• International Journal of Precision Engineering and Manufacturing
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• v.6 no.4
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• pp.55-59
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• 2005

This paper presents a feasibility study whether Shida's constitutive equation being widely used for plain carbon steel in steel manufacturing industry can be extended to alloy steels with a due carbon equivalent model. T,he constitutive relation of the alloy steels (SAE9254, AISI52100 and AISI4140) is measured using hot deformation simulator (GLEEBLE 3500C) at high temperatures ($800^{\circ}C{\~}1000^{\circ}C$) within strain rates of $0.05{\~}40\;s^{-1}$. It has been found the predicted flow stress behavior (constitutive relation) of AISI52100 steel is in agreement with the measured one. On the other hand, the measured flow stress behavior of SAE9254 and AISI4140 steel partly concords with the predicted one when material experiences relatively high strain rate ($10{\~}40\;s^{-1}$) deformation at low temperature ($800^{\circ}C$). It can be deduced that, for AISI52100 steel, Shida's equation with the carbon equivalent model can be applicable directly to the roughing and intermediate finishing stand in hot rolling process for calculating the roll force and torque.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.625-631
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• 2014

To investigate the deformation properties of TiC-(5-20) mol% Mo solid solution single crystals at high temperature by compression testing, single crystals of various compositions were grown by the radio frequency floating zone technique and were deformed by compression at temperature from 1250K to 2270K at strain rates from $5.1{\times}10^{-5}$ to $5.9{\times}10^{-3}/s$. The plastic flow property of solid solution single crystals was found to be clearly different among a three-temperature range (low, intermediate and high temperature ranges) whose boundaries were dependent on the strain rate. From the observed property, we conclude that the deformation in the low temperature range is controlled by the Peierls mechanism, in the intermediate temperature range by the dynamic strain aging and in the high temperature range by the solute atmosphere dragging mechanism. The work softening tends to become less evident with an increasing experimental temperature and with a decreasing strain rate. The temperature and strain rate dependence of the critical resolved shear stress is the strongest in the high temperature range. The curves are divided into three parts with different slopes by a transition temperature. The critical resolved shear stress (${\tau}_{0.2}$) at the high temperature range showed that Mo content dependence of ${\tau}_{0.2}$ with temperature and the dependence is very marked at lower temperature. In the higher temperature range, ${\tau}_{0.2}$ increases monotonously with an increasing Mo content.

• Journal of Ocean Engineering and Technology
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• v.25 no.3
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• pp.73-84
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• 2011

This is the fifth in a series of companion papers dealing with the dynamic hardening properties of various marine structural steels at intermediate strain rates. Five steps of strain rate levels (0.001, 1, 10, 100, 200/s) and three steps of temperature levels (LT ($-40^{\circ}C$), RT, and HT ($200^{\circ}C$)) were taken into account for the dynamic tensile tests of three types of marine structural steels: API 2W50 and Classifications EH36 and DH36. The total number of specimens was 180 pieces. It was seen that the effects of dynamic hardening became clearer at LT than at RT. Dynamic strain aging accompanying serrated flow stress curves was also observed from high temperature tests for all kinds of steels. The dynamic hardening factors (DHFs) at the two temperature levels of LT and RT were derived at the three plastic strain levels of 0.05, 0.10, 0.15 from dynamic tensile tests. Meanwhile, no DHFs were found for the high temperature tests because a slight negative strain rate dependency due to dynamic strain aging had occurred. A new formulation to determine material constant D in a Cowper-Symonds constitutive equation is provided as a function of the plastic strain rate, as well as the plastic strain level. The proposed formula is verified by comparing with test flow stress curves, not only at intermediate strain rate ranges but also at high strain rate ranges.

• Tunnel and Underground Space
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• v.22 no.1
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• pp.12-21
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• 2012

Although the Mohr-Coulomb and Hoek-Brown failure criteria have been adopted widely in rock mechanics, they neglect the ${\sigma}_2$ effect. The result of true triaxial tests on rock samples, however, reveals that the ${\sigma}_2$ effect on strength of rocks is considerable, so that rock failure criteria taking into account the influence of ${\sigma}_2$ are necessary for the precise stability evaluation of rock structures. In this study, a new nonlinear 3-D failure criterion has been suggested by combining the Hoek-Brown criterion with the smooth octahedral shape function taken from Jiang & Pietruszczak (1988). The performance of the new criterion was assessed by comparing the strength predictions from both the suggested criterion and the corresponding linear 3-D criterion. The resulting fit of the new criterion to the true triaxial test data for six rock types taken from the literature shows that the criterion fits the experimental data very well. Furthermore, for the data sets having data taken in the low ${\sigma}_3$ range, the nonlinear failure criterion works better than the linear criterion.

• Journal of the Korean Geosynthetics Society
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• v.14 no.1
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• pp.11-21
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• 2015

This study aims at investigating of the behavioral characteristics of foundation ground subjected to a strip load in anisotropy. Using marine clays sampled at Shihwa area, a series of laboratory tests including triaxial compressive test, plane strain compressive and expansion tests that allows horizontal deformation only and zero strain (${\varepsilon}_2$) in the direction of intermediate stress (${\sigma}_2$) are conducted. In addition, a numerical analysis using parameters obtained from the tests is carried out. In the numerical analysis, Cam-clay model that simulates the behavior of natural deposited clay properly is adopted. The analysis results show that the vertical displacements of the plane strain compressive tests are relatively larger than those of triaxial compressive tests by 18-25%. Likewise, the horizontal displacements is 13-19% larger.

• The Korean Journal of Community Living Science
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• v.22 no.3
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• pp.429-444
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• 2011

The objective of this study was to identify the risk factor and protection factor related to suicide ideation in each life course based on an ecological-system perspective. A questionnaire was carried out for 393 adolescents, 473 adults and 376 aged men living nationwide. The results are as follows. First, the suicide ideation was low with 1.78 points in the full mark of 5 points. Second, the difference in suicide ideation, depression, hopelessness, stress in the organic system variables, family solidarity in the micro system variables, intermediate system variables, residence, the existence/inexistence of counselling center and the influence of mass media in mezo system variables in each life course were significant. Third, the relative influence of organic system variables on the suicide ideation were largest in all life courses. Further, the depression and the influence of mass media in all life courses were a risk factor of suicide ideation and stress was also a risk factor of suicide ideation in the case of adolescents and the aged. When examining protection factors of suicide ideation, family solidarity, minute as it is, works as the protection factor of suicide ideation in the case of adolescents. For the adults, living in a metropolis was a protection factor from suicide ideation. For the aged, family solidarity, family history of suicide and adult children's attention to their friends and neighbors (intermediate system variable) were protection factors from suicide ideation. I suggested that policy, service, counseling and educational program proper to each life course were necessary to lower risk factors of suicide ideation and to improve protection factors.

• Journal of the Korean GEO-environmental Society
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• v.12 no.8
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• pp.13-24
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• 2011

In the part of geotechnical engineering, soils are classified as either the coarse grained soil or the fine-grained soil following the fine content($F_c$=50%) according to the granularity, and appropriate design codes are used respectively to represent their mechanical behaviour. However, sand-clay mixtures, which are typically referred to as intermediate soils, cannot be easily categorized as either sand or clay. In this study, several monotonic undrained shear tests were carried out on Silica sand fine mixtures with various proportions, and a wide range of soil structures, ranging from one with sand dominating the soil structure to one with fines controlling the behaviour, were prepared using compaction method or pre-consoldation methods in prescribed energy. The shear strength of mixtures below the threshold fines content is observed that as the fines content increases, maximum deviator stress ratio decrease for dense samples while an increase is noted for loose samples. Then, by using the concept of fines content and granular void ratio, the monotonic shear strength of the mixtures was estimated. It was found that the shear behavior of mixtures is greatly dependent on the skeleton structure of sand particles.

• The Journal of the Acoustical Society of Korea
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• v.18 no.3
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• pp.17-26
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• 1999

We present the first speech coarticulation database of Korean, English and Konglish/sup 3)/ named "SORIDA"/sup 4)/, which is designed to cover the maximum number of representations of coarticulation in these languages [1]. SORIDA features a compact database which is designed to contain a maximum number of triphones in a minimum number of prompts. SORIDA contains all consonantal triphones and vowel allophones in 682 Korean prompts of word length and in 717 English prompt words, spoken five times by speakers of balanced genders, dialects and ages. Korean prompts are synthesized lexicons which maximize their coarticulation variation disregarding any stress phenomena, while English prompts are natural words that fully reflect their stress effects with respect to the coarticulation variation. The prompts are designed differently because English phonology has stress while Korean does not. An intermediate language, Konglish has also been modeled by two Korean speakers reading 717 English prompt words. Recording was done in a controlled laboratory environment with an AKG Model C-100 microphone and a Fostex D-5 digital-audio-tape (DAT) recorder. The total recording time lasted four hours. SORIDA CD-ROM is available in one disk of 22.05 kHz sampling rate with a 16 bit sample size. SORIDA digital audio-tapes are available in four 124-minute-tapes of 48 kHz sampling rate. SORIDA′s list of phonetically-rich-words is also available in English and Korean.

• Structural Engineering and Mechanics
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• v.43 no.6
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• pp.739-759
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• 2012

The tailoring optimization technique recently developed by the author for improving structural response and energy absorption of composites is extended to sandwich shells using a previously developed zig-zag shell model with hierarchic representation of displacements. The in-plane variation of the stiffness properties of plies and the through-the thickness variation of the core properties are determined solving the Euler-Lagrange equations of an extremal problem in which the strain energy due to out-of-plane strains and stresses is minimised, while that due to their in-plane counterparts is maximised. In this way, the energy stored by unwanted out-of-plane modes involving weak properties is transferred to acceptable in-plane modes. As shown by the numerical applications, the critical interlaminar stress concentrations at the interfaces with the core are consistently reduced without any bending stiffness loss and the strength to debonding of faces from the core is improved. The structural model was recently developed by the author to accurately describe strain energy and interlaminar stresses from the constitutive equations. It a priori fulfills the displacement and stress contact conditions at the interfaces, considers a second order expansion of Lame's coefficients and a hierarchic representation that adapts to the variation of solutions. Its functional d.o.f. are the traditional mid-plane displacements and the shear rotations, so refinement implies no increase of the number of functional d.o.f. Sandwich shells are represented as multilayered shells made of layers with different thickness and material properties, the core being treated as a thick intermediate layer.

• Speech Sciences
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• v.12 no.4
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• pp.95-112
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• 2005

We investigate Korean learners' speech-timing of English before and after instruction in comparison with native speech, in an attempt to resolve disagreements in the literature as to whether speech-timing is measurable (Lehiste, 1977; Roach, 1982; Dauer, 1983 vs. Low et al., 2000; Yun 2002; Jian, 2004). We measured the pair-wise variability between the adjacent stressed and unstressed syllables within a foot as well as that among adjacent feet in approximately 555 English sentences, which were read by 29 native speakers and 41 Korean learners in the intermediate proficiency level. The results show that in comparison with native American English, Korean learner speech is before instruction significantly (p<.001) smaller for the pair-wise variability between the adjacent stressed and unstressed syllables within a foot; and significantly (p=.01) bigger for the variability among adjacent feet within the utterance. The learner speech after instruction showed significant (p=.01) improvement in the pair-wise variability of syllable sequence toward native speech values. The variability among adjacent feet was progressively smaller for learner speech before and after instruction and for native speech (p=.03). We thus conclude that the speech timing difference between Korean English and American English is measurable in terms of the duration. of stressed and unstressed syllables and that the latter is stress-timed and the former is syllable-timing interfered.