In this thesis, an efficient rotation-free (RF) triangle is proposed and applied to drape/cloth simulations in which the cloth often under large displacements and rotations. The RF model is a class of thin plate/shell computational models possessing only 3 translational degrees of freedom per director whilst their domains of influence are larger than their domains of integration. An important advantage of RF models is that they do not use rotational degrees of freedom and, thus, are not plagued by the complication in finite rotations. Among the quadrilateral and triangular RF models, the latter possesses no practical restriction on the nodal distribution and appears to be a good candidate for drape/cloth simulations. The geometrical linear formulation of the RF model is firstly considered. For straight beams and plates, the curvature is directly obtained through a complete quadratic interpolation of the transverse deflection. For linear curved beams and shells, the curvature change is again derived by the interpolation and the transverse deflection is through projection. The linear RF model is then extended to the geometrical nonlinear analyses by using the corotational framework as well as the small strain and small curvature assumptions. For the RF straight beam and plate, constant tangential bending stiffness matrices which do not need to be updated during the iterative solution process are derived. For the RF curved beam and shell, the bending energies and bending internal forces become a bit complicated. However, the tangential bending stiffness matrices can still be approximated by using the constant matrices as if they are initially straight/flat. The constant approximation exhibits negligible adverse effect on the convergence. Comparing with other exiting RF models, the present RF triangle is simple and physical yet its accuracy is competitive. In its application to static drape simulations, realistic drape configurations with obvious folds are predicted. The RF beam is extended to consider static and dynamic analyses of cable structures. Under the same nodal distributions, the present RF model can tolerate larger load increment and time step in static and explicit dynamic analyses, respectively, with respect to the two-node C0beam finite element model. For virtual sewing and dynamic cloth simulations, an integrated system is developed by synergizing the RF triangle, explicit time integration, adaptive remeshing, collision handling, human body modeling, sewing forces and a supplementary bending energy to suppress the non-physical sharp fold formation. The predicted steady-state configurations of the garments after sewing appear to be realistic and agree with our daily perception. The predictions for cloth dynamic deformations on human body model also look realistic and natural. This thesis proposes a simple and efficient rotation-free triangle which is especially suitable for the problems involving large displacements and rotations. Its application in drape/cloth simulations and integration of various techniques in cloth simulations are explored. The present study is of significance in cloth simulations. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Not available / text

The hydration of cement in concrete is exothermic, which means it gives off heat. In large elements, the heat caused by hydration can dissipate at the surface, but is trapped in the interior, resulting in potentially large thermal gradients. The thermal expansion of concrete is greater at higher temperatures, so if the temperature differential between the surface and the interior becomes too great, the interior will expand more than the exterior. When the thermal stress from this mis-matched expansion exceeds the tensile strength of the material, the concrete will crack. This phenomenon is referred to as thermal cracking. Accurate characterization of the progress of hydration of a concrete mixture is necessary to predict temperature gradients, maximum concrete temperature, thermal stresses, and relevant mechanical properties of concrete that will influence the thermal cracking risk of concrete. Calorimetry is the most direct test method to quantify the heat evolution from a concrete mixture. There is currently no model, based solely on calorimetry, which completely describes the effects of mixture proportions, cement and SCM chemistry, and chemical admixture dosages on the temperature sensitivity and adiabatic temperature rise of concrete. The objective of this study is to develop a comprehensive model to describe these effects. First, the temperature sensitivity of the hydration reaction (described with activation energy, E[subscript a]) is needed to accurately predict the behavior of concrete under a variety of temperature conditions. A multivariate regression model is from isothermal calorimetry testing to describe the effects of water-cementitious materials ratio, cement chemistry, supplementary cementing materials, and chemical admixtures on the E[subscript a] of portland cement pastes. Next, a multivariate regression model is developed from semiadiabatic calorimetry testing that predicts the temperature development of concrete mixtures based on mixture proportions, cement and SCM chemistry, and chemical admixture dosages. The results of the models are validated using data from literature. The final model provides a useful tool to assess the temperature development of concrete mixtures, and thereby reduce the thermal cracking risk of the concrete structure.

No description available.

M. Tech. Polymer Technology / Reduced carbon dioxide emissions, improved fuel economy and better performance are just but a few pressures that have continued to define the automotive industry, globally. Low-cost and light weight materials have continually been used to replace metals as conventional raw materials in the manufacturing of automotives. Polymers have been a material of choice for meeting these demands; mainly due to their versatility, ease of processing and giving the manufacturers an option of parts integration. The industry has experienced remarkable product improvement from metal-to-plastic conversion and hence, further the plastic-to-plastic refinement of vehicle parts, from the interior, to body panels and to engine parts. Glass-filled polyamide 66 (PA66) composites have been extensively used in the production of engine components since post World War II era, which has paved the way for glass-filled polyamide 6 (PA6) composites, which has a lower melting point than PA66, to be used in technical applications for vehicle engine parts. This work attempts to investigate the use of layered double hydroxide (LDH) clay, the so called "anionic" clays for the preparation of PA6/LDH composites. In this study, PA6/LDH composites were prepared and the effect of organic modification of magnesium (Mg)-aluminium (Al) LDH clay was investigated. The aim of this research was to investigate the effect of organically modified and "unmodified" commercial Mg-Al LDH on the thermal, mechanical and physical properties of PA6 composites.

No description available.

Nonwovens represent one of the booming sectors in the textile industry today with a significant projected growth both domestically and globally. At present, cotton is supplanted by synthetic fibers in nonwovens, thereby limiting its utilization in an important market sector. One of the major challenges for cotton is the high variability and lack of uniformity associated with fiber properties. Currently, manufacturers do not take this variability into account while selecting cotton for nonwovens. Therefore, it is essential to understand the effect of fiber properties on the nonwoven fabric characteristics in order to address this problem of variability. Bridging this knowledge gap can help increase cotton’s market share in the nonwoven sector and maintain its competitiveness in the fiber market. This project was an exploratory study to investigate the effect of cotton fiber properties on nonwoven fabric properties. Twenty different samples of Upland cotton with various combinations of fiber length and maturity parameters were used for this research. The fabric mechanical properties – tensile and burst strength, pore structure characteristics and permeability were measured and investigated in this study. The relationships between various raw fiber properties and the measured fabric characteristics were analyzed. The breaking strength of the fabric showed significant relations with fiber length and maturity. Using multiple regression analysis, an equation was derived to predict the specific breaking strength of the fabric from the mean fiber length and maturity ratio values of its constituent fibers. Though bursting strength and permeability showed significant single relations with several fiber properties, the multiple regression analysis returned a single significant predictor in each case – fiber length and fabric density respectively. Results observed from this study show that the constituent fiber attributes have significant relationships with the nonwoven fabric characteristics. Taking these fiber properties into account during raw material selection for cotton nonwovens would be advantageous as manufacturers can optimize quality, and also predict final product characteristics. Future studies focusing on the inter-fiber interactions in cotton nonwovens, comparisons between 100% cotton and synthetic blended nonwovens etc. will help gain better understanding, and contribute towards improving cottons marketability and utilization in the nonwoven industry. / text

published_or_final_version / abstract / toc / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy