• 제목/요약/키워드: Static frictional force

검색결과 26건 처리시간 0.02초

결찰양식이 교정용 브라켓과 교정선 사이의 마찰력에 미치는 영향 (THE EFFECT OF LIGATION METHOD ON THE FRICTIONAL FORGE BETWEEN ORTHODONTIC BRACKET AND ARCHWIRE)

  • 신현정;권오원;김교한
    • 대한치과교정학회지
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    • 제28권5호
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    • pp.813-823
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    • 1998
  • 마찰력은 치아이동시 활주이동부에 유해한 인자로 인식되어져 왔으나 치아이동에 저항하는 고정원에 있어서는 유리한 인자로 받아들여질 수 있다. 즉 마찰력이 작은 결찰법들을 이용하여 효과적인 치아이동을 도모하는 반면 마찰력이 큰 결찰법들을 이용하여 브라켓의 걸림에 의해 치아이동이 거의 일어나지 않게 하면 고정원을 강화할 수 있다. 인공타액하에서 시간경과에 따른 교정선과 브라켓 사이의 마찰력 변화, 탄성 모듈과 스테인레스 강 결찰선을 이용하여 각각 결찰양식을 달리 하였을 때의 마찰력 변화 그리고 결찰재의 재료를 달리 하였을 때의 마찰력 변화를 알아보기 위하여 .018"x.025" 슬롯의 상악 중절치용 standard edgewise twin 브라켓과 .017"x.022" 스테인레스 강 교정선을 탄성 모듈, .009" 스테인레스 강 결찰선 그리고 .012" 스테인레스 강 결찰선을 이용하여 다양하게 결찰하였다. 또한 통상적인 방법으로 결찰한 탄성 모듈 결찰군을 결찰 직후와 1주 간격으로 4주간 마찰력을 측정하여 다음과 같은 결과를 얻었다. ${\cdot}$탄성 모듈 whole tie시 시간경과에 따른 마찰력은 4주 경과시 가장 높았으나 3주, 2주, 1주, 결찰 직후간에는 통계학적으로 유의한 차이가 없었다 (p>0.n). ${\cdot}$탄성 모듈로 결찰시 마찰력은 twisting tie가 가장 높았고 double overlay tie, whole tie, half tie 순으로 나타났으나 twisting tie와 double overlay tie 간에는 통계학적으로 유의한 차이가 없었다 (p>0.05). ${\cdot}$스테인레스 강 결찰선으로 결찰시 half tie 군이 whole tie 군보다 낮은 마찰력을 보였으며 ligature tying plier로 결찰한 경우가 needle holder로 결찰한 경우보다 더 높았고 .012" 결찰선을 이용한 경우가 .009" 결찰선을 이용한 경우보다 더 높았다 (p<0.05). ${\cdot}$통상적인 방법으로 탄성 모듈과 스테인레스 강 결찰선을 이용하여 결찰한 경우 두 군간에 유의한 차이가 없었다(p>0.05).

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Lab-based Simulation of Carton Clamp Truck Handling - Frictional Characteristics between Corrugated Packages

  • Park, Jong Min;Choi, Sang Il;Kim, Jong Soon;Jung, Hyun Mo
    • 한국포장학회지
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    • 제25권3호
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    • pp.131-137
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    • 2019
  • Carton clamps, one of forklift attachments, allow users to quickly handle shipping units such as unitized loads, large shipping cases, or crates without the requirement of pallets. As the use of palletless handling by clamp trucks increases, so does the need for simulation research on clamp truck handling. The frictional characteristics for various contact conditions of corrugated paperboards and their constituent boards were analyzed to obtain the data needed in the computer simulation for the handling of carton clamp truck. The overall mean of static-frictional coefficients between selected corrugated paperboards was 0.38 (±0.01), which was 1.3~1.6 times greater than 0.23~0.29 of the frictional coefficients between boards. The overall mean of static-frictional coefficients between the corrugated paperboards and the rubber contact pad was 0.82 (±0.02), which was about 1.1 to 2.8 times greater than 0.29~0.78 of the static-frictional coefficient between the linerboard and the rubber contact pad. The overall mean of kinetic-frictional coefficients between the corrugated paperboards was 0.35 (±0.01), and 0.76 (±0.02) between the corrugated paperboards and the rubber contact pad.

A comparative study of frictional force in self-ligating brackets according to the bracket-archwire angulation, bracket material, and wire type

  • Lee, Souk Min;Hwang, Chung-Ju
    • 대한치과교정학회지
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    • 제45권1호
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    • pp.13-19
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    • 2015
  • Objective: This study aimed to compare the frictional force (FR) in self-ligating brackets among different bracket-archwire angles, bracket materials, and archwire types. Methods: Passive and active metal self-ligating brackets and active ceramic self-ligating brackets were included as experimental groups, while conventional twin metal brackets served as a control group. All brackets were maxillary premolar brackets with 0.022 inch [in] slots and a $-7^{\circ}$ torque. The orthodontic wires used included 0.018 round and $0.019{\times}0.025$ in rectangular stainless steel wires. The FR was measured at $0^{\circ}$, $5^{\circ}$, and $10^{\circ}$ angulations as the wire was drawn through the bracket slots after attaching brackets from each group to the universal testing machine. Static and kinetic FRs were also measured. Results: The passive self-ligating brackets generated a lower FR than all the other brackets. Static and kinetic FRs generally increased with an increase in the bracket-archwire angulation, and the rectangular wire caused significantly higher static and kinetic FRs than the round wire (p < 0.001). The metal passive self-ligating brackets exhibited the lowest static FR at the $0^{\circ}$ angulation and a lower increase in static and kinetic FRs with an increase in bracket-archwire angulation than the other brackets, while the conventional twin brackets showed a greater increase than all three experimental brackets. Conclusions: The passive self-ligating brackets showed the lowest FR in this study. Self-ligating brackets can generate varying FRs in vitro according to the wire size, surface characteristics, and bracket-archwire angulation.

A study on calculation of friction coefficient and packing stress using static diagnosis test for a balanced globe valve in nuclear power plants

  • Kim, Jaehyung;Lim, Taemook;Ryu, Ho-Geun
    • Nuclear Engineering and Technology
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    • 제53권8호
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    • pp.2509-2522
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    • 2021
  • A valve assembly used in nuclear power plants must be qualified and supervised. New technical standards such as ASME QME-1 2007 particularly require detailed qualification using experiment and analysis. Particularly, diagnostic tests and engineering studies are required for qualification of ASME QME-1 2007. Among these studies, the research on the measurement of friction coefficient and packing stress is important. The irregular change of packing stress along the stroke distance occurs because of the abnormal phenomenon, which must be found and studied with quantitative methods. Packing stress should be analyzed conservatively through experimentation and analysis. In this study, various formulas were applied to measure and calculate coefficient of friction and packing stress. This study can be used in relation to qualification and supervision of packing materials. And the calculation using static diagnosis test can be used to find the packing frictional force in dynamic diagnosis test with flow pressure in a pipe. This study has made it possible to reliably consider packing frictional force generated in a valve body. And so, it is believed that more margin can be secured when evaluating the capacity of valve actuator by applying the accurate frictional force generated in the valve assembly.

Frictional responses of concrete-to-concrete bedding planes under complex loading conditions

  • Dang, Wengang;Konietzky, Heinz;Li, Xiang
    • Geomechanics and Engineering
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    • 제17권3호
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    • pp.253-259
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    • 2019
  • Concrete-to-concrete bedding planes (CCBP) are observed from time to time due to the multistep hardening process of the concrete materials. In this paper, a series of direct/cyclic shear tests are performed on CCBP under static and dynamic normal load conditions to study the frictional behavior effect by the shear velocities, normal impact frequencies, horizontal shear frequencies, normal impact force amplitudes, horizontal shear displacement amplitudes and normal load levels. According to the experimental results, apparent friction coefficient k ($k=F_{Shear}/F_{Normal}$) shows different patterns under static and dynamic load conditions at the stable shear stage. k is nearly constant in direct shear tests under constant normal load conditions (DCNL), while it is cyclically changing with nearly constant peak value and valley value for the direct shear tests under dynamic normal load conditions (DDNL), where k increases with decreasing normal force and decreases with increasing normal force. Shear velocity has little influence on peak values of k for the DCNL tests, but increasing shear velocity leads to increasing valley values of k for DDNL tests. It is also found that, the valley values of k ascend with decreasing impact normal force amplitude in DDNL tests. The changing pattern of k for the cyclic shear tests under constant and dynamic normal load conditions (CCNL and CDNL tests) are similar, but the peak value of k is smaller in CDNL tests than that in CCNL tests. Normal load levels, shear displacement amplitudes, vertical impact frequencies, horizontal shear frequencies and normal impact force amplitudes have little influence on the changing pattern of k for the cyclic shear tests. The tests of this study provide useful data in understanding the frictional behavior of the CCBP under distinct loadings, and these findings are very important for analyzing the stability of the jointed geotechnical structures under complicated in situ stress conditions.

Active Stick 제어기 개발에 관한 연구 (A study of an Active Stick Controlling System with Friction Observer)

  • 김명열;남윤수
    • 산업기술연구
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    • 제24권B호
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    • pp.207-214
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    • 2004
  • An active stick which supplies force feedback to the operator is developed in this study. A mathematical model of the active stick is derived, and compared with the experimental result. It turns out that the frictional torque due to the mechanical contacts of several parts of the stick is one of the major barriers to achieve high precision operation of the stick. The frictional effect of the stick is cancelled out by using a friction observer. The efficacy of the friction observer is verified through the numerical simulation. Because of the observer dynamics, there are some limitations in exact recovering the static friction and Stribeck effect. However, the friction observer follows the real friction on the average. It's anticipated that the application of the friction observer to the closed loop control of the active stick improves the performance of the displacement versus force characteristics, which will be proved experimentally in the further study.

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Frictional property comparisons of conventional and self-ligating lingual brackets according to tooth displacement during initial leveling and alignment: an in vitro mechanical study

  • Kim, Do-Yoon;Lim, Bum-Soon;Baek, Seung-Hak
    • 대한치과교정학회지
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    • 제46권2호
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    • pp.87-95
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    • 2016
  • Objective: We evaluated the effects of tooth displacement on frictional force when conventional ligating lingual brackets (CL-LBs), CL-LBs with a narrow bracket width, and self-ligating lingual brackets (SL-LBs) were used with initial leveling and alignment wires. Methods: CL-LBs (7th Generation), CL-LBs with a narrow bracket width (STb), and SL-LBs (In-Ovation L) were tested under three tooth displacement conditions: no displacement (control); a 2-mm palatal displacement (PD) of the maxillary right lateral incisor (MXLI); and a 2-mm gingival displacement (GD) of the maxillary right canine (MXC) (nine groups, n = 7 per group). A stereolithographic typodont system and artificial saliva were used. Static and kinetic frictional forces (SFF and KFF, respectively) were measured while drawing a 0.013-inch copper-nickel-titanium archwire through brackets at 0.5 mm/min for 5 minutes at $36.5^{\circ}C$. Results: The In-Ovation L exhibited lower SFF under control conditions and lower KFF under all displacement conditions than the 7th Generation and STb (all p < 0.001). No significant difference in SFF existed between the In-Ovation L and STb for a 2-mm GD of the MXC and 2-mm PD of the MXLI. A 2-mm GD of the MXC produced higher SFF and KFF than a 2-mm PD of the MXLI in all brackets (all p < 0.001). Conclusions: CL-LBs with narrow bracket widths exhibited higher KFF than SL-LBs under tooth displacement conditions. CL-LBs and ligation methods should be developed to produce SFF and KFF as low as those in SL-LBs during the initial and leveling stage.

공기윤활 포일 베어링의 특성해석 (An Analysis of Characteristics of Air-Lubricated Foil Journal Bearings)

  • 김종수;이준형;최상규
    • Tribology and Lubricants
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    • 제17권2호
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    • pp.97-108
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    • 2001
  • This paper describes the development of performance analysis technique for a leaf-type gas lubricated fail bearing. Stiffness coefficient and frictional damping due to the slip between all contacts of leaves are evaluated for various leaf structures. The fluid film thickness and pressure distribution are computed but it is not considered the elastic deformation by film pressure. The analysis results include the effects that the curvature radius and the length of leaf and the friction coefficient have on the static and dynamic characteristics of the foil bearings.

소형 원자로용 모듈화 격납구조의 내압성능 분석 (Analysis of Internal Pressure Capacity of Modular Containment Structure for Small Modular Reactor)

  • 박우룡;임성순
    • 한국산학기술학회논문지
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    • 제20권8호
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    • pp.362-370
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    • 2019
  • 격납구조는 사고시 방사능 유출을 막기 위해 내압성능을 확보해야 하므로 소형 원자로용 격납구조에 모듈 방식을 적용하기 위해서는 내압성능의 분석이 필요하다. 따라서 소형 원자로용 모듈화 격납구조의 내압성능 분석을 위해 프리캐스트 콘크리트 모듈과 모듈 사이의 연결부 접촉면과 긴장재 배치를 고려한 FEM모델을 작성하고 정적해석을 수행한다. 이를 통해 모듈화 격납구조의 하중단계별 변위 및 응력의 변화특성을 분석한다. 그리고 변수 분석을 위해 선정된 각 변수가 모듈화 격납구조의 내압성능에 미치는 영향을 분석한다. 비교를 위해 일체화 격납구조의 내압성능도 함께 분석한다. FEM해석을 통한 변수 분석을 통해 긴장력 크기, 긴장재 배치 간격, 콘크리트 두께방향 긴장재 위치, 연결부 접촉면 마찰 계수 크기, 콘크리트 두께 등과 같은 변수 값의 범위가 제시되었다. 모듈화 격납구조의 모듈 간 접촉면에서 합성효과를 발생시켜주는 주요인자는 긴장재에 의한 긴장력과 연결부 접촉면의 마찰력이다. 일체화 격납구조 대비 추가적인 긴장재배치를 통해 긴장력을 증가시키면 모듈화 격납구조에서도 일체화 격납구조와 동등 수준의 내압성능을 확보할 수 있다.

Effect of passive self-ligating bracket placement on the posterior teeth on reduction of frictional force in sliding mechanics

  • Kim, Kyu-Ry;Baek, Seung-Hak
    • 대한치과교정학회지
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    • 제46권2호
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    • pp.73-80
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    • 2016
  • Objective: The purpose of this study was to investigate the static (SFF) and kinetic frictional forces (KFF) in sliding mechanics of hybrid bracket systems that involve placing a conventional bracket (CB) or active self-ligating bracket (ASLB) on the maxillary anterior teeth (MXAT) and a passive SLB (PSLB) on the maxillary posterior teeth (MXPT). Methods: The samples consisted of two thoroughbred types (group 1, anterior-CB + posterior-CB; group 2, anterior-ASLB + posterior-ASLB) and four hybrid types (group 3, anterior-CB + posterior-PSLB-type 1; group 4, anterior-CB + posterior-PSLB-type 2; group 5, anterior-ASLB + posterior-PSLB-type 1; group 6, anterior-ASLB + posterior-PSLB-type 2) (n = 13 per group). After maxillary dentition alignment and maxillary first premolars removal in the stereolithographically-made typodont system, a $0.019{\times}0.025$-inch stainless steel wire was drawn through the right quadrant of the maxillary arch at 0.5 mm/min for 5 min. The SFF and KFF were measured with a mechanical testing machine and statistical analyses were performed. Results: Four different categories of SFF and KFF were observed among all groups (all p < 0.001). Group 1 demonstrated the highest SFF and KFF; groups 4 and 3 were second and third highest, respectively. The fourth category included groups 2, 5, and 6. Placing PSLBs on the MXPT resulted in significant SFF and KFF reductions in cases with CBs on the MXAT, but not in cases with ASLBs on the MXAT. Conclusions: These data might aid in the development of a hybrid bracket system that enables low-friction sliding of an archwire through the MXPT.