• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.617-626
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• 2008

This study is concerned with the effect of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels. Six kinds of steels were fabricated by varying alloying elements and hot-rolling conditions, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron back-scatter diffraction analysis. The tensile test results indicated that the B- or Cu-containing steels had the higher yield and tensile strengths than the B- or Cu-free steels because their volume fractions of bainitic ferrite and martensite were quite high. The B- or Cu-free steels had the higher upper shelf energy than the B- or Cu-containing steels because of their higher volume fraction of granular bainite. In the steel containing 10 ppm B without Cu, the best combination of high strengths, high upper shelf energy, and low energy transition temperature could be obtained by the decrease in the overall effective grain size due to the presence of bainitic ferrite having smaller effective grain size.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.103-111
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• 2007

Experimental study was carried out to investigate the structural performance of composite beams with steel fiber concrete and angle. For this purpose, seven specimens composed of two RC beams with or without steel fiber and five composite beams with steel fiber and angle were constructed and tested. All specimens had no web shear reinforcement. Main variables for the specimens were tensile reinforcement ratio and fiber volume fraction. Based on the test results, structural performance such as strength, stiffness, ductility and energy dissipation capacity was evaluated and compared with the predicted strength. The prediction of flexure and shear strength gives a good relationship with the observed strength. The strength, ductility and energy dissipation capacity are increased, as the fiber volume fraction is increased. Meanwhile, high tensile reinforcement ratio resulted in the reduction of ductility and energy dissipation capacity for the composite beams.

• Journal of Korean Society of Steel Construction
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• v.27 no.2
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• pp.251-260
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• 2015

The end plate connection is applied to beam-column moment connections in various forms. Such end plate connection displays changes in the behavioral characteristics, strength and stiffness, and energy dissipation capacity based on the thickness and length of the end plate, the number and diameter of the high strength bolt, the gauge distance of the high strength bolt, prying action force of the high strength bolt, and dimensions and length of the welds. Accordingly, this study has apprehended the axial tensile stiffness and prying action force of the high strength bolt connected on the tensile side based on the difference in thickness of the end plate, and was conducted to propose an analysis model for the prediction of such variables that affect the operating properties of the end plate. To achieve this, this study has conducted a three-dimensional non-linear finite-element analysis of the unstiffened expanding end plate connection by selecting only the thickness of the end plate as the variable.

• Transactions of Materials Processing
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• v.29 no.3
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• pp.151-156
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• 2020

In general, the cause of slab cracking during heat treatment has been analyzed with focus on processing conditions. However, in the present work, the cause of cracking is analyzed based on the microstructural evolution during heat treatment. The microstructural analysis indicates that the structure of the slab consists of three main regions as the top, quarter, and center parts. The tensile properties are investigated in each region of the slab in the temperature range from 25 to 350 ℃. Results demonstrate that the cracking is mainly attributed to the thermal stress and specific morphology of the microstructure. It is proposed that the cracking during the heat treatment is related to the presence of inclusion at the ferrite phase which is located at the boundary of pearlite grains.

• Steel and Composite Structures
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• v.19 no.3
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• pp.777-787
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• 2015

Production and properties of metal matrix composites reinforced with an in-situ high aspect ratio $AlB_2$ flake have been investigated. Boron 2.2wt.% was dissolved in pure Al and Al-Cu alloy at $1300^{\circ}C$ by adding directly boron oxide which resulted in 4 vol.% reinforcing phase. The in-situ $AlB_2$ flake concentration was increased up to 30 vol.% in order to increase the tensile strength of the composites. Hardness, compressive strength and tensile strength of the composite were measured and compared with their matrix. Results showed that 30 vol.% $AlB_2/Al$ composite show a 193% increase in the compressive strength and a 322% increase in compressive yield strength. Results also showed that ductility of composites decreases with adding $AlB_2$ reinforcements.

• Advances in concrete construction
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• v.4 no.4
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• pp.283-303
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• 2016

Several types of industrial byproducts are generated. With increased environmental awareness and its potential hazardous effects, the utilization of industrial byproducts in concrete has become an attractive alternative to their disposal. One such by-product is ground granulated blast furnace slag (GGBS), which is a byproduct of the smelting process carried out in the iron and steel industry. The GGBS is very effective in the design and development of high-strength and high-performance concrete. This paper reviews the effect of GGBS on the workability, porosity, compressive strength, splitting tensile strength, and flexural strength of concrete.

• Steel and Composite Structures
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• v.33 no.2
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• pp.299-306
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• 2019

The natural fibre composites are termed as bio-composites. They have shown a promising replacement to the current carbon/glass fibre reinforced composites as environmental friendly materials in specific applications. Natural fibre reinforced composites are potential materials for various engineering applications in automobile, railways, building and Aerospace industry. The natural fibre selected to fabricate the composite material is plant-based fibre e.g., sisal fibre. Sisal fibre is a suitable reinforcement for use in composites on account of its low density, high specific strength, and high hardness. Epoxy is a thermosetting polymer which is used as a resin in natural fibre reinforced composites. Hand lay-up technique was used to fabricate the composites by reinforcing sisal fibres into the epoxy matrix. Composites were prepared with the unidirectional alignment of sisal fibres. Test specimens with different fibre orientations were prepared. The fabricated composites were tested for mechanical properties. Impact test, tensile test, flexural test, hardness test, compression test, and thermal test of composites had been conducted to assess its suitability in industrial applications. Scanning electron microscopy (SEM) test revealed the microstructural information of the fractured surface of composites.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.146-156
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• 2020

Two High Tensile Strength Steel (EH47) plates with thickness of 70 mm were butt-welded together by multi-pass Submerged Arc Welding (SAW), also the hardness and welding residual stress were investigated experimentally. Based on Thermal-Elastic-Plastic Finite Element (TEP FE) computation, the thermal cycles during entire welding process were obtained, and the HAZ hardness of multi-pass butt welded joint was computed by the hardenability algorithm with considering microstructure evolution. Good agreement of HAZ hardness between the measurement and computational result is observed. The evolution of each phase was drawn to clarify the influence mechanism of thermal cycle on HAZ hardness. Welding residual stress was predicted with considering mechanical response, which was dominantly determined by last cap welds through analyzing its formation process.

• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.137-145
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• 2003

In this study, direct tensile fatigue tests of the PS bar were performed in terms of diameter, minimum stress level, and maximum stress level. In the static test, the stress - strain curve and ultimate streng th of the PS bar were determined. Results of the fatigue test indicate that the diameter of the PS bar was not influenced by fatigue life. Minimum stress also had quite an influence on the fatigue of the PS bar. Thus, the fatigue characteristic equation was proposed in terms of stress range and minimum stress through statistical process. Strains on specimen that loaded direct tension were measured in the fatigue test, with the secant modulus of elasticity calculated from measured strains. The strain development consisted of three different stages, i.e., rapid increases during the initial fatigue life, uniform increases during the middle stage, and rapid increases until failure. The secant modulus of elasticity decreased during the fatigue life with increasing strain. However, stress level seemed to have no influence on the secant modulus of elasticity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1107-1113
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• 2002

This study presents the hydrogen emblittlement in the metal, which decreases the ductility and then induces the brittle fracture. The contribution deals with the effect of strain rate and notch geometry on hydrogen emblittlement of 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, which are in use at high pressure vessel. Smooth and notched specimens were examined to obtain the elongation and tensile strength. For charging the hydrogen in the metal, the cathodic electrolytic method was used. In this process, current density is maintained constant. The amount of hydrogen penetrated in the specimen was detected by the hydrogen determenator(LECO RH404) with the various charging time. The distribution of hydrogen concentration penetrated in the specimen was obtained by finite element analysis. The amount of hydrogen is high in smooth specimen and tends to concentrate in the vicinity of surface. The elongation and tensile strength decreased with the passage of charging time in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels. The elongation increased and tensile strength decreased as strain rate increased. As a result of this study, it is supposed that 1.25Cr-0.5Mo steel is more sensitive than 2.25Cr-lMo steel in hydrogen embrittlement. Hydrogen embrittlement susceptibility of notched specimen after hydrogen charging is more remarkable than that of smooth specimen.