• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.902-910
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• 2002

Cast stainless steel may experience embrittlement when it is exposed approximately to 300$\^{C}$ for a long period. In the present investigation, the three classes of the thermally-aged CF8M specimen were prepared using an artificially-accelerated aging method. After the specimens were held for 300, 1800 and 3600hrs. at 430$\^{C}$, respectively, the specimens were quenched in water which is at room temperature. Load versus load line displacement curves and J-R curves were obtained using the unloading compliance method. talc values were obtained using the ASTM E813-87 and ASTM E 813-81 methods. In addition to these methods, talc values were obtained using the SZW (stretch zone width) method described in JSME S 001-1981. The results of the unloading compliance method are J$\_$Q/=543.9kJ/㎡ for virgin materials. The values of J$\_$IC/ for the degraded materials at 300, 1800 and 3600hrs. are obtained 369.25kJ/㎡, 311.02kJ/㎡, 276.7kJ/㎡, respectively. The results obtained by the SZW method are compared with those obtained by the unloading compliance method. Both results are quite similar. Through the elastic-plastic fracture toughness test, it is found that the value of loc is decreased with an increase of the aging time.

• Conservation and Restoration of Cultural Heritage
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• v.1 no.1
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• pp.9-22
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• 2012

The most widely excavated iron artifacts used as weapons or farm tools from central southern regions of Korea were subjects of non-metallic inclusion analysis through metallographic examination, microhardness measurement, and scanning electron microscopy with energy dispersive X-ray spectroscopy. Through metallographic interpretation and study of the analyzed results, the steel manufacturing and iron smelting using heat processing in the iron artifacts excavated from the central southern region of the ancient Korean peninsula was studied, and the analysis of the non-metallic inclusions mixed within the metallic structures was interpreted as the ternary phase diagram of the oxide to infer the type of iron ores for the iron products and the temperature of the furnace used to smelt them. Most of the ancient forged iron artifacts showed $Al_2O_3/SiO_2$ with high $SiO_2$ contents and relatively low $Al_2O_3$ contents for iron ore, indicating t hat for $Al_2O_3$ below 5%, it is presumed that magnetic iron ores were reduced to bloom iron (sponge iron) with direct-reduction process for production. The temperature for extraction of wustite for $Al_2O_3$ below 1% was found to be $1,020{\sim}1,050^{\circ}C$. Considering the oxide ternary constitutional diagram of glassy inclusions, the steel-manufacturing temperature was presumed to have been near $1,150{\sim}1,280^{\circ}C$ in most cases, and minimum melting temperature of casting iron part excavated in Daeseong-ri. Gyeonggi was near $1,400^{\circ}C$, and it is thought that hypoeutectic cast iron of about 2.3% carbon was casted and fragility of cast iron was improved by decarburizing in solid state.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.3
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• pp.397-412
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• 1995

The purpose of this study was to analyze the stress distribution in the dentin and post structures by the various post core materials and the amount of remaining coronal tooth structures. The 2-dimensional finite element models of mandibular 2nd premolars was divided into seven types according to the various amount of remaining coronal tooth structures. All types were modeled using equal length, diameter and shape of the post. 2 types of post and core materials were used : 1) cast gold post and core 2) stainless steel post and compsite resin core 10 Newton force was applied as follows 1) vertical force on occlusal fossa 2) $45^{\circ}$ oblique force on buccal surface of buccal cusp tip The results were as follows : 1. There was no apparent difference in the pattern of stress distribution according to the amount of remaining coronal tooth structure. 2. There was no apparent difference in the pattern of stress distribution within the dentin according to the post and core materials. A cast gold post and core generated lower dentin stress than a stainless steel post and resin core. 3. Max. dentinal stress resulting from vertical force was observed in the lingual side of dentin around the crown margin.This stress resulting from oblique force was observed in the lingual root surface of alveolar bone crest level.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.169-178
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• 1998

Bond strength of reinforcing bar to high-perfomance concrete using belite cement is explored using beam end test specimens. The key parameters for the bond test are slump of concrete, top bar effect, and strength of concrete in addition to concrete cover. The test results show that the specimens with belite cement concrete show approximately 10% higer bond strength than those with portland cement concrete. The results also show that the bond strength from the high strength concrete is function of the square root of concrete compressive strength. Bond strength of the top bar is less than bond strength of bottom bar, but the ratios of the bond strength of bottom-cast bars to those for top-cast bars are much less than the modification factor for top reinforcement found in the ACI 318-95 code. Comparisons with other reported tests identified that belite cement increased bond strength while silica fume or flyash used in high strength concrete decreased bond strength. The high-strength and high-slump concrete with belite cement performs well in terms of bond strength to reinforcing steel.

• Journal of Korean Society of Steel Construction
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• v.24 no.2
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• pp.207-215
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• 2012

The 45-degree cone failure theory has been used in concrete anchor bolts design under shear loading, but the CCD (Concrete Capacity Design) method was adopted as a new design method since 2000. However, the method was allowed only for anchor diameters of less than 50mm because it is based on the experimental results of small size anchor bolts. Therefore, it is necessary to develop a rational concrete breakout capacity equation for medium-to-large size anchor bolts with large edge distance. In this study, shear tests on M56 cast-in-place single anchor bolt with edge distance of 350mm were performed using four test specimens. Based on the test results and findings of existing studies, a new equation for the breakout capacity of anchor bolts under shear loading with edge distance of up to 750mm was proposed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2405-2412
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• 2000

A cast stainless steel may experience an embrittlement when it is exposed to approximately 30$0^{\circ}C$ for long period. In the present investigation, The three classes of the thermally aged CF8M specimie n are prepared using an artificially accelerated aging method. Namely, after the specimen are held for 300, 1800 and 3600hrs. at 43$0^{\circ}C$ respectively, the specimens are quenched in water to room temperature. Load versus load line displacement curves and J-R curves are obtained using the unloading compliance method. $J_{IC}$ values are obtained following ASTM E 813-87 and ASTM E 813-81 methods. In addition to these methods, JIC values are obtained using SZW(stretch zone width) method described in JSME S 001-1981. The results of the unloading compliance method are $J_Q$=485.7 kJ/m$^2$ for virgin material, $J_{IC}$ of the degraded materials associated with 300, 1800 and 3600hrs are obtained 369.25 kJ/m$^2$, 311.02 kJ/m$^2$, 276.7 kJ/m$^2$, respectively. The results of SZW method are similar to those of the unloading compliance method. Through the elastic-plastic fracture toughness test, it is found that the value of $J_{IC}$ is decreased with increasing of the aging time. The results obtained through the investigation can provide reference data for a leak before break(LBB) of reactor coolant system of nuclear power plants.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.1
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• pp.37-52
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• 1990

In this study, the characteristics of cooling and rolling during strip casting process is obtained in comparison with the experimental and analytical results. The prupose of this study is to effectively analyze the thermal and mechanical deformation of roller applying the results of the heat transfer and the pressure distribution to boundary conditions. And then the relation between strip thickness and roll deformation is shown. The second purpose is to obtain the proper condition of the continuous casting for stainless steel. The summary and conclusions can be made on the basis of the results obtained by the theories and experiments. a) The strip casting condition for the fine surface quality of tin-alloy as-cast material was obtained in accordance with the velocity of roll rotation and initial roll gap. b) The experimental condition that the dimension of the cast strip thickness coincide with that of the initial roll gap was according to the experimental result of continuous casting by twin-roll type. c) The thermoelastic finite element model to calculate the roll deformation is represented. Thermoelastic model prediction for the roll deformation are in good agreement with the experimental results considering the thermal expansion of the roll. d) The higher cooling rates were obtained by a twin-roller quenching technique. Also quenched microstructure of the rapidly solidified shell was verified. e) The magnitude of roll deformation due to the thermal expansion and roll separating force is quantit- atively represented in the analysis of continuous casting for stainless steel.

• Journal of Korean Society of Steel Construction
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• v.26 no.1
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• pp.21-30
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• 2014

In this study, an experimental study was performed to evaluate the shear resistance of cast-in-place(CIP) anchors reinforced with hairpin and stirrup bars under static and dynamic loads. The reinforcement was developed using D6 bars, and the anchors were installed with 20mm diameter and 120mm edge distance. Three tests were conducted for each type of reinforced anchor under static and dynamic shear load with a pulsating frequency of 1 Hz, respectively. It was found that the strength of hairpin-reinforced anchor was affected by the concrete cover and the dynamic tests showed no capacity reduction of anchors compared with static tests. The stirrup-reinforced anchor showed little increase of resistance compared with unreinforced anchor and the resistance under dynamic loading showed nearly same strength by static loading.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.493-501
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• 2011

The $45^{\circ}$cone failure theory has been used for concrete anchor bolt design, but the CCD (concrete capacity design) method was adopted as a new design method in 2000. The method was allowed to be used, however, only for anchors with a diameter of less than 50 mm and an embedment depth of less than 635 mm because it is based on the experiment results from medium-sized to small anchor bolts. Therefore, it is necessary to develop a rational concrete breakout capacity equation for medium-sized to large anchor bolts. In this study, tension tests on an M56 cast-in-place single anchor bolt with an effective embedment depth of 400-450 mm were carried out for the five test specimens. Based on the test results together with the other recent test results, the applicability of the concrete breakout capacity equation in the current design code to the large to medium-sized anchor bolts with an embedment depth of 280-1,200 mm was estimated.

• Transactions of Materials Processing
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• v.32 no.6
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• pp.344-351
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• 2023

The use of Zn-Al-Mg alloy coatings for enhancing the corrosion resistance of steel sheets is gaining prominence over traditional Zn coatings. There is a growing demand for the development of thermal spray wires made from Zn-Al-Mg alloys, as a replacement for the existing wires produced using Al and Zn. This is particularly crucial to secure corrosion resistance and durability in the damaged areas of coated steel sheets caused by deformation and welding. This study focuses on the casting and extrusion processes of Zn-2Al-1Mg alloy for the fabrication of such spray wires and analyzes the changes in microstructure during the extrusion process. The Zn-2Al-1Mg alloy, cast in molds, was subjected to a heat treatment at 250 ℃ for 3 hours prior to extrusion. The extrusion process was carried out by heating both the material and the mold up to 300 ℃. Microstructural analysis was conducted using FE-SEM and EDS to differentiate each phase. The mechanical properties of the cast specimen were evaluated through compression tests at temperatures ranging from 200 to 300 ℃, with strain rates of 0.1 to 5 sec^-1. Vickers hardness testing was utilized to assess the inhomogeneity of mechanical properties in the radial direction of the extruded material. Finite Element Analysis (FEA) was employed to understand the inhomogeneity in stress and strain distribution during extrusion, which aids in understanding the impact of heterogeneous deformation on the microstructure during the process.