STRENGTH OF END-TO-END JOINTS WITH THICK EPOXY-RESIN GLUE LINES

The tensile strength of epoxi resin-filled end to end joints of spruce were tested on specimens of 8 x 50 mm and 60 x 80 mm. The bond streng th was influenced by the viscosity of the resin at the time of specime n preparation. The tensile strength of the small specimen was about 1/ 4 of the strength of small clear solid wood specimens. The MOE decreas ed with increasing glue lines thickness from 8.000 N/mm(2) to 4.000 N/ mm(2). According to the analysis of fracture morphology the causes for the relative low strength of the end to end joints are due to weak me chanical and probable also chemical adhesion between wood surface and resin as well as in notch tension at the contact surface. The bending strength of scarf joints was about double that of butt joints. The max imum bending strength, however, reached only 70% of the solid timber. The tests have indicated that epoxi resin-filled end to end joints can not substitute solid timber for structural purposes because of insuffi cient mechanical strength. Further tests with other fillers such as po lymer concrete, and other timber joints show more encouraging results.