Energetic investigation of the fatigue of wood

Abstract

Abstract There are gaps in our knowledge regarding temporal changes in wood stability and mechanical properties in the context of wood durability. Energetic analyses have been performed in this study based on experimental results on the bending fatigue of wood under multiple loading conditions. New findings regarding the fatigue limit and fatigue life (Nf) are presented. The strain energy (SE) obtained from stress-strain envelopes until wood reaches its Nf is a value specific to wood species and static strength regardless of the loading conditions. This value is about 50% higher than the SE in static tests. The relationship between mean energy loss (EL) and stress level (SL) to the point of fatigue failure is bilinear, and the mean EL is closely related to Nf. Moreover, the SL – when mean EL approaches a specific value (∼1.10 kJ m-3 per cycle) as Nf approaches infinity – is considered to be the fatigue limit; the latter is estimated to be about 20–30% of static strength.