Individual yarns within ropes can be subject to axial compression even though the rope
as a whole is under tension. This leads to buckling in sharp kinks 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 continuous buckling or intermittent buckled zones alternating with slip
zones. The mechanics of axially compressed yarns within ropes are similar, but the
theory has been extended to cover plastic deformation at hinge points. The predicted
form of groups of saw-tooth buckles, which curve at the ends of the zones into the slip
lengths, is in agreement with observed effects. Numerical calculation gives quantitative
predictions in agreement with experimental results, despite uncertainty about the
correct values for bending stiffness and plastic yield moment, depending on whether the
yarns act as solid rods or freely slipping fibre assemblies.