• 한국소음진동공학회논문집
• /
• 제23권9호
• /
• pp.850-856
• /
• 2013

Torsional interaction between electrical network phenomena and turbine-generator shaft cause torsional stress on turbine-generator shaft and torsional fatigue fracture on vulnerable component, but the prediction of the torsional stress is difficult because the torsional stress is occurred instantly and randomly. Therefore continuous monitoring of the torsional stress on turbine-generator shaft is necessary to predict the torsional fatigue, but installing the sensors on the surface of the shaft directly to monitor the stress is impossible practically. In this study torsional vibration was measured using magnetic sensor at a point of turbine-generator rotor kit, the torsional stress of whole train of rotor kit was calculated using rotor kit's stress model and the calculated results were verified in comparison with the measured results using strain gauge at several point of turbine-generator rotor kit. It is expected that these experiment results will be used effectively to calculate the torsional stress of whole train of turbine-generator rotor in power plants.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 추계학술대회 논문집
• /
• pp.862-867
• /
• 2013

Torsional interaction between electrical network phenomena and turbine-generator shaft cause torsional stress on turbine-generator shaft and torsional fatigue fracture on vulnerable component, but the prediction of the torsional stress is difficult because the torsional stress is occurred instantly and randomly. Therefore continuous monitoring of the torsional stress on turbine-generator shaft is necessary to predict the torsional fatigue, but installing the sensors on the surface of the shaft directly to monitor the stress is impossible practically. In this study torsional vibration was measured using magnetic sensor at a point of turbine-generator rotor kit, the torsional stress of whole train of rotor kit was calculated using rotor kit's stress model and the calculated results were verified in comparison with the measured results using strain gauge at several point of turbine-generator rotor kit. It is expected that these experiment results will be used effectively to calculate the torsional stress of whole train of turbine-generator rotor in power plants.

• Structural Engineering and Mechanics
• /
• 제62권1호
• /
• pp.1-9
• /
• 2017

This paper describes laboratory tests carried out to evaluate the influence of class F fly ash (FA) on fracture toughness of plain concretes, specified at the third model fracture. Composites with the additives of: 0%, 20% and 30% siliceous FA were analysed. Fracture toughness tests were performed on axial torsional machine MTS 809 Axial/Torsional Test System, using the cylindrical specimens with dimensions of 150/300 mm, having an initial circumferential notch made in the half-height of cylinders. The studies examined effect of FA additive on the critical stress intensity factor $K_{IIIc}$. In order to determine the fracture toughness $K_{IIIc}$ a special device was manufactured.The analysis of the results revealed that a 20% FA additive causes increase in $K_{IIIc}$, while a 30% FA additive causes decrease in fracture toughness. Furthermore, it was observed that the results obtained during fracture toughness tests are convergent with the values of the compression strength tests.

• 열처리공학회지
• /
• 제20권1호
• /
• pp.22-30
• /
• 2007

Effects of ferrite grain size on static and dynamic deformation behaviors of SCM415 stels were investigated in this study. Dynamic torsional test was conducted using torsional Kolsky bar with the strain rate of $1.6{\times}10^3/s$. Specimens with three different grain size of ferrite, $4.6{\mu}m$, $11{\mu}m$, $35.5{\mu}m$ were used. Dimple fracture mode of the dynamic test specimens showed adiabatic shear bands on the beneath of fracture surface. Increased uniform elongation and decreased non-uniform elongation appeared as grain size of ferrite decreased in dynamic torsional test. However, shear strength was independent on grain size of ferrite.

• 대한치과교정학회지
• /
• 제37권4호
• /
• pp.293-304
• /
• 2007

본 연구에서는 임상에서 쓰이는 수종의 치과교정용 세라믹 브라켓에 교정용 호선으로 토오크 적용 시 파절에 저항하는 정도를 비교하고 그 파절 양상을 관찰하였다. $022\;{\times}\;028-inch$ slot을 가진 상악 중절치 세라믹 브라켓에 $0215\;{\times}\;027-inch$ 스테인레스 강 교정용 호선에서 발생하는 설측 치근 토오크를 적용시켜 각 15개씩 7종의 브라켓을 시험하였다. 파절 시험용 장치를 제작하고 토오크 각도를 증가시키면서 만능시험기로 세라믹 브라켓이 파절되는 순간의 토오크 값을 측정하였다. 또한 세라믹 브라켓의 파절 양상을 알아보고자 토오크 값 측정 후 파절이 일어난 부위를 관찰하고 그 위치를 기록한 주사전자현미경으로 파절면을 관찰하였다. 나타난 결과를 토대로 볼 때 세라믹 브라켓의 결정구조와 제조 방법이 파절 저항성에 크게 영향을 주는 것으로 나타났다. 단결정 알루미나 (Inspire) 브라켓이 InVu를 제외한 다결정 알루미나 브라켓에 비하여 토오크에 대한 파절 저항성이 유의성 있게 크게 나타났다 (p < 0.05). Metal slot이 삽입된 브라켓은 그렇지 않은 브라켓과 토오크에 대한 저항성에서 유의한 차이를 보이지 않았다 (p >0.05). 파절 양상에 관한 관찰에서는 metal slot이 있는 다결정 알루미나 브라켓인 Clarity는 모두 절단측 slot base에서 부분적으로만 파절이 일어났고 다른 종류의 브라켓들은 다양한 부위에서 파절이 일어났다. 본 연구 결과, 실험에 사용한 모든 세라믹 브라켓에서 파절이 일어난 순간의 토오크 값과 토오크 각은 실제로 상악 중절치의 치근을 이동하는데 필요한 토오크보다 큰 것이었으므로, 실제 임상 치료 시 적절한 파절 저항을 나타낼 것으로 보였다.

• 대한치과의사협회지
• /
• 제57권11호
• /
• pp.672-678
• /
• 2019

AIM: The purpose of this study was to evaluate and compare the torsional fracture resistances, cyclic fatigue resistance, and bending stiffness of two nickel-titanium (NiTi) rotary instruments made of different heat-treated alloy: Aurum Blue (heat-treated) and Aurum Pro (conventional). Methods: Forty-five Aurum Blue and Aurum Pro NiTi files were selected for the three mechanical tests (n=15). For the torsional resistance test, 3 mm file tip was fixed and the shaft was driven clockwise at 2 rpm until fracture occurred by using a customized device. Cyclic fatigue resistance was evaluated by rotating instruments in artificial canal with dynamic mode. Bending stiffness was tested by observation of the bending moment on attaining a 45° bend. The results were analyzed by student-t tests at a significance level of 95%. The fractured surface of each groups were examined under a scanning electron microscope (SEM). Results: Aurum Blue showed significantly higher toughness, ultimate strength, distortion angle, and number of cycles to failure than those of Aurum Pro (p < 0.05). However, Aurum Blue and Aurum Pro did not differ significantly in terms of bending stiffness. SEM showed typical topographic appearances of the cyclic fatigue and torsional fracture. Conclusions: Under the limitations of this study, heat-treated instruments showed higher flexibility and fracture resistances than conventional NiTi instruments.

• Restorative Dentistry and Endodontics
• /
• 제42권3호
• /
• pp.216-223
• /
• 2017

Objectives: The aim of this study was to compare the mechanical properties of various nickel-titanium (NiTi) files with similar tapers and cross-sectional areas depending on whether they were surface-treated. Materials and Methods: Three NiTi file systems with a similar convex triangular cross-section and the same ISO #25 tip size were selected for this study: G6 (G6), ProTaper Universal (PTU), and Dia-PT (DPT). To test torsional resistance, 5 mm of the straightened file's tip was fixed between polycarbonate blocks (n = 15/group) and continuous clockwise rotation until fracture was conducted using a customized device. To evaluate cyclic fatigue resistance, files were rotated in an artificial curved canal until fracture in a dynamic mode (n = 15/group). The torsional data were analyzed using 1-way analysis of variance and the Tukey post-hoc comparison test, while the cyclic fatigue data were analyzed using the Mann-Whitney U test at a significance level of 95%. Results: PTU showed significantly greater toughness, followed by DPT and G6 (p < 0.05). G6 showed the lowest resistance in ultimate torsional strength, while it showed a higher fracture angle than the other files (p < 0.05). In the cyclic fatigue test, DPT showed a significantly higher number of cycles to failure than PTU or G6 (p < 0.05). Conclusions: Within the limitations of this study, it can be concluded that the torsional resistance of NiTi files was affected by the cross-sectional area, while the cyclic fatigue resistance of NiTi files was influenced by the surface treatment.

• 열처리공학회지
• /
• 제17권6호
• /
• pp.327-335
• /
• 2004

Effect of spherodization of cementite on static and dynamic deformation behaviors of SCM415 steels was investigated in this study. Dynamic torsional test was conducted using torsional Kolsky bar with the strain rate of $1.6{\times}10^3/s$. Three type of specimens were used with different spherodization degree of cementite. Dynamic test results were analyzed comparing with static tensile results and microstructural changes. The obtained results are as follows; 1) All the specimens of static and dynamic tests showed a ductile fracture mode of dimple. Specimens of the dynamic test showed adiabatic shear bands on the beneath of fracture surface. 2) In static tensile test, decreased tensile strength and increased uniform and non-uniform elongations appeared as spherodization degree of cementite increased. 3) In dynamic torsional test, decreased shear strength and increased uniform elongation appeared as spherodization degree of cementite increased. 4) Due to the largest uniform elongation, superior cold forgeability at high speed is expected on high spherodization degree of cementite.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2008년도 춘계학술대회 논문집
• /
• pp.427-430
• /
• 2008

The influence of subsequent annealing treatment on the dynamic deformation and the fracture behavior of submicrocrystalline Al-4.4%Mg alloy is investigated in this study. After inducing an effective strain of 8 via equal-channel angular pressing at $200^{\circ}C$, most of the grains are considerably reduced to nearly equiaxed grains of $0.3{\mu}m$ in size. With an increment of various subsequent heat treatments for 1 hour, resultant microstructures are found to be fairly stable at temperatures up to $200^{\circ}C$, suggesting that static recovery will be dominantly operative, whereas grain growth is pronounced above $250^{\circ}C$. The results of tensile tests show that yield and ultimate tensile strength decrease, but elongation-to-failure and strain hardening rate increase with an increase in annealing temperatures. The dynamic deformation and the fracture behavior retrieved with a series of torsional tests are explored with respect to annealed microstructures. Such mechanical response is analyzed in relation to resultant microstructure and fracture mode.

• 한국기계가공학회지
• /
• 제10권4호
• /
• pp.8-15
• /
• 2011

In this paper, the influence of a crack on the natural frequency of cracked cantilever L-shaped beam with coupled bending and torsional vibrations by analytically and experimentally is analyzed. The L-shaped beam with a crack is modeled by Hamilton's principle with consideration of bending and torsional energy. The two coupled governing differential equations are reduced to one sixth-order ordinary differential equation in terms of the flexural displacement. The crack is assumed to be in the first, second and third mode of fracture and to be always opened during the vibrations. The theoretical results are validated by a comparison with experimental measurements. The maximal difference between the theoretical results and experimental measurements of the natural frequency is less than 7.5% in the second vibration mode.