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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
121

The effect of cathodic overprotection on the corrosion fatigue behaviour of API 5L X85 graded welded tubular joints

Smith, Alan T. January 1995 (has links)
No description available.
122

Flaw identification using the inverse dual boundary element method

Mellings, Sharon Christine January 1994 (has links)
No description available.
123

Crack analysis by distributed strain nuclei with application to indentation testing

Lin, Shiann January 1997 (has links)
No description available.
124

Multi-scale modelling of compressive behaviour of materials with pronounced internal microstructure

Winiarski, Bartlomiej January 2010 (has links)
Aviation and aerospace structural components made of composite laminates due to their internal structure and manufacturing methods contain a number of inter- and intracomponent defects, which size, dispersion and interaction alter significantly the critical compression strain level. While there are a plethora of theoretical and experimental work on the problems stability loss and fracture of composites with internal defects in the scope of classic problems of fracture mechanics, there are few theoretical and numerical analyses available for the nonclassical problems of fracture mechanics of composites compressed along layers with interface cracks. These analyses usually have been considered the simplest problems, where the composite material with pronounced microstructure and interface defects (cracks, delaminations) have been analysed as two-dimensional (2-D) continuum in the condition of plane strain state. In the scope of these analyses only parallel defects have been considered, allowing for the interpenetration of the stress-free crack faces, or assuming so-called interfacial cracks with connected edges. This thesis broadens knowledge in the area of non-classical problems of fracture mechanics. It investigates the effect of interfacial cracks interaction on the critical buckling strain in layered and fibrous composite materials under compressive static loading. The behaviour of composite is analysed on several length-scales, starting from a ply and laminate levels (in 2-D approximation), down to a single-fibre level (a full 3-D model). The statements of the problems are based on the model of piecewise-homogeneous medium model, the most accurate within the framework of the mechanics of deformable bodies as applied to composite materials with pronounced microstructure. All composite constituents are modelled as linear-elastic material, where both isotropic and anisotropic materials are considered depending on the length-scale. It is assumed that the moment of stability loss in the microstructure of materials is treated as the onset of the fracture process. Besides that, the critical strain that corresponds to loss of stability in the microstructure of the composite, either surface or internal instability, must be smaller than the critical strain that corresponds to loss of stability of the entire composite. This project involves parameterised variables, such as the crack size, the crack spacing, the layer volume fraction and the fibre volume fraction. At each length-scale two types of cracks are analysed, namely, cracks with stress-free crack faces and cracks with frictionless Hertzian contact of the crack faces. A number of finite-element models for each length-scale are developed, and are validated analytically and numerically. The models' ability to simulate practical composite structures to a useful degree of accuracy with suitable material properties is discussed. A number of parameters, which quantifies the interfacial crack interaction and crack faces contact interaction phenomena, are introduced and discussed. Qualitative discussion on the crack faces contact zones, post-critical behaviour of composites and crack propagation are presented and discussed. Finally, the subject areas for the future work are outlined.
125

Numerical simulation of fracture in plain and fibre-reinforced concrete

Bui, Thanh Tien, Civil & Environmental Engineering, Faculty of Engineering, UNSW January 2007 (has links)
Localised failure in quasibrittle materials is due mainly to the effects of combined shear and compression. Once the cohesion strength is reached, shear tractions generate slip and aggregate interlocking that cause dilatancy inducing crack opening. Further damage reduces the cohesion and dilatancy so that eventually only a residual friction state remains. The energy dissipated due to friction and interlocking needs to be considered in the constitutive law. Initially, a Mohr-Coulomb yield surface with a tension cut-off will be investigated. A compression cap will be included when the modelled interfaces are not appropriately aligned and compressive failure must be controlled. The evolution of the yield surface and the appropriate flow rules to be used in the interface/particle model, are questions which will be examined. The particle/interface model with plasticity concentrated at the interface nodes, which can produce the correct volumetric expansion, will also be studied. A composite model has been developed to represent the heterogeneity of concrete consisting of coarse aggregates, mortar matrix and the mortar-aggregate interface. The constituents of concrete are modelled using triangular elements with six interface nodes along their sides. Fracture is captured through a constitutive softening-fracture law at the interface nodes, which bound the elastic domain inside each element. The inelastic displacement at an interface node represents the crack opening, which is associated to the conjugate internodal force by a single branch softening law. The path-dependent softening behaviour is derived in irreversible rate formulation within a quasi-prescribed displacement control. At each event in the loading history, all equilibrium solutions for the prescribed mesh can be obtained and the critical equilibrium path with the minimum increment of external work adopted. The crack profile develops restrictively to the interface boundaries of the defined mesh. No re-meshing is carried out. Solutions to the irreversible rate formulation are obtained using a mathematical programming procedure in the form of a linear complementary problem. Other work is aimed at incorporating fibre reinforcement in the model. Fibre particles are modelled by introducing additional linear elements interconnecting distant interface nodes in the matrix media after the generation of matrix-aggregate structure.
126

On Coating Durability of Polymer Coated Sheet Metal under Plastic Deformation

Huang, Yu-Hsuan 2010 May 1900 (has links)
Polymer coated sheet metal components find diverse applications in many industries. The manufacturing of the components generally involves forming of sheet metal into the desired shape and coating of the formed part with organic coating. An alternative manufacturing route is to coat the sheet metal first before forming. The change in the manufacturing sequence can potentially improve cost and reduce environmental impact. This approach, however, requires the coating to survive the deformation process. Thus, the effect of plastic deformation on coating adhesion is of primary interest to many engineers and researchers. This research aims at developing a methodology to predict the adhesion of coating after metal forming processes. A pull-off apparatus that measures the coating pull-off stress was used to indicate the coating adhesion strength. Several types of specimen were designed to obtain uniaxial tension, biaxial tension, and tension-compression deformation modes on pre-coated sheet by using a uniaxial tensile tester. Experimental results from two selected polymer coated sheet metals show that coating adhesion was affected by plastic deformation. An analytical model based on a virtual interface crack concept was developed to indicate the adhesion potential of the coating-substrate interface. From interfacial fracture mechanics, the initial adhesion potential is defined as the energy release rate characterized by the virtual interface crack and the initial pull-off stress. The analytical model was used to predict coating adhesion loss after deformation in uniaxial tension mode. The analytical model predictions agreed well with experimental results. Finite element analysis tool was applied to simulate more complex deformation modes in stamping of coated sheet meals. The stress field near the interface crack tip was used to calculate the energy release rate and predict the adhesion loss under different deformation modes. The predictions obtained from numerical method are also in good agreements with the experimental results in biaxial tension and tension-compression modes. The research has led to a better understanding of the effects of plastic deformation on coating adhesion. The developed adhesion test methods can be used to generate useful information on coating durability for diverse practical use. It is also expected that the results of the research will facilitate the development of better polymer coated sheet metal to be used in sheet metal forming processes.
127

Processing improvement of moiré interferometry for accurate crack-tip deformation measurement

Kamil, Ridha. January 2001 (has links)
Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains v, 81 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 80-81).
128

Time-dependent, mixed-mode fracture of solid rocket motor bondline systems /

Wu, Jenq-dah, January 1999 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 130-135). Available also in a digital version from Dissertation Abstracts.
129

Experimental study and analytical modeling of translayer fracture in pultruded FRP composites

El-Hajjar, Rani Fayez. January 2004 (has links) (PDF)
Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2004. / Dr. Zureick, Abdul-Hamid, Committee Member; Dr. White, Donald, Committee Member; Dr. Saxena, Ashok, Committee Member; Dr. Jacobs, Laurence, Committee Member; Dr. Haj-Ali, Rami, Committee Chair; Dr. Armanios, Erian, Committee Member. Vita. Includes bibliographical references (leaves 164-172).
130

Fracture mechanics analysis of damage initiation and evolution in fiber reinforced composites /

Pupurs, Andrejs, January 2009 (has links)
Lic.-avh. Luleå : Luleå tekniska universitet, 2009.

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