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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 Effect of plate thickness on crack-tip plasticity(Kluwer Academic Publ, 2001) Kotooussov, A.; Wang, C.Item Metadata only Stress intensity factor for small-to-medium cracks(EMAS Publishing, 2002) Kotooussov, A.; Jones, R.; European Conference on Fracture (14th : 2002 : Krakow, Poland)Item Metadata only Thermo-mechanical effect and criterion of crack propagation(EMAS Publishing, 2002) Kotooussov, A.; European Conference on Fracture (14th : 2002 : Krakow, Poland)Item Metadata only Dugdale-type model for a crack in a plate of arbitrary thickness(Swets & Zeitlinger, 2002) Kotooussov, A.; Rose, L.; Wang, C.; International Conference on Structural Integrity and Fracture (2002 : Perth, W.A.)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 Strip yield model for a crack in a plate of arbitrary thickness(EMAS Publishing, 2002) Kotooussov, A.; Wang, C.; European Conference on Fracture (14th : 2002 : Krakow, Poland); Ostachowicz, W.M.; DulieuBarton, J.M.; Holford, K.M.; Krawczuk, M.; Zak, A.This paper presents new analytical results on the crack tip opening displacement (CTOD) for a through-the-thickness crack in an infinite plate of arbitrary thickness. These results are based on a new fundamental solution for an edge dislocation obtained earlier and published elsewhere. The analytical predictions of CTOD for various ratios of the crack length to the plate thickness are compared with an independent three-dimensional elasto-plastic finite element (FE) study. It is shown that both analytical and numerical results are in a good agreement when the numerical calculations are not affected by the size of the FE mesh and finite boundaries of the FE model.Item Metadata only Plastic deformation at a notch in a finite thickness plate(World Scientific, 2002) Wang, C.; Kotooussov, A.; Australasian Congress on Applied Mechanics (3rd : 2002 : Sydney, N.S.W.)Item Open Access Cold cracking and segregation in multipass welds of a quenched and tempered steel(ASM International, 2002) Powell, G.; Linton, V.; Brown, I.; Davidson, J.; International Conference on Trends in Welding Research (6th : 2002 : Phoenix, Ariz. USA.); al, S.Item Metadata only Three-dimensional solutions for stress concentrators in transversally isotropic plates(World Scientific, 2002) Kotooussov, A.; Wang, C.; Australasian Congress on Applied Mechanics (3rd : 2002 : Sydney, N.S.W.)Item Metadata only Calculation of the stress intensity factor for small-to-medium cracks with applications to shape optimisation problems(World Scientific, 2002) Kotooussov, A.; Jones, R.; Australasian Congress on Applied Mechanics (3rd : 2002 : Sydney, N.S.W.)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 Features of fatigue crack growth due to repeated thermal shock(Blackwell Science Ltd, 2002) Kerezsi, I.; Price, J.; Kotooussov, A.Thermal shock loading, such as that which occurs when a hot material is sprayed with cold water, produces a very high stress level near the exposed surface that eventually may lead to the development of cracks. Further growth of the cracks under repeated thermal shock is a very complex phenomenon due to the transient nature of the highly non-linear thermal stresses and the strong influence of the environment. There are cases in industry where cracks created by thermal shocks have arrested and stopped, and others where the cracks have progressed. Understanding this difference in behaviour is very important to the operators of pressure plant. This paper describes an experimental examination of crack growth in pressure vessel steel specimens exposed to repeated thermal shock. A test-rig that achieves large-scale thermal shocks through the repeated water quenching of heated flat plate specimens is used. The effect of steady-state loads on the growth is also analysed. Environmental effects due to the aqueous nature of the testing environment are found to be a major contributor to the crack growth kinetics.Item Metadata only Three-dimensional solutions for transversally isotropic composite plates(Elsevier Sci Ltd, 2002) 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 generalised 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 circular inclusion are derived. © 2002 Elsevier Science Ltd. All rights reserved.Item Metadata only Fundamental solutions for the generalised plane strain theory(Pergamon-Elsevier Science Ltd, 2002) Kotooussov, A.; Wang, C.This paper presents some fundamental solutions of the three-dimensional stress distribution pertaining to a point force and an edge dislocation in an infinite plate of arbitrary thickness. These solutions are obtained using the generalised plane strain theory, which assumes that the through-the-thickness extensional strain is uniform in the thickness direction. These solutions recover, as special cases, the plane-strain solutions of the classical theory of elasticity close to the source and the plane-stress solution at large distance away from the source. Using these new solutions, the problem of a through-crack in an infinite plate of arbitrary thickness has been solved analytically. © 2002 Elsevier Science Ltd. All rights reserved.Item Metadata only Three-dimensional stress constraint in an elastic plate with a notch(Pergamon-Elsevier Science Ltd, 2002) Kotooussov, A.; Wang, C.This paper presents analytical solutions for the three-dimensional stress distribution around typical stress concentrators in an isotropic plate of arbitrary thickness. Based on the assumption of a generalised plane-strain theory, which assumes that the through-the-thickness extensional strain is uniform in the thickness direction, an exact three-dimensional solution has been obtained for an annulus subjected to arbitrary loading along its edges. Emphasis has been placed on the through-the-thickness stress constraint, which is a pre-requisite to analysing the effect of plate thickness on the elastic-plastic deformation at a notch root. Important results are presented on the effects of the plate thickness and Poisson's ratio on the in-plane stress concentration factor and the out-of-plane stress constraint factor. By extending the theoretical method to a plate with a non-circular notch, an approximate solution has been obtained for the through-the-thickness constraint factor in a plate with a V-shaped notch having a circular tip. The present solutions have been shown to correlate well with numerical results obtained using the finite element method. © 2002 Published by Elsevier Science Ltd.Item Metadata only Method for calculating the stress intensity factor for small-to-medium edge cracks(Kluwer Academic Publ, 2002) Kotooussov, A.; Jones, R.This paper presents a new and relatively simple engineering method for calculating the stress intensity factors for small-to-medium cracks emanating from a notch under arbitrary loading. The formulation can be used in calculating the fatigue life of notched components as well as in the shape optimisation problems with durability constraints. Several examples are considered to demonstrate the advantages of the present method in comparison with both existing approximate approaches and finite element techniques.Item Metadata only On a thermo-mechanical effect and criterion of crack propagation(Kluwer Academic Publ, 2002) Kotooussov, A.A thermo-mechanical effect from partial conversion of fracture work into heat energy during crack propagation is considered with a simple mathematical model. It is assumed that the heat production zone in the vicinity of the crack tip is very small. Thus, the crack propagation process can be viewed as propagation of the crack in elastic material with a point thermal heat source fixed at the tip of the crack. This thermal heat source generates its own temperature and stress fields around the crack tip. As shown in this paper it also generates a negative stress intensity factor that specifies fracture mode I and has to be accounted for in the energetic fracture criterion. The model developed may help to explain many experimental observations such as the increase in the specific surface energy that accompanies an increase in the crack speed and why fracture mode I has a special role in crack propagation phenomena.Item Metadata only Relationship of laboratory tests of rock bolt SCC to service failures of rock bolts(TMS, 2003) Gamboa, E.; Atrens, A.; International Conference on Hydrogen Effects on Material Behavior and Corrosion Deformation Interactions (2002 : Moran, Wyo.); Moody, N.The stress corrosion cracking of rock bolts has been explored using Linearly Increasing Stress Tests (LIST). In LIST testing, a sample is exposed to the environment of interest and the stress is slowly increased until failure. SEM examination of the fracture surfaces is used to help identify the fracture mechanism. Rock bolt steel subjected to LIST testing in air and distilled water showed ductile failure and a dimple rupture failure surface. In contrast, rock bolt steel subjected to LIST testing in dilute sulphate/chloride solutions showed subcritical crack growth followed by brittle fracture. Analyses of rock bolts, which have failed in service, have indicated similar failures. The LIST test in the sulphate pH 2.1 provides a good foundation for a test to mimic service SCC, to be used to study the influences of rock bolt metallurgy and to explore countermeasures to service SCC. The transgranular nature of the SCC fracture, and the fact that SCC occurs at room temperature in the sulphate pH 2.1 solution point to the likelihood that the SCC mechanism probably involves hydrogen. Current work is (1) exploring the details of the fracture mechanism, (2) carrying out a detailed fractographic comparison between the service failures and the sulphate pH 2.1 fractures, and (3) exploring the issue of environment specificity.Item Metadata only Fractography of SCC features for rock bolts(2003) Gamboa, E.; Atrens, A.; International Conference on Environmental Degradation of Engineering Materials (2nd : 2003 : Bordeaux, France)