Abstract Experimental studies on various strengthening systems for steel elements under fatigue loading showed that the use of carbon fiber reinforced polymer (CFRP) strengthening system could significantly enhance the fatigue lifetime. Besides, more recently it was shown that the use of prestressed unbonded CFRP strengthening system results in an additional reduction of the fatigue crack propagation rate and promotes crack arrest. Different models have been proposed to evaluate the fatigue lifetime of CFRP-strengthened steel members (e.g. S-N curves and fracture mechanics-based models making use of Paris’ law or similar). As an alternative approach in this study, the numerical assessment of mode I (tensile mode) fatigue crack growth of an existing macrocrack in unstrengthened and CFRP-strengthened (both nonprestressed bonded and prestressed unbonded) tensile steel members is investigated by using a cyclic cohesive zone model (CZM). The key advantage, compared to the above-mentioned methods, is that it introduces a constitutive relationship of the material, capable of being calibrated for different materials and being used for any geometry and loading condition. In this way, the crack initiation, crack propagation, crack retardation as well as crack arrest are the natural outcomes of the model. It is shown that the finite element (FE) model can be readily coupled with an interface traction-separation law (TSL), to predict the damage evolution in the steel-CFRP interface. The comparison between the numerical and experimental results validated the proposed FE modelling, which has also been used to perform a parametric study with respect to the main design parameters.

中文翻译：

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用于预测 CFRP 强化钢板 I 型疲劳裂纹扩展的不可逆循环内聚区模型

摘要 疲劳载荷下钢构件各种强化体系的实验研究表明，使用碳纤维增强聚合物（CFRP）强化体系可以显着提高疲劳寿命。此外，最近的研究表明，使用预应力无粘结 CFRP 强化系统会进一步降低疲劳裂纹扩展速率并促进裂纹止裂。已经提出了不同的模型来评估 CFRP 强化钢构件的疲劳寿命（例如 SN 曲线和利用巴黎定律或类似定律的基于断裂力学的模型）。作为本研究的替代方法，通过使用循环内聚区模型 (CZM) 研究了未强化和 CFRP 强化（非预应力粘合和预应力非粘合）拉伸钢构件中现有宏观裂纹的模式 I（拉伸模式）疲劳裂纹扩展的数值评估。与上述方法相比，其关键优势在于它引入了材料的本构关系，能够针对不同材料进行校准，并适用于任何几何形状和负载条件。这样，裂纹萌生、裂纹扩展、裂纹延迟以及裂纹停止是模型的自然结果。结果表明，有限元 (FE) 模型可以很容易地与界面牵引分离定律 (TSL) 结合，以预测钢-CFRP 界面的损伤演变。