The influence of torsion on braided rope performance, modelling and tests
Résumé
Twist may be introduced accidentally into braided ropes during operations at sea, and it is important to know how this will affect both rope integrity and safety coefficients. This paper describes the use of simulation tools to evaluate how twisting can change the tensile properties of braided ropes. The case of a 300 kN break load 12 strand braided HMPE rope is examined. An original numerical modelling approach is presented, and results are compared with results from tensile tests performed on ropes with different levels of twist. A drop in strength of around 4% per turn per meter, and an increase in elongation, were observed as the number of turns per meter increased, corresponding to progressive removal of the load-bearing capacity of half the braided strands. The model shows how load is progressively redistributed within the braid. However, very high twist levels (>10 T/m) are required to reduce strength below 50% of the initial value.