Identification of model parameters for predicting long term behaviour of marine ropes

There are many marine applications of synthetic ropes, from small handling lines for oceanography to very large mooring lines for offshore platforms. The fibres used in these ropes are visco-elastic and this behaviour affects their long term performance under constant and cyclic loads. In order to predict long term response a model has been developed which accounts for time-dependent behaviour. This model requires parameters to be identified which characterise elastic, visco-elastic and, where necessary visco-plastic components of strain. A procedure has been defined which allows these parameters to be determined rapidly, either at yarn or rope scale. A specific loading sequence of creep and recovery tests involving strain measurement by accurate non-contact image analysis is presented, which provides the necessary input data to allow strain at a given time to be predicted for any loading history. Examples are discussed for aramid and polyester materials.