Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Book Description
This research aims to develop, analyze, and evaluate a new type of structural element that will enhance the crashworthiness of naval vehicles by providing outstanding energy absorption with minimal weight. The structural element is an array of concentric fiber reinforced composite tubes with extension-twist coupling and ultra-high Poisson's ratio. The tubes are configured to crush or shear internal foam as a means of absorbing energy. This interim report includes technical progress, plans, publications, and various administrative matters. In the current period, work has focused on evaluating the mechanisms of energy absorption in composite tubular structures and the development of analytical models for predicting the deformation and damage in these tubular structures. A significant effort was dedicated towards developing the manufacturing and testing technology for tubes having extension-twist coupling. This effort culminated in the successful demonstration, for the first time, of energy dissipation in extension-twist coupled tubes with sandwich foam.
Author: A.G. Mamalis
Publisher: CRC Press
ISBN: 1351457551
Category : Technology & Engineering
Languages : en
Pages : 270
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Book Description
FROM THE INTRODUCTION Vehicle crashworthiness has been improving in recent years with attention mainly directed towards reducing the impact of the crash on the passengers. Effort has been spent in experimental research and in establishing safe theoretical design criteria on the mechanics of crumpling, providing to the engineers the ability to design vehicle structures so that the maximum amount of energy will dissipate while the material surrounding the passenger compartment is deformed, thus protecting the people inside. During the last decade the attention given to crashworthiness and crash energy management has been centered on composite structures. The main advantages of fibre reinforced composite materials over more conventional isotropic materials, are the very high specific strengths and specific stiffness which can be achieved. Moreover, with composites, the designer can vary the type of fibre, matrix and fibre orientation to produce composites with proved material properties. Besides the perspective of reduced weight, design flexibility and low fabrication costs, composite materials offer a considerable potential for lightweight energy absorbing structures; these facts attract the attention of the automotive and aircraft industry owing to the increased use of composite materials in various applications, such as frame rails used in the apron construction of a car body and the subfloor of an aircraft, replacing the conventional materials used. Our monograph is intended to provide an introduction to this relatively new topic of structural crashworthiness for professional engineers. It will introduce them to terms and concepts of it and acquaint them with some sources of literature about it. We believe that our survey constitutes a reasonably well-balanced synopsis of the topic.
Author: A. Praveen Kumar
Publisher: Springer Nature
ISBN: 9819952891
Category : Technology & Engineering
Languages : en
Pages : 121
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Book Description
This book summarizes many of the recent advances in the design and application of thin-walled composite protective structures. The past few decades have seen outstanding advances in the use of composite materials in structural applications. Composites have revolutionized traditional design concepts and made possible an unparalleled range of new and exciting possibilities as viable materials for construction. This book presents an extensive survey on recent improvements in the research and development of composites and biocomposites that are used to make structures in various applications. This book deals with design, research and development studies, experimental investigations, theoretical analysis, and fabrication techniques relevant to the application of composites in load-bearing components for assemblies, ranging from individual components such as plates and shells to complete composite structures. This book also focuses the recent advances in biocomposite materials from renewable resources and introduces a potential application of this material. The content is this book benefits the academics, researchers, scientists, engineers, and students in the field of epoxy blends for application as lightweight advanced composite structures.
Author: Bonnie Wade
Publisher:
ISBN:
Category : Absorption
Languages : en
Pages : 368
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Book Description
As fiber reinforced composite material systems become increasingly utilized in primary aircraft and automotive structures, the need to understand their contribution to the crash worthiness of the structure is of great interest to meet safety certification requirements. The energy absorbing behavior of a composite structure, however, is not easily predicted due to the great complexity of the failure mechanisms that occur within the material. Challenges arise both in the experimental characterization and in the numerical modeling of the material/structure combination. At present, there is no standardized test method to characterize the energy absorbing capability of composite materials to aide crash worthy structural design. In addition, although many commercial finite element analysis codes exist and offer a means to simulate composite failure initiation and propagation, these models are still under development and refinement. As more metallic structures are replaced by composite structures, the need for both experimental guidelines to characterize the energy absorbing capability of a composite structure, as well as guidelines for using numerical tools to simulate composite materials in crash conditions has become a critical matter. This body of research addresses both the experimental characterization of the energy absorption mechanisms occurring in composite materials during crushing, as well as the numerical simulation of composite materials undergoing crushing. In the experimental investigation, the specific energy absorption (SEA) of a composite material system is measured using a variety of test element geometries, such as corrugated plates and tubes. Results from several crush experiments reveal that SEA is not a constant material property for laminated composites, and varies significantly with the geometry of the test specimen used. The variation of SEA measured for a single material system requires that crush test data must be generated for a range of different test geometries in order to define the range of its energy absorption capability. Further investigation from the crush tests has led to the development of a direct link between geometric features of the crush specimen and its resulting SEA. Through micrographic analysis, distinct failure modes are shown to be guided by the geometry of the specimen, and subsequently are shown to directly influence energy absorption. A new relationship between geometry, failure mode, and SEA has been developed. This relationship has allowed for the reduction of the element-level crush testing requirement to characterize the composite material energy absorption capability. In the numerical investigation, the LS-DYNA composite material model MAT54 is selected for its suitability to model composite materials beyond failure determination, as required by crush simulation, and its capability to remain within the scope of ultimately using this model for large-scale crash simulation. As a result of this research, this model has been thoroughly investigated in depth for its capacity to simulate composite materials in crush, and results from several simulations of the element-level crush experiments are presented. A modeling strategy has been developed to use MAT54 for crush simulation which involves using the experimental data collected from the coupon- and element-level crush tests to directly calibrate the crush damage parameter in MAT54 such that it may be used in higher-level simulations. In addition, the source code of the material model is modified to improve upon its capability. The modifications include improving the elastic definition such that the elastic response to multi-axial load cases can be accurately portrayed simultaneously in each element, which is a capability not present in other composite material models. Modifications made to the failure determination and post-failure model have newly emphasized the post-failure stress degradation scheme rather than the failure criterion which is traditionally considered the most important composite material model definition for crush simulation. The modification efforts have also validated the use of the MAT54 failure criterion and post-failure model for crash modeling when its capabilities and limitations are well understood, and for this reason guidelines for using MAT54 for composite crush simulation are presented. This research has effectively (a) developed and demonstrated a procedure that defines a set of experimental crush results that characterize the energy absorption capability of a composite material system, (b) used the experimental results in the development and refinement of a composite material model for crush simulation, (c) explored modifying the material model to improve its use in crush modeling, and (d) provided experimental and modeling guidelines for composite structures under crush at the element-level in the scope of the Building Block Approach.
Author: David C. Fleming
Publisher:
ISBN: 9781605956466
Category : Composite materials
Languages : en
Pages : 329
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Book Description
Author: Nageswara Rao Janapala
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Fiber reinforced composites currently being used in myriad applications including aerospace, defense and wind industries due to their light weight, higher specific strength and stiffness, compared to traditional metallic structures. For crashworthiness applications, advanced textile composites such as fabrics and braids, are showing superior performance over traditional tape laminated composites structures. Kevlar fabric composites, in particular, are offering a great potential as the next generation energy absorbing material for the rotorcraft applications. Unfortunately, none of the existing material models can predict the behavior of Kevlar fabric composites for the crashworthiness applications. The prime objective of this investigation is to develop a computationally efficient and robust material model based on a unified unit-cell approach to simulate the crush response of tubular and honeycomb structures made of Kevlar fabric composites under quasi-static and dynamic loading conditions. Tests are conducted at various levels to understand the constitutive behavior of Kevlar fabric composites. Based on experimental observations, a physics based material model is developed. This material model is then implemented in commercial finite element software such as LS-DYNA and ABAQUS as a User Material (UMAT) Routine. The material model is built by considering majority of length scales in the composites: Kevlar composite tows at the meso-scale, a fabric unit cell at macro-scale and overall structural level. The material model identifies a smallest repetitive unit (i.e. unit-cell) within the composite material. The tow geometry within the unit-cell is represented using a simplified three-dimensional description. An elastic-plastic constitutive law is developed to simulate the behavior of Kevlar composite tows. Efficient homogenization scheme along with appropriate failure criteria is implemented to calculate the effective quantities such as stiffness and stress and predict the response of the unit-cell. Coupon tests are conducted on unidirectional Kevlar and plain woven Kevlar fabric flat plaques. The unidirectional coupon tests are conducted to characterize the material properties such as stiffness, strength and plastic parameters necessary as input to the material model. The plain woven fabric coupon tests are conducted to verify the initial stiffness, strength and damage progression predictions of the model at the ply-level. Several tubes with square and circular cross-section are crushed quasi-statically using both flat-plate and plug-type crush initiators. During crushing, Kevlar fabric composite tubes buckled locally and failed progressively by forming folds similar to aluminum tubes. Test results show that the failure mode and overall energy absorption is not affected significantly by the change in fabric angle or the method of crushing. Dynamic crush tests on Kevlar fabric honeycomb structures also exhibited global folding failure mechanism with very little fiber fracture. During crushing, honeycombs typically reach a peak load and then crush at constant, sustained load which is a characteristic of an ideal crash energy behavior. The material module is verified by carrying out simulations at different levels. Coupon test data is initially validated for both the initial stiffness and the strength predictions. Tubular and honeycomb crush data is validated for the deformation behavior, the failure mechanism and the crash energy absorption characteristics. Strong correlation between simulation and experiments suggests that the model can be used as state-of-the-art computational tool for predicting the crushing behavior of tubular and honeycomb structures made of Kevlar fabric composites.
Author: G Lu
Publisher: Elsevier
ISBN: 1855738589
Category : Technology & Engineering
Languages : en
Pages : 419
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Book Description
This important study focuses on the way in which structures and materials can be best designed to absorb kinetic energy in a controllable and predictable manner. Understanding of energy absorption of structures and materials is important in calculating the damage to structures caused by accidental collision, assessing the residual strength of structures after initial damage and in designing packaging to protect its contents in the event of impact. Whilst a great deal of recent research has taken place into the energy absorption behaviour of structures and materials and significant progress has been made, this knowledge is diffuse and widely scattered. This book offers a synthesis of the most recent developments and forms a detailed and comprehensive view of the area. It is an essential reference for all engineers concerned with materials engineering in relation to the theory of plasticity, structural mechanics and impact dynamics. - Important new study of energy absorption of engineering structures and materials - Shows how they can be designed to withstand sudden loading in a safe, controllable and predictable way - Illuminating case studies back up the theoretical analysis
Author: J. K. Wells
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: I.H. Marshall
Publisher: Springer
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 872
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Book Description
The papers contained herein were presented at the Sixth International Conference on Composite Structures (ICCS/6) held at Paisley College, Scotland in September 1991. The Conference was organised and sponsored by Paisley College. It was co-sponsored by Scottish Enterprise, the National Engineering Laboratory, the US Army Research, Development and Standardisation Group-UK, Strathclyde Regional Council and Renfrew District Council. It forms a natural and ongoing progression from the highly successful ICCS/1/2/3/4 and 5 held at Paisley in 1981, 1983, 1985, 1987 and 1989 respectively. As we enter the final decade of this century many organisations throughout the world are adopting a prophetic role by attempting to forecast future scientific advances and their associated impact on mankind. Although some would argue that to do so is folly, without such futuristic visionaries the world would be that much poorer. IntelJigent speculation based on research trends and historical advances, rather than fanciful theories, breathes a healthy air of enthusiasm into the scientific community. Surely this is the very oxygen necessary to ignite the fir~s of innovation and invention amongst pioneers of research.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
In this investigation the effects of material, structural and testing parameters of carbon epoxy braided composite tubes were analysed with respect to their performance in crush and impact conditions. An original method of manufacturing the composite tubes with vacuum infusion together with an expandable foam core to form multi-cellular structures was used. Low cost, 24k tow carbon fibre braids were used and their performance was compared with that of the more expensive l2k tow size fibres. The specimens produced were axially crushed at constant quasi-static low velocities and at higher impact velocities using an instrumented falling weight machine. Load displacement data gathered from such tests were used to evaluate the test specimens with respect to their specific energy absorption values. The effects of a number of parameters, including fibre tow size, braid architecture, resin content and loading type, were evaluated. From the experimental results analysed from the test specimens it can be concluded that: The 24k fibre showed lower specific energy absorption values than specimens made from l2k fibre; Epoxy resin content rather than epoxy resin type can significantly affect the specific energy absorption values. In general, specimens tested in impact loading exhibited lower specific energy absorption values than the same specimens test in quasi-static crush. A reasonably good correlation between global density and specific energy absorption for the type of structures examined was found.
