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  • 1
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    Graphite/epoxy Composite Laminates with Co-cured Interlaminar Damping Layers (1993)
    In:  CASI
    Details
    Publication Date: 2014-08-29
    Description: Damped composite laminates were fabricated by co-curing viscoelastic damping film with graphite/epoxy prepreg plies. The dynamic response of the damped plates was measured using an impulse response technique and compared with the response of similar undamped laminates. Modal damping was computed from the frequency response data. Micrographs of the damped laminates showed that the damping layers retained their integrity during the fabrication process. The layers significantly increased the damping in the composite laminates. The use of the constrained viscoelastic film as an integral part of composite structures appears to be a feasible approach to passive vibration control. Composite plates manufactured with co-cured damping layers may have commercial applications in cases where light weight, strength, and vibration and noise reduction are important considerations.
    Keywords: COMPOSITE MATERIALS
    Type: NASA, Washington, Technology 2002: The Third National Technology Transfer Conference and Exposition, Volume 1; p 250-255
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Stress distribution in composite flatwise tension test specimens (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A finite element analysis was conducted to determine the stress distribution in typical graphite/epoxy composite flat wise tension (FWT) specimens under normal loading conditions. The purpose of the analysis was to determine the relationship between the applied load and the stress in the sample to evaluate the validity of the test as a means of measuring the out-of-plane strength of a composite laminate. Three different test geometries and three different material lay ups were modeled. In all cases, the out-of-plane component of stress in the test section was found to be uniform, with no stress concentrations, and very close to the nominal applied stress. The stress in the sample was found to be three-dimensional, and the magnitude of in-plane normal and shear stresses varied with the anisotropy of the test specimen. However, in the cases considered here, these components of stress were much smaller than the out-of-plane normal stress. The geometry of the test specimen had little influence on the results. It was concluded that the flat wise tension test provides a good measure of the out-of-plane strength for the representative materials that were studied.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-106074 , E-7683 , NAS 1.15:106074
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Improved Transverse Crack Detection in Composites (1990)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: A modified ultrasonic C-scan technique was implemented for improving the detection of a certain type of damage in composite specimens. The type of damage being studied is transverse (through the thickness) cracking of unidirectional off-axis graphite-epoxy specimens. These cracks are difficult to detect using standard through-transmission C-scan techniques. The modification is based on mode conversion to produce transmitted shear waves from incident longitudinal waves. While mode conversion is used extensively with isotropic materials, its use with composites is more limited. This is largely because the computation of wave propagation parameters is significantly more complicated with highly anisotropic materials than with isotropic materials. The appropriate incident angles to produce the desired mode conversion were computed based on the mechanical properties of the composite. Once the angles were computed the technique was simple to implement and resulted in marked improvement in detection of the transverse cracks being studied.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-103261 , E-5650 , NAS 1.15:103261 , Society of Plastics Engineers Regional Technical Conference; Oct 16, 1990 - Oct 18, 1990; Los Angeles, CA; United States
    Format: application/pdf
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