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The exploitation of sandwich structures as a means toachieve high specific strength and stiffness is relatively new.Therefore, the knowledge of its damage tolerance is limitedcompared to other structural concepts such as truss bars andmonocoque plate solutions. Several aspects of the damage tolerance of sandwichstructures are investigated. The influence of impact velocityonresidual strength is investigated. Sandwich panels withfaces of glass fiber reinforced vinylester are impacted bothwith very high velocity and quasi static. The residual strengthafter impact is found to be similar for both cases of impactvelocity. Curved sandwich beams subjected to opening bending momentare studied. Faceñcore debonds of varying size areintroduced between the compressively loaded face sheet and thecore. Finite element analysis in combination with a pointstress criterion is utilized to predict the residual strengthof the beams. It is shown that it is possible to predict thefailure load of the beams with face-core debond. Using fractography the governing mode of failure ofcompressively NCF-carbon is characterized. Sandwich panelssubjected to compression after impact are shown to fail byplastic micro buckling. The residual compressive strength after impact of sandwichpanels is investigated. Sandwich panels with face sheets ofnon-crimp fabric (NCF) carbon are subjected to different typesof impact damages. Predictions of residual strength are madeusing the Budiansky, Soutis, Fleck (BSF) model. The residualstrength is tested, and the results are compared topredictions. Predictions and tests correlate well, and indicatethat the residual strength is dependent on damage size and notthe size of the damaged panel. A study of the properties of a selection of fiberreinforcements commonly used in sandwich panels is conducted.The reinforcements are combined with two types of core materialand three types of matrix. Also the influence of laminatethickness is tested. Each combination materials is tested inuni-axial compression, compressive strength after impact andenergy absorption during quasi static indentation. Thespecimens which are tested for residual strength are eithersubjected to quasi-static or dynamic impact of comparableenergy level. Prediction of the residual strength is made andcorrelates reasonably whith the test results. The tests showthat if weight is taken into account the preferred choice offiber reinforcement is carbon.

<p>The exploitation of sandwich structures as a means toachieve high specific strength and stiffness is relatively new.Therefore, the knowledge of its damage tolerance is limitedcompared to other structural concepts such as truss bars andmonocoque plate solutions.</p><p>Several aspects of the damage tolerance of sandwichstructures are investigated. The influence of impact velocityonresidual strength is investigated. Sandwich panels withfaces of glass fiber reinforced vinylester are impacted bothwith very high velocity and quasi static. The residual strengthafter impact is found to be similar for both cases of impactvelocity.</p><p>Curved sandwich beams subjected to opening bending momentare studied. Faceñcore debonds of varying size areintroduced between the compressively loaded face sheet and thecore. Finite element analysis in combination with a pointstress criterion is utilized to predict the residual strengthof the beams. It is shown that it is possible to predict thefailure load of the beams with face-core debond.</p><p>Using fractography the governing mode of failure ofcompressively NCF-carbon is characterized. Sandwich panelssubjected to compression after impact are shown to fail byplastic micro buckling.</p><p>The residual compressive strength after impact of sandwichpanels is investigated. Sandwich panels with face sheets ofnon-crimp fabric (NCF) carbon are subjected to different typesof impact damages. Predictions of residual strength are madeusing the Budiansky, Soutis, Fleck (BSF) model. The residualstrength is tested, and the results are compared topredictions. Predictions and tests correlate well, and indicatethat the residual strength is dependent on damage size and notthe size of the damaged panel.</p><p>A study of the properties of a selection of fiberreinforcements commonly used in sandwich panels is conducted.The reinforcements are combined with two types of core materialand three types of matrix. Also the influence of laminatethickness is tested. Each combination materials is tested inuni-axial compression, compressive strength after impact andenergy absorption during quasi static indentation. Thespecimens which are tested for residual strength are eithersubjected to quasi-static or dynamic impact of comparableenergy level. Prediction of the residual strength is made andcorrelates reasonably whith the test results. The tests showthat if weight is taken into account the preferred choice offiber reinforcement is carbon.</p>

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23020号 / 理博第4697号 / 新制||理||1674(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 時任 宣博, 教授 若宮 淳志, 教授 依光 英樹 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Lightweight structures in vehicles are a proven way to reduce fuel consumption and the environmental impact during the use. Lower structural weight can be achieved by using high performance materials such as composites or using the material efficiently as a sandwich structure. Traditional composite materials such as carbon or glass fiber reinforced polymers have high weight specific mechanical properties but are inherently brittle and expensive. They consist of at least two different materials making recycling a difficult endeavor.The best composite material would have good weight specific properties and is ductile, cheap and comprises of a reinforcement and matrix material based on the same recyclable material making recycling easy. In self-reinforced polymer (SrP) composite materials, reinforcing fibers and matrix material are based on the same recyclable thermoplastic polymer making recycling to a straightforward process. SrP composite materials are ductile, inexpensive and have a high energy absorption potential. The aim of this thesis is to investigate the potential of SrP composites in structural applications. Firstly, the quasi-static and dynamic tensile and compression properties of a self-reinforced poly(ethylene terephthalate) (SrPET) composite material are investigated confirming the high energy absorption potential. Sandwich structures out of only SrPET with a lattice core are manufactured and tested in quasi-static out-of-plane compression showing the potential of SrPET as core material. Corrugated sandwich structured out of only SrPET are manufactured and tested in out-of-plane compression over a strain rate range10−4 s−1 - 103 s−1. The corrugated SrPET core has similar quasi-static properties as commercial polymeric foams but superior dynamic compression properties. Corrugated sandwich beams out of only SrPET are manufactured and tested in quasi-static three-point bending confirming the high energy absorption potential of SrPET structures. When comparing the SrPET beams to aluminum beams with identical geometry and weight, the SrPET beams shows higher energy absorption and peak load. The experimental results show excellent agreement with finite element predictions. The impact behaviorof corrugated SrPET sandwich beams during three-point bending is investigated. When comparing SrPET sandwich beams to sandwich beams with carbon fiber face sheets and high performance thermoset polymeric foam with the same areal weight, for the same impact impulse per area, the SrPET shows less mid-span deflection. / <p>QC 20151012</p> / ECO2

Aluminium foam has a range of properties that are desirable in many applications. These properties include good stiffness and strength to weight ratios, impact energy absorption, sound damping, thermal insulation and non combustibility. Many of these characteristics are particularly attractive for core materials within sandwich structures. The combination of aluminium foam cores with thermoplastic composite skins is easily manufactured and has good potential as a multifunctional sandwich structure useful in a range of applications. This thesis has investigated the flexural behaviour of such structures using a combination of experimental and modelling techniques. The development of these structures towards commercial use requires a thorough understanding of the deformation and strain mechanisms of the structure, and this will, in turn, allow predictions of their structural behaviour in a variety of loading conditions. ¶ The experimental research involved the use of an advanced 3D optical measuring technique that produces realtime, full-field strain evolution during loading. This experimental characterisation of strain evolution in this class of sandwich structure under flexural loading is the first of its kind in the world. The experimental work studied the sandwich structure undergoing four-point bend testing. Initial studies compared the behaviour of the aluminium foam structure with a more traditional polymer foam sandwich structure. The aluminium foam structure was found to have equivalent or improved mechanical properties including more ductile deformation and an enhanced energy absorption. An investigation was conducted on the effect of core and skin thickness on the metal structure and a range of flexural behaviours were observed. Analysis of the strain distribution showed a complex development including localised effects from the non-uniform cellular structure of the material. An understanding of the variation with size is important in establishing design methods for utilising these structures. In particular, it is desirable that finite element simulations can be used to predict behaviour of these structures in a diverse range of loading conditions. This aspect was considered in the second half of this study. An existing constitutive model for aluminium foam, developed for use in compression energy absorption studies, was used to investigate finite element simulations of the flexural behaviour of the sandwich structure. The FE model was able to predict the general deformation behaviour of the thinner skinned structures although the magnitude of the load-displacement response was underestimated. It is suggested this may be related to the size effect on the input parameter characterisation. The strain distribution corresponded well with the experimental strain measurements. It was found a simple increase in the material model input parameters was able to more closely match the magnitude of the load-displacement response while maintaining the appropriate strain distribution. The general deformation shape of the model with the thicker skin corresponded reasonably well with the experimental observations. However, further work is necessary on the element failure criterion to capture the shear cracking observed. The strain distributions of the model predicted this failure with high strain concentrations matching those of the experimental contours. The last part of the thesis describes a parametric study on the effect of the foam material model input parameters on the flexural behaviour of the sandwich structure model. An important conclusion of this work is that this material model for aluminium foam can, with some development, be utilized to provide a viable method for simulating aluminium foam composite sandwich structures in flexural loading situations.

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.