• Tunnel and Underground Space
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• v.23 no.5
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• pp.362-371
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• 2013

We conducted hollow cylinder tensile strength tests and Brazilian tests in Seokmo granite to measure tensile strength necessary for estimating the magnitude of the maximum horizontal principal stress in hydraulic fracturing stress measurements. Two different pressurization rates were used in hollow cylinder tests. Tensile strengths were determined to be higher at higher pressurization rate, which suggests that tensile strength should be measurement at the same rate used in actual in situ hydraulic fracturing tests. Considering the effect of pressurization rate and specimen size on tensile strength, the hollow cylinder tests and Brazilian tests yield similar results each other. This demonstrates that Brazilian tests can be utilized to produce representative tensile strengths for interpretation of hydraulic fracturing test results.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.211-219
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• 2005

Nowadays, various grades of high-strength steels are available. The application of ultra-high grades of steels for building structures, however, is limited only to the elements stressed under tension. The highest grade of steels generally used has a tensile strength of around 600N/mm2. Most research is focused on lower yield ratios of high strength steel in the inelastic range to ensure the stability of structures. In this paper, however, the possibility of an effective application of high strength steel with high yield ratio to building structures is discussed. An efficient structural system and a design method based on earthquake response analysis and experimental results are proposed.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.595-600
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• 2011

This paper investigates the effect of strain rate on the anisotropic deformation behavior of advanced high strength steel sheets. Uniaxial tensile tests were carried out on TRIP590 and DP780 steel sheets at strain rates ranging from 0.001/sec to 100/sec to determine yield stresses and r-values at various loading angles from the reference rolling direction. R-values were determined by the digital image correlation technique. Hill48 and Yld2000-2d yield functions were tested for their capability to describe the plastic deformation anisotropy of the materials. Initial yield loci were constructed using the Yld2000-2d yield function, which adequately described the anisotropic behavior of the materials. The shape of the initial yield loci was found to change with different strain rate, and the anisotropic behavior decreased with increasing strain rate.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.1
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• pp.66-76
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• 2017

This paper is concerned with investigating the plastic material properties of steel plate formed by line heating method, and is aimed at implementing more rational design considering the accidental limit states such as collision or grounding. For the present study, line heating test for marine grade steel plate has been carried out with varying plate thickness and heating speed, and then microscopic examination and tensile test have been carried out. From the microscopic, it is found that the grain refined zones like ferrite and pearlite are formed all around the heat affected zone. From the tensile test results, it is seen that yield strength, tensile strength, fracture strain, hardening exponent and strength coefficient vary with plate thickness and heat input quantity. The formulae relating the material properties and heat input parameter should be, therefore, derived for the design purpose considering the accidental impact loading. This paper ends with describing the extension of the present study.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.1
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• pp.255-263
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• 2001

The main purpose of this paper is to investigate strength characteristics of Aluminum 2024-T3 in high temperature environment. Tensile test of Aluminum 2024-T3 has been carried out in high temperature environment. The stress-strain relations are investigated with temperature and Young's modulus, yield strength and ultimate strength are deduced from the test results. The modulus and strength of the test are compared with those of MIL HANDBOOK and tips on structural design in high temperature environment are suggested.

• Journal of Power System Engineering
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• v.4 no.1
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• pp.74-80
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• 2000

This present study was investigated effect of Ni contents on the high temperature strength characteristic in 9Cr ferritic heat-resistant steel added 1.7%W in place of Mo in order to restraint laves phase formation. Precipitation amount of carbide, number of particle per unit area and particle size of carbide were decreased with increase of Ni content. In the steels, carbides of $M_{23}C_6$ type was mainly precipitated, but laves phases could not precipitated. Tensile and yield strength, creep strength and creep rupture time was decreased, but elongation were increased due to decreasing of particle number per unite area and carbide amount precipitated with increase of Ni content.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.153-160
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• 1998

The sectional dimensions and initial crookedness of the RHS(rectangular hollow section, ${\boxe}-75{\times}75{\times}3.2,\;{\boxe}-100{\times}100{\times}4.2,\;{\boxe}-125{\times}125{\times}6.0$) were measured. The axial compressive strength tests for columns with slenderness $46{\sim}84$ were performed as well as stub tests and tensile tests. FEM analysis was also used. The measurement shows that the errors of sectional dimensions are negligible. For the column length corresponding to ${\lambda}=100$, the initial crookedness with the 2.5% probability estimated from the measured results is 1/490, 1/1121 1/1395 for each section respectively. The yield strengths obtained from tensile test are higher than the specified minimum value by more than 30%. The column test shows that the maximum axial resistances are almost same as, or a little higher than the FEM results and the specified strength curves of AISC Specification and Eurocode, when the maximum strengths from the stub tests are used as the yield strength of the steel. But the test results show much higher column strength than those specified in the Standard and Code, when the specified minimum yield strength of the steel is used.

• Journal of Korean Society of Steel Construction
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• v.24 no.5
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• pp.503-510
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• 2012

High performance, high strength steels were developed and used in steel structures recently. Since the newly developed high strength steels posses different toughness, weldability, yield strength ratio, etc. in compare with conventional structural steels, it is requred to investigate the applicability of the design strength of fillet weld specified in the existing design codes. The comparison of the design strengths of various codes from domestic and overseas shows quite a difference. Test results for fillet weld strengths were collected and statistically analysed. Each of yield strength, tensile strength of parent material and tensile strength of weld metal was selected as a main parameter for each estimation equation respectively. All the estimation equations yield almost same values for each type of steel regardless the type of main parameter selected. Considering the behaviour of fillet welded joints and for practical purposes, it is proposed that the equation with tensile strength of parent material is to be used in design codes. The comparison with the proposed nominal strengths of fillet welds shows that the existing design codes could lead to an uneconomical result for low strength steels and lie on an unsafe side for high strength steels.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.20 no.1
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• pp.66-74
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• 2024

This study investigates the effects of temperatures and strain rates on the strength and ductility of Gr.91 (ASME Grade 91) steel which is widely being used as a heat-resistant material in Generation IV nuclear and super critical thermal power plants. The tensile behavior of modified 9Cr-1Mo (Gr.91) steel was studied for the three strain rates of 6.67×10^-5/s, 6.67×10^-4/s and 6.67×10-3/s over the temperature range from room temperature (RT) to 650℃. Experimental results showed that at specific combinations of temperatures (300~400℃) and strain rates, serrations appeared in the stress-strain curves. Concurrently, abnormal behaviors such as a plateau in yield strength and tensile strength, a minimum in ductility and negative strain rate sensitivity were observed. These phenomena were analyzed as significant characteristics of dynamic strain aging (DSA). Since this abnormal behavior in Gr.91 steel affects the material strength, it is judged that a correlation analysis between DSA and material strength should be crucial in the design and integrity evaluation of Gr. 91 steel pressure vessel and piping subjected to high-temperature loading.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.2
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• pp.75-81
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• 2015

Effects of B and Cu additions on the microstructure and mechanical properties of high-strength bainitic steels were investigated in this study. Six kinds of high-strength bainitic steels with different B and Cu contents were fabricated by thermo-mechanical control process composed of controlled rolling and accelerated cooling. The microstructures of the steels were analyzed using optical and transmission microscopy, and the tensile and impact tests were conducted on them in order to investigate the correlation of microstructure with mechanical properties. Depending on the addition of B and Cu, various low-temperature transformation products such as GB (granular bainite), DUB (degenerated upper bainite), LB (lower bainite), and LM (lath martensite) were formed in the steels. The addition of B and Cu increased the yield and tensile strengths because of improved hardenability and solid solution strengthening, but decreased the ductility and low-temperature toughness. The steels containing both B and Cu had a very high strength above 1.0 GPa, but showed a worse low-temperature toughness of higher DBTT (ductile-to-brittle transition temperature) and lower absorbed energy. On the other hand, the steels having GB and DUB showed a good combination of tensile and impact properties in terms of strength, ductility, yield ratio, absorbed energy, and DBTT.