AbstractThis study evaluates the effectiveness of externally bonded small-patch ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) plates of 460 GPa modulus in extending fatigue life and slowing crack propagation in steel plates with simulated fatigue cracks. The study investigates a range of very short bond lengths for applications where bonding space may be limited or accessibility restricted, together with the effect of single- versus double-sided application, on fatigue performance. It also compares short UHM CFRP plates with similar length normal modulus (NM) (165 GPa) CFRP plates with regard to extending fatigue life and reducing stress concentration at the crack tip. Distributed fiber-optic sensors (DFOS) and digital-image correlation (DIC) are used to capture the full strain field and track crack growth. Results showed that fatigue life was increased by up to 2.0 and 2.34 times for single- and double-sided UHM CFRP repairs. As bond length increased from 25 to 100 mm, fatigue life increased from 1.36 to 2.0. UHM CFRP more effectively reduced stress concentration at the crack tip, by 60% compared with 37% for NM CFRP, indicating that it has the potential for superior fatigue life gains, relative to NM CFRP if the necessary bond length to prevent or delay debonding is provided. As debonding failure governed in this study, NM CFRP plates achieved comparable fatigue life extension. DIC tracking of crack growth matched the traditional “beach marking” technique with less than 6% difference.

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