Kwang-Bok Shin

A Study on Low-Velocity Impact Characterization of Various Sandwich Panels for the Korean Low Floor Bus Application

In this paper, a study on low-velocity impact response of four different sandwich panels for the hybrid bodyshell and floor structure application of the Korean low floor bus vehicle was done. Square samples of 100mm sides were subjected low-velocity impact loading using an instrumented testing machine at six energy levels. Impact parameters like maximum force, time to maximum force, deflection at maximum force and absorbed energy were evaluated and compared for four different types of sandwich panels. The impact damage size and depth of the permanent indentation were measured by 3-Dimensional Scanner. Failure modes were studied by sectioning the specimens and observed under optical microscope. The impact test results show that sandwich panel with composite laminate facesheet could not observe damage mode of a permanent visible indentation after impact and has a good impact damage resistance in comparison with sandwich panel with metal aluminum facesheet.

Numerical study on crashworthiness assessment and improvement of composite carbody structures of tilting train using hybrid finite element model

This paper describes the numerical results on crashworthiness assessment and improvement scheme of tilting train made of composite materials. The bodyshell of tilting train was composed of aluminum honeycomb sandwich panels and carbon-fabric/epoxy laminate composites. The input parameters for numerical analysis were obtained from material tests. Crashworthiness analysis of the tilting train was conducted using the explicit finite element analysis code LS-DYNA3D and according to four collision scenarios of the Korean railway safety rule. The hybrid finite element modeling technique, which is made up of 2D shell and 3D solid elements for three cars in the front and 1D equivalent element for the rest cars in the rear, was introduced to ensure fast and accurate design verification for crashworthiness of railway vehicle. The numerical results showed that hybrid modeling technique was an economical approach for the analyzed results, finite element modeling, and calculating time in comparison with conventional modeling method using 2D shell and 3D solid elements for railway vehicles.

Experimental and Numerical Simulation Studies of Low-Velocity Impact Responses on Sandwich Panels for a BIMODAL Tram

This paper describes the results of experiments and numerical simulation studies on the impact and indentation damage created by low-velocity impact subjected onto honeycomb sandwich panels for application to the BIMODAL tram. The test panels were subjected to low-velocity impact loading using an instrumented testing machine at six energy levels. Contact force histories as a function of time were evaluated and compared. The extent of the damage and depth of the permanent indentation was measured quantitatively using a 3-dimensional scanner. An explicit finite element analysis based on LS-DYNA3D was focused on the introduction of a material damage model and numerical simulation of low-velocity impact responses on honeycomb sandwich panels. Extensive material testing was conducted to determine the input parameters for the metallic and composite face-sheet materials and the effective equivalent damage model for the orthotropic honeycomb core material. Good agreement was obtained between numerical and experimental results; in particular, the numerical simulation was able to predict impact damage area and the depth of indentation of honeycomb sandwich composite panels created by the impact loading.

Progressive Failure Analysis of Adhesive Joints of Filament-Wound Composite Pressure Vessel

* Graduate School of Mechanical Design Engineering, Hanbat Nat’l Univ., ** Dept. of Mechanical Engineering, Hanbat Nat’l Univ.,*** Agency for Defence Development (Received June 20, 2014 ; Revised August 12, 2014 ; Accepted August 15, 2014)Key Words: Composite Pressure Vessel(복합재 압력용기), Cohesive Zone Model(접착영역모델), Interlaminar Fracture Toughness(층간파괴인성치), Progressive Failure Analysis(점진적 파손 해석)초록: 본 논문에서는 CZM(Cohesive Zone Model)을 이용하여 돔 분리형 복합재 압력용기 접착 체결부의 점진적 파손 해석에 대한 연구를 수행하였다. 접착 요소(cohesive element)의 물성을 도출하기 위해 모드 I, II 그리고 혼합모드에 대한 층간파괴인성들을 시험을 통해 도출하였다. 이때, 모든 시험편은 복합재 압력용기와 동일한 필라멘트 와인딩 제작공정을 통해 제작되었다. 이중 겹치기 이음(double-lap joint) 시험은 접착제의 전단강도와 CZM을 이용한 점진적 파손해석의 신뢰도 검증을 위해 수행하였다. 그 결과, 접착제의 전단강도는 시험으로부터 32MPa을 얻었고, 시험과 해석의 오차는 약 4.4%의 오차가 발생하여 CZM이 접착 체결부의 점진적 파손 거동을 비교적 잘 모사함을 확인하였다. 최종적으로 신뢰성이 검증된 CZM을 복합재 압력용기 접착 체결부에 적용하여 운용하중조건에서의 점진적 파손해석을 수행한 결과, 전체 200mm를 갖는 접착 체결부 길이의 약 5.8%만이 점진적 파손이 발생하는 것으로 나타나 복합재 압력용기의 구조 안전성에는 영향을 주지 않음을 확인하였다.Abstract: This study performed the progressive failure analysis of adhesive joints of a composite pressure vessel with a separated dome by using a cohesive zone model. In order to determine the input parameters of a cohesive element for numerical analysis, the interlaminar fracture toughness values in modes I and II and in the mixed mode for the adhesive joints of the composite pressure vessel were obtained by a material test. All specimens were manufactured by the filament winding method. A mechanical test was performed on adhesively bonded double-lap joints to determine the shear strength of the adhesive joints and verify the reliability of the cohesive zone model for progressive failure analysis. The test results showed that the shear strength of the adhesive joints was 32MPa; the experiment and analysis results had an error of about 4.4%, indicating their relatively good agreement. The progressive failure analysis of a composite pressure vessel with an adhesively bonded dome performed using the cohesive zone model showed that only 5.8% of the total adhesive length was debonded and this debonded length did not affect the structural integrity of the vessel.

A Study on Low-Velocity Impact Characterization of Honeycomb Sandwich Panels According to the Changes of Impact Location and Core Fabrication Angles

Abstract In this paper, a study on low-velocity impact response of honeycomb sandwich panels was done for the changes of impact location and core fabrication angles. The test specimens were made of glass/epoxy laminate facesheet and aluminum honeycomb core. Square samples of 100mm and 100mm sides were subjected under low-velocity impact loading using instrumented testing machine at three energy levels. Impact parameters like maximum force, time to maximum force, deflection at maximum force and absorbed energy were evaluated and compared for the changes of impact location and core fabrication angle. The impact damage size were measured at facesheet surface by 3-Dimensional scanner. Also, sandwich specimens after impact test were cut to analyse the failure mode. * 한밭대학교 기계설계공학과, 경량구조 및 CAE실험실 †책임저자, 회원, 한밭대학교 기계설계공학과 E-mail : shin955@hanbat.ac.kr TEL : (042)821-1156 FAX : (042)821-1587** (주)한국화이바 차량사업부 1. 서 론 에너지 효율과 환경문제가 중시되는 오늘날 항공기, 선박 및 자동차 등과 같은 운송수단의 경량화는 지구 온난화의 주범인 대기오염을 줄이고 에너지 효율의 극대화를 얻을 수 있는 장점을 갖는다. 이러한 운송수단의 경량화를 얻기 위하여 기존구성 재질을 보다 가벼운 재질로 대체하는 방법이 주를 이루고 있으며,

Analysis of Heat and Smoke Flow according to Platform Screen Door and Fan Conditions on Fire in Underground Platform

In this study, a three-dimensional flow analysis of underground subway station was conducted by applying ventilation mode in operation and platform screen door (PSD) opening and closing conditions on fire in underground platform. In order to analyze optimal smoke control and heat removal conditions, the whole underground subway station was set as a model, and a total of eight cases were analyzed by changing the operating conditions of fans for each area under the opening and closing conditions of the PSDs. The analysis results confirmed that the operation mode of supply fan in platform E and I areas located at the third floor underground is more effective than that of exhaust fan in the event of a fire in underground subway station when the PSD is closed. The amount of CO entering a waiting room increased, and the overall CO distribution in the underground subway station was also increased when the PSD is opened. In addition, the CO distributions due to the opening and closing of the PSD were similar to one another when a fire occurred on the platform, which suggests that the operating conditions of the fan affects the formation of CO distribution in the underground subway station rather than the discharge of CO.

Effect of Temperature on Interlaminar Fracture Toughness of Filament-Wound Carbon/Epoxy Composites

This paper reports an experimental study for evaluating the effect of temperature on the mode I, mode II and mixed-mode interlaminar fracture toughness of adhesive joints with a curved cross-section of filament-wound dome-separated composite pressure vessel. Mode I and mixed-mode interlaminar fracture toughness were evaluated using DCB specimens, while mode II interlaminar fracture toughness was determined using ENF specimens. , and () winding specimens with the curved cross-section were considered. In-situ temperature environments were simulated with a range of using an environmental chamber and furnace. Experimental results on the effect of temperature indicate that interlaminar fracture toughness tends to be high at low temperature and is degraded with increase in temperature. For specimen types, it was found that interlaminar fracture toughness of winding specimens considered as adhesive joints of dome and helical part was higher than other specimens.

A Study on the Weight-Reduction Design of High-Speed Maglev Carbody made of Aluminum Extrusion and Sandwich Composite Roof

* Graduate School of Dept. of Mechanical Design Engineering, Hanbat Nat’l Univ. ** Dept. of Mechanical Engineering, Hanbat Nat’l Univ.*** Woojin Industrial Systems (Received April 7, 2014 ; Revised June 8, 2014 ; Accepted June 29, 2014)Key Words: Maglev Train(자기부상열차), Weight-Reduction(경량화), Hybrid Carbody(하이브리드 차체), Sandwich Composite(샌드위치 복합재), Aluminum Extrusion(알루미늄 압출재)초록: 본 논문의 목적은 알루미늄 압출재와 샌드위치 복합재를 사용한 초고속 자기부상 열차의 하이브리드 차체 경량화 설계를 제안하는 것이다. 샌드위치 복합재는 무게 감소를 위해 2차 부재인 루프에 적용되었다. 용접에 의한 샌드위치 복합재 루프와 알루미늄 압출재 사이드 프레임과 접합시키기 위해 샌드위치 복합재 네 옆면에 가이드 알루미늄 프레임을 갖도록 고안하였다. 가이드 알루미늄 프레임의 체결력은 3점 굽힘 시험을 통해 검증하였으며, 차체의 구조 안전성 및 충돌 안전도는 상용 유한요소해석 프로그램을 이용하여 철도안전법에 따라 평가하고 검증하였다. 연구결과, 알루미늄 압출재와 샌드위치 복합재로 이루어진 하이브리드 차체는 알루미늄 압출재로만 이루어진 차체에 비해 무게 절감 효과와 향상된 구조 성능을 얻을 수 있다.Abstract: The purpose of this paper is to suggest a weight-reduction design method for the hybrid carbody of a high-speed maglev train that uses aluminum extrusion profiles and sandwich composites. A sandwich composite was used on the roof as a secondary member to minimize the weight. In order to assemble the sandwich composite roof and aluminum extrusion side frame of the carbody using welding, a guide aluminum frame located at the four sides of the sandwich composite roof was introduced in this study. The clamping force of this guide aluminum frame was verified by three-point bending test. The structural integrity and crashworthiness of the hybrid carbody of a high-speed maglev train were evaluated and verified according to the Korean Railway Safety Law using a commercial finite element analysis program. The results showed that the hybrid carbody composed of aluminum extrusion frames and a sandwich composite roof was lighter in weight than a carbody made only of aluminum extrusion profiles and had better structural performance.

A study on evaluation of fatigue strength of a GFRP composite bogie frame for urban subway vehicles

The fatigue strength and life of a GFRP composite bogie frame for urban subway trains were evaluated in this study. The GEP224 glass fabric/epoxy was selected as the structural material of a composite bogie frame to save its weight. In order to obtain the fatigue characteristics of the GEP224 glass/epoxy composite material, the tension–compression fatigue test was done with three different stacking sequences of warp direction, fill direction, and warp/fill direction, respectively. A fatigue test was conducted with a stress ratio, R of 0.1 and −1, and up to endurance limit of 107 with frequency of 5 Hz. The fatigue strength of the GFRP composite bogie frame was evaluated on the basis of the S-N curve and Goodman diagrams obtained from GEP224 glass/epoxy composites according to the JIS E 4207 and UIC 515/615-4. The result shows that fatigue strength of the GFRP composite bogie has satisfied the design requirements. Also, the GFRP composite bogie frame had a good fatigue performance in comparison with conventional metal bogie frame, considering its weight.

Evaluation of Mechanical Properties and Low-Velocity Impact Characteristics of Balsa-Wood and Urethane-Foam Applied to Impact Limiter of Nuclear Spent Fuel Shipping Cask

This paper aims to evaluate the low-velocity impact responses and mechanical properties of balsa-wood and urethane-foam core materials and their sandwich panels, which are applied as the impact limiter of a nuclear spent fuel shipping cask. For the urethane-foam core, which is isotropic, tensile, compressive, and shear mechanical tests were conducted. For the balsa-wood core, which is orthotropic and shows different material properties in different orthogonal directions, nine mechanical properties were determined. The impact test specimens for the core material and their sandwich panel were subjected to low-velocity impact loads using an instrumented testing machine at impact energy levels of 1, 3, and 5 J. The experimental results showed that both the urethane-foam and the balsa-wood core except in the growth direction (z-direction) had a similar impact response for the energy absorbing capacity, contact force, and indentation. Furthermore, it was found that the urethane-foam core was suitable as an impact limiter material owing to its resistance to fire and low cost, and the balsa-wood core could also be strongly considered as an impact limiter material for a lightweight nuclear spent fuel shipping cask.