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  • 1
    Keywords: Engineering ; Materials
    ISBN: 9781402085840
    Language: English
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  • 2
    Publication Date: 2009-06-30
    Print ISSN: 0376-9429
    Electronic ISSN: 1573-2673
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 3
    Publication Date: 2018-06-02
    Description: Super-elements can greatly improve the computational efficiency of analyses of tile-reinforced structures such as the hull of the Composite Armored Vehicle. By taking advantage of the periodicity in this type of construction, super-elements can be used to simplify the task of modeling, to virtually eliminate the time required to assemble the stiffness matrices, and to reduce significantly the analysis solution time. Furthermore, super-elements are fully transferable between analyses and analysts, so that they provide a consistent method to share information and reduce duplication. This paper describes a methodology that was developed to model and analyze large upper hull components of the Composite Armored Vehicle. The analyses are based on two types of superelement models. The first type is based on element-layering, which consists of modeling a laminate by using several layers of shell elements constrained together with compatibility equations. Element layering is used to ensure the proper transverse shear deformation in the laminate rubber layer. The second type of model uses three-dimensional elements. Since no graphical pre-processor currently supports super-elements, a special technique based on master-elements was developed. Master-elements are representations of super-elements that are used in conjunction with a custom translator to write the superelement connectivities as input decks for ABAQUS.
    Keywords: Composite Materials
    Format: text
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  • 4
    Publication Date: 2019-06-15
    Description: The fatigue life and damage tolerance of composite stiffened panels with indentation damage are investigated experimentally using single-stringer compression specimens. The indentation damage was induced to one of the two flanges of the stringer of every panel. The advantages of indentation compared to impact are the simplicity of application, less dependence on boundary conditions, better controllability, and repeatability of the imparted damage. The tests were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in situ ultrasonic scanning. Specimens with initial indentation damage ranging between 32 and 56 mm in length were tested quasi-statically and in fatigue, and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed. The stress intensity measure provides the means to compare the collapse loads of specimens with different damage types and damage sizes, while the Paris law is used to compare the damage propagation rates in specimens subjected to different cyclic loads. This approach enables a comparison of different tests and the potential identification of the effects that influence the fatigue lives and damage tolerance of postbuckled structures with defects.
    Keywords: Structural Mechanics; Composite Materials
    Type: NF1676L-26424 , Journal of Composite Materials (ISSN 0021-9983) (e-ISSN 1530-793X); 52; 7; 931-943
    Format: application/pdf
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  • 5
    Publication Date: 2019-07-13
    Description: A progressive failure analysis method based on shell elements is developed for the computation of damage initiation and growth in stiffened thick-skin stitched graphite-epoxy panels loaded in axial compression. The analysis method involves a step-by-step simulation of material degradation based on ply-level failure mechanisms. High computational efficiency is derived from the use of superposed layers of shell elements to model each ply orientation in the laminate. Multiple integration points through the thickness are used to obtain the correct bending effects through the thickness without the need for ply-by-ply evaluations of the state of the material. The analysis results are compared with experimental results for three stiffened panels with notches oriented at 0, 15 and 30 degrees to the panel width dimension. A parametric study is performed to investigate the damage growth retardation characteristics of the Kevlar stitch lines in the pan
    Keywords: Composite Materials
    Type: AIAA Paper 99-1435 , 40th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 12, 1999 - Apr 15, 1999; Saint Louis, MO; United States
    Format: application/pdf
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  • 6
    Publication Date: 2019-07-13
    Description: A criterion for matrix failure of laminated composite plies in transverse tension and in-plane shear is developed by examining the mechanics of transverse matrix crack growth. Matrix cracks are assumed to initiate from manufacturing defects and can propagate within planes parallel to the fiber direction and normal to the ply mid-plane. Fracture mechanics models of cracks in unidirectional laminates, embedded plies and outer plies are developed to determine the onset and direction of propagation for unstable crack growth. The models for each ply configuration relate ply thickness and ply toughness to the corresponding in-situ ply strength. Calculated results for several materials are shown to correlate well with experimental results.
    Keywords: Structural Mechanics
    Type: 9th Portuguese Conference on Fracture; Feb 18, 2004 - Feb 20, 2004; Setubal; Portugal
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  • 7
    Publication Date: 2019-07-13
    Description: The durability and damage tolerance of postbuckled composite structures are not yet completely understood, and remain difficult to predict due to the nonlinearity of the geometric response and its interaction with local damage modes. A research effort was conducted to investigate experimentally the quasi-static and fatigue damage progression in a single-stringer compression (SSC) specimen. Three specimens were manufactured with a hat-stiffener, and an initial defect was introduced with a Teflon film embedded between one flange of the stringer and the skin. One of the specimens was tested under quasi-static compressive loading, while the remaining two specimens were tested by cycling in postbuckling. The tests were performed at the NASA Langley Research Center under controlled conditions and with instrumentation that allows a precise evaluation of the postbuckling response and of the damage modes. Three-dimensional digital image correlation VIC-3D systems were used to provide full field displacements and strains on the skin and the stringer. Passive thermal monitoring was conducted during the fatigue tests using an infrared camera that showed the location of the delamination front while the specimen was being cycled. The live information from the thermography was used to stop the fatigue tests at critical stages of the damage evolution to allow detailed ultrasonic scans.
    Keywords: Composite Materials; Structural Mechanics; Quality Assurance and Reliability
    Type: NF1676L-18235 , US-Japan Conference on Composite Materials, ASTM-D30 Joint Conference; Sep 08, 2014 - Sep 11, 2014; La Jolla, CA; United States|ASTM-D30 Committee Meeting; Sep 08, 2014 - Sep 11, 2014; La Jolla, CA; United States|American Society for Composites Technical Conference, 16th US-Japan Conference on Composite Materials, ASTM-D30 Joint Conference; Sep 08, 2014 - Sep 11, 2014; La Jolla, CA; United States
    Format: application/pdf
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  • 8
    Publication Date: 2019-07-13
    Description: A method is proposed and assessed for the experimental characterization of through-the-thickness crack propagation in multidirectional composite laminates with a cohesive law. The fracture toughness and crack opening displacement are measured and used to determine a cohesive law. Two methods of computing fracture toughness are assessed and compared. While previously proposed cohesive characterizations based on the R-curve exhibit size effects, the proposed approach results in a cohesive law that is a material property. The compact tension specimen configuration is used to propagate damage while load and full-field displacements are recorded. These measurements are used to compute the fracture toughness and crack opening displacement from which the cohesive law is characterized. The experimental results show that a steady-state fracture toughness is not reached. However, the proposed method extrapolates to steady-state and is demonstrated capable of predicting the structural behavior of geometrically-scaled specimens.
    Keywords: Composite Materials
    Type: NF1676L-18222 , US-Japan Conference on Composite Materials; Sep 08, 2014 - Sep 10, 2014; La Jolla, CA; United States|ASTM-D30 Meeting; Sep 08, 2014 - Sep 10, 2014; La Jolla, CA; United States|American Society for Composites Technical Conference; Sep 08, 2014 - Sep 10, 2014; La Jolla, CA; United States
    Format: application/pdf
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  • 9
    Publication Date: 2019-07-13
    Description: Unmanned Aerial Vehicles (UAV) are fundamental components in several aspects of research at NASA Langley, such as flight dynamics, mission-driven airframe design, airspace integration demonstrations, atmospheric science projects, and more. In particular, NASA Langley Research Center (Langley) is using UAVs to develop and demonstrate innovative capabilities that meet the autonomy and robotics challenges that are anticipated in science, space exploration, and aeronautics. These capabilities will enable new NASA missions such as asteroid rendezvous and retrieval (ARRM), Mars exploration, in-situ resource utilization (ISRU), pollution measurements in historically inaccessible areas, and the integration of UAVs into our everyday lives all missions of increasing complexity, distance, pace, and/or accessibility. Building on decades of NASA experience and success in the design, fabrication, and integration of robust and reliable automated systems for space and aeronautics, Langley Autonomy Incubator seeks to bridge the gap between automation and autonomy by enabling safe autonomous operations via onboard sensing and perception systems in both data-rich and data-deprived environments. The Autonomy Incubator is focused on the challenge of mobility and manipulation in dynamic and unstructured environments by integrating technologies such as computer vision, visual odometry, real-time mapping, path planning, object detection and avoidance, object classification, adaptive control, sensor fusion, machine learning, and natural human-machine teaming. These technologies are implemented in an architectural framework developed in-house for easy integration and interoperability of cutting-edge hardware and software.
    Keywords: Air Transportation and Safety; Cybernetics, Artificial Intelligence and Robotics
    Type: NF1676L-23576 , Simon Stevin Symposium 2016; Mar 16, 2016; Eindhoven; Netherlands
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  • 10
    Publication Date: 2019-07-13
    Description: The development of durable bonded joint technology for assembling composite structures for launch vehicles is being pursued for the U.S. Space Launch System. The present work is related to the development and application of progressive damage modeling techniques to bonded joint technology applicable to a wide range of sandwich structures for a Heavy Lift Launch Vehicle. The joint designs studied in this work include a conventional composite splice joint and a NASA-patented Durable Redundant Joint. Both designs involve a honeycomb sandwich with carbon/epoxy facesheets joined with adhesively bonded doublers. Progressive damage modeling allows for the prediction of the initiation and evolution of damage. For structures that include multiple materials, the number of potential failure mechanisms that must be considered increases the complexity of the analyses. Potential failure mechanisms include fiber fracture, matrix cracking, delamination, core crushing, adhesive failure, and their interactions. The joints were modeled using Abaqus parametric finite element models, in which damage was modeled with user-written subroutines. Each ply was meshed discretely, and layers of cohesive elements were used to account for delaminations and to model the adhesive layers. Good correlation with experimental results was achieved both in terms of load-displacement history and predicted failure mechanisms.
    Keywords: Composite Materials
    Type: NF1676L-15977 , SAMPE 2013; May 06, 2013 - May 09, 2013; Long Beach, CA; United States
    Format: application/pdf
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