Microstructure-related multifield-modelling for wood
The goal of this research project is the development of a multifield-model to describe the aging processes in wood related to the microstructure. In this regard the model shall consider mecha- nical, hygric and thermal impacts. Furthermore, the model is to be used to model degradation processes.
The durability of a wooden construction results from the external impacts and their mutual de- pendence. For example, there is a strong dependence of the mechanical behavior on the hygric and thermal state. This dependence can be represented in the form of moisture and tempe- rature dependent stiffness and strength parameters and additional deformation components. Moreover, the thermal and hygric state affects the long-term behavior of wood, i.e. the creep deformation. In addition, the degradation processes are affected by the hygric and thermal state. Degradation of the wooden structure by wood-destroying fungi occurs exclusively in a specific climatic range. The degradation of cellulose and lignin, which are the main components of wood, leads to a mass reduction on the one hand and to a softening on the other hand. With a model, which depicts the individual coupled fields, a statement about the durability of woo- den components can be made.
The decribed processes can be explained by the porous microstructure of wood. Regarding the microstructure, wood consists of cells, which are composed of a cell wall and a cavity, the cell lumen. For the illustration of this cell structure, the discretization is to be based on the PFEM (polygonal finite element method). The PFEM extends the common FEM by polygonal elements. Thus it is possible to represent a wood cell with only two elements. The cell lumen can be discretized with a convex polygonal shaped element and the cell wall with a non-convex polygonal shaped element.