No description available.

No / Polypropylene sheets have been stretched at 160 °C to a state of large biaxial strain of extension ratio 3, and the stresses then allowed to relax at constant strain. The state of strain is reached via a path consisting of two sequential planar extensions, the second perpendicular to the first, under plane stress conditions with zero stress acting normal to the sheet. This strain path is highly relevant to solid phase deformation processes such as stretch blow moulding and thermoforming, and also reveals fundamental aspects of the flow rule required in the constitutive behaviour of the material. The rate of decay of stress is rapid, and such as to be highly significant in the modelling of processes that include stages of constant strain. A constitutive equation is developed that includes Eyring processes to model both the stress relaxation and strain rate dependence of the stress. The axial and transverse stresses observed during loading show that the use of a conventional Levy-Mises flow rule is ineffective, and instead a flow rule is used that takes account of the anisotropic state of the material via a power law function of the principal extension ratios. Finally the constitutive model is demonstrated to give quantitatively useful representation of the stresses both in loading and in stress relaxation.

No description available.

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

A finite element formulation for the shear-deformable analysis of beams, plates and shells, based on a strain energy expression defined in terms of total and flexural displacement components, is presented. The effects of transverse shear deformation are considered while the normal strain is neglected. The finite element representation requires independent descriptions of total and flexural displacement components. The flexural strain energy term involves second derivatives of flexural displacement component and thereby necessitates slope-compatible shape functions. This requirement is relaxed by adopting the 'discrete Kirchhoff' hypothesis for the flexural displacement component. An element of triangular shape is formulated for the analysis of laminated composite plates and shallow shells. Numerically exact integration is employed in the calculation of element stiffness matrix and corresponding load vectors. The resulting finite element possesses twelve degrees of freedom at each corner node of the triangle. Numerical results obtained for an extensive range of thickness and planform aspect ratios, laminate configurations, mesh sizes, edge conditions, types of loading and geometry of the structure demonstrate the efficacy of the finite element formulation. The element is applicable to a full range of thicknesss ratios. The present formulation is employed for dynamic and stability analysis of beams, as a precursor to the inclusion of these effects in the analysis of plates and shells.

No description available.

The stimuli response of a polymer – metal bilayer architecture was investigated. This solvent activated system showed a dynamic response when exposed to a particular solvent. Polymer wires were fabricated using a glass capillary array (GCA) as a template. The synthesized wires were then sputtered with silver and exposed to dichloromethane (DCM). The solvent activated response results in a number of physical distortions of which the circular deformation was the most predominant. The thicknesses of the metal coating and the direction of the solvent front were studied in an effort to determine their relationship to the observed wired deformations.

The aim of this study was to analyze water chemical samples and diatoms to determine if there are any differences between the sample points in deformations, tax numbers and metal contents. Furthermore the aim is to investigate whether there is a correlation between metals and deformations, to study the bioavailable content of metals and whether deformations and tax loss are area specific. The data is from the years 2015-2018 and comprises 114 sample points from water streams in northern Sweden. The data includes diatoms, deformations, tax numbers and content measurements from the metals As, Cu, Cd, Ni, Pb, U and Zn. Regression analysis was performed between the bioavailable content of metal (Cu, Ni, Pb, Zn) and dissolved content, and also between the metal contents and the deformations to investigate a possible correlation. Two different regression analyzes where made for the metal contents and the deformations, because there are two test points that have very high deformations (10,5% and 9,5%). The comparison between the different sample points shows that it is not obvious that elevated metal contents have an influence on the diatom community. The first regression analysis (n=114) for metals and deformations indicates that Ni and Zn are significant, both the bioavailable- and the dissolved content. The second regression analysis (n=112) indicates that the bioavailable content of Cu and the dissolved content of U are significant. For both analysis the coefficient of determination is far too low for it to be reliable. More studies need to be done, including more metals and diatom species.

Chan, Kai Leung. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leave 78). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.