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    IBOLT: A Composite Bolted Joint Static Strength Prediction Tool

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    The objective of this paper is to describe the bolted joint analysis method developed and used by LM Aeronautics (named IBOLT) including the theoretical basis, required input, and coupon-level strength-prediction validation. IBOLT performs a fracture-mechanics-based static strength prediction for a rectangular composite joint element subjected to any combination of biaxial membrane loads, shear loads, and an off- axis bolt load. Out-of-plane bending moments are also treated. Joint configuration effects (single- or double-shear) are modeled by a beam-on-elastic-foundation analysis to account for the thickness and stiffness of the joint members as well as the bolt bending and shear stiffness. Empirical equations are included to account for fastener head geometry, effects of filled versus open holes, fastener/hole clearance, and fastener torque. Required input, in addition to the usual geometry, loads, fastener, and substrate elastic properties, includes a variety of special laminate-level joint properties. Uni-axial notched, un-notched, and bolted-joint coupon tests are conducted to develop these properties. In addition to these uniaxial coupon tests, bearing/bypass tension and bearing/bypass compression tests have been performed to validate the accuracy of IBOLT strength predictions. An overview of these validation results is provided, along with a brief summary of IBOLT's strengths and weaknesses as a practical bolted joint stress analysis tool.


    composite material, failure, failure criteria, strength, structural requirements, failure modes, allowables, stress analysis, failure analysis, fracture mechanics

    Author Information:

    Eisenmann, JR
    Senior Staff Engineer, Lockheed Martin Aeronautics Company, Fort Worth, TX

    Rousseau, CQ
    Senior Staff Engineer, Lockheed Martin Aeronautics Company, Fort Worth, TX

    Committee/Subcommittee: D30.05

    DOI: 10.1520/STP12589S