A fatigue model which predicts cycles-to-failure for helically armored cables subjected to fluctuating axial tension is proposed. Electrical-optical communication cables, power cables, and bridge and track strands normally derive structural strength from two or more layers of round steel wires contrahelically laid around a cylindrical core. In cases where wires are laid in direct contact with wires in adjacent layers, Hertz contact stresses produce wire failures leading to ultimate cable failure at tensions well below the static breaking strength. The proposed model treats cross-wire Hertz contact stresses as equivalent geometric notches in conjunction with the numerical solution of the governing helical wire cable equations. Model and physical test results show good agreement.

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