• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1450-1457
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• 2003

Structural integrity of either a passenger car or a light truck is one of the basic requirements for a full vehicle engineering and development program. The results of the vehicle product performance are measured in terms of durability, noise/vibration/harshness (NVH), crashworthiness and passenger safety. The level of performance of a vehicle directly affects the marketability, profitability and, most importantly, the future of the automobile manufacturer. In this study, we used the Virtual Proving Ground (VPG) approach for obtaining the dynamic stress or strain history and distribution. The VPG uses a nonlinear, dynamic, finite element code (LS-DYNA) which expands the application boundary outside classic linear, static assumptions. The VPG approach also uses realistic boundary conditions of tire/road surface interactions. To verify the predicted dynamic stress and fatigue critical region, a single bump run test, road load simulation, and field test have been performed. The prediction results were compared with experimental results, and the feasibility of the integrated life prediction methodology was verified.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.65-72
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• 2001

This paper demonstrates an explicit-implicit, finite element analysis for linear as well as nonlinear hygrothermal stress problems. Additional features, such as moisture diffusion equation, crack element and virtual crack extension(VCE) method for evaluating J-integral are implemented in this program. The Linear Elastic Fracture Mechanics(LEFM) Theory is employed to estimate the crack driving force under the transient condition for an existing crack. Pores in materials are assumed to be saturated with moisture in the liquid form at the room temperature, which may vaporize as the temperature increases. The vaporization effects on the crack driving force are also studied. The ideal gas equation is employed to estimate the thermodynamic pressure due to vaporization at each time step after solving basic nodal values. A set of field equations governing the time dependent response of porous media are derived from balance laws based on the mixture theory. Darcy's law is assumed for the fluid flow through the porous media. Perzyna's viscoplastic model incorporating the Von-Mises yield criterion are implemented. The Green-Naghdi stress rate is used for the invariant of stress tensor under superposed rigid body motion. Isotropic elements are used for the spatial discretization and an iterative scheme based on the full Newton-Raphson method is used for solving the nonlinear governing equations.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2097-2107
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• 1996

The dynamic photoelastic technique had been utilized to investigate the possibillity of relieving the large local singular stresses induced at the corner of a right- angle- indenter. The indenter compressed a semi-infinite body dynamically with an impact load applied on the top of the indenter. The effects of the geometric changes of the indenter in terms of the diameter (d) and the location (1) of the stress relieving notch on the behavior of the dynamic contact stresses were investigated. The influence of stress relieving notches positioned along the edge of the semi-infinite body on the dynamic contact stresses were also studied by changing the diameter (D) and the location (L) of the notch. A multi-speak-high speed camera with twelve sparks were used to take photographs of full field dynamic isochromatic fringe patterns. The contact singular stresses were found to be released significantly by the stress relief notches both along the indenter and the edge of the semi-infinite body. The optimal position and geometry of the stress relieving notches were obtained with the aid of limited experimental results.

• Journal of Mechanical Science and Technology
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• 제16권2호
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• pp.165-174
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• 2002

In the present study, interfacial cracks between an isotropic and orthotropic material, subjected to static far field tensile loading are analyzed using the technique of photoelasticity. The fracture parameters are extracted from the full-field isochromatic data and the same are compared with that obtained using boundary collocation method. Dynamic photoelasticity combined with high-speed digital photography is employed for capturing the isochromatics in the case of propagating interfacial cracks. The normalized stress intensity factors for static cracks are greate. when ${\alpha}$: 90$^{\circ}$(fibers perpendicular to the interface) than when ${\alpha}$=0$^{\circ}$(fibers parallel to the interface), and those when ${\alpha}$=90$^{\circ}$are similar to ones of isotropic material. The dynamic stress intensity factors for interfacial propagating cracks are greater when ${\alpha}$=0$^{\circ}$ than ${\alpha}$=90$^{\circ}$. For the velocity ranges (0.1 < C/C$\sub$s1/<0.7) observed in this study, the complex dynamic stress intensity factor │K$\sub$D/│increases with crack speed c, however, the rate of increase of │K$\sub$D/│with crack speed is not as drastic as that reported for homogeneous materials.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
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• pp.45-52
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• 2003

A finite element procedure to estimate ultimate strength of space frames considering spread of plasticity is presented. The improved displacement field is introduced based on inclusion of second order terms of finite rotations. All the nonlinear terms due to bending and torsional moment as well as axial force are precisely considered. The concept of plastic hinge is introduced and the incremental load/displacement method is applied for the elasto-plastic analysis. The initial yield surface is defined based on the residual stress and the full plastification surface is considered under the combined action of axial force, bending and torsional moments. The elasto-plastic stiffness matrices are derived using the flow rule and the normality condition of the limit function. Finite element solutions for ultimate strength of space frames are compared with available solutions and experimental results.

• 한국도로학회논문집
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• 제16권4호
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• pp.1-9
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• 2014

PURPOSES: The objective of this study is to evaluate construction issues and design for transverse steel in continuously reinforced concrete pavement(CRCP). METHODS : The first continuously reinforced concrete pavement(CRCP) design procedure appeared in the 1972 edition of the "AASHTO Interim Guide for Design of Pavement Structures", which was published in 1981 with Chapter 3 "Guide for the Design of Rigid Pavement" revised. A theory that was accepted at that time for the analysis of steel stress in concrete pavement, called subgrade drag theory(SGDT), was utilized for the design of reinforcement of CRCP - tie bar design and transverse steel design - in the aforementioned AASHTO Interim Guide. However SGDT has severe limitations due to simple assumptions made in the development of the theory. As a result, any design procedures for reinforcement utilizing SGDT may have intrinsic flaws and limitations. In this paper, CRCP design procedure for transverse steel was introduced and the limitations of assumptions for SGDT were evaluated based on various field testing. RESULTS: Various field tests were conducted to evaluate whether the assumptions of SGDT are reasonable or not. Test results show that 1) temperature variations exist along the concrete slab depth, 2) very little stress in transverse steel, and 3) warping and curling in concrete slab from the field test results. As a result, it is clearly revealed out that the assumptions of SGDT are not valid, and transverse steel and tie bar designs should be based on more reasonable theories. CONCLUSIONS : Since longitudinal joint is provided at 4.1-m spacing in Korea, as long as joint saw-cut is made in accordance with specification requirements, the probability of full-depth longitudinal cracking is extremely small. Hence, for transverse steel, the design should be based on the premise that its function is to keep the longitudinal steel at the correct locations. If longitudinal steel can be placed at the correct locations within tolerance limits, transverse steel is no longer needed.

• Steel and Composite Structures
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• 제49권2호
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• pp.231-244
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• 2023

Many of the recent investigations in the field of geotechnical engineering focused on the bearing capacity theories of multilayered soil. A number of factors affect the bearing capacity of the soil, such as soil properties, applied overburden stress, soil layer thickness beneath the footing, and type of design analysis. An extensive number of finite element model (FEM) simulation was performed on a prototype slope with various abovementioned terms. Furthermore, several non-linear artificial intelligence (AI) models are developed, and the best possible neural network system is presented. The data set is from 3443 measured full-scale finite element modeling (FEM) results of a circular shallow footing analysis placed on layered cohesionless soil. The result is used for both training (75% selected randomly) and testing (25% selected randomly) the models. The results from the predicted models are evaluated and compared using different statistical indices (R² and RMSE) and the most accurate model BBO (R²=0.9481, RMSE=4.71878 for training and R²=0.94355, RMSE=5.1338 for testing) and TLBO (R²=0.948, RMSE=4.70822 for training and R²=0.94341, RMSE=5.13991 for testing) are presented as a simple, applicable formula.

• 생물환경조절학회지
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• 제26권4호
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• pp.402-410
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• 2017

본 연구에서는 실대형 실험과 구조해석을 통하여 현장에서 사용되는 기둥-서까래-도리, 기둥-도리-방풍벽 접합부를 적용한 강관 골조 플라스틱 연동온실의 정적 구조성능을 분석하였다. 실대형 재하실험 결과는 접합부를 강접합으로 가정한 구조해석 결과와 비교하여 구조물의 횡방향 강성과 각 부재의 하중분담률에서 많은 차이를 보였다. 동고 높이에서 측정한 수평변위는 실험과 구조해석의 차이가 40%이었고 수직변위는 89%의 차이를 보였다. S3 부재의 발생응력을 기준으로 한 각 부재별 하중분담률을 비교한 결과 실험과 구조해석에서 두 배 이상의 차이를 보이는 부재가 있었으며, 하부측벽이음(S2), 기둥 상부(S7) 등 주요 부재의 실험결과가 구조해석의 하중분담률을 재현하지 않았다. 현장에서 사용하는 접합부가 충분한 강성을 확보하지 않음으로써 구조물에 작용하는 외력을 각 부재에 적절하게 전달하지 못했으며 이로 인해 구조물의 강성이 저하되는 현상이 나타났다. 설계 단계에서 일반적으로 구조해석에 의해 결정되는 구조성능의 신뢰도는 접합부의 특성을 보다 면밀하게 고려했는지 여부에 따라 좌우 될 수 있다. 따라서 온실 구조 성능에 대한 신뢰성을 높이기 위해서는 온실에 사용되는 다양한 접합부를 고려할 수 있는 구조해석 기술의 개발이 필요하며 설계 기준에서 상세 설계 방법을 보다 명확히 규정해야 할 것으로 판단된다.

• 한국안전학회지
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• 제11권4호
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• pp.143-150
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• 1996

본 연구는 선형, 비선형 hygrothermal 응력 문제를 위한 explicit-Implicit 유한요소 해석 모델 개발에 관한 것이다. 부가적으로 moilsture 확산 방정식, J-적분 평가를 위한 균열 요소 및 가상 균열 진전법이 도입된다. 시간 변화에 따른 균열 추진력을 계산하기 위하여 선형 탄성 파괴 역학(LEFM)이론이 고려되며 재료의 기공은 실온에서 액체 상태의 습기로 포화되어 있으며 온도가 상승함에 따라 증기화된다는 가정하에서 균열 추진력과 증기 효과의 관계가 연구된다. 이상 기체방정식은 각 시간 단계에서 증기에 의한 열역학적 압력을 계산하기 위하여 이용된다. 다공질 재료의 시간 종속 응답을 지배하는 방정식들은 혼합이론에 기초하며 다공질 재료의 유체 흐름을 위한 Darcy의 법칙과 Von-Mises 항복 기준을 포함하고 있는 Perzyna의 점소성 모델이 첨가된다. 또한 Green-Naghdi 응력률이 중첩된 강체 운동하에서 응력 텐서 invariant로 사용되며, 모델링을 위하여 사각요소가 이용되고 비선형 지배 방정식을 풀기 위하여 full Newton-Raphson법에 의한 반복법이 사용된다. 본 연구를 통하여 얻은 결과는 다음과 같다. 1) 본 유한요소 프로그램은 복합재의 hygrothermal 파괴 해석에 매우 유용하게 적용될 수 있다. 2) 습기의 온도에 의한 영향을 가지는 재료의 J-적분을 정확히 예측하기 위하여는 증기 효과를 고려하여야 한다. 왜냐하면 초기단계에 균열 전파력이 가속되기 때문이다. 3) 본 해석을 위해 Uncoupled scheme에 의한 결과도 Coupled scheme에 결과에 비해 아주 타당하므로 CPU 측면에서 매우 경제적인 Uncoupled scheme이 추천된다.

• 대한조선학회논문집
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• 제51권6호
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• pp.489-494
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• 2014

Estimation of correct ice load under various operating conditions is important during the design and the operation stages of an icebreaker. Normal operating conditions are expected from the official field ice trials and also from general ice transit action. In this paper ice load for the Korean icebreaking research vessel, ARAON, under normal operating condition, is discussed. Published ice load data from full-scale sea trials of six icebreakers were analysed to derive an empirical ice load prediction formula. The IBRV ARAON had sea ice trials during 2010 and 2012 summer season. Strain gauge signal were recorded during her icebreaking voyage and the measured strain data were converted to the equivalent hull stress values. The effect of ARAON's speed in ice and the hull stresses are investigated. By comparing the empirical formula and ice load calculation based von measured data, it is recommended to use the empirical ice load estimation formula for the initial design stage.