PSI - Issue 64

Yining Zhang et al. / Procedia Structural Integrity 64 (2024) 1334–1338 Y. Zhang and L. Hu/ Structural Integrity Procedia 00 (2019) 000 – 000

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(2022) and the fatigue performance of steel with different steel grades varies Moe et al. (2023), investigating the fatigue performance of welded UHSS Q960 and Q890 is of great importance. Using carbon fiber reinforced polymer (CFRP) to strengthen the steel plates can reduce stress near crack tips, decrease crack opening displacement, and increase the crack closure effect, ultimately improving fatigue performance Colombi et al. (2015). A previous study by Amraei et al. (2021) demonstrated that CFRP strengthening can compensate for the mechanical property deterioration caused by welding, and the fatigue life of the strengthened welded UHSS may even surpass its base metal. As one of the most common flaws in structures, surface crack propagation behavior has been investigated. According to Huang et al. (2022), the enhancement of CFRP increases as the number of CFRP layers, bond width, and modulus increase. Li et al. (2020) found that the CFRP strengthening effect decreases at the depth point and increases at the surface point. In this study, the fatigue behavior of butt-welded UHSS Q960 and Q890 strengthened by CFRP was studied by surface crack propagation (SCP) experiment. The fatigue life of unstrengthened and strengthened specimens and the failure mode of CFRP were discussed. 2. Material and specimen 2.1. UHSSs and filler materials This study chose quenched and tempered (Q+T) UHSSs Q960 and Q890 as base metals (BM). Weld wire ER120S-G specified in AWS A5.28/A5.28M (2022) was chosen as the filler material. The stress-strain curves are depicted in Fig. 1. The mechanical properties, including yield strength f y , tensile strength f t , elastic modulus E , and elongation δ are summarized in Table 1 .

Fig. 1. Stress-strain curves of UHSSs and filler material.

Table 1. Mechanical properties of UHSSs and filler material. Material f y (MPa) f t (MPa) E (GPa)

δ (%)

Q960 Q890

898.5 853.7 822.7

1003.8

198.8 198.3 201.3

17.5 16.9 17.6

945.0 965.7

ER120S-G