• Tunnel and Underground Space
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• v.28 no.1
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• pp.97-110
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• 2018

The application of sprayed waterproofing membrane with high adhesion and ductility is considered to be promising as a measure for repair and reinforcement of a tunnel structure. Therefore, a powder-type and one-component membrane prototype with high tensile and bond strengths was made in this study. Then, its reinforcement effect on a shield segment was evaluated by carrying out a series of full-scale loading tests of segment specimens on which the membrane was sprayed. From the tests, it was confirmed that the initial cracking loads increased by approximately 34% due to cracking retardation by membrane coating. Even though the increase of failure loads were not so high as cracking loads, the strain-softening behaviors were observed from specimens coated by the membrane. Therefore, it is expected that the membrane coated on the inner surface of a lining might be effective in preventing its brittle failure.

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.591-597
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• 2012

For heat exchanger applications, 2-ply clad materials were fabricated by rolling of aluminum (Al) and mild steel sheets. Effects of annealing temperature on interface properties, especially on inter-layer formation and softening of strain hardened mild-steel, for Al/mild steel clad materials, were investigated. To obtain optimum annealing conditions for the Al/mild steel clad materials, annealing temperature was varied from room temperature to $600^{\circ}C$. At the annealing temperature about $450^{\circ}C$, an inter-layer was formed in an island-shape at the interface of the Al/mild steel clad materials; this island expanded along the interface at higher temperature. By analyzing the X-ray diffraction (XRD) peaks and the energy dispersive X-ray spectroscopy (EDX) results, it was determined that the exact chemical stoichiometry for the inter-layer was that of $Fe_2Al_5$. In some samples, an X-layer was formed between the Al and the inter-layer of $Fe_2Al_5$ at high annealing temperature of around $550^{\circ}C$. The existence of an X-layer enhanced the growth of the inter-layer, which resulted in the delamination of the Al/mild-steel clad materials. Hardness tests were also performed to examine the influence of the annealing temperature on the cold deformability, which is a very important property for the deep drawing process of clad materials. The hardness value of mild steel gradually decreased with increasing annealing temperature. Especially, the value of hardness sharply decreased in the temperature range between $525^{\circ}C$ and $550^{\circ}C$. From these results, we can conclude that the optimum annealing temperature is around $550^{\circ}C$ under condition of there being no X-layer creation.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.62-68
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• 2001

In order to characterize the microscopic fracture behaviour of the weldment din stress corrosion cracking(SCC) phenomena, SCC and acoustic emission(AE) tests were carried out simultaneously and the correlation between mechanical paramenters obtained from SCC and AE tests was investigated. In the case of base metal, much more AE events were produced at -0.5V than at -0.8V because of the dissolution mechanism before the maximum load. Regardless of the applied voltages to the specimens, however, AE events decreased after the maximum load. In the case of weldment, lots of AE events with larger amplitude $range(40{\sim}100dB)$ were produced because of the singularities of weld HAZ in comparision to the base metal and post-weld heat-treated(PWHT) specimens. Numerous and larger cracks for the weldment were observed on the fractured surfaces by SEM examination. From these results, it was concluded that SCC for the weldment appeared most severely in synthetic seawater. Weld HAZ was softened by PWHT which also contributed to the reduced susceptibility to corrosive environment in comparison to the weldment.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.259-266
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• 2009

The steel pipe of steel-concrete composite piles increases the pile strength and induces the ductile failure by constraining the deformation of the inner concrete. In this research, the numerical models and the related input parameters were analyzed to simulate the axial load-movement relations, which were obtained from the compression loading tests for the cylindrical specimens of the steel pipe, the concrete, and the steel-concrete composite. As the results, the behavior of the steel pipe was simulated by the von-Mises model and that of the concrete by the strain-softening model, which decreases cohesion and dilation angles as the function of plastic strains. In addition, the reinforcing bars in the concrete were simulated by applying the yielding moment and decreasing the sectional area of the bars. The applied numerical models properly simulated the yielding behavior and the reinforcement effect of the steel-concrete composite piles. The parametric study for the real-size piles showed that the material strength of the steel-concrete composite pile increased about 10% for the axial loading and about 20~45% for the horizontal loading due to the reinforcement effect by the surrounding steel pipe pile.