No description available.

Pattern formation, i.e., the outcome of self-organization, has fascinated scientists for centuries. A large effort was devoted to understand the formation of regular patterns in dissipative structures. More recently, it appears that self-organized structures could also be achieved near equilibrium. There is a great variety of physical and chemical systems that, near equilibrium, exhibit periodic patterns. For instance, stripes or bubbles could be observed in thin films of magnetic garnet, superconducting materials, block copolymers, liquid crystals, phospholipids, and ferrofluids. Wrinkling instability of compressed rigid membranes on soft elastic substrates leads also to the formation of periodic patterns near equilibrium. Since the seminal paper of Bowden et al. (Nature 1998), various systems were proposed to generate nano- and micrometric wrinkles via the application of compressive stresses to multilayers. In addition to its purely fundamental interest, these instabilities also offer a new route to build in a simple, cost-effective, and well-defined way nano- and microstructured surfaces without the use of the traditional, robust techniques developed in the microelectronics industry. In this thesis, we develop a new system, metal-polymer-substrate trilayers, that exhibit wrinkling when heated above the glass transition temperature of the polymer. We explain in detail the mechanism at the origin of wrinkling and expand existing models to obtain a complete description of the relevant parameters that govern both the amplitude and the wavelength of the obtained pattern. In light of this, we show that by playing with the rheological properties of the polymer we are able to control precisely the geometry of the wrinkles. Furthermore, to generate surfaces with a tailor-made buckling pattern, we develop an original variant of the experiments. We tune the boundary conditions at the polymer-substrate interface by chemically patterning the substrates with regions of high and low adhesion. In this way, we obtain patterns with wrinkles being oriented differently above the sticky and the slippery regions. This last result is very surprising since it seems, at first sight, unrealistic to imagine that the chemical nature of the substrate could affect the elastic instability of the skin through a micron-thick polymer film. To explore wrinkled patterns with complex morphologies, we couple the wrinkling instability with solvent diffusion. Molecular diffusion in the polymer layer triggers the transition from an unwrinkled to a wrinkled state, provided that stimuloresponsive mutlilayers are used. The wrinkled pattern obtained is determined by the geometry of the diffusion process. To understand this surprising observation, we explain in detail how the scalar field related to the solvent concentration affects so strongly the elastic instabilities usually determined by the tensorial stress field. This mechanism allows us thus to grant exotic stress distributions which lead to very intriguing patterns (e.g. parallel or radial folds, herringbones). Interestingly, we find that under specific conditions, a hierarchical wrinkled morphology, i.e. pattern of wrinkles branching into generations of ever-higher folds, develops. We study other manifestations of hierarchical structures existing around us. In this frame, we derive a general concept that a plate constrained at one edge (with a fixed wavelength) but free at the opposite one evolves naturally to larger wavelengths to minimize its bending energy. We show theoretically that the evolution results from a compromise between the gain in bending energy and the energetic penalties related to the change of wavelength. We demonstrate the universality of these concepts by showing that our commonplace suspended curtain behaves like nanometer-thick polystyrene films deposited on water and further compressed. We close this thesis by making a short review of the main applications related to wrinkling that are already described in literature and develop in detail one of them, the use of wrinkling to investigate cell contact guidance.

This thesis presents a new method for the controllable damping of deformable objects. The method evolves from physically based techniques; however, it allows for non-physical, but visually plausible motion. This flexibility leads to a simple interface, with intuitive control over the behaviour of the material. This method is particularly suited for strongly damped materials, which account for the majority of objects of interest to animation, since it produces non-oscillatory behaviour. This is similar to critical damping, except that it affects all modes independently. The new method is based on the minimization of a slightly modified version of total energy. This framework can be used to simulate many other physical phenomena, and therefore lends itself to coupling with other simulations. Implementation details for a simple example are given. Results are shown for varying parameters and compared to those produced by a traditional method.

Advances in the field of medicine have extended the average human life expectancy worldwide. As a result an increasing number of people will suffer from problems associated with their mineralized tissues and will require orthopedic and dental implants to restore their quality of life. Ideally, implants should have mechanical and structural properties compatible with the original mineralized tissue, and should also promote faster and stronger implant fixation. An improved understanding of the properties of mineralized tissues can help with the improvements of implants. This thesis focuses on improving the understanding of two aspects related to mineralized tissues and implant systems: the mechanical properties of peri-implant bone, and the mechanical, composition and structural properties of dentin and jawbone. Studies have shown that local delivery of alendronate, an anti-osteoporosis drug, enhances new bone formation; however, the effects of the drug on the elastic modulus of new formed bone are unknown. In this study, nanoindentation was used to evaluate and compare the elastic modulus of peri-implant bone with and without the presence of alendronate. To better understand the properties of dentin and jawbone, nanoindentation and qualitative backscattered electron imaging were used to measure their elastic modulus, mineral content and volume fraction, and regression analyses were used to establish correlation between the properties. In this thesis, mineralized tissue samples were collected from an animal study. To study the effects of alendronate on the elastic modulus of peri-implant bone, porous tantalum implants with three different coating treatments were used: non-coated (Ta), calcium phosphate coated (Ta-CaP), alendronate-immobilized-calcium-phosphate coated (Ta-CaP-ALN). The calcium phosphate coatings, with or without alendronate, increased the elastic modulus of peri-implant Ingrown Bone by approximately 22% (3GPa). The addition of alendronate did not significantly increase the elastic modulus of peri-implant. For the study of dentin and jawbone, regression analyses showed that the elastic modulus of dentin is strongly dependent on the porosity and to a lesser extent on the calcium content. The elastic modulus of jawbone and dentin were compared and the elasticmodulus of jawbone was generally higher than that of dentin while the mineral content was lower.

Abstract In this paper, the mechanical properties of carbon-fiber reinforced polyether-ether ketone (PEEK) with and lay-up subject to impact and temperature reaction have been investigated.The drop-weight impact tests were performed by a 4mm diameter semi spherical nosed projectile. Incident impact height adopts 0.8m and 1.6m incident height. After impact testing, the static tension tests were performed to measure the ultimate strengths and elastic modulus at 25¢J¡B75¢J¡B125¢J¡B145¢J,so that the effects of stacking sequence and the damage mechanism subjected impact at elevated temperature was obtained. By the parametric study and research , there are very important results as follow: The destructive crack of AS4/PEEK laminates subject to impact were arised from the tension sides toward the pressure sides, and the lay-up was more serious than the lay-up. Although more excellent ultimate strength than the lay-up, the must be quantities of decay When the incident height increase as well as elevated temperature. Keywords: Composite, Impact, Temperature, Strength, Elastic Modulus, Fracture.

Thesis (Ph. D.)--California Institute of Technology, 1977. UM #77-24,050. / Advisor names found in the Acknowledgments pages of the thesis. Title from home page (viewed 03/09/2010). Includes bibliographical references.

No description available.

No description available.

No description available.

No description available.