Ductility and strain rate-dependency of adhesively-bonded timber joints

One of the most important characteristics of load-bearing structures is ductility, i.e. the ability of a material or a structure to sustain inelastic deformation prior to failure, without loss of resistance. The topic of this PhD Thesis was to develop ductile adhesively bonded timber joints, in order to compensate for the inherent lack of ductility of timber. After the rate-dependent true tensile and compressive properties of the acrylic adhesive had been established (including Poisson ratio, ductility and recovery), two types of adhesively-bonded timber joints were experimentally studied in tension and compression: stiff epoxy and ductile acrylic joints. The latter ones exhibited lower stiffness but higher capacity and ductility, as explained by the extracted stresses and strains too. Furthermore, finite element (FE) models, including these strain rate-dependent properties of the acrylics, were developed to validate all the experimental results obtained and study the parametric effect of the different applied displacement rates on the acrylic joints. Extensive simulation using the developed FE models has shown their capacity to accurately predict the rate effect on bonded joints' mechanical response: stiffness, yield, ductility, ultimate failure. Finally, the behavior of the developed bonded joints over mechanical joints was analytically compared, based on Eurocode and the results confirmed the promising potential of the developed joint concept. To summarize, if ductile adhesives are used, it is possible to create ductile timber joints, which can perform better compared to other existing assembling techniques (i.e. mechanical fasteners or epoxy-adhesives) and their complex, rate-dependent behavior can be modeled with precision with the help of FE. This knowledge can lead to a broader and more efficient use of timber, contributing subsequently to achieving more sustainable modern structures.