• Korean Journal of Materials Research
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• v.23 no.10
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• pp.568-573
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• 2013

The deformation properties of a TiC-Mo eutectic composite were investigated in a compression test at temperatures ranging from room temperature to 2053 K and at strain rates ranging from $3.9{\times}10^{-5}s^{-1}$ to $4.9{\times}10^{-3}s^{-1}$. It was found that this material shows excellent high-temperature strength as well as appreciable room-temperature toughness, suggesting that the material is a good candidate for high-temperature application as a structure material. At a low-temperature, high strength is observed. The deformation behavior is different among the three temperature ranges tested here, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurs, and from the beginning the work hardening level is high. At a high temperature, a yield drop occurs again, after which deformation proceeds with nearly constant stress. The temperature- and yield-stress-dependence of the strain is the strongest in this case among the three temperature ranges. The observed high-temperature deformation behavior suggests that the excellent high-temperature strength is due to the constraining of the deformation in the Mo phase by the thin TiC components, which is considerably stronger than bulk TiC. It is also concluded that the appreciable room-temperature toughness is ascribed to the frequent branching of crack paths as well as to the plastic deformation of the Mo phase.

• Structural Engineering and Mechanics
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• v.18 no.6
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• pp.769-790
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• 2004

The compressive behavior up to failure of short concrete members reinforced with fiber reinforced plastic (FRP) is investigated. Rectangular cross-sections are analysed by means of a simplified elastic model, able also to explain stress-concentration. The model allows one to evaluate the equivalent uniform confining pressure in ultimate conditions referred to the effective confined cross-section and to the effective stresses in FRP along the sides of section; consequently, it makes it possible to determine ultimate strain and the related bearing capacity of the confined member corresponding to FRP failure. The effect of local reinforcements constitute by single strips applied at corners before the continuous wrapping and the effect of round corners are also considered. Analytical results are compared to experimental values available in the literature.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.122-129
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• 2013

The microstructure and deformation behavior in 22Cr-0.2N micro-duplex stainless steels with various Ni and Mn contents were compared using by OM, TEM, and XRD. The 22Cr-0.2N duplex stainless steel plates were fabricated and hot rolled, followed by annealing treatment at the temperature range of $1,000-1,100^{\circ}C$. All the samples showed the common strain hardening behaviour during the tensile test at a room temperature. The steels tested at the temperatures of $-30^{\circ}C$ or $-50^{\circ}C$ showed a distinct inflection point in the stress-strain curves, which should be resulted from the formation of strain-induced martensite(SIM) of austenite phase. This was confirmed by TEM observations. The onset strain of a inflection point in a stress-strain curve should be depended up the value of $M_d30$. With the decrease of the tensile test temperature, the inflection point appeared earlier, and the strength and fracture strain were higher. The tensile behaviour was discussed from the point of austenite stability of the micro-duplex stainless steels with the different Ni and Mn content.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.311-317
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• 2008

This study was carried out to improve our understanding about the influence of silt content on the stress-strain of sand under cyclic loading. Soil specimens were prepared by wet-tamping method as same void ratio and specimen's silt contents on total weights was changed from 0% to 20%. Also, effects of the silt contents on the stress-strain response were studied at different anisotropic consolidation ratio, Kc=1.0, 1.5, 2.0 condition. As a result, cyclic shear strength decreased as silt contents increased in same stress ratios. In same silt contents, cyclic shear strength increased as Kc increased in lower silt contents, but in higher silt contents, it had reverse results.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.285-290
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• 1994

The influence of elevated temperatures on the mechanical properties of concrete is important for fire-resistance studies and also for understanding the behavior of containment vessel, such as nuclear reactor pressure vessels, during service and ultimate condition. The present study is to clarify the damage/deterioration of concrete structures that are subjected to high temperature exposure. To this end, comprehensive experiments are conducted. The major test variables are the peak temperatures, rate of temperature increase, and sustained duration at peak temperature. The results include weight loss residual compressive strength and stress-strain curve. From those results, residua compressive strength formula and stress-strain relationship are proposed.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.246-248
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• 2004

It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.253-255
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• 2005

It has been well known that ductile fracture of steels are accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. The present study focuses on the effects of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality. In this study evaluate the criterion for ductile crack initiation in strength mismatch specimen effect of location of notch root.

• The Journal of Engineering Geology
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• v.26 no.3
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• pp.307-314
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• 2016

Shear characteristics of soils can be investigated using various types of shear stress measuring apparatus. Ring shear tests are often applied for examining the residual shear strength under the unlimited deformation. This paper presents drainage-consolidation-shear velocity dependent undrained shear strengths measured in terms of water leakage. A series of ring shear tests were performed under the constant normal stress (50 kPa) and controled shear velocity ranging from 0.01~1 mm/sec under the undrained condition. As a result, undrained shear strengths are dependent on shear velocity. It exhibits that straining hardening behavior is observed for the shear velocity lower than 0.1 mm/sec; however, the strain softening behavior is observed for the shear velocity higher than 0.1 mm/sec. Water leakage can cause the increase in shear stress irrespective of shear velocity. Shear stress increases with increasing amount of water leakage. It is due to the fact that the small grains and water flow out through the rubble edge in the ring shear box. Repetitive saturation and consolidation processes may minimize the error.

• Journal of Ocean Engineering and Technology
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• v.16 no.3
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• pp.59-64
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• 2002

In the present study, we examined the influence of prestrain on creep strength of Class M alloy(STS310S) and Class A(STS310J1TB) alloys containing precipitates. Prestrain was given by prior creep at a higher stress than the following creep stresses. Creep behaviour before and after stress change and creep rate of pre-strained specimens were compared with that of virgin specimens. Pre-straining produced the strain region where the strain rate was lower than that of a virgin specimen both for STS310J1TB and STS310S steels. The reason for this phenomenon was ascribable to the viscous motion of dislocations, the interaction between dislocations and precipitates in a STS310J1TB steel, and the interaction of dislocations with sub-boundaries in a STS310S steen which has the higher dislocation density and smaller subgrain size resulted from pre-straining at higher stress.