Tensile stress-strain measurements

Networks were prepared in all cases using the amount of endlinking agent necessary to give a minimum Mc. Values of Mc were calculated from the Mooney-Rivlin elasticity coefficient Cj, determined from tensile stress-strain measurements (10),... 

Both series of polyurethanes were prepared using a prepolymer technique in which reactants were mixed at 70 °C/1 hour, cast into molds at 105 °C/2 hours, and cured at 80 °C/14 hours. The BD/MDI hard segment contents ranged from 0% (transparent, colorless homopolyurethanes) to 30% w/w (opaque, white copolyurethanes). All elastomers were characterized using DSC, dynamic mechanical, and tensile stress-strain measurements. 

Elongation to failure measured in tensile stress-strain measurements at room temperature (i.e., approximately 25 C) vary significantly as the composition of the polymer is varied from the glassy PS to the elastomeric PB (Figure 6). Also it is clear that the tensile properties of the random copolymer is significantly different from the same composition block copolymer. This difference is due, in part, to the differences in molecular weight (Table 1). 

Polystyrene and polybutadiene homopolymers as well as random and block copolymers of these mers have been studied via dielectric relaxation spectroscopy and tensile stress-strain measurements. The results suggest that some block copolymer systems studied have styrene rich surfaces which appear to partially crosslink upon initial exposure to ozone even though surface oxygen concentrations are not significantly affected. After continued exposure these samples appear to then undergo chain scission. Complex plane analysis implies that after degradation... 

Tensile stress-strain measurements were performed on solvent-cast (10% w/v) films using an Instron tensile tester. 

The tensile stress-strain measurements (Figure 8) indicate that the PNF s are becoming cross-linked upon irradiation, as evidenced by the increase in the ultimate tensile properties. 

Each box contained six test pieces for tensile stress/strain measurements, two strain test pieces, one test piece for low temperature measurements, two large compression set pieces which also serve for hardness measurements, four small compression set discs for swelling measurements, one Lupke disc for both electrical resistivity and resilience tests and the special compression annulus test piece for long term set. All test pieces except the long term compression set annulus were exposed in the unstrained state. A completed box without the lid is shown in Figure 3. 

Following the manner of presentation in the previous sections, the subject of viscoelasticity will be explained by reference to experiments familiar to the practitioner of rubber technology. This is a rather unorthodox approach and different from the usual one, which begins with an introduction of the theory. The experiment is tensile stress-strain measurement. In the rubber industry tensile measurements are routinely performed with crosslinked specimens. Here, we are concerned with gum-rubber behaviour. Therefore, we must perform the measurements with uncrosslinked specimens. First, compression-moulded specimens must be prepared they require special attention, which will be described next. 

Examples are presented in Section 4.1 of the characterisation of two samples of NBR using tensile stress-strain measurements. The presentation concerns deformational behaviour only, and the failure behaviour will be discussed in Section 4.4. 

Bearing the cost-benefit relationship in mind, an important question is what is the minimum activity required for obtaining sufficient information on the characteristics of a given gum rubber. Section 6.6 showed that at least two types of measurement are required one is the dynamic mechanical measurements over the temperature and the frequency region covering processing conditions. The other is the tensile stress-strain measurements at room temperature with at least three and preferably four strain rates. In this section examples are presented to show how this characterisation scheme is used to determine structure-processability relationships. 

Figure 6.63 Viscosity evaluated from tensile stress-strain measurements no formation of master curve, showing inapplicability of strain-time correspondence principle, EP ACM.

Figure 7.5 (a) Viscosities of gum rubber B obtained by capillary extrusion, dynamic oscillatory and tensile stress-strain measurements. 

The behaviour of rubber at the capillary entrance is similar to that in the transient region observed by the rotational rheometer, see Figure 4.6 [2], The peak of the torque-rise curve is interpreted to be breaking strain and compared to that observed with the tensile stress-strain measurement, see Fignre 8.4 [3]. 

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