Determination of S-N fatigue curves for damaged steel plates strengthened with prestressed CFRP plates under tension loading

摘要

To promote a straightforward design guideline, a determination model of S-N fatigue curves was established to consider effects of the initial crack and stress ratio (R-ratio) on the fatigue performance of damaged steel plates strengthened with non- and prestressed CFRP (Carbon Fiber-reinforced Polymer) plates. The modified Paris’ law employing the effective stress intensity factor range was first used to model the fatigue crack growth data obtained from an extensive literature review for variousR-ratios, including edge- and center-notched reinforced steel plates under fatigue loadings. Based on these analysis, the fatigue S-N curve function including the fatigue strength Δσcand fatigue threshold ΔσL, was derived to consider the effects of the initial crack andR-ratio. The model was validated using fatigue results of approximately two hundred specimens with various notch sizes and stress ratios. Specific handbooks provided distinctly different values ofCandmfor mild steel, and among them the recommended values are 6.86 × 10−12(with the unit of MPa and meter) and 3.0 through the validation using existing test data reported in the literatures. The comparison of the experimental and predicted fatigue lives confirms the feasibility of the proposed S-N curve determination. Furthermore, the practical valueUof the crack closure effect is recommended as 1.0 in the negativeRregion (R 收起