ABSTRACT of the Doctoral Thesis

Modeling and Simulation of Highly Porous Open Cell Structures - Elasto-Plasticity and Localization versus Disorder and Defects

by Mathias H. Luxner (2006)

Cellular materials are a unique class of materials and can be found in nature (bone, wood, cork, etc.) as well as in engineering applications (in the cores of sandwich panels, crash protection, packaging, etc.). Their excellent properties such as high energy absorption potential, good formability, and excellent insulation capability are mainly determined by their microstructure.

The possibility of tailoring their overall properties for certain service conditions by controlling their microstructure makes them highly attractive for engineering applications. In this context the introduction of Rapid Prototyping techniques opens the possibility of building cellular structures with predetermined properties.

In addition to the ability to control the production process, an understanding of the mechanical behavior of cellular materials is crucial for the success of the designed material.

In the present thesis numerical simulations regarding the mechanical behavior of regular and irregular open cell structures are carried out with the focus on open cell structures fabricated by Rapid Prototyping.

In Chapter 2 several approaches regarding the modelling of open cell structures by means of the Finite Element Method are presented. The structures are treated as infinite and finite media, respectively, employing continuum element based models as well as beam element based models with and without an adaption of stiffness in the vicinity of the vertices. The linear elastic properties of various cell architectures are predicted and a comparison to experimental results is shown.

In Chapter 3 the investigations are extended to the nonlinear behavior of open cell materials, taking into account elastic-plastic bulk material behavior, large strain theory, and deformation localization.

Disordered structures are generated by randomly shifting the vertex positions of regular structures. The influence of structural disorder on the elastic anisotropy, the nonlinear mechanical response, the distribution of the mechanical energy, and the deformation localization is investigated for two different finite structures subjected to uniaxial compression.

The influence of the size and the shape of finite cellular structures on their mechanical response is discussed in Chapter 4. The nonlinear response and the deformation localization mechanisms of cuboidal and cylindrical finite samples subjected to uniaxial compression are compared.

Based on the findings of the previous chapters, new open cell structures with predetermined mechanical properties are introduced in Chapter 5. The design goal is high overall stiffness at low elastic anisotropy. Furthermore, their nonlinear properties are discussed and a comparison to experimental results is presented.

Finally, the effect of defects on the mechanical behavior of regular and disordered open cell structures is investigated in Chapter 6. Three different types of defects, all representing the same amount of missing struts, are introduced to cylindrical samples with varying lattice orientations and their nonlinear mechanical responses under uniaxial compression is compared.

revised 060621 (hjb)