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Emil Engelund Thybring
Linking observed tensile creep and recovery in
Norway spruce with molecular
level mechanisms of deformation
Motivation
Loading a piece of wood
Mechanical properties at the nano-scale Elastic properties of amorphous wood polymers depend on hydrogen bonding Nissan’s theory for hydrogen bonded solid materials
Mechanical properties at the cell wall level Elastic properties based on lamellar composite theory Shearing deformation based on Eyring’s deformation kinetic theory
Experiment
Constant tensile load (creep) for 90 min followed by stress-free relaxation (recovery) for 90 min
Experiment Creep and recovery strain normalized with elastic strain Moisture has an effect on the response No effect of temperature
Creep Recovery
Recovery
Creep
Linearly increasing difference between creep and recovery curves
Computer modelling Full recovery predicted by computer model
Computer model
Physical experiment
Removing linear creep of middle lamella, cell creep is fully reversible as predicted
Effect of water is attempted incorporated by decreasing elastic properties and increased shear rate
Removing linear creep of middle lamella, cell creep is fully reversible as predicted
Effect of water is attempted incorporated by decreasing elastic properties and increased shear rate Not enough to explain effect of water!
Computer modelling
Experiments hint at both reversible (cell) and irreversible (middle lamella) time-dependent deformations The effect of water can be explained by changing mechanical properties alongside a change in microfibril orientation
In conclusion...
ET Engelund, L Salmén (2012) Holzforschung, DOI 10.1515/hf-2011-0172
ET Engelund (2011) Wood-water interactions, PhD thesis, Technical University of Denmark