An analytical procedure is presented for predicting the loss in integrity of composite structures subjected to simultaneous intense heating and applied mechanical loads. An in tegral part of the method is a nonlinear, two-dimensional, finite difference thermal analysis which considers the effects of surface ablation, re-irradiation losses, and temperature-dependent thermophysical properties. Another important feature of the structural survivability model is a flat-plate finite element code, based on the Mindlin theory, which is coupled to a maximum stress failure criterion. Predictions from the analysis methodology are compared with experimental results obtained on 24, 48, and 96 ply graphite epoxy tension specimens which were spot-irradiated at various intensity levels.

Breakup of individual wires in a wire rope is associated with fatigue damage and reduction in tensile strength. lin earlier paper 1 showed that wire break density, .plotted as a function of cyclic load, forms a continuous curve with a single maximum. Specific break-count and location of the maximum value varies with rope material and construction. In the earlier paper, substantial increases in cyclic life were obtained through periodic overloading. Continuing laboratory studies ont-in.-diameter wire rope pendants have shown that the major increase in life is achieved by the initial overload, with periodic overloading of only minor additional benefit. lin initial overload reduces the compliance of a rope pendaht so that subsequent use loads.cause less deflection. Cyclic-life data from overloaded specimens fall below those for the control specimens when normalized as a function of specimen deflection.

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Periodic overloads have shown pronounced improve ments in the fatigue endurance of wire rope, typicall;y limited in servi~e use to loads one-fifth of static breaking strength. This enhanced life is attributed to overload crack retardation and to readjustment-or stresses within the rope by movement of contact points between wires during overloads. The optimum overload is thought to be that which just begins to result in rope yield. To optimize rope life one must also look at number of overload cycles, frequency of overload application and rope material and construction as well.