• Korean Journal of Materials Research
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• v.29 no.3
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• pp.189-195
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• 2019

The effect of C, Mn, and Al additions on the tensile and Charpy impact properties of austenitic high-manganese steels for cryogenic applications is investigated in terms of the deformation mechanism dependent on stacking fault energy and austenite stability. The addition of the alloying elements usually increases the stacking fault energy, which is calculated using a modified thermodynamic model. Although the yield strength of austenitic high-manganese steels is increased by the addition of the alloying elements, the tensile strength is significantly affected by the deformation mechanism associated with stacking fault energy because of grain size refinement caused by deformation twinning and mobile dislocations generated during deformation-induced martensite transformation. None of the austenitic high-manganese steels exhibit clear ductile-brittle transition behavior, but their absorbed energy gradually decreases with lowering test temperature, regardless of the alloying elements. However, the combined addition of Mn and Al to the austenitic high-manganese steels suppresses the decrease in absorbed energy with a decreasing temperature by enhancing austenite stability.

• Steel and Composite Structures
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• v.31 no.2
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• pp.113-123
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• 2019

In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of $8.5g/m^2$ to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.

• Composites Research
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• v.13 no.3
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• pp.1-8
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• 2000

Excellent environmental durability and handy installation procedure as well as high specific strength and stiffness have introduced fiber-reinforced polymeric composite materials into the civil and architectural engineering field. This study presents the considerably enhanced strength characteristics of the mortal beams by being reinforced with epoxy-bonded carbon fiber sheets(CFS). Three point bending and Charpy impact tests were performed on both of bare and reinforced mortar specimens. The influences of length, and the number of reinforcing plies were investigated. Strength reduction due to pre-existent notch was lessened dramatically. The acoustic emission(AE) measurement revealed the progressive damage process in reinforced specimens.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.381-386
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• 1993

This paper describes the dynamic fracture behavior of brittle materials under impact loading by using INSAMCR program with instrumented charpy test machine. To calculate the Dynamic Stress Intensity Factor The finite element analysis methods program, INSAMCR, was used. Dynamic fracture characteristic was researched to verify a relationship between Dynamic Stress Intensity Factor and crack tip propagation velocity in WC-6%Co. The relationship between Dynamic Stress Intensity Factor and crack tip velocity revealed typical .GAMMA. shape. INSAMCR was run to verify experimental results in WC-6%Co and shows a good coincidence.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.138-140
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• 2004

In case of applying offshore standard of some class societies, the required impact test temperature is lower than that of class rule to be applied for general commercial ship. This study is performed to consider whether the impact value to be required at offshore standard of BV can be obtained or not under SAW method, 1 run both side welding, to be mainly used for butt joint of plates at domestic ship builder.

• Journal of the Korean Society for Nondestructive Testing
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• v.5 no.1
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• pp.24-33
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• 1985

A study has been made on the correlation between ultrasonic attenuation and mechanical properties with different prior austenite grain size. It was found that ultrasonic attenuation is increased with increasing grain size, decreasing yield strength and increasing charpy impact energy value for ALSI 4140 steel.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.635-640
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• 1995

Two techniques for the verification of the phase separation in ferrite phase of primary pressure bounary component materials, the primary cause of thermal aging embrittlement, are presented. Data base of room-temperature Charpy V-notch impact energy during reactor service was estimated as a measure of the degree of embrittlement. The serviceable period of CF-3 and CF-8 alloys as the primary pressure boundary components may be acceptably extended for 60 years of lifetime. However, the integrity of CF-8M alloys can be degraded seriously after several years of service in the nuclear reactor.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04a
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• pp.578-584
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• 1995

This investigation evaluates dynamic fracture characteristics of two alloy steels (STD-11 and STS-3 and a gray cast iron (GG-30). The dynamic crack initiation fracture toughness and some of the dynamic fracturing characteristics were evaluated by using the instrumented Charpy impact testing procedures. It was found from experimental results that inertia force strongly depends on impact velocity. The duration of inertia force was constant regardless of impact velocities in steel specimens.

• Journal of Korean Society of Steel Construction
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• v.17 no.3 s.76
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• pp.365-373
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• 2005

There is increasing need for high-strength steel especially for the high-rise steel building structure. High- strength steels, however, may have mechanical properties that are significantly different from those of the conventional steels.The application of high-strength steels to building structures should be reviewed as to whether inelastic behavior equivalent to that of conventional steels can be attained or not. In this study, SM570TMC steel, which was developed recently in Korea, was tested to evaluate mechanical properties and welding characteristics for use as a structural steel. Yield phenomenon of SM570TMC steel, which is continuous yielding, is quite different from that of conventional steel. The distributions of yield strength of SM570TMC steel were uniform regardless of thickness, while the minimum yield strength was 440MPa. Also, the flat distributions of hardness in z-direction were found to comprise one of the important properties. Results of the charpy impact tests at -5oC revealed toughness values of SM570TMC steel, which were higher than those of equivalent as rolled steel. Carbon equivalent(Ceq) values of SM570TMC steel, which were related to welding performance, were lower than those of equivalent as rolled steel.

• Journal of Welding and Joining
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• v.35 no.1
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• pp.26-33
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• 2017

This study aims to investigate the suitability of requirement for post-weld heat treatment(PWHT) temperature when different P-No. materials are welded, which is defined by ASME Sec. III Code. For SA-516 Gr. 60 and SA-106 Gr. B carbon steels that are typical P-No. 1 material, simulated heat treatment were conducted for 8 h at $610^{\circ}C$, $650^{\circ}C$, $690^{\circ}C$, and $730^{\circ}C$, last two temperature falls in the temperature of PWHT for P-No. 5A low-alloy steels. Tensile and Charpy impact tests were performed for the heat-treated specimens, and then microstructure was analyzed by optical microscopy and scanning electron microscopy with energy-dispersive spectrometry. The Charpy impact properties deteriorated significantly mainly due to a large amount of cementite precipitation when the temperature of simulated heat treatment was $730^{\circ}C$. Therefore, when dissimilar metal welding is carried out for P-No. 1 carbon steel and different P-No. low alloy steel, the PWHT temperature should be carefully selected to avoid significant deterioration of impact properties for P-No. 1 carbon steel.