Anna Benešová

Evaluation of FRP/wood adhesively bonded epoxy joints on environmental exposures

This article describes the evaluation of the durability of joints composed of wood adherends with a bonded layer of fibre-reinforced polymer (FRP) fabric. Carbon and glass fibres in an epoxy matrix were studied. The main purpose of FRP usage with timber in the construction industry is generally to improve the stiffness/strength of reinforced members without any influence on their service-life or any environmental impact. From the perspective of the timber reinforcement process, optimal dimensional stability during moisture changes in wood should be one of the most important criteria for such joints. Therefore, FRP/wood joints were evaluated with regard to the influence of real external environmental conditions on the bondline over a period of 40 months. During exposure to these conditions, specimen failures and defects were continuously visually evaluated. The decisive factor in this evaluation was bond integrity, verified by the tensile shear strength of the FRP/wood joint. After the experimental study, it was noted that the first 20 months have a significant effect on bondline failure occurrences, which involve decreases in tensile shear strength. In the next 20 months, the FRP/wood bondlines resist other severe hygrothermal stresses without significant strength decreases. An additional observed parameter was the percentage of wood failure in the bonded area of single lap joints, which characterises the mode of failure of the bonded joint. To determine the influence of ageing on adhesive due to ultraviolet radiation and varying temperature, infrared absorption spectroscopy analysis was performed to reveal changes in the macromolecular structure of the epoxy adhesive. Findings showed that UV radiation had a significant influence on the degradation of the adhesive structure.

The Influence of Silane Coupling Agent on Glued Spruce Wood Using Epoxy Adhesive

The paper deals with the evaluation of epoxy adhesive modification by silane coupling agent used for gluing process of spruce wood. Moreover, the usage of primer containing the silane coupling agent was performed to find out, whether better compatibility between spruce wood and epoxy adhesive at the interface bondline can ensure sufficient resistance to delamination process. As the main criterion, tensile shear strength properties of glued specimens in different thermal and moisture exposures were carried out.

The Evaluation of Modifications to Glued Joints Utilizing Epoxy-Based Adhesive for Structural Timber Bonding

The behavior of two types of modifications to glued joints utilizing epoxy resin-based adhesive was examined in a manner specified by the EN 302 standard using adherent beech wood specimens. The investigation was focused on the improvement of glued joint strength and adhesive properties. The first type of modification involved reinforcement of the epoxy-based adhesive with scattered polypropylene fibers with the aim of enhancing the tensile shear strength of the assembly. The other type of glued joint modification was the electrical discharge plasma treatment of the adherend surface. This technique for treating the surfaces of materials enables the greater spreading of liquids due to the increase in surface wettability it provides. Relevant characteristics of the test specimen – tensile shear strength and wood failure - were tested in order to analyze the behavior of the thus-modified epoxy-based adhesive-glued joints.