• 대한기계학회논문집A
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• 제21권7호
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• pp.1081-1088
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• 1997

The purpose of this work is to investigate the working limit of carbon steel and forging condition of cold forging. The fracture criteria which was proposed by Oyane and Osakada was used. Compression test, hardness study and tension test by Oyane's creteria, microstructure study by Osakada's were carried out. The results were compared with each other. It was found that working limit on compressive hydrostatic stress is increased in comparison with that of tensile stress field and can be forecasted the fracture limit of closed cold forging.

• Steel and Composite Structures
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• 제27권1호
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• pp.95-108
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• 2018

A new composite reinforced method, namely self-compacting concrete filled circular CFRP-steel jacketing, was proposed in this paper. Experimental tests on eight RC square short columns reinforced with the new composite reinforced method and four RC square short columns reinforced with CFS jackets were conducted to investigate their eccentrically compressive behaviour. Nine reinforced columns were subjected to eccentrically compressive loading, while three reinforced columns were subjected to axial compressive loading as reference. The parameters investigated herein were the eccentricity of the compressive loading and the layer of CFRP. Subsequently, the failure mode, ultimate load, deformation and strain of these reinforced columns were discussed. Their failure modes included the excessive bending deformation, serious buckling of steel jackets, crush of concrete and fracture of CFRP. Moreover, these reinforced columns exhibited a ductile failure globally. Both the eccentricity of the compressive loading and the layer of CFRP had a significant effect on the eccentrically compressive behaviour of reinforced columns. Finally, formulae for the evaluation of the ultimate load of reinforced columns were proposed. The theoretical formulae based on the ultimate equilibrium theory provided an effective, acceptable and safe method for designers to calculate the ultimate load of reinforced columns under eccentrically compressive loading.

• 대한금속재료학회지
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• 제48권6호
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• pp.477-488
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• 2010

Zr-based amorphous alloy matrix composites reinforced with stainless steel (STS) and tantalum continuous fibers were fabricated without pores or defects by a liquid pressing process, and their quasi-static and dynamic deformation behaviors were investigated by using a universal testing machine and a Split Hopkinson pressure bar, respectively. The quasi-static compressive test results indicated that the fiberreinforced composites showed amaximum strength of about 1050~1300 MPa, and its strength maintained over 700 MPa until reaching astrain of 40%. Under dynamic loading, the maximum stresses of the composites were considerably higher than those under quasi-static loading because of the strain-rate hardening effect, whereas the fracture strains were considerably lower than those under quasi-static loading because of the decreased resistance to fracture. The STS-fiber-reinforced composite showed a greater compressive strength and ductility under dynamic loading than the tantalum-fiber-reinforced composite because of the excellent resistance to fracture of STS fibers.

• 한국정밀공학회지
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• 제8권1호
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• pp.41-49
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• 1991

A knowledge of the resdual stress distribution at circumferential weldments can normally increase the accuracy of a fracture assessment in pipe line. In this paper, we present the measurements about the residual stress distributions at three kinds of circumferential butt welded pipes using the holl drilling strain gage method. By this experiment, we have obtined the following characteristics. At the inner surface of the pipe region near the center line of welding is under high tensile residual stress. However, as the distance from the center line of welding increases, the tensile component decreases and finally becomes compressive residual stress at region far away from the center line of welding. The longitudinal residual stress at the outer surface is compressive regardless of the diameter of pipe and the circumferential stress is changed from compressive to tensile as pipe diameter increases. The results also demonstrate that the residual stress is mainly caused by self-restraint bending force in the pipe welding.

• 한국재료학회지
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• 제15권11호
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• pp.697-704
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• 2005

The deformation behavior of a bulk amorphous and crystallized amorphous $Zr_{22.5}Ti_{14}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy extracted from a commercial golf club head was characterized at room temperature ana $300^{\circ}C$. At room temperature, amorphous specimens revealed higher yield stress and ductility than partially crystallized alloy specimens. Amorphous alloy displayed some plasticity before fracture, which resulted from strain hardening and repeated crack initiation and propagation. The fracture is mainly localized on one major shear band, and the compressive fracture angle of the amorphous specimen between the stress axis and the fracture plane was about $40^{\circ}$ Scanning electron microscope observations revealed mainly a vein-like structure in the amorphous alloy But the fracture surface of partially crystallized amorphous alloy consisted of vein-like and featureless fracture structure. The partially crystallized alloy extracted from the thick part of the club fractured in the elastic region, at a much lower stress level than the amorphous, suggesting that relatively coarse crystal particles formed during cooling cause the brittle fracture.

• Structural Engineering and Mechanics
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• 제56권3호
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• pp.473-490
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• 2015

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-to-concrete bonded joints. The section analysis that considers the effect of concrete's tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.162-169
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• 2004

In press forming of sheet metals, the material sheet is usually subjected to very large plastic strain under in-plane stressing. Moreover, the sheet also very often is subjected to out-of-plane compressive force between tools such as the upper and lower dies, the blank holder and the die, and so forth. In this paper, it is clearly demonstrated theoretically that out-of-plane stress may notably raise the forming limit strain and thus it can be effectively utilized to avoid earlier fracture of the sheet in press forming.

• 한국재료학회지
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• 제14권3호
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• pp.181-185
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• 2004

The mechanical properties of a bulk amorphous alloy ($Zr_{41.2}$ $Ti_{13.8}$ /$Cu_{10}$ $Ni_{10}$ $Be_{22.5}$ /at.%) before and after an annealing treatment were investigated. For the bulk amorphous alloy, the compressive strength was about 2.0 GPa, irrespective of the strain rates in the range of $10^{-4}$ to $10^3$$ sec^{-1}$ . Fine-sized nanocrystalline particles (10～100 nm) were precipitated homogeneously in the bulk amorphous matrix after the annealing treatments. Compared to the bulk amorphous materials, these composite materials, composed of the nanocrystalline phases and a bulk amorphous matrix had much different mechanical properties. The strength and strain of coposite materials measured by a compressive test showed a peak-maximum values at 7 vol.% of the nanocrystalline phases. The values in higher volume fraction of the crystalline phases in the amorphous matrix were decreased, as measured by both quasi-static and high strain rate. The decrease in fracture strength is due to presence of the dispersed large-crystalline phases in the amorphous matrix.

• 한국농공학회지
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• 제44권1호
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• pp.93-102
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• 2002

Steel fiber and polymer are used widely for reinforcement material of RC structures because of its excellences of the durability, serviceability as well as mechanical properties. The purpose of this study is to investigate the shear behavior of polymer cement high strength concrete beams mixed with steel fiber. The compressive strength of concrete was based on the 100$\times$200 mm cylinder specimens. The compressive strength of concrete are 320$kgf/cm^2$, 436 $kgf/cm^2$ and 520 $kgf/cm^2$ in the 28 days. The static test was carried out to measure the ultimate load, the initial load of flexural and diagonal cracking, crack patterns and fracture modes. Also, load-strain and load-deflection examined. During the test cracks were sketched against the load values according to the growth of crack. result are as follows; (1) The failure modes of the specimens are increased in rigidity and durability with mixing steel fiber and polymer. (2) The load of initial crack was similar a theory of shear-crack strength. (3) The deflection and strain at failure load of Polymer-steel fiber high strength concrete beams were increased, improving the brittleness of the high strength concrete.

• Advances in concrete construction
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• 제12권6호
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• pp.451-459
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• 2021

The mechanical behaviors and chloride resistance performance of fiber reinforced cementitious composites (FRCC) with hybrid polyethylene (PE) and steel fiber (in total 2% by volume) were investigated. Based on micro-mechanics and fracture mechanics, the reason why the tensile strain capacity of FRCC changed obviously was obtained. Besides, the effects of the total surface area of fiber in FRCC on compressive strength and chloride content were clarified. It is found that the improvement of the tensile strain capacity of FRCC with hybrid fiber is attributed to the growth of strain-hardening performance index (the ratio of complementary energy to crack tip toughness). As the total surface area of fiber related with the interfacial transition zone (ITZ) between fiber and matrix increases, compressive strength decreases obviously. Since the total surface area of fiber is small, the chloride resistance performance of FRCC with hybrid PE and steel fiber is better than that of FRCC containing only PE fiber.