• Structural Engineering and Mechanics
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• 제44권6호
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• pp.753-762
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• 2012

The ratcheting characteristics of cylindrical shell under cyclic axial loading are investigated. The specimens are subjected to stress-controlled cycling with non-zero mean stress, which causes the accumulation of plastic strain or ratcheting behavior in continuous cycles. Also, cylindrical shell shows softening behavior under symmetric axial strain-controlled loading and due to the localized buckling, which occurs in the compressive stress-strain curve of the shell; it has more residual plastic strain in comparison to the tensile stress-strain hysteresis curve. The numerical analysis was carried out by ABAQUS software using hardening models. The nonlinear isotropic/kinematic hardening model accurately simulates the ratcheting behavior of shell. Although hardening models are incapable of simulating the softening behavior of the shell, this model analyzes the softening behavior well. Moreover, the model calculates the residual plastic strain close to the experimental data. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. Simulations show good agreement between numerical and experimental results. The results reveal that the rate of plastic strain accumulation increases for the first few cycles and then reduces in the subsequent cycles. This reduction is more rapid for numerical results in comparison to experiments.

• Geomechanics and Engineering
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• 제2권3호
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• pp.203-211
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• 2010

An experimental program of isotropic loading tests on a compacted kaolin using a conventional triaxial equipment modified for testing unsaturated soils was perform to investigate a loading collapse curve of unsaturated soils along wetting and drying paths. The test data are presented in terms of effective stress on a range of constant suction. The suction hardening behavior was observed for both wetted and dried samples. With the use of an appropriate effective stress parameter, the unique relationship for loading collapse curve for wetting and drying processes was obtained.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1685-1696
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• 2001

A novel indentation theory is proposed by examining the data from the incremental plasticity theory based finite element analyses. First the optimal data acquisition location is selected, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five. Numerical regressions of obtained data exhibit that strain hardening exponent and yield strain are the two main parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides the stress-strain curve with an average error less than 5%.

• Journal of Welding and Joining
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• 제12권4호
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• pp.151-161
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• 1994

FCAW has wide application in ship fabrication, maintenance and field erection. It has many advantages over SMAW.SAW and GMAW process. In many applications, the FCAW provides highquality weld metal. This method can reduce weld defects especially porosity and spatter. But the fatigue characteristics of those deposited metal have been rarely investigated. The purpose of this study is to investigate the cyclic stress-strain behavior and fatigue tests by the constant strain control were carried out on the rounded smooth specimen with deposited metal using the metal type flux cored wire. As the results of this study for the deposited metal welded by the metal type flux cored wire, the hardening or softening characteristics under cyclic load were investigated and cyclic stress-strain curve, strain-fatigue life curve, stress-strain function and fatigue life relation which are useful to estimate the fatigue life under the stress concentration condition were obtained.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.185-192
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• 2000

A novel indentation theory is proposed by examining the data from the incremental plasticity theory based finite element analyses. First the optimal data acquisition location is selected, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five. Numerical regressions of obtained data exhibit that strain hardening exponent and yield strain are the two main parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides the stress-strain curve with an average error less than 3%.

• 한국정밀공학회지
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• 제15권9호
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• pp.175-181
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• 1998

The coil spring is used in the suspension of automotive vehicles and small omnibus. Recently, it can be adopted hardening type spring which spring constant is accompanied by increasing displacement to increase passenger comfortability. One of methods which assert this characteristic is cylindrical-taper section coil spring. In this paper we calculate ideal spring characteristic curve from the given vehicle conditions, and show the design method of the cylindrical-taper section coil spring.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 추계학술대회 논문집
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• pp.65-66
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• 2007

• 한국해양공학회지
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• 제23권2호
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• pp.74-80
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• 2009

Surface hardening treatments, such as using the high-frequency induction hardening method, are widely used to increase the fatigue life and prevent the failure of materials by locally increasing the surface hardness. This method, in particular, brings an improvement in static strength by compressive residual surface stress due to the hardening. In this study, the mechanical properties of high-frequency induction hardened SCM440 steel were investigated. These results were also compared with those for base metal and a Q/T (tempering after quenching) treatment specimen. The test results showed that partially high-frequency induction hardened SCM440 steel specimens were more improved in static strength, surface hardness, fatigue limit, and anti-wear than the base metal and Q/T treatment specimens. In particular, the fatigue limit of the high-frequency induction hardened SCM440 steel increased by more than about 52% compared to that of base metal and by about 25% compared to that of the Q/T specimen.

• Geomechanics and Engineering
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• 제11권3호
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• pp.325-343
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• 2016

A total stress-based bounding surface model is developed to predict the undrained behaviour of saturated soft clays under cyclic loads based on the anisotropic hardening modulus field and bounding-surface theories. A new hardening rule is developed based on a new interpolation function of the hardening modulus that has simple mathematic expression and fewer model parameters. The evolution of hardening modulus field is described in the deviatoric stress space. It is assumed that the stress reverse points are the mapping centre points and the mapping centre moves with the variation of loading and unloading paths to describe the cyclic stress-strain hysteresis curve. In addition, by introducing a model parameter that reflects the accumulation rate and level of shear strain to the interpolation function, the cyclic shakedown and failure behaviour of soil elements with different combinations of initial and cyclic stresses can be captured. The methods to determine the model parameters using cyclic triaxial compression tests are also studied. Finally, the cyclic triaxial extension and torsional shear tests are performed. By comparing the predictions with the test results, the model can be used to describe undrained cyclic stress-strain responses of elements with different stress states for the tested clays.

• 한국산학기술학회논문지
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• 제17권3호
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• pp.380-388
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• 2016

본 논문에서는 판형 열교환기 등에 널리 이용되고 있는 순 티타늄 판재의 프레스 성형성을 평가하기 위해 인장실험을 수행하였고 인장실험결과를 가장 잘 피팅할 수 있는 가공경화 모델을 제안하였다. 또한 항복곡면의 도출을 위해 단축변형, 평면변형, 순수전단변형 등 다양한 변형모드 하에서의 인장실험을 실시하였다. 이 제안된 모델을 Hora의 수정된 최대하중조건식에 적용하여 프레스 성형성을 평가하기 위해서 널리 사용되고 있는 성형한계선을 예측하였고 그 결과를 장출성형실험에서 구한 성형한계선과 비교하였다. 도출한 항복곡면을 잘 묘사하기 위한 이방성 항복조건식과 본 연구에서 제안된 가공경화 모델은 순 티타늄 판재의 프레스 성형성의 척도인 성형한계선을 잘 예측함을 알 수 있었다.