Force/Pressure
Testing
Apparatus
Bit
Ohm Meter
Membrane
Electric Insulator
Steel Plate
Figure 9. Schematic of the puncture failure detection system.
The room temperature during the test must be
onstrate that the proposed test method is effective
kept approximately constant. It is recommended
at rating membranes by their resistance to punc-
that the air temperature during testing be kept at
ture. Some of the dispersion of the test results is
about 20C 5C. The temperature of the envi-
inherent of the test methodology, and some indi-
ronment, the specimen, and the test apparatus of
cate the degree of consistency found throughout
the proposed test method were designed for ease
the specimens from a given source. Therefore, some
of implementation. This avoids the need for heat-
membranes clearly have superior puncture resis-
ers or refrigeration. It is acknowledged that the
tance than others, but in some cases, the differences
real field puncture temperature will normally be
were not clear because their magnitude was com-
higher. Evaluating membranes for their resistance
parable to the magnitude of the data dispersion.
to puncture at temperatures representative of field
Figures 11 through 13 show that the test results
conditions may be another good approach to
were mostly consistent across the different test
evaluating membranes, but it would increase the
sets. Appendix D shows the test results for each
complexity of the test method. This later approach
test set in tabular format.
falls outside the scope of the current research and
development effort, but it may be a valuable com-
Statistical significance of the test results
ponent of future work.
Table 4 shows statistical results derived from
the three test sets presented in Figures 11 through
13. The test results were ordered from most resis-
Test results
To use a commercially available instrument to
tant to least resistant according to the average of
perform the proposed puncture tests, a number
all three test sets. The coefficient of variation is the
of preliminary tests were conducted. The critical
most significant statistical parameter applicable to
parameter for this calibration was the tip angle. A
this case. It indicates the magnitude of the scatter-
very acute tip angle rendered the test results clus-
ing of the data expressed in a format that allows
tered at the lower sector of the valid range of mea-
comparison across the various sheet membranes.
surement of the apparatus. A very obtuse angle
The coefficient of variation allows comparison that
caused many of the tests to fall outside the upper
is scaled to the magnitude of the average values
measurement limit of the apparatus. Figure 10
of the test results. The data indicate that, out of
shows the test results of a set of 20 puncture tests
the six membranes evaluated, the Soprema speci-
for each of the six membranes under evaluation.
mens have clearly superior puncture resistance.
The figure illustrates how some of the values ex-
Soprema's lowest coefficient of variation also in-
ceeded the 200-lb (91-kg) measurement range of
dicates superior consistence from specimen to
the apparatus. These values corresponded to a tip
specimen. The puncture resistance of the various
angle of 110.
sheet membranes was influenced by a combina-
Figures 11 through 13 show the test results of
tion of their properties such as thickness, surface
three separate sets of 20 tests for each of the six
layer material, and properties of the base mem-
sheet membranes under study. These figures dem-
brane material. The bridge designer must consider
12
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