• Journal of Biosystems Engineering
• /
• 제41권3호
• /
• pp.221-231
• /
• 2016

Purpose: The objective of this study was to develop cushion curves models and analyze the cushioning performance of multi-layered corrugated structures (MLCS) using a method based on dynamic stress-energy relationship. Methods: Cushion tests were performed for developing cushion curve models under 12 combinations of test conditions: three different combinations of drop height, material thickness, and static stress for each of four levels of energy densities between 15 and $60kJ/m^3$. Results: Dynamic stress and energy density for MLCS followed an exponential relationship. Cushion curve models were developed as a function of drop height, material thickness, and static stress for different paperboards and flute types. Generally, the differences between the shock pulse (transmitted peak acceleration) and cushion curve (position and width of belly portion) for the first drop and the averaged second to fifth drop were greater than those for polymer-based cushioning materials. Accordingly, the loss of cushioning performance of MLCS was estimated to be greater than that of polymer-based cushioning materials with the increasing number of drops. The position of the belly of the cushion curve of MLCS tends to shift upward to the left with increasing drop height, and the belly portion became narrower. However, depending on material thickness, under identical conditions, the cushion curve of MLCS showed an opposite tendency. Conclusions: The results of this study can be useful for environment-friendly and optimal packaging design as shock and vibrations are the key factors in cushioning packaging design.

• 한국산학기술학회논문지
• /
• 제12권9호
• /
• pp.4199-4204
• /
• 2011

아스팔트 혼합물의 동탄성계수는 포장체의 내구성 및 공용성을 평가하는데 매우 중요한 지표이다. 최근 미국의 AASHTO 2002 설계법 및 한국형 포장설계법에서도 아스팔트 포장체의 가장 중요한 물성중 하나를 동탄성계수로 정의하였고, 이를 아스팔트 포장의 설계 및 해석에 적극 이용하고 있다. 동탄성계수를 설계에 이용하기 위해서는 마스터곡선을 작성하여야 한다. 마스터곡선은 각각의 아스팔트 혼합물을 이용하여 평가된 동탄성계수 값을 이용하여 결정한다. 마스터곡선을 결정하는 방법은 표준화되어 있으나, 저온영역(-10도)에서는 시험장비 계측장비의 결로로 인한 측정오차 및 고온영역(55도)에서는 아스팔트 바인더의 유체화 및 실험기기 세팅상의 문제들이 발생하여 측정 결과값에 큰 영향을 준다. 따라서, 이러한 온도대역의 자료를 제외한, 5도, 21도 및 40도에서 측정된 결과값을 이용하여 마스터곡선을 작성 및 분석하였고, 이를 기존의 표준방법으로 결정한 마스터곡선과 비교하였다. 본 연구에서 제안된 방법을 이용하여 결정된 마스터곡선은 고온영역에서 차이가 있기는 하지만, 충분히 사용가능한 것으로 판단되었다.

• 한국자동차공학회논문집
• /
• 제12권1호
• /
• pp.106-113
• /
• 2004

Most of mechanical structures are composed of many substructures connected to one another by various types of mechanical joints. In automotive engineering, it is important to study these connected structures under various dynamic forces for the evaluations of fatigue life and stress concentration exactly. In this study, the dynamic response of vehicle structure to external forces is classified an inverse problem involving strains from the experiment and the analysis. The practical dynamic forces are determined by the combination of the analytical and experimental method with analyzed strain by quasi-static finite element analysis under unit force and with measured strain by a strain gage under driving load, respectively. In a stressed body, inter-molecular chemical bonds are failed beyond the certain magnitude. The failure of molecular structure in material is considered as a time process of which rate is determined by mechanical stress. That is, the failure of inter-molecular chemical bonds is the fatigue lift of material. This kinetic concept is expressed as lethargy coefficient. And S-N curve is obtained with the lethargy coefficient from quasi-static tensile test. Equivalent practical dynamic force is obtained from the identification of practical dynamic force for one loading point. Using the practical dynamic force and S-N curve, fatigue life of a window pillar is analyzed with FEM under the identified force by the procedure of above mentioned.

• Geomechanics and Engineering
• /
• 제32권4호
• /
• pp.411-426
• /
• 2023

Soft clay is widely distributed in the southeast coastal areas of China. Many large underground structures, such as subway stations and underground pipe corridors, are shallow buried in the soft clay foundation, so the dynamic characteristics of the soft clay must be considered to the seismic design of underground structures. In this paper, the dynamic characteristics of saturated soft clay in Shanghai under the bidirectional excitation for earthquake loading are studied by dynamic triaxial tests, comparing the backbone curve and hysteretic curve of the saturated soft clay under different confining pressures with those under different vibration frequencies. Considering the coupling effects of the confining pressure and the vibration frequency, a fitting model of the maximum dynamic shear modulus was proposed by the multiple linear regression method. The M-D model was used to fit the variations of the dynamic shear modulus ratio with the shear strain. Based on the Chen model and the Park model, the effects of the consolidation confining pressure and the vibration frequency on the damping ratio were studied. The results can provide a reference to the earthquake prevention and disaster reduction in soft clay area.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1997년도 춘계학술대회 논문집
• /
• pp.85-90
• /
• 1997

In the stroke sensitive shock absorber, the oil path is formed along the internal cylinder surface to make the eli flow during piston's upper-lower reciprocation movement. With constraint to the conventional shock absorbers which show one dynamic characteristic curve, stroke sensitive shock absorber shows two kins of dynamic characteristic according to the stroke, In the study, analysis on the damping force generation process and dynamic behaviour characteristics of stroke sensitive shock absorber is performed, the valve characteristics being considered more precise information about design and damping performance analysis.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1997년도 추계학술대회 논문집
• /
• pp.790-794
• /
• 1997

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as seismic loading are required to provide appropriate safety assessment to those mechanical structures. The Split Hopkinson Pressure Bar(SHPB) technique with a special experimental behavior under high strain rate loading condition In this paper, dynamic deformation behaviors of A15052-H32 under high strain rate tensile loading are determined using the SHPB technique.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 1998년도 창립기념 춘계학술대회 논문집
• /
• pp.502-509
• /
• 1998

The scheme to reduce jerking phenomena in one push-pull type trainset was proposed. To simulate the jerking between coaches, dynamic analysis model was made. This model could analyze longitudinal dynamic behavior between locomotives and coaches caused by spring and damping characteristics of couplers and center pivots; characteristic curves of traction and braking. To validate the analysis results, tests were conducted in the same driving and braking condition. Comparison of longitudinal acceleration between simulation and test results shows a good agreement. To minimize the jerking phenomena, lots of dynamic simulations were conducted with varying driving/braking effort curve. From the results of simulations, an efficient and economic way to reduce jerking phenomena was found to be to reduce slope of tractive effort curve and synchronize braking time between locomotives and coaches. Test results show that this way could reduce the jerking Phenomena. To express jerkins Phenomena quantitatively, maximum peak to peak values of acceleration were used.

• 한국기계가공학회지
• /
• 제20권2호
• /
• pp.72-79
• /
• 2021

The present paper aims to set forth a two-dimensional theory for the dynamics of plates that is valid over a large range of excitation. To construct a dynamic plate theory within the long-wavelength approximation, two dimensional-reduction procedures must be used for analyzing the low- and high-frequency behaviors under the dynamic variational-asymptotic method. Moreover, a separate and logically independent step for the short-wavelength regime is introduced into the present approach to avoid violation of the positive definiteness of the derived energy functional and to facilitate qualitative description of the three-dimensional dispersion curve in the short-wavelength regime. Two examples are presented to demonstrate the capabilities and accuracy of all of the formulas derived herein by using various dispersion curves through comparison with the three-dimensional finite element method.

• 한국정밀공학회지
• /
• 제14권11호
• /
• pp.11-16
• /
• 1997

In the stroke sensitive shock absorber, the oil path is formed along the internal cylinder surface to make the oil flow during the piston's upper-lower reciprocation movement. In constrast with the conventional shock absorbesr which show one dynamic characteristic curve, stroke sensitive shock absorber shows two kinds of dynamic characteristics according to the stroke. In this study, in order to obtain more precise information about design and damping performance analysis, the analysis on the damping force generation process and dynamic behaviour characteristics of stroke sensitive shock absorber are performed by considering the valve characteristics.

• 한국지반환경공학회 논문집
• /
• 제24권10호
• /
• pp.51-58
• /
• 2023

지진 시 상부구조물을 지지하는 무리말뚝의 동적거동은 상부구조물의 관성력과 지반의 운동력에 의해 서로 다른 복잡한 동적 메커니즘에 영향을 받는다. 지진 시 상부구조물의 관성력과 지반의 운동력에 의한 지반, 말뚝기초, 상부구조물의 상호작용을 고려하여 말뚝기초의 동적거동을 분석하는 방법으로 동적 p-y 곡선이 사용되고 있다. 말뚝기초의 동적 p-y 곡선을 확인하기 위한 대부분의 연구는 사질토 및 점성토로 이루어진 단일지반에 설치된 말뚝기초를 대상으로 확인되었을 뿐 다층지반에 설치된 말뚝기초의 동적 p-y 곡선을 확인하기 위한 연구는 미비한 실정이다. 이에 본 연구에서는 서로 다른 상대밀도를 갖는 이층지반의 상·하지반의 지층비가 상부구조물을 지지하는 무리말뚝의 동적거동에 미치는 영향을 확인하기 위해 1g 진동대 모형실험을 수행하였다. 그 결과 지층비가 증가할수록 지반, 말뚝캡, 상부구조물에서의 최대가속도는 증가하고, 말뚝기초의 최대휨모멘트의 발생 위치는 변화하는 것으로 나타났다. 그리고 말뚝기초의 동적 p-y 곡선의 기울기는 지층비에 따라 감소 및 증가하는 것으로 확인되었다.