The Effect of Glue Cohesive Stiffness on the Elastic Performance of Bent Wood–CFRP Beams

Abstract

This paper presents experimental, theoretical and numerical studies of wood-CFRP beams bonded with polyurethane (PUR) adhesive. The analyses include two types of CFRP (carbon fibre-reinforced polymer) strengthening configurations and pure glue laminated timber beams as a reference. Through detailed analyses of a double-lap connection on blocks with and without CFRP strips, the authors state that neglecting the cohesive stiffness of adhesive layers may lead to an overestimation of an overall beam’s stiffness. This is significant with wood–CFRP connections, which showed values two times lower than with wood–wood connections. Theoretical modelling of the equivalent area used in a theory of composites provided much stiffer behaviour of the beams than in laboratory experiments. It proves that a PUR glue eliminates the possibility of using simple models that assume a perfect connection between bonded parts. These conclusions led the authors to use the finite element method (FEM) to take into account the cohesive stiffness. The FEM, based on the properties obtained from a double-lap joint analysis, allowed for the precise prediction of the elastic stiffness of the beams.

A Model of Damage for Brittle and Ductile Adhesives in Glued Butt Joints

“…Within the last decades, adhesive bonding became a very common assembly technique in many industrial sectors, such as aeronautical (e.g., in composite aircraft to bond the stringers to fuselage and wing skins to stiffen the structures against buckling [1]), civil (e.g., in glass-fiber-reinforced polymer pultruded beams [2] or in carbon-fiber-reinforced polymer beams [3]), automotive (e.g., in both closures and structural modules [4]), and biomedical engineering (to fix implants in bone tissue in orthopedic or dentistry surgery [5]), as an alternative to conventional joining techniques, such as welding and riveting [6]. Adhesive bonding provides several advantages, including reduced stress concentrations, higher corrosion resistance, water tightness, and the ability to join materials with dissimilar properties.…”

Densified delignified wood as bio-based fiber reinforcement for stiffness increase of timber structures

“…However, for the series Carbon 3 layer, an overestimation of 7.0% is obtained. A previous study, conducted on carbon fiber-reinforced polymer (CFRP) tape reinforcements of wood, reported that an overestimation can be attributed to the neglecting of the adhesive layer's cohesive stiffness [51]. According to de la Rosa Garcia et al [52], this effect may also be explained by a potential slippage at the interface due to high shear stresses induced by the large difference of elastic moduli between wood and carbon fibers.…”

Application of Digital Image Correlation to Evaluate Strain, Stiffness and Ductility of Full-Scale LVL Beams Strengthened by CFRP

“…They achieved significant improvement of the destructive force and deflection of the strengthened beams equal to 56% and 77.5% in comparison to the unstrengthened beams. Kawecki and Podgórski [ 20 ] conducted experimental, theoretical and numerical studies on glue laminated timber beams strengthened with the CFRP laminates—proving the necessity of including cohesive stiffness of the adhesive layers in the evaluation of the stiffness of the composite wood–CFRP. Rheological relaxation of OSB (Oriented Strand Boards) beams reinforced with CFRP tape was investigated by Socha et al [ 21 ].…”