• Proceedings of the KSME Conference
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• 2001.06a
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• pp.169-174
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• 2001

Low cycle fatigue tests are performed on high strength low alloy steels that be developed for submarine material. The relation between absorbed plastic strain energy and numbers of cycle to failure is examined in order to predict the low cycle fatigue life of structural steels by using plastic strain energy method. The cyclic properties are determined by a least square fit techniques. The life predicted by the plastic strain energy method is found to coincide with experiment data and results obtained from the Coffin-Manson method. Also the cyclic behavior of structural steels is characterized by cyclic softening with increasing number of cycle at room temperature. Especially, low cycle fatigue characteristics and microstructural changes of structural steels are investigated according to changing tempering temperatures. In the case of PFS steels, the $\varepsilon$-Cu is formed in 550C of tempering temperature and enhances the low cycle fatigue properties.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.125-133
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• 1988

To establish the rational design method, it is very important that predict accurately load-deformation response on reinforced concrete members. Torque-twist curves of reinforced concrete members in pure torsion were proposed recently by Collins and Hsu, etc. But, it is found that torsional strength of reinforced concrete members based on Hsu's theory is underestimated in the over-all load region except the ultimate state. In this paper, an attempt is made to present the higher-precision of torsional strength on arbitrary loading condition. For this purpose, constitutive equations are derived from which an estimate can be made of the torsional behavior of reinforced concrete members under the pure torsion. Tension stiffness of concrete in both the cracked and uncracked state have been considered. A softening effect that reduces the strength of the concrete by the diagonal cracking of concrete have been appropriately deliberated. Particularly, the experiments was done with 14 test beams to investigate the validity of theoretical analysis.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.446-451
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• 2018

In this study, different formulations of magnesium oxide and various modifiers (phosphoric acid, ferrous sulfate, pure acrylic emulsion, silicone acrylic emulsion, glass fiber, and polypropylene fiber) were used to prepare magnesium oxychloride cement composites. The compressive strength of the magnesium oxychloride cement was tested, and the softening coefficients of the composites after soaking in water were also calculated. The results showed that a magnesium oxychloride cement sample could not be coagulated when the MgO activity was 24.3%, but the coagulation effect of the magnesium oxide cement sample was excellent when the MgO activity was 69.5%. While pure acrylic emulsion, silicon-acrylic emulsion, and glass fiber showed insignificant modification effects on the magnesium oxychloride cement, ferrous sulfate heptahydrate, phosphoric acid, and polypropylene fiber could effectively improve its water resistance and compressive strength. When the phosphoric acid, ferrous sulfate heptahydrate, and polypropylene fiber contents were 0.47%, 0.73%, and 0.25%, respectively, the softening coefficient of a composite soaked in water reached 0.93 after 7 days, and the compressive strength reached 64.3 MPa.

• Journal of the Korean GEO-environmental Society
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• v.12 no.7
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• pp.13-21
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• 2011

In seasonal frozen areas with climatic features, which have a temperature difference in the winter and thawing season, changes of mechanical properties of the soil in the zone could be seen between the freezing and thawing surface. In particular, in soil with many fine particles, a softening of the roadbed usually occurs from frost and thawing actions. The lower bearing capacity is a rapidly progressive the softening of roadbed, and occurred a mud-pumping by repeated loading. In this study, the three kind of sandy soil with contents of fine particles were conducted by directly shear box test with the number of cyclic in freeze-thawing and the water content of soil. Subsequently, the relationship between the shear strength and freeze-thaw cycling time was obtained. The shear strength was decreased with the increase of the freeze-thaw cycling time. A shear stress deterioration of the soil with power function modal is proposal.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.563-564
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• 2009

Ultra-High Performance Concrete (UHPC) compared to normal concrete is exhibiting extremely high strength characteristics with compressive strength and tensile strength reaching 200MPa and 15MPa, respectively. The mechanical characteristics of UHPC can be thus exploited advantageously in the construction of structure through the reduction of the cross-sectional area and fabrication of slim and light-weight of the structural members. In the case where the structural member is made of UHPC, the occurrence of crack can be prevented by releasing the restraint provided by the form in due time. This research performs parametric study of the failure characteristics of concrete such as failure energy and softening curve suggested by the viscous crack model approximating the failure of concrete. The scope of this research contains the results of tests performed to investigate the strength of UHPC during early elapsed time.

• Journal of Welding and Joining
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• v.4 no.3
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• pp.43-49
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• 1986

Weldability of the TMCP steel manufactured by controlled rolling followed by accelerated cooling process was investigated. For comparison, two other steel plates produced by different manufacturing processes were selected; normalized and controlled rolled. Tandem submerged arc welding with both side one run technique was carried out. The results of this study can be summarized as follows; TMCP steel having the lowest carbon equivalent shows the best combination of mechanical properties, not only in the base metal but also in the heat affected zone. In the HAZ, the accelerated colling effect imarted on the trengthis releved by the weld thermal cycles, and thus the strength of the welded joint decrease substantially accompanied with the fracture in the HAZ. On the other hand, not only the softening but the fine microstructure can preserve the high toughness of TMCP steel in the HAZ.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.408-413
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• 2003

Dies may have to be replaced for a number of reasons, such as changes in dimensions due to die wear or plastic deformation, deterioration of the surface finish, break down of lubrication and cracking or breakage. In this paper, die cooling methods have been suggested to improve die service life considering die wear and plastic deformation in hot forging process. The yield strength of die decreases at higher temperatures and is dependent on hardness. Also, to evaluate die life due to wear, modified Archard's wear model has been proposed by considering the thermal softening of die expressed in terms of the main tempering curve. It was found that the use of die with cooling hole was more effective than that of direct cooling method to increase the die service life for spindle component.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.121-128
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• 2004

A constiutive model was proposed in order to model dilatancy under $K_0$ conditions. The model includes an anisotropic hardening rule with bounding surface and hypothetical peak stress ratio and dilatancy function which are dependent on a state parameter. The triaxial stress-strain relationship under $K_0$ conditions was calculated reasonably by the proposed model. In particular the model could consistently predict dilatancy in volume change, softening with peak strength and small strain behavior.

• Journal of Welding and Joining
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• v.12 no.4
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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.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.10a
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• pp.171-177
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• 1995

Fracture mechanics does work for concrete, provided that one uses a proper, nonlinear form of fracture mechanics in which a finite nonlinear zone at fracture front is being considered. The fracture process zone is a region ahead of a traction-free crack, and the development of model of fracture process zone is most important to describe fracture phenomena in concrete. This paper is about fracture behavior of concrete cylinder under lateral pressure. Concrete cylinders were made of high strength normal connote, steel fiber reinforced concrete and steel fiber reinforced polymer-impregnated concrete and concrete and the fracture behavior such as cracking propagation and ultimate load are observed. The fracture process zone is modelled by a Dugdale-Barenblatt type model with linear tension-softening curve and are implemented to the boundary element technique for the fracture analyses of the cylinders. The experimental results are compared with analysis results and tension-softening curves for the steel fiber reinforced concrete and steel fiber reinforced polymer-impregnated concrete are obtained by back analyses.