Double-elastic curve

The first step of this method is to simulate an EEA model of a noncorroded pipe. The load is then plotted as the ordinate while the strain is plotted as the abscissa in a linear graph. Subsequently, a double-elastic curve (DEC) that has a gradient half of the linear elastic region of the load—strain curve is plotted through the origin. The PACE corresponds to the intersection of the DEC and stress—strain curves. Finally, the DL is determined by dividing the PACE with a margin value, which in this case is 2. The maximum permissible strain limit is defined as the strain value at the intersection of the DEC and DE curves. 

Most extmded latex fibers are double covered with hard yams in order to overcome deficiencies of the bare threads such as abrasiveness, color, low power, and lack of dyeabiUty. During covering, the elastic thread is wrapped under stretch which prevents its return to original length when the stretch force is removed thus the fiber operates farther on the stress—strain curve to take advantage of its higher elastic power. Covered mbber fibers are commonly found in narrow fabrics, braids, surgical hosiery, and strip lace. 

Replicate tests were conducted at 3, 25 and 75% RH and good repeatability was observed. The elastic modulus as function of RH calculated from these stress-strain curves is also shown. The shape of the stress-strain curve can be approximated by two linear segments. It is clear that RH affects the elastic modulus and the yield stress of these MEAs with Nation-type membrane. Note that the elastic modulus more than doubled when the MEA was dried from 75 to 3% RH. However, the yield strain and the slope of the second linear segment are affected to a lesser degree it is notable that the 3% RH condition exhibited the lowest strain-to-failure. Despite some variations, the MEAs tested at all four RH levels were found to be fairly ductile, with strain-to-failure exceeding 100%. The yield stress varies from approximately 12 MPa to 17.5 MPa and the strain-to-failure varies from 86.4 to 152.7%. This is indicative of the initial non-uniformity of the MEA and the presence of initial random defects in the as-fabricated membrane or MEAs. 

Fig. 7.2.27 [Klil] Amplitudes of double-quantum coherences from deuterons of 1,4-deuterated butadiene oligomers incoipotated into elastic bands of natural rubber as a fimction of the preparation time Tp of the MQ filter and the stretching ratio A of the rubber bands. The curves drawn serve to guide the eye.

In Fig. 40b, which pertains to c = 0.2, curve 1 refers to translation and curve 2 to reorientation, which concern, respectively, the T- and V-bands. Both (solid) curves calculated from the rigorous formulas (138) and (139) are double-humped. On the contrary, each of the dashed curves, 3 and 4, which are found from the simplified Eqs. (148), has one peak. This distinction arises, since in the second case (for curves 3 and 4) the interrelation between the elastic translations and reorientations is disregarded. 

The elastic modulus can be derived directly from the shape of the stress-strain curve and is equal to its initial, constant slope. Its value equals that of the stress that would be required to double the length of the fiber at the initial conditions it is therefore measured in units of stress or specific stress. The work of rupture, a measure of the toughness of the fiber, is defined as the energy needed to break the fiber and may be represented by the following equation ... 

Here, F is the force applied to the dragline, S is the cross sectional area of the double filament, L is the initial length of the dragline, and AL is the elongation of the dragline when the F is applied. The F and AL are determined from the force-elongation curve within the elastic limit point and the S from the electron scanning microscopy. 

Fig. 4.2. Upper and lower limit curves, iimax 6k) (dashed line) and Hmin(6k) (solid line), respectively, determining the range for flexodomains (grey region) in the (Sk,ix) plane. The rectangular region marked as ST shows the range for the spatially periodic splay-twist Preedericksz structure for Sk > 0.53, ei—63 = 0 and > 0. The double arrow indicates in the one-elastic-constant approximation (Sk = 0) the range for flexodomains...

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