Mechanical response of nickel–titanium instruments with different cross-sectional designs during shaping of simulated curved canals

Kim, H. C.,Kim, H. J.,Lee, C. J.,Kim, B. M.,Park, J. K.,Versluis, A. Blackwell Publishing Ltd 2009 International endodontic journal Vol.42 No.7

<P>Abstract</P><P>Aim </P><P>To evaluate how different cross-sectional designs affect stress distribution in nickel–titanium (NiTi) instruments during bending, torsion and simulated shaping of a curved canal.</P><P>Methodology </P><P>Four NiTi rotary instruments with different cross-sectional geometries were selected: ProFile and HeroShaper systems with a common triangle-based cross section, Mtwo with an S-shaped rectangle-based design and NRT with a modified rectangle-based design. The geometries of the selected files were scanned in a micro-CT and three-dimensional finite-element models were created for each system. Stiffness characteristics for each file system were determined in a series of bending and torsional conditions. Canal shaping was simulated by inserting models of the rotating file into a 45° curved canal model. Stress distribution in the instruments was recorded during simulated shaping. After the instruments were retracted from the canal, residual stresses and permanent bending of their tips due to plastic deformation were determined.</P><P>Results </P><P>The greatest bending and torsional stiffness occurred in the NRT file. During simulated shaping, the instruments with triangle-based cross-sectional geometry had more even stress distributions along their length and had lower stress concentrations than the instruments with rectangle-based cross sections. Higher residual stresses and plastic deformations were found in the Mtwo and NRT with rectangle-based cross-sectional geometries.</P><P>Conclusions </P><P>Nickel–titanium instruments with rectangle-based cross-sectional designs created higher stress differentials during simulated canal shaping and may encounter higher residual stress and plastic deformation than instruments with triangle-based cross sections.</P>

만곡 근관에서 삼각 혹은 장방형 단면 구조의 니켈-티타늄 파일 응력 분포에 관한 3차원 유한요소 연구

김현주,이찬주,김병민,박정길,허복,김현철 대한치과보존학회 2009 Restorative Dentistry & Endodontics Vol.34 No.1

이 연구의 목적은 3차원 유한요소 모형 분석을 이용하여 삼각 대칭형과 S형태의 단면 및 변형된 사각 형태인 장방형 단면으로 분류되는 네 종류의 니켈티타늄 파일이 만곡 근관 적용 시의 응력 분포를 비교하는 것이다. 삼각 대칭형 단면 구조의 ProFile #30 / .06과 HeroShaper #30 / .06,장방형 단면구조의 Mtwo #30 / .05와 NRT #30 / .06 파일을 마이크로컴퓨터 단층촬영을 하고 reverse engineering을 통하여 파일의 구조를 얻고 삼차원 유한요소모형을 제작하였다. 모형 근관 내에서 파일이 근관장 끝까지 진입하여 회전할 때 발생하는 von Mises 응력 분포 및 파일의 제거후의 잔류 응력의 분포양상을 ABAQUS 프로그램을 이용하여 비교하였다. 근관 내 회전 시에 발생하는 응력을 관찰하였을 때 NRT 파일에서 가장 큰 응력을 나타냈으며 , 각 파일에서의 최고 응력과 최저 응력을 비교하였을 때 Mtwo파일에서 가장 큰 차이가 나타났다. 응력의 내부 분포 경향을 보았을때 장방형 구조의 단면을 가진 Mtwo 및 NRT 파일에서 불연속적인 응력의 집중 부위가 관찰되었으며 , 근관 외부로 파일을 제거하여 탄성 회복이 일어난 후의 잔류 응력도 NRT 파일에서 가장 높게 나타났다. 이상의 결과로 유추할 때, 삼각대칭 단면 구조를 가진 파일보다 S-형태의 단면과 변형된 사각 형태의 단면 등의 장방형 단면 구조의 파일이 파절의 위험성이 더 클 것으로 사료된다. The purpose of this study was to compare the stress distributions of NiTi rotary instruments bascd on their cross-sectional geometries of triangular shape-based cross-sectional design. S-shaped cross-sectional design and modified rectangular shape-based one using 3D FE models. NiTi rotary files of S-shaped and modified rectangular design of cross-section such as Mtwo or NRT showed larger stress change while file rotation during simulated shaping. The stress of files with rectangular cross-section design such as Mtwo, NRT was distributed as an intermittent pattern along the long axis of file. On the other hand, the stress of files with triangular cross-section design was distributed continuously. When the residual stresses which could increase the risk of file fatigue fracture were analyzed after their withdrawal, the NRT and Mtwo model also presented higher residual stresses. From this result, it can be inferred that S-shaped and modified rectangular shape-based files were more susceptible to file fracture than the files having triangular shape-based one.

Experimental and FE Simulation Study on Cross-Section Distortion of Rectangular Tube under Multi-Die Constraints in Rotary Draw Bending Process

Kuanxin Liu,Yuli Liu,He Yang 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

The rotary draw bending of thin-walled rectangular tube is a complex process with multi-nonlinearity under multi-die constraints. Theconstraints of various dies on the cross-section distortion ratio are studied by experiment and the friction coefficients are obtainedby twist-compression test. It is found that the effects of bend die, mandrel die and pressure die on cross-section distortion aresignificant. The significant influencing factors include bend angle, bend radius, clamp pressure, core number and the boost velocity. A three-dimensional finite-elements model of this process is built under the ABAQUS/explicit environment based on the solution ofseveral key techniques, such as model creation, material properties definition, contact boundary condition treating, meshingtechnology, and it is validated to be credible. Furthermore, the orthogonal experimental design is used to investigate the interactiveeffects of friction on cross-section distortion ratio, and the optimal combination is obtained.

Strength and strain enhancements of concrete columns confined with FRP sheets

Campione, G.,Miraglia, N.,Papia, M. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.6

The compressive behavior up to failure of short concrete members reinforced with fiber reinforced plastic (FRP) is investigated. Rectangular cross-sections are analysed by means of a simplified elastic model, able also to explain stress-concentration. The model allows one to evaluate the equivalent uniform confining pressure in ultimate conditions referred to the effective confined cross-section and to the effective stresses in FRP along the sides of section; consequently, it makes it possible to determine ultimate strain and the related bearing capacity of the confined member corresponding to FRP failure. The effect of local reinforcements constitute by single strips applied at corners before the continuous wrapping and the effect of round corners are also considered. Analytical results are compared to experimental values available in the literature.

Dimensionless analysis of composite rectangular and circular RC columns

Ali Massumi,Alireza Badkoubeh 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.2

A numerical procedure is presented that provides ultimate curvature and moment domains for composite rectangular and circular cross-sections of reinforced concrete columns with or without an embedded steel section subjected to combined axial loading and biaxial bending. The stress resultants for the concrete and reinforcement bars are calculated using fiber analysis and the stress resultants for the encased structural steel are evaluated using an exact integration of the stress-strain curve over the area of the steel section. A dimensionless formula is proposed that can be used for any section with similar normalized geometric and mechanical parameters. The contribution of each material to the bearing capacity of a section (resistance load and moments) is calculated separately so that the influence of each geometric or mechanical parameter on the bearing capacity can be investigated separately.

BFRP 보강이 직사각형 단면 철근콘크리트 기둥의 지진거동에 미치는 영향

이혜린 ( Hyerin Lee ),조정현 ( Junghyun Cho ),이승건 ( Seung-geon Lee ),이수형 ( Su-hyung Lee ),홍기증 ( Kee-jeung Hong ) 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 논문집 Vol.24 No.6

지진동 하의 구조 시스템에서 기둥은 가장 중요한 구조 요소 중 하나이다. 이러한 관계로, 철근콘크리트(RC) 기둥의 내진 성능에 FRP 보강이 미치는 영행을 평가하기 위하여 광범위한 실험 연구가 이루어졌다. 이 중 상당수는 CFRP 또는 GFRP로 보강된 원형 단면 또는 정사각형 단면의 RC 기둥의 지진 거동에 집중하였다. 단면의 형태가 FRP 보강으로 인한 구속 효과에 영향을 미치기 때문에, 보강 효과와 최종 파괴 패턴이 형상에 따라 상이할 수 있다. 본 연구에서는 현무암 섬유를 함유한 BFRP 시트와 복합섬유 패널로 보강한 직사각형 단면을 가진 RC기둥의 지진 거동을 살펴보기 위하여 반복하중 실험을 수행하였다. 실험 결과는 보강 효과가 크지 않았음을 보여주는데, BFRP 시트와 복합섬유 패널에 의한 구속 효과의 증가가 미미했음을 의미하며, 이는 기둥 단면 형상에 일부 기인하는 것으로 판단된다. Columns are one of the most critical parts of a structural system subjected to earthquake excitations. In this regard, extensive experimental studies have been conducted to evaluate the effect of fiber reinforced polymer (FRP) wrapping on the seismic performance of reinforced concrete (RC) columns. Among them, many studies focused on the behavior of circular or square RC columns strengthened with CFRP or GFRP sheets. Since the cross-sectional shape affects confinement by FRP wrapping, its strengthening effect and final damage pattern may differ with shapes. In this study, a series of cyclic tests was conducted to investigate the seismic behavior of rectangular reinforced concrete columns strengthened with basalt-based fiber reinforced polymer (BFRP) sheets and composite fiber panels. The result shows that the effect of strengthening is not significant, and it implies a little increase of confinement by BFRP sheets and composite fiber panels, which is considered partly due to the cross-sectional shape of the columns.

Prediction of Surface Settlement with Ultra-shallow-burial and Large Rectangular Cross-section Urban Underpass

Chaoyang Heng,Song Sun,Zhi Zhou,Jiantao Zhang 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.11

Based on the actual measured surface settlement of two super-shallow buried large rectangular-section urban underpass, a settlement fitting function is established. The superposition curve used the reduction of settlement trough. By comparing the results of fitting analysis with Peck formula result, settlement characteristics and simple prediction method for super-shallow and large rectangular section urban underpass are proposed, including: 1) The settlement trough is a superposition of three normal distribution curves, with the maximum surface settlement appeared above the central line of each single passage; 2) The depth and width of the middle passage settlement trough should be uniformly reduced. The reduction coefficient is calculated based on the ratio of the middle passage width to the side passage; 3) The loss rate of the side passage is 0.7% − 1.0%, while it is 0.4% − 0.6% for the middle passage, 4) If the underpass is excavated in staggered sequence, the peck formula can be used to calculate the surface settlement. The surface settlement of a single passage is calculated firstly, and then the surface settlement of three passages is superimposed to obtain the final settlement.

Turbulence Generation by Ultrasonically Induced Gaseous Cavitation in the $CO_2$Saturated Water Flow

Lee, Seung-Youp,Park, Young-Don The Korean Society of Mechanical Engineers 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.8

Emission of ultrasonic vibration to turbulent flow promotes the turbulence generation due to the resonantly oscillating pressure field and thereby induced cavitation. In addition, ultrasonic vibration is well transmitted through water and not dissipated easily so that the micro-bubbles involved in the fluid induce the gaseous cavitation if the bubbles are resonated with the ultrasonic field. In the present study, we found through LDV measurement that the gaseous cavitation induced by ultrasonic vibration to CO$_2$saturated water flow in the rectangular cross-sectioned straight duct enhances turbulence much more than the case of non-ultrasonic or normal ultrasonic conditions without gaseous cavitation. We also found that the fluctuating velocity component induced by emitting the ultrasonic vibration in normal direction of a rectangular channel flow can be redistributed to stream-wise component by the agitation of gaseous cavitation.

신라 석축산성의 성벽통과식 배수장치

차용걸 한국성곽학회 2011 한국성곽학보 Vol.19 No.-

신라왕조의 석축 산성에서 조사된 성벽을 관통하는 배수장치에 대한 기왕의 연구를 보충하였다. 조사된 사례가 3개소에서 12개소 이상으로 증가된 고고학적 발굴조사 성과를 반영하여 형식적 구분을 다시 하였다. 성곽에서의 배수장치로서의 수문은 교량형(橋梁形)과 암거형(暗渠形), 누조(漏槽) 등으로 크게 구분된다. 이글에서는 특히 성벽 통과형 암거형식을 다루고, 그 시설된 숫자에 따라 단구식(單口式)과 다구식(多口式)을 구분하였다. 다구식은 성내의 수위 변화에 대비하여 수위(水位)에 따른 배수가 가능하게 만든 것들이다. 종래 출수구(出水口) 외면의 형태에 따라 형태를 구분하였던 점을 고쳐서 입수구와 출수구를 잇는 수로의 횡단면 형태에 따라 오각형, 사다리꼴, 사각형에 추가하여 삼각형의 유형이 있음을 새로 추가하였다. 이중 가장 보편적인 사례는 방형 단면의 것들이며, 이런 형태는 신라 하대에서 고려를 거쳐 조선시대 후기까지도 그 사례를 찾을 수 있는 반면, 나머지 형태는 신라의 5세기 후반에서 7세기에 걸쳐 다양하게 축조되었다. 이들 여러 형태 가운데 단면 사각형은 중세와 근세의 산성까지 가장 오랫동안 시설되었다. In the age of Korean Antiquity, the stone walled fortresses were constructed by characteristic manner at the strategic points around the territory of Silla Dynasty (B.C 57 ~ A.D 935). This study aims to repletion for our former reports on the wall penetrate water drainage system at stone walled fortresses constructed in Silla Dynasty by structural reclassification based on over 12 archaeological excavation cases, which is much enriched supports compared to former 3 cases. The water drainage system in the stone walled fortress can be sorted into three categories including bridge style watergate, culvert style watergate and slip hole. In particular, we have focused on the wall penetrated culvert style Watergate in this article. The wall penetrated culvert style Watergate can be divided into two types, such as one opening type and plural opening type, according to the number of constructed watergates. The plural opening styles were designed for efficient water drainage corresponding to water level within the fortress. While former reports were based on the classification according to shape of outer drainage face, we have applied new base for the classification according to cross sectional shape of channel connecting drainage inner face and outer face. In this classification, the wall penetrate water drainage system can be divided into four categories such as pentagonal cross section type (5 angled cross section type), trapezoid cross section type, rectangular cross section type and triangular cross section type. Particularly, triangular cross section type was novel finding by additional investigation. Among these types, the rectangular cross section type was most common case. This type had been utilized from Silla Dynasty to late Joseon Dynasty through Goreo Dynasty. However, other types were constructed in Silla Dynasty from late 5th century to 7th century.

합성개구레이더용 전방향 반사기의 설계

장지성 ( Ge Ba Chang ),양찬수 ( Chan Su Yang ),오이석 ( Yi Sok Oh ) 大韓遠隔探査學會 2007 大韓遠隔探査學會誌 Vol.23 No.6

본 연구에서는 합성개구레이더(synthetic aperture radar, SAR) 영상의 보정에 사용되고 있는 반사기(corner reflector, CR)를 이용하여 목표물의 식별과 인식을 위한 기초적인 연구를 실시하였다. 사각형 삼면 전파반사기를 기반으로 전방향(omni-directional) 반사기를 제작하였다. 여기서는 한 변의 길이가 15cm인 4-배열 사각형 삼면 전파반사기를 사용하여 C-밴드(주파수: 5.3 GHz) 의 편파별(VV, HH, VH, HV) RCS(radar cross section)특성을 해석하였다. 전파반사기는 대칭형이므로 방위각 180도 범위에 대해서 레이더 산란단면적 패턴을 측정하였다. VV편파의 경우 방위각에 따른 RCS값의 차이가 8dB정도로 다른 편파보다 전방향 특성이 더 좋은 것으로 확인되었고 방위각이 0˚(단면과 동일 방향)와 45˚(이웃하는 단면들의 중앙) 일 때, 가장 높은 RCS값을 보였다. 또한, 실험에서 얻어진 RCS값을 수치 해석 시뮬레이션과 이론적 계산과 비교를 실시한 결과, 서로 잘 일치하는 것으로 나왔다. Basic research is conducted to identify a target using corner reflectors which are commonly used in calibration of synthetic aperture radar (SAR) systems. At first, an omni-directional reflector is fabricated by combining four 15-cm rectangular trihedral corner reflectors. Then, its radar cross section (RCS) characteristics are measured at C-band (5.3 GHz) for vv-, hh-, hv-, and vh-polarizations at a range of horizontal angle, -90˚≤Φ≤90˚. The measured RCS angular variation of the omni-directional reflector is much smaller for vv-polarization than other polarizations, and the difference between the maximum and minimum RCSs for vv-polarization is about 8 dB. Peak RCS values are shown at 0˚ (normal to plates) and 45˚ (direction of bore sight). It is shown that the measurements agree quite well with numerical simulation and theoretical computation results.