2020 Fiscal Year Research-status Report
Development of anti-corrosion technique of CFRP strengthened steel structures and durability prediction under atmospheric environment
| Project/Area Number |
19K15074
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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, 特任助教 (70836519)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | Composite structure / CFRP / Adhesive strength / Thermal properties / Durability |
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| Outline of Annual Research Achievements |
This study aims to enhance the bond strength and environmental durability of CFRP-strengthened steel structures and examine a carbon fiber fabric-based wet layup system, whose entire fabrication process is generally conducted in the field. A systemic experimental study was conducted to investigate the improvements in the surface treatment of the steel substrate, thermal properties of the epoxy resin, and curing process of the composite. The results showed that the steel-adhesive interfacial bonding behavior can be improved by increasing the surface roughness and using a low-viscosity primer to enhance the wettability. During the initial curing, a lower ambient temperature during the gel time can reduce the porosity of the multi-CFRP laminate; however, a disadvantage is the occurrence of epoxy infiltration in the fabric. However, raising the initial curing temperature is advantageous for the mechanical and thermal properties of the composite. In addition, the thermal properties of the epoxy matrix were clarified by differential scanning calorimetry tests, based on which isothermal curing degree curves of the system were drawn. The results demonstrated that post-curing at 80 °C is vital for increasing the glass transition temperature, which is also appropriated for the primer. Finally, the moisture and thermal effects on the deterioration of the adhesive joint were examined by conducting short-period aging tests in immersion and wet-dry cyclic environments, during which delamination strength reduction and failure mode transformation were observed.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Among the three critical issues in the proposal, two of them are progressing well. The first one is about adhesive debonding failure due to environmental exposure: a systemic experimental study was conducted to clarify the environmental effects on the deterioration of the adhesive joint. A short period of immersion and wet-dry tests demonstrated the moisture and thermal effects on the deterioration and failure mode of the adhesive joint. Besides, the discussion on improvements in the surface treatment of the steel substrate, thermal properties of the epoxy resin, and curing process of the composite are exceeding the initial plan.
About the second issue of research, the fundamental study on the electrochemical properties of CFRP was almost finished. The anisotropic electrochemical behavior and resistance properties of single carbon fiber/CFRP were investigated by EIS and CV methods. This study also established a water film measurement system to simulate the atmospheric environment so that the galvanic corrosion rate can be evaluated with accuracy.
The third issue, which is the safety criteria and durability prediction of CFRP strengthened steel structures, has been carried out preliminary.
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| Strategy for Future Research Activity |
The following two research schemes are the main work next stage.
1) Effect of the anisotropic electrochemical behavior of CFRP on macro-galvanic corrosion of steel in the atmospheric environment, mainly conducting an electrochemical test on array electrodes, considering the water film condition.
2) Study on bond strength between corroded steel plate and carbon fiber sheet by optimizing curing conditions and steel surface treatment. The steel plates with different corrosion degrees were prepared using accelerated exposure, and the effects of various steel surface cleaning methods on adhesion bond strength would be considered. An in-door aging test on adhesion joint would also be conducted to clarify the deterioration mechanism.
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| Causes of Carryover |
Because of the impact of COVID-19, most business trips were suspended for the entire last year. All of the international conferences only can participate in online meetings, so the use of scientific research fees was less.
Regarding the purchase of materials, the purchase amount of last year was relatively smaller than that of the previous year, because there were carbon fiber sheets and other materials left over from the first year.
Starting from this year, a large number of corrosion tests will continue, and there is an urgent need to use the remaining funds to purchase new materials, to carry out atmospheric exposure tests, on-site inspections, and environmental monitoring.
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