• Title/Summary/Keyword: yield criterion

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Computer Simulation of Hemispherical Forming Process Texture-based Work hardening and Anisotropy (집합조직 기초 가공경화와 이방성에 의한 반구 성형공정의 전산 시뮬레이션)

  • Sim, J.K.;Keum, Y.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.199-202
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    • 2006
  • The hardening and anisotropy based on the crystal plasticity is considered in the numerical simulation of hemispherical sheet forming process to find more realistic simulation results For calculating the yield shear stresses of each crystal, Taylor's model of the crystalline aggregate is employed. The yield stress of crystalline aggregate is computed by averaging the yield stresses of the crystal. The hardening is evaluated by using the Taylor factor and the critical resolved shear stress of the crystal. In addition, by observing the crystallographic texture and slip system, the anisotropy of the sheet is traced during the forming process. The anisotropy and hardening behaviors of the sheet found by the crystal plasticity are described better than those of obtained from the Hill's quadratic criterion based on the continuum plasticity.

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Determining the Harest Time for Maximum Yield and Qualty of Ochardgrass Swards (Orchardgress 단파초지의 최고생산과 질적향상을 위한 취확적기의 결정)

  • Chang, Nam-Kee;Lee, Sung-Kyu;Kim, Sung-Ha
    • Journal of The Korean Society of Grassland and Forage Science
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    • v.3 no.2
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    • pp.86-91
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    • 1983
  • The harvest schedule for maximum total yield and quality of orchardgrass sward was studied on the basis of theoretical analysis due to Chang's total yield equation. Harvesting at the 10% bloom stage of morphological development of orchardgrass swards was selected as a criterion which provided highest dry matter (DM) yield in conjunction with high and consistent levels of in vitro dry matter digestibility (IVD) and crude protein contents (CP) from harvest to harvest. However, since orchardrass after the 1st cutting do not bloom, the harvest time for the maximum yield and quality of orchardgrass swards is replaced by the three should time of the ceiling leaf area index (LAI).

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Plastic deformation characteristic of titanium alloy sheet (Ti-6Al-4V) at elevated temperature (티타늄 합금판재(Ti-6Al-4V)의 고온 소성면형특성(1))

  • Park, J.G.;Kim, J.H.;Park, N.K.;Kim, Y.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.05a
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    • pp.158-163
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    • 2009
  • Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle. However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. In the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile and biaxial tensile test of Ti-6Al-4V alloy sheet with thickness of 1.0mm were performed at elevated temperature of 873k. Biaxial tensile tests with cruciform specimen were performed until the specimen was breakdown to characterize the yield locus of Ti-6Al-4V alloy sheet. The experimental results for yield locus are compared with the theoretical predictions based on Von Mises, Hill, Logan-Hosford, and Balat's model. Among these Logan-Hosford's yield criterion well predicts the experimental results.

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Random Regression Models Are Suitable to Substitute the Traditional 305-Day Lactation Model in Genetic Evaluations of Holstein Cattle in Brazil

  • Padilha, Alessandro Haiduck;Cobuci, Jaime Araujo;Costa, Claudio Napolis;Neto, Jose Braccini
    • Asian-Australasian Journal of Animal Sciences
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    • v.29 no.6
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    • pp.759-767
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    • 2016
  • The aim of this study was to compare two random regression models (RRM) fitted by fourth ($RRM_4$) and fifth-order Legendre polynomials ($RRM_5$) with a lactation model (LM) for evaluating Holstein cattle in Brazil. Two datasets with the same animals were prepared for this study. To apply test-day RRM and LMs, 262,426 test day records and 30,228 lactation records covering 305 days were prepared, respectively. The lowest values of Akaike's information criterion, Bayesian information criterion, and estimates of the maximum of the likelihood function (-2LogL) were for $RRM_4$. Heritability for 305-day milk yield (305MY) was 0.23 ($RRM_4$), 0.24 ($RRM_5$), and 0.21 (LM). Heritability, additive genetic and permanent environmental variances of test days on days in milk was from 0.16 to 0.27, from 3.76 to 6.88 and from 11.12 to 20.21, respectively. Additive genetic correlations between test days ranged from 0.20 to 0.99. Permanent environmental correlations between test days were between 0.07 and 0.99. Standard deviations of average estimated breeding values (EBVs) for 305MY from $RRM_4$ and $RRM_5$ were from 11% to 30% higher for bulls and around 28% higher for cows than that in LM. Rank correlations between RRM EBVs and LM EBVs were between 0.86 to 0.96 for bulls and 0.80 to 0.87 for cows. Average percentage of gain in reliability of EBVs for 305-day yield increased from 4% to 17% for bulls and from 23% to 24% for cows when reliability of EBVs from RRM models was compared to those from LM model. Random regression model fitted by fourth order Legendre polynomials is recommended for genetic evaluations of Brazilian Holstein cattle because of the higher reliability in the estimation of breeding values.

Inclusion of bioclimatic variables in genetic evaluations of dairy cattle

  • Negri, Renata;Aguilar, Ignacio;Feltes, Giovani Luis;Machado, Juliana Dementshuk;Neto, Jose Braccini;Costa-Maia, Fabiana Martins;Cobuci, Jaime Araujo
    • Animal Bioscience
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    • v.34 no.2
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    • pp.163-171
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    • 2021
  • Objective: Considering the importance of dairy farming and the negative effects of heat stress, more tolerant genotypes need to be identified. The objective of this study was to investigate the effect of heat stress via temperature-humidity index (THI) and diurnal temperature variation (DTV) in the genetic evaluations for daily milk yield of Holstein dairy cattle, using random regression models. Methods: The data comprised 94,549 test-day records of 11,294 first parity Holstein cows from Brazil, collected from 1997 to 2013, and bioclimatic data (THI and DTV) from 18 weather stations. Least square linear regression models were used to determine the THI and DTV thresholds for milk yield losses caused by heat stress. In addition to the standard model (SM, without bioclimatic variables), THI and DTV were combined in various ways and tested for different days, totaling 41 models. Results: The THI and DTV thresholds for milk yield losses was THI = 74 (-0.106 kg/d/THI) and DTV = 13 (-0.045 kg/d/DTV). The model that included THI and DTV as fixed effects, considering the two-day average, presented better fit (-2logL, Akaike information criterion, and Bayesian information criterion). The estimated breeding values (EBVs) and the reliabilities of the EBVs improved when using this model. Conclusion: Sires are re-ranking when heat stress indicators are included in the model. Genetic evaluation using the mean of two days of THI and DTV as fixed effect, improved EBVs and EBVs reliability.

Design of a Thrust Stand Using Flexure (플렉셔를 적용한 추력 시험대 설계)

  • Jin, Juneyub;Park, Youngseok;Lee, Changwook;Jeong, Sangseop;Lee, Juhyung;Baek, Cheulwoo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.49 no.3
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    • pp.205-212
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    • 2021
  • In this study, two types of thrust stand modeling were proposed for the design of a thrust stand using flexure. Type A model generate combined load for tangential (thrust) and axial compressive load (self weight). And type B generate combined load for tangential and axial tensile load. The research was done by comparing the influence of the load between the models through a 1D calculation and computational analysis. The 1D calculated value and the computational analysis value were compared for a total of 10 sections and the results were confirmed to be very similar. In order to prove the validity of the analysis results, the equivalent stress was confirmed from the computational analysis of the flexure, and the production of the Type B model was selected from the evaluation of the yield condition (Von-Mises Yield Criterion).

Structural stability analysis of waste packages containing low- and intermediate-level radioactive waste in a silo-type repository

  • Byeon, Hyeongjin;Jeong, Gwan Yoon;Park, Jaeyeong
    • Nuclear Engineering and Technology
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    • v.53 no.5
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    • pp.1524-1533
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    • 2021
  • The structural stability of a waste package is essential for containing radioactive waste for the long term in a repository. A silo-type disposal facility would require more severe verification for the structural integrity, because of radioactive waste packages staked with several tens of meters and overburdens of crushed rocks and shotcretes. In this study, structural safety was analyzed for a silo-type repository, located approximately 100 m below sea level in Gyeongju, Korea. Finite element simulation was performed to investigate the influence of the loads from the backfilling materials and waste package stacks on the mechanical stress of the disposed of wastes and containers. It was identified that the current design of the waste package and the compressive strength criterion for the solidified waste would not be enough to maintain structural stability. Therefore, an enhanced criterion for the compressive strength of the solidified waste and several reinforced structural designs for the disposal concrete container were proposed to prevent failure of the waste package based on the results of parametric studies.

Seismic behavior of Q690 circular HCFTST columns under constant axial loading and reversed cyclic lateral loading

  • Wang, Jiantao;Sun, Qing
    • Steel and Composite Structures
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    • v.32 no.2
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    • pp.199-212
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    • 2019
  • This paper presents an investigation on seismic behavior of out-of-code Q690 circular high-strength concrete-filled thin-walled steel tubular (HCFTST) columns made up of high-strength (HS) steel tubes (yield strength $f_y{\geq}690MPa$). Eight Q690 circular HCFTST columns with various diameter-to-thickness (D/t) ratios, concrete cylinder compressive strengths ($f_c$) and axial compression ratios (n) were tested under the constant axial loading and reversed cyclic lateral loading. The obtained lateral load-displacement hysteretic curves, energy dissipation, skeleton curves and ductility, and stiffness degradation were analyzed in detail to reflect the influences of tested parameters. Subsequently, a simplified shear strength model was derived and validated by the test results. Finally, a finite element analysis (FEA) model incorporating a stress triaxiality dependent fracture criterion was established to simulate the seismic behavior. The systematic investigation indicates the following: compared to the D/t ratio and axial compression ratio, improving the concrete compressive strength (e.g., the HS thin-walled steel tube filled with HS concrete) had a slight influence on the ductility but an obvious enhancement of energy dissipation and peak load; the simplified shear strength model based on truss mechanism accurately predicted the shear-resisting capacity; and the established FEA model incorporating steel fracture criterion simulated well the seismic behavior (e.g., hysteretic curve, local buckling and fracture), which can be applied to the seismic analysis and design of Q690 circular HCFTST columns.

Forming Limit Diagrams of Zinc and Zinc Alloy Coated Steel Sheets (아연도금강판의 성형한계도)

  • 권재욱;이동녕;김인수
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1994.03a
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    • pp.92-100
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    • 1994
  • Forming limit diagrams for three different galvanized deep drawing quality steel sheets have been measured by hemispherical punch stretching. The experimental forming limit diagrams have been compared with results calculated using the shear instability criterion and the M-K model which takes into account a strain gradient effect resulting from bending (curvature) of a flat sheet by punch stretching. The measured data were in good agreement with the results calculated using exponent M value of 8 in Hosford's yield criterion for the M-K model and M= 6 for the shear instability model.

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Prediction of Forming Limit Diagram Dependent on Strain History in Sheet Metal Forming (변형경로를 고려한 판재의 성형한계도 예측)

  • Kim, Nak-Su;Choe, Gwang-Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.7
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    • pp.1107-1118
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    • 2001
  • The forming limit diagram introduced by Keeler and Goodwin has been used generally to analyze the formability of sheet metal. However, path dependent forming limit curves based on the state of strain can be explained only by a single criterion which is based on the state. In this study, experimental forming limits in strain space of some metal sheets are transformed into forming limit curves in stress space. Effects of yield criterion are investigated in transforming the forming limit curves. Some important design aspects which are based on the close prediction of movements in forming limit curves during sheet forming are concluded.