<p>Many novel engineering materials such as metal foams, glass ceramics or hemp fiber-reinforced concrete are classified as porous materials and have wide use in many areas of applied sciences and engineering. Porous materials own their widespread use in engineering applications (e.g. spaceflight technology, energy conversion, or energy storage) to the combination of mutually beneficial properties, such as low relative density, heat insulation, high heat resistance, chemical resistance, or extreme hardness. Porous materials have small pores that may be open, connected, or closed and alongside mechanical loads might be subjected to thermal influence at the internal and the external boundaries. For example, plasma sprayed ceramic coatings consisting of randomly orientated fibers of various oxides are recently becoming popular in many rigid sealing concepts for solid oxide fuel cells due to their high-temperature operation range and better mechanical properties compared to conventional glass-ceramic sealing. But they are still subjected to the sharp stresses arising from the mismatch of thermal expansion coefficients of the cell components. Furthermore, plasma-sprayed coatings additionally bring some challenges during operation. Primarily mechanical properties, which are strongly coupled to their microstructural setup. This leads to the severe influence of porosities and micro cracks on the stiffness and fracture behavior. These characteristics and operational environment demand an understanding of the underlying porous microstructure and its influence on the material properties. The variation of pore structures at the microscopic level presents considerable challenges in understanding thermo-mechanical mechanisms in such porous material. Such variation in the underlying pore structure is usually ignored in continuous modeling. This is mainly due to the difficulty in capturing the complex relationship between macroscopic material properties and stochastic microscopic pore structure. In this presentation, the effect of a complex micropore morphology on effective thermo-mechanical properties of a porous material will be numerically investigated. A coupled thermo-mechanical problem is governed by the balance equations of linear momentum and energy, in which linear momentum equation is a function of Cauchy stress tensor and the body force per unit of deformed volume, while energy equation is defined by using the Fourier equation for heat transfer. To account for the variability in the pore shapes and sizes, we adopt the higher-order homogenization method. The second-order scheme used in this study incorporates third-order macroscopic second gradient deformation tensor into the kinematical macro–microscale transition. The developed formulation is fully coupled and encapsulates the two physics of the problem, through firstly determining the thermal parameters and then considering thermal effects onto the mechanical behavior. By employing this model we are able to solve a nonlinear and temperature dependency of porous materials’ deformation response at the microscopic level and then transmit this information to the macroscopic level. The new formulation is benchmarked against various tests to showcase its capability.</p>

Thermo-Mechanics of Heterogeneous Porous Material: A Second-Order Homogenization Approach

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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