Buckling of fibres and yarns within ropes and other fibre assemblies

Individual yarns within ropes can be subject to axial compression even thou gh the rope as a whole is under tension. This leads to buckling in sharp ki nks and then to failure by axial-compression fatigue after repeated cycling . An existing elastic theory, which applies to heated pipelines subject to lateral and axial restraint, predicts alternative modes of either continuou s buckling or intermittent buckled zones alternating with slip zones. The m echanics of axially compressed yarns within ropes are similar, but the theo ry is extended to cover plastic deformation at hinge points. The predicted form of groups of sawtooth buckles, which curve at the ends of the zones in to the slip lengths, is in agreement with observed effects. Numerical calcu lation gives quantitative predictions in agreement with experimental result s, despite uncertainty about the correct values for bending stiffness and p lastic-yield moment, depending on whether the yarns act as solid rods or fr eely slipping fibre assemblies.