Agriculture Reference
In-Depth Information
100
influences on the test result, the samples were
tested with an appropriate testing instrument
from Dia-Stron Ltd (Andover, UK).
Collective strength, cN/tex
Mean / Stand. deviation
Gravimetric fineness, tex
Number of elements in clamp
80
60
40
20
0
DIA
-
STRON
.
Samples GA, MA, FA, GAD and
GADO from trial K1 were tested with a Dia-
Stron system. The device and the method are
explained in an earlier section. Table 10.9
gives detailed information about the meas-
ured values. In addition to the cross-sectional
area and the area-related strength, the gravi-
metric fineness and the mass-related strength
(both measured in tex) were calculated using
a mean density of 1.5 g/cm
3
. Comparing the
calculated gravimetric fineness with the meas-
ured values given in Table 10.9, a good cor-
relation can be found. The values identified
whether coarser (e.g. sample FA) or finer
(e.g. GAD) fibre bundles were used in the ten-
sile test in comparison to the mean gravimet-
ric fineness.
From the values given in Table 10.9, it
can be concluded that the damage to fibre
bundles in the separation process is small to
negligible. These results underline the need
for modified testing methods for bast fibres to
obtain exact physical properties. Exact fibre
data are extremely important if used in
numerical simulation software to calculate the
properties of fibre-reinforced plastics (Müssig
et al
., 2006).
Separation samples
Fig. 10.20.
Influence of the number of tested
elements on the collective strength (Müssig, 2001a).
(Instron, Pfungstadt, Germany). For these
trials, Pressley clamps covered with Plexiglas
were used. The clamping length was 3.2 mm
and the testing speed 2 mm/min. The results
are given in Fig. 10.21. Beside the mean value,
the median and the maximum and minimum
values are shown graphically.
Based on the results shown in Fig. 10.21,
the differences in strength when using the
single-element method are much smaller
compared to the collective test. It should be
mentioned that the values are not normally
distributed and the resulting values are left-
skewed for all samples. It seems that there is
still a correlation between strength decrease
and the separation step.
Therefore, two important aspects should
be introduced into the discussion: (i) what is
the influence of the calculation of a mass-
related strength using a mean mass measured
for all the tested samples; and (ii) is 50 meas-
urements enough to give more than just a
trend?
Problems with the implementation of
such tests (mass-related, single-element
strength with clamped samples) relate particu-
larly to:
Strength summary
The design of a testing method (collective or
single-element test) has a fundamental influ-
ence on the results.
If the values of hemp fibre bundles
tested in a collective test were compared
with other results, the number of tested ele-
ments should be nearly identical, otherwise
a comparison would not be possible. The
'number index' gives a better understanding
of differences between the values. Our pro-
posal is to add the information about fine-
ness of the tested collectives and the number
index to the tensile strength values of a col-
lective. Having these data in mind, it is eas-
ier to decide if a smaller collective strength
value is caused by damage to the fibre bun-
dles or by an increase in fibre bundle
fineness.
•
the influence of the clamping mechanism
and of fibre slip in the clamp;
the determination of the mass of the tested
•
elements;
the calculation of the fibre mass-related
•
tensile strength by using the mass of the
elements as a mean value.
In order to solve the problems mentioned
above and to reduce the number of possible
