Time-temperature superposition tensile creep

Since the relaxation mechanisms characteristic of the constituent blocks will be associated with separate distributions of relaxation times, the simple time-temperature (or frequency-temperature) superposition applicable to most amorphous homopolymers and random copolymers cannot apply to block copolymers, even if each block separately shows thermorheologically simple behavior. Block copolymers, in contrast to the polymethacrylates studied by Ferry and co-workers, are not singlephase systems. They form, however, felicitous models for studying materials with multiple transitions because their molecular architecture can be shaped with considerable freedom. We report here on a study of time—temperature superposition in a commercially available triblock copolymer rubber determined in tensile relaxation and creep. 

FIG. 13.48 Small-strain tensile creep of rigid PVC. Left short-time tests (t < 1000 s) at a te of 2 h after quenches from 90 °C to various temperatures (f/fe < 0.13). The master curve at 20 °C was obtained by time-temperature superposition (compare Section 13.4.8) the dashed curves indicate the master curves at other temperatures. Right, long-term tests (t = 2 x 106 s, fe = 1/2 h, t/te = 1100). The dashed lines are the master curves at 20 and 40 °C for a te of 1/2 h they were derived from the left-hand diagram. From Struik (1977,1978). Courtesy of the author and of Elsevier Science Publishers. 

For both tensile and flexural loads, the validity of hypothesis (B) - same time-temperature superposition principle for all strengths - and hypothesis (C) - linear cumulative damage law - were confirmed for static and creep strength. 

Although time-temperature superposition is applicable to any viscoelastic response test (creep, dynamic, etc.), here, we will focus on its application to stress relaxation. Figure 16.12 shows tensile stress relaxation data at various temperatures for polyisobutylene, plotted in the form of a time-dependent tensile (Young s) modulus E t) versus, time on a log-log scale ... 

GSIO Accelerated Tensile Creep Rupture of Geosynthetic Materials Based on Time—Temperature Superposition Using Stepped Isothermal Method D6992... 

Figure 7.14 Comparison of the prediction by time-temperature superposition for UHMWPE with extrapolation of the curve-fit the short-term creep data under a tensile load at 37°C and 1 MPa. From [155],...

Equations based on time-temperature superposition are given in Ref 42 for PTFE with a crystalline content of approximately 58%. These relationships permit calculation of tensile creep modulus at any stress, time, or temperature in die tempaature range of 35-100°C and stress levels below the elastic limit. Ref. 41 provides similar data over a wider rai e cf condilicRis. 

Figure 10.13 Small-strain tensile creep curves for glassy poly(vinyl chloride) quenched from 90°C (about 10°C above to 40°C and stored at that temperature for four years. The different curves were measured for various times t, elapsed after the quench. The master cunre gives the result of superposition by shifts that were almost horizontal the shifting direction is shown by the arrow. The crosses refer to another sample quenched in the same way, but only measured for creep at of 1 day (29).

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