Properties of Polyester Tire Cords for NVH Applications: Strain and Frequency Effects

ABSTRACT Dynamic material properties of a polyethylene terephthalate (PET) tire cord that can be used in tire NVH simulations are presented. Dynamic mechanical analysis (DMA) is used to determine room‐temperature, frequency‐dependent storage and loss moduli of the PET cord under various mean tensile strains. Time–temperature superposition is used to extend the frequency range over 1 kHz by conducting DMA tests between −35°C and 5°C and adjusting the preload on the specimen to maintain constant mean strains. Adjustment of the preload to maintain a constant mean strain is necessary because the PET cord becomes stiffer and expands with decreasing temperature. Both horizontal and vertical shifting of the DMA results are required to produce master curves for the storage modulus and loss modulus at five mean strains ranging from 0.33% to 1.86%. The storage modulus increases with increasing frequency and mean strain. Below 1 Hz, the loss modulus decreases with increasing frequency, while it increases with increasing frequency above 1 Hz. Below 40 Hz, the loss modulus decreases with increasing mean strain, but above 40 Hz, it increases with increasing mean strain up to 0.85% strain. These variations are mostly attributed to molecular alignment, chain mobility, and strain‐induced crystallization of PET fibers.