The bond behaviour of CFRP-to-steel bonded joints with varying bond properties at elevated temperatures

The mechanical properties of different adhesives at elevated temperatures can change differently due to the differences in adhesive molecular chain structure. Therefore, a profound understanding of the effect of these property changes on the bond behaviour of carbon fibre reinforced polymer (CFRP)-to-steel bonded joints is of great importance when designing bonded CFRP strengthening systems for steel structures. Existing studies on CFRP-to-steel bonded joints under monotonic loading have clearly shown that both adhesive mechanical properties and geometrical properties of the bonded joints (e.g. bond length) may significantly influence the bond strength. Existing studies on adhesive mechanical properties under elevated temperatures have shown that the variation of adhesive mechanical properties, especially fracture energy with temperature depends significantly on the adhesive type. No comprehensive study exists so far on understanding the effects of key mechanical and geometrical parameters of a CFRP-to-steel bonded joints at elevated temperatures on bond strength. This paper presents a study aimed at understanding the effects of different parameters such as temperature dependent mechanical properties of adhesive and bond length on the behaviour of CFRP-to-steel bonded joints at elevated temperatures. Results of this study showed that (1) load-displacement behaviour of the bonded joints is sensitive to temperature variations, (2) for bonded joints with sufficiently long bond length, the ultimate load depends only on the fracture energy of the final temperature, and (3) the maximum load of the bonded joints depends on the ratio between the loading and heating rates

On Micropolar Elastic Foundations

The modelling of heterogeneous and architected materials poses a significant challenge, demanding advanced homogenisation techniques. However, the complexity of this task can be considerably simplified through the application of micropolar elasticity. Conversely, elastic foundation theory is widely employed in fracture mechanics and the analysis of delamination propagation in composite materials. This study aims to amalgamate these two frameworks, enhancing the elastic foundation theory to accommodate materials exhibiting micropolar behaviour. Specifically, we present a novel theory of elastic foundation for micropolar materials, employing stress potentials formulation and a unique normalisation approach. Closed-form solutions are derived for stress and couple stress reactions inherent in such materials, along with the associated restoring stiffness. The validity of the proposed theory is established through verification using the double cantilever beam configuration. Concluding our study, we elucidate the benefits and limitations of the developed theory by quantifying the derived parameters for materials known to exhibit micropolar behaviour. This integration of micropolar elasticity into the elastic foundation theory not only enhances our understanding of material responses but also provides a versatile framework for the analysis of heterogeneous materials in various engineering applications

Fire behaviour of a timber composite with GFRP reinforcement compared to unreinforced laminated timber

Engineered timber is becoming increasingly popular due to many advantages such as sustainability andease of installation. However, its fire performance is largely hindering implementation of timberstructures. Combination of timber with composites such as glass fibre-reinforced polymers (GFRP) canimprove the fire performance of timber structures. Glass fibres are inorganic, thus not oxidising whenexposed to fire conditions. This paper presents a comparative study between the fire behaviour of atimber-GFRP composite laminate versus a pure timber laminate. The composite samples consisted ofsix timber veneers in between seven layers of GFRP. Tests were conducted using a Cone Calorimeterwith an external heat flux of 35 kW/m. Heat release rate (HRR), mass and in-depth temperature weremeasured to investigate fire performance improvement.Results showed that samples without GFRP burned until under 10 % of their initial mass was left,whereas samples with GFRP reached flame self-extinction at 50 % of their initial mass. After an initialshort peak, the HRR of composite samples quickly declined to values below 100 kW/m, while puretimber samples experienced delamination and a fluctuating HRR around 300 kW/m until burnout.GFRP-samples showed a significant heat gradient through the thickness with rear surface temperaturesof below 200 °C, while samples without GFRP reached 700 °C. This work shows that the glass fibresact as a barrier hindering oxidation of the charred timber, thus better insulating the deeper layers.Furthermore, if stitched adequately, the glass fibres can mechanically prevent the charred timber layersfrom delaminating

Cyclic behaviour of FRP-to-concrete bonded joints: An experimental study

Flexural strengthening of reinforced concrete structures using externally bonded FRP laminates has gain wide acceptance among design professionals as an effective strengthening and retrofitting technique. Effectiveness of such strengthening systems relies heavily upon the interfacial shear stress transfer mechanism of the bonded interface. Extensive research has been carried out to better understand and model the behaviour of FRP-to-concrete bonded interfaces under quasi-static monotonic loading. On the contrary, much less work has been done so far on understanding the behaviour of FRP-to-concrete bonded joints under cyclic loading. Ability to understand and model the behaviour of FRP-to-concrete bonded interfaces is essential in predicting the long-term performance of FRP-to-concrete bonded joints. This paper presents the results from a series of single-shear pull off tests aimed at investigating the behaviour of FRP-to-concrete bonded joints under quasi-static cyclic loading. Load-displacement, strain distribution along the bond-length at different loads, interfacial shear stress distribution along the bond length at different loads, and bond-slip curves at different locations along the bond length are presented and discussed. Test results are used to verify the accuracy of several assumptions made in existing theoretical bond-slip models under cyclic loading. Some of the assumptions made in developing the existing theoretical solutions were found to be not in agreement with the test observations