Improving the tensile shear strength of lap joints of beech wood by adding basalt fibers to polyurethane adhesive

The purpose of this study was to assess the shear strength of the lap joints of beech wood. To achieve this objective, a one-component polyurethane adhesive filled with basalt fibers was used to create waterproof joints. The shear strength of the bonded joint was carried out according to EN 302-1. The results showed that the lap joints bonded with a one-component polyurethane adhesive containing 3% basalt fibers had significantly higher shear strength. While the average value of the shear strength of lap joints glued with one-component polyurethane without the filler in the hydrothermal stress was 8.8 N/mm², the lap joints with basalt fibers achieved more than a 14% higher average shear strength of 10.1 N/mm². In addition, the experimental data showed a higher occurrence of joint failure in the wood substrate when the modified adhesive was used, which contrasts with the behavior observed for reference joints bonded with an unmodified one-component polyurethane adhesive without basalt fibers.