Relationship Between Mechanical-property and Energy-absorption Trends for Composite Tubes PDF Download

Author: WESS HUI-SHIH TAO
Publisher:
ISBN:
Category :
Languages : en
Pages : 366

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flat plate gave the lowest volume specific energy absorption and the plate with radius of curvature 9.5 mm gave the highest.

Author: Gary L. Farley
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 20

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Author: Thomas Jay Brimhall
Publisher:
ISBN:
Category : Automobiles
Languages : en
Pages : 430

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 26

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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:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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In passenger vehicles the ability to absorb energy due to impact and be survivable for the occupant is called the ''crashworthiness'' of the structure. To identify and quantify the energy absorbing mechanisms in candidate automotive composite materials, test methodologies were developed for conducting progressive crush tests on composite plate specimens. The test method development and experimental set-up focused on isolating the damage modes associated with the frond formation that occurs in dynamic testing of composite tubes. Quasi-static progressive crush tests were performed on composite plates manufactured from chopped carbon fiber with an epoxy resin system using compression molding techniques. The carbon fiber was Toray T700 and the epoxy resin was YLA RS-35. The effect of various material and test parameters on energy absorption was evaluated by varying the following parameters during testing: fiber volume fraction, fiber length, fiber tow size, specimen width, profile radius, and profile constraint condition. It was demonstrated during testing that the use of a roller constraint directed the crushing process and the load deflection curves were similar to progressive crushing of tubes. Of all the parameters evaluated, the fiber length appeared to be the most critical material parameter, with shorter fibers having a higher specific energy absorption than longer fibers. The combination of material parameters that yielded the highest energy absorbing material was identified.

Author: Gary L. Farley
Publisher:
ISBN:
Category : Tubular steel structures
Languages : en
Pages : 252

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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: Nageswara Rao Janapala
Publisher:
ISBN:
Category :
Languages : en
Pages :

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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: Norman Jones
Publisher: Butterworth-Heinemann
ISBN:
Category : Science
Languages : en
Pages : 472

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