No description available.

No description available.

Typescript, etc. / Digitized by Kansas Correctional Industries

Photocopy of typescript. / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

The miniaturization of energy, chemical and biological systems for distributed and portable applications, known as process intensification, is realized by the enhancement in heat and mass transfer performance within high surface-to-volume ratio microchannels. Fabrication of devices for process intensification is achieved in part by microlamination techniques. These techniques consist of patterning, aligning, and bonding thin layers of material into monolithic devices. Even though the fabrication techniques used in microlamination are generally accurate and consistent, small amounts of dimensional variation in microlaminated structures can strongly affect the device performance. One significant finding of this dissertation is that fin warpage, which is commonly induced during bonding, generally has more adverse device performance effects than misalignment. A heat exchanger that contains fin warpage as small as 25 percent of the microchannel height (on the order of 10 ��m) needs to almost double the number of flow channels to gain the same thermal effectiveness as the uniform one. Therefore, the focus of this dissertation is to investigate, understand, and learn how to control the cause and effect of buckling warpage produced within microlaminated structures. The microlamination discussed in this dissertation is performed with a thermally-controlled registration process, which facilitates metallic bonding at elevated temperatures. Another finding of this dissertation is that the tolerance limits of the fixture used in this registration process exceed the accuracy of the machine tools used to produce the fixture. Fixture tolerance limits on the order of 10 ��m are necessary to align and bond laminae with thicknesses below 100 ��m. An alternative technique based on the compliance of the fixture is proposed in order to improve these limits. This technique helps compensate for the excessive registration force due to over-constrained bonding, which extends the range of fixture tolerance limit to over 100 ��m well within current process capability of machine tools. Another approach to controlling fin warpage, based on the induction of higher modes of fin buckling, is also discussed. An analytical evaluation shows that the effect of fin warpage is minor as the mode of buckling reaches mode 10. A preliminary experiment confirms that the induction of fin buckling into a higher mode can be achieved by constraining the fin at specific locations along the fin during microlamination. / Graduation date: 2002

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Bi-layered materials are a reduced weight derivative of the sandwich structure and are comprised of one thin skin face reinforced by a thick layer of low density material. Bi-layered materials are characterized by high flexural stiffness and are a viable alternative to conventional sandwich materials in applications where the functional requirements can be met without the second face sheet of the sandwich. For structural applications bi-layered materials are required to have oil canning and buckling resistance. This work addresses the buckling of shallow bi-layered arches using numerical and analytical approaches. A numerical, finite element model is developed to simulate the buckling phenomenon and the results were compared with known experimental data. An analytical model was developed using the energy method analysis and the buckling load was predicted from the minimum energy criterion. Comparison of the numerical and analytical results yielded fairly good agreement. An imperfection analysis conducted by means of the numerical model indicated that the load carrying capacity of bi-layered structures is reduced by up to 40% due to the presence of material and geometric imperfections. A parametric study conducted using the analytical model has been described to setup design guidelines for shallow bi-layered arches. It was found that the use of bi-layered structures can result in weight reduction of around 70% when compared with equivalent single layered structure.

Bi-layered materials are a reduced weight derivative of the sandwich structure and are comprised of one thin skin face reinforced by a thick layer of low density material. Bi-layered materials are characterized by high flexural stiffness and are a viable alternative to conventional sandwich materials in applications where the functional requirements can be met without the second face sheet of the sandwich. For structural applications bi-layered materials are required to have oil canning and buckling resistance. This work addresses the buckling of shallow bi-layered arches using numerical and analytical approaches. A numerical, finite element model is developed to simulate the buckling phenomenon and the results were compared with known experimental data. An analytical model was developed using the energy method analysis and the buckling load was predicted from the minimum energy criterion. Comparison of the numerical and analytical results yielded fairly good agreement. An imperfection analysis conducted by means of the numerical model indicated that the load carrying capacity of bi-layered structures is reduced by up to 40% due to the presence of material and geometric imperfections. A parametric study conducted using the analytical model has been described to setup design guidelines for shallow bi-layered arches. It was found that the use of bi-layered structures can result in weight reduction of around 70% when compared with equivalent single layered structure.

Thesis--University of Florida. / Manuscript copy. Vita. Description based on print version record. Bibliography: leaves 149-152.