Influence of Cyclic Humidification on the Strength of Multi-layer Laminated Veneer Lumber

This paper presents a study of hygro fatigue – the effect of repeated cyclic moistening on the strength of laminated veneer lumber (LVL). The method of cyclic humidity used for laminated veneer composite material in the work is described. Samples made of such material were pre-conditioned for extended periods under high-humidity conditions. Cross-fibre compressive strength across fibres in the plane of veneer layers has been investigated. The influence of technological weakening (notching) on the crack opening process of peeled veneer has been proven. It has also been revealed that the area around the knot of the tree, which leads to the curvature of the growth layers, is a place of crack concentration. A significant reduction in the strength properties of multi-layer laminated veneer lumber under cyclic moistening (up to 18% after three cycles) has been proven. The dynamics of crack growth due to the influence of the moisture factor is given. The need to treat LVL elements with wax-containing compositions to reduce the negative impact of humidity on the engineering wood was confirmed.