Molecular fatigue in steamed wood

Cyclical off-axis compression was applied to steamed Spruce wood in uniaxial strain under stress control. It has previously been shown that stiffness decrement and plastic strain due to mechanical fatigue loading are closely related, and both depend on the greatest accumulated strain. Molecular fatigue response was now investigated in terms of Differential Scanning Calorimetry. In accordance with classical Coffin-Manson theory, it was found that the creation of fatigue damage depends on plastic strain amplitude, not depending on the applied stress, applied strain, or the amount of dissipated energy as such. Molecular reorganization becomes more pronounced along with further energy application, as well as with increased process temperature.