STP787: Experimental Investigations of Fiber Composite Reinforcement of Cracked Metallic Structures

    Ratwani, MM
    Manager, Engineering Specialist, Senior Engineer, and Senior Technical Specialist, Northrop Corporation, Hawthorne, Calif.

    Kan, HP
    Manager, Engineering Specialist, Senior Engineer, and Senior Technical Specialist, Northrop Corporation, Hawthorne, Calif.

    Fitzgerald, JH
    Manager, Engineering Specialist, Senior Engineer, and Senior Technical Specialist, Northrop Corporation, Hawthorne, Calif.

    Labor, JD
    Manager, Engineering Specialist, Senior Engineer, and Senior Technical Specialist, Northrop Corporation, Hawthorne, Calif.

    Pages: 18    Published: Jan 1982


    Abstract

    The results of an experimental program, carried out to investigate the influence of composite repair patches on the life of cracked metallic structures, are discussed. The influence of parameters such as moisture, temperature, composite patch material, thickness, width, length, and ply orientations on the crack growth life of the repaired metallic structure has been investigated. The metallic materials selected were 7075-T6 and 2024-T3 aluminum alloys, and the composite patch materials selected were graphite/epoxy and boron/epoxy. The adhesive used was FM73. All the repaired specimens were tested under typical wing spectrum loading with a maximum stress of 270 MPa (39.2 ksi) tension and a minimum stress of 68.9 MPa (10.0 ksi) compression.

    Experimental results indicate that composite patches can significantly reduce crack growth rate. Moisture conditioning of the composite patch increases the crack growth rate as compared with the dry patch. However, the improvement is still substantial over that of unreinforced cracked metal part. The width of the patch has considerable influence on the crack growth life. Wider patches give longer life. The length and thickness of the patch have no significant effect on the crack growth life if the patch length and thickness are sufficient to cause full load transfer to the patch.

    Experimental data show that the stacking sequence of the composite patch—that is, putting ±45 or 0 deg plies near the crack surface—has no effect on the crack growth life of the metallic structure.

    Keywords:

    composite materials, crack growth, repair patches, moisture conditioning, spectrum loading


    Paper ID: STP28499S

    Committee/Subcommittee: D30.05

    DOI: 10.1520/STP28499S


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