Fibre Rope Modeller (FRM)
A CAD program for the Performance Prediction of Advanced Cords and Ropes under Complex Loading Environments.
S. Banfield, J.W.S. Hearle, C. M. Leech, R.Tebay, and C.A.Lawrence
Two factors are driving advances in synthetic fibre yarns, cords and rope technology. The first is the development and exploration of first and second generation synthetic fibres and the introduction of new rope constructions that offer the potential for major improvements in rope properties. The second is the growing range of synthetic fibre engineering applications being studied. A number of major ventures have already been brought to realisation. For example, the US Navy interest in mooring a large “air-base” in deep water in the Pacific and the exploitation of oil fields in greater water depths (500 – 3000m) makes light weight fibre ropes an attractive practical alternative to wire ropes or chains. Fibre structures are also replacing steel wire structures in some other traditional uses and have the potential for important advances in tyre cords, medical ligaments, bridges, textile architectural buildings, towed arrays, space structures and other engineering applications.
Polymeric fibres have complex mechanical properties and fibre structures can be geometrically complex involving interactions between millions of fine fibres. These features lead to the major difficulty of predicting fibre structure performance when subjected to complex loading over long periods of time. As a result the traditional practice for structural engineers is to use designs based on practical experience. In contrast to steel wire ropes which operate in the linear elastic range, fibre structures have non-linear, inelastic and visco-elastic properties, partly resulting from the organic polymeric materials used to make them and partly from friction between fibres and the compacting of the structure. Modelling of the performance of synthetic structures is therefore a necessary step in the design life prediction of new fibre products for engineering applications. The provision of CAD software is therefore essential to the future competitiveness of synthetic structure manufacturers, consultants and structural engineers.
This paper describes and demonstrates FRM developed for the design and performance prediction of yarns, cords and ropes for complex loading in marine, civil and aerospace applications. FRM is modular in form. The two basic modules cover the synthetic structure construction and tension, torque, elongation and twist response. Other modules cover fatigue effects. The geometry is hierarchical, through the levels of structure in a rope :e.g. filament, textile yarn, rope yarn, strand, rope. Strains are determined from imposed deformations. External and internal forces are computed by the principle of virtual work. Fatigue effects are computed, in sequence, for single cycles and then extrapolated for many cycles before re-computing. The information presented will be of interest to oil, engineering, civil and aerospace companies as there is now a growing need to employ more computer and IT techniques in the design and development of new products.