본 논문에서는 전자기파에 대한 수치적 파동흡수 경계모델인 Perfectly-Matched-Layer(PML)를 개발하고 PML을 연동시킨 유한요소법에 의해 콘크리트 구조물을 통과하는 마이크로파의 전파거동을 해석하는 수치적 기법을 제시한다. 콘크리트 부재와 공기로 구성된 무한매질을 PML을 경계로 하는 유한영역으로 치환하고, 이 유한영역에서 평면 전자기파에 대한 시간영역 맥스웰방정식의 수치 해를 혼합유한요소법에 의해 계산하였다. 공기로만 이루어진 균일매질의 경우와 콘크리트 구조물이 존재하는 비균일 매질의 경우에 대하여 단일주파수 및 복합주파수를 갖는 마이크로파의 전기장을 계산하였고, 오차분석을 위해 L2-놈 형태로 표현되는 정해와 수치 해의 상대오차를 정의하여 수치 해의 정확도를 평가하였다. 이 연구는 마이크로파를 이용한 철근콘크리트 구조물의 건전도평가 및 손상평가에 적용될 수 있다.

In Part I, we disccussed of joint between PHC pile and steel column in foundation of large space structures, one prototype of a joint of PHC pile to steel pipe column was suggested on the basis of analytical studies. In this paper, I explain the Joint of PHC pile to steel tube column and more detail of analysis

To overcome disadvantages of usual spread foundation in large space structure, some prototypes of a joint of the PHC pile to steel pipe column that directly connects a column to a PHC pile are analytically studied. With the consideration of strength requirement and stress concentration of joint of the PHC pile to column, we suggest the most appropriate one.

This study performed a finite element crash analysis of support structures made of various composite materials for road facilities. The effects of different material properties of composites for various parameters are studied using the finite element commercial package for this study. In this study, the existing finite element analysis of composite post structures using the LS-DYNA program is further extended to compare dynamic behaviors against car crash of the structures made of various composite materials. The several numerical examples show the comparison of the nonlinear dynamic effects for different materials.

Orthodontic is important to apply the optimal orthodontic force. The orthodontic bracket is deformed and the stress caused by tension and torsion of the wire. In this study, using the ANSYS the material that is currently widely used in orthodontic bracket material of stainless steel, ceramic, titanium, polycarbonate, by applying the nitinol analyzed the strain and the stress distribution on the bracket side. Simulation results on the stress distribution and deformation, and it was found a difference of each material.

The purpose of this study is to analyze the structural stability of pavement due to water infiltration at the road with infiltration trench as using the FEM(finite element analysis). Five cases for FEM is divided considering the amount of rainfall and rain duration time. The results of FEM show that the more rainfall in a short period time is faster the change of moisture content. Also, it is the proportional relationship between and changing area of moisture content of more than 40% due to rainfall. Case 3 and 4 are necessary to check the installation of infiltration trench because of moisture content of more than 40%, recovery time of initial moisture content, and changing area of more than 40%. Case 1,2, and 5 have no a significant effect on road pavement structure due to lower moisture content and shorter duration time of higher moisture content.

본 연구에서는 프리스트레스트 콘크리트 보의 처짐 예측을 위해 재료비선형이 고려된 콘크리트 및 철근, 강연선의 거동을 고려할 수 있는 구성모델을 조합하여 적층 쉘 요소를 사용한 유한요소해석 모델에 적용하였다. 이를 기존 연구자들의 실험결과와 비교함으로써 모델의 타당성을 검증하였고, 스팬-깊이비, 편심 그리고 프리스트레싱 크기에 대한 처짐을 해석하고 이를 수계산 결과와 비교하였다. 그 결과, 스팬-깊이비가 커질수록, 편심이 작아질수록, 프리스트레싱 크기가 작아질수록 처짐이 증가하는 것을 확인하였다. 또한, 편심이 매우 작을 경우와 프리스트레싱 크기가 매우 작을 경우에는 수계산이 처짐을 과대평가한다는 것을 확인하였다.

In recent years, industrial demands for superior mechanical properties of powder metallurgy steel components with low cost are rapidly growing. Sinter hardening that combines sintering and heat treatment in continuous one step is cost-effective. The cooling rate during the sinter hardening process dominates material microstructures, which finally determine the mechanical properties of the parts. This research establishes a numerical model of the relation between various cooling rates and microstructures in a sinter hardenable material. The evolution of a martensitic phase in the treated microstructure during end quench tests using various cooling media of water, oil, and air is predicted from the cooling rate, which is influenced by cooling conditions, using the finite element method simulations. The effects of the cooling condition on the microstructure of the sinter hardening material are found. The obtained limiting size of the sinter hardening part is helpful to design complicate shaped components.

In this study, the behavior of densification of copper powders during high-pressure torsion (HPT) at room temperature is investigated using the finite element method. The simulation results show that the center of the workpiece is the first to reach the true density of copper during the compressive stage because the pressure is higher at the center than the periphery. Subsequently, whole workpiece reaches true density after compression due to the high pressure. In addition, the effective strain is increased along the radius during torsional stage. After one rotation, the periphery shows that the effective strain is increased up to 25, which is extensive deformation. These high pressure and severe strain do not only play a key role in consolidation of copper powders but also make the matrix harder by grain refinement.

A strain-gradient crystal plasticity constitutive model was developed in order to predict the Hall Petch behavior of a Ni-base polycrystalline superalloy. The constitutive model involves statistically stored dislocation and geometrically necessary dislocation densities, which were incorporated into the Bailey-Hirsch type flow stress equation with six strength interaction coefficients. A strain-gradient term (called slip-system lattice incompatibility) developed by Acharya was used to calculate the geometrically necessary dislocation density. The description of Kocks-Argon-Ashby type thermally activated strain rate was also used to represent the shear rate of an individual slip system. The constitutive model was implemented in a user material subroutine for crystal plasticity finite element method simulations. The grain size dependence of the flow stress (viz., the Hall- Petch behavior) was predicted for a Ni-base polycrystalline superalloy NIMONIC PE16. Simulation results showed that the present constitutive model fairly reasonably predicts 0.2%-offset yield stresses in a limited range of the grain size.

The porous metallic material has the most superior physical property and the best mechanical capability. This study is investigated with the simulation analysis by compressing three kinds of specimens. Three aluminum foams with the thickness of 10 mm are bonded at Case 1. Two aluminum foams with the thicknesses of 10 mm and 20 mm are bonded at Case 2. It is one aluminum foam with the thickness of 30 mm at Case 3. The two dimensional model is done by ANSYS design modeler and the finite element analysis is performed by ANSYS structural analysis. As the forced displacement of 1 mm during the elapsed time of 60 sec is applied, the forced displacement of 10 mm during the total elapsed time of 600 sec is applied. As the analysis result, the most reaction force is shown at case 2 among three cases. Case 2 is estimated as the best structure. The analysis result of this study is thought to be the data necessary for the safe design about mechanical structure and the development of composite material.

A progressive failure analysis procedure for composite laminates is completed in here. An anisotropic plastic constitutive model for fiber-reinforced composite material is implemented into computer program for a predictive analysis procedure of composite laminates. Also, in order to describe material behavior beyond the initial yield, the anisotropic work-hardening model and subsequent yield surface are implemented into a computer code, which is Predictive Analysis for Composite Structures (PACS). The accuracy and efficiency of the anisotropic plastic constitutive model and the computer program PACS are verified by solving a number of various fiber-reinforced composite laminates with and without geometric discontinuity. The comparisons of the numerical results to the experimental and other numerical results available in the literature indicate the validity and efficiency of the developed model.

The automotive bumper has the functions of strength, rigidity and fine sight. It protects the driver, front and rear sides of car body through shock absorption at the traffic accident of car. This study investigates the impacts on front side and corner with the low speed of 4.5 km/h by using the model of SUV car body. The models are modelled by CATIA program with three dimensions and are analyzed by the finite element program of ANSYS Explicit STR. The maximum equivalent stresses at impacts of front side(case 1) and corner (case 2) at bumper are 261.72MPa and 365.02MPa respectively. As this stress at case 2 becomes 40% higher than at case 1, the impact of corner is happened easier than at the damage at the impact of front side. These stresses at case 1 and case 2 are shown above the yield stress at material property of steel, it is thought that there are the possibilities of plastic damages at two cases. The maximum deformation and equivalent stress at the support 2 of case 2 become 5 times and 3 times higher than at the support 1 respectively. The damage possibility due to impact at low speed is investigated by the basic analysis result of this study. And this result can be utilized at inspecting the result of impact test on bumper hereafter.

최근 국내 이상기후로 인한 집중호우로 사회기반 시설물인 도로 파손 문제가 대두 되고 있다. 이를 해 결하기 위해 아산탕정지구에 840개의 침투도랑을 포함한 LID(Low Impact Development) 빗물관리시설 물이 도로인접부에 설치되었다. 하지만 침투도랑에 유입된 유입수의 거동이 침투도랑 인접 부도로 내부로 흘러들어가 도로구조의 안정성에 부정적인 영향을 발생시킬 가능성이 있다. 그럼에도 불구하고 도로안전 성을 검증하기 위한 실내시험 및 현장시험은 전무한 상태이다. 본 연구에서는 실내시험 및 현장시험을 보다 정확히 하기 위하여 침투수에 의한 도로안정성 구조해석 이 필수적인 사항이라고 판단하였다. 침투수 유입에 따른 도로하부구조의 유체거동과 포장골재 및 노상의 함수비 변화에 따른 공용성을 분석하였다. 도로하부구조의 유체거동과 함수비 변화를 역학적으로 예측하 기 위해 유한요소 해석을 실시하였다. 유한요소 해석을 통해 침투도랑이 도로 공용성에 미치는 영향 분석 의 전체적인 연구 절차는 아래 그림 1과 같다.

강화재의 복잡한 배열로 인하여 복합재 구조에 대한 유한요소 모델링은 상당히 까다로운 문제가 될 수 있다. 본 논문에서는 복합재 구조에 대하여 효율적으로 주기 격자망을 생성시킬 수 있는 기법을 제안한다. 먼저 육면체 유한요소로 구성된 규칙적인 격자망을 준비하고, 이를 복합재 내의 강화재에 대한 표면 정보에 맞추어 깎아낸다. 강화재와 기지재 사이에서 깎여진 육면체 유한요소는 임의의 절점과 면을 가질 수 있는 다면체 유한요소에 해당한다. 일관된 알고리즘을 이용하여 육면체 유한요소를 깎아내기 때문에 강화재와 기지재 사이의 요소는 자동적으로 적합한 형태로 구성된다. 또한 대표체적영역 내에서 강화재의 주기성을 추가적으로 고려하면, 대표체적영역에 대한 각각의 주기 경계 쌍에서 절점과 요소의 형태가 모두 일치하는 주기 격자망을 효율적으로 생성시킬 수 있다. 그러므로 별도의 처리 없이 대표체적영역에 주기 경계조건을 부여할 수 있다. 수치예제에서는 본 논문에서 제안한 기법의 효용성을 검증한다.

The latest weight reduction research of automotive industry and technology was improved. In this paper, we aim to evaluate the composite frame to manufacture the floor assembly of commercial vehicle. The design of subframe incorporated into the floor module was determined by FEM(Finite Element Method) simulation. The mechanical properties used for the simulations were obtained from the tests for samples of glass fiber/epoxy composites. We made two kinds of pultrusion products, one was aluminum profile, the other was unidirectional composites with aluminum profile. Based on the results from the simulation and bending test, the design of the subframe was finally determined prior to adoption of the commercial vehicle floor.

The monolithic glass, without damage, subjected to ballistic impact, is studied by the use of the coded finite element program. To analyze the impact response of monolithic glass like ordinary annealed glass and tempered glass, a finite element approach based on the Hertzian contact law and Sun's higher-order beam finite element is proposed. For verifying effectiveness of this finite element program, the contact force history is analyzed in conjunction with the loading and unloading processes. And, also, the time history of the impact responses such as the strain and stress according to the thickness changes due to transverse impact at the center are calculated

In recent years, there was many conflagration about special structure such as wooden cultural assets, warehouses and factories. The common causes of increase in the fire damage were difficulty of the initial suppression and absence of equipment for appropriate disaster prevention. In this study, the destruction-spray nozzles, a core technology of destruction-spray fire vehicle which is possible for fire suppression of special structure was studied using the finite element method. As a result, the maximum deviation of the part nozzle was 18.1% compared with the reference value. Second, the maximum deviation of the nozzle module was 13.5% compared with the part nozzle. Third, the safety factor about internal pressure of the nozzle module was suitable as 13.6. Finally, the performance of the designed destruction-spray nozzle was satisfied with 4,652.1L/min in excess of the target performance.

본 연구에서는 다면체 요소의 개발을 위하여 Wachspress 좌표계와 이동최소자승 근사를 기반으로하는 형상함수와 수치적분 방법을 제시하고 있다. 사면체 요소를 사면체 영역으로 분할하여 형상함수가 구성이 되고 이 영역을 사용한 일관성있는 수치적분이 수행되게 된다. 다면체 요소 면에서 Wachspress 좌표계를 사용하고 요소 내부에서 라플라스 방정식을 적용하여 이동최소자승 근사의 가중함수를 정의하게 된다. 본 연구에서 개발되는 다면체 요소의 형상함수와 수치적분 방법은 일반적인 유한요소와 유사한 특성을 갖게 되는데 수치 예제를 통하여 유효성을 보여주었다.

동역학의 새로운 변분이론인 혼합 합성 변분이론은 수학물리학을 비롯한 공학에 있어 초기치-경계치 문제해석에 광범위하게 적용될 수 있는 기반을 제공하는 것으로, 본 논문은 이 이론을 토대로 시간에 대한 이차의 형상함수가 적용된 시간 유한요소해석법을 개발하고 그 해석법의 수치특성 확인을 통해 향후 다양한 동적시스템 해석의 적용에 대한 가능성을 살펴보았다. 이를 위해 가장 기본적인 선형탄성의 단자유도계가 고려되었다. 에너지 보존시스템의 경우(비감쇠 시스템에 외력이 작용치 않는 경우), 제안된 알고리즘 모두는 time-step에 관계없이 안정적이며 수치감쇠가 없이 에너지와 모멘텀이 보존되는 symplecticity property를 가지고 있음을 확인할 수 있었고, 감쇠시스템인 경우, time-step이 점점 작아질수록 정확한 해에 빠르게 수렴하는 것을 확인하였다.