• Journal of the Society of Disaster Information
• /
• v.15 no.2
• /
• pp.186-197
• /
• 2019

Purpose: This study intends to develop a nonlinear cyclic plasticity damage model in the framework of finite element formulation, which is capable of taking large deformation effects into account, in order to accurately predict the hysteretic behavior of stainless steel structures. Method: The new cyclic constitutive equations that utilize the combined isotropic-kinematic hardening rule for plastic deformation is incorporated into the damage mechanic model in conjunction with the large strain formulation. The damage growth law is based on the experimental observations that the evolution of microvoids yields nonlinear damage accumulation with plastic deformation. The damage model parameters and the procedure for their identification are presented. Results and Conclusion: The proposed nonlinear damage model has been verified by simulating uniaxial strain-controlled monotonic and cyclic loading tests, and successfully applied to a thin-walled stainless steel pipe subjected to constant and alternating strain-controlled cyclic loadings.

• Geomechanics and Engineering
• /
• v.37 no.4
• /
• pp.383-393
• /
• 2024

Monopile foundations of offshore wind turbines embedded in soft clay are subjected to the long-term cyclic lateral loads induced by winds, currents, and waves, the vibration of monopile leads to the accumulation of pore pressure and cyclic strains in the soil in its vicinity, which poses a threat to the safety operation of monopile. The researchers mainly focused on the hysteretic stress-strain relationship of soft clay and kinds of stiffness degradation models have been adopted, which may consume considerable computing resources and is not applicable for the long-term bearing performance analysis of monopile. In this study, a modified cyclic stiffness degradation model considering the effect of plastic strain and pore pressure change has been proposed and validated by comparing with the triaxial test results. Subsequently, the effects of cyclic load ratio, pile aspect ratio, number of load cycles, and length to embedded depth ratio on the accumulated rotation angle and pore pressure are presented. The results indicate the number of load cycles can significantly affect the accumulated rotation angle of monopile, whereas the accumulated pore pressure distribution along the pile merely changes with pile diameter, embedded length, and the number of load cycles, the stiffness of monopile can be significantly weakened by decreasing the embedded depth ratio L/H of monopile. The stiffness degradation of soil is more significant in the passive earth pressure zone, in which soil liquefaction is likely to occur. Furthermore, the suitability of the "accumulated rotation angle" and "accumulated pore pressure" design criteria for determining the required cyclic load ratio are discussed.

• Geomechanics and Engineering
• /
• v.37 no.1
• /
• pp.49-64
• /
• 2024

Rocks undergoing repeated loading and unloading over an extended period, such as due to earthquakes, human excavation, and blasting, may result in the gradual accumulation of stress and deformation within the rock mass, eventually reaching an unstable state. In this study, a CNN-CCM is proposed to address the mechanical behavior. The structure and hyperparameters of CNN-CCM include Conv2D layers × 5; Max pooling2D layers × 4; Dense layers × 4; learning rate=0.001; Epoch=50; Batch size=64; Dropout=0.5. Training and validation data for deep learning include 71 rock samples and 122,152 data points. The AI Rock Constitutive Model learned by CNN-CCM can predict strain values(ε₁) using Mass (M), Axial stress (σ₁), Density (ρ), Cyclic number (N), Confining pressure (σ₃), and Young's modulus (E). Five evaluation indicators R², MAPE, RMSE, MSE, and MAE yield respective values of 0.929, 16.44%, 0.954, 0.913, and 0.542, illustrating good predictive performance and generalization ability of model. Finally, interpreting the AI Rock Constitutive Model using the SHAP explaining method reveals that feature importance follows the order N > M > σ₁ > E > ρ > σ₃.Positive SHAP values indicate positive effects on predicting strain ε₁ for N, M, σ₁, and σ₃, while negative SHAP values have negative effects. For E, a positive value has a negative effect on predicting strain ε₁, consistent with the influence patterns of conventional physical rock constitutive equations. The present study offers a novel approach to the investigation of the mechanical constitutive model of rocks under cyclic loading and unloading conditions.

• Geomechanics and Engineering
• /
• v.17 no.4
• /
• pp.333-342
• /
• 2019

Geological dynamic hazards during coal mining can be caused by the failure of a composite system consisting of roof rock and coal layers, subject to different loading rates due to different advancing velocities in the working face. In this paper, the uniaxial compression test simulations on the composite rock-coal layers were performed using $PFC^{2D}$ software and especially the effects of loading rate on the stress-strain behavior, strength characteristics and crack nucleation, propagation and coalescence in a composite layer were analyzed. In addition, considering the composite layer, the mechanisms for the advanced bore decompression in coal to prevent the geological dynamic hazards at a rapid advancing velocity of working face were explored. The uniaxial compressive strength and peak strain are found to increase with the increase of loading rate. After post-peak point, the stress-strain curve shows a steep stepped drop at a low loading rate, while the stress-strain curve exhibits a slowly progressive decrease at a high loading rate. The cracking mainly occurs within coal, and no apparent cracking is observed for rock. While at a high loading rate, the rock near the bedding plane is damaged by rapid crack propagation in coal. The cracking pattern is not a single shear zone, but exhibits as two simultaneously propagating shear zones in a "X" shape. Following this, the coal breaks into many pieces and the fragment size and number increase with loading rate. Whereas a low loading rate promotes the development of tensile crack, the failure pattern shows a V-shaped hybrid shear and tensile failure. The shear failure becomes dominant with an increasing loading rate. Meanwhile, with the increase of loading rate, the width of the main shear failure zone increases. Moreover, the advanced bore decompression changes the physical property and energy accumulation conditions of the composite layer, which increases the strain energy dissipation, and the occurrence possibility of geological dynamic hazards is reduced at a rapid advancing velocity of working face.

• Journal of Environmental Health Sciences
• /
• v.16 no.1
• /
• pp.29-43
• /
• 1990

The purpose of this study is to investigate the vairous change in the toxicity of cadmium by the simultaneous administration of selenium and zinc, which have been reported to change -the toxicity of cadmium through the interaction with cadmium, to rat. For the experiment, 42 rats of Sprague-Dawley strain were used. The experimental groups were divided into 6 groups: a control group, a cadmium (100ppm) alone treatment group, a cadmium (100ppm) and zinc (100ppm) combined treatment group, and three cadmium (100ppm), zinc (100ppm) and selenium (1, 4, and 8ppm) combined treatment groups. The rats were allocated seven to each group and observed for seven weeks. The results of experiment are as follows: 1. The food consumptions of each group were reduced, compared with a control group, especially, in a cadmium and zinc combined treatment group and a cadmium $\cdot$ zinc and selenium(1ppm) combined treatment group to the significant level compared with a control group (p < 0.05). The water consumptions of each group were reduced to the very significant level compared with a control group (p < 0.01). The feed efficiencies of each group were lower than a control group, and among them the highest group was cadmium $\cdot$ zinc and selenium (8ppm) combined treatment group as 90% of a control group. 2. In all groups, the weight gains were highest in the second week and the total weight gains were reduced to the very significant level compared with a control group (p < 0.01). 3. In all groups, the relative weights of liver were reduced, compared with a control group, especially, a cadmium alone treatment group was reduced to the significant level (p < 0.05). The relative weight of kidney was high to the significant level in a cadmium alone treatment group (p < 0.05) compared with a control group. In all groups, the relative weights of testis were reduced, compared with a control group, but the levels were not significant. 4. The accumulation of cadmium was highest in the kidney and the order of height was in liver, testis and blood, respectively. In all groups, the amount of cadmium accumulation was high to the very significant level compared with a control group (p < 0.01). In liver, the amount of acdmium accumulation in. a cadmium alone treatment group was high to the significant level compared with a cadmium $\cdot$ zinc and selenium (8ppm) combined treatment group (p < 0.05), and in kidney, the amount of cadmium accumulation in a cadmium alone tretment group was high to the very significant level compared with the cadmium $\cdot$ zinc and selenium (4, 8ppm) combined treatment groups (p < 0.01). However, in testis, among the treatment groups the level was not significant and in blood, a cadmium alone treatment group was low to the significant level compared with the cadmium $\cdot$ zinc and selenium (4, 8ppm) combined treatment groups (p < 0.05). 5. According to the histopathological finding on the testis, some of the seminiferous tubules of a group treated with cadmium alone showed severe necrosis and atrophy. But the testis of cadmium $\cdot$ zinc and selenium (8ppm) combined treatment group was similar to that of a control group. From the results of this study, it can be concluded that the repeated simultaneous oral administration of large doses of selenium with the cadmium produces the partial amelioration of cadmium toxicity, whereas zinc does not.

• Journal of Ginseng Research
• /
• v.15 no.3
• /
• pp.183-187
• /
• 1991

Effect of ginseng hairy and native roots on body absorption, fecal and urinary excretion of Ingested radiostrontium were investigated in the mouse(NIH-strain, male) treated with or without pre-feeding of each ginseng soluble fraction. The test groups were fed with basic diet supplemented with 1% each ginseng soluble fraction for 7 darts before the radiostrontium were administered by intragastric intubation. In the groups of treated with soluble fraction from ginseng hairy roots, the radioactivities of fecal and urinary excretion increased about 15% over than that of control groups and the whole body retention were about 38%. In the groups of treated with soluble fraction from native ginseng roots, the radioactivities of fecal and urinary excretion increased about 25% over than that of control groups and the whole body retention were about 28%. Also, the levels of radiostrontium accumulation retained significantly the higher percent in skeletons than in other organs.

• 한국생물공학회:학술대회논문집
• /
• 2000.04a
• /
• pp.295-298
• /
• 2000

In order to maximize the RNA accumulation and biomass production in Saccharomyces cerevisiae MTY62, a high-content RNA yeast strain, fed-bach cultures were performed with optimized industrial medium including molasses and corn steep liquor. Among the feeding modes examined, the constant feeding mode resulted in the cell concentration of 35.7 g-DCW/L and the RNA concentration of 5434 ${\mu}g-RNA/mL$, which were about 2-fold increased levels, compared to the results of bach culture. However, the RNA content (153 mg-RNA/g-DCW) in the fed-batch cultures was lower than that in the batch culture (171 mg-RNA/g-DCW).

• KSBB Journal
• /
• v.14 no.2
• /
• pp.136-140
• /
• 1999

Characteristics of organic acid degradation by isolated yeast strain was investigated. Optimum initial pH was 5. Increase in cell mass was proportional to the decrease in organic acid degradation. Also no accumulation of byproduct was observed during degradation. Acetic acid degraded fast, followed by butyric acid and propionic acid in order. No significant substrate inhibition was observed up to 12 g/L of acetic acid 7 g/L of propionic acid, respectively. However, inhibition of butyric acid was significant above 4 g/L. Cell mass yield was 0.2-0.4 g cell/g acids and decreased at high decreased at high organic acid concentration. 95% of organic acid (7.5 g/L), corresponding to 13,000 ppm, was degraded in 30-40 hours.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.337-340
• /
• 2005

The effect of residual stress on fatigue crack growth was investigated in terms of finite element analysis. Simulations were performed on a CT specimen in plane strain. An interface-cohesive element that accounts for damage accumulation due to fatigue along the notch direction has been used. Numerical results show that fatigue crack growth rate slows down when compressive residual stress field exists in front of the crack tip.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1989.10a
• /
• pp.21-24
• /
• 1989

The effect of superplasticizing agents on the mechanical properties in hardened concrete have been analyzed and investigated under various mix proportions of water cement ratio of 0.40, 0.50, 0.60 and 0.70, Superplasticizing agents of NL-4000, and Rheobuild-716, and addition rate of sp. agents of 0.0, 0.5, 1.0, 1.5 and 2.0 in the practical range. It is the aim of this study to provide the fundamental data on the compressive strength, dynamic and static modulus of elasticity, stress and strain curve of hardened concrete comparing with base concrete and conventional concrete for the practical use and research data accumulation of superplasticized concrete in the side of development of concrete construction technology and management.