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  • 1
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    Large deflection behavior of circular quasi-isotropic laminates under point loading (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: COMPOSITE MATERIALS
    Type: AIAA Journal (ISSN 0001-1452); 25; 99-106
    Format: text
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  • 2
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    Basic principles of material selection in fracture-critical applications (1976)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A concept of material characterization which shows the relation between initial crack size, stress range, and life to failure is presented. This presentation is used to determine if a particular application is fracture-critical and to choose a suitable material. The influence of design stress inaccuracies on the material selection is assessed.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Format: text
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  • 3
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    Prediction of impact force and duration due to low-velocity impact on circular composite laminates (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two simple and improved models - energy-balance and spring-mass - were developed to calculate impact force and duration during low velocity impact of circular composite plates. Both models include the contact deformation of the plate and the impactor as well as bending, transverse shear, and membrane deformations of the plate. The plate was transversely isotropic graphite/epoxy composite laminate and the impactor was a steel sphere. Calculated impact forces from the two analyses agreed with each other. The analyses were verified by comparing the results with reported test data.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME, Transactions, Journal of Applied Mechanics (ISSN 0021-8936); 52; 674-680
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  • 4
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    Large deflections of circular isotropic membranes subjected to arbitrary axisymmetric loading (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Circular membranes with fixed peripheral edges, subjected to arbitrary axisymmetric loading were analyzed. A single governing differential equation in terms of radial stress was used. This nonlinear governing equation was solved using the finite difference method in conjunction with Newton-Raphson method. Three loading cases, namely: (1) uniformly loaded membrane, (2) a membrane with uniform load over an inner portion, and (3) a membrane with ring load, were analyzed. Calculated central displacement and the central and edge radial stresses for uniformly loaded membrane, agreed extremely well with the classical solution.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 21; 3, 19
    Format: text
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  • 5
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    A fracture mechanics analysis for delamination growth during impact on composite plates (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A fracture mechanics analysis has been developed that describes the progress of delamination damage in composite plates struck by a hard spherical object. The analysis is based on large deflection plate mechanics for circular isotropic plates wherein multiple axisymmetric delaminations grow. Test data show that the analysis predicts the influence of plate thickness, support conditions, and matrix toughness on the onset and propagation of delamination.
    Keywords: STRUCTURAL MECHANICS
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  • 6
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    The Significance of Small Cracks in Fatigue Design Concepts as Related to Rotorcraft Metallic Dynamic Components (2000)
    In:  CASI
    Details
    Publication Date: 2017-09-27
    Description: In this paper the significance of the "small" crack effect as defined in fracture mechanics will be discussed as it relates to life managing rotorcraft dynamic components using the conventional safe-life, the flaw tolerant safe-life, and the damage tolerance design philosophies. These topics will be introduced starting with an explanation of the small-crack theory, then showing how small-crack theory has been used to predict the total fatigue life of fatigue laboratory test coupons with and without flaws, and concluding with how small cracks can affect the crack-growth damage tolerance design philosophy. As stated in this paper the "small" crack effect is defined in fracture mechanics where it has been observed that cracks on the order of 300 microns or less in length will propagate at higher growth rates than long cracks and also will grow at AK values below the long crack AK threshold. The small-crack effect is illustrated herein as resulting from a lack of crack closure and is explained based on continuum mechanics principles using crack-closure concepts in fracture mechanics.
    Keywords: Aircraft Design, Testing and Performance
    Type: Application of Damage Tolerance Principles for Improved Airworthiness of Rotorcraft; 1 - 1 - 1 - 14; RTO-MP-24
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  • 7
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    Rotorcraft fatigue life-prediction: Past, present, and future (1994)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: In this paper the methods used for calculating the fatigue life of metallic dynamic components in rotorcraft is reviewed. In the past, rotorcraft fatigue design has combined constant amplitude tests of full-scale parts with flight loads and usage data in a conservative manner to provide 'safe life' component replacement times. This is in contrast to other industries, such as the automobile industry, where spectrum loading in fatigue testing is a part of the design procedure. Traditionally, the linear cumulative damage rule has been used in a deterministic manner using a conservative value for fatigue strength based on a one in a thousand probability of failure. Conservatism on load and usage are also often employed. This procedure will be discussed along with the current U.S. Army fatigue life specification for new rotorcraft which is the so-called 'six nines' reliability requirement. In order to achieve the six nines reliability requirement the exploration and adoption of new approaches in design and fleet management may also be necessary if this requirement is to be met with a minimum impact on structural weight. To this end a fracture mechanics approach to fatigue life design may be required in order to provide a more accurate estimate of damage progression. Also reviewed in this paper is a fracture mechanics approach for calculating total fatigue life which is based on a crack-closure small crack considerations.
    Keywords: STRUCTURAL MECHANICS
    Type: AGARD, An Assessment of Fatigue Damage and Crack Growth Prediction Techniques; 31 p
    Format: text
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  • 8
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    The Effect of Matrix and Fiber Properties on Impact Resistance (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The basic material properties which control impact damage are identified and testing techniques are assessed. It is demonstrated that static indentation tests can provide better information about failure processes than impact tests, and they are simpler to conduct. In thin and thick laminates, it was found that the matrix shear strength controls the onset of delamination damage and that the fiber strength controlled the penetration phase. In thin laminates, tough matrices do little to enhance impact resistance.
    Keywords: COMPOSITE MATERIALS
    Type: Tough Composite Mater.; p 99-121
    Format: text
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  • 9
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    Dissemination, resuspension, and filtration of carbon fibers (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Carbon fiber transport was studied using mathematical models established for other pollution problems. It was demonstrated that resuspension is not a major factor contributing to the risk. Filtration and fragmentation tests revealed that fiber fragmentation shifts the fiber spectrum to shorter mean lengths in high velocity air handling systems.
    Keywords: COMPOSITE MATERIALS
    Type: Assessment of Carbon Fiber Elec. Effects; p 59-71
    Format: application/pdf
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  • 10
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    The effect of matrix properties and fiber properties on impact failure mechanics (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The low-velocity impact problem in graphite/epoxy composite sheets must be solved before large amounts of that material can be used in commercial aircraft. Many of the low-velocity impacts that affect aircraft parts occur during normal ground operations and maintenance. Service equipment and tools have masses above 1 kg, and at velocities of less than 3 m/s can impact structural parts with energies higher than composites can endure without degradation of stiffness or strength. Simple solutions were developed for large-mass, low-velocity impacts which can be modeled as quasi-static events. Static test data and impact data show that the fiber properties control the impact energy which can be absorbed before penetration. Matrix shear strength and peel resistance control the extent of delamination. Comparison of results from tough matrix and brittle matrix composites show that although tough matrices reduce the extent of delamination, they lead to more fiber damage in the contact area.
    Keywords: STRUCTURAL MECHANICS
    Type: Delaware Univ. Abstr. of the 20th Ann. Meeting, Society of Engineering Science, Inc.; p 57
    Format: text
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