Softening rate curves

Once it had been demonstrated that NaCl enhanced the rate of cucumber tissue softening, the next question was whether and in what way calcium ions would inhibit the rate of softening. To answer this question a combination of 1.5 M NaCl and 0 to 80 mM calcium ions were added first to blanched cucumber slices and then to cucumber mesocarp tissue (47) (Fig. 5). In both experiments there was an excellent fit of a hyperbolic curve to the softening rates as a function of calcium added, since the hyperbolic model accounted for over 99% of the experimental variation. For the cucumber slices (Fig. 5a), half of the observed inhibition of softening rate occurred at 6.3 mM calcium. For the mesocarp pieces (Fig. 5b), half maximal inhibition occurred at 1.5 itiM calcium ion. These results indicated that even in the presence of high NaCl concentrations low calcium ion concentrations could saturate some binding site that resulted in inhibition of texture loss. 

Plasticity can be studied using a device known as the Gieseler plastometer. A constant torque is appHed to a shaft with rabble arms imbedded in coal in a cmcible heated at a fixed rate. The rate of rotation of the shaft indicates the duidity of the coal and is plotted as a function of the coal temperature. These curves, as shown in Figure 8, have a well-defined peak for coking coals usually near 450°C. Softening occurs at 350—400°C. At a normal heating rate of 3°C/min, the duid hardening may be complete by 500°C. 

The collagen shield, fabricated from procine scleral tissue, is a spherical contact lens-shaped film whose thickness can be made to vary from 0.027 to 0,071 mm. It has a diameter of 14.5 mm and a base curve of 9 mm. Once the shield is hydrated by tear fluid and begins to dissolve, it softens and conforms to the corneal surface. Dissolution rates can be varied from 2 to as long as 72 hr by exposing the shields to ultraviolet radiation in order to achieve varying degrees of crosslinking. 

Depending on the material and deformation conditions (strain rate, temperature) other stress-strain curve shapes can be observed (Fig. 2b and c). In Fig. 2b, the plastic flow occurs at the same stress level as that required for the yielding so the strain softening does not exist. In the case shown in Fig. 2c, the strain hardening happens very close to yielding, suppressing both strain softening and plastic flow behaviour. 

Fig. 17 Temperature and strain rate dependencies of the stress-strain curve shapes of PMMA small (less than 10 MPa) and larger strain softening (From [33])...

As above described, depending on temperature and strain rate, the stress-strain curves present a strain softening of variable amplitude. 

Fig.2 displays the normalized Cu removal rate as a function of storage time. For reference, the sheet resistance self-annealing curve is also displayed in the graph. As the graph demonstrates, during film transformation, the CMP removal rate increased by -35%. TTie increase of Cu removal rate over time was in part caused by the 43% mechanical softening of the... 

Pure torsion tests were performed on ice single crystals at a constant imposed external shear stress". Softening was evidenced as the creep curves revealed a strain-rate increase, up to a cumulated plastic strain of 7%, see figure 1. Note that such a behaviour was also observed during compression and tension tests. ... 

Another important effect of Zr addition is the effect associated with vacancies, in particular it reduces the concentration of the free vacancies. In Figure 4 the warm forming torsion curves are plotted the flow curves of the material after 200 °C show a classical behavior with a net increase in stress with strain up to the maximum followed by a limited flow softening. The flow stress of the material increases with increasing strain rate and decreasing temperature. 

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