• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.4
• /
• pp.92-100
• /
• 2015

The aim of this study is to evaluate the fracture characteristics of ductile fiber reinforced cement based composites with 1.5 volume ratio of polyvinyl alcohol and steel fiber by high velocity impact of steel projectile. We used gunpowder impact facility to evaluate the fracture characteristics of ductile fiber reinforced cement based composites by collision of steel projectile, and the impact velocity was from about 150 to 1,000m/s. The results of evaluation on the fracture characteristics of ductile fiber reinforced cement based composites were penetration grade, which is the kinetic energy more than three times of no-fiber reinforced specimen (Plain). In addition, ductile fiber reinforced cement based composites did not occurred critical damage other than the debris. In the case of mass loss, Plain specimen was proportional to kinetic energy of steel projectile, while ductile fiber reinforced cement based composites was not significantly affected by kinetic energy of steel projectile. In particular, this tendency had a close relationship with the fracture characteristics of back side of specimens, and the scabbing inhibiting efficiency of PVA specimen was higher than S specimen. In the results of verifying relationship between front and back side calculated by local damage, scabbing occurred at the region close to the back side in the ductile fiber reinforced cement based composites unlike Plain specimen. Thus, in this study, we examined principal fracture behaviors of ductile fiber reinforced cement based composites under collision of steel projectile, and verified that impact resistance performance was improved as compared to Plain specimen.

• Corrosion Science and Technology
• /
• v.15 no.4
• /
• pp.171-181
• /
• 2016

In this work, synergistic corrosion inhibition effect of nitrite and 3 kinds of ethanolamines on ductile cast iron using chemical and electrochemical methods was evaluated. This work attempts to clarify the synergistic effect of nitrite and ethanolamines. The effects of single addition of TEA, DEA, and MEA, and mixed addition of nitrite plus TEA, DEA or MEA on the corrosion inhibition of ductile cast iron in a tap water were evaluated. A huge amount of single addition of ethanolamine was needed. However, the synergistic effect by mixed addition was observed regardless of the combination of nitrite and triethanolamines, but their effects increased in a series of MEA + nitrite > DEA + nitrite > TEA + nitrite. This tendency of synergistic effect was attributed to the film properties and polar effect; TEA addition couldn't form the film showing high film resistance and semiconductive properties, but DEA or MEA could build the film having relatively high film resistance and n-type semiconductive properties. Moreover, it can be explained that this behaviour was closely related to electron attractive group within the ethanolamines, and thus corrosion inhibition power depends upon the number of the electron attractive group of MEA, DEA, and TEA.

• Journal of Korea Foundry Society
• /
• v.11 no.3
• /
• pp.217-227
• /
• 1991

The present study was conducted to estimate the fatigue crack growth rate of the Mo-Ni alloyed ductile cast iron for the influence of austempering temperature and time. The fatigue crack growth rate was affected by retained austenite. Retained austenite volume were higher with the ductile cast irons which were austempered at $360^{\circ}C$ than austempered at $260^{\circ}C$, and the fatigue crack growth rate of the former was lower than that of the latter. Also, the fatigue growth rate of the former was the lowest at austempering for 1 hour and that of the latter was the lowest at austempering for 3 hours.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.112-116
• /
• 2003

This paper describes the need for a ductile of Fiber Reinforced Plastic(FRP) reinforcement for concrete structures. The criteria to be met by the FRP, which are based on the properties of the steel rebar it is to replace, are threefold: high initial modulus, a definite yield point and a high level of ultimate strain. It is shown that the use of a fiber architecture based design methodology facilitates the optimization of the performance of FRP through material and geometric hybrid. Ductile hybrid FRP bars were successfully fabricated at 3mm and 5mm nominal diameters using an in-line braiding and pultrusion process.

• Journal of Korea Foundry Society
• /
• v.18 no.6
• /
• pp.593-603
• /
• 1998

Commercial ductile iron was coated with titanium and aluminum powders by low pressure plasma spraying and then irradiated with a $CO_2$ laser to produce anti-corrosive TiC composite layer. TiC carbides were precipitated homogeneously in a laser alloyed layer by in-situ reaction between carbon existed in the base metal and titanium with thermal sprayed coating. The formation of gas pores and brittle limited mixing zone with ledeburite microstructure in TiC composite layer were surpressed by the complementary alloying of aluminum. The hardness of TiC composite layer obtained by addition of titanium and aluminum was between 600 and 660 Hv, which was three times as high as the hardness of ferritic ductile iron. From the results of isothermal oxidation at 1123k for 24 hours in air, high temperature oxidation resistance of the TiC composite layer with aluminum was improved and doubled when compared with the TiC composite layer without aluminum.

• Journal of Korea Foundry Society
• /
• v.15 no.6
• /
• pp.558-565
• /
• 1995

Effects of high Si-P addition on microstructure and mechanical properties of thin ductile cast iron have been investigated. The amount of silicon addition have fixed on 4.0wt% and the amounts of phosphorus addition and thickness of specimen have been varied from 0.05 to 0.8wt% and ${\phi}13mm$, ${\phi}10mm$ and ${\phi}6mm$, respectively. As the casting thickness decreased, the average diameter of spheroidal graphite was decreased and the hardness of the cast iron increased. By adding P, the average diameter of spheroidal graphite was increased and the count of the spheroidal graphite was decreased continuously. And the tensile strength and the elongation was decreased, and the hardness was increased. With the P added more than 0.2wt%, the abraded amount was decreased significantly. The addition of P improved the wear resistance and the hardness of thin ductile cast iron.

• Journal of Korea Foundry Society
• /
• v.28 no.4
• /
• pp.170-174
• /
• 2008

Mechanical properties of high strength ductile cast iron for the brake caliper of truck were investigated. Meanwhile the nodularity and nodule count decreased respectively from 92 and 95 to 80% and $60/mm^2$ with increased thickness, the volume fractions of graphite, pearlite and ferrite didn't change much and were in the ranges of 12.0-13.5, 52.6-55.0 and 33.0-35.2, respectively. Hardness, tensile strength and elongation in the mechanical properties of the castings of brake caliper were BHN 241, 710 MPa and 9.5%, respectively.

• Nuclear Engineering and Technology
• /
• v.48 no.5
• /
• pp.1252-1263
• /
• 2016

This paper presents a numerical method to simulate ductile tearing in cracked components under high strain rates using finite element damage analysis. The strain rate dependence on tensile properties and multiaxial fracture strain is characterized by the model developed by Johnson and Cook. The damage model is then defined based on the ductility exhaustion concept using the strain rate dependent multiaxial fracture strain concept. The proposed model is applied to simulate previously published three cracked pipe bending test results under two different test speed conditions. Simulated results show overall good agreement with experimental results.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.313-316
• /
• 2005

In the recent design of high ductile fiber-reinforced cementitious composite ECC, which exhibits tensile strain-hardening behavior in the hardened state, optimizing both processing mechanical properties for specific applications is critical. This study introduced a method to develop useful ECCs in field, which possess the different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or spray processing). Control of rheological modulation was regarded as a key factor to allow the performance of the desired processing, while retaining the ductile material properties. To control the rheological properties of the composite, we first determined basic ECC compositon, which is based on micromechanics and steady-state cracking theory. The stability and consequent viscosity of suspensions were, then, mediated by optimizing dosages of chemical and mineral admixtures. The rheological properties altered by this approach were revealed to be effective in obtaining ECC hardened properties, allowing us to readily achieve the desired function of the fresh ECC.

• Journal of Korea Foundry Society
• /
• v.27 no.5
• /
• pp.203-208
• /
• 2007

The high temperature properties of vanadium and molybdenum added high silicon ductile iron, so called V-Mo-Si ductile iron, were investigated. The (V,Mo) complex carbides and Mo carbides precipitated at the cellular boundaries of the as-cast specimens. The microhardness of the (V,Mo) carbides were in the range of 553-619, while that of the Mo carbides in the range of 341-390. The thermo-mechanical tests were carried out with a Gleeble system at 700 and $800^{\circ}C$ under vacuum condition. The tensile strengths of the specimen tested at $700^{\circ}C$ with the dynamic deformation rate of 50 mm/sec and those with the static deformation rate of 0.15 mm/sec were 235.7 and 115.3 MPa, while the reduction in area were 23.7 and 22.4%, respectively. At the high dynamic deformation rates, the tensile strength was steeply increased due to promoting the brittle fracture of pearlite in the matrix of the specimens. But the changes of the reduction in area with the deformation rates on the same specimens were negligible. The weight gain of the V-Mo-Si specimens oxidized in the air atmosphere for 6 hours at 800 and $900^{\circ}C$ were 1.1 and 4.1.%, respectively. The cross-sectional microstructure of oxidized specimens consisted of the porous external scale layer grown outside from the original surface, the dense internal scale layer grown into the original surface, the decarburized ferrite layer between the internal scale and the matrix of base metal. The (V,Mo) carbides and Mo carbides formed in the matrix of as-cast specimen did not decompose during oxidation at 900 for 24 hours in air atmosphere.