Fatigue Behaviour under Cyclic Loading
topic
Polyester fibre fatigue under cyclic tensile loading: S–N curve shows endurance limit at ~50% of breaking load for 10⁷ cycles. Flex fatigue (MIT fold endurance tester) important for industrial uses (conveyor belts, air bags). Failure by progressive fibrillation: microcracks nucleate at crystal boundaries, propagate along fibril interfaces. Hysteresis (area of σ–ε loop) converts to heat, causing thermal fatigue in high-speed applications. PET tyre cord must withstand 10⁸ flex cycles.
Role
Fatigue resistance is critical for industrial polyester applications — tyres, belts, ropes, parachutes — and is a demanding test of structure–property understanding integrating fracture mechanics, polymer physics, and thermomechanics.
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