• Title/Summary/Keyword: composite element

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Multi-objective optimization of tapered tubes for crashworthiness by surrogate methodologies

  • Asgari, Masoud;Babaee, Alireza;Jamshidi, Mohammadamin
    • Steel and Composite Structures
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    • v.27 no.4
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    • pp.427-438
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    • 2018
  • In this paper, the single and multi-objective optimization of thin-walled conical tubes with different types of indentations under axial impact has been investigated using surrogate models called metamodels. The geometry of tapered thin-walled tubes has been studied in order to achieve maximum specific energy absorption (SEA) and minimum peak crushing force (PCF). The height, radius, thickness, tapered angle of the tube, and the radius of indentation have been considered as design variables. Based on the design of experiments (DOE) method, the generated sample points are computed using the explicit finite element code. Different surrogate models including Kriging, Feed Forward Neural Network (FNN), Radial Basis Neural Network (RNN), and Response Surface Modelling (RSM) comprised to evaluate the appropriation of such models. The comparison study between surrogate models and the exploration of indentation shapes have been provided. The obtained results show that the RNN method has the minimum mean squared error (MSE) in training points compared to the other methods. Meanwhile, optimization based on surrogate models with lower values of MSE does not provide optimum results. The RNN method demonstrates a lower crashworthiness performance (with a lower value of 125.7% for SEA and a higher value of 56.8% for PCF) in comparison to RSM with an error order of $10^{-3}$. The SEA values can be increased by 17.6% and PCF values can be decreased by 24.63% by different types of indentation. In a specific geometry, higher SEA and lower PCF require triangular and circular shapes of indentation, respectively.

Axial compressive behavior of special-shaped concrete filled tube mega column coupled with multiple cavities

  • Wu, Haipeng;Qiao, Qiyun;Cao, Wanlin;Dong, Hongying;Zhang, Jianwei
    • Steel and Composite Structures
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    • v.23 no.6
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    • pp.633-646
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    • 2017
  • The compressive behavior of special-shaped concrete filled tube (CFT) mega column coupled with multiple cavities is studied by testing six columns subjected to cyclically uniaxial compressive load. The six columns include three pentagonal specimens and three hexagonal specimens. The influence of cavity construction, arrangement of reinforcement, concrete strength on failure feature, bearing capacity, stiffness, and residual deformation is examined. Experimental results show that cavity construction and reinforcements make it possible to form a combined confinement effect to in-filled concrete, and the two groups of special-shaped CFT columns show good elastic-plastic compressive behavior. As there is no axial bearing capacity calculation method currently available in any Code of practice for special-shaped CFT columns, values predicted by normal CFT column formulas in GB50936, CECS254, ACI-318, EC4, AISCI-LRFD, CECS159, and AIJ are compared with tested values. The calculated values are lower than the tested values for most columns, thus the predicted bearing capacity is safe. A reasonable calculation method by dividing concrete into active and inactive confined regions is proposed. And high accuracy shows in estimating special-shaped CFT columns either coupled with multiple cavities or not. In addition, a finite element method (FEM) analysis is conducted and the simulated results match the test well.

Flexural performance of cold-formed square CFST beams strengthened with internal stiffeners

  • Zand, Ahmed W. Al;Badaruzzaman, W.H. Wan;Ali, Mustafa M.;Hasan, Qahtan A.;Al-Shaikhli, Marwan S.
    • Steel and Composite Structures
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    • v.34 no.1
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    • pp.123-139
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    • 2020
  • The tube outward local buckling of Concrete-Filled Steel Tube (CFST) beam under high compression stress is still considered a critical problem, especially for steel tubes with a slender section compared to semi-compact and compact sections. In this study, the flexural performance of stiffened slender cold-formed square tube beams filled with normal concrete was investigated. Fourteen (14) simply supported CFST specimens were tested under static bending loads, stiffened with different shapes and numbers of steel stiffeners that were provided at the inner sides of the tubes. Additional finite element (FE) CFST models were developed to further investigate the influence of using internal stiffeners with varied thickness. The results of tests and FE analyses indicated that the onset of local buckling, that occurs at the top half of the stiffened CFST beam's cross-section at mid-span was substantially restricted to a smaller region. Generally, it was also observed that, due to increased steel area provided by the stiffeners, the bending capacity, flexural stiffness and energy absorption index of the stiffened beams were significantly improved. The average bending capacity and the initial flexural stiffness of the stiffened specimens for the various shapes, single stiffener situations have increased of about 25% and 39%, respectively. These improvements went up to 45% and 60%, for the double stiffeners situations. Moreover, the bending capacity and the flexural stiffness values obtained from the experimental tests and FE analyses validated well with the values computed from equations of the existing standards.

Development of Main Wing Structure of Long Endurance Electric Powered UAV (24시간 장기체공 전기 동력 무인항공기 주익 구조 개발)

  • Park, Sang Wook;Shin, Jeong Woo;Park, Ill Kyung;Lee, Mu-Hyoung;Woo, Dae Hyun;Kim, Sung Joon;Ahn, Seok Min
    • Aerospace Engineering and Technology
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    • v.12 no.1
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    • pp.1-9
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    • 2013
  • In order to increase endurance flight efficiency of long endurance electric powered UAV with solar cell, the light weight airframe design techniques are important. In this paper, the design of the main wing of electric powered UAV manufactured using Mylar film and fiber reinforced composite was conducted in order to achieve weight reduction and structural integrity of the structure. The shape of spar and size were determined using beam theory analysis. The finite element analysis of the wing was performed under various load condition derived from flight environment of EAV-2H. Finally, the static strength test of the main wing was conducted to verify structural integrity. It was found that the developed main wing weigh less than 42% than the previous EAV-2 and the main wing passed static strength test under ultimate load.

Long-term structural analysis and stability assessment of three-pinned CFST arches accounting for geometric nonlinearity

  • Luo, Kai;Pi, Yong-Lin;Gao, Wei;Bradford, Mark A.
    • Steel and Composite Structures
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    • v.20 no.2
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    • pp.379-397
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    • 2016
  • Due to creep and shrinkage of the concrete core, concrete-filled steel tubular (CFST) arches continue to deform in the long-term under sustained loads. This paper presents analytical investigations of the effects of geometric nonlinearity on the long-term in-plane structural performance and stability of three-pinned CFST circular arches under a sustained uniform radial load. Non-linear long-term analysis is conducted and compared with its linear counterpart. It is found that the linear analysis predicts long-term increases of deformations of the CFST arches, but does not predict any long-term changes of the internal actions. However, non-linear analysis predicts not only more significant long-term increases of deformations, but also significant long-term increases of internal actions under the same sustained load. As a result, a three-pinned CFST arch satisfying the serviceability limit state predicted by the linear analysis may violate the serviceability requirement when its geometric nonlinearity is considered. It is also shown that the geometric nonlinearity greatly reduces the long-term in-plane stability of three-pinned CFST arches under the sustained load. A three-pinned CFST arch satisfying the stability limit state predicted by linear analysis in the long-term may lose its stability because of its geometric nonlinearity. Hence, non-linear analysis is needed for correctly predicting the long-term structural behaviour and stability of three-pinned CFST arches under the sustained load. The non-linear long-term behaviour and stability of three-pinned CFST arches are compared with those of two-pinned counterparts. The linear and non-linear analyses for the long-term behaviour and stability are validated by the finite element method.

Influence of the cylinder height on the elasto-plastic failure of locally supported cylinders

  • Jansseune, Arne;De Corte, Wouter;Vanlaere, Wesley;Van Impe, Rudy
    • Steel and Composite Structures
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    • v.12 no.4
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    • pp.291-302
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    • 2012
  • Frequently, steel silos are supported by discrete supports or columns to permit easy access beneath the barrel. In such cases, large loads are transferred to the limited number of supports, causing locally high axial compressive stress concentrations in the shell wall above the supports. If not dealt with properly, these increased stresses will lead to premature failure of the silo due to local instability in the regions above the supports. Local stiffening near the supports is a way to improve the buckling resistance, as material is added in the region of elevated stresses, levelling these out to values found in uniformly supported silos. The aim of a study on the properties of local stiffening will then be to increase the failure load, governed by an interaction of plastic collapse and elastic instability, to that of a discrete supported silo. However, during the course of such a study it was found that, although the failure remains local, the cylinder height is also a parameter that influences the failure mechanism, a fact that is not properly taken into account in current design practice and codes. This paper describes the mechanism behind the effect of the cylinder height on the failure load, which is related to pre-buckling deformations of the shell structure. All results and conclusions are based on geometrically and materially non-linear finite element analyses.

Analysis of mixed mode crack problems for anisotropic composite laminates using the $J_k$ integral ($J_k$ 적분을 이용한 이방성 복합적층판에 대한 혼합 모우드 파괴문제의 해석)

  • 주석재;홍창선
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.3
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    • pp.479-489
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    • 1989
  • The $J_{k}$ integral method for determining mixed mode stress intensity factors separately in the cracked anisotropic plate is developed. Stress intensity factors are indirectly determined from the values of $J_{1}$ and $J_{2}$. The $J_{2}$ integral can be evaluated efficiently from a finite element solution, neglecting the contribution from the portion of the integration contour along the crack faces, by selecting the integration contour in the vicinity of the crack tip. Using functions of a complex variable, the complete relations between $J_{1}$, $J_{2}$ and $K_{I}$ , $K_{II}$ for anisotropic materials are derived conveniently by selecting narrow rectangular contours shrinking to the crack tip. Compared to the existing path independent integral methods, the present method does not involve calculating the auxiliary solution and hence numerical procedures become quite simple. Numerical results to various problems are given and demonstrate the accuracy, stability and versatility of the method.

Numerical study on buckling of steel web plates with openings

  • Serror, Mohammed H.;Hamed, Ahmed N.;Mourad, Sherif A.
    • Steel and Composite Structures
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    • v.22 no.6
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    • pp.1417-1443
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    • 2016
  • Cellular and castellated steel beams are used to obtain higher stiffness and bending capacity using the same weight of steel. In addition, the beam openings may be used as a pass for different mechanical fixtures such as ducts and pipes. The aim of this study is to investigate the effect of different parameters on both elastic and inelastic critical buckling stresses of steel web plates with openings. These parameters are plate aspect ratio; opening shape (circular or rectangular); end distance to the first opening; opening spacing; opening size; plate slenderness ratio; steel grade; and initial web imperfection. The web/flange interaction has been simplified by web edge restraints representing simply supported boundary conditions. A numerical parametric study has been performed through linear and nonlinear finite element (FE) models, where the FE results have been verified against both experimental and numerical results in the literature. The web plates are subject to in-plane linearly varying compression with different loading patterns, ranging from uniform compression to pure bending. A buckling stress modification factor (${\beta}$-factor) has been introduced as a ratio of buckling stress of web plate with openings to buckling stress of the corresponding solid web plate. The variation of ${\beta}$-factor against the aforementioned parameters has been reported. Furthermore, the critical plate slenderness ratio separating elastic buckling and yielding has been identified and discussed for two steel grades of DIN-17100, namely: ST-37/2 and ST-52/3. The FE results revealed that the minimum ${\beta}$-factor is 0.9 for web plates under uniform compression and 0.7 for those under both compression and tension.

Numerical and Experimental Investigation on Impact Performance of Fiber Metal Laminates Based on Thermoplastic Composites (열가소성 복합재료를 기반한 섬유금속적층판의 충격 거동에 관한 실험 및 수치적 연구)

  • Lee, Byoung-Eon;Kang, Dong-Sik;Park, Eu-Tteum;Kim, Jeong;Kang, Beom-Soo;Song, Woo-Jin
    • Transactions of the Korean Society of Automotive Engineers
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    • v.24 no.5
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    • pp.566-574
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    • 2016
  • Fiber metal laminates, which are hybrid materials consisting of metal sheets and composite layers, have contributed to aerospace and automotive industries due to their reduced weight and improved damage tolerance characteristics. In this study, the impact performance of the laminates, which are comprised of a self-reinforced polypropylene and two aluminum sheets, and the pure aluminum alloy sheet material were investigated experimentally via numerical simulation. In order to compare the impact performance, the laminates and aluminum alloy were examined by assessing the impact force, energy time histories, and specific energy absorption. ABAQUS is a commercial software that is used to simulate the actual drop-weight tests. Based on this study, it is noted that the impact performance of the laminates was superior to that of the aluminum alloy. In addition, a good agreement between the experimental and numerical results can be achieved when the impact force and energy time histories from the experiments and the numerical simulations are compared.

Design and Evaluation of Intelligent Helmet Display System (지능형 헬멧시현시스템 설계 및 시험평가)

  • Hwang, Sang-Hyun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.5
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    • pp.417-428
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    • 2017
  • In this paper, we describe the architectural design, unit component hardware design and core software design(Helmet Pose Tracking Software and Terrain Elevation Data Correction Software) of IHDS(Intelligent Helmet Display System), and describe the results of unit test and integration test. According to the trend of the latest helmet display system, the specifications which includes 3D map display, FLIR(Forward Looking Infra-Red) display, hybrid helmet pose tracking, visor reflection type of binocular optical system, NVC(Night Vision Camera) display, lightweight composite helmet shell were applied to the design. Especially, we proposed unique design concepts such as the automatic correction of altitude error of 3D map data, high precision image registration, multi-color lighting optical system, transmissive image emitting surface using diffraction optical element, tracking camera minimizing latency time of helmet pose estimation and air pockets for helmet fixation on head. After completing the prototype of all system components, unit tests and system integration tests were performed to verify the functions and performance.