• Steel and Composite Structures
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• v.49 no.5
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• pp.487-502
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• 2023

In the realm of nanotechnology, the nonlocal strain gradient theory takes center stage as it scrutinizes the behavior of spinning cantilever nanobeams and nanotubes, pivotal components supporting various mechanical movements in sport structures. The dynamics of these structures have sparked debates within the scientific community, with some contending that nonlocal cantilever models fail to predict dynamic softening, while others propose that they can indeed exhibit stiffness softening characteristics. To address these disparities, this paper investigates the dynamic response of a nonlocal cantilever cylindrical beam under the influence of external discontinuous dynamic loads. The study employs four distinct models: the Euler-Bernoulli beam model, Timoshenko beam model, higher-order beam model, and a novel higher-order tube model. These models account for the effects of functionally graded materials (FGMs) in the radial tube direction, giving rise to nanotubes with varying properties. The Hamilton principle is employed to formulate the governing differential equations and precise boundary conditions. These equations are subsequently solved using the generalized differential quadrature element technique (GDQEM). This research not only advances our understanding of the dynamic behavior of nanotubes but also reveals the intriguing phenomena of both hardening and softening in the nonlocal parameter within cantilever nanostructures. Moreover, the findings hold promise for practical applications, including drug delivery, where the controlled vibrations of nanotubes can enhance the precision and efficiency of medication transport within the human body. By exploring the multifaceted characteristics of nanotubes, this study not only contributes to the design and manufacturing of rotating nanostructures but also offers insights into their potential role in revolutionizing drug delivery systems.

• Journal of the Korean Ceramic Society
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• v.22 no.4
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• pp.47-53
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• 1985

Various amount of $P_2O_5$ were added to $PbO-B_2O_3$ binary glass system to investigate its effect on the phase separation and physical properties of the glass. Experiments such as infrared spectroscopy scanning electron microscopy thermal expansion softening point and microhardnesses were done. Phase separation with $B_2O_3$ rich phase matrix and PbO rich phase droplet was observed for the glasses con-taining less than 10m/o of PbO while the opposite morphology of phase separation for the glasses containing more than 11m/o of PbO. By adding increasing amount of $P_2O_5$ their phase separation region was extended to the glass containing more than 20m/o of PbO. These effects can be interpreted in terms of the inoic field strength difference of each ions in the glasses. The abrupt changes of physical properties such as softening point thermal expansion and microhardness were observed for the glass with around 10m/o of PbO in this system. These changes are by the matrix composition change from TEX>$B_2O_3$ rich phase to PbO rich phase depending on PbO concentration.

• The Korean Journal of Food And Nutrition
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• v.20 no.4
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• pp.421-426
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• 2007

This study was carried out to investigate the properties of Kimchi made with potato as compared to Kimchi made with radish. The pH, acidity, hardness, and number of lactic acid bacteria were examined as properties of the Kimchi to determine the suitability of adding the potato and with focus on the possible duration of storage. First in the case of pH, the storage duration at pH $4.2{\sim}4.3$, which is the state for optimal tasting Kimchi, was approximately 10days in the control group, while that of the experimental group was 10 to 16 days, and thus, longer than the control. Second in the case of acidity, representing the maturity of Kimchi, we examined the time it took to reach 0.6% acidity, in which the experimental group took more longer time than the control. Although the experimental group was slower to mature than the control, the period for keeping at the proper pH was longer than that of the control group. Thirdly, in the case of hardness, which relates to softening, the experimental group had remarkably high values. This suggests that the Kimchi in the experimental group had a more rigid texture and more difficultly softening than the control group. Lastly in the case of the number of lactic acid bacteria, which closely relates to the process of fermentation, there were no significant differences. In conclusion, these results indicate that adding potato to Kimchi can extend its storage period.

• Journal of Korean Society of Steel Construction
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• v.8 no.4 s.29
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• pp.133-133
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• 1996

Application of the relationship $da/dN=C({\Delta}K)^{m}$ is effective in the analysis of fatigue crack growth life. The values of material constant C and m have great influences on the predicted fatigue life and the relationship between fatigue crack growth rate(da/dN) and stress intensity factor range(${\Delta}K$) is effective in fatigue crack growth behavior. In this paper, fatigue crack growth behavior of the welded joints in HT60 grade TMCP(Thermo Machanical Control Process) steel have been studied. To evalute the fatigue crack growth rates of HT60 grade TMCP steel, fatigue test was performed by base metal(BM), heat affected zone(HAZ) and weld metal(WM) in TMCP steel at room temperature. We determined the relationship of $da/dN-{\Delta}K$ by correlation between C and m obtained from the Paris-Erdogan power law data supplied HT60 grade TMCP steel. The obtained results from this study indicate that fatigue crack growth rate of TMCP steel is not influenced by softening effect which occurs in the HAZ when high heat input weld is carried out. Softening effects, which affect fatigue properties. are shown that it is not affected to the fatigue growth rates significantly.

• International Journal of Precision Engineering and Manufacturing
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• v.5 no.4
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• pp.5-13
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• 2004

This study explains the effects of lubricant and surface treatment on the life of hot forging dies. The thermal load and thermal softening, that occur when there is contact between the hotter billet and the cooler dies in hot forging, cause wear, thermal cracking and fatigue, and plastic deformation. Because the cooling effect and low friction are essential to the long life of dies, the proper selection of lubricant and surface treatment is very important in hot forging process. The two main factors that decide friction and heat transfer conditions are lubricant and surface treatment, which are directly related to friction factor and surface heat transfer coefficient. Experiments were performed for obtaining the friction factors and the surface heat transfer coefficients in different lubricants and surface treatments. For lubrication, oil-base and water-base graphite lubricants were used, and ion-nitride and carbon-nitride were used as surface treatment conditions. The methods for estimating die service life that are suggested in this study were applied to a finisher die during the hot forging of an automobile part. The new techniques developed in this study for estimating die service life can be used to develop more feasible ways to improve die service life in the hot forging process.

• Structural Engineering and Mechanics
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• v.58 no.5
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• pp.799-823
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• 2016

A finite element model for the non-linear dynamic analysis of a reinforced concrete (RC) containment shell of a nuclear power plant subjected to extreme loads such as impact and earthquake is presented in this work. The impact is modeled by using an uncoupled approach in which a load function is applied at the impact zone. The earthquake load is modeled by prescribing ground accelerations at the base of the structure. The nuclear containment is discretized spatially by using 20-node brick finite elements. The concrete in compression is modeled by using a modified $Dr{\ddot{u}}cker$-Prager elasto-plastic constitutive law where strain rate effects are considered. Cracking of concrete is modeled by using a smeared cracking approach where the tension-stiffening effect is included via a strain-softening rule. A model based on fracture mechanics, using the concept of constant fracture energy release, is used to relate the strain softening effect to the element size in order to guaranty mesh independency in the numerical prediction. The reinforcing bars are represented by incorporated membrane elements with a von Mises elasto-plastic law. Two benchmarks are used to verify the numerical implementation of the present model. Results are presented graphically in terms of displacement histories and cracking patterns. Finally, the influence of the shear transfer model used for cracked concrete as well as the effect due to a base slab incorporation in the numerical modeling are analyzed.

• Korean Membrane Journal
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• v.10 no.1
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• pp.13-19
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• 2008

Water softening is a very promising field for membranes and especially ultra low pressure membranes. Nanofiltration membranes based on pore-filling technology was prepared by using a new technique: the in-situ cross-linking. This route involves introducing a pre-formed polymer into the pores of a host membrane and then locking the polymer in the pores by in-situ cross-linking with an appropriate reagent. By this way, it is possible to make robust and competitive, pore-filled, anion-exchange membranes with excellent control over the properties of the incorporated gel without affecting the host membrane. In this paper, the possibilities of tuning such membranes for ultra low pressure water softening was examined by altering pore-filling chemistry (by changing cross-linking and aminating reagents). The results showed that tuning the chemistry of the pore-filling has important effects. In particularly, it had been shown that the correct selection of cross-linking reagent was not only essential to get pore-filled membranes but it could control their properties. Moreover, the aminating reagent could improve membrane performance. It was found that an increase in hydrophobicity could improve the Darcy permeability.

• Journal of the Korean Society of Food Science and Nutrition
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• v.20 no.6
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• pp.565-571
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• 1991

A short time microwave heat treatment, bringing in hot NaCl solution, addition of KCI, CaCl2, MgCl2 into brining solution and salts mixture of phosphates into half fermented dongchim were investigated for their effects on some quality of dongchimi, a Korean pickle of Chinese radish roots, during fermentation. The reference dongchimi was prepared by brining the radish roots in 7% NaCl added with seasonings at $25^{\circ}C$. The result showed that microwave heat treatment affected little on the pH or total acidity change during fermentation. Soaking the roots in 80-9$0^{\circ}C$ hot salt solution significantly reduced the fermentation and softening rate of dongchimi while a rather rapid fementation was found for those soaked in 7$0^{\circ}C$. Addition of KCI and CaCl2 into brining solution slowed the pH decrease and softening of the roots, respectively. The dangchimi added with the salts mixture of phosphate, citrate and nitrite was significantly extreneded the fermentation time to pH 4.0 by more than two folds.

• Computers and Concrete
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• v.4 no.5
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• pp.377-402
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• 2007

The paper presents quasi-static plane strain FE-simulations of strain localization in reinforced concrete beams without stirrups. The material was modeled with two different isotropic continuum crack models: an elasto-plastic and a damage one. In case of elasto-plasticity, linear Drucker-Prager criterion with a non-associated flow rule was defined in the compressive regime and a Rankine criterion with an associated flow rule was adopted in the tensile regime. In the case of a damage model, the degradation of the material due to micro-cracking was described with a single scalar damage parameter. To ensure the mesh-independence and to capture size effects, both criteria were enhanced in a softening regime by nonlocal terms. Thus, a characteristic length of micro-structure was included. The effect of a characteristic length, reinforcement ratio, bond-slip stiffness, fracture energy and beam size on strain localization was investigated. The numerical results with reinforced concrete beams were quantitatively compared with corresponding laboratory tests by Walraven (1978).

• Journal of Industrial Technology
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• v.18
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• pp.117-124
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• 1998

In recently, according to increase the construction rate of steel bridge, it is necessary to develop the high strength, high toughness steel. Thus, this study show to evaluate the fatigue characteristic of SWS 570 B first used within a country. With the weld-joined compact tension specimens compared with each other, that is, transverse and lengthwise about the crack propagation, high and low in the input heat level, the fatigue test were performed. The log-log curves between the fatigue crack propagation rate da/dN and the transition range of the stress intensity factor ${\Delta}K$ ahead the crack tip were drawed, with these data. By using this curve, we obtained C and m which is material constant from Paris-Erdogan power law. The obtained results from this study indicate that fatigue crack growth rate of SWS 570 B is not influenced by softening effect which occurs in the HAZ(heat-affected zone) when high and low heat input weld is carried out. Softening effects, which affect fatigue properties, are shown that it is not affected to the fatigue growth rates significantly.