitatively and quantitatively to all other parameters associated with overload transient behaviour. It is proposed that the effect of crack tip plasticity on the non-linearity of the compliance curve can be separated to obtain reliable crack closure measurement. In this project, different methods are used to better understand the transient retardation process so that the damage tolerance design (DTD) of the components made of aluminium alloys can be enhanced. Another important parameter for fatigue and damage tolerance design (DTD) of engineering components is the threshold stress intensity factor range for fatigue crack growth, ∆K_th. A small variation in identification of ∆K_th can lead to a big change in overall estimation of fatigue life. In this project, an analytical model has been developed for aluminium alloys by fitting an analytical curve with raw crack growth data in order to identify the ∆K_th. This model has the capacity to identify ∆K_th for different aluminium alloys at various R ratios. There is a great demand for enhanced fatigue life of aluminium alloys in the transport industry. This project has carried out a detailed investigation of electromagnetic treatment (ET) in the form of electropulsing treatment to develop an efficient technique for fatigue resistance enhancement. ET parameters including the treatment intensity, treatment time and the number of applications have been optimised. It is suggested that the duration of ET treatment can be used as the main parameter among all these to control the fatigue resistance of the aluminium alloy. The improvement in fatigue resistance has been explained by the change in microhardness and conductivity of aluminium alloy due to ET. Additionally, the fracture morphology was analysed using scanning electron microscopy (SEM). The precipitates and dislocation characteristics were also studied using transmission electron microscopy (TEM). The outcomes of this investigation will help improve structural integrity by enhancing fatigue resistance of aluminium alloys.
9
Ali, Muhammad Sarfraz. "Microstructural modelling of fatigue in layered bearing architectures." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/64768/.
Full textAbstract:
Small automotive plain engine bearings are used to provide the relative motion between the engine block and the crankshaft via the connecting rod. Under rapidly changing engine loads, these bearings may suffer fatigue damage during service. In modern multilayered bearing designs, fatigue resistance is a complex function of engine loading coupled with the layer architecture and a multiphase lining alloy. This research has mostly focussed upon micro-scale fatigue damage initiation on thin (0.2-0.3mm thickness) lining surface and its subsequent growth leading towards gross failure. The systems examined comprise Al alloys and sintered bronze as relatively soft and conformable lining layers. The weight percent composition of Al lining alloy was Al-6.5Sn-2.5Si-1Cu-1Ni-0.25Mn roll bonded to a stiffer and thicker backing steel layer (1.5-1.8mm thick) via an even thinner Al foil (0.04mm) as an interlayer. The other system comprised an Al lining (Al-20Sn–1Cu) alloy spray coated on to a medium carbon steel layer in the form of a flat bar. All these systems were compared with the previously investigated Al based designs with lining compositions: Al-12Sn-4Si-1Cu and Al-20Sn-1Cu-0.25Mn (manufactured by roll bonding processes). The performance evaluation was based upon the investigation of microstructural features involved in early fatigue initiation and their effect upon short crack growth on the surface. Subsurface crack growth through the layers has also been assessed and finally the observed fatigue life of various components linked to these behaviours. A 3-point bend test configuration was adopted for laboratory fatigue tests. Fatigue comparison was made on the basis of lining surface plastic strain amplitude vs. number of cycles to failure according to a uniform predefined criterion for all the systems. Maximum plastic strains developing at the lining surface were estimated using a combination of finite element analysis (FEA) and strain gauge measurements so that the fatigue life of all systems studied was presented as strain-life data. Specimens in the form of both finished bearings and flat bars were tested. Similar fatigue behaviour was observed for the two testing geometries, giving greater confidence in the fatigue evaluation process and allowing detailed observations of small crack initiation and growth processes in flat bars to be related to behaviour of the actual bearing geometry. In the previous research, the coarser Si particles in the Al-12Sn-4Si-1Cu lining and Sn particles in the Al-20Sn-1Cu-0.25Mn alloys were identified as potential crack initiation sites, though the relationship between particle geometry and arrangement/clustering was found to be important. The newly developed Al-6.5Sn-2.5Si-1Cu-1Ni-0.25Mn lining alloy with finer and fewer Sn and Si particles showed a delayed initiation of short fatigue cracks compared to the previous systems. However, a large number of widely scattered intermetallics in the new linings were observed to fracture causing early fatigue initiation at the micro-scale level with some more complex processes of detaching Sn layers from harder intermetallics and Si particles. Using the mechanical property data for bulk lining and secondary phase particles obtained from tensile testing and instrumented hardness testing, stress fields were investigated within the hard particles (intermetallics), surrounding thin layers and the matrix on the basis of the analytical and numerical modelling. On the basis of these modelling results, optimum particle shapes were defined to minimize tensile stresses (within the particles) and hydrostatic stresses (at the particle matrix interfaces). The experimental growth data of a dominant crack when combined with a Hobson type growth model based upon measured particle distributions and experimental crack growth rates, helped in predicting fatigue life of a similar component at different stress levels. Surface crack driving force reduces considerably when subsurface crack deflection occurred within softer Al interlayer. Replacing this interlayer with a harder brazed sheet did not give any significant difference in the observed fatigue life. In the HVOF systems, crack initiation was observed to be from the weaker interface between a harder matrix and softer circular unmelts as well as from various scattered pores. The overall fatigue life of the HVOF systems was comparable to the previous roll bonded systems; however subsurface deflection of crack at the lining-backing interface resulted in the debonding of the lining and hence the observed lining fatigue resistance may not be a good indication of the overall performance in a bearing system. At similar lining surface plastic strain levels, the bronze bearing with very thin Sn and Ni as overlay layers (~7 microns each) showed comparable fatigue resistance to the currently investigated RB Al based designs. However annealing this system resulted in the formation of hard Ni3Sn intermetallics at the Sn-Ni interface, and the observed fatigue resistance of this system was higher than the RB systems. This has been linked to very fine scale local crack deflection in the overlay layers (although these have not been observed clearly). All these layered bearing systems provide a complex fatigue problem. Factors which reduce initiation /early growth behaviour are likely to offer the best service performance enhancements in view of the relatively HCF nature expected in service.
10
Dandre, C. A. "Computer modelling of fatigue in titanium alloys." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636342.
Full textAbstract:
A computer package has been developed that models the inter-granular stress distributions that are considered to be responsible for the fatigue crack initiation and short crack growth stages in near-α titanium alloys. The computer package incorporates the finite element method, and by modelling stress distributions at the microstructural level, this research is placed at the forefront of the field. A computer program generates at hypothetical uniform grain structure consisting of hexagonal grains. However, in order to model the anisotropic nature that is inherent in titanium alloys, a texture is developed for the computer generated structure. The directional variations for elastic and plastic properties are incorporated into the model by allocating crystallographic orientations to each grain individually. Since failure in near-α titanium alloys has been attributed to slip on the basal plane, the grain orientations describe the inclination of the basal plane to the direction of applied stress. The computer package models the principal inter-granular stress redistributions that occur at grain discontinuities, where 'weak' grains off-load stress onto adjacent 'strong' grains. Certain grains that are suitably orientated for slip experience an increased stress. When resolved onto the basal plane, this is evident as a unique combination of tensile and shear stresses that are considered to activate the separation of slip bands that have formed. In order to support the theoretical model, a limited material testing programme was devised which was considered to provide important information regarding the failure mechanisms. Four-point bend tests were performed on IMI 829 barstock material which was heat-treated to produce a coarse grain structure consisting of colonies of aligned α-platelets. SEM measurements were taken to determine the texture at crack initiation sites. The computer package was implemented to model the inter-granular stresses for these local textiles. Stress contour plots indicated that significant inter-granular stress distributions existed which were unique to each initiation site. These results were supported by the fatigue observations in the bend specimen.
11
Guengoeor, Salih. "Fatigue studies in Al-Mg-Si alloys." Thesis, Open University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276359.
Full text
12
Geary, W. "Fatigue crack growth in iron silicon alloys." Thesis, Sheffield Hallam University, 1985. http://shura.shu.ac.uk/20609/.
Full textAbstract:
A technique for accurately monitoring fatigue crack growth at near threshold growth rates has been established. The characteristics of near threshold fatigue crack growth of a number of iron-silicon alloys has been quantitatively and qualitatively investigated. Relationships have been established relating the stress intensity factor, AK, and the fatigue crack growth rate da/dN. At fatigue crack growth rates approaching threshold the material has shown some microstructural sensitivity and this has been related to the stress intensity factor and the yield stress. A relationship has been shown to exist between the value of the threshold stress intensity factor and the inverse root of the grain size, d~2, for each of the alloys investigated. A model for near threshold fatigue crack growth has been proposed and includes the contributions made by grain size and crack tip plasticity. This work has also shown that fatigue crack closure plays an important role in the micromechanisms of fatigue crack growth near the threshold at low R ratio s. A number of mechanisms have been identified: crack closure due tothe presence of oxidation products on fracture surfaces in tests conducted in air, and closure due to the presence of fatigue fretting, facet contact and a contribution of mixed mode opening.
13
Zhang, Yahui. "Low cycle fatigue of shape memory alloys." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLY004/document.
Full textAbstract:
Dans cette thèse, nous proposons une analyse globale multi-échelles de la fatigue à faible nombre de cycles des matériaux à mémoire de forme (MMF). Dans un premier temps, une large campagne d’essais a été menée pour différents chargements thermomécaniques comprenant des tests de fatigue sous contrainte et déformation imposée et pour différentes fréquences de chargement. A partir des résultats des essais, un critère de fatigue, basé sur l’énergie de déformation, a été développé ; on montre que l’énergie de déformation est un paramètre pertinent pour prédire la fatigue des MMF en tenant compte du couplage thermomécanique et du type de chargement : contrainte ou déformation imposée. Ensuite, en prenant appui sur la répartition de l’énergie de l’hystérésis en dissipation et énergie stockée, on avance une interprétation physique du mécanisme de la fatigue des MMF. Dans la troisième partie, on propose une modélisation multi-échelles de l’initiation des fissures de fatigue dans les MMF à partir de la notion de plasticité de transformation (PlTr). Dans ce cadre, on montre que la fatigue de MMF est contrôlée par la (PlTr) et que la température maximale lors de la transformation de phase est le paramètre à retenir pour prédire la rupture par fatigue des MMF. Le modèle permet également de prédire le lieu d’initiation des premières fissures de fatigue. Enfin, un procédé – fondé sur l’«éducation» des MMF – permettant d’améliorer la résistance à la fatigue est proposéThe thesis proposes a multi-scale comprehensive analysis of low cycle fatigue of shape memory alloys (SMAs). First, low cycle fatigue of SMAs is experimentally investigated; comprehensive tensile-tensile fatigue tests under both stress and strain controlled loadings at different frequencies are carried out and results are discussed. Second, a new strain energy-based fatigue criterion is developed; it is shown that the use of total strain energy is a relevant parameter to predict fatigue lifetime of SMAs for different thermomechanical conditions and under different types (strain-control or stress-control) loadings. A physical interpretation of the mechanism related to the low-cycle fatigue of SMAs is then provided based on the conversion of hysteresis work into dissipation and stored energy. Third, fatigue crack initiation during cyclic stress-induced phase transformation is modeled based on transformation induced plasticity (TRIP); it is shown that the maximum temperature during the cyclic loading is a relevant indicator of the fatigue of SMA. Furthermore, the effect of the macroscopic mechanical load on the the fatigue lifetime is addressed as well as the spatial location of crack initiation. Finally, a mechanical training process that allows enhancing resistance to low cycle fatigue of SMAs is proposed
14
Turner, Michael. "Brush plating of bearing alloys on aluminium alloy shells." Thesis, Aston University, 1986. http://publications.aston.ac.uk/11919/.
Full textAbstract:
The turbocharging of diesel engines has led to increase in temperature, load and corrosive attack of plain bearings. To meet these requirements, overlay plated aluminium alloys are now preferred. Currently, lead-tin alloys are deposited using a zincate layer and nickel strike, as intermediate stages in the process. The nickel has undesirable seizure characteristics and the zincate can given rise to corrosion problems. Consequently, brush plating allows the possible elimination of these stages and a decrease in process together with greater automation. The effect of mode application, on the formation of zincate films, using film growth weight measurements, potential-time studies, peel adhesion testing and Scanning Electron Microscopy was studied, for both SIC and AS15 aluminium alloys. The direct plating of aluminium was also successfully achieved. The results obtained indicate that generally, although lower adhesion resulted when a brush technique was used, satisfactory adhesion for fatigue testing was achieved. Both lead-tin and tin-cobalt overlays were examined and a study of the parameters governing brush plating were carried out using various electrolytes. An experimentally developed small scale rig, was used to produce overlay plated bearings that were fatigue tested until failure. The bearings were then examined and an analysis of the failure mechanisms undertaken. The results indicated that both alloy systems are of the regular codeposition type. Tin-cobalt overlays were superior to conventional lead-tin overlays and remained in good condition, although the lining (substrate) failed. Brush plated lead-tin was unsatisfactory. Sufficient understanding has now been gained, to enable a larger scale automated plant to be produced. This will allow a further study of the technique to be carried out, on equipment that more closely resembles that of a full scale production process.
15
Fu, Hanwei. "Microstructural alterations in bearing steels under rolling contact fatigue." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270311.
Full textAbstract:
The formation of microstructural alterations in bearing steels under rolling contact fatigue (RCF) is systematically studied. A literature review summarizes current understanding in this field, leading to the key to the formation of these microstructural features being carbon redistribution as a consequence of cyclic rolling contact. In this context, a novel theory is postulated to describe the migration of carbon caused by gliding dislocations. The theory combines the Cottrell atmosphere theory with the Orowan equation and is capable of quantifying the dislocation-assisted carbon flux. Based on the proposed theory, models are suggested for different types of microstructural alterations formed in rolling contact fatigued bearings – dark etching regions (DERs), white etching bands (WEBs) and white etching areas (WEAs). Very good agreement is obtained between the predications made by the models and the experimental data from both this research and the literature. Moreover, the models consider the effects of contact pressure, temperature, rotational speed and number of cycles, and thus can be applied for universal RCF testing conditions. The reproduced microstructural features are also characterized using advanced characterization techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT), with the observation validating the postulated formation mechanisms. It is demonstrated that DERs, WEBs and WEAs follow the same principle during formation – strain induced carbon redistribution. This is the first time that these microstructural alterations are quantitatively described using a unified theory. The achievements obtained from this research can be far reaching. It not only leads to great progress in understanding the phenomenology of RCF in bearing steels, but also can be further extended to other scenarios with similar phenomena such as severe plastic deformation and hydrogen embrittlement.
16
Jung, Hie-young. "Characterization of fatigue crack propagation in Al-Li 2090 alloys." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/20692.
Full text
17
Fair, G. H. "The effect of shot peening on fatigue and fretting-fatigue of aluminium alloys." Thesis, University of Nottingham, 1988. http://eprints.nottingham.ac.uk/12723/.
Full textAbstract:
Plain-fatigue and fretting-fatigue tests have been carried out on the two peak-aged, high-strength aluminium alloys, 7010 and 8090, in the unpeened and shot peened conditions. Shot peening produced a highly deformed surface containing many deep dimples and folds from which fatigue cracks rapidly initiated. Although initiation was early, propagation through the peened surface layers was retarded by the residual compressive stresses introduced by the peening treatment; this retardation being greatest at a depth corresponding to that of the peak residual compressive stress. Shot peening improved the plain-fatigue properties of the 7010 alloy at high applied stresses and this improvement decreased as the applied stress was reduced. A reversed trend was observed in the 8090 alloy with shot peening being beneficial to the fatigue properties at low applied stresses and detrimental at high applied stresses. The poor resistance of the 7010 alloy to fretting-fatigue was eliminated by shot peening and this was again attributed to the residual compressive stress induced by the peening treatment. Since the 8090 alloy in the unpeened condition is relatively insensitive to the effects of fretting, shot peening resulted in only a minor improvement in the fretting-fatigue behaviour of this alloy.
18
Fielding, S. E. "Fatigue and the Bauschinger effect in ferritic alloys." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304216.
Full text
19
Yang, Jing. "Fatigue crack propagation threshold in lamellar TiAl alloys." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5620/.
Full textAbstract:
In the present study, the effect of lamellar spacing, volume fraction of equiaxed gamma grains and lamellar orientation on fatigue crack propagation threshold have been assessed for three as-cast γ-TiAl alloys, Ti45Al2Mn2Nb1B (4522XD), Ti45Al2Mn2Nb (4522) and Ti46Al8Nb (at %). The influence of alloying elements, Nb and Ta on fatigue threshold was also studied with five forged alloys, Ti45Al2Mn2Nb1B, Ti45Al2Nb2Ta1B, Ti45Al2Mn2Ta1B, Ti45Al2Mn4Ta1B and Ti45Al2Mn4Nb1B. The fatigue crack propagation threshold tests were carried out at 650°C in air at a stress ratio R=0.1 and frequency of 10HZ. In addition, the microstructural characterisation of fatigue crack growth fracture surface was also examined by SEM. The samples assessed for fatigue crack propagation threshold failed mainly by translamellar fracture and interlamellar fracture. Interlamellar cracking occurs in lamellar colonies at any lamellar orientation at high stress intensity factor, ΔK, while at low ΔK cracking occurs in lamellar colonies only when the lamellar interface is parallel to the fracture plane. Therefore, the fracture behaviour is determined by both lamellar orientation and ΔK. The fatigue crack propagation threshold shows little sensitivity to lamellar spacing and volume fraction of equiaxed gamma grains with 4522XD variants in the studied range.
20
Schooling, Jennifer Mary. "The modelling of fatigue in Ni-base alloys." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627446.
Full text
21
Harty, Brian Dudley. "Corrosion fatigue of engineering alloys in aqueous environments." Doctoral thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/18215.
Full textAbstract:
A comparative study of the fatigue crack growth rate (FCGR) behaviour of five alloys in air and in aqueous environments has been performed. The alloys tested include: mild steel as a reference material, a corrosion resistant dual phase steel, 3CR12, a proprietary martensitic stainless steel, AISI 431, a newly developed 8% Cr martensitic steel, Alloy 825, and a newly developed corrosion-abrasion resistant metastable austenitic alloy, 1210. Tests were conducted in laboratory air, distilled water at rest potential, 500 ppm chloride solution at rest potential, 1000 ppm chloride solution at rest potential, and 1000 ppm chloride solution at -1200 m V see; solution temperatures were maintained at 25⁰ C. Crack growth rate tests were performed using sinusoidal loading at a load ratio R = 0.1, a frequency of 3Hz in the laboratory air, and a frequency of 1 Hz in the aqueous environments. At the completion of testing, fracture surfaces were studied using a scanning electron microscope. In air, the mild steel and 3CR12 display comparable rates of cracking and exhibit a greater resistance to fatigue crack propagation than the martensitic AISI 431 and Alloy 825; Alloy 825 shows the least resistance to fatigue crack propagation. The deformation induced transformation in 1210 gives this alloy the greatest resistance to fatigue crack propagation in air. Fatigue crack growth rates were all enhanced in the aqueous environments. The greatest overall rate of environmentally assisted cracking was shown by alloy 825 while the lowest was shown by the mild steel. Although the rate of cracking of 1210 in the aqueous environments was less than that of Alloy 825, 1210 was influenced the most by the aqueous environments. An environmentally assisted cracking index shows that the rate of fatigue crack propagation in 1210 is increased by 32 times in the 500 ppm chloride solution at low stress intensities. The fatigue crack growth rates of mild steel and AISI 431 were significantly influenced by the cathodically polarised conditions in the 1000 ppm chloride solution, compared to the rest potential conditions. In these cases hydrogen was seen to be evolved from the specimen surfaces. Changes in the fatigue crack growth rate behaviour were accompanied by changes in the fracture surface morphologies. The observed changes varied for each alloy and for each environment, and were manifest by the degree of intergranular cracking, cleavage, quasi cleavage, and increased coarseness of the transgranular cracking. The fracture surface morphologies are reported and discussed in detail. In general, the fracture surface morphologies could be directly related to the relative degrees of environmental influence on the rate of cracking; results are explained in terms of existing hypotheses. It is suggested that the environmentally assisted cracking of mild steel and AISI 431 at cathodic potentials in the 1000 ppm chloride solution could only be attributed to hydrogen assisted cracking. Similarly, it is suggested that the large crack growth rate acceleration of 1210 in the aqueous environments could also be attributed to hydrogen. The similar fracture surface morphologies observed on the other specimens after tests in the aqueous environments suggests-that hydrogen could be responsible for the environmentally assisted cracking of all the steels in aqueous environments.
22
Child, Daniel. "Corrosion-fatigue interactions of high-temperature nickel alloys." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/9732.
Full textAbstract:
Corrosion and fatigue aspects of high temperature turbine components made from Alloy 720Li and RR1000 have been studied with a view to understanding the potential failure mechanisms occurring in these materials. Understanding of such failure mechanisms is important in order to make safety improvements and significant cost savings by reducing engine downtime. Some exservice discs currently exhibit pit-like features at a specific location on the firtree lobes, which potentially may lead to more serious alloy fissuring. Shot peening is currently employed to improve fatigue resistance at the surface of components. This work aims to fully characterise these pits and fissure features in addition to shot peening, and the components in general, using advanced analytical techniques, in order that the failure mechanism(s) can be determined and mitigated against.
23
Shabestari, Saeed G. "Formation of iron-bearing intermetallics in aluminum-silicon casting alloys." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28920.
Full textAbstract:
The formation of iron-bearing intermetallics in the 413 type of aluminum alloys was investigated comprehensively. Both synthetic and commercial 413 alloys were studied with iron concentrations in the range of 0.4-1.2 wt. % and manganese up to 0.5 wt.%. The effects of cooling rate during solidification and of melt chemistry on the morphology of iron intermetallic phases were determined. Image analysis was used to quantify the intermetallic size, volume fraction, and number, as a function of both melt chemistry and cooling rate. The total volume fraction of intermetallic compounds in these alloys was related to cooling rate by an exponential equation.The kinetics of both dissolution of intermetallics on melting, and of re-formation on cooling of the liquid were investigated by means of quenching experiments. Quantitative evaluation of intermetallic size and number revealed that the change in volume fraction of intermetallics in the liquid state is controlled by nucleation.
The effect of settling time and the rate of gravity segregation of intermetallic compounds in a stagnant liquid metal were investigated. It was found that, in the absence of convection, settling obeys Stokes' law with the terminal velocity reached at very short times and very close to the melt surface.
Strontium was used to modify or eliminate the iron-intermetallics. (Abstract shortened by UMI.)
24
Highsmith, Shelby Jr. "Probabilistic fatigue crack life prediction in a directionally-solidified nickel superalloy." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5410.
Full text
25
Araujo, Jose Alexander. "On the initiation and arrest fretting fatigue cracks." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342243.
Full text
26
Tsutsumi, Mitsuyoshi. "FATIGUE AND CREEP FATIGUE BEHAVIOR OF HEAT RESISTANT ALLOYS WITH ANISOTROPIC AND COMPOSITE MICROSTRUCTURES." Kyoto University, 1998. http://hdl.handle.net/2433/182333.
Full text
27
Highsmith, Shelby. "Probabilistic fatigue crack life prediction in a directionally-solidified nickel superalloy." Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180222/unrestricted/highsmith%5Fshelby%5F200312%5Fms.pdf.
Full text
28
Webb, Graham. "Cyclic deformation, damage, and effects of environment in the Ni₃Al ordered alloy at elevated temperature." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/19981.
Full text
29
Russ, Stephan M. "Effect of underloads on fatigue crack growth of Ti-17." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180348/unrestricted/russ%5fstephan%5fm%5f200312%5fphd.pdf.
Full text
30
Subramaniam, Ameendraraj. "Fatigue behavior of copper zinc aluminum shape memory alloys." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0013/MQ32256.pdf.
Full text
31
Kan, Nathan Yu-Kwong. "Fatigue failure from internal defects in nickel base alloys." Thesis, University of Portsmouth, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308845.
Full text
32
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.
Full text
33
Cree, Alistair Murray. "Fatigue in boric acid-sulphuric acid anodised aluminium alloys." Thesis, Open University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247058.
Full text
34
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.
Full textAbstract:
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.
35
Jiang, Jiayun. "Fatigue and fracture of the friction welded titanium alloys." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/7006/.
Full textAbstract:
The autogenous friction welded- titanium alloys, Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo, were studied during this Ph.D. degree. An investigation was conducted on the microstructure evolution, fracture toughness and fatigue crack propagation behaviour of autogenous inertia welded Ti-6Al-2Sn-4Zr-6Mo. The microstructure and fatigue threshold behaviour of linear friction welded Ti-6Al-4V were also assessed in both the as-welded and the post weld heat treated conditions, and the fracture toughness was assessed at room temperature in post weld heat treated condition only. The fatigue threshold behaviour of the autogenous linear friction welded Ti-64 in the as-welded condition was assessed to help understand the edge cracking phenomenon which was observed in the as-welded linear friction welded Ti-6Al-4V BLISK joints.
36
Moffat, Andrew James. "Micromechanistic analysis of fatigue in aluminium silicon casting alloys." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/52400/.
Full textAbstract:
Due to increasingly stringent environmental legislation, there is a requirement for lower emissions and greater overall efficiency of light vehicle diesel (LVD) engines. This continues to be achieved through the optimisation of design and careful selection of the materials used in key LVD engine components, for example pistons, so that they are lighter and can operate at higher temperatures. Pistons are non-serviceable parts and so must be able to withstand the fatigue and high temperature environment of the car engine. It is therefore important to understand the mechanisms of fatigue in these alloys to help inform alloy development for the next generation of pistons. Pistons are typically produced from multi-component Al-Si casting alloys. These alloys exhibit a complex, multiphase microstructure comprising α-aluminium as the matrix with silicon particles and several intermetallic phases. Previous research on Al-Si casting alloys has demonstrated that porosity is detrimental to fatigue life as cracks initiate freely at pores. However, with improved casting techniques porosity can be greatly reduced and other microstructural features influence fatigue life. In particular, Si particles have been shown to play an important role in the initiation and subsequent propagation of fatigue cracks. This study assesses the role of Si content and other microstructural features on fatigue behaviour by testing a set of well-characterised multi-component, Al-Si casting alloys with varying Si content. Fatigue initiation behaviour was investigated at room temperature using S-N and short fatigue crack growth experiments. Pores, Si particles and intermetallic phases were shown to cause fatigue crack initiation. In a 0.67wt% Si containing alloy, large-scale porosity was observed and was the foremost reason for fatigue initiation. In two alloys the Al9FeNi phase was observed to be the most detrimental hard particle causing fatigue crack initiation. Nanoindentation results showed that Al9FeNi had a lower hardness and higher modulus than Si and so Al9FeNi may be expected to fracture preferentially, consistent with the fatigue results. X-ray computed tomography demonstrated that all the alloys investigated contained a complex, interconnected, intermetallic sub-structure. As a result, the micromechanisms of fatigue are different to those in conventional particulate Al-Si alloys because particle fracture is required to ensure a level of crack continuity. At room temperature and 350˚C, and at low and high crack growth rates, the crack tip may be described as a diffuse region of micro-damage and intact ligaments. It is the extent of this damage in the alloys that controls the crack growth rates exhibited and simple trends between the Si content and roughness, reported for particulate systems, do not hold true in the alloys investigated in this study. The balance of the micromechanisms of fatigue was shown to be dependent on temperature. This highlights the importance of fatigue studies at temperatures that are characteristic of those experienced in service.
37
Zhao, Tianwen. "Fatigue of aluminum alloy 7075-T651 /." abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3342620.
Full textAbstract:
Thesis (Ph. D.)--University of Nevada, Reno, 2008."December, 2008." Includes bibliographical references (leaves 76-83). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2009]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.
38
Balanza, Erquicia R. A. "Wear of high aluminium zinc-based alloys in plain bearing applications." Thesis, Aston University, 1993. http://publications.aston.ac.uk/15273/.
Full textAbstract:
Two zinc-based alloys of high aluminium content, Super Cosmal alloy containing 60% Al, 6% Si, 1% Cu, 0.3% Mn and HAZCA alloy containing 60% Al, 8% Si, 2% Cu, 0.06% Mg were produced by sand casting. Foundary characteristics in particular, fluidity, mode of solidification and feeding ability were examined. Metallographic analysis of structures was carried out using optical and scanning electron microscopy and their mechanical properties were determined using standard techniques. Dry wear characteristics were determined using a pin-on-disc test, and boundary-lubricated wear was studied using full bearing tests. Results from casting experiments were evaluated and compared with the behaviour of a standard ZA-27 alloy and those from tribological tests with both ZA-27 alloy and a leaded tin-bronze (SAE660) under the same testing conditions. The presence of silicon was beneficial, reducing the temperature range of solidification, improving feeding efficiency and reducing gravity segregation of phases. Use of chills and melt degassing was found necessary to achieve soundness and enhanced mechanical properties. Dry wear tests were performed against a steel counterface for sliding speeds of 0.25, 0.5, 1.0 and 2 m/s and for a range of loads up to 15 kgf. The high aluminium alloys showed wear rates as low as those of ZA-27 at speeds of 0.25 and 0.5 m/s for the whole range of applied loads. ZA-27 performed better at higher speeds. The build up of a surface film on the wearing surface of the test pins was found to be responsible for the mild type of wear of the zinc based alloys. The constitution of the surface film was determined as a complex mixture of aluminium, zinc and iron oxides and metallic elements derived from both sliding materials. For full bearing tests, bushes were machined from sand cast bars and were tested against a steel shaft in the presence of a light spindle oil as the lubricant. Results showed that all zinc based alloys run-in more rapidly than bronze, and that wear in Super Cosmal and HAZCA alloys after prolonged running were similar to those in ZA-27 bearings and significantly smaller than those of the bronze.
39
Rycerz, Pawel. "Propagation of surface initiated rolling contact fatigue cracks in bearing steel." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/44525.
Full textAbstract:
The useful life of mechanical components which experience highly stressed rolling/sliding contacts, such as rolling element bearings or gears, is limited by rolling contact fatigue (RCF). Surface initiated pitting is a mode of RCF which has in recent years received particular attention from industry due to its frequent occurrence in service. This work focuses on the growth behaviour of RCF cracks before they develop into surface pits. A three-contact disc machine was used to perform pitting experiments on bearing steel samples. Preliminary tests showed that surface initiated cracks could be reproduced under high contact pressure and mixed lubrication regime. However, it was not possible to detect them using the vibration monitoring system installed on the test rig. This led to the development of a high sensitivity crack detection system which employs the principle of magnetic flux leakage (MFL). The existing test rig was modified to accommodate an inductive sensor and required signal acquisition electronics. In addition, a signal processing procedure was developed to enable analysis in real time. It was shown that the MFL technique is significantly more sensitive than commonly used alternatives. The system is capable of automatically finding cracks down to about 100 μm in length. In addition, results have shown a linear relationship between defect size and signal amplitude which enables in-situ sizing of cracks. Using the crack detector, a procedure to generate cracks and extract their growth rates was established. Crack growth was first studied under high contact pressure. It was found that initiation occurred very early in total life, which was attributed to high asperity stresses due to mixed lubrication regime. Total life to pitting was dominated by crack propagation, the speed of which was shown to depend on crack size. Small cracks grew at a steady and slightly decreasing rate until a critical size is reached at which propagation speed rapidly increases, shortly followed by pitting. Further study at lower loads confirmed that contact pressure is the main parameter controlling propagation speed. In order to identify a suitable crack propagation law, the measured crack growth rates were plotted against a stress intensity parameter expressed in terms of maximum contact pressure and crack size. The results suggest that after reaching certain length, rolling contact fatigue cracks grow according to a Paris-type power law, where the exponent of stress intensity parameter, and therefore contact pressure, was found to be approximately 7.5.
40
Clark, Yvonne Yumiko. "Antioxidant Treatment of Muscle Wasting and Fatigue in Tumor-Bearing Mice." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373844738.
Full text
41
Kang, JeeHyun. "Mechanisms of microstructural damage during rolling contact fatigue of bearing steels." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245255.
Full textAbstract:
Bearings are employed in a number of applications under extremely demanding conditions. During long operation times, the material undergoes rolling contact fatigue where microstructural damage manifests as dark-etching regions and white-etching areas, which display different properties from the surrounding region. The aim of this study is to identify the mechanisms for such damage and to suggest models that can explain the influence of the initial microstructure and test conditions. In order to appraise the stress state in rolling contacts, two testing techniques were employed and it was examined if the testing methods could reproduce the same damage as in bearing operation. During ball-on-rod fatigue testing, microcracks were generated adjacent to inclusions and some were decorated with white-etching areas. Repetitive push tests showed a similar extent of subsurface hardening compared to the ball-on-rod tests, and allowed the strain per stress cycle to be measured. The microstructural alterations in a white-etching area were studied both on a macroscale and on an atomic-scale. The degree of stress concentration near a microcrack was calculated employing a nite element method. The microstructure, as well as the segregation behaviour of alloying elements in the white-etching area, were investigated by employing transmission electron microscopy and atom probe tomography. A nanocrystalline structure with scattered carbide particles was observed in the white-etching area. Carbon and silicon segregation was highly pronounced in some boundaries of dislocation cell structures. Models were suggested to account for the microstructural alterations during rolling contact fatigue. Carbide coarsening in dark-etching regions was modelled by considering how carbon di usion is assisted by dislocation glide. The predicted hardness evolution was consistent with experimental observation. The kinetics of carbide dissolution in white-etching areas was calculated by taking two processes into account: deformation accumulation and carbon diffusion. These models suggest that the microstructural changes during bearing operation can be controlled by tailoring the initial microstructure and managing the test conditions.
42
Nicholls, David John. "Structure-property relations in aluminium-lithium alloys." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238194.
Full textAbstract:
This work describes the effect of microstructure on the behaviour of small fatigue cracks in the two Al-Li-Cu-Mg-Zr alloys 8090 and 8091. The slip distribution in these alloys was varied through thermo-mechanical processing. Although slip distribution affected tensile, cyclic and long fatigue crack behaviour, it did not affect small fatigue crack behaviour due to low levels of closure and reduced slip reversibility near to a free surface. Similarly, underageing and overageing had no effect on small fatigue crack behaviour. Therefore, small fatigue crack growth is concluded to be insensitive to precipitate size and distribution. Due to differences in grain size, small fatique cracks in 8091 were observed to propagate twice as slowly as in 8090. Small fatigue cracks grew more rapidly than long fatigue cracks under the same nominal K and displayed no threshold behaviour. This was shown to be due to the combined effects of the low closure levels, high applied stresses and proximity to the surface. Corrections to K to account for these factors were shown to be less effective than using J as a correlating parameter. None of these factors affected the suitability of K for characterizing microstructural effects. Small and long fatigue crack data were comparable when plotted versus calculated plastic zone size. Low cycle fatigue behaviour was shown to be related to small fatigue crack behaviour and similar microstructural effects were observed. Total rather than plastic strain was identified as the critical parameter when comparing small fatigue crack and LCF behaviour. Small fatigue crack growth behaviour was shown to be inconsistent with the plastic work accumulation criterion for the exhaustion mechanism of fatigue. Finally, because of low K's and the lack of closure, fatigue mechanisms may be easier to study in small cracks than in long cracks. (D91005)
43
Bernard, Richard Joseph. "The fatigue crack growth behavior of Ti-24A1-11Nb as a function of temperature and load ratio." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/20187.
Full text
44
Morrissey, Ryan J. "Frequency and mean stress effects in high cycle fatigue of Ti-6A1-4V." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17095.
Full text
45
Kupkovits, Robert Anthony. "Thermomechanical fatigue behavior of the directionally-solidified nickel-base superalloy CM247LC." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28160.
Full textAbstract:
Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Dr. Richard W. Neu; Committee Member: Dr. David L. McDowell; Committee Member: Dr. W. Steven Johnson.
46
Ammar, Hany. "Effet des imperfections de la coulée sur les propriétés en fatigue des alliages de fonderie aluminium silicium = Effect of casting imperfections on the fatigue properties of aluminum-silicon casting alloys /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2006. http://theses.uqac.ca.
Full text
47
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/.
Full textAbstract:
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.
48
Simundjuntak, Sarinova. "Relationship between microstructure and fatigue performance of 26XX aluminium alloys." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251604.
Full text
49
Davies, H. M. "Low temperature dwell sensitive fatigue in near alpha titanium alloys." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636387.
Full textAbstract:
The ambient temperature fatigue response of the near alpha titanium alloy Timetal 834 has been evaluated using specimens manufactured from two material sources:- hot-rolled barstock and an isothermally forged compressor disc. The effects of dwell periods imposed at peak stress and different R values were assessed. Significant differences were observed between the two alloy variants particularly with respect to their sensitivity to dwell loading. In particular it was found that dwell sensitivity is enhanced by high R values (R = 0.5) and longer dwell times but is reduced by compressive minimum loads (R = -0.5). Variations in microstructural morphology together with differences in localised texture were found to control the contrasting dwell performance in the two materials. Sub-surface fatigue crack initiation has been observed for both coarse grained Timetal 685 and the two Timetal 834 forms. With typical as received hydrogen concentrations of 40-60ppm these initiation sites are characterised by quasi-cleavage facetting. EBSD analysis has demonstrated that the facets are of a near basal orientation with respect to the hexagonal crystal lattice. At high hydrogen concentration in Timetal 685, fractographic and EBSD studies combined with mechanical data from a previous investigation, show that premature fatigue failures are associated with the operation of alternative failure mechanisms. These include strain induced alpha/beta interface cracking and the shear related separation of basal planes. Fatigue crack propagation in the disc material, under dwell and cyclic loading, was explored using three specimen designs: CC, DEN and TDEN. The CC and DEN geometries allowed the behaviour of part through cracks to be evaluated in a uniform stress field and within a plastically deformed stress gradient. The TDEN enabled through section crack behaviour to be quantified. Growth rates were dependent on R-ratio but unaffected by dwell periods at peak load. Increased growth rates at higher R values were attributed to the fact that a high mean stress encourages enhanced strain accumulation and facet formation. The lack of a dwell effect on crack propagation is due to stress relaxation at the crack tip. It could also be associated with compression in the crack tip plastic zone on unloading.
50
Suddell, B. C. "Optimising fatigue through the control of texture in titanium alloys." Thesis, Swansea University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639128.
Full textAbstract:
Titanium alloys are used extensively throughout the aerospace sector in blades and discs of the low and intermediate sections of the compressors of modern Aeroengines. Titanium is used primarily as it has a high strength-to-weight ratio and good Fatigue and Creep resistance. Titanium 6-4 (Ti-6Al-4V) is the general "Workhorse" alloy of the Titanium family of alloys and has been extensively studied over the past 50 yeas. It is known that texture plays an important role in terms of its effect on the materials mechanical properties. The mechanical response of textured Ti 6/4 plate material is assessed through an evaluation of monotonic properties under tension and torsion loading and fatigue testing of plain and notched specimen geometries. Significant variations in modulus, yield strength, ultimate tensile strength and ductility are demonstrated for test pieces taken from the plate materials parallel to either the transverse or longitudinal rolling direction or perpendicular to the longitudinal direction i.e. in the Short Transverse orientation. Cyclic performance is also shown to be sensitive to orientation with different cyclic stress-strain curves applying to each orientation. The relationship between the principle stress axis and the dominant basal plane texture is shown to control fatigue crack initiation lives and the ultimate mode of fracture. These effects are discussed with reference to the inherent, anisotropic mechanical response of α+β titanium alloys, which results from the hexagonal crystallographic form of the α phase and the availability of preferential slip systems. The anisotropic response could be utilised to an engineering advantage by matching critical stressing directions to the specific properties offered by the texture.