• 한국해양공학회지
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• 제2권2호
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• pp.112-121
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• 1988

A study on friction welding of carbon steel bar (SM45C) to chrome molybedenum steel bar(SCM4) is examined experimentally through tensile test, hardness test, microstructure test and fatigue test. so, this paper deals with optimizing the welding concitions and analyzing various mechanical properties about friction welds of SM45C to SCM4 steel bars. The results obtained are summarized as follows; 1) For friction welded joints of SM45C to SCM4 steel bars, the total upset(U)increases linearly with an increase of heating time ($t_{1}$) till 6s. 2) The determined optimum welding conditions are heating time ($t_{1}$)2s, upsetting time($t_{2}$), 3s, heating pressure($p_{1}$), 4kgf/$mm^{2}$(39.2MPa), upsetting pressure($p_{2}$, 8kgf/mm$^{2}$(78.4MPa) and rotating speed(N), 2, 000rpm when the total upset(U) is 3.4mm, resulting in a computed relationship between the joint tensile strength .sigma.$_{t}$ (kgf/mm$^{2}$and the total upset U(mm); .sigma.$_{t}$ =$0.21U^{3}$ - $3.38U^{2}$ +17.03U + 66.00 3) As the elongation is increased more and more, the fracture position becomes away from weld interface and the fractures are similar to those of SM45C. Fracture is taken place on SM45C side. 4) The weld interface of two dissimilar materials is mixed strongly, and the heat affected zone is about 2.0mm at SM45C while about 2.7 mm at SCM4 side. Therefore, the welded zone and heat affected zone are very narrow, comparing with those of the joints welded by the other welding methods. 5) The fatigue strengths at N=10$^{6}$ cycles of SM45C, SCM4 and friction welded joints are 23kgf/$mm^{2}$, 33kgf/$mm^{2}$(220.5 MPa), and 22.5kgf/$mm^{2}$(220.5MPa) respectively, and fracture at friction welded joint takes place at the side of SM45C. 6) The hardness of the friction weld interface is 3 times higher than that of base metal. 7) Fatigue strength of friction welded joint is higher than that of base metal. 8) Notch sensitivity factor of friction welded joint is lower than that of base metal.

• 한국해양공학회지
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• 제22권1호
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• pp.53-57
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• 2008

Friction welding was performed to investigate mechanical properties for Ni-base superalloy with 15 mm diameter solid bar. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness surveys of the bond of area and heat affected zone. And then, the nondestructive technique to evaluate the weld quality was carried out by acoustic emission(AE) and ultrasonic attenuation coefficient. The tensile strength of the friction welded joint was shown up to 90 % of the Alloy718 base metal under the condition of the heating time over 5 sec. The optimal welding conditions were n=2,000 rpm, $P_1=200$ MPa, $P_2=200$ MPa, $t_1=8$ sec and $t_2=5$ sec when the total upset length was 4.4 mm.

• 소성∙가공
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• 제27권5호
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• pp.281-288
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• 2018

This study deals with the microstructure and tensile properties of 600 and 700 MPa-grade high-strength seismic reinforced steel bars. High-strength seismic resistant reinforced steel bars (SD 600S and SD 700S) were fabricated by TempCore process, especially the SD 700S specimen was more rapid cooled than the SD 600S specimen during the TempCore process. Although two specimens had microstructure of tempered martensite in the surface region, the SD 600S specimen had ferrite-degenerated pearlite in the center region, whereas the SD 700S specimen had bainite-ferrite-degenerated pearlite in the center region. Therefore, their hardness was highest in the surface region and revealed a tendency to decrease from the surface region to the center region because tempered martensite has higher hardness than ferrite-degenerated pearlite or bainite. The SD 700S specimen revealed higher hardness in the center region than SD 600S specimen because it contained a larger amount of bainite as well as ferrite-degenerated pearlite. On the other hand, tensile test results indicated the SD 600S and SD 700S specimens revealed continuous yielding behavior because of formation of degenerated pearlite or bainite in the center region. The SD 600S specimen had a little higher tensile-to-yield ratio because the presence of ferrite and degenerated pearlite in the center region and the lower fraction of tempered martensite enhance work hardening.

• 콘크리트학회지
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• 제6권2호
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• pp.169-179
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• 1994

주택건설은 극심한 건축자재 부족과 인력수급등의 많은 어려움을 격고 있는데, 이에 대한 문제의 해결방은 중 하나로 철근콘크리트 공사에서 철근의 가공조립공정을 보다 간소화하면서 그 기능의 효율성을 높이는 방법으로 구조용 용접철망과 루프형 용접철망을 이용한 공법이 제기되고 있다. 본 연구에서는 일방향 슬래브에 콘크리트 예상 압축강도가 $210kg/cm^2$일 때, 최대균열폭과 소성변형 능력에 영향을 미치는 요인인 사용철근의 종류, 최소철근비를 기준으로 한 인장철근비(${\rho}t$), 주변지지조건, 겹이음길이의 4가지 주요변수로 하여 슬래브의 구조적 특성 및 휨거동을 파악하는데 그 목적을 두었다. 연구결과, 소성변형능력은 이형철근을 사용한 슬래브가 용접철망을 사용한 슬래브보다 월등히 큰 것으로 나타났고, 겹이음된 슬래브에서는 겹이음길이 30D가 적절한 것으로 나타났다. 또한 최대균열폭은 용접철망과 루프형 용접철망을 사용한 슬래브가 이형철근을 사용한 슬래브 보다 균열폭을 억제하는 것으로 나타났다.

• 대한치과보철학회지
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• 제43권3호
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• pp.322-330
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• 2005

Statement of problem. In distal extension removable partial denture, the preservation of health of abutment teeth is very important, but abutment teeth are subjected to unfavorable stress. Purpose. The purpose of this study was to investigate the biomechanical effects of mandibular removable partial dentures with various prosthetic designs using strain gauge analysis. Material and methods. Artificial teeth of both canines were anchored bilaterally in a mandibular edentulous model made of resin. Bilateral distal extension removable partial dentures with splinted and unsplinted abutments were fabricated. Group 1 : Clasp-retained mandibular removable partial denture with unsplinted abuhnents Group 2 : Clasp-retained mandibular removable partial denture with splinted abutments by 6-unit bridge Group 3 : Bar-retained mandibular removable partial denture Strain gauges were bonded on the labial plate of the mandibular resin model, approximately 2 mm close to the abutments. Two vertical experimental loadings (100N and 200N) were applied subsequently via two miniature load cells that were placed at mandibular first molar regions. Strain measurements were performed and simultaneously monitored from a computer connected to data acquisition system. For within-group evaluations, t-test was used to compare the strain values and for between-group comparisons, a one-way analysis of variance (ANOVA) was used and Duncan test was used as post hoc comparisons. Results. Strain values increased as the applied load increased from 100N to 200N for all groups (p<.05). The strain values of group 1 and 2 were tensile under loadings. In contrast, strain values of group 3 were compressive in nature. Under 100N loading, group 1 showed higher strain values than group 3 in absolute quantity (p<.05). Under 200N loading, group 3 showed higher strain values than group 1 and 2 in absolute quantity (p<.05). Group 1 showed higher strain values than group 2 (p<.05). Conclusion. Splinting of two isolated abutments by bridge reduced the peri-abutment strain in comparison with unsplinted abutments. Strain of bar-retained removable partial denture increased much more as applied load increased, but was compressive in nature.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.899-904
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• 2009

This paper presents the analysis result of load-transfer mechanism and pile movements associated with the development of frictional resistance to understand the engineering characteristics of micropile behavior. An field load tests were performed for two different types of micropiles and they are (i) thread bar reinforcement with D=50mm and (ii) hollow steel pipe reinforcement with $D_{out}$=82.5mm and $D_{in}$=60.5mm and wrapped with woven geotextile for post-grouting. The load test results indicated that micropiling with pressured grouting provided better load-transfer characteristics than micropiling with gravity grouting under both compressive and tensile loading conditions in that unit skin frictional resistance is well distributed along installation depth. The unit weight and unconfined compressive strength of cured grout were obtained for each piling method. The strength and unit weight of micropile with pressured grouting was higher than those with gravity grouting. The fact that load bearing quality with pressured grouting is better than that of gravity grouting could be attributed to the dense mutual adhesion between surrounding ground and pile due to pressurized grouting method and better grout quality.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.311-324
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• 2015

The purpose of this study was to investigate experimentally the fatigue performance of reinforced concrete (RC) beams with hot-rolled ribbed fine-grained steel bars of yielding strength 500MPa (HRBF500). Three rectangular and three T-section RC beams with HRBF500 bars were constructed and tested under static and constant-amplitude cyclic loading. Prior to the application of repeated loading, all beams were initially cracked under static loading. The major test variables were the steel ratio, cross-sectional shape and stress range. The stress evolution of HRBF500 bars, the information about crack growth and the deflection developments of test beams were presented and analyzed. Rapid increases in deflections and tension steel stress occured in the early stages of fatigue loading, and were followed by a relatively stable period. Test results indicate that, the concrete beams reinforced with appropriate amount of HRBF500 bars can survive 2.5 million cycles of constant-amplitude cyclic loading with no apparent signs of damage, on condition that the initial extreme tensile stress in HRBF500 steel bars was controlled less than 150 MPa. It was also found that, the initial extreme tension steel stress, stress range, and steel ratio were the main factors that affected the fatigue properties of RC beams with HRBF500 bars, whose effects on fatigue properties were fully discussed in this paper, while the cross-sectional shape had no significant influence in fatigue properties. The results provide important guidance for the fatigue design of concrete beams reinforced with HRBF500 steel bars.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1118-1125
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• 2009

본 연구는 국내의 초연약지반에 적용 가능한 표층보강재를 이용한 연약지반 표층처리공법을 정립시키기 위한 기초적 연구로서 표층처리공법에 사용되는 보강재의 강성도를 고려한 지 지력산정방법을 제안하는 것을 목적으로 하고 있다. 이를 위하여 직포, 지오그리드, 강봉(대나무 대채재료)을 이용하여 광폭인장시험 및 보강재의 단부 구속조건을 완전구속, 부분구속(3종류)으로 한 21 종류의 실내모형실험을 수행하였다. 실험결과, Terzaghi의 지지력이론식은 직포와 지오그리드와 같은 연성보강재 사용시에는 지지력산정이 적절하나, 대나무 망과 같은 강성도가 큰 재료에 대해서는 강성도를 적절히 표현하지 못하는 것으로 평가되었으며, 초연약지반 표층처리공법의 지지력산정방법을 Terzaghi 지지력이론식을 수정하여 강성도의 영향을 정확히 평가하는 새로운 지지력이론식을 제안하였다.

• 한국강구조학회 논문집
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• 제16권6호통권73호
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• pp.769-780
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• 2004

본 논문의 목적은 인장용 연결 플레이트를 갖는 냉간성형 각형강관 갭 N형 접합부의 실험연구를 통하여 접합부 거동을 평가하는데 있다. 실험을 위한 주요 변수로는 주관의 폭두께비, 주관에 대한 지관의 폭의 비, 편심비, 압축지관 형상, 지관의 각도, 주관 상부 플랜지면 보강 등이 있다. 이와 같은 변수들로 구성된 갭 N형 접합부에 대한 내력 및 파괴모드 등에 대하여 실험을 통해 고찰하고자 한다. 실험결과, 갭 N형 접합부는 폭비에 관계없이 접합부의 인장측 변위가 선행하여 접합부의 내력이 결정되었으며, 접합부 파괴는 접합된 주관면의 찢어짐 파괴모드로 결정되었다. 인장 및 압축측 폭비(${\beta}$)가 클수록 주관 폭두께비가 작을수록 접합부의 항복하중 및 최대하중은 선형으로 상승하는 것으로 나타났다. 주관의 폭두께비($2{\gamma}$)가 작을수록 접합부의 내력비교 곡선은 급격히 상승함을 알 수 있다. 인장용 연결 플레이트를 갖는 갭 N형 접합부에 대하여 변수에 따른 접합부의 하중, 초기강성, 연성능력 및 파괴모드 변화 등에 대한 결과에 대해서도 정리하여 나타내었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.685-688
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• 2008

콘크리트는 압축에 강한 특성을 지닌 재료이지만, 인장 및 휨강도가 낮고 균열에 대한 저항성이 약한취성재료라는 단점을 가지고 있어 이에 대한 보완책으로서 철근이 사용되어 왔다. 하지만, 포러스콘크리트는 내부에 존재하는 다량의 연속공극으로 인하여 철근보강시 철근이 공기에 노출되어 부식되는 문제점을 보이고 있다. 따라서, 본 연구에서는 강섬유를 혼입과 목표공극률에 따른 공극률, 압축강도,휨강도 및 휨인성 특성을 검토하였다. 실험결과, 강섬유의 혼입에 따른 실측공극률은 증가하는 것으로 나타났으며, 강도특성에서는 강섬유의 혼입률이 증가 함에 따라 증가하는 것으로 나타났으나 일정량 이상의 섬유가 혼입되었을 경우에는 강도가 오히려 감소되는 것으로 나타났다. 또한, 휨인성평가에서는 강섬유를 혼입하지 않은 포러스콘 크리트에 비하여 처짐변형 성능이 현저히 개선되는 것으로 나타났다. 따라서 강섬유를 포러스콘크리트에 활용한 2차제품 및 포장재료 등에 적용하기 위한 강도 및 휨저항성능 향상재료로 사용가능성을 확인하였다.