• Transactions of Materials Processing
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• v.33 no.1
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• pp.18-35
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• 2024

In the present work, the evolution rules for the internal variables including continuum damage factors are obtained using the thermodynamic framework, which are in turn facilitated to derive the elastic-plastic constitutive relation for the particulate composites. Using the Mori-Tanaka scheme, the homogenization on state and internal variables such as back-stress and damage factors is carried out to procure the rate independent plasticity relations. Moreover, the degradation of mechanical properties of constituents is depicted by the distinctive damages such that the phase and interfacial damages are treated individually accordingly, whereas the kinematic hardening is depicted by combining the Armstrong-Frederick and Phillips' back-stress evolutions. On the other hand, the present constitutive relation for each phase is expressed in terms of the respective damage-free effective quantities, then, followed by transformation into the damage affected overall nominal relations using the aforementioned homogenization concentration factors. An emphasis is placed on the qualitative analyses for strain localization by observing the perturbation growth instead of the conventional bifurcation analyses. It turns out that the proposed constitutive model offers a wide range of strain localization behavior depending on the evolution of various internal variable descriptions.

• Korea-Australia Rheology Journal
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• v.13 no.4
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• pp.189-196
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• 2001

The phase morphology is an important factor in the rheology of immiscible polymer blends. Through its size and shape, the interface between the two phases determines how the components and the interface itself will contribute to the global stresses. Rheological measurements have been used successfully in the past to probe the morphological changes in model blends, particularly for dilute systems. For more concentrated blends only a limited amount of systematic rheological data is available. Here, viscosities and first normal stress differences are presented for a system with nearly Newtonian components, the whole concentration range is covered. The constituent polymers are PDMS and PIB, their viscosity ratio can be changed by varying the temperature. The data reported here have been obtained at 287 K where the viscosities of the two components are identical. By means of relaxation experiments the measured stresses are decomposed into component and interfacial contributions. The concentration dependence is quite different for the two types of contribution. Except for the component contributions to the shear stresses there is no clear indication of the phase inversion. Plotting either the interfacial shear or normal stresses as a function of composition produces in some cases two maxima. The relaxation times of these stresses display a similar concentration dependence. Although the components have the same viscosity, the stress-component curves are not symmetrical with respect to the 50/50 blend. A slight elasticity of one of the components seems to be the cause of this effect. The data for the more concentrated blends at higher shear rates are associated with a fibrillar morphology.

• Geotechnical Engineering
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• v.14 no.1
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• pp.93-108
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• 1998

In this study, the analytic solutions and numerical methods were used to estimate the shape and size effects on the stability of underground openings. The stability of underground openings was evaluated by scrutinizing the effects of the rock mass quality, the state of in-situ stresses and the lateral earth pressure coefficient on the displacement, the stress concentration and the plastic region developed in the vicinity of the openings. The analytic solutions have shown that the stress concentration factor is inversely proportional to the radius of curvature of openings. Through parametric study on the various shapes and sizes of underground openings the characteristics of the controlling factors concerned with the stability were analyzed. Then, the study was extended to the horseshoe-shaped openings commonly used for under ground storage. Through the extended study the effects of the stress ratio and the height-towidth ratio of openings on the maximum displacement and plastic region developed around the openings were estimated. The results have shorn that the height-to-width ratio of domestic storage caverns can be increased economically without stability problem, as far as the lateral earth pressure coefficient is appropriate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1439-1450
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• 1995

Bellows is a familiar component in piping systems as it provides a relatively simple means of absorbing thermal expansion and providing system flexibility. In routine piping flexibility analysis by finite element methods, bellows is usually considered to be straight pipe runs modified by an appropriate flexibility factor; maximum stresses are evaluated using a corresponding stress concentration factor. The aim of this study is to develop a bellows finite element, which similarly includes more complex shell type deformation patterns. This element also does not require flexibility or stress factors, but evaluates more detailed deformation and stress patterns. The proposed bellows element is a 3-D, 2-noded line element, with three degrees of freedom per node and no bending. It is formulated by including additional 'internal' degrees of freedom to account for the deformation of the bellows corrugation; specifically a quarter toroidal section of the bellows, loaded by axial force, is considered and the shell type deformation of this is include by way of an approximating trigonometric series. The stiffness of each half bellows section may be found by minimising the potential energy of the section for a chosen deformation shape function. An experiment on the flexibility is performed to verify the reliability for bellows finite element.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.10
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• pp.84-91
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• 2002

The shaft with the circular cross section have symmetric structural combination parts to keep the rotating balance. Hence the crack usually emanate from symmetric combination parts due to the stress concentration of these parts. In this study to estimate the fatigue behavior of symmetric cracks, the fatigue test was performed by using rotary bending tester and the specimen with symmetric defects in circular cross section. From the facts the characteristics of crack initiation and propagation on the symmetric surface cracks in circular cross section was examined. Also we observed the internal crack using oxidation coloring and investigated the fatigue behavior using the relationship between surface crack and internal crack. As a result of fatigue lift of symmetric cracks was reduced to 35% compared to single crack’s. We examined the characteristics of fatigue behavior in element with symmetric cracks using internal crack propagation rate and maximum stress intensity factor range obtained from approximation method.

• International Journal of Precision Engineering and Manufacturing
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• v.5 no.4
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• pp.36-42
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• 2004

The shaft with the circular cross section has symmetric structural combination parts to keep the rotating balance. Hence the crack usually initiates from symmetric combination parts due to the stress concentration of these parts. In this study to estimate the fatigue behavior of symmetric cracks, the fatigue test was performed by using a rotary bending tester and the specimen with symmetric defects in circular cross section. The characteristics of crack initiation and propagation on the symmetric surface cracks in circular cross section were examined. We also observed the internal crack using the oxidation coloring method and investigated the fatigue behavior using the relationship between the surface crack and the internal crack. As a result, the fatigue life of symmetric cracks was reduced by 35% compared to that of a single crack. We examined the characteristics of fatigue behavior of elements with symmetric cracks using internal crack propagation rate and maximum stress intensity factor range that were obtained from an approximation method.

• Animal Bioscience
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• v.34 no.8
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• pp.1403-1414
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• 2021

Objective: This study explored the mechanism of the Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway under conditions of zearalenone (ZEA)-induced oxidative stress in the duodenum of post-weaning gilts. Methods: Forty post-weaning gilts were randomly allocated to four groups and fed diets supplemented with 0, 0.5, 1.0, or 1.5 mg/kg ZEA. Results: The results showed significant reductions in the activity of the antioxidant enzymes total superoxide dismutase and glutathione peroxidase and increases the malondialdehyde content with increasing concentrations of dietary ZEA. Immunohistochemical analysis supported these findings by showing a significantly increased expression of Nrf2 and glutathione peroxidase 1 (GPX1) with increasing concentrations of ZEA. The relative mRNA and protein expression of Nrf2, GPX1 increased linearly (p<0.05) and quadratically (p<0.05), which was consistent with the immunohistochemical results. The relative mRNA expression of Keap1 decreased linearly (p<0.05) and quadratically (p<0.05) in the duodenum as the ZEA concentration increased in the diet. The relative mRNA expression of modifier subunit of glutamate-cysteine ligase (GCLM) increased quadratically (p<0.05) in all ZEA treatment groups and the relative mRNA expression of quinone oxidoreductase 1 (NQO1) catalytic subunit of glutamate-cysteine ligase decreased linearly (p<0.05) and quadratically (p<0.05) in the ZEA1.0 group and ZEA1.5 group. The relative protein expression of Keap1 and GCLM decreased quadratically (p<0.05) in the duodenum as the ZEA concentration increased in the diet, respectively. The relative protein expression of NQO1 increased linearly (p<0.05) and quadratically (p<0.05) in all ZEA treatment groups in the duodenum. Conclusion: These findings suggest that ZEA regulates the expression of key factors of the Keap1-Nrf2 signaling pathway in the duodenum, which enables resistance to ZEA-induced oxidative stress. Further studies are needed to examine the effects of ZEA induced oxidative stress on other tissues and organs in post-weaning gilts.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.379-395
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• 2021

For the complicated structural details in ships and offshore structures, the traditional hotspot stress approaches are known to be sensitive to the element variables of element topologies, sizes, and integration schemes. This motivated to develop a new approach for predicting reasonable hotspot stresses, which is less sensitive to the element variables and easy to be implemented the real marine structures. The three-point bending tests were conducted for the longitudinal attachments with the round and rectangular weld toes. The tests were reproduced in the numerical simulations using the solid and shell element models, and the simulation technique was validated by comparing the experimental stresses with the simulated ones. This paper considered three hotspot stress approaches: the ESM method based on surface stress extrapolation, the Dong's method based on nodal forces along a weld toe, and the proposed method based on nodal forces perpendicular to an imaginary vertical plane at a weld toe. In order to study the element sensitivities of each method, 16 solid element models and 8 shell element models were generated under the bending and tension loads, respectively. The element sensitivity was analyzed in terms of Stress Concentration Factors (SCFs) in viewpoints of two statistical quantities of mean and bias with respect to the reference SCFs. The average SCFs predicted by the proposed method were remarkably in good agreement with the reference SCFs based on the experiments and the ship rules. Negligibly small Coefficients of Variation (CVs) of the SCFs, which is measure of statistical bias, were drawn by the proposed method.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.3
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• pp.279-284
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• 2016

Finite element analysis along with DOE scheme has been performed to obtain robust design of crankshaft assembly. This study focused on obtaining optimized fillet radius of crankshaft mainly by statistical approach. 27 design cases using 3 factors with 3 levels are constructed by design of experiment. Changes of design factors and noise factor may influence the durability of crankshaft system. General two stages of robust design may enhance the durability of crankshaft model. Increasing crank arm thickness was adopted as a shrink step and change of fillet radius was used as a shift step. By combining these two steps, the stress concentration at the fillet area is reduced and adequate fillet radius is determined for the robust design of crankshaft.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.4 s.97
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• pp.122-128
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• 1999

Bolted joint assembly for nuclear power plants consists of various components : cover plate, retainer plate, manway flange, gasket and stud bolts/nuts. To guarantee the soundness of the joint, it is important to prevent leakage through the gasket and reduce the stress concentration factor at the thread root. In this paper, Submodeling technique for the finite element method is proposed to accurately compute three dimensional contact stresses which govern the sealing performance and the maximum contact stresses at the threads root. For verification of global solutions used as boundary conditions of submodel solution, the stresses on the cover plate and the manway flange are measured by strain gages when internal pressure is applied to the bolted joint assembly. The numerical results are compared with the experimental results.