APPENDIX C: TENSILE AND ELONGATION TEST DATA
The data are presented in groupings of six graphs, one group per membrane.
Each grouping corresponds to a particular test temperature. Elongation was mea-
sured using two methods: (1) change in distance between the grips (6.5 in. apart),
and (2) change in distance between contact points of an extensometer affixed to the
specimen (2.5 in. apart). Each graph consists of two curves where each curve repre-
sents the average of three samples: one curve for measurements made with the
extensometer compared to those made with the grips.
The elongation measured by movement of the grips is, in nearly all cases, mark-
edly different from that obtained with the extensometer. The explanation is that as
the membrane stretches, the gauge length increases as the bitumen deforms back
into the grips. In the worst case, the membrane pulls free. With the extensometer
there is no slippage. Thus the crosshead movement measurements are not as reli-
able as the extensometer measurements. However, for large strains the crosshead
measurements are necessary to determine ultimate elongation when the membrane
stretches past the limits of the extensometer. The decision to present load-strain vs.
stressstrain data results from the variations exist in specimen thickness. These varia-
tions produce variations in reinforcing fabric cross-sectional ratios that influence
test results. Hence, to provide more direct comparison between membranes, all
tensile strengths are given in load per unit width of specimen.
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