The representative curves for bending specimens prestrained to 10 and 20 % bending strain, are shown in Figs. 28.6 and 28.7. The strains around the bend axis of the sample are shown in (a) and the strains parallel to the bend axis are shown in (b). The estimated thermal expansion curve is once again used for comparison against the measured strains. The different heating cycles are also represented in each graph and are evident in the difference in strains during the first temperature dwell. A negative residual strain exists around the bend axis for all specimens when they are returned to room temperature after heating. Fig. 28.5 Strains measured at the center of a 20 % uniaxially prestrained dogbone sample subjected to a A-type thermal cycle a 5000 A- xx C- xx A- est C- est A- est C- est A- yy C- yy 4000 3000 2000 Strain (m ) 1000 0 -1000 -2000 0 4000 8000 12000 Time (s) 16000 20000 0 4000 8000 12000 Time (s) 16000 20000 b 5000 4000 3000 2000 Strain (m ) 1000 0 -1000 ∋ ∋ ∋ ∋ ∋ ∋ ∋ ∋ ∋ ∋ Fig. 28.6 Experimental data from a 10 % prestrained bending specimen during A and C thermal cycles: (a) Strains measured around the bend axis compared to the estimated thermal strain. (b) Strains measured parallel the bend axis compared to the estimated thermal strain 230 J.L. Smith et al.
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