Stress Analysis of B-52b and B-52h Air-Launching Systems Failure-Critical Structural Components

The operational life analysis of any airborne failure-critical structural component requires the stress-load equation, which relates the applied load to the maximum tangential tensile stress at the critical stress point. The failure-critical structural components identified are the B-52B–Pegasus®* pylon adapter shackles, B-52B–Pegasus® pylon hooks, B-52H airplane pylon hooks, B-52H airplane front fittings, B-52H airplane rear pylon fitting, and the B-52H airplane pylon lower sway brace. Finite-element stress analysis was performed on the said structural components, and the critical stress point was located and the stress-load equation was established for each failure-critical structural component. The ultimate load, yield load, and proof load needed for operational life analysis were established for each failure-critical structural component. NOMENCLATURE ALTV approach and landing test vehicle B-52B the NASA “B” model B-52 air launching aircraft B-52H the NASA “H” model B-52 air launching aircraft C coefficient of Walker crack growth equation, E Young’s modulus, lb/in2 E23 bar element with axial stiffness only E33 triangular combined membrane and bending element E43 quadrilateral combined membrane and bending element G shear modulus, lb/in2 JLOC joint location KIC mode I critical stress intensity factor, Kmax mode I stress intensity factor associated with maximum stress of one cycle, m Walker exponent associated with Kmax n Walker exponent associated with R R stress ratio of one stress cycle SRB/DTV solid rocket booster/drop-test vehicle t thickness, in. V applied load, lb V* proof load, lb VU ultimate load which causes critical stress point to fail, lb VY yield load which causes critical stress point to yield, lb x, y, z Cartesian coordinates x displacement in x direction y displacement in y direction r displacement in radial direction stress-load coefficient, ksi/lb *Pegasus® is a registered trademark of Orbital Sciences Corporation, Fairfax, Virginia. in cycle -----------ksi in m –