• Computers and Concrete
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• 제22권6호
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• pp.527-538
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• 2018

Buckling of longitudinal bars is a brittle failure mechanism, often recorded in reinforced concrete (RC) structures after an earthquake. Studies in the literature highlights that it often occurs when steel is in the post elastic range, by inducing a modification of the engineered stress-strain law of steel in compression. A proper evaluation of this effect is of fundamental importance for correctly evaluating capacity and ductility of structures. Significant errors can be obtained in terms of ultimate bending moment and curvature ductility of an RC section if these effects are not accounted, as well as incorrect evaluations are achieved by non-linear static analyses. This paper presents a numerical investigation aiming to evaluate the engineered stress-strain law of reinforcing steel in compression, including second order effects. Non-linear FE analyses are performed under the assumption of local buckling. A role of key parameters is evaluated, making difference between steel with strain hardening or with perfectly plastic behaviour. Comparisons with experimental data available in the literature confirm the accuracy of the achieved results and make it possible to formulate recommendations for design purposes. Finally, comparisons are made with analytical formulations available in the literature and based on obtained results, a modification of the stress-strain law model of Dhakal and Maekawa (2002) is proposed for fitting the numerical predictions.

• 소성∙가공
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• 제20권7호
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• pp.491-497
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• 2011

This work describes a method for determining material parameters included in recrystallization and grain growth models of metallic materials. The focus is on the recrystallization and grain growth models of Ni-Fe based superalloy, Alloy 718. High temperature compression test data at different strain, strain rate and temperature conditions were chosen to determine the material parameters of the model. The critical strain and dynamically recrystallized grain size and fraction at various process conditions were generated from the microstructural analysis and strain-stress relationships of the compression tests. Also, isothermal heat treatments were utilized to fit the material constants included in the grain growth model. Verification of the determined material parameters is carried out by comparing the average grain size data obtained from other compression tests of the Alloy 718 specimens with the initial grain size of $59.5{\mu}m$.

• 한국지반공학회지:지반
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• 제12권2호
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• pp.9-18
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• 1996

실험실에서 재 성형한 정규압밀점토에 대하여 실시된 일련의 삼축압축시험 거동결과를 등방단일경화구성모델에 의한 예측치와 비교검토한다. 이 모델사용에 필요한 열한개의 계수는 등방압밀공시체에 대한 비배수삼축압축시험 결과로부터 간단히 결정된다. 이렇게 결정된 계수를 활용한 이 모델로 이방압밀공시체를 대상으로 한 비배수삼축압축시험시의 응력-변형률 및 간극 수압의 거동이 예측된다. 또한 등방압밀공시체 및 이방압밀공시체를 대상으로 실시한 배수삼축 압축시의 응력-변형률 및 체적변형률 거동예측에도 이 모델을 적용하였다. 예측치와 시험치의 비교결과 비배수삼축압축시험의 경우는 등방압밀공시체와 이방압밀공시체 모두에 좋은 일치를 보이고 있다. 그러나 배수삼축압축시험의 경우는 초기 체적변형률의 예측치가 시험치보다 약간 작게 나타나다가 파괴점에 근접함에 따라서는 예측치가 시험치보다 커지는 경향을 보이고 있다. 그러나 전반적인 응력 -변형률거동은 좋은 일치를 보이고 있음을 알 수 있다. 따라서, 본 연구결과 이 모델은 정규압밀점토의 거동예측에 적용성이 충분히 있다고 생각된다.

• 소성∙가공
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• 제4권3호
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• pp.245-256
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• 1995

SMC(Sheet Molding Compound), a thermoset composite material which consists of unsaturated polyester resin, fiberglass strands, fillers, and various chemical additives for curing agent, has been widely used in fabrication of structural components. The mechanical properties of molded SMS parts are strongly dependent on material flow results during compression molding process, while such flow in molds is affected by material characteristics. For numerical simulation of SMC molding process, estimation of material property of SMC must be accomplished. In this study, flow resistance of SMC was estimated through a simple compression test using a lubricant with grease oil under the constant strain rate condition at various temperatures and the result was compared with other material data available in the literature. The accuracy of the experimentally determined flow resistance was tested by finite element analyses of compression molding of SMC. Simulation results were compared with experimental results under the plane strain condition.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.619-626
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• 2005

This work aims at studing the stress-strain-strength behavior of an CSG(cemented sand and gravel) materials. An analysis of the mechanical behavior of the CSG is performed from the interpretation of results by unconfined compression test, large triaxial compression test in which the influence of both the degree of cementation and age. For CSG, It was concluded that the characterristics of compression are direct measurment of the degree of cementation and age. In addition, hyperbolic model is adopted to express the relation between elastic moduli and cementation, age, confined stress in small strain. The results of the test show that clear correlation with each other

• 한국수소및신에너지학회논문집
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• 제20권4호
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• pp.274-282
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• 2009

Diaphragm compressor is widely used for hydrogen compression because it achieves high gas pressure without gas contamination. Diaphragm deflecting in the cavity with high pressure formed by an oil compression is the most important component in the compressor. Therefore, it is necessary to obtain deflection degree of diaphragm to predict the damage point of diaphragm. The objective of this study is to estimate the diaphragm's damage point through diaphragm deflection test by implementing with strain gauges attached on several radial points. Without gas compression, strain sum of each points varied as similarly as the variation of the pressure with respect to time. And while the motor speed was slower than 400rpm, the strain near the rim was larger than that of the center. When motor speed, however, was over 500rpm, strain became similar to that of the center and the rim. With gas compression, it was shown that the variation of the strain sum was delayed against that of the pressure and the strain near the rim was much higher than that of the center.

• International Journal of Concrete Structures and Materials
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• 제10권2호
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• pp.143-147
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• 2016

In recent years, some modifications were introduced in the stress-strain relationship of the steel in order to develop a more efficient shear model for reinforced concrete members. The last contribution in this sense corresponding to the Refined Compression Field Theory (RCFT, 2009); this theory proposed a steel constitutive model that has account the tension stiffening area prescribed by technical codes, what simplifies all the design process. However, under certain design conditions supported by such codes, the RCFT model does not provide a real (non-complex) solution for the steel yield strain when the prescribed tension stiffening area is considered; then the load-strain response cannot be computed. In this technical note, the tension stiffening area is fixed in order to guarantee the application of the embedded steel constitutive model for all the standard design range.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.435-438
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• 2008

High temperature deformation of Ti-6Al-4V alloy with a lamellar colony microstructure was investigated by hot compression and torsion tests. The torsion and compression tests were carried out under a wide range of temperatures and strain rates with true strain up to 2 and 0.7, respectively. The processing maps were generated on the basis of compression and torsion test data and using the principles of dynamic materials modeling (DMM). The shapes of the strain-stress curves in alpha-beta region and processing maps obtained on the two different tests have been compared with a view to evaluate the effect of the microstructure evolution on the flow softening behavior of Ti-6Al-4V alloy with a lamellar colony microstructure.

• Structural Engineering and Mechanics
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• 제69권6호
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• pp.627-635
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• 2019

In order to study the axial compression performance of sand-lightweight concrete-filled steel tube (SLCFST) stub columns, three circular SLCFST (C-SLCFST) stub column specimens and three SLCFST square (S-SLCFST) stub column specimens were fabricated and static monotonic axial compression performance testing was carried out, using the volume ratio between river sand and ceramic sand in sand-lightweight concrete (SLC) as a varying parameter. The stress process and failure mode of the specimens were observed, stress-strain curves were obtained and analysed for the specimens, and the ultimate bearing capacity of SLCFST stub column specimens was calculated based on unified strength theory, limit equilibrium theory and superposition theory. The results show that the outer steel tubes of SLCFST stub columns buckled outward, core SLC was crushed, and the damage to the upper parts of the S-SLCFST stub columns was more serious than for C-SLCFST stub columns. Three stages can be identified in the stress-strain curves of SLCFST stub columns: an elastic stage, an elastic-plastic stage and a plastic stage. It is suggested that AIJ-1997, CECS 159:2004 or AIJ-1997, based on superposition theory, can be used to design the ultimate bearing capacity under axial compression for C-SLCFST and S-SLCFST stub columns; for varying replacement ratios of natural river sand, the calculated stress-strain curves for SLCFST stub columns under axial compression show good fitting to the test measure curves.

• Advances in concrete construction
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• 제9권3호
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• pp.249-256
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• 2020

This paper aims at investigating the effect of crumb rubber size and content on compressive behaviors of concrete under axial compression. Concrete specimens are designed and produced by replacing natural aggregate with crumb rubber content of 0%, 5%, 10%, 15% and three different sized crumb rubbers (No. 20, No. 40, No. 80 crumb rubber). And the failure mode, compressive strength, elastic modulus, stress-strain curves, peak strain and ultimate strain are experimentally studied. Based on the test results, formulas have been presented to determine the compressive strength, elastic modulus, the relationship between prism compressive strength and cube compressive strength, stress-strain curves and peak strain of crumb rubber concrete (CRC). It is found that the proposed formulas agree well with the test result on the whole, which may be used to practical applications.