Mechanical Properties of Cellular Materials

Cellular materials have useful properties that allow wide range of applications like absorbers of kinetic energy, thermal isolation and so on. They appear in nature (for instance cork and wood) or they can be manufactured (polymers). Nowadays the importance of cellular media is higher because new technologies allow to foam metals and ceramics and also other kinds of manufacturing are developed. Consequently the class of solids from which cellular media are formed as well as variety of the shape of these solids are wider than before. Thus better methodologies that describe the properties of cellular media are needed and the ones that allow to obtain explicit analytical results of the set of parameters that may describe the properties are preferable. This thesis is concerned with mechanical properties of cellular media in linear as well as non-linear range. New methodologies that are based on general homogenization theories of highly heterogeneous composites. They simplify the computation using structural theories and at the same time generalize and correct the previously developed methodologies based on structural theories. The new methodologies in linear range allow to obtain (Often in explicit analytical form) effective constitutive constants of any specific cellular medium with periodic microstructure. For members of group of media with random microstructure of special kind (which covers main part of natural effectively isotropic media) they yield (close enough) specific bounds on these constants. New methodology was also developed for establishing of general bounds on these constants of wide classes of cellular media and some new upper bounds were proved. In non-linear range attention was focused on plastic behaviour of the basic material and its influence on the effective non-linear behavior of the cellular material. Specifically the effective yield surface was investigated, and an industrial application was computedAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga