Deciphering wood mechanobiology through multiscale modeling

Construction industry has discovered timber as eco-friendly and promising alternative to conventional building materials. However, in order to use timber as building material, it has to fulfill certain requirements in terms of quality and workability. In this context, the question is raised whether intentionally influencing the dynamics and progress of tree growth may be a beneficial factor. This project deals with exactly this question, addressing the hypothesis that multiscale modeling of the mechanical and biological aspects of wood growth provides the sought-after insights leading to an improved understanding. To that end, multiscale tree mechanics models will be developed, relating the mechanical features of wood on the microstructural level to the corresponding structural behavior. Furthermore, the mechanobiological regulation of growth processes will be fundamentally taken into account. Hence, the coupled and combined effects of both biological and mechanical factors will be taken into consideration for the development of respective wood growth models. All modeling methods will be coupled and tested thoroughly based on comparison of model predictions with respective experimental data available in the open literature. This way, the field of wood mechanobiology in particular, and of plant mechanobiology in general will be fundamentally extended, by introducing mathematical modeling into a research field which was so far driven by mainly experimental approaches. In the long run, the foreground of this project may serve as important basis for sustainably reducing detrimental environmental effects in timber industry.

In the course of the project WOODgrowth, a mathematical model was developed based on two fundamental modeling concepts. On the one hand, a micromechanics model serves for upscaling of eigenstrains to the macroscopic level. Notably, eigenstrains originate in the cell walls of hardwoods during the formation of so-called tension wood. They lead, in further consequence, to the reorientation of such wood structures, and are hence a key mechanism in wood growth. In the model developed in WOODgrowth, the such upscaled eigenstrains then enter a Euler-Bernoulli-type beam model, by means of which both simple and more complicated wood structures can be replicated. The such obtained coupled model could be calibrated based on experimental data provided by literature, and applied. The modeling approach developed in WOODgrowth constitutes a crucial step beyond the state of the art of this field of research. For the first time, the eigenstrains emerging in reaction wood are not introduced in structural models based on ad hoc assumptions, but they result from a well-founded mathematical model. The project results and methods can be considered a valuable basis for future research endeavors aiming for understanding and predicting the dynamics of wood growth by means of mathematical models. In this context, the mechanobiological regulation of the growth process (i.e., the biological response of wood to mechanical stimuli) is key. In WOODgrowth, this regulatory mechanism has been considered in purely phenomenological manner, based on simplified growth laws. A respective model improvement is deemed a promising perspective for follow-up projects. The application range of the developed model is diverse. On the one hand, the individual modeling concepts can be applied irrespective of the particular research field - for any adaptive beam structures and for any composite material that is microscopically subjected to eigenstrains. On the other hand, the developed model may provide an immediate basis for tackling and achieving a number of concrete research goals. This concerns both studying the dynamics of wood growth in general, and specific technological applications (such as the optimization of plant growth in space flight).