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Academic literature on the topic 'Stiffened structures'

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Published: 4 June 2021
Last updated: 1 February 2022

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Journal articles on the topic "Stiffened structures"

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Sirajudeen, Rahima Shabeen, and Alagusundaramoorthy P. "GFRP Stiffened Plate with Square Cutout under Axial and Out-of-Plane Load." Polymers 13, no. 8 (April 7, 2021): 1185. http://dx.doi.org/10.3390/polym13081185.

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The high-strength-to-weight ratio and corrosion resistance properties of glass-fiber-reinforced polymer (GFRP) composites makes them potentially well-suited for application in ship structures, bridges and off-shore oil platforms. These structures are often formed by stiffened plates and are subjected to axial load and out-of-plane load. Cutouts and openings are provided in the plates for access and maintenance. The main objective of this study was to examine the buckling behavior of GFRP-stiffened composite plates with square cutouts under a combination of axial and out-of-plane load up to failure. Four blade-stiffened composite plates without a cutout and four with square cutout were fabricated with stiffeners as a continuous layup of the flange plate using glass fiber and epoxy resin. The initial geometric imperfections were measured, and plate imperfections (Δx), stiffener imperfections (Δsy) and overall imperfections (Δsx) were calculated from the measurements. All fabricated-stiffened composite plates were tested up to failure. The finite element model was developed in ANSYS software and validated with the experimental results. It was observed that GFRP-stiffened composite plates failed by stiffener compression/stiffener tension mode of failure. The presence of out-of-plane loads and cutouts reduced the axial load carrying capacity of the stiffened composite plates.
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Abdel Nasser, Yehia, Aly Aliraqi, and Bader El Din Ali. "Collision Analysis of Ship Side." Advanced Materials Research 199-200 (February 2011): 119–25. http://dx.doi.org/10.4028/www.scientific.net/amr.199-200.119.

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Structural design of ships against collision requires prediction of the extent of damage to stiffened plates subjected to impact. In ship structures, stiffened plates are furnished with vertical or horizontal stiffeners to sustain conventional loads such as shearing, bending and local buckling. The consideration of collision in ship structural design is especially important for tankers where accidents may cause serious environmental pollution. In predicting the extent of collision damage, FE modeling of stiffened plates using ABAQUS software is applied to demonstrate different collision scenario. Typical stiffened plates of tankers in service with different configurations of stiffeners are used to examine absorbed energy in each case. The aim of this paper is to examine the stiffener shape that absorbs more deformation energy.
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KALNINS, KASPARS, ROLANDS RIKARDS, JANIS AUZINS, CHIARA BISAGNI, HAIM ABRAMOVICH, and RICHARD DEGENHARDT. "METAMODELING METHODOLOGY FOR POSTBUCKLING SIMULATION OF DAMAGED COMPOSITE STIFFENED STRUCTURES WITH PHYSICAL VALIDATION." International Journal of Structural Stability and Dynamics 10, no. 04 (October 2010): 705–16. http://dx.doi.org/10.1142/s0219455410003695.

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A metamodeling methodology has been proposed for postbuckling simulation of stiffened composite structures with integrated degradation scenarios. The presence of artificial damage between the outer skin and stiffeners has been simulated as softening of the material properties in predetermined regions of the structure. The proposed methodology for the fast design procedure of axially or torsionally loaded stiffened composite structures is based on response surface methodology (RSM) and design and analysis of computer experiments (DACE). Numerical analyses have been parametrically sampled by means of the ANSYS/LS-DYNA probabilistic design toolbox extracting the load-shortening response curves in the preselected domain of interest. These response curves have been simplified using piecewise linear approximation identifying the buckling and postbuckling stiffness ratios along with the values of the skin and the stiffener buckling loads. Three stiffened panel designs and a closed box structure with preselected damage scenarios have been elaborated and validated with the tests performed within the COCOMAT project. The resulting design procedure provides a time-effective design tool for preliminary study and for elaboration of the optimum design guidelines for composite stiffened structures with material degradation restraints.
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Elsayed, Tarek, and Alaa Mansour. "Reliability-Based Specification of Welding Distortion Tolerances for Stiffened Steel Panels." Journal of Ship Research 47, no. 01 (March 1, 2003): 39–47. http://dx.doi.org/10.5957/jsr.2003.47.1.39.

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The purpose of this study is to analytically derive a simple and reasonably accurate expression for the maximum allowable unfairness tolerance of longitudinally stiffened panels in ship structures. The stiffened panels under consideration are typical of those found in the deck, bottom, or side shell of longitudinally stiffened ships. They are assumed to be under still water and wave-induced loads, resulting in predominantly compressive loads. A plate-stiffener combination model is used as representative of the stiffened panel. Ultimate strength is determined based on a strut approach taking into account the effects of initial stiffener deflection and welding residual stresses in the stiffener. A series of stiffener reliability analyses relative to the ultimate failure strength of the stiffener for varying proportions of column slenderness ratios is carried out. Based on the computed results, a simple expression for predicting the maximum allowable unfairness tolerance of the stiffener is derived. The developed expression, expressed in terms of the stiffener slenderness ratio, can be useful for the assessment of fairness limits of plating with frames, or as a design guideline in ship structures during construction.
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Wang, Wei Yuan, Yuan Yuan Li, and Hai Sheng Shu. "Sound Insulation Property of Bionic Thin-Walled Stiffened Plate Based on Plants Venations Growth Mechanism." Journal of Biomimetics, Biomaterials and Biomedical Engineering 20 (June 2014): 35–44. http://dx.doi.org/10.4028/www.scientific.net/jbbbe.20.35.

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The leaf can be seen as shin plate structures with stiffener(vein) and the venation distributions are closed related to the external environment load. Leaf venation growing algorithm (VGA) is the abstract description of vein growing process and reflects an ideological of learning from nature. This article concerns the sound insulation property of thin-walled stiffened plates. Numerical method is used to analyze three types of plants: non-stiffened plate, traditional stiffened plate and VGA stiffened plate. The VGA stiffened plate optimized by leaf venations growth algorithm method can reflect the influence of venations layout structure on the noise reduction performance of forest belts. The computational model of sound transmission through a stiffened plate excited by a harmonic oblique incident plane wave and mounted in an infinite baffle using the coupled finite element/boundary element approach is presented. The proposed model also takes the acoustic fluid- structure coupling into account. The results show that the sound transmission losses are closely dependent on the natural frequency. The sound transmission losses of bionic thin-walled stiffened plate are 0.17-2.45dB more than that of traditional stiffened plate in the range of 900-2000Hz. It indicated that the layout of stiffeners is an influence factor for noise reduction for plate structures, just like that of vein layout for tree belts. There is a certain merit to use the method of bionic plant leaves for acoustic optimization.
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Sheikh, Abdul Hamid, and Madhujit Mukhopadhyay. "Transverse Vibration of Plate Structures With Elastically Restrained Edges by the Spline/Finite Strip Method." Journal of Vibration and Acoustics 115, no. 3 (July 1, 1993): 295–302. http://dx.doi.org/10.1115/1.2930348.

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The newly developed spline finite strip method has been applied to determine the natural frequencies of plates and stiffened plates with edged elastically restrained against translation and rotation. The stiffener has been modelled so that it can be situated anywhere within the plate strip. The formulation has been generalized in such a manner that it can handle general shaped plates and stiffeners having arbitrary orientation and eccentricity. A consistent formulation has been adopted to incorporate the contribution of the edge restraints in the structural stiffness matrix. Numerical examples as available in the literature are solved and the comparison of the results indicates good accuracy of the method. New results in the form of natural frequencies corresponding to the higher modes particularly for plates/stiffened plates with nonclassical boundaries are presented.
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Wang, Wei Yuan, Yuan Yuan Li, and Ping Wang. "Mechanical Analysis for Thin-Walled Stiffened Plates on the Base of Plants Venations Growth Algorithm." Applied Mechanics and Materials 541-542 (March 2014): 299–302. http://dx.doi.org/10.4028/www.scientific.net/amm.541-542.299.

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The reinforced shin shell structures are widely used in many fields such as mechanical, architecture, aerospace and shipbuilding, etc. The leaf can be seen as shin plate structures with stiffener (vein) and the venation distributions are closed related to the external environment load. Leaf venation growing algorithm is the abstract description of vein growing process and reflects an ideological of learning from nature. This article concerns the mechanical analysis for thin-walled stiffened plates, which consist of static mechanical behavior and dynamic performance. Numerical method is used to analyze three types of plants: non-stiffened plate, traditional stiffened plate and stiffened plate optimized by leaf venations growth algorithm (VGA) method. The calculation results proved that the VGA stiffened plate has better mechanical performances than traditional method and illustrated the effectiveness of the bionic venations layout method for stiffened structures.
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Roberts, J. C., and G. J. White. "Experimental Results for Bending and Buckling of Rectangular Orthotropic Fiber-Reinforced Plastic Plate Structures." Marine Technology and SNAME News 36, no. 01 (January 1, 1999): 22–28. http://dx.doi.org/10.5957/mt1.1999.36.1.22.

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Solid unstiffened, sandwich, and hat-stiffened rectangular orthotropic fiber-reinforced plastic (FRP) plates were tested in uniaxial in-plane compression and out-of-plane uniform pressure. The two short edges of all plates were clamped, whereas the two long edges of the unstiffened and sandwich plates were simply supported and the same edges of the hat-stiffened plate were left free. Unstiffened plates reached global buckling at about 688 kN (155 klb); however, the plates did not collapse up to the machine load limit of 1334 kN (300 klb). Sandwich plates never reached the overall elastic buckling load; they collapsed in local buckling by face sheet delamination and core shear failure at loads of about 939 kN (211 klb). Hat-stiffened plates exhibited local buckling of the outer unsupported flanges at a load of about 356 kN (80 klb). All hat-stiffened plates collapsed under uniaxial compression due to a combination of face sheet to stiffener delamination followed by hat-stiffener local buckling at loads of about 939 kN (211 klb). The stresses and deflections due to out-of-plane uniform pressure were compared between the unstiffened, sandwich, and hat-stiffened plates from pressures of 6.895 kPa (1 psi) to 34 kPa (5 psi). With the plates under uniaxial compression and out-of-plane uniform pressure simultaneously, there was a general decrease in buckling and collapse with an increase in out-of-plane uniform pressure.
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Chen, Hao, Yuanming Xu, Junhao Hu, and Xi Wang. "Optimization of lightweight sub-stiffened panels with buckling analysis and imperfection sensitivity analysis." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 15 (June 13, 2019): 5507–21. http://dx.doi.org/10.1177/0954410019856782.

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On the purpose of improving the structural efficiency of stiffened panels, which is widely used in engineering, three promising layouts of sub-stiffened thin-walled structures were optimized in view of structure's initial buckling and further analyzed through post-buckling and imperfection-sensitivity analysis. The optimization tasks were carried out using an integrated framework, which is based on the multidisciplinary optimization platform Model Center and finite element method software ABAQUS. The particle swarm optimization algorithm was applied to optimize layout parameters. Three optimal sub-stiffened panels were then evaluated based on their performance on critical buckling loads and post-buckling ultimate strength under uniaxial loading. Imperfection-sensitivity analysis was also conducted to investigate the stability behavior of the proposed panels with defect. The results indicate that the introduction of sub-stiffeners into the traditional stiffened panel can achieve significant improvements on the panel's buckling loads and ultimate strength under uniaxial loading, which are favorable to expand design space for engineering structures under requirements of lightweight with high bending stiffness and bucking resistance.
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Shojaee, T., B. Mohammadi, and R. Madoliat. "Experimental and numerical investigation of stiffener effects on buckling strength of composite laminates with circular cutout." Journal of Composite Materials 54, no. 9 (September 23, 2019): 1141–60. http://dx.doi.org/10.1177/0021998319874101.

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In the notched structures, to achieve maximum buckling resistance in comparison with structural weight, the optimal design of a stiffener is very important. In this research, after a review of the existing literature, nonlinear buckling behavior of composite plates containing the cutout with three different designs of stringer was investigated. The considered stiffeners are planer, longitudinal, and ring types. The buckling experiments were carried out on the stiffened plates containing a circular notch. Moreover, to achieve an efficient prediction of the buckling in the stiffened laminate with the hole, a finite strip method is developed based on the Airy stress function and von Karman’s large deformation equations. Studies show that there is a good agreement between the postbuckling behaviors derived from developed finite strip method with experimental results. Fast convergence of the considered finite strip method compared with the finite element results shows its efficiency for prediction of buckling behavior in laminated composites. The results show that the buckling load-bearing capacities of perforated plates with a longitudinal and planer stiffener are higher compared with the other stiffener, respectively. The detailed parametric study on the effects of thickness of the plate and stiffener and opening diameter on buckling behavior was performed using experiments and modeling.
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Dissertations / Theses on the topic "Stiffened structures"

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Yetman, Joanne Emma. "Skin stiffener debonding of top-hat stiffened composite structures." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/422913/.

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Top-hat stiffened plates provide an effcient structure for engineering applications. During service debonding between the stiffener and the plate is a common failure mechanism. Therefore, an extensive understanding of the residual strength is required to rapidly and effciently determine precautions to be taken to ensure the safety of the structure. Critical assessment of necessary repairs reduces the through life costs and in design damage assessment can lead to optimisation through tolerance of common damage incidents. Research on damaged stiffened structures to date is primarily focused on airframe applications and considers open sections with co-cured stiffeners which are not typical of marine structures. These studies have shown that debond size and location have a significant effect on the damage mode of the panel. However, they do not consider the interaction of failure modes or ultimate failure. Typical marine composite joints are manufactured by post-curing sub-components using a chopped strand mat layer at the interface. To predict failure of these joints requires accurate assessment of the material and fracture properties and a consistent set of data which is lacking in the literature. Therefore, the research in this thesis considers the damage tolerance of top-hat stiened panels containing a debond between the stiffener and plate through numerical and experimental work. The focus of the work is post-cured top-hat multi-stiffened panels used in large marine applications manufactured from heavy weight glass vinylester woven roving. An automated tool using non-linear finite element analysis capable of modelling debond damage and assessing the ultimate and the residual strength of the panel is verified. A parametric study investigating panel topology, damage parameters and stiener type show the complexities of the damage case. Results show that top-hat stiffened panels exhibit a trend between ultimate strength and the debond size with crack initiation not necessarily propagating as geometric imperfections accelerate buckling but can provide an arrest point for crack propagation. Nominal lateral pressures are shown to significantly increase the damage tolerance. Full characterisation of typical materials is conducted experimentally providing a complete data set of mechanical characterisation and fracture data for both co-cured interfaces, typical of mid-laminate debonds and sub-component joints. Tensile, compressive, shear and exural tests are conducted and a model for the non-linearity of the woven roving in tension and shear is proposed. The fracture results show the post-cured joint exhibits a 20% increase in mode I and II strain energy release rates. The experimental data is used in a number of studies to further verify and optimise the finite element model. Mode I and II tests are simulated to ascertain the cohesive element interface strengths and Turon's interface parameters. The material data is shown to give accurate results for the structural response, crack initation and debonding of an as built large scale top-hat stiffened panel which is tested experimentally under four point bend. Therefore, the effect of skin-stiffener debonding has been investigated for top-hat stffiened panels, providing improved characterisation of the material and interfaces and guidance on the damage tolerance to damage and design parameters.
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Eksik, Ömer. "Structural performance of GRP top hat stiffened marine structures." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431952.

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Kontis, Nikolaos. "Damage tolerance of composite stiffened structures." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488883.

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Composite stiffened panels have been extensively used in primary aerospace applications, due to their efficient stiffness/weight ratio and the ability to tailor properties. Despite their apparent superiority to metals, the susceptibility of composites to damage has proved to be a critical factor. A common example in practice is the barely visible impact damage caused by a low velocity impact event. Such events can generate inter-laminar defects (delaminations), which under compressive loading can reduce the strength and stability of the structure. There is a need to establish the influence of such damage on composite stiffened structures. Current practice allows for delamination induced strength reduction by applying strain limits to the material that ensure delamination does not produce failure before uhimate levels of loading. However, these limits are established via coupon tests, which focus on the scale of the delamination only and do not account for the interaction at the structural scale.
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Faggiani, Andrea. "Optimisation of postbuckling stiffened composite structures." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/8001.

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The thesis starts off with an introductory chapter on composite materials. This includes a definition of composites, a brief history of composite materials, their use in aerostructures (primarily as stiffened structures), and also optimization of composite structures. A literature review is then presented on postbuckling stiffened structures. This includes both experimental investigations on stiffened composite panels and investigations into secondary instabilities and mode jumping as well as their numerical modelling. Next, the Finite Element (FE) modelling of posthuckling stiffened structures is discussed, relating how ABAQUS models are set up in order to trace stiffened composite panels' buckling and postbuckling responses. An experimental programme conducted on an I-stiffened panel is described, where the panel was tested in compression until collapse. The buckling and postbuckling characteristics of the panel are presented, and then an FE model is described together with its predicted numerical behaviour of the panel's buckling and postbuckling characteristics. Focus then shifts to the modelling of failure in composites, in particular delamination failure. A literature review is conducted, looking at the use of both the Virtual Crack Closure Technique (VCCT) and interface elements in delamination modelling. Two stiffener runout models, representing two specimens previously tested experimentally, are then developed to illustrate how interface elements may be used to model mixed mode delamination. The previously discussed panel is revisited, and a global-local modelling approach used to model the skin-stiffener interface. FE models of a stiffened cylindrical shell are also considered, and again the postbuckling characteristics of the shell are compared with experimental results. . The thesis then moves on to optimization of composite structures. This starts off with a literature review of existing optimization methodologies. A Genetic Algorithm (GA) is devised to increase the damage resistance of the I-stiffened panel. The global-local ABAQUS model discussed earlier is used in conjunction with the GA in order to find a revised stacking sequence of both the panel flanges and skin so as to minimize skin-stiffener debonding subject to a variety of design constraints. A second optimization is then presented, this time linked to the FE model of the stiffened cylindrical shell. The objective is to increase the collapse load of the shell, again subject to specific design constraints. The thesis concludes by summarising the importance of the work conducted. FE models were created and validated against experimental work in order to model a variety of composite stiffened structures in their buckling and postbuckling regimes. These models were able to capture the failure characteristics of these structures relating to delamination at the skin-stiffener interface, a phenomenon widely observed experimentally. Various optimizations, able to account for failure mechanisms which may occur prior to overall structural collapse, were then conducted on the analysed structures in order to obtain more damage resistant designs.
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Peiffer, John P. "Fatigue testing of stiffened traffic signal structures." Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1888253611&sid=11&Fmt=2&clientId=18949&RQT=309&VName=PQD.

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Young, Andrew J. "Active control of vibration in stiffened structures." Title page, contents and abstract only, 1995. http://hdl.handle.net/2440/37722.

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Active control of vibration in structures has been investigated by an increasing number of researchers in recent years. There has been a great deal of theoretical work and some experiment examining the use of point forces for vibration control, and more recently, the use of thin piezoelectric crystals laminated to the surfaces of structures. However, control by point forces is impractical, requiring large reaction masses, and the forces generated by laminated piezoelectric crystals are not sufficient to control vibration in large and heavy structures. The control of flexural vibrations in stiffened structures using piezoceramic stack actuators placed between stiffener flanges and the structure is examined theoretically and experimentally in this thesis. Used in this way, piezoceramic actuators are capable of developing much higher forces than laminated piezoelectric crystals, and no reaction mass is required. This thesis aims to show the feasibility of active vibration control using piezoceramic actuators and angle stiffeners in a variety of fundamental structures. The work is divided into three parts. In the first, the simple case of a single actuator used to control vibration in a beam is examined. In the second, vibration in stiffened plates is controlled using multiple actuators, and in the third, the control of vibration in a ring-stiffened cylinder is investigated. In each section, the classical equations of motion are used to develop theoretical models describing the vibration of the structures with and without active vibration control. The effects of the angle stiffener(s) are included in the analysis. The models are used to establish the quantitative effects of variation in frequency, the location of control source(s) and the location of the error sensor(s) on the achievable attenuation and the control forces required for optimal control. Comparison is also made between the results for the cases with multiple control sources driven by the same signal and with multiple independently driven control sources. Both finite and semi-finite structures are examined to enable comparison between the results for travelling waves and standing waves in each of the three structure types. This thesis attempts to provide physical explanations for all the observed variations in achievable attenuation and control force(s) with varied frequency, control source location and error sensor location. The analysis of the simpler cases aids in interpreting the results for the more complicated cases. Experimental results are given to demonstrate the accuracy of the theoretical models in each section. Trials are performed on a stiffened beam with a single control source and a single error sensor, a stiffened plate with three control sources and a line of error sensors and a ring-stiffened cylinder with six control sources and a ring of error sensors. The experimental results are compared with theory for each structure for the two cases with and without active vibration control.
Thesis (Ph.D.)--Mechanical Engineering, 1995.
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Walsh, Stephen James. "Vibrational power transmission in curved and stiffened structures." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242224.

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Jrad, Mohamed. "Multidisciplinary Optimization and Damage Tolerance of Stiffened Structures." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/52276.

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The structural optimization of a cantilever aircraft wing with curvilinear spars and ribs and stiffeners is described. The design concept of reinforcing the wing structure using curvilinear stiffening members has been explored due to the development of novel manufacturing technologies like electron-beam-free-form-fabrication (EBF3). For the optimization of a complex wing, a common strategy is to divide the optimization procedure into two subsystems: the global wing optimization which optimizes the geometry of spars, ribs and wing skins; and the local panel optimization which optimizes the design variables of local panels bordered by spars and ribs. The stiffeners are placed on the local panels to increase the stiffness and buckling resistance. The panel thickness, size and shape of stiffeners are optimized to minimize the structural weight. The geometry of spars and ribs greatly influences the design of stiffened panels. During the local panel optimization, the stress information is taken from the global model as a displacement boundary condition on the panel edges using the so-called "Global-Local Approach". The aircraft design is characterized by multiple disciplines: structures, aeroelasticity and buckling. Particle swarm optimization is used in the integration of global/local optimization to optimize the SpaRibs. The interaction between the global wing optimization and the local panel optimization is usually computationally expensive. A parallel computing technology has been developed in Python programming to reduce the CPU time. The license cycle-check method and memory self-adjustment method are two approaches that have been applied in the parallel framework in order to optimize the use of the resources by reducing the license and memory limitations and making the code robust. The integrated global-local optimization approach has been applied to subsonic NASA common research model (CRM) wing, which proves the methodology's application scaling with medium fidelity FEM analysis. Both the global wing design variables and local panel design variables are optimized to minimize the wing weight at an acceptable computational cost. The structural weight of the wing has been, therefore, reduced by 40% and the parallel implementation allowed a reduction in the CPU time by 89%. The aforementioned Global-Local Approach is investigated and applied to a composite panel with crack at its center. Because of composite laminates' heterogeneity, an accurate analysis of these requires very high time and storage space. In the presence of structural discontinuities like cracks, delaminations, cutouts etc., the computational complexity increases significantly. A possible alternative to reduce the computational complexity is the global-local analysis which involves an approximate analysis of the whole structure followed by a detailed analysis of a significantly smaller region of interest. We investigate here the performance of the global-local scheme based on the finite element method by comparing it to the traditional finite element method. To do so, we conduct a 2D structural analysis of a composite square plate, with a thin rectangular notch at its center, subjected to a uniform transverse pressure, using the commercial software ABAQUS. We show that the presence of the thin notch affects only the local response of the structure and that the size of the affected area depends on the notch length. We investigate also the effect of the notch shape on the response of the structure. Stiffeners attached to composite panels may significantly increase the overall buckling load of the resultant stiffened structure. Buckling analysis of a composite panel with attached longitudinal stiffeners under compressive loads is performed using Ritz method with trigonometric functions. Results are then compared to those from ABAQUS FEA for different shell elements. The case of composite panel with one, two, and three stiffeners is investigated. The effect of the distance between the stiffeners on the buckling load is also studied. The variation of the buckling load and buckling modes with the stiffeners' height is investigated. It is shown that there is an optimum value of stiffeners' height beyond which the structural response of the stiffened panel is not improved and the buckling load does not increase. Furthermore, there exist different critical values of stiffener's height at which the buckling mode of the structure changes. Next, buckling analysis of a composite panel with two straight stiffeners and a crack at the center is performed. Finally, buckling analysis of a composite panel with curvilinear stiffeners and a crack at the center is also conducted. ABAQUS is used for these two examples and results show that panels with a larger crack have a reduced buckling load. It is shown also that the buckling load decreases slightly when using higher order 2D shell FEM elements. A damage tolerance framework, EBF3PanelOpt, has been developed to design and analyze curvilinearly stiffened panels. The framework is written with the scripting language PYTHON and it interacts with the commercial software MSC. Patran (for geometry and mesh creation), MSC. Nastran (for finite element analysis), and MSC. Marc (for damage tolerance analysis). The crack location is set to the location of the maximum value of the major principal stress while its orientation is set normal to the major principal axis direction. The effective stress intensity factor is calculated using the Virtual Crack Closure Technique and compared to the fracture toughness of the material in order to decide whether the crack will expand or not. The ratio of these two quantities is used as a constraint, along with the buckling factor, Kreisselmeier and Steinhauser criteria, and crippling factor. The EBF3PanelOpt framework is integrated within a two-step Particle Swarm Optimization in order to minimize the weight of the panel while satisfying the aforementioned constraints and using all the shape and thickness parameters as design variables. The result of the PSO is used then as an initial guess for the Gradient Based Optimization using only the thickness parameters as design variables. The GBO is applied using the commercial software VisualDOC.
Ph. D.
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Ahmad, Naveed. "Passive Damping in Stiffened Structures Using Viscoelastic Polymers." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/79566.

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Noise and vibration suppression is an important aspect in the design process of structures and machines. Undesirable vibrations can cause fatigue in a structure and are, therefore, a risk to the safety of a structure. One of the most effective and widely used methods of mitigating these unwanted vibrations from a system is passive damping, by using a viscoelastic material. This dissertation will primarily focus on constrained layer passive damping treatments in structures and the investigation of associated complex modes. The key idea behind constrained damping treatment is to increase damping as affected by the presence of a highly damped core layer vibrating mainly in shear. Our main goal was to incorporate viscoelastic material in a thick stiffened panel with plate-strip stiffeners, to enhance the damping characteristics of the structure. First, we investigated complex damped modes in beams in the presence of a viscoelastic layer sandwiched between two elastic layers. The problem was solved using two approaches, (1) Rayleigh beam theory and analyzed using the principle of virtual work, and (2) by using 2D plane stress elasticity based finite-element method. The damping in the viscoelastic material was modeled using the complex modulus approach. We used FEM without any kinematic assumptions for the transverse shear in both the core and elastic layers. Moreover, numerical examples were studied, by including complex modulus in the base and constraining layers. The loss factor was calculated by modal strain energy method, and by solving a complex eigenvalue problem. The efficiency of the modal strain energy method was tested for different loss factors in the core layer. Complex mode shapes of the beam were also examined in the study, and a comparison was made between viscoelastically damped and non-proportionally damped structures. Secondly, we studied the free vibration response of an integrally stiffened and/or stepped plate. The stiffeners used here were plate-strip stiffeners, unlike the rib stiffeners often investigated by researchers. Both plate and stiffeners were analyzed using the first-order shear deformation theory. The deflections and rotations were assumed as a product of Timoshenko beam functions, chosen appropriately according to the given boundary conditions. Unlike Navier and Levy solution techniques, the approach used here can also be applied to fully clamped, free and cantilever supported stiffened plates. The governing differential equations were solved using the Rayleigh-Ritz method. The development of the stiffness and the mass matrices in the Ritz analysis was found to consume a huge amount of CPU time due to the recursive integration of Timoshenko beam functions. An approach is suggested to greatly decrease this amount of CPU time, by replacing the recursive integration in a loop structure in the computer program, with the analytical integration of the integrand in the loop. The numerical results were compared with the exact solutions available in the literature and the commercially available finite-element software ABAQUS. Some parametric studies were carried out to show the influence of certain important parameters on the overall natural frequencies of the stiffened plate. Finally, we investigated the damped response of an adhesively bonded plate employing plate-strip stiffeners, using FSDT for both the plate and stiffeners. The problem was analyzed using the principle of virtual work. At first, we did not consider damping in the adhesive in order to validate our code, by comparing our results with those available in the literature as well as with the results obtained using ABAQUS 3D model. The results were found to be highly satisfactory. We also considered the effect of changing the stiffness of the adhesive layer on the vibration of the bonded system. As a second step, we included damping in the stiffened structure using complex modulus approach, a widely used technique to represent the rheology of the viscoelastic material. We observed an overall increase in the natural frequencies of the system, due to the damping provided by the viscoelastic material. Moreover, it was noticed that when the thickness of the adhesive layer is increased, the natural frequencies and loss factor of the stiffened structure decrease. A viscoelastic material with high loss factor and small thickness will be a perfect design variable to obtain overall high damping in the structure.
Ph. D.
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Lam, Daniel F. "STRAIN CONCENTRATION AND TENSION DOMINATED STIFFENED AEROSPACE STRUCTURES." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1145393262.

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Books on the topic "Stiffened structures"

1

Kolisnik, Henry M. A survey of methods of analysis for stiffened shell structures. Kingston, Ont., Canada: Dept. of Civil Engineering, Royal Military College, 1985.

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Driscoll, Jennifer Culbertson. Crushing characteristics of web girders in unidirectionally stiffened double hull structures. Springfield, Va: Available from the National Technical Information Service, 1992.

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Daniels, H. A. M. A CAD-system for the design of stiffened panels in wing box structures. Amsterdam: National Aerospace Laboratory, 1985.

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Simitses, George J. Buckling of delaminated long panels under pressure and of radially-loaded stiffened annular plates. Atlanta, Ga: Georgia Institute of Technology, 1985.

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Munroe, J. Integral airframe structures (IAS): Validated feasibility study of integrally stiffened metallic fuselage panels for reducing manufacturing costs. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 2000.

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Ko, William L. Thermal and mechanical buckling analysis of hypersonic aircraft hat-stiffened panels with varying face sheet geometry and fiber orientation. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1996.

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Hales, Stephen J. Structure-property correlations in Al-Li alloy integrally stiffened extrusions. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 2001.

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Danielson, D. A. Tripping of stiffened plates using a refined beam theory. Monterey, Calif: Naval Postgraduate School, 1988.

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L, Phillips John. Structural analysis and optimum design of geodesically stiffened composite panels. Blacksburg, Va: Virginia Polytechnic Institute and State University, Center for Composite Materials and Structures, 1990.

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Nast, Trina E. Cyclic behavior of stiffened gusset plate-brace member assemblies. Edmonton: Dept. of Civil and Environmental Engineering, University of Alberta, 1999.

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Book chapters on the topic "Stiffened structures"

1

Farkas, József, and Károly Jármai. "Stiffened Plates." In Optimum Design of Steel Structures, 143–209. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-36868-4_7.

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Shama, Mohamed. "Buckling of Stiffened Panels." In Buckling of Ship Structures, 267–304. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-17961-7_11.

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Okumoto, Yasuhisa, Yu Takeda, Masaki Mano, and Tetsuo Okada. "Design of Stiffened Panel." In Design of Ship Hull Structures, 253–65. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-540-88445-3_13.

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Wiggenraad, J. F. M., and N. R. Bauld. "Interlaminar Stress Analysis at the Skin/Stiffener Interface of a Grid-Stiffened Composite Panel." In Composite Structures, 415–31. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3662-4_32.

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Smith, C. S., and R. S. Dow. "Compressive Strength of Longitudinally Stiffened GRP Panels." In Composite Structures 3, 468–90. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-4952-2_33.

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Smith, C. S., and R. S. Dow. "Interactive Buckling Effects in Stiffened FRP Panels." In Composite Structures 4, 122–37. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3455-9_9.

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Moreira, P. M. G. P., V. Richter-Trummer, and P. M. S. T. de Castro. "Lightweight Stiffened Panels Fabricated Using Emerging Fabrication Technologies: Fatigue Behaviour." In Structural Connections for Lightweight Metallic Structures, 151–72. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/8611_2010_49.

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Chao, C. C., W. S. Kuo, and I. S. Lin. "Buckling of Unstiffened/Stiffened Orthotropic Foam Sandwich Cylindrical Shells." In Composite Structures 3, 452–67. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-4952-2_32.

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Tripathy, Biswajit, and K. P. Rao. "Optimum Design for Buckling of Plain and Stiffened Composite Cylindrical Panels." In Composite Structures, 371–81. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3662-4_29.

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Lu, Tianjian, and Fengxian Xin. "Vibroacoustics of Stiffened Structures in Mean Flow." In Springer Tracts in Mechanical Engineering, 159–205. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-55358-5_3.

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Conference papers on the topic "Stiffened structures"

1

Alali, Amier, Yehia Abdel-Nasser, and Swielm A. Swielm. "Collision Analysis of Stiffened Plates." In ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/omae2010-20612.

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Structural design of ships against collision requires prediction of the extent of damage to stiffened plates subjected to impact. Structural components such as stiffened plates, bulkheads are our concern. In ship structures stiffened plates are furnished with vertical or horizontal stiffeners to sustain conventional acting loads such as shearing, bending and local buckling. The consideration of collision in ship structural design is necessary for tankers where accidents may cause serious environmental pollution. In predicting the extent of collision damage, finite elements (FE) modeling of stiffened plates using ABAQUS software is applied to demonstrate collision scenario. Typical stiffened plates of tanker in service with different configurations of stiffeners are selected to examine absorbed energy for each one. The aim of this paper is to select the proper stiffener shape absorbing more deformed energy. These analyses of stiffened plates will guide ship designers to properly select effective stiffener absorbing higher deformed energy when simulate full scale ship against collision.
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Ren, Huilong, Yifu Liu, Chenfeng Li, Xin Zhang, and Zhaonian Wu. "Numerical Investigation of Ultimate Strength of Stiffened Plates With Various Cross-Section Forms." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77756.

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There is an increasing interest in the lightweight design of ship and offshore structures, more specifically, choosing aluminum alloys or other lightweight high-performance materials to build structure components and ship equipments. Due to its better mechanical properties and easy assembly nature, extruded aluminum alloy stiffened plates are widely used in hull structures. When the load on the hull reaches a certain level during sailing, partial or overall instability of stiffened plate makes significant contribution in an event of collapse of the hull structure. It is very necessary to investigate the ultimate strength of aluminum alloy stiffened plate to ensure the ultimate bearing capacity of large aluminum alloy hull structure. Most of studies of the ultimate strength of stiffened plates deal with stiffened plates with T–shaped stiffeners. Stiffeners of other shapes have seldom been explored. In this research, the ultimate strength of six different cross–section aluminum alloy stiffened plates and one steel stiffened plate was studied based on the non–linear finite element analysis (FEA). Taking into account stiffness, weight and other issues, the new cross–section aluminum stiffener has finally been concluded for replacing the original steel stiffener in upper deck of a warship.
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Mulani, Sameer, Davide Locatelli, and Rakesh Kapania. "Grid-Stiffened Panel Optimization Using Curvilinear Stiffeners." In 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2011. http://dx.doi.org/10.2514/6.2011-1895.

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Bhatia, Manav, and Rakesh Kapania. "Stiffener Effectiveness Approach for Optimal Stiffener Placement on Curvilinear Stiffened Panel." In 50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2009. http://dx.doi.org/10.2514/6.2009-2640.

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Lotsberg, Inge, and Harald Rove. "Stress Concentration Factors for Butt Welds in Plated Structures." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-23316.

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Geometric stress concentration factors for butt welds in stiffened plates have been investigated by finite element analysis. The purpose of these analyses has been to establish a data basis that can be used to develop an analytical expression for stress concentration factors (SCF) for butt welds in stiffened plates. The geometry investigated is that typical used in stiffened plates in floating production vessels and ships. The geometry is also considered to be in the relevant range for semisubmersibles. Stress concentration factors are derived at the butt weld in the midway between the longitudinal stiffeners and at butt welds in way of cope holes of the longitudinal stiffener. Based on the performed work an equation accounting for eccentricity of plates due to fabrication tolerances and difference in thickness is derived that also has been included in the DNV Recommended Practice for fatigue analysis.
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Watson, Andrew, Carol Featherston, and David Kennedy. "Optimization of Postbuckled Stiffened Panels with Multiple Stiffener Sizes." In 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2007. http://dx.doi.org/10.2514/6.2007-2207.

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Blochberger, Joseph A. "Analysis of Structural Acoustic Design Variables for a Periodically Stiffened Plate Using the Finite Element Method." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10259.

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Abstract Investigating the acoustic radiation of stiffened plate structures is significant to the advancement of aircraft, automobile, and marine vehicle design. Plate and stiffener design variables affect how the global structure vibrates and radiates sound. The objective of this paper is to provide insight into how sensitive a periodically stiffened plate radiates sound in air with respect to its design variables. This paper examines a clamped plate that is periodically stiffened along one direction. Finite element analysis is used to quantify the structural acoustic behavior of the plate subject to a harmonic point load at the plate’s center. Fourier transforms are performed along the plate’s surface to reveal the wavenumber content of the plate. Lastly, radiated sound power from the plate surface is computed. A baseline plate without stiffeners is used for finite element modeling validation. Next, periodically spaced beams used for plate stiffening are inserted and varied in thickness. In addition, the plate thickness is also varied. Varying the plate thickness and the stiffener thickness provides insight to each design variable’s contribution to vibration and radiated sound power. The quantified findings from these parametric case studies serve as an insight into the structural acoustic performance of periodically stiffened structures.
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KASSAPOGLOU, CHRISTOS. "STRESS DETERMINATION AT SKIN-STIFFENER INTERFACES OF COMPOSITE STIFFENED PANELS UNDER GENERALIZED LOADING." In 34th Structures, Structural Dynamics and Materials Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1993. http://dx.doi.org/10.2514/6.1993-1509.

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VAICAITIS, R. "Response of discretely stiffened structures." In 28th Structures, Structural Dynamics and Materials Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1987. http://dx.doi.org/10.2514/6.1987-915.

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van der Veen, Sjoerd, and Daniel Coatta. "Stiffened Panels in Compression: Redirecting Loads Toward High-Strength Stiffeners." In 45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics & Materials Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2004. http://dx.doi.org/10.2514/6.2004-2051.

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Reports on the topic "Stiffened structures"

1

Thornell, Travis, Charles Weiss, Sarah Williams, Jennifer Jefcoat, Zackery McClelland, Todd Rushing, and Robert Moser. Magnetorheological composite materials (MRCMs) for instant and adaptable structural control. Engineer Research and Development Center (U.S.), November 2020. http://dx.doi.org/10.21079/11681/38721.

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Magnetic responsive materials can be used in a variety of applications. For structural applications, the ability to create tunable moduli from relatively soft materials with applied electromagnetic stimuli can be advantageous for light-weight protection. This study investigated magnetorheological composite materials involving carbonyl iron particles (CIP) embedded into two different systems. The first material system was a model cementitious system of CIP and kaolinite clay dispersed in mineral oil. The magnetorheological behaviors were investigated by using parallel plates with an attached magnetic accessory to evaluate deformations up to 1 T. The yield stress of these slurries was measured by using rotational and oscillatory experiments and was found to be controllable based on CIP loading and magnetic field strength with yield stresses ranging from 10 to 104 Pa. The second material system utilized a polystyrene-butadiene rubber solvent-cast films with CIP embedded. The flexible matrix can stiffen and become rigid when an external field is applied. For CIP loadings of 8% and 17% vol %, the storage modulus response for each loading stiffened by 22% and 74%, respectively.
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Biskner, Adam, and John Higgins. Design and Evaluation of a Reinforced Advanced-Grid Stiffened Composite Structure. Fort Belvoir, VA: Defense Technical Information Center, January 2005. http://dx.doi.org/10.21236/ada443361.

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CAPACITY EVALUATION OF EIGHT BOLT EXTENDED ENDPLATE MOMENT CONNECTIONS SUBJECTED TO COLUMN REMOVAL SCENARIO. The Hong Kong Institute of Steel Construction, September 2021. http://dx.doi.org/10.18057/ijasc.2021.17.3.6.

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The extended stiffened endplate (8ES) connection is broadly used in the seismic load-resisting parts of steel structures. This connection is prequalified based on the AISC 358 standard, especially for seismic regions. To study this connection’s behaviors, in the event of accidental loss of a column, the finite element model results were verified against the available experimental data. A parametric study using the finite element method was then carried out to investigate these numerical models’ maximum capacity and effective parameters' effect on their maximum capacity in a column loss scenario. This parametric analysis demonstrated that these connections fail at the large displacement due to the catenary action mode at the rib stiffener's vicinity. The carrying capacity, PEEQ, Von-Mises stress, middle column force-displacement, critical bolt axial load, and the beam axial load curves were discussed. Finally, using the Least Square Method (LSM), a formula is presented to determine the displacement at the maximum capacity of these connections. This formula can be used in this study's presented method to determine the maximum load capacity of the 8ES connections in a column loss scenario.
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