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    Fatigue of Notched Fiber Composite Laminates: Analytical and Experimental Evaluation

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    This paper describes the analytical/experimental correlation study performed to develop an understanding of the behavior of notched boron/epoxy laminates subjected to tension/tension fatigue loading. The static failure analysis of notched laminates used herein treats the following modes of failure: axial cracking in the load direction, and transverse cracking across the specimen. The “mechanistic wearout” fatigue analysis uses this static failure model and embodies the concept that material properties in the notch region are continually changing with cyclic loading and that, if these properties are known at a given time, they could be used in the static failure analysis to compute residual strength and preferred mode of crack propagation. In order to verify the fatigue model, an experimental program of limited scope was undertaken to obtain boron/epoxy lamina static and fatigue data (longitudinal and transverse tension and in-plane shear), unnotched [02/±45]s laminate static data, and notched [02/±45]s laminate static and fatigue data. Laminate fatigue behavior was determined from lamina fatigue data, and analysis predictions were compared with the notched-laminate fatigue data. The specific phenomena of interest are the initiation of fatigue damage and its growth as a function of load cycles, fatigue life and mode of failure, and the residual strength after a predetermined number of cycles and the corresponding mode of failure. Certain predicted phenomena such as the increase in residual strength after fatigue loading and both axial and transverse damage growth were observed experimentally. However, correlation of theory and experiment was hampered by the following factors: delamination of the 0-deg surface layers in the region of the longitudinal projection of the notch diameter, lack of statistically significant data base for lamina fatigue properties in general, and absence of lamina axial compression fatigue data in particular. The principal deficiency appears to be the lack of a capability to predict growth of delaminations. Therefore, the interplay of stacking sequence and various failure modes needs to be investigated analytically and experimentally in detail.


    composite materials, fracture tests, fatigue (materials), notch strength, failure

    Author Information:

    Kulkarni, SV
    Senior engineer and president, Materials Sciences Corporation, Blue Bell Office Campus, Blue Bell, Pa.

    McLaughlin, PV
    Associate professor, Villanova University, Villanova, Pa.

    Pipes, RB
    Associate professoraffiliate staff member, University of DelawareMaterials Sciences Corporation, Newark, Del.

    Rosen, BW
    Senior engineer and president, Materials Sciences Corporation, Blue Bell Office Campus, Blue Bell, Pa.

    Committee/Subcommittee: D30.02

    DOI: 10.1520/STP26936S