The General Relations for Flow in Solids and Their Application to the Plastic Behavior of Tire Cords

Numerous researches on metals, rocks, glass, rubber, and textiles are cited to show that what may be regarded as normal creep in amorphous and polycrystalline solids conforms to the general relation $${\mathrm{\epsilon =\epsilon }}_1\mathrm{+at+b}\log t$$ , where ε is the total strain at time t, ε₁ is a parameter interpretable as the approximate initial strain, and a, b are other parameters. A special form of this equation, having a = 0, has been frequently applied. Reference is made to several other studies on the same class of solids, which have established for normal relaxation the relation $${\mathrm{\sigma =\sigma }}_1\mathrm{-\beta }\log t$$ , where σ is the stress at time t, σ₁ is the stress at unit time, and β is a parameter. A theoretical foundation for both equations is provided by the reaction‐rate theory of plastic flow. Observations in the present study indicate that creep extension in cotton and rayon tire cords over prolonged periods of time follows the above creep equation, and, in general, is not adequately represented by an equation omitting the term at. From the presence of this term in the equation, the existence of a component of the viscous type in tire cord growth is deduced. The pattern of creep recovery in cotton tire cord appears to be set by the behavior of the cord in creep extension.