A Modification of Combined Kinematic/Isotropic Hardening Behavior at Elevated Temperatures for Magnesium Alloy Sheet and Application of V-Bending Spring-back Prediction

누엔늑뚜안(Nguyen Duc-Toan),박진기(Park Jin-Gee),김영석(Kim Young-Suk) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

Magnesium alloys usually exhibit low ductility at the room temperature due to the unusual mechanical behaviour of its hexagonal close-packed structure. Thus, press forming of magnesium alloy sheets is performed at elevated temperatures of 200℃ to 250℃. Therefore, in this paper a modification of combined kinematic/isotropic hardening model considering the unusual plastic behaviour for magnesium alloy sheet at elevated temperature following Johnson-Cook model was carried out via a user-material subroutine, using explicit finite element code. The simulation results at room temperature was presented and compared with measurements of tension/compression, compression/tension, and validated by bending/unbending simulation for the proposed hardening model. Tension/compression and compression/tension curves at elevated temperature have been predicted. As a case study, the V-bending process for magnesium alloy sheets at elevated temperatures was performed in order to verify spring-back and then compared with spring-back predictions of FE simulation results. The proposed hardening model showed the good agreement between simulation results and corresponding experiments.

Effect of Superficial Back Line Stretching on Range of Motion and Neck Disability Index in Tension-Type Headache

김민아,안호정,김용연,최정현 국제물리치료연구학회 2023 Journal of International Academy of Physical Ther Vol.14 No.4

Background: Most non-pharmacological interventions for tension-type headache (TTH) focus on direct intervention in areas associated with headaches, with limited research exploring the indirect effects of interventions utilizing the fascia. Objectives: To investigate the effects of superficial back line (SBL) stretching and head-neck massage interventions on the range of motion (ROM) and neck disability index (NDI) of TTH. Design: Randomized controlled trial. Methods: The study participants were randomly allocated into three groups: SBL stretching group (n=9), head-neck massage group (n=9), and combined group (n=9). Prior to the intervention, measurements were taken for neck flexion ROM, straight leg raising test (SLRT) ROM, and NDI. The intervention consisted of 30-minute sessions conducted twice a week for 8 weeks. The second measurement took place 4 weeks after the intervention, followed by a third measurement conducted after an additional 4 weeks of intervention. Results: Comparing neck flexion ROM within each group, a significant increase was observed in the SBL stretching group after 8 weeks compared to before the intervention (P<.05). Regarding the comparison of SLRT ROM within each group, a significant increase was noted after 8 weeks compared to before the intervention in the SBL stretching, head-neck massage, and combined groups (P<.05). In terms of the comparison of NDI within each group, a significant decrease was observed in all three group after the intervention compared to before the intervention (P<.05). Conclusion: 8-week intervention involving SBL stretching, head-neck massage, and their combined application demonstrated effectiveness in improving neck flexion ROM, SLRT ROM, and the NDI for individuals with TTH.

압하력, 장력에 따른 조질 압연에서의 소재 변형률 예측에 관한 연구

정종현(Jong Hyeon Jeong),고성현(Seong Hyun Ko),김미정(Mi-Jeong Kim),황운봉(Woon Bong Hwang),박현철(Hyun Chul Park) 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.4

조질 압연은 소재의 잔류 응력 및 표면 평탄도 등의 제품 문제를 해결하기 위한 하나의 중요한 공정이다. 유한요소 해석을 기반으로 하는 기존의 연구들은 하나의 스탠드에서의 압연 상황만을 고려하였으며, 소재에 작용하는 장력에 의한 영향에 관하여 수행되지 않았다. 이에 본 연구에서는 2D 유한요소 모델을 통하여 압하력과 장력이 소재 압하에 어떠한 영향을 미치는지에 관한 분석을 수행하였으며, 임의의 해석 조건을 통하여 분석 결과를 검증하였다. 또한 3D 해석 모델을 통하여 소재 폭 방향에 대하여 압연 시 소재가 어떻게 변형하는지에 관한 분석을 수행하였다. Skin pass rolling is an important process to resolve product problems such as strip wave or residual stress. Previous research based on finite element method (FEM) has only considered one stand without the effects of back tension. In this study, the relationships between roll force, back tension, and strain of the workpiece are proposed, and they are verified using randomly selected FEM conditions based on a 2D FEM model composed of two stands and a tension reel. Simulation based on a 3D FEM model is also performed to account for the width directional strain, and the reliability is verified by comparing these results to those of the 2D model.

양궁 백 텐션 국면에서 최우수 양궁선수의 동작특성 평가

이재훈 ( Jae Hun Yi ),하종규 ( Chong Ku Hah ),류지선 ( Ji Seon Ryu ),김기찬 ( Ki Chan Kim ) 한국운동역학회 2007 한국운동역학회지 Vol.17 No.3

역해석기법을 이용한 행어케이블의 장력 추정

김남식,박동욱,박용명,정진환 한국지진공학회 2007 한국지진공학회논문집 Vol.11 No.3

현수교 행어케이블의 장력은 현수교의 상태점검에 있어 중요한 요소이다. 현재 케이블의 장력 추정에는 여러 이론식에 의한 간접적인 방법들이 사용되고 있으며, 케이블의 가속도신호로부터 고유진동수를 측정한 후 고유진동수와 장력과의 관계로부터 케이블의 장력을 추정하는 진동법이 대표적이다. 하지만 운동방정식을 기반으로 하는 진동법은 휨강성의 영향이 큰 짧은 케이블의 장력추정에는 적합하지 않다. 본 논문에서는 10m 미만의 짧은 케이블에 대해서도 전기 가능한 새로운 장력 추정 방법으로 단변분탐색법과, 최적화 기법을 이용한 역해석 기법을 제시하였다. 이론에 대한 검증을 위해 국내에 사용 중인 광안대교 행어케이블을 대상으로, 역해석과 진동법에 의한 추정장력들과 설계장력을 상호 비교하였고, 이를 통해 역해석기법이 길이에 상관없이 장력추정에 유용하다는 결론을 얻었다. In general, the tension forces of hanger cable in suspension bridges play an important role in evaluating the bridge conditions. The vibration method, as a conventional one, has been widely applied to estimate the tension forces by using the measured frequencies on hanger cables. However, the vibration method is not applicable to short hanger cables because the fiequencies of short cables are severely sensitive to flexural rigidity. Thus, in this study, the tension forces of short hanger cables, of which the length is shorter than 10 meters, were estimated through back analysis of the cable fiequencies measured from Gwang-An suspension bridge in Korea. Direct approach to back analysis is adopted using the univariate method among the direct search methods as an optimization technique. The univariate method is able to search the optimal tension forces without regard to the initial ones and has a rapid convergence rate. To verify the feasibility of back analysis, the results from back analysis and vibration method are compared with the design tension forces. From the comparison, it can be inferred that back analysis results are more reasonable agreement with the design tension forces of short hanger cable. Therefore, it is concluded that back analysis applied in this study is an appropriate tool for estimating tension forces of short hanger cables.

현수교 행어케이블의 장력 추정을 위한 직접탐색법 기반의 역해석 기법의 적용

김진수,박재봉,박광림,박동욱,김성완 한국구조물진단유지관리공학회 2023 한국구조물진단유지관리공학회 논문집 Vol.27 No.5

행어케이블의 장력은 현수교의 건전성과 안전성을 확인할 수 있는 주요 응답 중 하나이다. 일반적으로 공용 중인 현수교에서 행어케이블의 장력을 추정하기 위해 진동법이 주로 사용되고 있다. 진동법은 행어케이블에서 고유진동수들을 측정하고 행어케이블의 형상 조건을이용하여 간접적으로 장력을 추정하는 방법이다. 이 연구에서는 영상계측시스템을 이용하여 팔영대교의 행어케이블에 대하여 장력을 추정하였다. 영상계측시스템은 측정의 편의성과 경제성을 고려하여 디지털 캠코더와 삼각대를 사용하였다. 영상계측시스템을 이용하여 측정된 행어케이블의 응답은 변위 기반이므로 진동법을 적용하기 위한 고차모드의 고유진동수는 측정하기 어려울 수 있다. 이 연구에서는 저차모드의 고유진동수를 이용하여 장력을 추정할 수 있는 역해석 기법을 적용하였다. 역해석 기법은 현장에서 측정된 행어케이블의 고유진동수들과 유한요소해석을 이용하여 산정된 고유진동수들의 오차를 목적함수로 정의하여 최적화를 수행하였다. 최적화 방법은 목적함수의 편미분이 필요 없는 직접탐색법을 적용하였다. 역해석 기법을 이용하여 산정된 장력과 진동법을 이용하여 추정된 장력을 비교 분석하여 역해석 기법에 대한 신뢰도와정확도를 확인하였다. 그 결과 역해석 기법을 적용하면 저차모드의 고유진동수를 이용하여도 신뢰성 있는 장력의 추정이 가능하였다. Hanger cable tension is a major response that can determine the integrity and safety of suspension bridges. In general, the vibration method is used to estimate hanger cable tension on operational suspension bridges. It measures natural frequencies from hanger cables and indirectly estimates tension using the geometry conditions of the hanger cables. This study estimated the hanger cable tension of the Palyeong Bridge using a vision-based system. The vision-based system used digital camcorders and tripods considering the convenience and economic efficiency of measurement. Measuring the natural frequencies for high-order modes required for the vibration method is difficult because the hanger cable response measured using the vision-based system is displacement-based. Therefore, this study proposed a back analysis technique for estimating tension using the natural frequencies of low-order modes. Optimization for the back analysis technique was performed by defining the difference between the natural frequencies of hanger cables measured in the field and those calculated using finite element analysis as the objective function. The direct search method that does not require the partial derivatives of the objective function was applied as the optimization method. The reliability and accuracy of the back analysis technique were verified by comparing the tension calculated using the method with that estimated using the vibration method. Tension was accurately estimated using the natural frequencies of low-order modes by applying the back analysis technique.

등경락마사지가 CLBP(Chronic Low back pain) 중년여성의 근 긴장도 및 체열변화에 미치는 영향

윤신중 ( Shin Jung Yun ),신명희 ( Myung Hee Shin ) 한국미용학회 2012 한국미용학회지 Vol.18 No.4

This research was performed to explore the muscle tension and body heat change before and after the back meridian massage treatment, which operated 60 minutes session, 3 times a week for 6 weeks. The objects were middle-aged women who complain of chronic low back pain. The results were as followed: For the RMS recordings, in MG, samchosu (p<.05) and daejangsu (p<.01) were significantly decreased after performing the back meridian massage. For the body heat differences, in MG, samchosu (p<.05) and daejangsu (p<.01) were significantly decreased after performing the back meridian massage. There was no significant difference found before and after the treatment in control group. Therefore, back meridian massage treatment can be the useful way to blood circulation.

중량 앵커리지 블록과 연결된 조립 스테이 케이블의 장력 추정

정운(Jeong, Woon),김남식(Kim, Nam-Sik) 한국소음진동공학회 2005 한국소음진동공학회 논문집 Vol.15 No.3

In this paper, the tension of assembly stay cable connected with massive anchorage block was calculated through back analysis of in-situ frequencies measured from a stadium structure. Direct approach to back analysis is adopted using the univariate method among the direct search methods as an optimization technique. The univariate method can search the optimal tension without regard to the initial ones and has a rapid convergence rate. To verify the reliability of back analysis, Tension formulas proposed by Zui et al. and Shimada were used. Tensions estimated by three methods are compared with the design tension, and are in a reasonable agreement with an error of more or less than 15%. Therefore, it is shown that back analysis applied in this paper is appropriate for estimation of cable tension force.

영상신호를 이용한 현수교 행어케이블의 장력 추정

김성완,윤다운,박시현,공민준,박재봉 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 논문집 Vol.24 No.3

In suspension bridges, hanger cables are the main load-supporting members. The tension of the hanger cables of a suspension bridge is a very important parameter for assessing the integrity and safety of the bridge. In general, indirect methods are used to measure the tension of the hanger cables of a suspension bridge in traffic use. A representative indirect method is the vibration method, which extracts modal frequencies from the cables’ responses and then measures the cable tension using the cables’ geometric conditions and the modal frequencies. In this study, the image processing technique is applied to facilitate the estimation of the dynamic responses of the cables using the image signal, for which a portable digital camcorder was used due to its convenience and cost-efficiency. Ambient vibration tests were conducted on a suspension bridge in traffic use to verify the validity of the back analysis method, which can estimate the tension of remote hanger cables using the modal frequencies as a parameter. In addition, the tension estimated through back analysis method, which was conducted to minimize the difference between the modal frequencies calculated using finite element analysis of the hanger cables and the measured modal frequencies, was compared with that measured using the vibration method. 최근 재료 및 시공 기술의 지속적인 발전으로 인하여 장대교량의 건설이 증가하고 있다. 특히 케이블을 이용한 장대교량에서는 시공 중, 그리고 공용상태에서 케이블의 장력을 측정하여 교량의 안전성을 지속적으로 감시하는 것이 중요하다. 케이블 장력을 측정하기 위한 다양한 방법이 있으며, 그중에서도 케이블의 형상조건과 고유진동수를 이용하여 장력을 산정하는 진동법은 로드셀 등을 이용하여 케이블의 응력을 측정하는 직접법에 비해 경제적이며 편리하므로 현재 널리 활용되고 있다. 본 연구에서는 영상신호를 이용하여 케이블의 응답을 측정하기 위해 영상처리기법을 적용하였으며 사용의 편의성과 경제성을 고려하여 상업용 디지털 캠코더를 사용하였다. 모드별 고유진동수들을 변수로 하여 원거리에 위치한 행어케이블의 장력을 추정할 수 있는 역해석 방법의 타당성을 검증하기 위하여 공용중인 현수교에서 상시진동실험을 수행하였다. 그리고 각 행어케이블의 해석모델을 통해서 계산된 모드별 고유진동수와 계측된 모드별 고유진동수의 차이를 이용하여 역해석하여 추정된 장력을 진동법에 의해 산정된 장력과 비교하였다.

롤 포밍 공정에서의 롤 패스의 수에 따른 스프링 백 영향 연구

김동홍(Dong-Hong Kim),장애(Ya Zhang),정동원(Dong-Won Jung) 한국기계가공학회 2016 한국기계가공학회지 Vol.15 No.1

This study was analyed V-bending in order to analyze the spring-back phenomenon in the roll forming process. The material of forming sheet used in the roll forming process is high tension steel and the product name of sheet material is POSTEN 60. The most important variable is the number of roll passes (3-Pass, 4-Pass, 5-Pass, 6-Pass and 10-Pass) and other roll forming process variables were fixed. To determine the characteristics of the tension and compression, the forming sheet was analyzed by dividing the layer (Upper and Bottom) in the thickness direction from the center line. The results of FEM simulation analysis was derived to von-mises stress equivalent strain, and the spring-back value was calculated according to the final forming shape. The more number of the roll pass, von-mises stress and equivalent strain value of forming sheet were lowed. Also, spring-back values tended to decrease. The results of this study can be utilized for prediction and trend of spring-back value in the roll forming process applied to high tension steel sheet. So, development time and cost of the roll forming process is expected to be reduced.