Rate-dependent isotropic‒kinematic hardening model in tension‒compression of TRIP and TWIP steel sheets

Joo, Geunsu,Huh, Hoon Elsevier 2018 International journal of mechanical sciences Vol.146 No.-

<P><B>Abstract</B></P> <P>This paper presents a rate-dependent isotropic‒kinematic hardening model in tension‒compression of TRIP and TWIP steel sheets. The isotropic‒kinematic hardening model is widely utilized to describe the Bauschinger effect, transient behavior and permanent softening under reverse loading which are indispensable for numerical simulation of springback in sheet metal forming. The isotropic‒kinematic hardening model, however, has not yet been suggested for the strain rate effect higher than several tens per second although the high strain rate prevails in practical automotive sheet metal forming. This paper proposes a rate-dependent model based on tension‒compression tests of TRIP980 and TWIP980 steel sheets at various strain rates ranging from 0.001 s<SUP>−1</SUP> to 100 s<SUP>−1</SUP>. A proposed rate-dependent model is extended from the rate-independent Chaboche type model based on single-surface plasticity. Among three Chaboche type models, the Zang's model is selected as the basic rate-independent model considering both a small change of the work-hardening rate in monotonic loading and a constant stress offset of permanent softening in reverse loading. With the basic rate-independent model, the material parameters are acquired at each strain rate to check their dependency on the strain rate and then formulated as linear or exponential functions of the logarithmic scale of the strain rate. Consequently, the present rate-dependent model is proposed with incorporation of the basic rate-independent model and the rate-dependent functions for the material parameters.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A rate-dependent isotropic‒kinematic hardening model is proposed. </LI> <LI> Rate-dependent tension‒compression tests are performed for TRIP980 and TWIP980. </LI> <LI> The present model is extended from the rate-independent Chaboche type model. </LI> <LI> Material parameters are interpolated by rate-dependent functions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>This paper presents a rate-dependent isotropic‒kinematic hardening model in tension‒compression of TRIP and TWIP steel sheets. </P> <P>[DISPLAY OMISSION]</P>

Al-Li합금의 항복응력에 대한 변형속도 및 온도의존성에 관한 연구

오창섭 ( Chang Sup Oh ),한창석 ( Chang Suk Han ) 한국열처리공학회 2011 熱處理工學會誌 Vol.24 No.6

The effect of strain rate on the yield stress of an Al-Li alloy has been investigated at temperatures between 77 and 523 K and over the strain rate range from 1.77x10-4s-1 to 1.77x10-2s-1. At testing temperatures below 373 K, the yield stress is almost independent of strain rate at any aging stage. At testing temperatures above 373 K, the yield stress increases linearly with the logarithm of strain rate, and the strain rate dependence increases with increasing testing temperature. The yield stresses of under-aged alloy at temperatures between 373 and 473 K at high strain rates are greater than the yield stress at 77 K. For the alloy under-aged or aged nearly to its peak strength, the temperature range within which the positive temperature dependence of yield stress appears expands to the higher temperature side with increasing strain rate. The strain rate dependence of the yield stress is slightly negative at this aging stage. The yield stress of the over-aged alloy decreases monotonically with decreasing strain rate and with increasing testing temperature above 373 K. The modulus normalized yield stress is nearly constant at testing temperatures below 373 K at any strain rate investigated. And, strength depends largely both on the aging conditions and on the testing temperature. The peak positions in strength vs. aging lime curves shift to the side of shorter aging time with increasing testing temperature. For the specimens aged nearly to the peak strength, the positive temperature dependence of yield stress is observed in the temperature range. The shift of peak positions in the aging curves are explained in terms of the positive temperature dependence of cutting stress and the negative temperature dependence of by-passing stress. (Received August 30, 2011; Revised September 15, 2011; Accepted October 4, 2011)

Rate-dependent hardening model for polymer-bonded explosives with an HTPB polymer matrix considering a wide range of strain rates

Park, Chunghee,Huh, Hoon,Park, Jungsu SAGE Publications 2015 Journal of composite materials Vol.49 No.4

<P>This article is concerned with the effect of the strain rate on the strain hardening behavior of polymer-bonded explosives at a wide range of strain rates ranging from 0.0001 s<SUP>–1</SUP> to 3870 s<SUP>−1</SUP>. Inert polymer-bonded explosive simulants are prepared as specialized particulate composites to acquire analogous mechanical characteristics to polymer-bonded explosives for safety reasons. Uniaxial compressive tests were conducted from quasi-static states to intermediate strain rates ranging from 0.0001 s<SUP>−1</SUP> to 100 s<SUP>−1</SUP> with cylindrical specimens using a dynamic material testing machine (INSTRON 8801) and a high-speed material testing machine. An experimental method was developed for uniaxial compressive tests at intermediate strain rates ranging from 10 s<SUP>−1</SUP> to 100 s<SUP>−1</SUP>. Split Hopkinson pressure bar tests were performed at high strain rates ranging from 1250 s<SUP>−1</SUP> to 3870 s<SUP>−1</SUP>. Deformation behavior was investigated using captured images from a high-speed camera. The strain hardening behavior of polymer-bonded explosive simulants was formulated as a function of the strain rate with the proposed rate-dependent hardening model based on the DSGZ model. The model is capable of representing the complicated strain rate effects on the strain hardening behavior for rate-sensitive materials with a second-order exponentially-increasing function of the strain rate sensitivity. The rate-dependent hardening model of polymer-bonded explosives can be readily applied to prediction of deformation modes of polymer-bonded explosives in a warhead that undergoes severe dynamic loads.</P>

일 대학병원에서의 알코올 의존 환자의 외래 추적시 12개월 추적률

서유나(Yu-Na Seo),정희정(Hee-Jeong Jeong),김성곤(Sung-Gon Kim),신성현(Sung-Hyun Shin),위승범(Seung-Bum Wi),변원탄(Won-Tan Byun),박선희(Sunhee Park) 한국중독정신의학회 2010 중독정신의학 Vol.14 No.1

Alcohol dependence has high prevalence and recurrence rates. To reduce these recurrence rates, alcohol dependent patients must receive continuous follow-up. However, our country has rarely studied follow-up rates for these patients. Therefore, in this study, we retrospectively investigated 3-month and 12-month ambulant follow-up rates by reviewing the hospital charts of alcohol-de-pendent patients who had received treatment in a university hospital from 2001 to 2005. The results were as follows:1) During the 5 year period, 26.6% of subjects did not make a second hospital visit in the 3 months after their first visit, and statistical analyses of alcohol-dependent patients’ follow-up rates excluded them. The patient group that was ambulant for their first psychiatric examination (outpatients) showed significantly lower rates of incomplete hospital revisiting than did the hospitalized patient group (Inpatient). 2) Regarding the final subjects, the 3-month follow-up rates was 47.9%, and the 12-month follow-up rate was 12.1%. We found no differences between the outpatient and the inpatient groups in terms of the follow-up rates. In addition, com-pared to patients admitted by psychiatric residents, patients admitted by psychiatric specialists did not show significantly lower follow-up rates. This study is the first in our country to investigate the 12-month follow-up rates for both inpatients and outpatients in this population. This study shows the need for a prospective clinical study with more participants.

지역 합계출산율에 영향을 미치는 요인 분석: 횡단면 의존성을 고려한 모형을 이용하여

김소연,류수열 강원대학교 경영경제연구소 2024 Asia-Pacific Journal of Business Vol.15 No.1

Purpose - Low fertility rate is a serious problem, and this study analyzes factors affecting total fertility rate using panel data from 16 metropolitan cities and provinces in Korea from 2000 to 2022. Design/methodology/approach - Estimating the SAR model considering the weak cross-sectional dependence that exists in variables related to the regional total fertility rate, and using the DKSE estimation method considering the strong cross-sectional dependence. Findings - Estimation results considering weak and strong cross-sectional dependence were similar, confirming the robustness of the results. Female labor force participation rate has a positive effect on total fertility rate, and employment rate has no effect. However, the interaction term is a negative (-) sign. Crude marriage rate has a positive effect on total fertility rate, and apartment price has a slightly positive effect. Environmental factor has no effect, and policy factor has a negative effect. Research implications or Originality - In order for an increase in the female labor force participation rate to lead to an increase in the total fertility rate, qualitative improvements in female employment must be made. Financial investment policies for childbirth must increase their effectiveness. The problem of low fertility rate requires not only population policy but also social, economic, cultural, environmental, and policy conditions to be considered.

Approximate Calculation of Order Fill Rate under Purchase Dependence

Changkyu Park(박창규) 한국산업경영시스템학회 2017 한국산업경영시스템학회지 Vol.40 No.4

For the competitive business environment under purchase dependence, this paper proposes a new approximate calculation of order fill rate which is a probability of satisfying a customer order immediately using the existing inventory. Purchase dependence is different to demand dependence. Purchase dependence treats the purchase behavior of customers, while demand dependence considers demand correlation between items, between regions, or over time. Purchase dependence can be observed in such areas as marketing, manufacturing systems, and distribution systems. Traditional computational methods have a difficulty of the curse of dimensionality for the large cases, when deriving the stationary joint distribution which is utilized to calculate the order fill rate. In order to escape the curse of dimensionality and protect the solution from diverging for the large cases, we develop a greedy iterative search algorithm based on the Gauss-Seidel method. We show that the greedy iterative search algorithm is a dependable algorithm to derive the stationary joint distribution of on-hand inventories in the retailer system by conducting a comparison analysis of a greedy iterative search algorithm with the simulation. In addition, we present some managerial insights such as : (1) The upper bound of order fill rate can be calculated by the one-item pure system, while the lower bound can be provided by the pure system that consists of all items; (2) As the degree of purchase dependence declines while other conditions remain same, it is observed that the difference between the lower and upper bounds reduces, the order fill rate increases, and the order fill rate gets closer to the upper bound.

Approximate Calculation of Order Fill Rate under Purchase Dependence

박창규 한국산업경영시스템학회 2017 한국산업경영시스템학회지 Vol.40 No.4

For the competitive business environment under purchase dependence, this paper proposes a new approximate calculation of order fill rate which is a probability of satisfying a customer order immediately using the existing inventory. Purchase dependence is different to demand dependence. Purchase dependence treats the purchase behavior of customers, while demand dependence considers demand correlation between items, between regions, or over time. Purchase dependence can be observed in such areas as marketing, manufacturing systems, and distribution systems. Traditional computational methods have a difficulty of the curse of dimensionality for the large cases, when deriving the stationary joint distribution which is utilized to calculate the order fill rate. In order to escape the curse of dimensionality and protect the solution from diverging for the large cases, we develop a greedy iterative search algorithm based on the Gauss-Seidel method. We show that the greedy iterative search algorithm is a dependable algorithm to derive the stationary joint distribution of on-hand inventories in the retailer system by conducting a comparison analysis of a greedy iterative search algorithm with the simulation. In addition, we present some managerial insights such as : (1) The upper bound of order fill rate can be calculated by the one-item pure system, while the lower bound can be provided by the pure system that consists of all items; (2) As the degree of purchase dependence declines while other conditions remain same, it is observed that the difference between the lower and upper bounds reduces, the order fill rate increases, and the order fill rate gets closer to the upper bound.

지역출산율의 공간적 상호의존성과 영향요인에 관한 연구 : 공간패널분석을 활용하여

김동현(Kim, Dong-Hyun),전희정(Jun, Hee-Jung) 대한국토·도시계획학회 2021 國土計劃 Vol.56 No.4

Most studies that examine local fertility rates by considering spatial dependence use cross-sectional data. Moreover, only a few studies have undertaken a comprehensive analysis that takes into account all the economic, socio-cultural, and policy environments at the local level. To fill this gap in the literature, this study asks the following research questions: 1) Are local fertility rates spatially dependent? 2) How does the economic environment affect the local fertility rate? 3) How does the socio-cultural environment affect the local fertility rate? 4) How does the policy environment affect the local fertility rate? To answer these research questions, this study used a variety of local information, including data on local fertility, housing price, and childbirth support, as well as childcare statistics. Then, a spatial panel model was employed. The empirical analysis showed: First, local fertility rates are spatially dependent. The spatial analyses show that localities with higher fertility rates are clustered around Jeolla-do and Gyeongsang-do while those with lower fertility rates are clustered around Seoul and Busan Metropolitan City. Second, we found that the economic, socio-cultural, and political environments at the local level are related to the local fertility rate. Specifically, the level of the regional economy, housing price, and the level of womens participation in the labor market are negatively related to local fertility rates. Third, the marriage rate, childbirth incentives, and childcare facilities are all positively related to local fertility rates. As the findings show that local fertility rates are spatially dependent, this study suggests that cooperation among neighboring localities can increase local fertility rates more effectively. Moreover, localities should provide public rental housing for newly-weds and cooperative childcare facilities. Finally, gender equality should be promoted in workplaces.

Tension-Compression Asymmetry in the Off-Axis Nonlinear Rate-Dependent Behavior of a Unidirectional Carbon/Epoxy Laminate at High Temperature and Incorporation into Viscoplasticity Modeling

Kawai, M.,Zhang, J.Q.,Saito, S.,Xiao, Y.,Hatta, H. The Korean Society for Composite Materials 2009 Advanced composite materials Vol.18 No.3

Off-axis compressive deformation behavior of a unidirectional CFRP laminate at high temperature and its strain-rate dependence in a quasi-static range are examined for various fiber orientations. By comparing the off-axis compressive and tensile behaviors at an equal strain rate, the effect of different loading modes on the flow stress level, rate-dependence and nonlinearity of the off-axis inelastic deformation is elucidated. The experimental results indicate that the compressive flow stress levels for relatively larger off-axis angles of $30^{\circ}$, $45^{\circ}$ and $90^{\circ}$ are about 50 percent larger than in tension for the same fiber orientations, respectively. The nonlinear deformations under off-axis tensile and compressive loading conditions exhibit significant strain-rate dependence. Similar features are observed in the fiber-orientation dependence of the off-axis flow stress levels under tension and compression and in the off-axis flow stress differential in tension and compression, regardless of the strain rate. A phenomenological theory of viscoplasticity is then developed which can describe the tension-compression asymmetry as well as the rate dependence, nonlinearity and fiber orientation dependence of the off-axis tensile and compressive behaviors of unidirectional composites in a unified manner. It is demonstrated by comparing with experimental results that the proposed viscoplastic constitutive model can be applied with reasonable accuracy to predict the different, nonlinear and rate-dependent behaviors of the unidirectional composite under off-axis tensile and compressive loading conditions.

천연가스의 계절별 변동유량을 고려한 이중터보팽창기 감압시스템을 이용한 전기에너지회수에 관한 연구

박철우,유한빛,김효 한국가스학회 2019 한국가스학회지 Vol.23 No.2

천연가스 운송기지에서 전기에너지를 회수하기위하여 팽창 터빈시스템을 사용하는 것은 잘 알려진 기술이다. 터보팽창기의 효율은 천연가스의 유량과 터보팽창기 설계유량의 비에 따라 달라진다. 그러나 감압기지에서 계절적 공급패턴, 즉 여름에는 낮은 유량으로 반면에 겨울에는 높은 유량으로 공급되기 때문에, 단일 터보팽창기로는낮은 유량의 천연가스로부터 감압에너지를 충분히 회수하기가 비효율적이다. 따라서 본 연구에서는 대용량과 소용량의 이중 터보팽창기의 새로운 개념을 제안하게 되었다. 본 연구에서는 저압 정압기지에서 팽창밸브의 평균 입구, 출구 압력조건인 18.5 bar에서 7.5 bar로 감압될 때 입구의 온도, 유량조건에 따라서 생산 가능한 전력을 이론적배경을 통해 계산하였다. 최저 설계 효율 0.72에서 회수 가능한 전력생산량은 단일 터보팽창기로 운전될 때에는12.4 MW이었으나, 여기서 제안한 이중터보팽창기에서는 16.1 MW로 약 30% 증가한 결과를 얻게 되었다. Expansion turbine system to recover the electricity energy from natural gas transmission stations is a well-known technique. The turbo-expander efficiency depends on the ratio of the natural gas flow rates to the design flow rate of the turbo-expander. However, if there is a big difference of the natural gas flow rate through the pressure letdown station because of seasonal supply pattern, that is, high flow rate in winter while low flow rate in summer, single turbo-expander system is not so efficient as to recover the pressurized energy from the low flow-rate natural gas. Therefore, we have proposed a new concept of double turbo-expander system: one is a big capacity and the other a small capacity. Here we have theoretically computed the electric powers at the pressure reduction from 18.5 bar to 7.5 bar depending on the inlet conditions of temperature and flow rate. The calculated electricity generation has been increased by 30% from 12.4 MW in a single turbo expander to 16.1 MW in the proposed double turbo-expander system when a minimal design efficiency of 0.72 is applied.