Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Master)--İzmir Institute of Technology,İzmir, 2004 / Includes bibliographical references (leaves. 100).

Thesis (Master)--İzmir Institute Of Technology, İzmir, 2005. / Keywords: Aluminum matrix composites, thermal conductivity, sound insulation, foam, metal matrix composites, aluminum foam. Includes bibliographical references (leaves. 77-81).

Thesis (Master)--İzmir Institute of Technology, İzmir, 2005. / Keywords:crushing, aluminum foam, foam filling, energy absorber, composite tubes. Includes bibliographical references (leaves. 93-96).

This study is concerned with the mechanical behavior of open-cell aluminum foams. In particular the compressive response of aluminum foams is analyzed through careful experiments and analyses. The microstructure of foams of three different cell sizes was first analyzed using X-ray tomography. This included characterization of the polyhedral geometry of cells, establishment of the cell anisotropy and statistical distribution of ligament lengths, and measurement of the ligament cross sectional area distribution. Crushing experiments were performed on various specimen sizes in the principal directions of anisotropy. The compressive response of aluminum foams is similar to that of many other cellular materials. It starts with a linearly elastic regime that terminates into a limit load followed by an extensive stress plateau. During the plateau, the deformation localizes in the form of inclined but disorganized bands. The evolution of such localization patterns was monitored using X-ray tomography. At the end of the plateau, the response turns into a second stable branch as most cells collapse and the foam is densified. The crushing experiments are simulated numerically using several levels of modeling. The ligaments are modeled as shear-deformable beam elements and the cellular microstructure is mainly represented using the 14-sided Kelvin cell in periodic domains of various sizes. Other geometries considered include the perturbed Kelvin cell, and foams with random microstructures generated by the Surface Evolver software. All microstructures are assigned geometric characteristics that derive directly from the measurements. Unlike elastic foams, for elastic-plastic foams the prevalent instability is a limit load. The limit load can be captured using one fully periodic characteristic cell. The predicted limit stresses agree with the measured initiation stresses very well. This very good performance coupled with its simplicity make the characteristic cell model a powerful tool in metal foam mechanics. The subsequent crushing events, the stress plateau and desification were successfully reproduced using models with larger, finite size domains involving several characteristic cells. Results indicate that accurate representation of the ligament bending rigidity and the base material inelastic properties are essential whereas the randomness of the actual foam microstructure appears to play a secondary role. / text

A novel aluminum foam-polymer hybrid material was developed by filling a 10 pore per inch (0.39 pores per millimeter), 7 % relative density Duocel® open-cell aluminum foam with a thermoplastic polymer of trade name Elvax®. The hybrid was developed to be completely recyclable and easy to process. The foam was solution treated, air quenched and then aged for various times at 180˚C and 220˚C to assess the effect of heat treatment on the mechanical properties of the foam and to choose the appropriate aging condition for the hybrid fabrication. An increase in yield strength, plateau height and energy absorbed was observed in peak-aged aluminum foam in comparison with underaged aluminum foam. Following this result, aluminum foam was utilized either at the peak-aged condition of 4 hrs at 220˚C or in the as-fabricated condition to fabricate the hybrid material. Mechanical properties of the aluminum foam-polymer hybrid and the parent materials were assed through uniaxial compression testing at static ( de/dt = 0.008s-1 ) and dynamic ( de/dt = 100s-1 ) loading rates. The damping characteristics of aluminum foam-polymer hybrid and aluminum foam were also obtained by compression-compression cyclic testing at 5 Hz. No benefit to the mechanical properties of aluminum foam or the aluminum foam-polymer hybrid was obtained by artificial aging to peakaged condition compared to as-fabricated foam. Although energy absorption efficiency is not enhanced by hybid fabrication, the aluminum foam-polymer hybrid displayed enhanced yield stress, densification stress and total energy absorbed over the parent materials. The higher densification stress was indicative that the hybrid was a better energy absorbing material at higher stress than the aluminum foam. The aluminum foam was found to be strain rate independent unlike the hybrid where the visco-elasticity of the polymer component contributed to its strain rate dependence. The damping properties of both aluminum foam and the aluminum foam-polymer hybrid materials were found to be amplitude dependant with the hybrid material displaying superior damping capability.

A novel aluminum foam-polymer hybrid material was developed by filling a 10 pore per inch (0.39 pores per millimeter), 7 % relative density Duocel® open-cell aluminum foam with a thermoplastic polymer of trade name Elvax®. The hybrid was developed to be completely recyclable and easy to process. The foam was solution treated, air quenched and then aged for various times at 180˚C and 220˚C to assess the effect of heat treatment on the mechanical properties of the foam and to choose the appropriate aging condition for the hybrid fabrication. An increase in yield strength, plateau height and energy absorbed was observed in peak-aged aluminum foam in comparison with underaged aluminum foam. Following this result, aluminum foam was utilized either at the peak-aged condition of 4 hrs at 220˚C or in the as-fabricated condition to fabricate the hybrid material. Mechanical properties of the aluminum foam-polymer hybrid and the parent materials were assed through uniaxial compression testing at static ( de/dt = 0.008s-1 ) and dynamic ( de/dt = 100s-1 ) loading rates. The damping characteristics of aluminum foam-polymer hybrid and aluminum foam were also obtained by compression-compression cyclic testing at 5 Hz. No benefit to the mechanical properties of aluminum foam or the aluminum foam-polymer hybrid was obtained by artificial aging to peakaged condition compared to as-fabricated foam. Although energy absorption efficiency is not enhanced by hybid fabrication, the aluminum foam-polymer hybrid displayed enhanced yield stress, densification stress and total energy absorbed over the parent materials. The higher densification stress was indicative that the hybrid was a better energy absorbing material at higher stress than the aluminum foam. The aluminum foam was found to be strain rate independent unlike the hybrid where the visco-elasticity of the polymer component contributed to its strain rate dependence. The damping properties of both aluminum foam and the aluminum foam-polymer hybrid materials were found to be amplitude dependant with the hybrid material displaying superior damping capability.

Espumas de alumínio são materiais de estrutura porosa que combinam as propriedades de materiais celulares com as dos materiais metálicos. A espuma metálica, com porosidade acima de 70%, pode ser obtida principalmente pela via “metal líquido” e via “metalurgia do pó”. Este trabalho visa uma contribuição para o desenvolvimento da produção de espumas de alumínio via Metalurgia do Pó (MP), inédita no Brasil. Busca-se estudar e definir os parâmetros para produzir a espuma de alumínio e estruturas sanduíche através do processo de MP e por fim conhecer o seu comportamento mecânico. É proposta, também, uma otimização do processo, pois, atualmente, a etapa de compactação do pó ocorre através do processo de extrusão, ou compactação a quente ou laminação, ou ainda a combinação desses. Para definir os parâmetros do processo foi estudada a condição de mistura, além da proporção do pó de alumínio e o agente expansor (TiH2). Foram estudadas as condições do processo de espumagem variando temperatura e tempo. A partir desses resultados foram obtidas as estruturas sanduíche, sendo que o foco foi tubos metálicos de aço preenchidos por espuma de alumínio. Posteriormente, foi estudado o comportamento mecânico da espuma e dos tubos preenchidos com espuma através dos ensaios de compressão e flexão. Os resultados das propriedades das espuma foram comparados com as propriedades previstas através de equações propostas por Ashby et. al.. Os resultados indicam a real possibilidade de realizar apenas a compactação axial a frio do pó metálico, atingindo densidade superior a 95% do material denso com 450 MPa de pressão de compactação. O processo de mistura dos pós mais adequado foi o realizado em misturador convencional do tipo “duplo V” por 2 horas, obtendo uma boa homogeneidade. A condição mais adequada de obtenção de espuma foi com a proporção de mistura de 1,0% de TiH2, com espumagem em 710oC por 10 minutos. Os ensaios mecânicos mostraram que os tubos preenchidos com espuma de alumínio apresentam um aumento considerável nas propriedades. / Aluminum foams are materials of porous structure that combine the properties of cell material with those of metallic materials. The metal foam, with porosity above 70%, can be achieved mainly by the "liquid metal route" and by "powder metallurgy". This study aims to contribute to the development of aluminum foam production by powder metallurgy process (PM), unprecedented in Brazil. The objective is to study and define the parameters for producing aluminum foam and sandwich structures by the process of PM, and understand its mechanical behavior. It is proposed also a process optimization, since nowadays the powder compaction phase takes place by the process of extrusion, hot compression or rolling, or even a combination of these. To establish the process parameters, the condition of mixing was studied, as well as the amount of aluminum and blowing agent (TiH2) powder. Were also studied the foaming process conditions by varying the temperature and time. From these results were obtained the sandwich structures, being the focus on steel metal tubes filled with aluminum foam. Subsequently, it was studied the mechanical behavior of the foam and the tubes filled with foam through bending and compression tests. The results of the properties of the foam were compared with the properties predicted by equations proposed by Ashby et. al .. The results showed real possibility to perform only cold axial compression of the metal powder, reaching a density greater than 95% with 450 MPa of compaction pressure. The most adequate mixing of the powders process was carried out in a conventional mixer such as "double V" for 2 hours to give a good homogeneity. The best condition for obtaining foam was with the mixing amount of 1.0% TiH2, with foaming at 710oC for 10 minutes. The mechanical tests showed that the tubes filled with aluminum foam present a considerable increase in the properties.

Espumas de alumínio são materiais de estrutura porosa que combinam as propriedades de materiais celulares com as dos materiais metálicos. A espuma metálica, com porosidade acima de 70%, pode ser obtida principalmente pela via “metal líquido” e via “metalurgia do pó”. Este trabalho visa uma contribuição para o desenvolvimento da produção de espumas de alumínio via Metalurgia do Pó (MP), inédita no Brasil. Busca-se estudar e definir os parâmetros para produzir a espuma de alumínio e estruturas sanduíche através do processo de MP e por fim conhecer o seu comportamento mecânico. É proposta, também, uma otimização do processo, pois, atualmente, a etapa de compactação do pó ocorre através do processo de extrusão, ou compactação a quente ou laminação, ou ainda a combinação desses. Para definir os parâmetros do processo foi estudada a condição de mistura, além da proporção do pó de alumínio e o agente expansor (TiH2). Foram estudadas as condições do processo de espumagem variando temperatura e tempo. A partir desses resultados foram obtidas as estruturas sanduíche, sendo que o foco foi tubos metálicos de aço preenchidos por espuma de alumínio. Posteriormente, foi estudado o comportamento mecânico da espuma e dos tubos preenchidos com espuma através dos ensaios de compressão e flexão. Os resultados das propriedades das espuma foram comparados com as propriedades previstas através de equações propostas por Ashby et. al.. Os resultados indicam a real possibilidade de realizar apenas a compactação axial a frio do pó metálico, atingindo densidade superior a 95% do material denso com 450 MPa de pressão de compactação. O processo de mistura dos pós mais adequado foi o realizado em misturador convencional do tipo “duplo V” por 2 horas, obtendo uma boa homogeneidade. A condição mais adequada de obtenção de espuma foi com a proporção de mistura de 1,0% de TiH2, com espumagem em 710oC por 10 minutos. Os ensaios mecânicos mostraram que os tubos preenchidos com espuma de alumínio apresentam um aumento considerável nas propriedades. / Aluminum foams are materials of porous structure that combine the properties of cell material with those of metallic materials. The metal foam, with porosity above 70%, can be achieved mainly by the "liquid metal route" and by "powder metallurgy". This study aims to contribute to the development of aluminum foam production by powder metallurgy process (PM), unprecedented in Brazil. The objective is to study and define the parameters for producing aluminum foam and sandwich structures by the process of PM, and understand its mechanical behavior. It is proposed also a process optimization, since nowadays the powder compaction phase takes place by the process of extrusion, hot compression or rolling, or even a combination of these. To establish the process parameters, the condition of mixing was studied, as well as the amount of aluminum and blowing agent (TiH2) powder. Were also studied the foaming process conditions by varying the temperature and time. From these results were obtained the sandwich structures, being the focus on steel metal tubes filled with aluminum foam. Subsequently, it was studied the mechanical behavior of the foam and the tubes filled with foam through bending and compression tests. The results of the properties of the foam were compared with the properties predicted by equations proposed by Ashby et. al .. The results showed real possibility to perform only cold axial compression of the metal powder, reaching a density greater than 95% with 450 MPa of compaction pressure. The most adequate mixing of the powders process was carried out in a conventional mixer such as "double V" for 2 hours to give a good homogeneity. The best condition for obtaining foam was with the mixing amount of 1.0% TiH2, with foaming at 710oC for 10 minutes. The mechanical tests showed that the tubes filled with aluminum foam present a considerable increase in the properties.

Espumas de alumínio são materiais de estrutura porosa que combinam as propriedades de materiais celulares com as dos materiais metálicos. A espuma metálica, com porosidade acima de 70%, pode ser obtida principalmente pela via “metal líquido” e via “metalurgia do pó”. Este trabalho visa uma contribuição para o desenvolvimento da produção de espumas de alumínio via Metalurgia do Pó (MP), inédita no Brasil. Busca-se estudar e definir os parâmetros para produzir a espuma de alumínio e estruturas sanduíche através do processo de MP e por fim conhecer o seu comportamento mecânico. É proposta, também, uma otimização do processo, pois, atualmente, a etapa de compactação do pó ocorre através do processo de extrusão, ou compactação a quente ou laminação, ou ainda a combinação desses. Para definir os parâmetros do processo foi estudada a condição de mistura, além da proporção do pó de alumínio e o agente expansor (TiH2). Foram estudadas as condições do processo de espumagem variando temperatura e tempo. A partir desses resultados foram obtidas as estruturas sanduíche, sendo que o foco foi tubos metálicos de aço preenchidos por espuma de alumínio. Posteriormente, foi estudado o comportamento mecânico da espuma e dos tubos preenchidos com espuma através dos ensaios de compressão e flexão. Os resultados das propriedades das espuma foram comparados com as propriedades previstas através de equações propostas por Ashby et. al.. Os resultados indicam a real possibilidade de realizar apenas a compactação axial a frio do pó metálico, atingindo densidade superior a 95% do material denso com 450 MPa de pressão de compactação. O processo de mistura dos pós mais adequado foi o realizado em misturador convencional do tipo “duplo V” por 2 horas, obtendo uma boa homogeneidade. A condição mais adequada de obtenção de espuma foi com a proporção de mistura de 1,0% de TiH2, com espumagem em 710oC por 10 minutos. Os ensaios mecânicos mostraram que os tubos preenchidos com espuma de alumínio apresentam um aumento considerável nas propriedades. / Aluminum foams are materials of porous structure that combine the properties of cell material with those of metallic materials. The metal foam, with porosity above 70%, can be achieved mainly by the "liquid metal route" and by "powder metallurgy". This study aims to contribute to the development of aluminum foam production by powder metallurgy process (PM), unprecedented in Brazil. The objective is to study and define the parameters for producing aluminum foam and sandwich structures by the process of PM, and understand its mechanical behavior. It is proposed also a process optimization, since nowadays the powder compaction phase takes place by the process of extrusion, hot compression or rolling, or even a combination of these. To establish the process parameters, the condition of mixing was studied, as well as the amount of aluminum and blowing agent (TiH2) powder. Were also studied the foaming process conditions by varying the temperature and time. From these results were obtained the sandwich structures, being the focus on steel metal tubes filled with aluminum foam. Subsequently, it was studied the mechanical behavior of the foam and the tubes filled with foam through bending and compression tests. The results of the properties of the foam were compared with the properties predicted by equations proposed by Ashby et. al .. The results showed real possibility to perform only cold axial compression of the metal powder, reaching a density greater than 95% with 450 MPa of compaction pressure. The most adequate mixing of the powders process was carried out in a conventional mixer such as "double V" for 2 hours to give a good homogeneity. The best condition for obtaining foam was with the mixing amount of 1.0% TiH2, with foaming at 710oC for 10 minutes. The mechanical tests showed that the tubes filled with aluminum foam present a considerable increase in the properties.