2023 Fiscal Year Research-status Report
Experimental study on irreversible deterioration mechanism of CFRP-steel bonding system and durability-based design optimization
| Project/Area Number |
23K13396
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| Research Institution | Kyushu University |
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Principal Investigator |
楊 沐野 九州大学, 工学研究院, 特任准教授 (70836519)
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| Project Period (FY) |
2023-04-01 – 2026-03-31
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| Keywords | Steel structure / Corrosion / Carbon fiber sheet / Bond behavior / Durability design |
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| Outline of Annual Research Achievements |
This research aims to elucidate the irreversible deterioration mechanism of the CFRP-steel bonding system. In the first stage, the study assessed the impact of corrosion on steel and the effectiveness of surface preparation techniques on the bonding behavior of CFRP-steel bonded joints. Steel specimens were fabricated based on three distinct corrosion levels of steel and three conventional surface preparation techniques. Furthermore, macro and microscale observations, topographical analysis, and comparison of surface indices were employed to understand steel surface characteristics and their influence on interfacial behavior. The findings revealed that when the target for repair shifted from a new steel substrate to a corroded one, the synergistic performance at the steel-adhesive interface decreased. This led to a decrease in the maximum shear stress at the plate end and an undesirable shift in the mode of failure.
Additionally, investigations into chloride-induced durability deterioration highlighted significant declines in joint capacity and displacement with increasing corrosion levels and aging periods. Deterioration mechanisms involved external factors such as corrosion at bonding edges and internal factors like chloride/rust residues, weakening steel-adhesive bonds.
Finally, an improved model for predicting the debonding capacity of CFRP-corroded steel bonded joints was introduced. Meanwhile, A time-dependent environmental reduction factor for the capacity model was also proposed and validated using collected data.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Regarding the key issues mentioned in the proposal, research progress is advanced.
Around the deterioration mechanism and durability-based prediction of CFRP-steel composite joint, a systemic experimental study was conducted. Test parameters discussed here including the corrosion level, surface preparation techniques, chloride-induced deterioration conditions. Besides, the proposed models for predicting the debonding capacity of CFRP-corroded steel bonded joints for bond deterioration are exceeding the initial plan.
In addition, the topic about the environmental effects on the irreversible deterioration mechanism of composite joint has also been started. This part of work mainly focused on fundamental research; hence progress has been gradual. Specifically, we investigate the irreversible deterioration of resin-impregnated CFRP-steel bonded joints under hydrothermal conditions. The current results revealed that the elevated temperatures exacerbate moisture absorption of epoxy matrix, resulting in alterations in thermal and mechanical properties. However, a slight recovery in joint mechanical performance after drying indicates partial reversibility of moisture absorption effects, particularly under extreme conditions.
These findings offer insights for evaluating capacity and durability of CFRP-steel bonded joint in various environments.
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| Strategy for Future Research Activity |
In the next phase, we will undertake the following research topics:
1)Temperature plays a crucial role in the galvanic corrosion rate between carbon fiber reinforced plastic (CFRP) and carbon steel, particularly for steel bridges that that are exposed to elevated temperatures during the summer months. To examine the impact of temperature on the galvanic corrosion between carbon fiber and steel, various electrochemical tests would be conducted. In future, by utilizing Arrhenius equation, the temperature-promoting factor will be employed to predict the corrosion rates of steel where electrical contacted by carbon fibers.
2)Our study will develop a Hybrid-Acid Pickling Method for rust removal of corroded steel members prior to localized repair or CFRP strengthening, to enhance the adhesion and durability in CFRP-steel bonded interface. A time-dependent evaluation will be conducted on both the steel surface characteristics and the state variation of the pickling agent, and the rust removal mechanism will be speculated from electrochemical level. Furthermore, a comparative study will be performed on conventional blasting, power tool grinding, and the proposed hybrid de-rusting method, via surface characterization of the steel substrate and deterioration testing on composite joints.
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Research Products
(19 results)
