Nonlinear analysis of a helically armored cable with nonuniform mechanical properties in tension and torsion

A procedure is reported for the stress analysis of straight cables subject to tension and torsion forces. Cables with one end free to rotate, or both ends fixed, are treated. Equations have been derived which are valid for a broad category of cable designs. Individual helical wires may have unique values for elastic modulus, strength and geometrical quantities; compressibility and material nonlinearity of the core element can be included; and geometric nonlinearity caused by large elongation or rotation is taken into account with exact mathematical expressions. The resulting equations are highly nonlinear; thus, they have been solved numerically on the computer. Approximate linear equations suitable for hand calculation also have been derived. Solutions have been obtained for two conventional steel cables and a cable utilizing armor wires fabricated from the organic filament, KEVLAR-49. In each case, good agreement with experimental results has been achieved.