• 소성∙가공
• /
• 제14권6호
• /
• pp.520-526
• /
• 2005

In recent years, there has been a growth of the manufacture and application of magnesium products because of its small specific gravity as well as its relatively high strength. However, there are so many studies to assure good formability because magnesium sheet alloy is difficult to form. In this study, uniaxial tensile and biaxial tensile tests of AZ31 magnesium sheet alloy with thickness of 1.2mm were performed at room temperature. Uniaxial tensile tests were performed until $7{\%}$ of engineering strain. Lankford values and stress-strain curve were obtained. Biaxial tensile tests with cruciform specimen were performed until the breakdown of the specimen occurs. The yield loci were calculated by application of plastic work theory. The results are compared with the theoretical predictions based on the Hill and Logan-Hosford model. In this study, Hill's 1979 yield function for the case of m=2.8 and Logan-Hosford yield function for the case of M=8 give good agreements with experimental results. However, next study will be performed at warm-temperature because the specimens are broken under the $0.5{\%}$ of equivalent strain at biaxial tensile test.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2007년도 정기 학술대회 논문집
• /
• pp.399-402
• /
• 2007

The classical two dimensional modulus of rupture test was generalized to three dimensions. Using this new method, the biaxial tensile strength can be measured with only one actuator. A circular plate is used in this method unlike a prismatic beam in the classical modulus of rupture test. The stress field in this specimen is isotropic and uniform in a plane paralle1 to the bottom surface of the specimen. The relation between the applied load and the maximum stress is derived analytical1y using Timoshenko's solution. A set of experimental data is presented.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
• /
• pp.877-880
• /
• 2006

The stochastic nature of the tensile strength of concrete is investigated theoretically and experimentally. The tensile strength of concrete was modeled by a theory based on the failure probability of a crack arbitrarily oriented within a concrete body. According to this model, the stochastic nature of the tensile strength depend on the current stress state. This aspect was checked experimentally using a classical three point bend specimen and a rectangular plate specimen loaded at the center. It has been known that the biaxial strength is no different from the uniaxial strength. However, if the region where the tensile strength is constant gets small, the biaxial tensile strength increases and its stochastical variation decreases.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 2001년도 춘계학술발표회요약집
• /
• pp.484.2-484
• /
• 2001

• 콘크리트학회논문집
• /
• 제15권1호
• /
• pp.69-77
• /
• 2003

콘크리트의 응력-변형률 관계 곡선을 도출하기 위하여 총 13개의 철근콘크리트 패널실험체를 이용하여 1축 및 2축 인장실험을 수행하였다. 실험결과를 이용하여 콘크리트의 인장 응력-변형률 관계곡선의 모델을 수식으로 제안하였다. 주요 실험변수로는 철근비와 도입된 2축 하중비가 고려되었다. 또한 초기균열하중을 이용하여 인장-인장 영역에서의 파괴포락선을 제시하였다. 실험결과 콘크리트는 균열 이후에도 인장에 어느 정도 견디는 것으로 나타났다. 그러나 본 연구에서 제안한 콘크리트의 응력-변형률 관계 곡선은 철근의 방향과 하중의 방향 혹은 주응력의 방향이 일치하는 경우에 가장 적합할 것으로 판단된다.

• 한국전산구조공학회논문집
• /
• 제32권6호
• /
• pp.409-416
• /
• 2019

본 논문에서는 폭발하중을 받는 철근콘크리트 슬래브의 비선형 해석을 위한 개선된 수치 모델을 제안한다. 제안된 모델은 2축 응력 상태를 반영한 등가 강도에 의해 정의된 응력-변형률 관계를 사용하여 응력 상태를 직접 결정하는 변형률 속도 의존 이등방성 구성 모델을 다룬다. 또한, 균열 발생 후 콘크리트와 철근 사이의 부착 슬립이 점차 확대되어 소성힌지 영역으로 집중된다. 2축 응력 상태에서 콘크리트의 균열 방향은 주응력 방향에 따라 달라지므로 이를 고려한 부착 슬립 모델을 해석에 도입하였다. 해석 모델의 검증을 위해 수치해석과 실험결과의 상관관계 연구(correlation studies)가 수행되었다. 해석결과는 재료모델의 2축 거동과 부착 슬립의 영향을 고려하는 것이 해석결과의 정확성 향상에 중요함을 보여주며 제안된 해석 모델이 철근콘크리트 슬래브 부재의 폭발해석에 효과적으로 사용될 수 있음을 확인하였다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2008년도 추계학술대회 논문집
• /
• pp.452-455
• /
• 2008

In the present study, blow forming characteristics of commercially roiled AZ31 alloy sheets were investigated. Two different kinds of AZ31 sheets were originally fabricated by using direct casting and strip casting methods respectively. Both sheets have similar grain sizes of about $7{\mu}m$ with a relatively equiaxed structure after rolling. A series of tensile tests were carried out to get flow behavior in terms of temperature and strain rate. Also, grain size effect was investigated by annealing as-received sheet at elevated temperatures. Elongation increased with temperature increment as well expected. However, the differences in tensile test condition did not give much difference in elongation even at the temperature range where a large elongation would be expected with such as fine grain of $7{\mu}m$. Blow forming experiments showed that forming condition did not result in higher difference in dome height. However, the interesting feature from this study was that formability of this AZ31 alloy got different with stress condition. Firstly, biaxial stress condition might result in lower temperature and strain rate dependencies compared to uniaxial tension results for both DC and SC sheets. Secondly, DC showed slower grain growth in uniaxial tension than in biaxial stress state while SC has much higher grain growth rage in uniaxial tension than in bulging.

• Nuclear Engineering and Technology
• /
• 제52권12호
• /
• pp.2901-2909
• /
• 2020

Thermal creep is a key property of zircaloy cladding. CZ developed by CGN is a new zircaloy used as PWR fuel cladding. This research is devoted to investigating the thermal creep behavior of CZ and build the thermal creep model of CZ. Twenty internal pressure creep tests were conducted, and the ranges of temperature and Tresca stress were 320-430 ℃ and 70-300 MPa, respectively. Real-time creep data were analyzed by separating primary creep and steady-state creep. Based on Soderberg model and creep test data, CZ thermal creep model is derived. As a whole, the mean value and the standard deviation of P/M of CZ saturated primary creep strain are very close to these from steady-state creep rate, however, the predictive effect of primary creep is less satisfactory. Four conditions, where there exists large deviation between predicted values and test data, are 320 ℃ and 300 MPa, 350 ℃ and 190 MPa, 380 ℃ and 160 MPa, 380 ℃ and 190 MPa, respectively. As primary creep was much smaller than steady-state creep in long-time operation, the thermal creep model built can be applied to predict the thermal creep behavior of CZ cladding.

• Structural Engineering and Mechanics
• /
• 제77권6호
• /
• pp.745-751
• /
• 2021

Concrete filled double skin tubular members (CFDST) consist of double concentric circular or square steel tubes with concrete filled between the two steel tubes. The CFDST members, having a hollow section inside the internal tube, are generally lighter than ordinary concrete filled steel tubular members (CFT) which have a solid cross-section. Therefore, when the CFDST members are applied to bridge piers, reduction of seismic action can be expected. The present study aims to investigate, experimentally, the behavior of CFDST stub columns with double concentric square steel tubes filled with concrete (SS-CFDST) when working under centric compression. Two test parameters, namely, inner-to-outer width ratio and outer square steel tube's width-to-thickness were selected and outer steel tube's width-to-thickness ratio ranging from 70 to 160 were considered. In the results, shear failure of the concrete fill and local buckling of the double skin tubes having largest inner-to-outer width ratio were observed. A method to predict axial loading capacity of SS-CFDST is also proposed. In addition, the load capacity in the axial direction of stub column test on SS-CFDST is compared with that of double circular CFDST. Finally, the biaxial stress behavior of both steel tubes under plane stress is discussed.

• 대한조선학회지
• /
• 제6권1호
• /
• pp.43-67
• /
• 1969

The effect of a circular hole reinforced by a ring of different material in a plate under biaxial loadings is considered. In this problem, an infinitely large flat is assumed. The reinforcing ring is of uniform rectangular cross-section of same thickness as the plate. The outer boundary of the ring is cemented to the inner boundary of the hole in the plate. The plate is subjected to hydrostatic tension and pure shear loadings. The stress distribution around the hole is obtained by means of the two dimensional theory of elasticity. To conform the validities of above solutions, a series of photo-elastic stress analysis for a composite model was carried out. Fair agreements were observed between two sets of values. The conclusions arrived at are as follows: 1) The theoretical solutions are exact ones for the case of infinitely large flat plate. 2) The solutions can be used for most case of engineering problem if the bonding between the plate and ring is perfect. 3) If the ratio of Young's moduli of the ring and the plate is increased, the stresses in the plate decrease whereas those in the ring increase. 4) The stress concentration near the hole has localized effect. 5) Under hydrostatic tension, maximum principal stress and maximum shear stress increase as the ratio of inner and outer diameters of the ring increases. 6) Under pure shear, the stresses depend upon angular orientations of the points and maximum principal stress and maximum shear stress appear at 45 degree. They increase as the ratio of inner and outer diameters of the ring increases.