Total-strain recovery ratio

A fiber that is strained and allowed to recover releases a portion of the work absorbed during straining. The ratio of the work recovered to the total work absorbed, measured by the respective areas under the stress—strain and stress—recovery curves, is designated as resiUence. 

With constant stress, G t) = Gy, where creep strain y t) is constant [y(t) = Gq/G] for a Hookean solid. It would be directly proportional to time for a Newtonian liquid [(y(0 = Go/r])t]. Here t is the initial time at which recovery of the viscoelastic material begins. For a viscoelastic fluid, when stress is applied, there is a period of creep that is followed by a period of recovery. For such liquids, strains return back toward zero and finally reach an equilibrium at some smaller total strain. For the viscoelastic liquid in the creep phase, the strain starts at some small value, but builds up rapidly at a decreasing rate until a steady state is reached. After that the strain simply increases linearly with time. During this linear range, the ratio of shear strain to shear stress is a function of time alone. This is shear creep compliance, J t) The equation of shear creep compliance can be written as follows ... 

The SME of this nanocomposite fiber was investigated by heating the fiber to 70°C, and stretching it to 100% strain at a speed of 10mm min . The fiber was cooled to ambient temperature (22°C) while keeping the applied stress. After unloading, the fiber was heated to 70°C under stress-free condition to recover its original permanent shape. This cycle was repeated four times for each fiber. The Rf N) and Ri N) at the Ath cycle as well as the total recovery ratio / rtot(/V) after Ath cycle were calculated and are listed in Table 2. 

Creep describes time-dependent permanent deformation of materials resulting from constant structural stress. The creep of polymers can be divided into two main stages primary creep and steady-state creep. The creep strain rate decreases with time in the primary creep and is constant in the steady-state creep. Strain recovery occurs with the removal of external load after a creep time. Therefore, the total strain (e) consists of three separate parts el, e2, and e3. The el and e2 are the immediate elastic deformation and delayed elastic deformation, respectively. The e3 is the Newtonian flow. It was found that the el and e2 decreased with increasing clay contenf indicating lower creep recovery with the addition of C20A. The creep compHance J, the ratio of strain and applied load, can be expressed as... 

Work recovery The ratio of recoverable work to the total work required to strain a fiber a specified amount under a given program of strain rate. 

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