R.E. Hobbs, M.S. Overington, J.W.S. Hearle and S.J. Banfield
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.
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