Michal Petrů

By Michal Petrů and Ondřej Novák

This chapter focuses on determination of mechanical properties of polyurethane foams applied in automotive industry and medicine. These materials have strong nonlinear viscoelastic behavior that is time dependent. A comprehensive description of their characteristics is very tough and difficult. Mechanical properties can to some extent be studied using mathematical models that need to be verified with measurements. This chapter describes selected mathematical relationships, rheological models, and also numerical simulations that can approximately describe mechanical properties. Mechanical properties of polyurethane foam are influenced by internal and external structure, shape and size of the cells, filling volume, and properties of the used polymer. Studied mechanical properties are contact pressures, stress distribution, and the dependence of stress on the strain rate.

Part of the book: Aspects of Polyurethanes

By Michal Petrů and Ivan Mašín

The mechanical behavior of plant seeds as a granular or particulate material dramatically differs from the mechanical behavior of solid materials. This difference is caused by the possibility of partially autonomous movement and rotation of seeds, their mutual contacts, or due to the occurrence of the second fluid phase among the seeds at the stage of their moving or processing. For obtaining the economic effects from the seeds (energy, nutrients, livestock, etc.), seeds must often be subjected to mechanical treatment. In this context application of mechanics as science concerned with the behavior of physical bodies when subjected to forces or displacements is very important and needed. One of the goals of this chapter is therefore to provide an overview for readers who are not primarily concerned with mechanics but who are interested in the behavior of seeds in the context of biology, agriculture, and pharmacy or food industry. This chapter is therefore focused on both an overview of the principles of mechanics of granular or particulate materials and the presentation of experimental results particularly in the area of mechanical extraction of oil from seeds.

Part of the book: Seed Biology

By Michal Petrů and Ondřej Novák

This chapter deals with studies of the mechanical properties of samples from long fiber-reinforced composite structures that would contribute to the optimization of the developed constructions made of them. First, the basic issues of composite structures reinforced with long fibers (carbon or glass) and generally of composites with the specification of parameters that would lead to the optimization of mechanical properties with respect to the theoretical strength are presented. Further, the possibilities and methods of measurements of composite reinforced with carbon and glass fibers are described. This is followed by the introduction of analytical models for the description of the transversal isotropic composite, where these mathematical relations allow the determination of unknown elastic constants and they are also important for the verification of numerical models. Finally, it is comprehensively outlined the problems of creating a numerical model of advanced composite fibrous structure for determining the mechanical properties, both through the description of the continuum, and complex numerical model with a structural configuration enabling approach to allow closer interaction among fibers and matrix. Compared to the averaged values obtained from experimental samples, numerical simulations show a similar trend of stress on strain, with results obtained from simulations.

Part of the book: Finite Element Method