SPR 접합법을 이용한 Al-5052 인장-전단 시험편의 피로강도

이만석 ( Man Suk Lee ),김택영 ( Taek Young Kim ),강세형 ( Se Hyung Kang ),김호경 ( Ho Kyung Kim ) 한국안전학회(구 한국산업안전학회) 2014 한국안전학회지 Vol.29 No.4

Self-piercing riveting(SPR) is a mechanical fastening technique which is put pressure on the rivet for joining the sheets. Unlike a spot welding, SPR joining does not make the harmful gas and CO2 and needs less energy consumption. In this study, static andfatigue tests were conducted using tensile-shear specimens with Al-5052 plates for evaluation of fatigue strength of the SPR joints. During SPR joining process for the specimen, using the current sheet thickness and a rivet, the optimal applied punching force was foundto be 21 kN. And, the maximum static strength of the specimen produced at the optimal punching force was 3430 N. During the fatiguetests for the specimens, interface failure mode occurred on the top substrate close to the rivet head in the most high-loading range region,but on the bottom substrate close to the rivet tail in the low -loading range region. There was a relationship between applied loadamplitude Pamp and lifetime of cycle for the tensile-shear,Pamp=3395.5 ×N- 0.078. Using the stress-strain curve of the Al-5052 fromtensile test, the simulations for fatigue specimens have been carried out using the implicit finite element code ABAQUS. The relationbetween von-Mises equivalent stress amplitude and number of cycles was found to be σeq=514.7×N-0.033.

냉간 압연강 판재 기계적 접합부의 인장-박리 피로 강도

이만석 ( Man Suk Lee ),박종민 ( Jong Min Park ),김택영 ( Taek Young Kim ),김호경 ( Ho Kyung Kim ) 한국안전학회 2012 한국안전학회지 Vol.27 No.5

온도변화에 따른 주석 도금한 전기 커넥터의 미동마멸 부식 거동

오만진(Man-Jin Oh),강세형(Se-Hyung Kang),이만석(Man-Suk Lee),김호경(Ho-Kyung Kim) 한국트라이볼로지학회 2014 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.30 No.3

In this study, we conduct fretting corrosion tests on tin-plated brass coupons to investigate the effect of temperature on fretting corrosion for various span amplitudes. We prepare a coupled fretting corrosion specimens using a tin-plated brass coupon with a thickness of 10 μm. One specimen is a flat coupon and the other specimen is a coupon with a protuberance in 1 mm radius, which is produced using 2 mm diameter steel ball. We conduct fretting corrosion tests at 25℃, 50℃, 75℃, 100℃ by rubbing the coupled coupons together at the contact between the flat and protuberance coupons. We measure electric resistance of the contact during the fretting corrosion test period. There is increase in resistance with fretting cycles. It is found that rate of increase in electric resistance becomes faster with increase in testing temperature. Magnitude of friction coefficient increases with fretting span amplitudes. And, change in friction coefficient becomes desensitized to the increment in span amplitude. Assuming that failure cycle is the cycle with an electric resistance of 0.01 Ω, we find that failure lifetime (Nf) decreases with increase in testing temperature. Furthermore, based on the assumption that the damage rate of the connector is inversely related to the failure cycle, we calculate the activation energy for fretting damage to be 13.6 kJ/mole by using the Arrhenius equation. We propose a method to predict failure cycle at different temperatures for span amplitudes below 30 μm. Friction coefficients generally increase with increase in span amplitude and decrease in testing temperature.

혼합모드 하중조건에서의 철도 차륜재의 피로균열 실험에 관한 연구

김택영 ( Taek Young Kim ),이만석 ( Man Suk Lee ),유인동 ( In Dong You ),김호경 ( Ho Kyung Kim ) 한국안전학회(구 한국산업안전학회) 2013 한국안전학회지 Vol.28 No.4

Fatigue crack growth tests were conducted on urban railway wheel steel under mode I and mixed-mode conditions. Fatigue crack growth rates were evaluated in terms of equivalent stress intensity factor ranges, using both the extended and projected crack lengths. The equivalent stress intensity factor range with the growth rate results obtained under mode I loading conditions can be used to predict the crack growth rate under mixed-mode loading conditions. Extended crack length rather than projected crack length is appropriate for the prediction of the crack growth rate under the mixed-mode loading conditions.

산악용 자전거 프레임의 피로 내구성 평가

김택영 ( Taek Young Ki ),이만석 ( Man Suk Lee ),임웅 ( Woong Lim ),김호경 ( Ho Kyung Kim ) 한국안전학회(구 한국산업안전학회) 2013 한국안전학회지 Vol.28 No.3

In order to evaluate fatigue endurance for an MTB(mountain bike)frame, FEM(finite element method)analysis was perforemed. For evaluating fatigue endurance of the MTB frame, the S-N data for Al-6061 fillet weldment were compared with the stress analysis results through FEM analysis of the frame. Three loading condition, pedaling, horizontal and vertical loading conditions were considered for fatigue endurance evaluation. Horizontal loading(+1200N)condition was found to be the most severe to the frame. The maximum von Mises stress of the frame under horizontal loading(+1200N)condition was determined 294 MPa trough FEM analysis of the frame. Conclusively, on the basis of fatigue strength of 200 MPa at the number of cycles of 50,000, MTB frame has an improper safety factor of approximately 0.25, suggesting that this frame needs reinforcement.

마그네틱 파우더 브레이크를 이용한 소형 진자형 충격시험기 개발

유인동(You In-Dong),이만석(Lee Man-Suk),김호경(Kim Ho-Kyung) 한국트라이볼로지학회 2011 한국윤활학회지(윤활학회지) Vol.27 No.3

A miniature pendular type impact testing machine was designed and developed, adopting a magnetic powder brake in order to investigate tensile and shear behavior of a small solder ball at high speed. In this testing system, the potential energy of the pendulum is transferred into the impact energy during its drop. Then, the impact energy is transmitted through the striker which is connected to the push rods to push the specimen for tensile loading. The tensile behavior of lead-free solder ball in diameter of 760 ㎛ was successfully investigated in a speed range of 0.15 m/s~1.25 m/s using this designed device. The maximum tensile strength of the solder joint decreases with the loading speed in the testing condition. The maximum tensile strength of the joint was 56 ㎫ in the low speed region.

강소성변형된 미세립 AM60 마그네슘 합금의 피로거동

유인동 ( In Dong You ),이만석 ( Man Suk Lee ),김호경 ( Ho Kyung Kim ) 한국안전학회(구-한국산업안전학회) 2012 한국안전학회지 Vol.27 No.3

The fatigue behavior of AM60 magnesium alloy produced by equal channel angular pressing(ECAP) process was investigated through fatigue lifetime and fatigue crack propagation rate tests. The grain structure of the material was refined from 19.2 μm to 2.3 μm after 6 passes of ECAP at 493 K. The yield strength(YS) and ultimate tensile strength (UTS) increase after two passes but decrease with further pressing, although the grain size becomes finer with increasing pass number. The softening effect due to texture anisotropy overwhelmed the strengthening effect due to grain refinement after 2 passes. A large enhancement in fatigue strength was achieved after two ECAP passes. The current finding suggests that two passed material is better than the multi-passed material in view of the static strength and fatigue performance

순환골재의 사용성 확대를 위한 연구: 원심력콘크리트로의 적용

심종성,박철우,박성재,김현중,김태광,이만석,Sim, Jong-Sung,Park, Cheol-Woo,Park, Sung-Jae,Kim, Hyun-Jung,Kim, Taeg-Wang,Lee, Man-Suk 한국건설순환자원학회 2006 한국건설순환자원학회지 Vol.2 No.1

순환골재의 생산기술이 향상됨에 따라 순환골재를 사용한 순환골재콘크리트의 품질은 일반골재를 사용한 콘크리트의 품질과 경쟁할 수 있는 수준으로 향상되었다. 따라서 순환골재를 구조부재에 사용하는 것은 가능할 것으로 예상되고 있다. 그러나 대부분의 연구들은 순환골재을 사용한 콘크리트의 강도, 내구성 등의 기초적인 연구에만 집중되고 있다. 본 연구에서는 순환골재의 구조부재로서의 사용처 확대를 위하여, 순환굵은골재 및 순환잔골재의 다양한 혼입률(순환굵은골재: 0%, 20%, 40%, 60%, 100%; 순환잔골재 0%, 30%, 60%, 100%)에 따른 원심력콘크리트의 강도 특성을 검증하고자 하였다. 또한 원심력콘크리트의 품질 및 성능향상을 기대하며 특수 가공된 셀룰로오스섬유의 다양한 혼입에 따른 강도특성을 검증하였다. 실험결과, 일반굵은골재와 순환잔골재을 혼입한 시험체(NR 시험체)의 강도는 72MPa로써 일반굵은골재와 일반잔골재를 사용한 기준시험체(NN 시험체)의 강도 74MPa과 유사한 수준을 나타내었다. 따라서 순환잔골재는 고강도 원심력콘크리트 제품에 100% 혼입사용이 가능한 것으로 판단된다. 또한 특수 가공 처리된 셀룰로오스섬유를 혼입한 모든 시험체의 강도는 약 70MPa로 측정되었으나, 섬유 혼입량이 증가할수록 시험체의 강도는 감소하는 것으로 나타났다. 그러나 특수 가공 처리된 셀룰로오스섬유는 원심력콘크리트 제품에 충분히 적용 가능 한 것으로 판단된다. Along with recent improvement of recycling technique, the quality of the recycled concrete aggregate have become very competitive to the natural concrete aggregate. Therefore, a practical use of the recycled concrete aggregate may be possible for structural members. Majority studies about the recycled concrete aggregate was emphasized a limitation of fundamental study concerned with a strength characteristics and durability of the recycled aggregate concrete, there is use for the structural members. Therefore, for the extension of application of recycled concrete aggregate, this investigation verifies the strength characteristics recycled concrete aggregate of the spun-concrete products with various coarse and fine recycled aggregate replacement ratio(coarse recycled aggregate: 0%, 20%, 40%, 60%, 100%; fine recycled aggregate: 0%, 30%, 60%, 100%) and with addition of cellulose fibers(0%, 0.01%, 0.03%, 0.05%, 0.08%). From the test results, The strength of spun concrete used with recycled aggregate [NR specimen], was measured as 72MPa, was found to be very approximately to the strength of spun concrete used with the natural aggregate(NN specimen), was measured as 74MPa, when only fine aggregate was replaced with the recycled. Therefore, the fine recycled concrete aggregate can be successfully used in the spun high strength concrete product. The compressive strength of all specimens used the specialty cellulose fiber were measured as about 70M Pa, however, the increasement of the specialty cellulose fiber content is showed to decrease compressive strength of spun concrete. Therefore, it is anticipated that the specialty cellulose fiber can be applied to the various spun concrete products.