2019 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 / Galvanic corrosion / Atmospheric environment / Durability / Adhesive strength / Moisture diffusion |
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| Outline of Annual Research Achievements |
This study investigated the bond behavior of CFRP/steel composite joint from several fundamental studies in the first period:
1) We performed the gravimetric measurement, DSC, and FTIR-ATR tests on the epoxy adhesive in various aging conditions, to estimate the reversible effect of water absorption in the composite. Water absorption leads to an increase of bound water content, acting as a plasticizer, and are responsible for glass transition temperature (Tg) decreasing. The modulus and strength of adhesives deteriorate as a consequence of moisture ingression.
2) Surface properties and adhesive strength of the blasted steel plate (5 types) were discussed using the dolly test, SEM-EDX, and box-counting method. Test results showed that the blasting angle would affect the roughness and chemical properties of the steel surface, also determine the adhesion strength of CFRP/steel composite. In the case of 75゜, low roughness surface condition, proper residual abrasive amount, and the most considerable adhesion strength could be obtained.
3) The FE cohesive zone model of a single-lap joint shows the different bond behaviors of brittle and ductile adhesive, that ductile adhesive owns a larger critical energy release rate and contributed to the ultimate load of joint significantly.
4) A preliminary test of the electrochemical corrosion between steel and CFRP plate was carried out in an immersion environment. The weighed metal loss is approximate to the equivalent value of galvanic current, although test data is not available yet for the case in an aggressive atmospheric environment.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
The galvanic corrosion mechanism of CFRP strengthened steel structures, and the corresponding anti-corrosion technique is the initial aim of the study. However, according to the preliminary investigations, we found the reinforcing methods provided by different companies are varies in both material and technical progress. Therefore, a large number of works have been spent on fundamental studies, such as electrical resistance properties of carbon fiber, dielectric properties of epoxy adhesive, reversible effects of water absorption, etc.
In addition, the research on the electrochemical corrosion test is slightly behind due to the failure of the preliminary test. The galvanic corrosion does exist between steel and carbon fiber in immersion environmental; however, the in-door simulation of a dynamic atmospheric environment is very complicated. A quantitative test designed for the galvanic corrosion estimation of a composite joint needs the development of a water film measurement system, and this also builds into the research plan.
Also, the composite structure needs to consider the physical and empirical knowledge of deterioration comprehensively. Until now, except for the FE analysis, we overemphasized the degradation mechanism of an individual component, that’s why the experiments have been prolonged. However, these are the most critical part of the research, and the research approach is still insisted.
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| Strategy for Future Research Activity |
From 2020, the study will focus on the indoor electrochemical/accelerated tests, and corrosion modeling of the actual atmospheric environment. On the one hand, the electrochemical analysis on the deterioration mechanism of hydrous adhesive and abrasive CFRP plate was conducted using potentiodynamic and Tafel polarization, etc. Besides, the through-thickness and longitudinal electric conductivity of unidirectional and woven carbon fiber sheets will be measured by the EIS method. Expecting results will have a significant impact on the possibility and fatalness estimation of galvanic corrosion in a specific environment.
On the other hand, the nonlinearity accelerating effects of atmospheric humidity and temperature on the corrosion rate are remarkable and should be considered in the dynamic environment. A corrosion kinetic model is needed to estimate the galvanic corrosion process over time, it will be established from ① time-metal loss curve according to wet-dry cyclic corrosion test, and ② galvanic corrosion current measured in a static environment.
Then a dynamic atmospheric environment is characterized by the statistical distribution and probability density function in range. A multi-parameter method is used to describe the effects of environmental factors on corrosion, and accelerating factors of RH and T correlating with the corrosion rate are calculated to correct the durability prediction of deteriorated CFRP-steel composite structure.
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| Causes of Carryover |
The first half-year in 2019, the research is in the planning stage. Instead of the experimental part of the research, the theoretical analysis and finite element calculation were dominant. The international conference has been canceled due to the spread of COVID-19. Thus, there was a surplus for the first year.
The amount will be used mainly in four parts in the next fiscal year. 1) Travel expenses: including several times of business trips in Japan and 1~2 times oversea. The main purpose is to communicate with peers and professors, discussing and meeting with project corresponding companies. 2) Presentations: registration fee for academic conferences, etc. 3) Equipment and laboratory supplies: Drying machine, resistance tester, camera, software, etc. 4) Consumables: Araldite adhesive, tweezers, steel plate, acrylic plate, beaker, electric wire, etc.
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