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주재황(Jai-Hwang Joo),강기주(Ki-Ju Kang) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Many studies have been performed on manufacture and optimization of truss PCM(periodic cellular metal) structures. The tetrahedral truss cores are manufactured through metal expanding and bending process and then brazed with solid face sheets. The new metallic sandwich plates with the tetrahedral truss cores subject to 3-point bending have been investigated. The equations of failure load corresponding to the eight failure modes are presented and then non-dimensional forms of the equations are derived. The maps of failure mechanism are constructed based on the analytical calculations in the non-dimensional parameters of geometry. The performance of modified octet truss sandwich plates are compared with similarly octet and honeycomb sandwich plates of the same materials.
부분충진된 WBK 트러스 다공질 금속의 압축 특성 평가
주재황(Jai-Hwang Joo),박종선(Jong-Sun Park),강기주(Ki-Ju Kang) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Lightweight cellular metals combining load supporting capability and thermal management characteristics are required for multifunctional applications. Recently, a new technique for fabricating cellular metal, known as Wire-woven Bulk Kagome (WBK), has been introduced, which is used for fabricating multilayered Kagome truss-type cellular metal. The WBK is composed of helically formed wires and it has been proved that it has high strength-per-weight. In this work, a partially filled WBK with very high specific strength was devised to suppress the elastic buckling of struts which is a typical failure mechanism of truss type PCM (periodic cellular metals). First, theoretical studies using elementary mechanics of material are presented to estimate the strength under out-of-plane compression. And the results are compared with those measured by experiments which were performed with specimens with various slenderness ratios of struts. It has been found that the partially filled WBK exhibited high specific stiffness and strength, absorption of energy in comparison with ordinary WBK.
확장금속망 공정으로 제작된 옥테트 트러스 다공질 금속 : 제3보: 굽힘하중에서의 기계적 성능
주재황(Jai-Hwang Joo),강기주(Ki-Ju Kang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Recently, a new idea was introduced for fabricating sandwich panels with tetrahedral truss cores by metal expanding and folding processes. The results from the three-point bending tests of sandwich panels were investigated. Specifically, the load capacity of the sandwich panel subjected to bending load was estimated by energy based approach for various failure modes. A failure map was constructed as functions of strut and face sheet thickness for a given core height, H<SUB>c</SUB>=16.33㎜ and for a given material parameter, ε<SUB>y</SUB>=0.00089. By using the map, three designs were chosen for maximum load per weight ratio. Namely, design variables for Design-1 specimen were based on the triple point of the face sheet buckling, face sheet yielding, and core shear-mode B plastic regime, whereas those of Design-2 and -3 specimens were based on the boundary between face sheet yielding and core shear-mode B plastic regime. Design-3 had the thickest truss struts and face sheets. In three-points bending tests, the critical loads and the corresponding failure modes were in good agreement with the estimated ones. However, Designs-1 was substantially inferior to Design-2 and -3 in terms of the energy absorption and deformation stability after the peak point.
알루미늄 나선형 와이어로 직조된 다층 Kagome Truss PCM의 유동 및 열전달 특성에 관한 연구
주재황(Jai-Hwang Joo),강보선(Bo-Seon Kang),강기주(Ki-Ju Kang) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.1
Recently, ultra-lightweight materials with open, periodic cell structures take much attention owing to its potential for multi-functionality such as load bearing, thermal dissipation, and actuation. This paper presents experimental results on the fluid flow and heat transfer characteristics for the Wire-woven Bulk Kagome (WBK) composed of aluminum 1100 wires. The overall pressure drop and heat transfer of the WBK specimen was experimentally investigated under forced air convection condition. The pressure loss and heat transfer performance of the aluminum WBK were compared with other heat dissipation media. It was shown that heat transfer characteristics depended on relative density and surface area density. Comparison with metal foams and other heat dissipation media such as packed beds, lattice frame materials, louvered fins, and others suggests that the aluminum WBK competes favorably with the best available heat dissipation media in heat transfer performance.
알루미늄 나선형 와이어로 직조된 다층 Kagome truss PCM의 유동 및 열전달 특성에 관한 연구
주재황(Jai-Hwang Joo),강보선(Bo-Seon Kang),강기주(Ki-Ju Kang) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
Recently, ultra-lightweight materials with open, periodic cell structures take much attention owing to its potential for multi-functionality such as load bearing, thermal dissipation, and actuation. This paper presents experimental results on the hydraulic and heat transfer characteristics for the Wire-woven Bulk Kagome(WBK) composed of aluminum 1100 wires. The overall pressure drop and heat transfer of the WBK specimen have been experimentally investigated under forced air convection condition. The pressure loss and heat transfer performance of the aluminum WBK are compared with other heat dissipation media. It was shown that heat transfer depended on relative density and surface area density. Comparison with metal foams and other heat dissipation media such as packed beds, lattice frame materials, louvered fins, and other materials suggests that the aluminum WBK competes favorably with the best available heat dissipation media in heat transfer performance.
확장금속망 공정으로 제작된 옥테트 트러스 다공질 금속 (Ⅰ)
주재황(Jai-Hwang Joo),이동석(Dong-Seok Lee),전인수(Insu Jeon),강기주(Ki-Ju Kang) 대한기계학회 2007 大韓機械學會論文集A Vol.31 No.11
This paper presents a new way for fabricating sandwich plates with tetrahedral truss cores. The tetrahedral truss cores are manufactured through metal expanding and bending process and then brazed with solid face sheets. The properties of sandwich plates with the tetrahedral truss cores composed of a wrought steel SS41 under compression and shear loading have been investigated. Good agreement is observed between the measured and predicted peak strengths. Comparisons with normalized compressive strength for other cellular metals have indicated that the tetrahedral truss structures outperform aluminum open cell forms and woven core sandwich plates.
준 카고메 트러스 심재를 갖는 최적화된 샌드위치 판재의 굽힘하중 하에서의 기계적 성능
임채홍,주재황,강기주,Lim, Chai-Hong,Joo, Jai-Hwang,Kang, Ki-Ju 대한기계학회 2007 大韓機械學會論文集A Vol.31 No.10
Three kinds of metallic sandwich panels with quasi-Kagome truss cores have been analyzed on their mechanical behaviors subjected to bending load. According to the results of previous work on the optimal design, they were designed to have similarly high strength per weight with the identical overall sizes, i.e., the total length, the width, the core height. Differences were in the face sheet thickness and/or the thickness of the metal sheet from which the core was fabricated through expanding and bending processes. Under the bending load, they performed well as designed, as far as the maximum load is concerned. However, after the maximum load, the load-displacement curves were different each other depending on the slenderness ratio of the truss elements composing the quasi-Kagome truss cores and the face sheet thickness. Namely, the slenderness ratio and the face sheet thickness governed stability of the elastic and plastic buckling. Therefore, if energy absorption characteristics or structural stability as well as the maximum load capacity are to be achieved, the sandwich panel with thick truss members and thick face sheet should be selected.
벌크형 와이어 직조 카고메 트러스 PCM의 압축거동에 미치는 와이어직경/피치비의 영향
최지은(Ji-Eun Choi),주재황(Jai-Hwang Joo),강기주(Ki-Ju Kang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
According to pervious works, the compression, shear and bending strength of Wire-woven Bulk Kagome cellular metals are compare able to those expected for Kagome trusses with ideal configuration, which are composed of straight struts. The results could be regarded unexpected or even doubtable if it is considered that WBK is composed of curved struts and that the main failure mechanism of WBK is buckling of the struts. This work intends to answer the question about the unexpected high strength of WBK. For the purpose, geometric and material parameters related to compression strength of WBK are screened and then the effect of each parameter is evaluated by finite element analysis on the unit cell of WBK under Periodic boundary condition.
박종선(Jong Sun Park),주재황(Jai Hwang Joo),이기원(Ki Won Lee),강기주(Ki Ju Kang) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4
Recently, a new periodic cellular metal (PCM) named as Wire-woven Bulk Kagome (WBK) was introduced. The mechanical strength and stiffness of WBK have been theoretically estimated on the assumption that WBK is composed of straight struts. However, in reality WBK is assembled with helically-formed wires. Consequently, the struts are curved, which resulted in errors in estimation based on the previous theoretical solution. In this work, to improve the theoretical solutions, the truss waviness effect is taken into account to estimate the strength and stiffness of WBK. And the results are compared with those measured by experiments and estimated by finite element analyses.
옥테트와 카고메 트러스 구조를 갖는 벌크형 PCM의 압축거동
현상일(Sangil Hyun),주재황(Jai-Hwang Joo),강기주(Ki-Ju Kang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Defect sensitivity of bulk PCMs (periodic cellular metals) composed of Kagome trusses to mechanical behaviors subjected to compression was compared with a counterpart composed of octet trusses. To investigate the mechanical characteristics of bulk PCMs composed of the two trusses, a hybrid approach was taken in this work. First, assuming perfectly uniform structure and deformation of bulk PCMs, the behavior of the bulk PCMs composed of infinite number of trusses was simulated by FE analysis for a unit cell with periodic boundary conditions. From the results, the force-displacement response of a single strut composing the trusses in each bulk PCM was estimated. Then, the effects of geometric imperfections and the inhomogeneous material properties were evaluated by network analyses, in which the force-displacement responses were used to characterize mechanical behaviors of the networks. The imperfections were modeled to have Gaussian distributions, and the analysis results of the two bulk PCMs were compared to evaluate their defect sensitivities. Consequently, the bulk PCMs composed of octet trusses were found to be more sensitive to the property imperfections than those of Kagome trusses.