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Item Metadata only A crack closure model of fatigue crack growth in plates of finite thickness under small-scale yielding conditions(Elsevier Science BV, 2009) Codrington, J.; Kotooussov, A.Crack growth rates are significantly affected by the thickness of the specimen when all other parameters are kept constant. A quantitative estimation of the thickness effect is thus necessary to make predictions of crack growth rates more accurate and reliable. For this purpose a theoretical model was developed based on the strip-yield assumption and first-order plate theory. No empirical or fitting parameters were used in this work unlike some previous studies. The theoretical values obtained for the normalised load ratio parameter, U, were employed to describe experimental data, obtained under small-scale yielding conditions, at various load ratios and plate thicknesses. Such a representation considerably narrowed the scatter in the crack growth rates versus the effective stress intensity factor range, ΔKeff, demonstrating the potential of the theoretical model.Item Metadata only A critical role for Al in regulating the corrosion resistance of nanocrystalline Mo(Si₁₋ₓAlₓ)₂ films(Royal Soc Chemistry, 2012) Xu, J.; Lai, D.; Xie, Z.; Munroe, P.; Jiang, Z.Novel nanocrystalline Mo(Si 1-xAl x) 2 films, with differing Al contents were synthesized by double cathode glow discharge. The films exhibited a compact columnar microstructure having a pronounced (111) preferred orientation. The corrosion behaviour of these films were characterized by using various electrochemical techniques including open circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. The corrosion resistance of the films increased with increasing Al content in the as-synthesized films. The composition and chemical state of the passive layers formed on the films were investigated by X-ray photoelectron spectroscopy (XPS). It was demonstrated that the passive layer formed on the binary MoSi 2 film was highly enriched in SiO 2 with minor amounts of MoO 4 2-, MoO 2 and SiO x. With the increase of Al content in the films, Al 2O 3 was generated and incorporated into the passive layers, enhancing the corrosion resistance of the films by inhibiting the dissolution of Mo. Built upon the experimental results, the first-principles density-functional theory was applied to calculate the inter-atomic bonding strength in Mo(Si 1-xAl x) 2 and elucidate the role of Al in controlling the corrosion resistance of the films. The new findings lay a solid basis for the development and application of MoSi 2 based corrosion-resistant films. © 2012 The Royal Society of Chemistry.Item Metadata only A generalized plane-strain theory for transversally isotropic plates(Springer-Verlag Wien, 2003) Kotooussov, A.; Wang, C.By adopting Kane and Mindlin’s assumption that the through-the-thickness extensional strain is uniform through the plate thickness, a generalized plane-strain theory is developed for transversely isotropic plates. The three-dimensional governing equations are successfully reduced to two coupled equations in the two-dimensional space. With the new theory, explicit solutions of the three-dimensional stresses, especially the through-the-thickness component, around a circular hole and a V-shaped notch in a transversely isotropic plate of arbitrary thickness are derived. The analytical solutions are verified by comparing with finite element results.Item Metadata only A method for obtaining approximate solutions for highly dynamic problems(Pergamon-Elsevier Science Ltd, 2001) Kotooussov, A.As a rule, a theoretical analysis of the behavior of highly dynamic systems is very difficult due to the strong non-linearity of the governing equations. Basic results are usually achieved by the application of the inverse scattering transform methods, methods of perturbation theory and numerical approaches. However, all the above-mentioned methods and approaches have well-known limits in their application. In this paper, a dynamic system described by linear hyperbolic partial differential equations with a non-linearity localized in a space-time domain is considered. The application of the theory of laws of conservation together with the Huygens' principle allows the generation of a family of integral inequalities by using the solution of the corresponding linear problem with the same initial data. In turn, these integral inequalities make it possible to formally reduce the initial problem for locally non-linear hyperbolic equations to an extremal problem at limitations (restrictions) defined by these integral inequalities. Thus, upper and lower bound estimates of the solution of the locally non-linear problem can be obtained from the solution of this extremal problem to which standard techniques can be applied. The method under development has many advantages when compared with known approaches. These advantages together with its limitations are discussed in this paper. Examples of this new method as applied to some locally non-linear problems of dynamic elasticity are also considered.Item Metadata only A New Machine to Characterize Microstructural Evolution of Semi-Solid Metal Billets through Viscometery(Elsevier Sci Ltd, 2007) Lashkari, O.; Ghomashchi, R.The methods to study the "rheological behavior" of semi-solid metal, SSM, slurries are all based on measuring the viscosity. The viscosity is an indication of SSM capability in filling the mould and determines the required force for its deformation and flow. One way to measure viscosity is the application of parallel plate compression viscometery. A new "parallel plate compression machine" for commercial scale is designed, fabricated and tested for viscosity measurement. It is based on monitoring and registering the height changes of the test piece with time. The registered data is treated mathematically to plot strain-time graph from which the viscosity is calculated. The machine is capable of differentiating amongst various SSM microstructures ranging from dendritic to rosette and globular morphologies of the primary phase. © 2006 Elsevier Ltd. All rights reserved.Item Metadata only A new passive defect detection technique based on the principle of strain compatibility(IOP Publishing Ltd, 2008) Wildy, S.; Kotooussov, A.; Codrington, J.This paper discusses the development of a new passive technique of on-line damage detection based on the most fundamental concept in continuum mechanics: strain compatibility. The main feature of this technique is its invariance to changing operating conditions. The technique is quite general and can be applied to structures made of isotropic or anisotropic materials and structural components experiencing elastic or plastic deformations. A few practical situations, involving the development of crack damage in plate structures, are considered to demonstrate the feasibility of this crack detection technique, as well as its potential for many practical applications. Future work will focus on the experimental validation of the technique.Item Metadata only A novel technique for microstructure characterization of garnet films(Elsevier Science BV, 2009) Wo, P.; Munroe, P.; Vasiliev, M.; Xie, Z.; Alameh, K.; Kotov, V.Bismuth-substituted iron garnet exhibits remarkable magneto-optical properties in magnetic photonic crystal (MPC) structures, and has the potential to improve performance in optical integrated circuits for communication networks and optical sensing applications. The microstructure and thickness of these garnet films has a strong influence over their optical, magnetic and magneto-optic (MO) properties. The thickness of these films has been measured indirectly via optical interference and ellipsometry, which are unable to map thickness variations due to surface roughness of both the film and the substrate. However, little direct observation has been carried out to provide detailed information about the microstructure of the garnet films, especially in cross-section. All these have resulted in a lack of understanding of processing-microstructure-MO property relationship, which in turn impedes the development of high-performance garnet films. The combined use of focused ion beam (FIB) milling and transmission electron microscopy (TEM), described as the FIB-TEM method hereafter, provides a reliable, direct means of characterization of site-specific micron-sized regions of a specimen within a reasonable length of time. A sound understanding of processing-microstructure-MO property relationship enabled by FIB-TEM method is crucial in the design of the manufacturing processes for such functional films as well as nanostructures that have garnet layers. This paper reports the experimental procedures of FIB-TEM technique for characterization of these films and discusses the strength and issues associated with its application on (Bi, Dy)3(Fe, Ga)5O12 garnet films. © 2009 Elsevier B.V. All rights reserved.Item Open Access A realistic assessment of recoverable thermal energy from Australian geothermal reservoirs: a simulation study(Geoscience Australia, 2012) Doonechaly, N.; Rahman, S.; Kotooussov, A.; Australian Geothermal Energy Conference (5th : 2012 : Sydney, Australia)This paper presents an innovative distributed dislocation theory for estimation of change in fracture aperture due fluid induced pressure. The new approach is used to analyze the potential for thermal energy recovery from the Patchawarra geothermal reservoir in Australia. Results of this study show that the time required to stimulate a 500 m2 reservoir rock and sustain commercial flow rate (80 l/s) is much greater (two to three folds) than that previously studied. These results, however, agree well with the experience of existing EGS trials around the world. Thermal stresses induced during the circulation of cold water have a significant bearing on the long term production rate. As thermal drawdown of the rock matrix takes place, tensile thermal stresses are induced which allow residing fractures to dilate and enhance permeability. This gradually increases the fluid velocities between the injector and producer, yielding increasing production rates with time. It was also observed that the maximum thermal energy that can be recovered by use of our current know-how would be as much as 42%.Item Metadata only A strip yield model for two collinear cracks(Pergamon-Elsevier Science Ltd, 2012) Chang, D.; Kotooussov, A.In this paper two alternative approaches for analysing the non-linear interaction between two equal-length collinear cracks subjected to remote tensile stress on infinity are developed. The approaches are based on the classical Dugdale strip yield model and utilise the distributed dislocation formulation to represent two through-the-thickness cracks in an infinite plate. In the first approach the solution is obtained analytically by solving Föppl integral equation; in the second a numerical procedure based on the Gauss-Chebyshev quadrature method is applied. The latter approach can be extended to other multi-crack problems or more complicated types of loading. The developed approaches are validated against previously published studies and new results for crack tip opening displacement are presented. © 2012 Elsevier Ltd.Item Metadata only A strip yield model for two collinear cracks in plates of arbitrary thickness(Kluwer Academic Publ, 2012) Chang, D.; Kotooussov, A.As two cracks grow and approach each other under fatigue loading, a deleterious interaction between them can considerably affect the crack growth rate, making theoretical evaluations and experimental data from a single isolated crack case considerably inaccurate. The aim of the present study is to investigate the interaction between two collinear cracks of equal length, taking into account the plate’s thickness effect, which was demonstrated to have a large effect on fatigue crack growth in the case of a single crack. The obtained solution to the problem is based on the Dugdale strip yield model and the distributed dislocation technique. In addition, a fundamental solution for an edge dislocation in a finite thickness plate is utilised. The present solution shows a very good agreement with previously published results for some limiting cases. The obtained results confirm a significant dependence of the interaction and stress intensity factors on the plate thickness, which can dramatically affect the plastic collapse conditions as well as fatigue crack growth rates.Item Metadata only A study of cortical bone microdamage and crack morphology utilising confocal microscopy and sequential labelling(ESIS, 2009) Codrington, J.; Kuliwaba, J.; Zarrinkalam, K.; Fazzalari, N.; International Conference on Crack Paths (2009 : Vicenza, Italy)The formation and accumulation of microdamage in bone plays an important role in the occurrence of stress and fragility fractures as well as in the initiation of bone remodelling. In this study a novel technique is presented for the investigation of bone microdamage and crack morphology using laser scanning confocal microscopy and sequential labelling with chelating fluorochromes. Compact tension fracture specimens machined from bovine tibial cortical bone, were mechanically tested in a wedge loaded crack-propagating tool. Sequential labelling with xylenol orange and calcein allowed for the crack propagation and microdamage progression to be assessed at each stage using confocal microscopy. Both twodimensional confocal images and three-dimensional z-series reconstructions displayed the formation of a microdamage process zone and wake surrounding the main crack. Further imaging demonstrated the significance of the bone microstructure, such as the vasculature and osteocytes, in the distribution of the microdamage.Item Metadata only Adhesively bonded joints under cyclic loading spectra(Blackwell Science Ltd, 2002) Jones, R.; Kotooussov, A.; Marshall, I.Current designs which involve the use of composite materials in primary aircraft structures are often conservative. This, in turn, significantly lowers the weight advantage that composites have over established metallic airframe materials. Strain restrictions are often applied because the failure mechanism(s) in (fibre) composite joints and stiffener runouts where the stress state is often complex, are not fully understood. Nevertheless, from the airworthiness perspective it is essential that both the static strength and the fatigue behaviour of the components subjected to complex multiaxial stress conditions are both understood and predicted. This topic is extremely complex, and numerous criteria ranging from the purely empirical to the theoretical have been proposed. In both cases, it is necessary to know the localised stress–strain history. One common design methodology is to keep the stresses so low that fatigue will not be an issue. However, this can lead to an overly conservative design. On the other hand, while a detailed (nonlinear) finite element analysis can be performed it is often both resource‐intensive and time‐consuming. The present paper shows that Glinka's hypothesis can be used in order to calculate the localised stresses and strains for a bonded joint subjected to cyclic loading. This is a new result and has not previously been noted. It has the potential to extend the Hart‐Smith design methodology to the adhesively bonded joints in order to encompass durability considerations. This formulation also raises the possibility of enabling the degree of conservatism inherent in traditional joint design to be relaxed provided that failure occurs in the adhesive. This paper also addresses the problem of variable adhesive thickness. We show that while variable adhesive thickness can change the stress and the energy fields, the peak in the strain energy density is relatively insensitive to the stress–strain relationship for the adhesive and that Glinka's hypothesis still appears to be true. This means that, for the present class of problems, even if there is variability in the thickness of the adhesive bond the energy field and, hence, the strength of the joint can be estimated from a purely linear elastic analysis of the joint, provided that failure occurs in the adhesive.Item Metadata only Al-B Master Alloys: A Worthy Alternative to Ti-based Grain Refiners for Al-Si Foundry Alloys(American Foundry Society, 2006) Ghomashchi, R.Item Metadata only An accurate methodology for determining the efficiency of energy harvesting PZ elements(Tambov State Technical University, 2006) Wornle, F.; Grainger, S.; Kotooussov, A.This paper describes a new experimental methodology for accurate measurements of the efficiency of energy conversion in PZ (piezoelectric) elements. These elements are often used to monitor on-line the progressive structural damage of engineering structures, such as bridges, aircrafts and pipelines. Harvesting energy from small amplitude mechanical vibrations of such structures can revolutionize these monitoring techniques by increasing their reliability, reducing the maintenance cost and making them fully autonomous. As the quantity of electrical energy that can be harvested from vibrations is rather low, it is important to ensure that the piezoelectric elements are operating at the best possible efficiency.Item Metadata only An application of the Kane and Mindlin theory to crack problems in plates of arbitrary thickness(Kluwer Academic Publ, 2004) Kotooussov, A.Classical plane solutions of the theory of elasticity, which are sometimes more than 100 years old, are still used today and provide a framework for the analysis of many practical problems. But, strictly speaking, these analytical solutions are only applicable to plates with vanishing thickness or infinite thickness, where the stress state could be classified as plane stress or plane strain, respectively. However, the through-the-thickness stresses that exist in a plate of given thickness have a significant impact in a number of practical applications; and these stresses are often inevitably ignored due to the lack of analytical tools. This paper presents new analytical results for crack tip opening displacement (CTOD) for the through-the-thickness crack in infinite plates with various thicknesses. These results are based on the solution for an edge dislocation in infinite plate of arbitrary thickness and an application of the distributed dislocation technique. The analytical predictions of the CTOD and the constraint factor are compared with the three-dimensional elasto-plastic finite element (FE) results. It is shown that both analytical and numerical results are in good agreement when the numerical calculations are not affected by the size of the FE mesh and by the boundaries of the FE model.Item Metadata only Analysis and design of functionally graded thermal coating(Institute of Materials Engineering Australasia, 2006) Tsukamoto, H.; Kotooussov, A.; Ho, S.; Codrington, J.; International Conference on Structural Integrity and Failure (2006 : Sydney, N.S.W.); Hoffman, M.; Price, J.Item Metadata only Analysis of a rock bolt failed in service(Curran Associates, 2002) Gamboa, E.; Atrens, A.; International Corrosion Congress (15th : 2002 : Granada, Spain)This paper describes a fractographic investigation of a rock bolt failed in service in a NSW colliery and relates the failure to service conditions. Optical microscopy revealed that the fracture surface contained a dark thumbnail shaped area 1.9 mm deep. The rest of the fracture surface was quite shiny. There was no necking or other evidence of plasticity. This fracture appearance is consistent with stress corrosion cracking (SCC) followed by fast brittle fracture. There were secondary cracks also indicative of SCC. SEM observation characterized the SCC surface. This failure analysis has indicated that rock bolts can fail in service in a brittle manner with no prior warning at stresses much lower than their ultimate tensile strength. This represents a new failure mode for a critical mine component, that is critical for mine safety. There is no prior experience with this failure mode, and laboratory work is needed to understand the failure mechanisms. With understanding of the failure mechanism, it will be possible to devise counter-measures.Item Metadata only Analysis of interfacial fracture in dental restorations(Elsevier Sci Ltd, 2011) Kotooussov, A.; Kahler, W.; Swain, M.Objectives
To provide a brief summary of the background theory of interfacial fracture mechanics and develop an analytical framework that identifies the critical factors for the analysis of the initiation and propagation of adhesion failure in composite restorations.Methods
A conceptual framework utilizing interfacial fracture mechanics and Toya's solution for a partially delaminated circular inclusion in an elastic matrix, which can be applied (with caution) to approximate polymer curing induced cracking about composite resins for class 1 cavity restorations.Results
The findings indicate that: (1) most traditional shear tests are not appropriate for the analysis of the interfacial failure initiation; (2) material properties of the restorative and tooth material have a strong influence on the energy realize rate; (3) there is a strong size effect; and (4) interfacial failure once initiated is characterized by unstable propagation along the interface almost completely encircling the composite.Significance
The work is important for the analysis of the reliability of composite class I restorations and provides an adequate interpretation of recent adhesion debonding experimental results utilizing tubular geometry of specimens. The approach clearly identifies the critical parameters including; curing strain, material modulii, size and interfacial strain energy release rate for reliable development of advanced restorative materials.Item Metadata only Analytical modelling of a pipe with flowing medium subjected to an impulse load(Pergamon-Elsevier Science Ltd, 2011) Mohammad, R.; Kotooussov, A.; Codrington, J.Pipes transporting gas or liquid can be subjected to impulse loading as a result of an accident. In many previous studies the effects of the flowing media on the transient response of pipes were largely ignored or considered to be negligible. This paper aims to shed light on the significance of these effects. First, we present a simplified mathematical model of a pipe filled with a flowing liquid or gas and subjected to dynamic loading. This model is based on the well-known Bernoulli-Euler beam theory, but also incorporates forces generated by the internal flow which follows the pipe lateral deflections and generates the inertia, centrifugal and Coriolis flow accelerations. Further, we develop asymptotic analytical and numerical methods for the analysis of the governing equation. Finally, as example, we investigate in detail the effect of the flow parameters on the dynamic response of a cantilever pipe subjected to impulse loading. Special attention is given to the pipe whip phenomenon, which causes growing unlimited displacements of the pipe regardless of how small the value of the applied loading is. The developed theoretical methods provide a framework for analysis of many other dynamic problems of pipes with flowing media subjected to arbitrary boundary and loading conditions. © 2010 Elsevier Ltd. All rights reserved.Item Metadata only Analytical modelling of the transient dynamics of pipes with flowing medium(IOP Publishing, 2009) Kotooussov, A.; Mohammad, R.; International Conference on Modern Practice in Stress and Vibration Analysis (7th : 2009 : Cambridge); DulieuBarton, J.M.The primary purpose of this work is to present an innovative approach to investigate the effect of a flowing medium on the transient response of a simply supported pipe due to impulsively applied loading. The importance of this problem is manifested in numerous applications in the field of transportation and power energy. In this paper we describe a simplified mathematical model of the pipe-filled-medium interactions adopting the classical Bernoulli-Euler beam theory. Further we develop an analytical procedure based on the perturbation method to analyse the dynamic response of the system due to an impulse loading and consider particular cases of the applied loading.