• 한국지반공학회논문집
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• 제40권2호
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• pp.19-28
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• 2024

본 연구에서는 유동성 채움재의 장기 압축강도 저하를 확인하고, 그 원인을 규명하고자 유동성 채움재와 물의 배합 비율 1:1 적용하여 시료를 제작하였으며, 재령 7일, 28일 기준 일축압축강도 시험을 수행하였다. 일축압축시험 결과 재령 28일 기준 압축강도는 7일 대비 2.85배 감소하였다. 또한, 똑같은 배합 조건에서 팽창제를 첨가하였을 경우 압축강도가 대폭 감소하였다. 현장에서 배합된 유동성 채움재를 재령 7일, 28일 기준으로 점하중강도 시험을 수행하였으며, 똑같은 배합 조건 및 재령 일 기준으로 일축압축강도와의 차이가 재령 7일 기준 29.27~58.76배, 재령 28일 기준 48.19~95.13배로 나타났다. 본 연구결과가 선행연구 결과와 다소 차이를 나타내고 있음에 대한 이유는 시험방법 및 시료 제작 과정에서의 정밀도 차이에 의한 것임으로 유동성 채움재 평가를 위하여 명확한 시험방법에 대한 규제가 필요하다.

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

• Steel and Composite Structures
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• 제27권1호
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• pp.89-94
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• 2018

Uniaxial ratcheting behavior of Z2CND18.12N austenitic stainless steel used nuclear power plant piping material was studied. The results indicated that ratcheting strain increased with increasing of stress amplitude under the same mean stress and different stress amplitude, ratcheting strain increased with increasing of mean stress under the same stress amplitude and different mean stress. Based on least square method, a suitable method to arrest ratcheting by loading the materials was proposed, namely determined method of zero ratcheting strain rate. Zero ratcheting strain rate occur under specified mean stress and stress amplitudes. Moreover, three dimensional ratcheting boundary surface graph was established with stress amplitude, mean stress and ratcheting strain rate. This represents a graphical surface zone to study the ratcheting strain rates for various mean stress and stress amplitude combinations. The graph showed the ratcheting behavior under various combinations of mean and amplitude stresses. The graph was also expressed with the help of experimental results of certain sets of mean and stress amplitude conditions. Further, experimentation cost and time can be saved.

• 대한기계학회논문집A
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• 제28권6호
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• pp.848-859
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• 2004

Mechanical testing methods to determine the material constants for large deformation nonlinear finite element analysis were demonstrated for natural rubber. Uniaxial tension, uniaxial compression, equi-biaxial tension and pure shear tests of rubber specimens are performed to achieve the stress-strain curves. The stress-strain curves are obtained after between 5 and 10 cycles to consider the Mullins effect. Mooney and Ogden strain-energy density functions, which are typical form of the hyperelastic material, are determined and compared with each other. The material constants using only uniaxial tension data are about 20% higher than those obtained by any other test data set. The experimental equations of shear elastic modulus on the hardness and maximum strain are presented using multiple regression method. Large deformation finite element analysis of automotive transmission mount using different material constants is performed and the load-displacement curves are compared with experiments. The selection of material constant in large deformation finite element analysis depend on the strain level of component in service.

• 대한기계학회논문집A
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• 제22권3호
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• pp.595-602
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• 1998

Specimens of 304 stainless steel were tested to failure at elevated temperatures under multiaxial stress states, uniaxial tension using smooth bar specimens, biaxial shearing using double shear bar specimens, and triaxial tension using notched bar specimens. Rupture times are compared for uniaxial, biaxial, and triaxial stress states with respect to the maximum principal stress, the von Mises effective stress, and the principal facet stress. The results indicate that the principal facet stress gives the best correlation for the material investigated, and this parameter can predict creep life data under multiaxial stress states with rupture data obtained with specimens under uniaxial stresses. The results also suggest that grain boundary cavitation, coupled with localized deformation processes such as grain boudary sliding, controls the lifetimes of the specimens.

• 한국해양공학회지
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• 제20권1호
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• pp.7-15
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• 2006

In this research, the behavior characteristics of cement mixing lightweight soil (CMLS) for recycling of dredged soil in the Nakdong River estuary are experimentally investigated. CMLS is composed of the dredged soil from Nakdong River estuary, cement, and air foam. For this purpose, uniaxial compression tests are carried out for artificially prepared specimens of CMLS, with various initial water contents, cement contents, and mixing ratio of dredged soils. The experimental results of CMLS indicated that the compressive strength is strongly influenced by the cement contents, rather than water contents and air foam. Compressive strength of CMLS increased with an increase in cement content, while it decreased with an increase in water content and air foam content. It was also found that the modulus of deformation E50 was in a range of 44 to 128 times greater than the value of uniaxial compressive strength, cured in 28 days.

• 화약ㆍ발파
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• 제16권4호
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• pp.18-28
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• 1998

Effects of blasting vibrations on curing concrete have not been well studied. As a result, unreasonable and strong blasting vibration constraints have been placed on blasting when it occur in the vicinity of curing concrete. To study the effects of blasting on curing concrete blocks of $33.3{\times}27.7{\times}16.2cm$ were molded and placed on the quarry. Several sets of concrete blocks were subjected separately to peak vibrations of 0.25, 0.5, 1.0, 5.0 and 10cm/sec. The impulses of blasting vibrations were applied with thirty-minute intervals. Along with unvibrated concrete blocks, the vibrated concrete samples cored with 60.3mm in diameter were measured for elastic moduli, sonic velocity and uniaxial compressive strength. Test results can be summarized as follows; 1. The blasting vibrations between 6 and 8 hours after pour generally lowered on the uniaxial compressive strength of the concrete. 2. A low blasting vibration of 0.25cm/sec did not affect the uniaxial compressive strength. As the magnitude of the blasting vibration increases, compressive strength of concrete is decreased. 3. Physical properties of the P-wave velocity, Young’s modulus, and Poisson's ratio showed a weakly decreasing trend in the concrete blocks vibrated between 6 and 8 hours after pour.

• Computers and Concrete
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• 제9권5호
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• pp.327-340
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• 2012

The search for a design that meets both performance and safety, with minimal cost and lesser environmental impact was always the goal of structural engineers. In general, the design of conventional reinforced concrete structures is an iterative process based on rules of thumb established from the personal experience and intuition of the designer. However, such procedure makes the design process exhaustive and only occasionally leads to the best solution. In such context, this work presents the development and implementation of a mathematical formulation for obtaining optimal sections of reinforced concrete columns subjected to uniaxial flexural compression, based on the verification of strength proposed by the Brazilian standard NBR 6118 (ABNT 2007). To minimize the cost of the reinforced concrete columns, the Simulated Annealing optimization method was used, in which the amount and diameters of the reinforcement bars and the dimensions of the columns cross sections were considered as discrete variables. The results obtained were compared to those obtained from the conventional design procedure and other optimization methods, in an attempt to verify the influence of resistance class, variations in the magnitudes of bending moment and axial force, and material costs on the optimal design of reinforced concrete columns subjected to uniaxial flexural compression.

• Steel and Composite Structures
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• 제15권6호
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• pp.659-677
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• 2013

This paper introduces new specimens of Steel-Carbon Fibre Reinforced Polymer composite developed in accordance with standard test method and definition for mechanical testing of steel (ASTM-A370). The main purpose of this research is to study the behaviour of steel-CFRP composite specimen under uniaxial tension to use it in beams in lieu of traditional steel bar reinforcement. Eighteen specimens were prepared and divided into six groups, depending upon the number of the layers of CFRP. Uniaxial tensile tests were conducted to determine yield strength and ultimate strength of specimens. Test results showed that the stress-strain curve of the composite specimen was bilinear prior to the fracture of CFRP laminate. The tested composite specimens displayed a large difference in strength with remarkable ductility. The ultimate load for Steel-Carbon Fibre Reinforced Polymer composite specimens was found using the model proposed by Wu et al. (2010) and nonlinear FE analysis. The ultimate loads obtained from FE analysis are found to be in good agreement with experimental ones. However, ultimate loads obtained applying Wu model are significantly different from experimental/FE ones. This suggested modification of Wu model. Modified Wu's model which gives a better estimate for the ultimate load of Steel-Carbon Fibre Reinforced Polymer (SCFRP) composite specimen is presented in this paper.

• Steel and Composite Structures
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• 제28권5호
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• pp.517-525
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• 2018

The specimens made by Z2CND18.12N austenitic stainless steel were conducted on a 100 kN closed loop servo hydraulic tension-compression testing machine with a digital controller. Uniaxial tension and uniaxial ratcheting effect tests were carried out at $25^{\circ}C$. Moreover, Uniaxial tension tests were conducted at $150^{\circ}C$, $250^{\circ}C$ and $350^{\circ}C$. Based on these experimental data, the prediction models of stress-strain curve and the relationship of ratcheting strain and number of cycles were established by the algorithm principle of BP neural network. The results indicated that the predicted results of neural network model were in well agreement with experimental data. It was found that the BP neural network model had high validity and accuracy.