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1
Wang, Lyang Suan. "Automating Parametric Redesign of Structural Thin-Walled Frames Based On Topology Optimized Structure." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu156618342438725.
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Kolhatkar, Tanmay. "Nonlinear dynamic interactions between a rigid attachment bolted to a thin-walled sheet metal structure." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587124580918153.
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Sonje, Abhijit Ravindra. "Experimental and finite element investigation into the effects of manufacturing variability on the dynamic response of a bolted interface between a bracket and a thin-walled sheet metal structure." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546418059243072.
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Achour, Belkacem. "Nonlinear behaviour of thin walled bars." Thesis, Cardiff University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314695.
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Zheng, Li Ph D. Massachusetts Institute of Technology. "Fracture of welded aluminum thin-walled structures." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/35629.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2006.Includes bibliographical references (leaves 269-279).
A comprehensive methodology was developed in the thesis for damage prediction of welded aluminum thin-walled structures, which includes material modeling, calibration, numerical simulation and experimental verification. An extensive experimental program was conducted on large-scale welded panels used on Inter City Express (ICE) high-speed European passenger trains. These panels consist of geometrically complex extrusions, which are welded together to form the final structure. A wealth of data was generated to validate the proposed methodology. The current work has demonstrated the efficiency and robustness required for mainstream industrial applications. As the first step, a local fracture criterion was validated on two types of aluminum components without welds: (i) S-rails under quasi-static and dynamic axial loading; (ii) large-scale extruded aluminum panels under 4-point bending. With the fracture parameter calibrated from uniaxial tensile tests, numerical simulations gave excellent predictions of crack formation for test articles. A novel technique was developed to calibrate heterogeneous weldments for plasticity and fracture. This technique eliminates the need for machining and testing of miniature tensile specimens, cut from different zones within the weldment.
(cont.) The calibrated data was validated by comparing the numerical results with small and intermediate-scale tests. Excellent agreement was achieved. A wide range of aluminum weldments, including those developed as part of this study and relevant examples found in the literature, were examined from the point of view of microstructure, hardness distributions, stress-strain relations, etc. This study concludes that aluminum weldments exhibit very different mechanical characteristics than comparable steel weldments considering the above factors. The relative strength mismatch ratio between the weld zone and the Coarse Grain Heat Affected Zone (CGHAZ) MR, was identified as the most critical parameter for the global load/deformation response, and for fracture initiation of typical aluminum weld joints. Finally, a unique series of large-scale Mode I and III fracture tests was performed on full-scale welded ICE panels. The mechanism for crack initiation and growth under these two types of loadings was then investigated numerically and compared with the test results. Prediction of crack growth using the discrete element removal technique in combination with the proposed fracture locus, was shown to be accurate and robust.
(cont.) The most impressive result from the Mode I simulation was its ability to model a sudden jump of the crack from the weld zone to the HAZ, which was witnessed in the tests. Despite the differences in global loading from Mode I and Mode III cases, fracture in both loading modes was shown to be tension dominant. The new technique is now ready for industrial applications.
by Li Zheng.
Ph.D.
6
Kwok, Raymond Moon Keung. "Mechanics of damaged thin-walled cylindrical shells." Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/993/.
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Al-Sheikh, Abdelraouf. "Behaviour of thin-walled structures under combined loads." Thesis, Loughborough University, 1985. https://dspace.lboro.ac.uk/2134/7413.
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The thesis is concerned with the theory of thin-walled beams of open section. The aim is to formulate a general beam element for analysis of this type of structure. Thus a general stiffness matrix for the element, and a transformation matrix for loads and displacements with respect to centroid and shear centre were derived, by taking into consideration the value of-bimoment due to an axial force offset from the shear centre. Internal forces including bimoments, and global displacements including warping were calculated, and the stress distributions on the cross-sections of a beam at each-element node, were evaluated. The problem of buckling of thin-walled beams was treated using a finite strip program which was formulated to solve problems with the following combination of stresses: a) Linearly distributed axial stresses b) Uniform lateral stresses c) Uniform shear streses The results for beams of cruciform, box and channel sections, under uniform axial stresses and linearly distributed axial stresses, also accounting for flexural stresses, were conpared with other theoretical and some experimental results. The agreement was satisfactory. A series of, laboratory tests on beams of channel sections under compression were carried out. The recorded failure load and critical buckling load, computed by the Southwell plot method, were compared with the finite strip results and satisfactory agreement was observed.
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Zhang, Boshu. "Bistable and multi-stable thin-walled structures." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:05e0e48f-2da6-4d53-914a-cc1b46b9e87d.
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This study aims to comprehend the bistable and multi-stable behaviour of flexible straws with the intention of utilising it for future engineering applications. This behaviour is achieved by the multiple inversions of conical frustum shells within the corrugation of a flexible straw. This study examined the effects of various material models, geometry variables and loading methods on the inversion of close-top and open-top conical frustum shells via experiments and FEM simulations. This thesis consists of three main parts, and the second and the third parts are complementary to each other: First, we investigated the effects of applying a uniform vertical load to the upper rim of open-top frustum shells via FEM simulations. A reference model was simulated based on the measurements of an ordinary polypropylene flexible straw specimen, using two material models - linear elastic and elastically perfectly plastic. The effects of the interactions between frusta of the corrugated segment of a flexible straw were also studied by evaluating the difference in responses between an individual frustum and conjugated models of two or three frusta. It was found that by constraining the rotation of its bottom rim, an individual frustum can fairly reproduce the complex bistable behaviour of the shorter frustum within the corrugated part of a flexible straw. Furthermore, detailed parametric studies that focused on the effects of various geometric parameters were conducted and generalised formulas that predicted the critical force were derived. A comparison between the simulated results and the analytical model in predicting progressive inversion was made to distinguish the geometric boundaries that separate the one-off snap-through to the progressive inversion of frustum shells. Next, the behaviour of close-top frustum shells in response to vertical point loading at various locations on the top surface was evaluated. A hyperelastic material was used to fabricate the physical specimens. During the experiments, the corresponding deformed shapes were recorded by 3D scanning in addition to measurements of the displacement and reaction force. We observed a close resemblance between the experimental and FEM simulated results, which validated the FEM models. Two local peaks were observed before the structure was fully inverted into its secondary stable state and the overall critical force of the structure was defined by the higher one of the two. The relationship between their magnitudes and the loading locations was analysed and an optimal loading location which gave the minimum critical force was proposed and verified by additional simulations. Furthermore, generalised formulas in predicting critical force were also acquired based on parametric studies. The optimal loading location was found to be constant in spite of variations in height and thickness. The third part of this thesis discussed the effects of lateral point loading on both close-top and open-top frustum shells at various locations on the side surface and supplemented the second part. It is found that the removal of the top surface could cause the critical force to decrease if a point load was applied laterally. Moreover, we were able to fully invert the structure with a lower critical force through lateral loading in comparison to vertical loading.
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Howells, Hugh Alan. "Collapse behaviour of space trusses with thin-walled members." Thesis, University of Surrey, 1985. http://epubs.surrey.ac.uk/1038/.
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Hamid, A. B. A. "Bending of thin-walled beams of shallow open section." Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303260.
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Nemir, M. T. M. "Finite element stability analysis of thin-walled steel structures." Thesis, University of Salford, 1985. http://usir.salford.ac.uk/2219/.
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Recent applications in the use of light gauge steel members have been concerned with developing large scale systems built entirely from cold-formed steel members. An explicit analysis of such structures is complicated by the different phenomena that the structure may be prone to during loading. In particular, elastic buckling phenomena is an important consideration in the design of such structures since the load at which buckling occurs often provides a close upper bound to the carrying capacity of the structure. The first part of this two-part thesis (Part I, Chaptersl-8) has been devoted to general methods of analysis of the torsional-flexural buckling of thin-walled structures. A review of previous investigations and the available methods of solution is presented. A general finite element formulation of the torsional-flexural buckling of thin-walled structures has been derived. The resulting elastic geometric matrix can be used to analyse structures with monosymmetrical members. It also includes the effect of sectorial-monosymmetry for cross-sections without any axis of symmetry. A general transformation matrix has been developed to allow for the application of the finite element method to the three-dimensional elastic stability analysis of space and portal frames. The validity and accuracy of the new finite element formulation have been checked by analysing a number of different elastic lateral buckling problems for which exact or highly accurate solutions by other techniques are available. An experimental program was carried out on simply supported cold-formed steel z-beams. The first part of this program was undertaken to check the validity of the finite element calculations of the bimoments caused by nonuniform torsion. The second part was devoted to elastic lateral buckling of z-beams under combined bending and torsion. The second part of this thesis (Part II, Chapter 9) deals with the analysis of hipped roof structures with corrugated steel roof sheeting. A simple theoretical model has been suggested. The model has been used to perform an elastic linear analysis of the behaviour of two types of the hipped roof structures. The theoretical results are compared with previous experimental results for these two structures.
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Kim, Ji Hoon. "Conceptual Design Tools for Hybrid Joints for Thin-Walled Structures." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595464214740813.
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Barlow, Analise. "Strength Investigation of Damaged and Repaired Thin-Walled Composite Structures." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7714.
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The purpose of this research was to quantify the strength of novel composite repair methods for thin-walled composite structures. Carbon/epoxy plates were manufactured and repairs were made at Gloyer-Taylor Laboratories. At BYU, specimens were damaged in a controlled and repeatable process. Three damage modes were implemented: impact, groove, and abrasive damage. Tensile strength tests were performed on control, damaged, and repaired specimens. Four 24 x 24 in (60 x 60 cm) carbon/epoxy plates were received. Each plate was made up of seven plies cured together with epoxy resin for a nominal total thickness of 0.04 in (1.02 mm). The thickness, however, was not uniform: each plate had a smooth side and a wavy side. This resulted in inconsistent damage depth. The plates were cut at BYU using a water-jet cutter into 1 in. (25.4 mm) wide by 8 in. (203.2 mm) long test specimens. Test specimens were grouped into four categories: control specimens, specimens inflicted with damage by machining a shallow groove ranging from 0.012 — 0.018 in. (0.30 — 0.46 mm) deep, specimens inflicted with an abrasive-type damage ranging from 0.006 — 0.012 in. (0.15 — 0.30 mm) deep, and specimens subjected to impact damage ranging from 1.47 — 3.23 J. Five specimens were placed in the control group. Ten specimens were placed in each of the remaining damage groups. All ten specimens were damaged, but only five of each were sent to be repaired. The randomization of the thickness variable was prevented by the desire to repair damaged specimens as a group with a single repair rather than performing repairs on every individual specimen. The stress-strain behavior confirm the control specimens generally exhibited the best overall behavior, as expected. Most damaged specimens, including the repaired specimens, exhibited lower ultimate stress than the undamaged control specimens. The repaired specimens exhibited a higher initial stiffness than either the control or damaged specimens, due to the stiffness of the composite patch. Although repaired specimens should exhibit higher strength than damaged specimens, but this however, was not always the case. In particular, repairs did not improve the ultimate strength of the specimens damaged by abrasion. Correlations between the different damage types were developed, relating damage intensity and strength was approximately. This suggests further investigation is needed.
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Khong, Poh Wah. "Development of a microcomputer finite strip analysis for thin walled structures." Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314703.
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Buhagiar, Spiridione. "Behaviour and design of structures using thin-walled cold-formed sections." Thesis, Imperial College London, 1993. http://hdl.handle.net/10044/1/8557.
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Kim, Heung-Soo 1971. "Crash behavior of three dimensional thin-walled structures under combined loading." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8711.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2001.Includes bibliographical references (leaves 197-204).
For the weight efficient and crashworthy design of the structural body of a transportation system, a thorough understanding of crushing behavior of thin-walled structural members such as spot-welded sheet metal beams or extruded aluminum beams must be gained. In the present thesis, the complex crushing process of three-dimensional thin-walled structures subject to combined loading is solved analytically and numerically. Also, several new design concepts of strengthening "S" shaped frame with regard to weight efficiency and energy absorption are proposed. The mechanics of biaxial bending collapse and the collapse under combined bending and compression of thin-walled prismatic member are formulated and initial and subsequent shrinking interaction curves between the loading components are constructed. All the analytical derivations show close correlations with the results of the accompanying finite element analysis. Based on these two complex crushing mechanisms, the analytical derivation of the crushing resistance of three-dimensional "S" shaped frame is presented. Extensive study on the strengthening of the three-dimensional "S" shaped frame is performed with two types of internal reinforcing member, diagonally positioned sheet metal stiffener and ultralight metallic foam-filler. The optimization process involving varying the cross-sectional shape and the type of reinforcing member for both aluminum-extruded member and spot-welded hat-type cross-section member is developed.
(cont.) Using the analytical closed form expression of the crushing force of "S" shaped frame, the optimization process was performed based on Sequential Quadratic Programming. As a more realistic application, a front side rail and subframe structure of a mid size passenger car is analyzed. The combinational optimization process of "Design of Experiment" and "Response Surface Method" is carried out with the objective of weight minimization while maintaining the same or higher level of crash energy absorption. Both methods of internal reinforcement show high increase in the energy absorption and weight efficiency. The gain in terms of the specific energy absorption varies from 37% to 267% depending on the method. The proposed theoretical understanding and the design methodologies could be used as crash oriented early-stage component design tools.
by Heung-Soo Kim.
Ph.D.
17
White, Mark Dermot. "Collapse performance of thin walled box beam structures under axial impact loading." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240750.
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Bates, David Nicholas. "The mechanics of thin walled structures, with special reference to finite rotations." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38231.
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Eslimy-Isfahany, Seyed Hamid Reza. "Dynamic response of thin-walled composite structures with application to aircraft wings." Thesis, City University London, 1998. http://openaccess.city.ac.uk/7719/.
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A general analytical method is developed to study first the buckling behaviour and then the dynamic characteristics of thin-walled composite structures with the presence of bending torsion coupling. The dynamic response theory incorporates the dynamic stiffness matrix approach and generalised coordinates using the normal mode method. Structural components considered are thin-walled laminated composite beams with carbon-fibre, glass-fibre or other reinforced plastic lay-ups. The examples of such beams and their applications include aircraft wings, hulls of ships, helicopter and wind turbine blades. All assumptions made in this work are based on elastic linear small deflection beam theory so that the overall response of the beam is represented by the superposition of all individual responses in each mode. Bending-torsion coupling effects arising from the anisotropic nature of fibrous composites, as well as due to non-coincident centroid and geometric shear centre of the beam crosssection, are the main contributory elements when developing the theory. The beam is subjected to time dependent forces and/or torques which can be either concentrated or distributed over its length. Both deterministic and random loads are considered. An important example of a deterministic load is one that varies harmonically in time. The Duhamel integral is employed to calculate the response to any arbitrary time dependent deterministic load. The random load is assumed to be Gaussian, having both stationary and ergodic properties. The evaluation of the response to the random load is carried out in the frequency domain by relating the Power Spectral Density (PSD) of the output to that of the input using the complex frequency response function. A number of PSD distributions are considered as random input in order to determine the PSD of the dynamic response. Atmospheric turbulence, which is considered to be one of the forms of random excitation, is modelled using the von Karman spectra for composite aircraft wings. In order to establish the methodology, bending-torsion coupled metallic beams are first ,investigated. The bending-torsion coupling in such beams occurs due to non-coincident centroid and geometric shear centre of the beam cross-section. The natural frequencies and mode shapes in undamped free vibration are obtained and the significance of generalised ,mass in each of the modes of vibration is evaluated. A normal mode method is then used to compute the frequency response function of the beam. The effects of shear deformation rotatory inertia and axial load on the frequencies, mode shapes and dynamic response characteristics are demonstrated. It was essential at an earlier stage of the investigation to validate the chosen composite beam modelling. Among all the different techniques used to determine the rigidities of a composite beam, the buckling load provides a reasonable estimate. The elastic critical buckling loads of thin-walled laminated composite columns for various end conditions are established theoretically using the exact stiffness method. The effect of shear deformation on the buckling characteristics of the column is demonstrated. Experiments are carried out to establish the elastic critical buckling load of metallic and laminated composite columns. Theoretical predictions of the buckling behaviour are corroborated by experimental results and other published results. The investigation is then focused on composite beams, but the response analysis of such beams is significantly more complicated than that of their metallic counterparts. This is mainly due to anisotropic characteristics of laminated fibrous composites. A detailed parametric study with the variation of significant composite parameters, such as ply angle, is undertaken and the importance of the results are highlighted. A suite of computer programs in FORTRAN is developed to predict the bucklingbehaviour, the free vibration and the responsec characteristics of thin-walled composite or metallic beams based on the theory proposed. Numerical results are presented, fully discussed and commented on.
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Meshreki, Mouhab. "Dynamics of thin-walled aerospace structures for fixture design in multi-axis milling." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32614.
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Milling of thin-walled aerospace structures is a critical process due to the high flexibility of the workpiece. Available models for the prediction of the effect of the fixture on the dynamic response of the workpiece are computationally demanding and fail to represent practical cases for milling of thin-walled structures. Based on the analysis of typical structural components encountered in the aerospace industry, a generalized unit-element, with the shape of an asymmetric pocket, was identified to represent the dynamic response of these components. Accordingly, two computationally efficient dynamic models were developed to predict the dynamic response of typical thin-walled aerospace structures. These models were formulated using Rayleigh's energy and the Rayleigh-Ritz methods. In the first model, the dynamics of multi-pocket thin-walled structures is represented by a plate with torsional and translational springs. A methodology was proposed and implemented for an off-line calibration of the stiffness of the springs using Genetic Algorithms. In the second model, the dynamics of a 3D pocket is represented by an equivalent 2D multi-span plate. Through a careful examination of the milling of thin-walled structures, a new formulation was developed to represent the continuous change of thickness of the workpiece due to the material removal action. Two formulations, based on holonomic constraints and springs with finite stiffness, were also developed and implemented to take into account the effect of perfectly rigid and deformable fixture supports. All the developed models and formulations were validated numerically and experimentally for different workpiece geometries andLe fraisage des structures aérospatiales à parois minces est un processus critique dû à la flexibilité élevée de la pièce. Les modèles disponibles pour la prévision de l'effet du système de fixation sur la réponse dynamique de la pièce sont basés sur des méthodes numériques très lentes et n'arrivent pas à représenter les cas pratiques du fraisage des structures à parois minces. Basé sur une analyse des composants structurels typiques produits dans l'industrie aérospatiale, un élément généralisé de base avec la forme d'une poche asymétrique, a été identifié pour représenter la réponse dynamique de ces composants. En conséquence, deux modèles dynamiques efficaces ont été développés pour prévoir la réponse dynamique des structures aérospatiales types à parois minces. Ces modèles ont été formulés en utilisant les méthodes de Rayleigh et Rayleigh-Ritz. Dans le premier modèle, les réponses dynamiques des structures de poches multiples à parois minces sont représentées par des plaques avec des ressorts de torsion et de translation. Une méthodologie a été proposée et mise en application pour calibrer la rigidité des ressorts en utilisant les algorithmes génétiques. Dans le deuxième modèle, la réponse dynamique d'une poche en 3D est représentée par une plaque équivalente de multi-travées en 2D. À travers une étude approfondie du fraisage des structures à parois minces, une nouvelle formulation a été développée pour représenter le changement continu de l'épaisseur de la pièce durant l'usinage. Deux formulations, basées sur des contraintes holonomes et des ressorts avec des rigidités finies, ont été$
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Kiymaz, Guven. "Stability criteria for thin-walled box columns of high performance steel in axial compression." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248129.
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Tan, S. H. "Experimental and analytical studies of cold-formed thin-walled frameworks with semi-rigid connections." Thesis, University of Strathclyde, 1991. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21269.
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The behaviour of symmetrical single and double storey frameworks, constructed with cold-formed thin-walled plain channel members and semi-rigid connections, is investigated both analytically and experimentally in this thesis. A method of analysis, which is based on the matrix stiffness method, is developed and written into a computer programme. Generalized relationships between forces and displacements at the ends of an element with semi-rigid connections are derived and presented in a matrix form. The analysis takes account of local and torsional flexural buckling, connection strength and full moment-rotation behaviour, axial load effects, member plasticity, initial imperfection and shortening due to flexure. Using the theoretical analysis, the full loading history of the framework can be traced up to the final failure load. Results are finally presented graphically and in tabulated form. Details of an experimental investigation, which was undertaken to obtain the moment-rotation relationship of connections of various stiffnesses, are given. From the experimental data, a standardized theoretical model capable of representing the full moment-rotation behaviour of the connections is developed. Results from the model are compared with the experimental data and the agreement is generally very good. The theoretical model is incorporated in to the theoretical analysis to account for the change in stiffness of the connection during loading. For the frameworks, an extensive experimental investigation was undertaken to ascertain the accuracy of the theoretical analysis. Details of the fabrication of the specimens, construction of the frameworks, testing equipment and procedures are also presented. Results of the framework experimental investigation are compared with the theoretical predictions. The agreement between theory and experiment is shown to be very close in general. Some wholly theoretical numerical results are also presented and discussed. The findings of the investigation are summarized and the main conclusions are listed.
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El-Hammasi, S. A. "Behaviour of open restrained thin-walled concrete beams under interaction of bending and torsion." Thesis, University of Bristol, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373830.
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Walker, B. D. "A combined finite strip/finite element method for the analysis of partially prismatic thin-walled structures." Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375679.
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Khan, Jehan Zeb. "Static, dynamic and aeroelastic behaviour of thin-walled composite structures with application to aircraft wings." Thesis, City University London, 1992. http://openaccess.city.ac.uk/7992/.
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Theoretical and experimental investigations of the static and dynamic behaviour of thin-walled structures are carried out with the ultimate aim of improving prediction procedures for various aeroelastic phenomena. The dynamic stiffness matrix approach is used for structural idealization, while strip theory and Theodorsen's function C(k) are used for the aerodynamic idealization. The dynamic composite beam with with an axial load centroid, has been carried out using Special cases, that been identified and stiffness matrix for a thin-walled geometric and material coupling together (compressive or tensile) applied at the developed. An exact analysis was then the derived dynamic stiffness matrix. are derivatives of the general case have discussed. A three stage program was developed to compute various static and dynamic properties of thin-walled closed or open section composite beams. In the first stage, equivalent elastic constants (overall laminate moduli) were evaluated for a given stacking sequence and material properties. In the second stage, various sectional properties were computed. When the outputs from these two stages were combined, valuable data on sectional rigidities, mass per unit length, polar mass moment of inertia, and shear centre location from the centroid were obtained. In the third stage of the program, all these properties were used to compute the natural frequencies and normal mode shapes of thin-walled composite structures. These programs can be used individually as well as in a combined manner. An experimental investigation of composite thin plates with varying degrees of bending-torsion coupling was conducted. Flexural and torsional rigidities, natural frequencies, normal mode shapes and flutter speed and frequency were experimentally determined. The results obtained were in close agreement with the theoretical predictions. Various open composite sections were experimentally studied for their static and dynamic properties. The results demanded a more refined investigation of the theory. In addition to the experimental study of composite open sections, a parametric study of uncoupled and coupled frequencies of such sections with common boundary conditions was also conducted. Thin-walled closed aerofoil shaped cantilevered structures were tested to establish flexural and torsional rigidities, shear centre, and the polar-mass-moment of inertia. Natural frequencies and normal mode shapes were also determined. The aeroelastic behaviour of these sections was investigated to establish divergence and flutter characteristics. Comparisons of the experimental results with theoretical predictions of flutter speed and frequency were in general satisfactory and the results provided an insight into the aeroelastic behaviour of thin-walled composite beams. The results are discussed and commented on.
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Back, Sung-Yong. "A shear-flexible finite element model for lateral torsional buckling analysis of thin-walled open beams." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/20999.
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Lo, Patrick Kar-Leung. "Comparison of theory and experiment for flexural-torsional buckling of laminated composite columns." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/50051.
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Vlasov’s one-dimensional structural theory for thin-walled open section bars was originally developed and used for metallic elements. The theory was recently extended to laminated bars fabricated from advanced composite materials. The purpose of this research is to provide a study and assessment of the extended theory. The focus is on flexural and torsional-flexural buckling of thin-walled, open section, laminated composite columns. Buckling loads are computed from the theory using a linear bifurcation analysis, and are compared to available experimental data. Also, a geometrically nonlinear beam column analysis by the finite element method is developed from the theory. Results from the nonlinear compression response analysis are compared to limited available test data. The merits of the theory and its implementation are discussed.Master of Science
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Dababneh, Odeh. "Design, Analysis And Optimization Of Thin Walled Semi-monocoque Wing Structures Using Different Structural Idealizations In The Preliminary Design Phase." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613759/index.pdf.
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This thesis gives a comprehensive study on the effect of using different structural idealizations on the design, analysis and optimization of thin walled semi-monocoque wing structures in the preliminary design phase. In the design part, wing structures are designed by employing two different structural idealizations that are typically used in the preliminary design phase. In the structural analysis part, finite element analysis of one of the designed wing configurations is performed using six different one and two dimensional element pairs which are typically used to model the sub-elements of semi-monocoque wing structures. The effect of using different finite element types on the analysis results of the wing structure is investigated. During the analysis study, depending on the mesh size used, conclusions are also inferred with regard to the deficiency of certain element types in handling the true external load acting on the wing structure. Finally in the optimization part, wing structure is optimized for minimum weight by using finite element models which have the same six different element pairs used in the analysis phase. The effect of using different one and two dimensional element pairs on the final optimized
configurations of the wing structure is investigated, and conclusions are inferred with regard to the sensitivity of the optimized wing configurations with respect to the choice of different element types in the finite element model. Final optimized wing structure configurations are also compared with the simplified method based designs which are also optimized iteratively.
Based on the results presented in the thesis, it is concluded that with the simplified methods, preliminary sizing of the wing structures can be performed with enough confidence, as long as the simplified method based designs are also optimized. Results of the simplified method of analysis showed that simplified method is applicable to be used as an analysis tool in performing the preliminary sizing of the wing structure before moving on to more refined finite element based analysis.
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Saadé, Katy. "Finite element modeling of shear in thin walled beams with a single warping function." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211043.
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The considerable progress in the research and development of thin-walled beam structures responds to their growing use in engineering construction and to their increased need for efficiency in strength and cost. The result is a structure that exhibits large shear strains and important non uniform warping under different loadings, such as non uniform torsion, shear bending and distortion.A unified approach is formulated in this thesis for 3D thin walled beam structures with arbitrary profile geometries, loading cases and boundary conditions. A single warping function, defined by a linear combination of longitudinal displacements at cross sectional nodes (derived from Prokic work), is enhanced and adapted in order to qualitatively and quantitatively reflect and capture the nature of a widest possible range of behaviors. Constraints are prescribed at the kinematics level in order to enable the study of arbitrary cross sections for general loading. This approach, differing from most published theories, has the advantage of enabling the study of arbitrary cross sections (closed/opened or mixed) without any restrictions or distinctions related to the geometry of the profile. It generates automatic data and characteristic computations from a kinematical discretization prescribed by the profile geometry. The amount of shear bending, torsional and distortional warping and the magnitude of the shear correction factor is computed for arbitrary profile geometries with this single formulation.
The proposed formulation is compared to existing theories with respect to the main assumptions and restrictions. The variation of the location of the torsional center, distortional centers and distortional rotational ratio of a profile is discussed in terms of their dependency on the loading cases and on the boundary conditions.
A 3D beam finite element model is developed and validated with several numerical applications. The displacements, rotations, amount of warping, normal and shear stresses are compared with reference solutions for general loading cases involving stretching, bending, torsion and/or distortion. Some examples concern the case of beam assemblies with different shaped profiles where the connection type determines the nature of the warping transmission. Other analyses –for which the straightness assumption of Timoshenko theory is relaxed– investigate shear deformation effects on the deflection of short and thin beams by varying the aspect ratio of the beam. Further applications identify the cross sectional distortion and highlight the importance of the distortion on the stresses when compared to bending and torsion even in simple loading cases.
Finally, a non linear finite element based on the updated lagrangian formulation is developed by including torsional warping degrees of freedom. An incremental iterative method using the arc length and the Newton-Raphson methods is used to solve the non linear problem. Examples are given to study the flexural, torsional, flexural torsional and lateral torsional buckling problems for which a coupling between the variables describing the flexural and the torsional degrees of freedom occurs. The finite element results are compared to analytical solutions based on different warping functions and commonly used in linear stability for elastic structures having insufficient lateral or torsional stiffnesses that cause an out of plane buckling.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
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WANG, YONGBING. "STRUCTURAL BEHAVIOR AND DESIGN OF TWO CUSTOM ALUMINUM EXTRUDED SHAPES IN CUSTOM UNITIZED CURTAIN WALL SYSTEMS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1147722350.
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Шейченко, Роман Ігорович. "Забезпечення міцності тонкостінних конструкцій із підвищеними технічними характеристиками." Thesis, Національний технічний університет "Харківський політехнічний інститут", 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/41327.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата технічних наук (доктора філософії) за спеціальністю 05.02.09 "Динаміка та міцність машин" (13 – Механічна інженерія). – Національний технічний університет «Харківський політехнічний інститут», Харків, 2019. Потреби сучасної промисловості, транспорту і сфери послуг у інноваційних виробах із підвищеними техніко-економічними характеристиками останнім часом різко зростають. При цьому велику частку серед такої продукції займають тонкостінні машинобудівні конструкції, у яких раціонально поєднуються масові і характеристики міцності. У той же час на багато виробів (літаки, судна, рухомий склад залізниць, крани, перевантажувачі, ємності високого тиску, апарати хімічної промисловості, устаткування агропромислового комплексу) поширюються суворі офіційні правила і норми, спрямовані, у першу чергу, на забезпечення безпеки експлуатації. Відповідно, при проектних дослідженнях використовуються усталені методики розрахунку, а також традиційні технічні рішення. Незважаючи на тиск сталої практики, що схиляється до створення виробів у вигляді «клонів» давно створених аналогів, діє також протилежна тенденція. Вона породжується загальним прагненням до прогресу, навіть у консервативних областях діяльності, а також економічними міркуваннями. Більш того, багато споживачів інноваційних виробів установлюють свої додаткові вимоги до продукції, що спрямовані на продовження терміну служби конструкцій, підвищення їхньої продуктивності, інтенсивності експлуатаційних режимів або навантажувальної здатності. У цих обставинах, окрім нормативних обмежень, з’являються додаткові, що ускладнює виконання вимог до проектованих конструкцій. Таким чином, виникла і посилюється у своїй актуальності та важливості науково-практична задача розробки методів забезпечення міцності інноваційних тонкостінних машинобудівних конструкцій при дії комплексу експлуатаційних навантажень. Її постановка, розв’язання та впровадження у практику проектних досліджень склала мету, зміст і напрями дисертаційних досліджень. У дисертаційній роботі розв’язана науково-технічна задача, яка полягає в удосконалення методів і моделей для проектного забезпечення міцності тонкостінних машинобудівних конструкцій при дії комплексу експлуатаційних навантажень. У роботі для аналізу напружено-деформованого стану тонкостінних машинобудівних конструкцій застосовуються співвідношення теорії пружності і методу скінченних елементів. Формування геометричної форми досліджуваних конструкцій здійснювалося методами твердотільного і поверхневого моделювання. Для варіативної зміни структури і розмірів досліджуваних об’єктів адаптовано і розвинено метод узагальненого параметричного моделювання стосовно інноваційних тонкостінних машинобудівних конструкцій. Експериментальні дослідження здійснювалися методами тензометрії та акселерометрії. У ході виконання дисертаційного дослідження отримано наступні наукові результати: 1) проведено аналіз умов експлуатації, нормативних вимог, а також методів розрахунку тонкостінних машинобудівних конструкцій з урахуванням обмежень на міцність, і на цій основі визначені напрями дисертаційних досліджень; 2) удосконалено методи і моделі для обґрунтування проектних параметрів інноваційних тонкостінних машинобудівних конструкцій за критеріями міцності при дії комплексу експлуатаційних навантажень із урахуванням нормативних обмежень; 3) здійснено розв’язання низки прикладних задач проектного обґрунтування технічних рішень для тонкостінних машинобудівних конструкцій за критеріями міцності та довговічності; 4) здійснено розрахунково-експериментальні дослідження напружено- деформованого стану інноваційних тонкостінних машинобудівних конструкцій, які спроектовано на основі рекомендацій із застосуванням результатів дисертаційних досліджень;
5) впроваджено результати досліджень у виробництво.Тhesis for candidate of technical science degree (Philosophy Doctor) in speciality 05.02.09 – Dynamics and Strength of Machines (13 – mechanical engineering). – National Тechnical University «Kharkov Polytechnic Institute», Kharkiv, 2019. The needs of modern industry, transport and services in innovative products with increased technical and economic characteristics have recently been increasing dramatically. Large proportion of such products are thin-walled engineering structures, which rationally combine mass and strength characteristics. At the same time, strict rules and regulations are applied to many products (aircraft, ships, rolling stock, cranes, reloaders, high-pressure vessels, chemical industry equipment, agricultural equipment) for ensure the operation safety. Accordingly, design studies use established computational methods, as well as traditional technical solutions. In spite of pressure of established practice, which tends to create products as "clones" of long-created analogues, opposite trend also applies. It is generated by general aspiration for progress, even in conservative areas of activity, as well as economic considerations. Moreover, many consumers of innovative products set their additional requirements for products aimed at extending service life of structures, increasing their productivity, intensity of operating modes or load capacity. In these circumstances, in addition to regulatory restrictions, there are additional ones, which complicates the requirements fulfillment for projected designs. Thus, the scientific and practical task of developing methods for strength ensuring of innovative thin-walled engineering structures under action of operating loads complex has appeared and is intensified in its urgency and importance. Its formulation, solution and implementation to design studies practice is goal, content and directions of dissertation research. In the dissertation work the scientific and technical problem is solved, which consists in methods and models improvement for strength ensurance of thin-walled engineering structures under action of operational loads complex. In the work for stress-strain state analysis of thin-walled engineering structures the theory of elasticity ratios and the finite element method are used. Geometric shape formation of investigated structures was carried out by methods of solid state and surface modeling. For structure and size variation of studied objects, the method of generalized parametric modeling for innovative thin-walled engineering structures is adapted and developed. Experimental studies were carried out using strain gauge and accelerometer methods. In course of dissertation research the following scientific results were obtained: 1) an analysis of operating conditions, regulatory requirements, as well as analysis methods of thin-walled engineering structures taking into account the constrains on durability, and on this basis, the dissertation research directions were determined; 2) methods and models for design parameters justification of innovative thin-walled engineering structures according to strength criteria under action of operational loads complex, taking into account regulatory constraints are improved; 3) solution of a number of applied tasks of technical solutions substantiation for the thin-walled engineering structures according to strength and durability criteria; 4) computational and experimental studies of stress-strain state of innovative thin-walled engineering structures that are designed on the basis of recommendations with application of dissertation research results; 5) research results are introduced into production.
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Шейченко, Роман Ігорович. "Забезпечення міцності тонкостінних конструкцій із підвищеними технічними характеристиками." Thesis, Національний технічний університет "Харківський політехнічний інститут", 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/41324.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.02.09 – динаміка таміцність машин. Національний технічний університет «Харківський політехнічний інститут», Міністерство освіти і науки України, Харків, 2019.
Дисертація присвячена удосконаленню методів і моделей для проектного забезпечення міцності тонкостінних машинобудівних конструкцій при дії комплексу експлуатаційних навантажень. Обґрунтування раціональних параметрів і конструктивних рішень ТСМБК здійснюється за критеріями мінімізації маси, зниження напружень, підвищення терміну експлуатації. Ураховуються апроксимації залежностей критеріальних величин, що поступово локалізуються, від варійованих параметрів. Узагальненими параметрами виступають структура, проектно-технологічні рішення ТСМБК, конструктивні параметри і експлуатаційні режими. При цьому забезпечується розв’язання задач одиничного аналізу, багатоваріантних досліджень, а також обґрунтування раціональних проектно-технологічних рішень. На розвиток відомих підходів розглянуті наступні узагальнення: уніфікація, доцільність, ефективності, ідентифікація навантажень, верифікація, прогнозування, відлаштування. Здійснена також алгоритмізація запропонованих методів розрахунку НДС тонкостінних машинобудівних конструкцій на основі поєднання переваг універсальних і спеціальних систем. Проведено розв’язання низки прикладних задач. Обґрунтовано раціональні проектні параметри інноваційних ТСМБК. Представлено результати експериментальних досліджень інноваційних вагону-цистерни, вагону-платформи і крана-перевантажувача, які спроектовано і виготовлено на основі впровадження рекомендацій за підсумками дисертаційних досліджень.Thesis for the degree of Candidate of Technical Sciences in specialty 05.02.09 – Dynamics and strength of machines. National Technical University «Kharkiv Polytechnic Institute», Ministry of Education and Science of Ukraine, Kharkiv, 2019. The thesis is devoted to the improvement of methods and models for the design ensuring of the strength of thin-walled engineering structures under the action of operational loadings complex. The justification for rational parameters and design solutions for thin-walled engineering structures is carried out according to the criteria of mass minimizing, stresses reducing, and service life increasing. Various additional criteria such as cost, manufacturability, economy, energy efficiency, can be taken into account in the formation of the quality function. The dependences approximations of criterion values, which are gradually localized, from variable parameters are taken into account. The structure, design and technological solutions of thin-walled engineering structures, structural parameters and operating modes are the generalized parameters. This provides a solution to the problems of a single analysis, multivariate studies, as well as the justification for rational design and technological solutions. The following generalizations are considered: unification, expediency, efficiency, loading identification, verification, forecasting, tune-up in development of known approach. The algorithmization of proposed methods for calculating of the stress strain state of thin-walled engineering structures has also been carried out based on a combination of the advantages of universal and special systems. A number of applied problems are solved. Parametric finite element models of researched objects have been developed based on a set of studies of the stress-strain state of the power elements. The rational design parameters of innovative thin-walled engineering structures are determined. The results of experimental studies of innovative tank cars, platform cars and loading cranes, which are designed and manufactured based on the implementation of recommendations from dissertation research, are presented. Comparative experimental and computational studies of the structures stress-strain state were carried out. They are combined with certification tests, during which the stresses in the power elements were recorded. The operational loadings are determined which are acting on thin-walled structures. During the tests, regularities were established that determine the dependence of the loadings components on the structure from various factors. Verification of the numerical models parameters of thin-walled engineering constructions elements was carried out. Designed on the basis of researches innovative structures have improved technical and economic characteristics compared with similar ones.
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Le, Thanh Nam. "Nonlinear dynamics of lexible structures using corotational beam elements." Phd thesis, INSA de Rennes, 2013. http://tel.archives-ouvertes.fr/tel-00954739.
Full textAbstract:
The purpose of this thesis is to propose several corotational beam formulations for both 2D and 3D nonlinear dynamic analyse of flexible structures. The main novelty of these formulations is that the cubic interpolation functions are used to derive not only the internal force vector and the tangent stiffness matrix but also the inertial force vector and the dynamic matrix. By neglecting the quadratic terms of the local transversal displacements, closed-form expressions for the inertial terms are obtained for 2D problems. Based on an extensive comparative study of the parameterizations of the finite rotations and the time stepping method, and by adopting an approximation of the local rotations, two consistent and effective beam formulations for 3D dynamics are developed. In contrast with the first formulation, the second one takes into account the warping deformations and the shear center eccentricity. The accuracy of these formulations is demonstrated through several numerical examples.
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Kim, Sangseop. "Determination of Wall Thickness and Height when Cutting Various Materials with Wire Electric Discharge Machining Processes." BYU ScholarsArchive, 2005. https://scholarsarchive.byu.edu/etd/294.
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This thesis looks at the capabilities of cutting thin webs on Wire EDM machines that are difficult or impossible to machine using conventional methods. Covered is an investigation of how different material and web thickness affect the capability of machining thin-walled parts.
Five different metals are used for the test; Aluminum 6061 T6, Yellow Brass SS360, 420 Stainless Steel, D2 unheat-treated tool steel 25-30 RC, and D2 heat-treated tool steel 60-65 RC. The small parts were cut to a 6mm (0.2362 inch) height with six different wall thicknesses: 0.30mm (0.0118 inch), 0.25mm (0.0098 inch), 0.20mm (0.0078 inch), 0.15mm (0.0059 inch), 0.10mm (0.0039 inch), and 0.05mm (0.0020 inch). A Sodick AQ325L Wire EDM machine was utilized for testing.
The methods employed during the study include the following:
• Machine settings and offsets were limited to the default setting selected from the Sodick AQ325L database.
• Two different pre-test cuts were taken on the material to check for web bending during the cutting process.
• Hardness was tested for comparison of the web heights.
This thesis shows that bending increased as webs became thinner and that bending occurred toward the wire as the second side of the web was cut. Bending does affect the height of the web. Physical properties of materials also impacted the height of the web with the hardest material staying intact during the cutting process. This study shows that two factors, physical properties of materials and web thickness, significantly affect cutting results for thin web parts.
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Picault, Elia. "Un modèle de poutre à section mince flexible - Application aux pliages 3D de mètres rubans." Phd thesis, Aix-Marseille Université, 2013. http://tel.archives-ouvertes.fr/tel-00921931.
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Ce travail a pour cadre une collaboration entre le LMA et Thales Alenia Space. Nous nous intéressons au comportement des structures flexibles et plus particulièrement des mètres rubans qui ont la particularité de pouvoir, grâce à l'aplatissement de la section, s'enrouler ou développer des pliages localisés. Une première thèse a permis d'une part la mise au point d'un nouveau type de mètre ruban au déroulement maîtrisable thermiquement et d'autre part le développement d'un modèle plan de poutre à section flexible. Dans le travail de thèse présenté ici, nous proposons une version étendue de ce modèle adaptée à la simulation du comportement dynamique tridimensionnel des mètres rubans en grands déplacements et en grandes rotations. Ce modèle est dérivé de la théorie des coques et repose sur l'introduction d'hypothèses cinématiques et sthéniques adaptées. La déformation de la section est caractérisée par celle de sa ligne moyenne qui peut se déformer dans son plan par flexion et torsion mais non par extension, ainsi que hors de son plan par gauchissement de torsion. Les fortes variations de forme de la section dans son plan peuvent alors être décrites par une cinématique de type Elastica, tandis qu'une cinématique de type Vlassov est utilisée pour définir le gauchissement dans le repère local attaché à la section. Le modèle unidimensionnel est obtenu par intégration sur la section des expressions de la théorie des coques, une approche énergétique permet ensuite de formuler le problème associé qui est résolu grâce au logiciel de modélisation par éléments finis COMSOL.
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(6593015), Prathamesh Narendra Chaudhari. "DESIGN OF AN ORIGAMI PATTERNED PRE-FOLDED THIN WALLED TUBULAR STRUCTURE FOR CRASHWORTHINESS." Thesis, 2019.
Find full textAbstract:
Thin walled tubular structures are widely used in the automotive industry because of its weight to energy absorption advantage. A lot of research has been done in different cross sectional shapes and different tapered designs, with design for manufacturability in mind, to achieve high specific energy absorption.
In this study a novel type of tubular structure is proposed, in which predesigned origami initiators are introduced into conventional square tubes. The crease pattern is designed to achieve extensional collapse mode which results in decreasing the initial buckling forces and at the same time acts as a fold initiator, helping to achieve a extensional collapse mode. The influence of various design parameters of the origami pattern on the mechanical properties (crushing force and deceleration) are extensively investigated using finite element modelling. Thus, showing a predictable and stable collapse behavior. This pattern can be stamped out of a thin sheet of material.
The results showed that a properly designed origami pattern can consistently trigger a extensional collapse mode which can significantly lower the peak values of crushing forces and deceleration without compromising on the mean values. Also, a comparison has been made with the behavior of proposed origami pattern for extensional mode verses origami pattern with diamond fold.
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Morozov, Konstantin E. "Crashworthiness modelling of thin-walled composite structures." Thesis, 2003. http://hdl.handle.net/10413/4222.
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This thesis is concerned with the study of the crashworthiness of thin-walled composite structures. Composites are being used more and more in different fields of engineering, particularly, in aerospace and automotive industries because of their high strength-to-weight and stiffness-to-weight ratios, quality and cost advantages. More and more metal parts in cars for instance become or are already replaced by new advanced materials. Composite materials are included in these new advanced materials with the following advantages: weight reduction, corrosion resistance, aesthetics and style, isolation and the ability to integrate several parts into one single structural component. The introduction of new composite structural components (body
panels, bumpers, crash absorbers, etc.) requires the development and implementation of new approaches to structural analysis and design. Crashworthiness is one of the foremost goals of aircraft and automotive design. It depends very much on the response of various components which
absorb the energy of the crash. In order to design components for crashworthy structures, it is necessary to understand the effects of loading conditions, material behaviour, and structural response. Due to the complexity of the material structure (matrix reinforced with fibres) and specific mechanical properties the nature of transforming the collision kinetic energy into material deformation energy differs from that of conventional metal alloys. The energy absorption mechanics are different for the advanced composites and depend on the material structure (type of reinforcement) and structural design. The primary function of the energy absorption for the composites belongs to the progressive crushing of the materials themselves and structural
components (beams, tubes, etc.) made of such materials. Since the mechanics of composite materials and structural components differs substantially from the conventional applications there is a need to develop an appropriate way of modelling and analysis relevant to this problem. Currently there are a large variety of design approaches, test results, and research investigations into the problem under consideration depending on the type of composite material and design geometry of the parts. It has been found that in general an application of fibre reinforced plastics (FRP) to vehicle compartments can satisfy the structural requirements of the passenger
compartment including high strength and light weight. Implementation of new advanced composite materials provides the opportunity to develop designs of reliable structural composite parts in high volume for improved automotive fuel economy. Structural optimisation and crashworthiness of composite components should be incorporated into design calculations to control the mechanical performance. The introduction which follows describes the aims of the present study of the crashworthiness modelling and simulation of the structural response of thin-walled composite components which are subjected to various loading conditions relevant to vehicle design. The
research programme undertaken within the framework of this project includes development and validation of the modelling and simulation methodology applicable to the crashworthiness analysis of thin-walled composite structures. Development of computerised dynamic modelling of structural
components offers the capability of investigating the design parameters without building the actual physical prototypes. In this approach, the dynamic behaviour of the structure is simulated for specified external inputs, and from the corresponding response data the designer is able to determine its dynamic response characteristics, and estimate the crashworthiness of the structure in
vehicle engineering applications.Thesis (Ph.D.)-University of Natal, Durban, 2003.
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(7039910), Shantanu Ramesh Shinde. "Origami inspired design of thin walled tubular structures for impact loading." Thesis, 2019.
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Thin walled structures find wide applications in automotive industry as energy absorption devices. A great deal of research has been conducted to design thin walled structures, where the main objective is to reduce peak crushing forces and increase energy absorption capacity. With the advancement of computers and mathematics, it has been possible to develop 2D patterns which when folded turn into complex 3D structures. This technology can be used to develop patterns for getting structures with desired properties.
In this study, square origami tubes with folding pattern (Yoshimura pattern) is designed and studied extensively using numerical analysis. An accurate Finite Element Model (FEM) is developed to conduct the numerical analysis. A parametric study was conducted to study the influence of geometric parameters on the mechanical properties like peak crushing force, mean crushing force, load uniformity and maximum intrusion, when subjected to dynamic loading.
The results from this analysis are studied and various conclusions are drawn. It is found that, when the tube is folded with the pattern having specific dimension, the performance is enhanced significantly, with predictable and stable collapse. It is also found that the stiffness of the module varies with geometrical parameters. With a proper study it is possible to develop origami structures with functionally graded stiffness, the performance of which can be tuned as per requirement, hence, showing promising capabilities as an energy absorption device where progressive collapse from near to end impact end is desired.
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Mursi, Mohanad Civil & Environmental Engineering Faculty of Engineering UNSW. "The behaviour and design of thin walled concrete filled steel box columns." 2007. http://handle.unsw.edu.au/1959.4/40494.
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This thesis investigates the behaviour of hollow and concrete filled steel columns fabricated from thin steel plates. The columns are investigated under axial, uniaxial and biaxial loading. The currently available international standards for composite structures are limited to the design of concrete filled steel columns with compact sections and yield stress of steel up to 460 N/mm2. This thesis consists of both experimental and analytical studies and design recommendations for future use. Three comprehensive series of experimental tests are conducted on hollow and concrete filled steel columns. The principal parameters that have been considered in the test programmes are the slenderness of the component plates, the yield stress of the steel and the loading conditions. In the first test series, three slender hollow steel columns and three slender composite columns are tested under uniaxial loading. The steel utilised is mild steel. High strength steel is utilised in the second test programme. In this test series four stub columns, eight short columns and eight slender columns are tested, each set consists of four hollow and four composite columns. Short columns are tested under axial loading to investigate the confinement effect provided by the steel casing. Slender columns are tested under uniaxial loading to investigate the coupled instability of local and global buckling. The third test programme is quite novel and considers the behaviour of hollow and concrete filled steel columns fabricated with high strength structural steel plate and subjected to biaxial bending. In this test eight short columns and ten slender columns each of them consisting of hollow and composite columns are investigated under biaxial loading. Analytical models are developed herein to elucidate the behaviour of the hollow and composite columns considering cross section slenderness, yield stress and loading conditions. An iterative model considering the coupled global and local buckling in the elastic and plastic range incorporating material nonlinearities is developed to investigate the behaviour of slender columns fabricated from mild steel. An improved deformation control model is developed to investigate the behaviour of slender high strength steel columns considering the confinement effect and local and post-local buckling in the elastic and plastic range. Then a numerical model for biaxial bending is developed to study the behaviour of short and slender concrete filled high strength steel columns under biaxial loading incorporating interaction buckling considering material and geometric nonlinearities. The scope of the thesis presents a wide range of experimental and theoretical studies of an extremely novel nature. It demonstrates the benefit of confinement and the consideration of local and post-local buckling in the elastic and plastic range. It is hoped that this research will contribute to the area of composite steel-concrete structural applications.
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Moradi, Mohammadreza. "Structural applications of metal foams considering material and geometrical uncertainty." 2011. https://scholarworks.umass.edu/dissertations/AAI3482649.
Full textAbstract:
Metal foam is a relatively new and potentially revolutionary material that allows for components to be replaced with elements capable of large energy dissipation, or components to be stiffened with elements which will generate significant supplementary energy dissipation when buckling occurs. Metal foams provide a means to explore reconfiguring steel structures to mitigate cross-section buckling in many cases and dramatically increase energy dissipation in all cases. The microstructure of metal foams consists of solid and void phases. These voids have random shape and size. Therefore, randomness, which is introduced into metal foams during the manufacturing processes, creating more uncertainty in the behavior of metal foams compared to solid steel. Therefore, studying uncertainty in the performance metrics of structures which have metal foams is more crucial than for conventional structures. Therefore, in this study, structural application of metal foams considering material and geometrical uncertainty is presented. This study applies the Sobol’ decomposition of a function of many random variables to different problem in structural mechanics. First, the Sobol’ decomposition itself is reviewed and extended to cover the case in which the input random variables have Gaussian distribution. Then two examples are given for a polynomial function of 3 random variables and the collapse load of a two story frame. In the structural example, the Sobol’ decomposition is used to decompose the variance of the response, the collapse load, into contributions from the individual input variables. This decomposition reveals the relative importance of the individual member yield stresses in determining the collapse load of the frame. In applying the Sobol’ decomposition to this structural problem the following issues are addressed: calculation of the components of the Sobol’ decomposition by Monte Carlo simulation; the effect of input distribution on the Sobol’ decomposition; convergence of estimates of the Sobol’ decomposition with sample size using various sampling schemes; the possibility of model reduction guided by the results of the Sobol’ decomposition. For the rest of the study the different structural applications of metal foam is investigated. In the first application, it is shown that metal foams have the potential to serve as hysteric dampers in the braces of braced building frames. Using metal foams in the structural braces decreases different dynamic responses such as roof drift, base shear and maximum moment in the columns. Optimum metal foam strengths are different for different earthquakes. In order to use metal foam in the structural braces, metal foams need to have stable cyclic response which might be achievable for metal foams with high relative density. The second application is to improve strength and ductility of a steel tube by filling it with steel foam. Steel tube beams and columns are able to provide significant strength for structures. They have an efficient shape with large second moment of inertia which leads to light elements with high bending strength. Steel foams with high strength to weight ratio are used to fill the steel tube to improves its mechanical behavior. The linear eigenvalue and plastic collapse finite element (FE) analysis are performed on steel foam filled tube under pure compression and three point bending simulation. It is shown that foam improves the maximum strength and the ability of energy absorption of the steel tubes significantly. Different configurations with different volume of steel foam and composite behavior are investigated. It is demonstrated that there are some optimum configurations with more efficient behavior. If composite action between steel foam and steel increases, the strength of the element will improve due to the change of the failure mode from local buckling to yielding. Moreover, the Sobol’ decomposition is used to investigate uncertainty in the strength and ductility of the composite tube, including the sensitivity of the strength to input parameters such as the foam density, tube wall thickness, steel properties etc. Monte Carlo simulation is performed on aluminum foam filled tubes under three point bending conditions. The simulation method is nonlinear finite element analysis. Results show that the steel foam properties have a greater effect on ductility of the steel foam filled tube than its strength. Moreover, flexural strength is more sensitive to steel properties than to aluminum foam properties. Finally, the properties of hypothetical structural steel foam C-channels foamed are investigated via simulations. In thin-walled structural members, stability of the walls is the primary driver of structural limit states. Moreover, having a light weight is one of the main advantages of the thin-walled structural members. Therefore, thin-walled structural members made of steel foam exhibit improved strength while maintaining their low weight. Linear eigenvalue, finite strip method (FSM) and plastic collapse FE analysis is used to evaluate the strength and ductility of steel foam C-channels under uniform compression and bending. It is found that replacing steel walls of the C-channel with steel foam walls increases the local buckling resistance and decreases the global buckling resistance of the C-channel. By using the Sobol’ decomposition, an optimum configuration for the variable density steel foam C-channel can be found. For high relative density, replacing solid steel of the lips and flange elements with steel foam increases the buckling strength. On the other hand, for low relative density replacing solid steel of the lips and flange elements with steel foam deceases the buckling strength. Moreover, it is shown that buckling strength of the steel foam C-channel is sensitive to the second order Sobol’ indices. In summary, it is shown in this research that the metal foams have a great potential to improve different types of structural responses, and there are many promising application for metal foam in civil structures.