Strain vs. time

Fig. 2-22 Viscoelastic creep behavior typical of many TPs under long-term stress to rupture (a) input stress vs. time profile and (b) output strain vs. time profile.

Figure 8.16 Strain vs. time for an anelastic solid during a stress cycle in which stress is...

Figure 4. Typical strain (%) vs. time plots for A1 in a vacuum at 743 K.

Fig. 33.4 Shear strain vs. time relationship at 70°C for a IK-MS system (Terostat MS937).

Table 33.3 Results of fitting Eq. (2) to experimental shear strain vs. time data at different temperatures.

Fig. 1. Experimental low-temperature creep strain-vs.-time curves for A1 (a), Ag (b), and Cu (c) single crystals under constant stress and at temperatures Ti

Fig. 3. Creep strain vs time curves for N720/A ceramic composite at 1000 °C in laboratory air and in steam environment.

Fig. 5. Creep strain vs time curves for N720/A CMC at 1200 °C in air and in steam (a) time scale chosen to show creep strains accumulated at 80 MPa and (b) time scale reduced to show creep curves at stresses > 125 MPa. Data from Ruggles-Wrenn et af ...

FIGURE 24.8. Stress relaxation represented by strain vs. time and stress vs. time curves. Explanation in text. 

The creep compliance of a Kelvin element is D(t) = l-e j. Using the Boltzman superposition principle, find an equation for the strain vs. time in a constant stress rate test. Sketch your results, i.e., e vs. t. 

When the stress is suddenly applied in a creep test, only the dashpot offers an initial resistance to deformation, so the initial slope of the strain vs. time curve is... 

Fig. 20. Recoverable strain vs. time after 100 seconds of stress relaxation, T = 205°C, 400,000.

If a constant strain is imposed on a metal or alloy, the stress relaxes with time as the system reduces its free energy. Dislocations are annihilated and the remaining dislocations move to lower-energy configurations. This is the nature of the recovery process. At higher temperatures, diffusional processes equivalent to creep occur. This phenomenon is very important for solder joints in electronic devices because the device spends much time at the strain extremes when it is turned on and off or put into a sleep mode and returned to active duty. Stress at constant strain vs. time curves for Sn-3.5Ag solder at 25 °C and 80 ° C, and at 0.3 % strain maximum are given in Fig. 6(a,b). The stress as a result of the coefficient of thermal expansion mismatches initially decreases very rapidly with time to a more or less steady state value. At 25 °C, the steady state value is about 15 MPa and is rather independent of the initial stress value however, at 80°C, the stress relaxes to zero. Thus when an electronic device is turned on, the thermal stress will relax to a low value possibly zero during use. 

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