• Geomechanics and Engineering
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• 제3권2호
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• pp.83-108
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• 2011

The effect of non-plastic fines (silt) on liquefaction and pore pressure generation characteristics of saturated sands was studied through undrained stress controlled cyclic triaxial tests using cylindrical specimens of size 50 mm diameter and height 100 mm at different cyclic stress ratios and at a frequency of 0.1 Hz. The tests were carried out in the laboratory adopting various measures of sample density through various approaches namely gross void ratio approach, relative density approach, sand skeleton void ratio approach, and interfine void ratio approach. The limiting silt content and the relative density of a specimen were found to influence the undrained cyclic response of sand-silt mixtures to a great extent. Undrained cyclic response was observed to be independent of silt content at very high relative densities. However, the presence of fines significantly influenced this response of loose to medium dense specimens. Combined analyses of cyclic resistance have been done using the entire data collected from all the approaches.

• 한국안전학회지
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• 제12권4호
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• pp.27-38
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• 1997

The effect of geometry factors on the combined mode stress intensity factor behaviors of a slant crack in a non-uniform thickness material was analysed by 2-dimensional theoretical analysis. The analysis is based on the Laurent's series expansions of complex potentials where the complex coefficients of the series are determined from the compatibility and the equilibrium conditions of the thickness interface and the stress free conditions of the crack surface. In numerical calculations the perturbation technique is employed. The expressions for the crack tip stress intensity factor are given in the form of power series of dimensionless crack length $\lamda$, and the function of crack slant angle $\alpha$ and thickness ratio $\beta$. The results of numerical calculations for each problems are represented as the correction factors F($\lamda$, $\alpha$, $\beta$). The results clearly show the following characteristics : The correction factors of the combined mode stress intensity factors for a non-uniform thickness material can be defined in the form of F($\lamda$, $\alpha$, $\beta$). The stress intensity factor values for a given crack length are decreased with increase of thickness ratio $\beta$.

• 대한기계학회논문집B
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• 제23권5호
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• pp.587-592
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• 1999

The combined effects of radius ratio and roughness pitch ratio on the turbulent fluid flow characteristics of the fully developed flow in the annullar tubes with rib-roughened core walls were determined for Reynolds number ranging from 12,000 to 66,000. To understand the underlying physical phenomena responsible for friction factor enhancement, measurements of velocity profiles and zero shear stress and maximum velocity positions were combined to propose the friction factor correlation. Friction factors were found to be a function of the roughness pitch ratio and radius ratio.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 춘계학술대회 논문집
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• pp.352-361
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• 2003

A fatigue damage accumulation model based on the continuum damage mechanics theory was develope(1 where modules decay ratios in tension and shear on used as indicators for damage variables D . In the model, the damage variables are considered to be second-order tensors. Then the maximum principal damage variable, $D^*$ is introduced According to the similarity to the Principal stress, $D^*$ is obtained as the maximum eigen value of damage tensor [D']. Under proportional tension and torsion loadings, fatigue lives were satisfactorily predicted at any combined stress ratios using the present model in which the fatigue characteristics only under uniaxial tension and pure torsion loadings on needed. Fatigue life prediction under uniaxial tension and pure torsion loadings, was performed based on the damage mechanics using boundary element method.

• 한국공작기계학회논문집
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• 제13권6호
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• pp.64-73
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• 2004

A fatigue damage accumulation model based on the continuum damage mechanics theory was developed where modulus decay ratios in tension and shear were used as indicators for damage variables D. In the model, the damage variables are considered to be second-order tensors. Then, the maximum principal damage variable, $D^*$ is introduced. According to the similarity to the principal stress, $D^*$ is obtained as the maximum eigen value of damage tensor [D]. Under proportional tension and torsion loadings, fatigue lives were satisfactorily predicted at any combined stress ratios using the present model in which the Fatigue characteristics only under uniaxial tension and pure torsion loadings were needed. Fatigue life prediction under uniaxial tension and pure torsion loadings, was performed based on the damage mechanics using boundary element method.

• Asian-Australasian Journal of Animal Sciences
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• 제24권3호
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• pp.414-420
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• 2011

A study was conducted to investigate the effects of the combined stressor induced by high stocking density with feed restriction on immunological parameters such as leukocyte differential counts and cytokine expression in laying hens. A total of forty White Leghorn laying hens were randomly allotted into the control (12 kg of body weight/$m^2$) and the stress (44 kg of body weight/$m^2$) groups, and then birds of the stress group were given 75% of voluntary intake of the control birds for 12-d on a daily basis. There was a significant decrease in body weight without affecting the relative weights of the liver and spleen after 12-d of the combined stressor. In hematological values, no significant difference in leukocyte differential counts including heterophils (H), lymphocytes (L), monocytes and H:L ratio was observed between the two groups. In cytokines, hepatic lipopolysaccharide-induced tumor necrosis factor-${\alpha}$ (LITNF-${\alpha}$) and inducible nitric oxide synthase (iNOS) expression levels in the stress group were significantly (p<0.05) higher compared with those in the control group. However, the expression levels of interleukin (IL)-4 and IL-6 in the liver were not affected by the combined stressor. Splenic LITNF-${\alpha}$ expression in the combined stressor group was significantly (p<0.05) up-regulated compared with that in the control birds. However, the combined stressor did not affect splenic IL-4, IL-6 and iNOS expression. In conclusion, the combined stressor caused by high stocking density with feed restriction enhanced some pro-inflammatory cytokines including LITNF-${\alpha}$ and iNOS in lymphoid and non-lymphoid organs of birds, suggesting that altered cytokine expression to given stressors can be another parameter that can be used in assessing stress responses of birds.

• 한국정밀공학회지
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• 제24권3호
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• pp.84-90
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• 2007

As a result of vehicle maintenance of rocker arm shaft for 4-cylinder SOHC engine, failure stress analysis of rocker arm shaft is needed. Because more than 30% of vehicles investigated have been fractured. Failure stress analysis is classified into an naked eyes, microscope, striation and X-ray fractography etc. Failure stress analysis by using striation is already established technology as means for seeking cause of fracture. But, although it is well known that striation spacing corresponds to the crack growth rate da/dN, it is not possible to determine ${\sigma}_{max}\;and\;{\sigma}_{min}$ under service loading only from striation spacing. This is because the value of striation spacing is influenced not only by ${\Delta}K$ but also by the stress ratio R. In the present paper, we determine the stress ratio using orthogonal array and ANOVA, and propose a prediction method of failure stress which is combined with FEM and striation.

• 대한기계학회논문집A
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• 제27권2호
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• pp.239-246
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• 2003

This paper proposes engineering estimation equations of elastic-plastic J and COD fur axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length. and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a reformulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.

• 한국압력기기공학회 논문집
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• 제18권2호
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• pp.61-68
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• 2022

Accurate evaluation of residual stress is important for stress corrosion cracking assessment. In this paper, electron beam welding experiment is simulated via finite element analysis and the sensitivity of the parameters related to the combined heat source model is investigated. Predicted residual stresses arecompared with measured residual stresses. It is found that the welding efficiency affects the size of the tensile residual stress area and the magnitude of maximum longitudinal residual stress. It is also found that the parameter related to the ratio of energy distributed to the two-dimensional heat source has little effect on the size of tthe tensile residual stress area, but affects the size of the longitudinal residual stress in the center of the weld.

• 콘크리트학회논문집
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• 제16권2호
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• pp.185-194
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• 2004

콘크리트의 크리프에 관한 기존의 연구결과들은 대부분 1축응력이 가해지는 경우에 대한 것으로 콘크리트 구조물 또는 부재가 다축응력 상태에 놓이는 경우에 적용하기가 어려운 점이 있다. 따라서 다축응력 상태의 콘크리트 크리프 특성에 관한 연구가 필요하다. 이 연구에서 다축응력 상태에 놓인 콘크리트의 크리프 특성을 실험을 통해 파악하였다. 세 가지 서로 다른강도를 갖는 배합의 콘크리트에 대해 각각 9개의 실험체를 제작하였으며, 1축, 2축, 3축 응력 상태에서 크리프 실험을 실시하였다. 하중이 가해지는 세 방향에서 시간에 따른 변형률을 측정하였다. 가압시점의 푸아송비와 크리프변형에 기인한 푸아송비 그리고 탄성변형과 크리프변형에 기인한 푸아송비를 구하였으며, 각 콘크리트에 대한 세 가지 푸아송비는 근사적으로 같은 것으로 나타났다. 가압시점의 푸아송비와 전체 변형에 대한 푸아송비는 콘크리트 강도의 증가에 따라 다소 증가하는 경향을 보였으며, 각 푸아송비는 응력상태에 따라 특정한 경향을 나타내지 않았다. 체적성분의 응력과 크리프변형률, 편차성분의 응력과 크리프변형률은 선형의 관계를 나타내었다.