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    Analytical Modeling and ND Monitoring of Interlaminar Defects in Fiber-Reinforced Composites

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    Interlaminar defects in laminated structural components made of fiber-reinforced composites originate during fabrication or service, or both. Fabrication defects occur during the preparation of the prepreg, laminate layup and cure, or assembly. Service damage may be precipitated by a fatigue load spectrum, impact, or environmental effects. An analytical evaluation of the critical flaw size as a function of the applied stress levels, fatigue cycles, and environment helps quantify the severity of such flaws. A methodology is developed to use nondestructive measurements of the flaw size, after a given period of service, to establish new bounds for fail-safe applications. The analysis considers delaminations in a cantilevered, laminated beam at arbitrary locations along the length of the beam and through its thickness. For an initial flaw size, the critical load at which the debond tends to propagate is estimated through the Griffith energy balance criterion. The beam is modeled as a Timoshenko beam and the individual laminae are graphite fiber-reinforced epoxy matrix composites. A wearout concept is used to account for property degradation with service and the resultant change in the criticality of the flaw. A family of plots for different loading cycles is used to establish bounds on the service life and the maximum growth of the flaw, for a given loading and any initial flaw size. In addition, a catastrophic debond growth boundary is also established. An ND monitoring of the defect size, in liaison with the above, will enhance the fail-safe design of the structural component by a nondestructive evaluation (NDE) analyst.


    composite materials, delaminations, nondestructive evaluation, Griffith criterion, wearout concept, crack propagation, fatigue (materials)

    Author Information:

    Ramkumar, RL
    Senior engineers, Materials Sciences Corp., Blue Bell Office Campus, Blue Bell, Pa.

    Kulkarni, SV
    Consulting engineer, Lansdale, Pa.

    Pipes, RB
    Associate professor, University of Delaware, Newark, Del.

    Chatterjee, SN
    Senior engineers, Materials Sciences Corp., Blue Bell Office Campus, Blue Bell, Pa.

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP34942S