Wood modification has become a thoroughly studied field of work in the last few decades. The ability to produce larger quantities of modified wood on an industrial scale is a relatively recent accomplishment. Therefore, it can be expected that the demand will increase and that new applications will be found. In some of these applications, modified wood will be exposed to a dynamic loading situation and hence experience material fatigue. Even though plenty of work has considered fatigue in solid wood or particle board as a material, only a few articles address modified wood products.
In some applications material fatigue could represent an as yet unconsidered problem. Since there is little previous work on the fatigue behaviour of modified wood, the object of this study was to evaluate the influence of a long-term cyclic loading situation on the moisture sorption and mechanical properties of Scots pine that had been subjected to three different modifications (acetylation, thermal modification and resin impregnation using a phenol formaldehyde resin). Small scale samples (1 mm x 5 mm x 45 mm) were subjected to over 25,000 load cycles at 20% of their static bending strength, using 1 Hz frequency.
Significant differences were seen between the EMC of samples with and without the fatigue loading, after conditioning at 20°C and 65% RH. These findings are discussed in the context of small-scale molecular rearrangements of the cell wall polymers.