The compression curves of the samples tested on cell 2 are shown in
Fig. 7. For a signal force of 100 N, sample E shows the lowest displacement,
whereas it is twice as much for samples H and L. Although force increase is
continuously recorded and the samples do not show the same behavior as for the preceding cell, differentiation between them is questionable, as the SD is
about 20 N, which leads to a relative experimental error close to the one
obtained for cell 1. This large value may be accepted as a feature inherent to
such complex products, at least in terms of geometry, but it implies that a
large number of trials (10) should be done, which makes tests tedious. Moreover,
it precludes the possibility of acoustic measurement because of the huge
quantity of data to be managed. We believe that these drawbacks are linked
to the small quantity of flakes taken from these packets for each test run,
compared with the high diversity in size and shape of those products that can
be encountered in only one packet. These drawbacks may be overcome by
increasing the sample mass to be tested.
Tests on cell 3 lead to different experimental curves (Fig. 8). As expected
for complete compressions, important forces (>1 kN) are required to cross
over the layer of flakes (Fig. 8A). Fmax and Slmax measurements have to be
completed by partial compression results, i.e., Slmin calculation, in order to
fully characterize the mechanical behavior of the samples (Fig. 8B). The
samples that behave in the same way during partial compression, i.e., H
(Slmin = 9.3 N/mm) and L (Slmin = 8.2 N/mm), are discriminated by complete
compression measurements, as Fmax: the maximum force is higher than 1.5 kN
for L and about 1.2 kN for H. The use of larger quantity of flakes leads to
more repeatable measurements as reflected by lower SDs (Table 3). The testing
volume, about 100 cm3, is close to the value of the smaller cell used by
Nixon and Peleg (1995) to test cornflakes in a simple compression geometry,
which maximized jaggedness. Although curves jaggedness (force fluctuations)
was not studied here, these results, from complete and partial compressions,
underline the satisfactory compromise achieved by the Kramer cell, which,
due to its specific geometry, takes into account the behavior of the whole bed
as well as that of individual flakes.