• Steel and Composite Structures
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• v.46 no.3
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• pp.385-401
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• 2023

Steel is becoming increasingly popular due to its high strength, excellent ductility, great assembly performance, and recyclability. In reality, steel structures serving for a long time in atmospheric, industrial, and marine environments inevitably suffer from corrosion, which significantly decreases the durability and the service life with the exposure time. For the mechanical properties of corroded steel, experimental studies are mainly conducted. The existing numerical analyses only evaluate the mechanical properties based on corroded morphology at the isolated time-in-point, ignoring that this morphology varies continuously with corrosion time. To solve this problem, the relationships between pit depth expectation, standard deviation, and corrosion time are initially constructed based on a large amount of wet-dry cyclic accelerated test data. Successively, based on that, an in-situ pitting evolution method for evaluating the residual tensile strength of corroded steel is proposed. To verify the method, 20 repeated simulations of mass loss rates and mechanical properties are adopted against the test results. Then, numerical analyses are conducted on 135 models of corrosion pits with different aspect ratios and uneven corrosion degree on two corroded surfaces. Results show that the power function with exponents of 1.483 and 1.091 can well describe the increase in pit depth expectation and standard deviation with corrosion time, respectively. The effect of the commonly used pit aspect ratios of 0.10-0.25 on yield strength and ultimate strength is negligible. Besides, pit number ratio α equating to 0.6 is the critical value for the strength degradation. When α is less than 0.6, the pit number increases with α, accelerating the degradation of strength. Otherwise, the strength degradation is weakened. In addition, a power function model is adopted to characterize the degradation of yield strength and ultimate strength with corrosion time, which is revised by initial steel plate thickness.

• Journal of the Korean Society for Railway
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• v.7 no.1
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• pp.14-19
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• 2004

The effect of surface damage on fatigue properties of catenary wires were investigated to estimate their service lift. As surface defects of the wires caused by surface corrosion increase, surface roughness gets worse, and as roughness increases, it is easy for moisture coming from rain and dew to be condensed around uneven parts of the surface. The condensed moisture causes a locally severe corrosion which leads to damage of the wires. Corrosion of catenaty wires can make their actual lifetime shorter than that originally designed. The amount of decrease was more prominent as environmental conditions became more corrosive. They are also vibrated with some amplitude everytime pantographs touch contact line. The frequent cyclic load on the wire may result in a fatigue fracture. Surface damage by corrosion can make formation of crack initiation at fatigue. In the present study, the fatigue life of the used wire was measured 35 to 50% compared with that of new one in average.

• Steel and Composite Structures
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• v.20 no.1
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• pp.91-106
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• 2016

Two-dimensional elastoplastic finite element formulation is employed to investigate the load- carrying capacity degradation of reinforced concrete piers wrapped with steel plates due to occurrence of corrosion at the pier base. By comparing with experimental results, the employed finite element analysis method is verified to be accurate. After that, a series of parametric studies are conducted to investigate the effect of corrosion ratio and corrosion mode of steel plates located near the base of in-service pier P2 on load-carrying capacity of the piers. It is observed that the load-carrying capacity of the piers decreases with the increase in corrosion ratio of steel plates. There exists an obvious linear relationship between the load-carrying capacity and the corrosion ratio in the case of even corrosion mode. The degradation of load-carrying capacity resulted from the web's uneven corrosion mode is more serious than that under even corrosion mode, and the former case is more liable to occur than the latter case in actual engineering application. Finally, the failure modes of the piers under different corrosion state are discussed. It is found that the principal tensile strain of concrete and yield range of steel plates are distributed within a wide range in the case of slight corrosion, and they are concentrated on the column base when complete corrosion occurs. The findings obtained from the present study can provide a useful reference for the maintenance and strengthening of the in-service piers.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.52-53
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• 2020

The thermal spray coating process is being used to protect the metals and alloys from wear, abrasion, fatigue, tribology, and corrosion failure. Therefore, in the present study, Al and Zn was deposited by plasma arc thermal spray process onto the steel substrate and their performance was assessed. The bond adhesion result shows that Al coating has higher value attributed to compact, dense, and less porous compared to Zn coating which contain defects/pores and uneven morphology assessed by scanning electron microscopy (SEM). Electrochemical results show that the Al coating exhibited higher impedance value compared to Zn in artificial ocean water solution at prolonged exposure periods. However, both coatings show the increment in polarization resistance with exposure periods which reveal that porosity of coatings is filled by the corrosion products.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.17-18
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• 2021

In the present study, Al-Zn coating was deposited by Arc thermal (AT) and plasma arc thermal (PAT) spray processes, and their corrosion characteristics were studied in 3.5% NaCl through electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and mechanical tests. The bond adhesion result showed that plasma arc sprayed coating had a higher value attributed to compact, dense, and less porous coating compared to arc thermal spray coating which contains defects/pores and uneven morphology as revealed by scanning electron microscope analysis. Electrochemical results revealed that the plasma arc sprayed coating had a high polarization resistance at early stage of immersion, suggesting its excellent corrosion protection performance.

• Korean Journal of Materials Research
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• v.28 no.10
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• pp.544-550
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• 2018

The passivation of AZ91D Mg alloys by plasma anodization requires deliberate choice of process parameters due to the presence of large amounts of structural defects. We study the dependence of pore formation, surface roughness and corrosion resistance on voltage by comparing the direct current (DC) mode and the pulse wave (pulse) mode in which anodization is performed. In the DC plasma anodization mode, the thickness of the electrolytic oxide film of the AZ91D alloy is uneven. In the pulse mode, the thickness is relatively uniform and the formed thin film has a three-layer structure. The pulse mode creates less roughness, uniform thickness and improved corrosion resistance. Thus, the change of power mode from DC to pulse at 150 V decreases the surface roughness (Ra) from $0.9{\mu}m$ to $0.1{\mu}m$ and increases the corrosion resistance in rating number (RN) from 5 to 9.5. Our study shows that an optimal oxide film can be obtained with a pulse voltage of 150 V, which produces an excellent coating on the AZ91D casting alloy.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.2
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• pp.169-177
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• 2020

Here, the stability of stainless steel 316 (SS-316) was investigated to identify its applicability in the oxide reduction process, as a component in related equipment, to produce a complicated gas mixture composed of O₂ and Cl₂ under an argon (Ar) atmosphere. The effects of the mixed gas composition were investigated at flow rates of 30 mL/min O₂, 20 mL/min O₂ + 10 mL/min Cl₂, 10 mL/min O₂ + 20 mL/min Cl₂, and 30 mL/min Cl₂, each at 600℃, during a constant argon flow rate of 170 mL/min. It was found that the corrosion of SS-316 by the chlorine gas was suppressed by the presence of oxygen, while the reaction proceeded linearly with the reaction time regardless of gas composition. Surface observation results revealed an uneven surface with circular pits in the samples that were fed mixed gases. Thermodynamic calculations proposed the combination of Fe and Ni chlorination reactions as an explanation for this pit formation phenomenon. An exponential increase in the corrosion rate was observed with an increase in the reaction temperature in a range of 300 ~ 600℃ under a flow of 30 mL/min Cl₂ + 170 mL/min Ar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.60-68
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• 2018

The Housing Act amended allows vertical extension up to three floors and increases the units of housing (or total floor area) to site up to 15%. Currently, the feasibility of performing vertical extension is evaluated based on safety diagnosis provisions and manuals with preliminary investigations on slope, uneven settlement, load-bearing capacity, and durability. However, a need for more reasonable evaluation methodology for the preliminary investigation is still required because the current procedures are borrowed from safety diagnosis provisions and manuals for reconstruction without detailed examinations on evaluation criteria and sampling methods. Accordingly, this study is intended to suggest a method to obtain feasible sampling size for durability assessment by statistically analyzing the safety evaluation data sets on concrete carbonation and steel corrosion obtained from apartment complexes. The results of this study are expected to be beneficial for establishing more reasonable field sampling size, and in turn, more reliable durability assessment protocol for vertical extension.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.197-205
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• 2020

In 2014, The Housing Act amended to allows vertical extension and increases the units of housing (or total floor area) to site. Currently, the feasibility of performing vertical extension is evaluated based on safety diagnosis provisions and manuals with 1st investigation stage on slope, uneven settlement, load-bearing capacity, and durability. However, a need for more reasonable evaluation criteria for the investigation is still required because there had not been any other case study on the diagnosis for the vertical extension, and the engineering basis on evaluation criteria were not suggested. Accordingly, this study is intended to suggest feasible evaluation criteria on the carbonation, chloride ion contents, corrosion of reinforcements, crack and surface deterioration of concrete for durability assessment by codes and standards of domestic and foreign countries. The results of this study are expected to be beneficial for establishing more reasonable durability evaluation criteria, and in turn, more reliable assessment protocol for vertical extension.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.1051-1057
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• 2013

In this study, an automatic surface-strain measurement system called "ASIAS-bio" has been developed. This system can be used even in cases in which it is very difficult to apply a regular grid pattern necessary for measuring surface-strain, such as curved or uneven surfaces; surfaces damaged by corrosion or contamination; or soft materials such as rubber, foam, and biological tissues. This system works independently of the measurement conditions including the material and its surface condition, grid pattern and size, grid marking method, and degree of deformation. A comparison between the strain distributions of the sheet metal parts measured by using this system and those obtained by a commercial system showed that this system was sufficiently reliable. In addition, the deformation of the swine joint capsule and human knee skin was measured by using this system to demonstrate its usefulness.