Compressive Behaviour, Bending and Buckling
topic
Polyester fibres are weak in compression (compressive strength ~20% of tensile: ~0.7 cN/dtex for FDY). Axial compression causes kink band formation (Euler buckling at fibre scale) at strain ~0.5%. Bending stiffness B = EI (E modulus × second moment of area): finer fibres are more flexible (lower B despite equal E). Single-fibre bending measured by cantilever beam method or loop formation test. Bending fatigue (flex resistance) measured by MIT tester.
Role
Understanding fibre bending and compression is essential for fabric mechanical modelling (handle, drape), composite reinforcement design, and understanding why fine fibres produce softer fabrics than coarse fibres of the same polymer.