• Title, Summary, Keyword: In-plane Size Effect

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Variation of the Fracture Resistance Curve with the Change of a Size in the CT Specimen (CT시험편의 크기 변화에 따른 파괴저항곡선의 변화)

  • Seok, Chang-Seong;Kim, Su-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.12
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    • pp.2963-2971
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    • 2000
  • In order to obtain more realistic fracture resistance curve, research is currently underway to introduce new parameter and to quantify the constraint effect. The objective of this study is to investigate the relationship between the constraint effect of a size(plane size and thickness) and the fracture resistance curve. In this paper fracture toughness tests were performed with various plane size and various thickness of specimens in two materials. The test results showed that the effects of plane size in th4 J-R curve were significant and the curve was risen with an increase in plane size. However, relatively weak influence was observed form the change of the specimen thickness and size. The stress fields near the crack tip of th specimen is close to the HRR field according to increasing the plane size and Q stress appears different value according to material properties and the plane size.

Estimation on a Contact Size Effect in Fretting Fatigue Between Cylindrical Pad and Flat Specimen (실린더형 패드와 평판 시험편간 프레팅 피로의 접촉폭 크기효과에 관한 평가)

  • Kim, Jin-Kwang;Cho, Sang-Bong
    • Journal of the Korean Society for Precision Engineering
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    • v.25 no.6
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    • pp.116-125
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    • 2008
  • In general, fretting is a contact damage process due to micro-slip associated with small amplitude oscillatory movement between two surfaces in contact. Previous studies in fretting fatigue have observed a contact size effect related to contact width. The volume-averaging method of theoretically predicted contact stress fields was required to emulate experimental trends and to predict the observed contact size effects. This contact size effect is captured by the mean values of stresses and strains at the element integration points of FE model and two critical plane models (SWT, FS) in the present paper. It is shown that crack nucleation and fretting fatigue life can be predicted by the FE-based critical plane models.

Assessment of In-plane Size Effect of Nuclear Materials Based on Damage Mechanics (손상역학에 근거한 원자력 재료의 평면크기 영향 분석)

  • Chang Yoon-Suk;Lee Tae-Rin;Choi Jae-Boong;Seok Chang-Sung;Kim Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.4
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    • pp.393-401
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    • 2006
  • The influences of stress triaxiality on ductile fracture have been investigated for various specimens and structures. With respect to a transferability issue, recently, the interests on local approaches reflecting micromechanical specifics are increased again due to rapid progress of computational environments. In this paper, the applicability of the local approaches has been examined through a series of finite element analyses incorporating modified GTN and Rousselier models as well as fracture toughness tests. The ductile crack growth of nuclear carbon steels is assessed to verify the transferability among compact tension (CT) specimens with different in-plane size. At first, the basic material constants were calibrated for standard CT specimens and used to predict fracture resistance (J-R) curves of larger CT specimens. Then, the in-plane size effects were examined by comparing the numerically estimated J-R curves with the experimentally determined ones. The assessment results showed that the in-plane size effect should be considered for realistic engineering application and the damage models might be used as useful tool for ductile fracture evaluation.

Finite Element Analysis of Fatigue Crack Closure under Plane Strain State (평면변형률 상태 하에서 유한요소해석을 이용한 균열닫힘 거동 예측 및 평가)

  • Lee, Hak-Joo;Song, Ji-Ho;Kang, Jae-Youn
    • Proceedings of the KSME Conference
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    • pp.202-207
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    • 2004
  • An elastic-plastic finite element analysis of fatigue crack closure is performed for plane strain conditions. The stabilization behavior of crack opening level and the effect of mesh size on the crack opening stress are investigated. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behavior is influenced by the crack growth increment and discontinuous opening behavior is observed. A procedure to predict the most appropriate mesh size for different stress ratio is suggested. Crack opening loads predicted by the FE analysis based on the procedure suggested resulted in good agreement with experimental ones within the error of 5 %. Effect of the distance behind the crack tip on the crack opening load determined by the ASTM compliance offset method based on the load-displacement relation and by the rotational offset method based on the load-differential displacement relation is investigated. Optimal gage location and method to determine the crack opening load is suggested.

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Ohmic Contact Properties of Nonpolar GaN Grown on r-plane Sapphire Substrate with Different Miscut Angle

  • Shin, Dongsu;Park, Jinsub
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.314.1-314.1
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    • 2014
  • The properties of Ni/Au Ohmic contacts formed on nonpolar a-plane GaN grown on r-plane sapphire substrate with different tilt angles are investigated using current-voltage (I-V) measurements. To investigate the effects of pattern direction and size on Ohmic contact properties of a-plane GaN, transmission line method (TLM) patterns are formed either along c-axis and m-axis on nonpolar GaN surface with different size. I-V measurement results show that the size of TLM pattern and formation direction of electrode have an effect on the electrical properties of a-plane GaN. The large sized patterns show the relatively lower sheet resistance compared to the small sized patterns. In addition, the sheet resistance of a-plane GaN along m-axis shows lower values than that along the c-axis. Finally, the effects of miscut angle of r-sapphire substrate ($0.2^{\circ}$, 0.4oand $0.6^{\circ}$) on electrical properties of a-plane GaN will be discussed.

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A Study on the Antenna Characteristic Variation according to Ground Plane Size of Print Type Antenna (프린트형 안테나의 접지면 크기에 따른 안테나 특성 변화에 관한 연구)

  • 송면규;양규식
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.4 no.2
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    • pp.365-370
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    • 2000
  • In this dissertation, in order to analyze the ground plane size which will affect the antenna characteristic, the appropriate antenna was designed and produced in compliance with the needs that the existing antenna should be improved, and then the optimum ground plane size was calculated. It was proved it affected the radiation characteristic greatly but didn't affect the impedance characteristic nearly when ground plane size of the existing folded slot antenna was enlarged with using the copper e cut in some size. Though it require the complicate procedure by the strict design in order to calculate exactly, if it is made of the antenna of the appropriate size that the effect of ground plane can be taken no account, it can be made easily.

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Measurement of Reflection Coefficient of Sound Absorbent Material with Respect to Angle of Incidence and Its Associated Errors (입사각에 따른 흡음재의 반사 계수 측정 방법론 및 오차에 대한 고찰)

  • 이수열;김상렬;김양한
    • Journal of KSNVE
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    • v.4 no.3
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    • pp.295-305
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    • 1994
  • The reflection coefficient of a material at oblique incidence is measured in a free field. The sound pressure distributions are measured at discrete points on two measurement lines and then decomposed into plane wave components by using spatial Fourier transform. The inciedent and reflected plane wave components are obtained from a set of "decomposition equations" of which uses the plane wave propagation theory. Numerical simulations and experiments have been performed to see the effect of finite size of measurement area. To reduce this effect, a window fuction has been performed to see the effects of finite size of mesurement area. To reduce this effect, a window function has been proposed and its effect on the measurement of sound absorbing material property has been studied as well. The reflection coefficient obtained by this method is compared with those obtained from other methods; 2-microphone method in a duct and an expirical equation of which determines the characteristic impedance .rho.c and propagation constant k of a material from flow resistance information.formation.

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Fretting fatigue life prediction for Design and Maintenance of Automated Manufacturing System (생산자동화 시스템의 설계 및 정비를 위한 프레팅 피로수명 예측)

  • Kim, Jin-Kwang
    • Journal of the Korean Society of Industry Convergence
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    • v.20 no.2
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    • pp.195-204
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    • 2017
  • Predicting the failure life of automated manufacturing systems can reduce overall downtime, maintenance costs, and total plant operation costs. Therefore, there is a growing interest in fatigue failure mechanisms as the safety or service life assessment of manufacturing systems becomes an important issue. In particular, fretting fatigue is caused by repeated tangential stresses that are generated by friction during small amplitude oscillatory movements or sliding between two surfaces pressed together in intimate contact. Previous studies in fretting fatigue have observed size effects related to contact width such that a critical contact width exists where there is drastic change in the fretting fatigue life. However, most of them are the two-dimensional finite element analyses based on the plane strain assumption. The purpose of this study is to investigate the contact size effects on the three-dimensional finite element model of a finite width of a flat specimen and a cylindrical pad exposed to fretting fatigue. The contact size effects were analyzed by means of the stress and strain averages at the element integration points of three-dimensional finite element model. This study shows that the fretting fatigue life of manufacturing systems can be predicted by three-dimensional finite element analysis based on SWT critical plane model.

A Method to Detect Multiple Plane Areas by using the Iterative Randomized Hough Transform(IRHT) and the Plane Detection (평면 추출셀과 반복적 랜덤하프변환을 이용한 다중 평면영역 분할 방법)

  • Lim, Sung-Jo;Kim, Dae-Gwang;Kang, Dong-Joong
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.57 no.11
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    • pp.2086-2094
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    • 2008
  • Finding a planar surface on 3D space is very important for efficient and safe operation of a mobile robot. In this paper, we propose a method using a plane detection cell (PDC) and iterative randomized Hough transform (IRHT) for finding the planar region from a 3D range image. First, the local planar region is detected by a PDC from the target area of the range image. Each plane is then segmented by analyzing the accumulated peaks from voting the local direction and position information of the local PDC in Hough space to reduce effect of noises and outliers and improve the efficiency of the HT. When segmenting each plane region, the IRHT repeatedly decreases the size of the planar region used for voting in the Hough parameter space in order to reduce the effect of noise and solve the local maxima problem in the parameter space. In general, range images have many planes of different normal directions. Hence, we first detected the largest plane region and then the remained region is again processed. Through this procedure, we can segment all planar regions of interest in the range image.

Evaluation of Material Properties for Yonggwang Nuclear Piping Systems(II) - Safety Injection System- (영광원자력 배관소재의 재료물성치 평가 (II) -안전주입계통-)

  • 김영진;석창성;장윤석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.6
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    • pp.1451-1459
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    • 1995
  • The objective of this paper is to evaluate the material properties of SA312 TP316 and SA312 TP304 stainless steels and their associated welds manufactured for safety injection system of Yonggwang 3,4 nuclear generating stations. A total of 62 tensile tests and 46 fracture toughness tests were conducted and the effects of various parameters such as pipe size, crack plane orientation, tests were conducted and the effects of various parameters such as pipe size, crack plane orientation, test temperature, welding on material properties were discussed. Test results show that the effect of test temperature on fracture toughness was significant while the effects of pipe size and crack plane orientation on fracture toughness were negligible. Fracture toughness of the weld metal was in general higher than that of the base metal.