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

Abstract

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-tosteel 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.

Bond Relationship of Carbon Fiber-Reinforced Polymer (CFRP) Strengthened Steel Plates Exposed to Service Temperature

“…Furthermore, He, et al [11] exposed the specimens for 160 min at temperatures ranging from 23 • C to 75 • C. The degradation of the adhesive elastic modulus led to a reduction in bond strength by 10% at T g − 15 • C and 70% when T g +15 • C. However, Chandrathilaka, et al [12] tested eighty-two CFRP/steel double strap joints and reported that the reduction of bond strength, Poisson's ratio and elastic modulus of CFRP/steel joint occurred in a similar manner. Chandrathilaka, et al [13] also found that, despite the type and thickness of CFRP, an elevated temperature caused the initial softening of the bond and substantially lowered the shear stress to 10 MPa when the temperature exceeded 90 • C. Similar behavior was observed by Zhou, et al [14], who found that the elastic modulus and initial stiffness of the bond-slip curve and the peak bond shear stress deteriorated with increasing temperature. However, the total fracture energy increased when temperature is below T g and then decreased when the temperature exceeded T g .…”

“…The present study was exposed under service temperatures for seven continuous days prior to testing to demonstrate environmental exposure on the CFRP-strengthened steel structures. Meanwhile, the existing studies that show a reduction in strength were exposed to short-term service temperatures, ranging from just 15 min to 120 min [15,39]. The increase in ultimate strength at service temperature has revealed that the transformation of the adhesive matrix at service temperature does not reduce the bond strength but enables the further enhancement of the interfacial bonding between the steel, CFRP and adhesive interfaces and thus, improves the overall bonding performance.…”

“…However, the total fracture energy increased when temperature is below T g and then decreased when the temperature exceeded T g . Nevertheless, Zhou, et al [15] argued that the geometrical properties of bonded joints' particularly insufficient bond length considerably affected the bond strength of the CFRPstrengthened steel plates.…”

Effect of temperature variation on the plate-end debonding of FRP-strengthened beams: A theoretical study

“…The FRP-strengthened beams in service are likely to experience significant temperature variations due to the daily and seasonal temperature changes (Al-Shawaf, 2010; Bai et al, 2021; Biscaia, 2019; Mhanna et al, 2020; Sahin and Dawood, 2016; Stratford and Bisby, 2012; Teng et al, 2021) and possible fire exposure (Gao et al, 2018; Kodur and Naser 2018; Kodur et al, 2019; Ouyang et al, 2021; Song et al, 2021; Yu and Kodur 2014). The temperature variations (i.e., thermal loadings) have two different effects on the interfacial behavior and the associated debonding failure: (a) thermal stresses at the FRP-to-steel/concrete interface that are induced by different thermal expansion coefficients of the FRP plate and the steel or concrete substrate (e.g., Gao et al, 2012; 2015a; Jia et al, 2021; Silva and Biscaia, 2008); (b) bond degradation of the FRP-to-steel/concrete interface due to the temperature-induced changes in the mechanical properties (e.g., strength and stiffness) of the bonding adhesive (e.g., Dai et al, 2013; Kodur et al, 2019; Zhou et al, 2019). It is noteworthy that the effects of thermal loadings on the mechanical properties of the reinforcing fibers of the FRP plate as well as the steel/concrete substrates are negligible (Nguyen et al, 2011; Sauder et al, 2004) compared with those of the bonding adhesives.…”

An Experimental and Numerical Study of Repairs on Composite Substrates with Composite and Aluminum Doublers Using Riveted, Bonded, and Hybrid Joints

“…The stress concentration at the ends of the overlap can be reduced by increasing the overlap length up to a certain magnitude, beyond which, it no longer has an effect [18]. Hao et al [19] investigated the behavior of CFRP-steel bonded joints at elevated temperatures, where significant effects of temperature-dependent bond-slip relation were observed under mode II loading. Li et al [11] studied pre-preg bonded composite single-lap joints.…”