Stretching curve

Figure 13. Experimental stress-stretch curves for solithane under uniaxial straining at several ambient pressures. A positive pressure corresponds to a negative mean stress. Data are re-plotted from Quested et al. Ref [16].

Fig. 27 Conductance histograms constructed from values of the plateaus of type III stretching curves for Au/l,9-nonanedithiol/Au junctions. A 1,600 out of 4,300 traces employing a 1 nA (max) preamplifier B 1,100 out of 4,300 traces recorded with the 10 nA (max) preamplifier. All other conditions are identical to those in Fig. 26. We notice that the low conductance sequence could only be resolved with the high sensitive preamplifier. The insets in A and B show that the current within each series scales approximately linearly with the number of peaks [208]...

Kofod used advanced materials models in an attempt to elucidate the effects that prestrain have on the actuation performance of a simple cuboid DE actuator [183]. The results are purely phenomenological however, they indicate that in the special case of a purely isotropic amorphous material, prestrain does not affect the electromechanical coupling directly. The enhancement in actuation strain due to prestrain occurs through the alteration of the geometrical dimensions of the acmator. Kofod also determined that the presence of an optimum load is related to the plateau region in the force-stretch curve and that prestrain is not able to affect the location of this region. 

The mechanical properties of the layered composites were tested on a custom-made thin film tensile strength tester (McAllister Inc.) recording the displacement and applied force by using pieces cut from ((PEI/PAA)(PEI/SWNT)5)6 and ((PEI/PAA)(PEI/SWNT)5)8 free-standing films. The tester was calibrated on similar pieces made from cellulose acetate membranes and Nylon threads. ((PEI/PAA)(PEI/SWNT)5)6 and ((PEI/PAA)(PEI/SWNT)5)8 samples had an average TEM thickness of 0.75 and 1.0 /um, respectively. Their typical stress (ct) vs strain (e) curves differed quite markedly from stretching curves seen previously... 

Fig. 9.7. Descriptions of muscle mechanics passive stretch curve, energy loss and elastic efhciency...

Fig. 12. The pH-stretch curve of the cross-laminated system The equilibrium pH value for the unstretched systems was 5.51 in the case of one system (experimental points marked AA A A ) and 5.55 for the three other systems. The broken curves (AB and CB ) represent theoretical curves (see...

The normalized values of the invariant R relative to the samples iPP4 and iPP5 are reported in Fig. 11.11 as a function of deformation. Curves a and b are not corrected for the decrease in thickness of the specimen during stretching. Curves a and b, instead, have been corrected for this effect, in the limiting hypothesis that the thickness t decreases according to the power law t = to loUT, with v = 0.5, in the whole deformation range, as expected for an ideal mbbeiy materials (Nitta and Yamana 2012). 

Fig. 10.5. Stretching curve measured for PEVA12 with a strain rate ch = 0.005 s (continuous line). Quasi-static stress-strain relationship (squares) [124]...

Tensile stress deforms PEVA12 homogeneously, i.e., without a necking. Figure 10.5 shows the stretching curve describing the relationship between... 

The stretching curve was measured with a fixed Hencky strain rate ch = 0.005s The shape of the curve is highly non-linear. It indicates a strain softening at a yield point, located at en 0.1. Later there follows a strain hardening, setting in at ch 0.6. 

A subtraction of the total amount of stress decay, Aazz(t oo), from the respective initial stresses measmed along the stretching curve gives the stress-true strain relationship associated with the limit of zero strain rates, i.e., under quasi-state conditions. The quasi-static stress-strain relationship obtained in this manner for PEVA12 is included in Fig. 10.5. 

Figures 10.9 to 10.11 illustrate how stretching curves and critical strains vary with temperature, again with results for PEVA12, and with the crystallinity here polyethylenes with different crystallinities are compared. Curves demonstrate a further general property of semicr3 talline pol5oners. While the stresses vary in systematic manner, there is no effect on the critical strains for softening (en 0.1) and hardening (en 0.6) and virtually no change in the elastic-plastic composition of the strains. Hence, tensile deformation of semicrystalline polymers is strain-controlled and changes the mechanism at two critical strains that are temperature and crystallinity invariant.

What is the background of these peculiar deformation properties A first insight is provided by the stretching curves in Fig. 10.11, when considering... 

Fig. 10.9. PEVA12 Stretching curves measured at the indicated temperatures (CH = 0.005s ) [125]...

Fig. 10.19. Decomposition of the stretching curve shown in Fig. 10.5 in the three components of the model in Fig. 10.18 Quasi-static elasto-plastic contribution of the crystal skeleton 4>cffc), elastic stress of the entanglement network ((1 — c)ffn) and relaxing viscous stress (<7r) [124]...

Figure 10.19 shows the decomposition of the stress into its three parts for the stretching curve of Fig. 10.5. For this polyethylene with low crystallinity skeleton force and viscous stresses are of similar magnitude. The network stress is at first negligible, but finally dominates. The plateau observed for CTc is conceivable. From the onset of fibril formation a further elongation of the crystal skeleton can be achieved by a morphological transition, namely the transformation of blocks into fibrils. This takes place at a constant or only slowly increasing stress.

Mrcp-IOOK protein stretching curve FFT analysis... 

Figure 15.23 shows both the tensile stretching curve and the recoveiy curve of a typical fiber. The stretching curve shows the typical stress-strain behavior, which includes both elastic and plastic deformations. The recovering curve shows only the elastic deformation (or strain) is recovered after the removal of the applied tensile stress. The elastic recoveiy, or strain recovery, ean then be defined as ... 

In addition to dimensional recoveiy, work recoveiy often is studied for tensile deformation. While stretching a fiber, the total work done is either stored in chemical bonds or is lost, typically in the form of heat. The work stored in the chemical bonds is recoverable, but the work lost is not. In Figure 15.23, the area under the stretch curve is the total work per unit volume done during stretching. The area under the recovery curve is the work per unit volume returned during recovery. Work recovery can then be defined as ... 

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