• 열처리공학회지
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• 제9권1호
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• pp.69-77
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• 1996

The fatigue crack initiation behavior of plasma ion nitrided SACM645 steel was investigated through the rotary bending fatigue test and residual stress measurement by XRD. It was shown by XRD and EPMA that the plasma ion nitrided surface was composed of ${\gamma}^{\prime}(Fe_4N)$phase and ${\varepsilon}(Fe_{2-3}N)$phase, and that the nitrogen atoms existed in Fe matrix in diffusion layer. The OM, SEM and Auger spectroscopy showed that the depth of compound layer, mixed compound and diffusion layer, and diffusion layer was $8{\mu}m$, $30{\mu}m$ and $300{\mu}m$, respectively. However, the microhardness test showed that the depth of hardened layer was $500{\mu}m$. The tensile strength of the ion nitrided SACM645 was lower than that of the unnitrided SACM645, and the ion nitrided specimen was fractured without plastic deformation. The nitrided SACM645 showed much poorer low cycle fatigue properties than the unnitrided one. In rotary bending fatigue, the fatigue strength of the ion nitrided SACM645 was higher than that of the unnitrided specimen, and the fatigue crack initiation sites changed by applied fatigue stress levels. The XRD result showed that the ion nitrided SACM645 has the compressive residual stress from surface to $600{\mu}m$ deep and the tensile residual stress from $600{\mu}m$ to deeper site. It is thought that crack initiation takes place at the point where the total stress of residual stress and applied stress is maximum.

• Journal of Welding and Joining
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• 제23권6호
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• pp.37-42
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• 2005

Most of the welding steel plate structures have complicated mechanical problems such as rolling directional characteristics and residual stresses caused by manufacturing process. For the enhancement of reliability and safety in those structures, therefore, a systematic investigation is required. SS400 steel plate used for common structures was selected and welded by FCAW butt-welding process for this study, and then it was studied experimently about characteristics of fatigue crack propagations with respect to rolling direction and welding residual stress of welded steel plates. When the angles between rolling direction and tensile loading direction in base material are increased, their ultimate strength not show a significant difference, but yielding strength are increased and elongations are decreased uniformly. It is also shown that fatigue crack growth rate can be increased from those results. When the angles between welding bead direction and loading direction in welded material are increase, fatigue crack growth rate of them are decreased and influenced uniformly according to the conditions of residual stress distribution. In these results, it is shown that the welded steel plate structures are needed to harmonize distributed welding residual stress, rolling direction and loading direction fur the improvement of safety and endurance in manufacture of their structures.

• 한국세라믹학회지
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• 제34권3호
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• pp.257-264
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• 1997

MPB조성영역에 MnO2를 첨가한 압전체를 제조하여 분극처리후에 반복압축응력을 부여함에 따른 압전열화 현상을 조사하고 분극처리 전후의 굽힘강도의 변화 및 파괴특성을 연구하였다. MnO2를 0.25wt.% 첨가한 시편에서 가장 적은 열화현상이 일어났다. 굽힘강도는 분극처리 후 하중방향에 평행한 방향으로 분극처리한 시편이 분극처리 전보다 높은 강도를 나타내었고, 수직한 방향으로 분극처리한 시편은 낮은 값을 나타내었다. 이는 분극처리시 발생하는 전계방향으로 압축잔류응력, 직각방향으로 인장잔류응력 때문인 것으로 사료된다.

• 한국주조공학회지
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• 제18권6호
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• pp.534-540
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• 1998

6061Al-matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by Permanent Mold Casting to investigate the mechanical properties of the smart composites. The composites have showed good interface bonding as a result of the analysis of SEM and EDX. The smartness of composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stresses in the matrix material when heated after being prestrained. The tensile strength of the composites was tested at temperatures between $90^{\circ}C$ and room temperature with increasing amount of pre-strain, and it showed that the tensile strength at $90^{\circ}C$ was higher than that of the room temperature. Especially, the tensile strength of the composite increases with increasing pre-strain. It showed that hardness of matrix was higher than that of common 6061Al alloy.

• 소성∙가공
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• 제18권1호
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• pp.45-51
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• 2009

Shape memory alloy has been used to improve the tensile strength of composite by the occurrence of compressive residual stress in matrix using its shape memory effect. In order to fabricate shape memory alloy composite, TiNi alloy fiber and Al2024 sheets were used as reinforcing material and matrix, respectively. In this study, TiNi/Al2024 shape memory alloy composite was made by using hot press method. In order to investigate bonding condition between TiNi reinforcement and Al matrix, the micro-structure of interface was observed by using optical microscope and diffusion layer of interface was measured by using Electron Probe Micro Analyser. And the mechanical properties of composite with three parameters(volume fraction of fiber, cold rolling amount and test temperature) were obtained by tensile test. The most optimum bonding condition for fabrication the TiNi/Al2024 composite material was obtained as holding for 30min. under the pressure of 60MPa at 793K. The strength of composite material increased considerably with the volume fraction of fiber up to 7.0%. And the tensile strength of this composite increased with the reduction ratio and it also depends on the volume fraction of fiber.

• 열처리공학회지
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• 제18권3호
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• pp.157-163
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• 2005

Effects of refinement of primary Si and residual stress on the mechanical properties of Aluminum B.390 alloy have been examined. Calcium was found to have an effect on the size of primary silicon particles. Primary silicon particle was refined as Ca content decreased. Refinement of primary Si particles led to an improvement in mechanical properties of the alloy; increase of elongation was prominent, above all. By the increase of compressive residual stress in the matrix alloy, tensile strength increased but elongation decreased.

• 한국정밀공학회지
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• 제16권1호통권94호
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• pp.227-237
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• 1999

As the interface bonding phenomenon between the matrix and the reinforcements has a large effect on the mechanical properties of MMCs, a sugestion of the strength analysis technique considering the residual stress and the interface bonding phenomenon is very important for the design of pans and the estimation of fatigue behavior. In this paper the three dimensional finite element anaysis is performed during the elasto-plastic deformation of the particulate reinforced metal matrix composites. It was analyzed with the volume fractions in view of microscale. Bonding strength. interface separation and matrix void growth between the matrix and the reinforcements will be predicted on deformation under tensile loading. An interface seperation is estimated by the fracture criterion which is a critical value of generalized plastic work per unit volume. The shape of the reinforcement is assumed to be a perfect sphere. And the type of the reinforcement distribution is assumed as FCC array. The thermal residual stress in MMCs is induced by the heat treatment. It is included at the simulation as an initial residual stress. The element birth and death method of the ANSYS program is used for the estimation of the interface bonding strength, void generation and propagation. It is assumed that the fracture in the matrix region begin to occur under the external loading when the plastic work per unit volume is equal to the critical value. The fracture strain will be defined. The experimental data of the extruded $SiC_p$>/606l Al composites are compared with the theoretical results.

• 한국자기학회지
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• 제3권1호
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• pp.61-64
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• 1993

비정질 세선(amorphous wite)의 인장응력(tensile strees)에 대한 자기적 특성의 변화를 측정하기 위하여 자화 주파수 범위가 1~20 kHz, 인장응력의 범위가 0~20인 N인 비정질 세선용 교류자 기이력곡선특성 측정장치를 제작하였다. 제작된 교류자기이력곡선 측정장치를 이용하여 비정질 세선의 인장응력에 따른 자기적 특성 (최대자기유도 $B_{max}$, 잔류자기 유도 $B_{r}$, 보자력 $H_{c}$)을 1% 의 정밀도로 측정할 수 있었다.

• 터널과지하공간
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• 제18권3호
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• pp.226-238
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• 2008

숏크리트의 지보성능을 보완하기 위해 사용되는 강지보재는 매우 효과적인 것으로 평가되지만 강지보재 종류별 성능이 파악되지 못하여 설계에 제대로 반영하지는 못하고 있다. 본 연구에서는 여러 가지 강지보재에 의해 보강된 숏크리트의 특성을 휨인성 시험을 통하여 파악하고, 그 결과를 수치해석에 반영하고자 하였다. 시험결과 철근보강 숏크리트는 H 형강이나 격자지보에 비해 지보능력이 다소 못 미치는 것으로 나타났는데, 이는 시험체가 휨인장 파괴를 유도하기에는 다소 짧아서 전단파괴가 발생하였기 때문인 것으로 나타났다. 수치해석을 이용한 안정성 해석 시 숏크리트와 강지보재를 별도로, 그리고 이들 복합체에 대한 등가물성을 구하여 각각 해석한 바 두 결과가 잘 일치하여 등가물성을 이용한 복합체 해석으로도 간편하게 강지보재의 효과를 모사할 수 있었다.

• 한국터널지하공간학회 논문집
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• 제12권1호
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• pp.51-60
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• 2010

최근 새로운 형태의 폴리올레핀 섬유에 대하여 성능향상 개발이 이루어지고 있으며, 기존 섬유와 혼입하여 사용하거나 폴리올레핀 섬유만을 사용한 콘크리트 특성에 대하여 연구와 검증이 필요하다. 본 연구의 목적은 강섬유와 폴리올레핀 섬유를 사용한 콘크리트의 휨 인성 및 휨 인장강도에 대한 성능을 확인하기 위하여 324개의 보 시편을 제작하고, KS F2566과 ASTM C 1399-02규격에서 제시한 4점 휨 실험을 수행하여 휨 인성지수, 등가 휨 인장강도, 평균잔류강도를 분석하였다. 실험결과, 섬유 혼입률, 섬유 형상비에 대한 휨 인성 및 인장강도에 대한 효과가 확인되었으며, 강섬유와 폴리올레핀의 최적의 혼입비율을 제시하였다.