• 대한기계학회논문집A
• /
• 제40권5호
• /
• pp.513-523
• /
• 2016

단순보와 외팔보의 U-노치 및 균열에 대한 응력집중계수 및 응력확대계수를 유한요소법 및 광탄성실험에 의해 해석하였다. 해석결과를 사용하여 응력집중계수 및 응력확대계수의 추정 그래프를 얻었다. 노치의 응력집중계수해석을 위하여 무차원 노치 길이 H(시편의 높이)/h=1.1~2, 무차원 틈 간격 r(노치선단의 반경)/h=0.1~0.5로 하였다. 여기서 h=H-c, c=노치길이이다. 해석결과 틈 길이가 증가할수록 그리고 틈 간격이 좁아질수록 응력집중계수는 증가 한다. 응력집중계수는 단순보가 외팔보다 더 크게 나타나나, 실제 일정한 하중과 노치길이 및 틈 간격 하에서 최대 응력값은 단순보보다 외팔보에서 크게 발생함을 알 수 있었다. 균열해석을 위하여 무차원 균열길이 a(균열길이)/H=0.2~0.5로 하였다. 균열의 길이가 증가 할수록 무차원 응력확대계수는 증가한다. 일정한 하중과 일정한 균열길이하에 응력확대계수값은 단순보 보다 외팔보에서 크게 발생함을 알 수 있었다.

• Structural Engineering and Mechanics
• /
• 제75권5호
• /
• pp.559-569
• /
• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.

• Journal of Advanced Marine Engineering and Technology
• /
• 제31권7호
• /
• pp.857-862
• /
• 2007

A novel compact ultra wideband(UWB) antenna for UWB application is proposed in this paper. The proposed antenna with $22mm{\times}26mm{\times}1.6mm$ covers the entire UWB bandwidth and has band notch characteristic for the frequency band of $5.15{\sim}5.825GHz$ limited by WLAN. The antenna has a concaved ground plane and staircase shape patch to achieve the wide bandwidth, and has an U shape slot with $\lambda/4$ length to notch the band. The return loss and group delay of the proposed antenna are measured.

• 한국생산제조학회지
• /
• 제7권5호
• /
• pp.120-126
• /
• 1998

Second step shot peening was applied on both smooth specimen and U-notch specimen in order to investigate the stress distribution and the improvement in fatigue strength. Various experiments and measurements such as rotary bending fatigue test and the measurement of compressive residual stress were performed. The results showed that the fatigue strength of second step shot peened specimens increased by 34 percent compared to that of unpeened ones. Compressive residual stress also considerably increased, which resulted in the increase of fatigue strength. finite element analysis showed that shot peening is effective in decreasing the bending stress by external force. The effectiveness of shot peening in reducing the compressive residual stress was anticipated by the superposition of the concentrated stress and the compressive residual stress.

• 한국전자파학회논문지
• /
• 제16권2호
• /
• pp.199-203
• /
• 2005

본 논문에서는 Ultra-Wideband(UWB)통신을 위한 새로운 소형 주파수 대역 저지 안테나를 설계 및 제작한다. 설계된 안테나는 초광대역 특성을 만족하면서, IEEE 802.11a와 HIPERLAN/2에 의해 사용이 제한된 $5.15\~5.825\;GHz$에서 주파수 대역 저지 특성을 갖는다. 안테나의 광대역 특성을 얻기 위해서 요철 모양의 접지면을 구현하였고, 또한 제한된 주파수 대역에서 저지 특성을 갖기 위해 U모양의 얇은 슬랏을 사각형 복사 패치 위에 구현 하였다. 제작된 안테나는 저지 대역인 $4.92\~5.866\;GHz$을 제외하고 $2.95\~11.7\;GHz$ 대역에서 정재파비 2 이하를 만족하는 광대역 특성을 나타낸다.

• Structural Engineering and Mechanics
• /
• 제74권5호
• /
• pp.601-609
• /
• 2020

In this article, the Strain Energy Density (SED) averaged over a well-defined control volume at a notch edge was applied in combination with the Equivalent Material Concept (EMC) to assess the fracture behaviors of some keyhole-notched specimens made of a High-Density Polyethylene (HDPE-PE80) material under mixed-mode loading conditions. An experimental program was performed and 54 new experimental data were totally provided. Additionally, different loading mode ratios were regarded by changing the inclination angles of the notches with respect to the applied load directions. The results obtained from the determined criteria were in good agreement with those of the experimental data.

• 한국생산제조학회지
• /
• 제25권1호
• /
• pp.89-95
• /
• 2016

This study investigated the design factors of the opening area in order to consider the kinematic stability of a valve plate, conducting an analysis of the reduction effects of pressure pulsation and flow ripple depending on the design factors, using the $SimulationX^{(R)}$ (Germany) hydraulic analysis program. Further, we performed a structure analysis to confirm the kinematic stability of the valve plate in a swash plate type piston pump, and analyzed the effects of pulsation on a 1-step V-type notch, 2-step V-type notch, and 2-step U-type notch to determine the effects of pulsation reduction. Finally, we show the effectiveness of our proposed design of the pre-compression sections on a valve plate in terms of low pulsation by using the hydraulic analysis program, $SimulationX^{(R)}$.

• 수산해양기술연구
• /
• 제30권1호
• /
• pp.45-52
• /
• 1994

The study was conducted to evaluate reliability of the longitudinal tensile properties of unidirectional carbon fiber reinforced composites. Two kinds of carbon fiber reinforced composites laminates were tested in order to examine the factors of variability and have the information concerning reliability improvement. Temperature dependence of the strength and its variability were investigated by means of testing at two kinds of temperatures. Statistical distributions of the respective mechanical properties were obtained from the tensile tests. As a result, strength of composites was directly proportional to the ultimate strain and was not proportional to the elastic modulus. The fracture behavior in bending of notched plate was studied for a composite material. The uniform bending tests of notched plates have been carried out for a wide range of notch radii. The experiment shows that the nominal stress at failure decreased with decreasing notch radius and it approaches a constant value when the notch radius is less than about 0.3mm. The critical maximum stress is governed by notch root radius alone in the case of a constant thickness of specimen.

• Journal of electromagnetic engineering and science
• /
• 제16권1호
• /
• pp.35-43
• /
• 2016

A compact ultra-wide band antenna with a quadruple band-notched characteristic is proposed. The proposed antenna consists of a slotted trapezoid patch radiator, an inverted U-shaped band stop filter, a pair of C-shaped band stop filters, and a rectangular ground plane. To realize the quadruple notch-band characteristic, a U-shaped slot, a complementary split ring resonator, an inverted U-shaped band stop filter, and two C-shaped band stop filters are utilized in this antenna. The antenna satisfies the -10 dB reflection coefficient bandwidth requirement in the frequency band of 2.88-12.67 GHz, with a band-rejection characteristic in the WiMAX (3.43-3.85 GHz), WLAN (5.26-6.01 GHz), X-band satellite communication (7.05-7.68 GHz), and ITU 8 GHz (8.08-8.87 GHz) signal bands. In addition, the proposed antenna has a compact volume of $30mm{\times}33.5mm{\times}0.8mm$ while maintaining omnidirectional patterns in the H-plane. The experimental and simulated results of the proposed antenna are shown to be in good agreement.

• 융합신호처리학회논문지
• /
• 제9권2호
• /
• pp.141-145
• /
• 2008

길이가 서로 다른 평행선로에 전류가 흐르는 경우, 커먼모드 전류(Common mode current)에 의한 전자파의 방사가 일어난다. 이러한 방사 원리를 이용하여 경량, 소형의 길이가 다른 2소자 선형 안테나가 제안되어 있다. 그러나 이 안테나의 경우 선으로 결합된 구조를 가지기 때문에 제작에 있어서 많은 제약이 따른다. 본 논문에서는 선형 안테나의 단점을 개선하고, 제작과 설계가 용이한 평면 기판에 길이가 다른 2소자 평면 안테나를 설계하고, 광대역(UWB: Ultra Wide Band)의 특성을 가지는 안테나를 설계하였다. 그리고 안테나 소자에 삼각형 패치 S, 노치, 테이퍼를 설계함으로서 방사특성은 다이 폴 안테나와 비슷하나 보다 넓은 대역에서 동작하는 안테나를 제작 할 수 있었다. 그 결과 비대역($VSWR{\le}2$)이 약 58%가 되었다.