Compression behavior of polymer fibrous systems is controlled by fiber bending, slippage with friction at contact points and irreversible fiber rearrangement reflected in the hysteresis during loading and unloading cycles. The load thickness graphs shown in Fig. 1a and b follow the pattern typical for textile fabrics [4–7], reinforced composite materials [8,9], and fiber assemblies in general [10,11].
The compression-release curves for the fifth cycle (Fig. 1b) were shifted to the left from the original compression-release curve together with the reduction of the hysteresis loop area with repeated cycling. The nonlinear response indicating the viscoe- lastic and plastic deformations of a material resulted from bending and slipping of fiber segments against the resistance due to crimp and inter-fiber friction. Due to irrecoverable fiber rearrangement at the previous compression cycles, the knitted fabrics became less compressible, and the nonelastic deformation also decreased. The thickness change does not go away with further cycles indicating that the mechanical conditioning of the sample was completed in five cycles [4]. Since the total deforma- tion at any point on a compression-release curve is the sum of the immediate elastic, viscoelastic and plastic components, they all