Project Details
Projekt
P4 "Wood": Fatigue-related failure resistance in living trees and harvested wood as inspiration for hydration-responsive minerals and bilayer composites
Subject Area
Polymeric and Biogenic Materials and Derived Composites
Term
since 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 516930787
Wood provides functionality both for the living tree and for human construction purposes. Saturated with water during life, it dries after harvest causing changes in mechanical properties and shape. While this is comparably well studied, much less is known about fracture and fatigue despite the fact that living trees can survive for many centuries under cyclic wind-loads. Furthermore, wood is now being investigated for the development of humidity fueled actuators, again little is known about fatigue in these systems. Another class of materials, minerals and ceramics, can also actuate upon changes in humidity. It is unclear how their properties change with moisture and their inherent brittleness limits their ability to reversibly change shape over many cycles. In this project we will attempt to transfer structural motifs observed in wood cell walls into artificial mineral-based composite materials and explore how fatigue behavior in both systems is linked to their microstructure. Fatigue resistance and fatigue-related damages will be explored at different length scales to clarify the role of repeated loading cycles for failure in wood and artificial cellular structures. We hypothesize that structural fibrous features on the microscopic, ultrastructural and/or macromolecular level are important for fatigue resistance in green wood. We furthermore assume that pre-stresses in the tree contribute to fatigue-resistance as well as adaptation by growth. Hence, fatigue-properties of wood in the living tree need to be separated from those of harvested wood and the most relevant length scales for fatigue-resistance need to be identified. We envision the fabrication of architectured composites that mimic structural features of wood (e.g. oriented fibres and cellular structure) to be used as non-biogenic model systems for structure-property studies. Specifically, we will use hydration-responsive mineral bilayer systems composed of an active (i.e. sensitive to moisture) layer of polymer-mediated minerals and a passive pre-structured layer directing the folding patterns. Upon drying, the non-uniform responses of the active and the passive layers induce strain along the surface normal direction of the 2D bilayer system, which is eventually released by self-rolling into complex spiral morphologies. The possibility to study the effects of different highly anisometric nano- and meso-structural motifs in the passive layer on the hydration-driven passive motion of the composites, will contribute to the elucidation of correlations between the fatigue characteristics and the structural anisotropy.
DFG Programme
Research Units
