• Structural Engineering and Mechanics
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• 제67권3호
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• pp.277-281
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• 2018

The analytical solution of two functionally graded layers with Volterra type screw dislocation is investigated under anti-plane shear impact loading. The energy dissipation of FGM layers is modeled by viscous damping and the properties of the materials are assumed to change exponentially along the thickness of the layers. In this study, the rate of gradual change ofshear moduli, mass density and damping constant are assumed to be same. At first, the stress fields in the interface of the FGM layers are derived by using a single dislocation. Then, by determining a distributed dislocation density on the crack surface and by using the Fourier and Laplace integral transforms, the problem are reduce to a system ofsingular integral equations with simple Cauchy kernel. The dynamic stress intensity factors are determined by numerical Laplace inversion and the distributed dislocation technique. Finally, various examples are provided to investigate the effects of the geometrical parameters, material properties, viscous damping and cracks configuration on the dynamic fracture behavior of the interacting cracks.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.818-823
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• 2012

Assessment of the dynamics properties, like damping, dynamic stiffness and resonance sharpness is essential for the development of a robust system, specifically for the reduction of a traction motor noise. A practical method for identifying dynamic characteristics of a traction motor hosing for an electric vehicle is proposed. Assembling using interference fit of the components of the motor is attributed to the main cause of strong nonlinearity. It is well known that nonlinearity of a structure makes it difficult to assess damping properties or dynamic characteristics of the system. This research presents a practical damping or dynamic stiffness identifying procedures for a nonlinear system according to the boundary condition between assembled components. Based on the simple idea that impact forces of modal tests are highly affected on the condition of the hammer tip, Auto Power Spectrum of the impact forces are used to assess the assembling condition and dynamic characteristics of the system, especially, damping of the system.

• 열처리공학회지
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• 제24권1호
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• pp.23-30
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• 2011

This study was carried out to investigate the effect of aging treatment on the mechanical properties and damping capacity of 12Cr heat resistant steel with ferrite phase. While hardness values in ferrite phase was not changed, that in martensite phase was dramatically dropped in early stage of aging treatment and then gradually decreased with increase of aging time. As aging treatment was carried out, the precipitation was not detected in ferrite phase, while carbides were precipitated in martensite phase. With increasing the aging time, tensile strength eventually decreased while impact toughness increased rapidly in the early stage of aging and then gradually increased. Besides, it was confirmed that damping capacity was not changed in the early stage of aging and then gradually increased with increase of aging time.

• Journal of Communications and Networks
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• 제9권4호
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• pp.490-498
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• 2007

BGP route flap damping(RFD) was anecdotally considered to be a key contributor to the stability of the global Internet inter-domain routing system. However, it was recently shown that RFD can incorrectly suppress for substantially long periods of time relatively stable routes, i.e., routes that only fail occasionally. This phenomenon can be attributed to the complex interaction between BGP path exploration and how the RFD algorithm identifies route flaps. In this paper we identify a distinct characteristic of BGP path exploration following a single network event such as a link or router failure. Based on this characteristic, we distinguish BGP route updates during BGP path exploration from route flaps and propose a novel BGP route flap damping algorithm, RFD+. RFD+ has a number of attractive properties in improving Internet routing stability. In particular, it can correctly suppress persistent route flaps without affecting routes that only fail occasionally. In addition to presenting the new algorithm and analyzing its properties, we also perform simulation studies to illustrate the performance of the algorithm.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.883-886
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• 2001

The mechanical properties such as the Young's modulus, damping ratio, vibration mode and hardness of the disk materials heat-treated under various conditions are measured, and the relations between there properties and the cutting characteristics such as early tip fracture are examined. The results obtained from this study are as follows. The circular saw with the V-Cr added disk has higher young's modulus and damping ratio than the saw with STC5 disk, preventing the early fracture of tungsten carbide due to the above properties. The circular saw with the disk which is subjected to the heat treatment at the quenching temperature of $830^{\circ}C$ and at the temperature of $550^{\circ}C$ have the best tool life and surface roughness.

• Earthquakes and Structures
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• 제13권3호
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• pp.299-307
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• 2017

High Damping Rubber bearings (HDR bearings) have been used in the seismic design of bridge structures widely in China. In earthquakes, structural natural periods will be extended, seismic energy will be dissipated by this kind of bearing. Previously, cyclic loading method was used mainly for test studies on mechanical properties of HDR bearings, which cannot simulate real seismic responses. In this paper, Real-Time Substructure (RTS) test study on mechanical properties of HDR bearings was conducted and it was found that the loading rate effect was not negligible. Then the influence of peak acceleration of ground motion was studied. At last test results were compared with a numerical simulation in the OpenSees software framework with the Kikuchi model. It is found that the Kikuchi model can simulate real mechanical properties of HDR bearings in earthquakes accurately.

• 패션비즈니스
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• 제15권3호
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• pp.84-96
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• 2011

With the advancements in the computer graphics sectors, the visual quality of the virtual clothing implemented by using the 3-dimensional digital clothing software system has been much improved during the past decade. Most of the cloth simulation procedures are complicated due to the multitude of parameters involved in the simulation in order to achieve the appearance of the actual textile fabrics or the movement of the actual clothing as close as possible. Bending properties affect the tactile and visual qualities of the textile fabrics along with the shear and tensile properties. In this study, dynamic bending properties, focused on the movement of the textile fabrics including damping ratio and amplitude, were measured by using a dynamic bending test system.

• Composites Research
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• 제34권3호
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• pp.192-198
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• 2021

전기차의 수요 및 보급이 확대됨에 따라 차량 내 이음(buzz, squeak, rattle, BSR) 개선에 대한 요구가 커지고 있다. 이에 풍절음, 도어 글라스 및 차량 진동을 차단하는 인너벨트 웨더스트립(innerbelt weatherstrip)의 댐핑(damping) 특성 향상을 통해 BSR을 저감하는 기술 개발이 필수적이다. 기존 열경화성(thermoset) 탄성체 대비 가볍고 재활용이 가능한 열가소성(thermoplastic) 탄성체가 주목을 받고 있지만 낮은 소재 댐핑과 영구압축줄음률(compression set)로 인해 도어 글라스와 웨더스트립 간 마찰 소음을 발생하는 문제가 있다. 고분자 댐핑 특성은 점탄성(viscoelastic)에 좌우되므로, 본 연구에서는 인너벨트 웨더스트립과 도어 글라스 간 마찰 소음을 개선하기 위해 EPDM (ethylene-propylene-diene monomer)/PP (polypropylene) thermoplastic vulcanizates (TPV)의 재료설계인자(EPDM/PP 비율, EPDM 내 ENB 함량)에 따른 점탄성 분석을 통해 소재 댐핑 특성을 평가하였다. EPDM/PP 비율에 따른 분석을 통해 PP 비율이 낮을수록 소재가 연화되고, 탄성회복력(resilience)이 증가하여 저장탄성률(storage modulus)은 10.8% 감소하고 댐핑 특성을 의미하는 감쇠계수(tanδ)는 88.2% 증가함을 확인하였다. 또한 EPDM 내 ENB 함량이 높을수록 소재의 가교밀도(crosslink density)가 증가하지만, 동적가교(dynamic vulcanizate) 과정 중 PP에 분산된 EPDM particle의 크기가 감소한다. 이로 인해 증가된 EPDM/PP 계면 간 면적 증가로 인해 계면 미끄러짐에서 기인한 손실탄성률(loss modulus)이 24.7% 증가하여 댐핑 특성이 향상되었다. 재료설계인자에 따른 물성분석을 바탕으로 최적 소재(낮은 PP 비율(14 wt%), 높은 ENB 함량 (8.9 wt%))를 배합한 결과 소재 댐핑 특성(tanδ peak)은 기존 소재(PP27, EPDM/PP 30/27, ENB content 5.7 wt%) 대비 140% 증가하여 재료설계인자에 따라 댐핑 특성을 제어할 수 있음을 확인하였다. 설계된 소재의 글라스 마찰 소음 개선 효과를 확인하기 위해 stick-slip 시험을 통해 마찰 소음을 평가하였다. 소재 댐핑 특성이 향상됨에 따라 마찰 진동의 가속도 peak가 약 57.9% 감소하였다. 이러한 결과로부터 재료설계인자에 따른 소재 댐핑 특성 향상을 통해 인너벨트 웨더스트립의 글라스 마찰 소음을 개선할 수 있음을 확인하였으며, 향후 소재 재료설계인자에 따른 물성 제어를 통해 부품의 요구 성능에 맞는 다양한 재료설계에 활용할 수 있을 것으로 기대된다.

• 임산에너지
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• 제17권1호
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• pp.47-55
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• 1998

사용온도 및 주파수 범위를 고려할 경우 진동흡수재료로서 사용하는 폴리머는 다소 넓은 온도범위에서 높은 손실계수를 지녀야한다. IPN's은 두 개 또는 그 이상의 고분자가 상호 침투하여 망목상으로 얽혀있는 혼합계로서 강제적으로 상분리가 제한되어 어느 정도의 상용성을 부여할 수 있으므로 폭 넓은 진동흡수재료의 분자설계에 적합하다. 본 실험에서는 공중합조성이 다른 여러 가지 코폴리머를 IPN's화하여 폭 넓은 온도 범위에서 높은 손실 계수를 나타내는 고분자의 합성을 시도하였으며, 고분자의 점탄성 및 가교밀도가 적충재의 진동흡수성능에 미치는 영향을 검토하였다. 동력학적 측정의 결과 IPN's의 상용성은 IPN's화시키고자하는 폴리머의 상용성 및 가교밀도에 의존하는 경향을 나타내 공중합조성이 다른 코폴리머를 IPN's화시키거나, 가교밀도를 조절하면 폭넓은 진동흡수성능을 지니는 폴리머의 조제가 가능함을 시사하였다. IPN's을 적층한 복합체의 진동흡수계수는 폴리머의 E'가 대략 5$\times$$10^7$~109 dyne/$cm^2$의 범위에서 높은 손실계수를 지닌 경우 높아졌다. 특히, 3%의 DEGDM을 사용하여 함성한 poly(2-EHA80-co-St20)/poly(2-EHA20-co-St80) IPN's은 상온을 중심으로 넓은 범위에서 비교적 높은 댐핑성능을 나타내었다.

• 임산에너지
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• 제18권2호
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• pp.55-61
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• 1999

본 실험에서는 화학조성이 다른 일련의 에틸렌/초산비닐 공중합체의 점탄성(또는 화학조성)이 목재/고분자/목재 샌드위치 복합체의 진동·충격음 흡수성능에 미치는 영향을 검토하였다. 그 결과는 다음과 같다. 복합체의 진동·충격음 흡수성능은 고분자의 분자 운동상태에 민감하다. 즉, 복합체의 진동·충격음 흡수성능 고분자가 시험온도에 있어서 유리전이 상태일 때(대략 초산 비닐 55∼75%) 가장 크며, 고분자가 고무상태(초산비닐 47∼20%) 또는 유리상태(초산비닐 100∼87%)일 때는 작다. 또한 유리전이상태의 고분자 적층재는 약 6∼12dB의 충격음 저감효과가 있었다.