Yarn Level FEM Simulation for Bending Over Sheaves of Braided Ropes

Braiding is classic, but complex, structure in textile industry. The multi-layer layout of braids makes it hard to detect the inner yarns of a braided rope is hard to detect while they often bear the main stress. Especially when ropes are used to manoeuvre and regulate sails, they undergo a variety of dynamic stresses. This study focused on the complex problem of (cyclic) bending over sheaves (CBOS), and a full dynamic Finite Element Method (FEM) simulation process of a braided rope bending over a sheave is carried out with commercial software Abaqus/Explicit. FEM is advantageous for this as it enables to capture the complex processes occurring inside the rope to high accuracy, considering the complex structure of a braided rope.

A theoretical deduction is performed to determine the braided yarn paths. The external yarns are modelled as 3D rather than beam element types. Under certain assumption and specific boundary conditions, the relative movement between braided yarns (including the interlacing point) is better assessed and estimation of yarn relative displacement obtained. Parametric studies are conducted to better understand the factors that effect the yarn sliding. The ratio between the diameter of the sheave and the rope (D/d), and the braiding angle, are found to be crucial on the relative movement, while the number of yarns and their diameters have little influence.

The successful simulation demonstrates the feasibility of modelling and analysing the complex interaction occurring in braided structures using FEM. The calculated estimated displacement can contribute to further investigations such as the friction and heat generation problem in braided ropes. Such method can provide alternatives in predicting lifespan of braided products that cannot be easily inspected.