Analysis of Relaxation Phenomena in Textile Fibres: Part I: Stress Relaxation

A considerable amount of work has been carried out on stress relaxation phenomenon in polymers, particularly, polymeric fibres. However, there is almost no published work available on a newly observed phenomenon, known as ‘Inverse Relaxation’. The theoretical work on stress relaxation carried out until now has been based on the consideration that a polymeric fibre is instantaneously extended upto a predetermined strain and is then allowed to relax at that strain. In order to explain inverse relaxation, a knowledge of the behaviour of the polymeric fibre during extension upto the predetermined strain is required and hence the above approach needs modification. In view of this, equations have been proposed in this paper for stress relaxation phenomena after considering the extension of the fibre at a constant rate. Equations for inverse relaxation are considered in Part II. Experiments carried out on a polyester sample show good agreement between theoretically calculated stress relaxation curves and those obtained experimentally.