Constant rate of load

It is also possible to mn tensile tests at a constant rate of loading. If the cross-sectional area is continuously monitored and fed back into a control loop, constant-stress-rate tests can be made. In this case the initial slope... 

A similar argument may be applied to a constant rate of loading in which o-Rt... 

The distinction between plastics, fibers, and elastomers is most easily made in terms of the tensile stress-strain behavior of representative samples (Rudin, 1982). The curves shown in Fig. 1.17 are typical of those obtained in tension for a constant rate of loading. The parameters of each curve are normal stress (force applied on the specimen divided by the original cross-sectional area), nominal strain (increase in length divided by original length), and the modulus (slope of stress-strain curve). The slope of the curve near zero strain gives the initial modulus. 

This discussion of the speed of testing assumes that the tests arc made at constant rate of tra erse (of the testing machine moving member), and this is far and away the most common for polymer testing. The alternative of constant rate of loading is rarely met with. 

The stress-strain behavior of plastics measured at a constant rate of loading provides a basis for quality control and comparative evaluation of various plastics. The diagram shown in Figure 3.2a is most typical of that obtained in tension for a constant rate of loading. For compression and shear the behavior is quite similar except that the magnitude and the extent to which the curve is followed are different. 

Tear-Propagation Resistance The force required to propagate a slit in a flexible plastic film or thin sheeting at a constant rate of loading, calculated as an average between the initial and the maximum tear-propagation forces. Also called Tear Resistance, Propagated. 

This experiment involves increasing the engineering stress at a constant rate and the strain is determined as a function of time. In our experiments one characteristic of the constant rate of loading experiments was that as soon as the specimen necked it broke. In Figure 5 is shown log strain versus log time for... 

In a third constant rate of loading experiment, shown by the dashed line In Figure 5, the data were obtained using two different rates of loading. The Initial rate was the same as that for the specimen subjected to a rate of 1.83xl0 s". Then when a stress of 2.20x10 Pa was reached, the rate was changed... 

Stress-strain curves at constant rate of loading or of elongation are also measured by various devices, often with cycling of the loading pattern, and often with automatic recording. ... 

If the viscoelastic behavior is nonlinear, stress-strain curves at constant rate of loading or deformation will be so a fortiori, since they can depart from linearity even without this complication. Calculations by Van Holde show that the nonlinearity of tensile creep in nitrocellulose implies a stress-strain curve at constant rate of loading with a sharp change in slope at strains of about 5% which resembles the apparent yield points observed in such experiments on many textile fi-bers. 5 6... 

Tensile, R = 0.1, various temperatures. lO N/s constant rate of loading. 

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