• Journal of Biosystems Engineering
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• 제16권3호
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• pp.263-271
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• 1991

When grains is subjected to oscillating load, the dynamic viscoelastic behavior of the material will be describe the complex modulus of the material. The complex modulus and therefore the storage modulus, the loss modulus, and the phase angle for the sample should be obtainable with a given static viscoelastic property of the material under static load. The complex relaxation moduli of the rough rice kernel were computed from the Burger's model describing creep behavior of the material which were obtained in the previous study. Also, the effects of cyclic load and moisture content of grain on the dynamic viscoelastic behavior of the samples were analized. The storage modulus of the rough rice kernel slightly increased with the frequency applied but at above the frequency of 0.1 Hz it was nearly constant with the frequency, and the loss modulus of the sample very rapidly decreased with increase in the frequency on those frequency ranges. It was shown that the storage modulus and the loss modulus of the sample increased with decrease in grain moisture content. Effect of grain moisture content on the storage modulus of the sample was highly significant than effect of the frequency applied, but effect of the frequency on the loss modulus of the sample was more significant than effect of grain moisture content.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.98-103
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• 2006

The hunting is the natural characteristics of the railway wheelset which is originated from the contact between the conical type wheel profile and rail. The critical speed of rolling-stock is called when the hunting is occurred, and it is closely connected with vehicle stability. The parameters which influence the hunting motion are like wheel profile, primary spring property and wheelset dimension, etc. The studies for these parameters are reported diversely. In this study, we aim to analyze the influence of parameters on hunting with the change of wheel profile produced by wheel wear and material property produce by aging of primary spring. For this, we made a dynamic model for wheelset and vehicle. Using these models, we analyzed the critical speed with the variations of the parameters like as wheel profile and primary spring property and we show the results.

• 한국재료학회지
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• 제4권5호
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• pp.502-509
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• 1994

dynamic strain gage와 12bit AD(analog to digital converter)를 이용한 새로운 제진특성 측정 장치를 제작하였다. 이 장치를 이용하여 일반재료와 고제진재료의 제진특성을 연구하였다. 또한 열처리 조건, 초기 진동 진폭, 그리고 내부응력의 변화에 따른 SDC(specific damping capacity)변화에 관하여 연구하였다. 일반재료와 제진재료의 비교에서, 제진재료는 진동을 가한 후 0.4초 이내에 진동 진폭이 거의 사라졌지만, 같은 시간에 일반재료의 진동 진폭은 거의 감소하지 않았다. Fe-16wt. %Cr계 합금의 제진 특성은 노냉일 때 SDC max 가 40%이상이었고, Fe-5.5wt.%Ai합금의 제진 특성은 공냉일 때 SDC max값이 30%이상이었다. 초기 진동 진폭이 증가할수록 최대 제진 특성치는 낮은 진동 진폭 영역으로 이동하였다. 제진 특성은 내부 응력이 증가할수록 급격한 감소를 보였으며, 본 연구에서 개발한 제진측정 장치는 낮은 진동 진폭의 영역에서 정확한 제진 특성 측정이 가능하였다.

• 한국항공우주학회지
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• 제48권5호
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• pp.363-372
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• 2020

고 변형률 속도에 대한 소재의 동적 압축 물성은 고속 충돌 및 고속 성형 등 동적 환경에서의 유한요소 해석의 신뢰성 향상을 위해 필수적이다. 일반적으로 고 변형률 속도에 대한 소재의 동적 압축 물성은 SHPB(Split Hopkinson Pressure Bar) 장비를 통해 획득 가능하다. 본 연구에서는 최근 무인 항공기에 확대 적용되고 있는 Woven type CFRP(Carbon Fiber Reinforced Plastic) 소재에 대한 충돌 해석에 대응하기 위해 SHPB 장비를 활용하여 해당 소재의 동적 압축 물성을 획득하였다. 또한 Pulse shaper를 활용하여, Elastic-brittle 특성을 지니는 소재에 대한 일정한 변형률 속도 확보 및 실험 데이터에 대한 신뢰도를 향상시켰다. CFRP 소재의 경우 방향 별 기계적 물성이 다른 이방성 소재이므로 두께 방향과 면내 방향 시편을 제작하여 각각 실험을 수행하였다. SHPB 실험 결과 면내 방향 시편의 경우 일정한 변형률 속도 영역에 도달하기 전, 시편의 파단이 발생하여 데이터의 재현성 및 신뢰성 확보에 어려움이 있는 반면, 두께 방향의 시편의 경우 시편 전·후면 응력일치도가 우수하여 데이터 신뢰도가 높으며, 일정한 변형률 속도 영역을 획득할 수 있다. LS-dyna를 활용한 유한요소해석을 통해, 압력봉으로부터 측정되는 데이터는 시편과 압력봉의 변형에 의해 변형률이 과도하게 예측되는 것을 확인하였다.

• Steel and Composite Structures
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• 제15권4호
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• pp.379-397
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• 2013

Conoidal shells are doubly curved stiff surfaces which are easy to cast and fabricate due to their singly ruled property. Application of laminated composites in fabrication of conoidal shells reduces gravity forces and mass induced forces compared to the isotropic constructions due to the high strength to weight ratio of the material. These light weight shells are preferred in the industry to cover large column free open spaces. To ensure design reliability under service conditions, detailed knowledge about different behavioral aspects of conoidal shell is necessary. Hence, in this paper, static bending, free and forced vibration responses of composite conoidal shells are studied. Lagrange's equation of motion is used in conjunction with Hamilton's principle to derive governing equations of the shell. A finite element code using eight noded curved quadratic isoparametric elements is developed to get the solutions. Uniformly distributed load for static bending analysis and three different load time histories for solution of forced vibration problems are considered. Eight different stacking sequences of graphite-epoxy composite and two different boundary conditions are taken up in the present study. The study shows that relative performances of different shell combinations in terms of static behaviour cannot provide an idea about how they will relatively behave under dynamic loads and also the fact that the points of occurrence of maximum static and dynamic displacement may not be same on a shell surface.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.721-724
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• 2005

With the advantages of large vibration energy dissipation of structures, the granular materials are used as vibration and acoustic treatments. In this case of vibro acoustic controls, a finite dynamic strength of the solid component (frame) is an important design factor. The dynamic stiffness of hollow cylindrical beams containing porous and granular materials as damping treatment was measured. Using the Rayleigh-Ritz method, the effects of damping materials on the dynamic characteristics of beams were investigated. The results suggested that the acoustic structure Interaction between the frame and the structure enhances the dissipation of the vibration energy significantly. The same methods were applied also to vibration control of sandwich panels. By filling the cavities of honeycomb cores using unconsolidated granular materials, its sound transmission toss was improved significantly.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.89-94
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• 2006

In this paper, the effects of the system parameters on the high cycle fatigue life based on structural dynamic analysis of a turbine blade are investigated. Conventional studies have forcused on the fatigue life of turbine blades with specific system parameters. However, each parameter has statistical deviation because of inhomogeneity of material property, tolerance, and operating conditions. Therefore a methodology that estimates the effects of system parameter on the fatigue lift deviation is demonstrated.

• 한국정밀공학회지
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• 제23권10호
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• pp.88-95
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• 2006

Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold-spray uses supersonic gas flow to carry metallic powders to the substrate. Its low process temperature can minimize thermal stress and also reduce the deformation of the substrate. Most researches on cold-spray have focused on micro scale coating, but in this study macro scale deposition was conducted. Properties of aluminum layer by cold-spray deposition such as coefficient of thermal expansion (CTE), modulus of elasticity. hardness, and electric conductivity were measured. The results showed that properties of aluminum layer by cold-spray deposition were different from properties of pure aluminum and aluminum alloy.

• Smart Structures and Systems
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• 제13권1호
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• pp.25-39
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• 2014

The axisymmetric dynamic instability of polar orthotropic sandwich annular plate combined with electrorheological (ER) fluid core layer and constraining layer are studied in this paper. And, the ER core layer and constraining layer are used to improve the stability of the annular plate system. The boundaries of instability regions for the polar orthotropic sandwich annular plate system are obtained by discrete layer annular finite element and the harmonic balance method. The rheological property of an electrorheological material, such as viscosity, plasticity, and elasticity can be controlled by applying different electric field strength. Thus, the damping characteristics of the sandwich system are more effective when the electric field is applied on the sandwich structure. Additionally, variations of the instability regions for the polar orthotropic sandwich annular plate with different applying electric field strength, thickness of ER layer and some designed parameters are investigated and discussed in this study.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.96-100
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• 2003

In the tensile loading of sheet metals made from polycrystalline aluminum alloys, a single deformation band appears inclined to the elongation axis in the early stage of plastic deformation, and symmetric double bands are observed in the later stage. This character of the localized deformation bands has been analyzed by a perturbation method. Macroscopic slip modes composed of slip planes and slip directions were assumed to describe the tensile and shear strains. Along time integration path, the value of the perturbation growth parameter was checked to find at which angle to the elongation axis the localized deformation bands are generated. It was shown that the mode of the localized deformation is related to asymmetry of material property.