مدل سازی عددی رفتار لغزش تنش برشی چسبندگی کامپوزیت های فولادی/CFRP
Abstract
1- Introduction
2- Overview of the test programme
3- Numerical modelling
4- Transient heat analysis
5- Thermo-mechanical analysis
6- Parametric study
7- Conclusions
References
Abstract
This paper presents a numerical model developed to predict the bond characteristics of CFRP/steel composites cured under different curing conditions and their behaviour at elevated temperatures. The measured material properties and their degradation with the temperature exposure were considered. The predicted bond performance was in a good agreement with the test results. The strain variation in the CFRP sheet was used to develop the bond shear stress-slip variations. Parametric studies were also conducted to evaluate the effects of bond line parameters on the bond shear stress-slip relationship at elevated temperature. The results indicate that the maximum bond shear stress of the joint lies in the range between 25 MPa and 28 MPa at ambient conditions, irrespective of the curing type. A rapid decrease in the maximum bond shear stress appears with exposure to the elevated temperature. Maximum shear stress reaches 10 MPa when the bond line temperature exceeds 90 °C. The elevated temperature curing, exposed temperature during service and the bond thickness notably affects on the bond slip behavior.
Introduction
Superior mechanical and thermal properties of Carbon Fiber Reinforced Polymer (CFRP) material has attracted the attention of the civil and construction industry. The use of elevated temperature curing conditions may improve the performance of CFRP strengthened structural members [1]. In this case, it is vital to understand the bond mechanism of the system cured under different curing conditions and their behavior at elevated temperatures. Nguyen et al. [2,3] has observed the effects of curing conditions at ambient temperature and also the behaviour of ambient temperature cured joints at elevated temperature. They found a significant degradation of bond properties with the temperature exposure of the bond between CFRP and steel, cured under ambient conditions. Gamage et al. [4] also noted the similar behavior from CFRP/concrete composites cured at ambient conditions. Some research studies conducted on the CFRP/concrete joints indicated the negative influence on the substrate properties from elevated temperature curing [5-7]. However, these studies were conducted in a controlled environment. The curing was also done using a standard which are not practically feasible in civil engineering applications [3,8-10]. Chandrathilaka et al. [11] introduced a set of halogen floodlights for elevated temperature curing of the CFRP/epoxy/steel bond. They have exaggerated the feasibility of this system for the application in curing of large structures with high performance. Bond shear stress-slip variation is one of the key parameters which determines the bond behavior, irrespective from the geometrical properties of CFRP/steel composite. However, there is a lack of knowledge on the steel/CFRP bond slip behavior if it is both cured and exposed to elevated temperature. In general, collecting all required data from experiments is impractical and also not economical. In such cases, Finite Element Analysis (FEA) can be applied to predict the performance. Many researches have successfully applied FEA technology to predict the behavior of CFRP/steel composites [12,13]. Xia and Teng [14] has proposed a bi-linear bond slip model using experimental data which suitable for the CFRP/steel joints cured and tested at ambient conditions. However, developing a bond shear stressslip model using experimental results require more resources and time [14-16]. Fawzia et al. [15] successfully used the bi-linear bond-slip model to evaluate the steel/CFRP bond performance using experimental and numerical data of the joints cured and tested under ambient conditions. However, the effects of bond line temperature were not discussed with the bond slip relationships. However, Fawzia et al. [15] has mentioned that CFRP/epoxy/steel bond length should higher than the effective bond length to have a bond shear stress-slip model to independent from CFRP/epoxy/steel bond length. Chandrathilaka et al. [11] has used higher bond length than the effective bond length in CFRP/epoxy/steel bond in the experiment.