Timber engineering sets high expectations on adhesive bonding as a joining method to overcome a series of limitations related to partly obsolete traditional techniques. Research on adhesively bonded timber joints has proved their superiority over mechanical fasteners in terms of strength and stiffness, but this research was often limited to softwood. Despite its abundant availability in Central Europe and its high mechanical resistance, beech is only rarely considered as a structural material. Furthermore, research on adhesively bonded timber joints almost exclusively focused on tests at room temperature. Elevated temperatures, however, are critical in conjunction with adhesives, making it paramount to shed more light on that particular aspect. Based on experimental and numerical investigations, it was found that the capacity of adhesively bonded hardwood joints increased asymptotically with overlap length to a ceiling value; furthermore, it was concluded that temperature negatively impacts capacity. Glass transition temperature, T g , marked a clear transition, but joints still sustained relatively high loads beyond T g . A probabilistic approach was validated and successfully applied to predict the joint capacity. The research contributes to fill knowledge gaps by offering the basis for subsequent dimensioning methods that at term will enable practitioners to design their structures accordingly.
Research has repeatedly pointed out the suitability of adhesive bonding to substitute to "traditional" joining techniques for numerous materials and loads, including timber to glass. Practitioners, however, are still reluctant to implement them into their designs. Adhesion as a method of joining, particularly in the context of hybrid structures, presupposes knowledge of all involved materials, including codes and procedures; most practitioners however tend to be focused on just a subset of materials. While such specialization is not unusual, it makes it challenging to implement novelty (i.e. new materials or techniques). Additionally, when it comes to adhesion where most of the knowledge has been generated by chemists, the lines become even more blurred. Taking the example of a pedestrian timber-glass bridge, this research shows how design and dimensioning of complex bonded hybrid structures can be performed in accordance with "traditional" engineering practice. The paper guides through every step, from the first concepts to the final design, including the manufacturing, of a relatively complex structure, in which timber and glass act together as equivalent members. The compliance of this process with engineering models is emphasized, and the embedment into existing codes and standards is sought after to ensure acceptancy by practitioners.
Pure torsional shear tests of joints glued with two different aerospace grade adhesives were performed using a specifically designed and constructed torsional shear test equipment. The developed test equipment allows for measuring of pure torsional shear strength under cryogenic and at elevated temperature conditions. The adhesives Hysol EA 9321 and 3M Scotch-Weld EC-9323-2 B/A were used to join steel torsional shear test specimens. Torsional shear tests were performed from -180°C to 150°C. In addition torsional shear fatigue tests were also performed at various loads and the effect of cryogenic aging (cyclic cooling and warming) on the torsional strength of the joints was investigated. The results showed that both sets of adhesive joints achieved three times higher torsional shear strength at -180°C compared to room temperature.
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