Compression Cells Evaluation
Taking into account the preceding results, the mechanical testing was
performed on a representative sample for each of the four groups evidenced
on the CVA map (Fig. 5A): samples E, B, L and H in increasing order of
crispness as given by the first sensory dimension. Sample J was also tested at
this stage in order to better establish the practical limits of the mechanical
measurements, such as sensor range. For every compression cell, force–
displacement curves show a similar behavior for all the flake samples,
jaggedness being the common feature for the three devices: a low resistance
followed by an important force increase for cell 1 (Fig. 6) and a regular force
increase for cell 2 (Fig. 7). The signals obtained in cell 3 cumulates both
features (Fig. 8A,B).
Experimental curves from samples tested in cell 1 hardly differentiate
from one to another, and significant force values are measured only after a 5-
mm displacement, upon a 10-mm initial gap between plates (Fig. 6). Sample
L reaches a higher force value (about 150 N) whereas sample J exhibits the
lowest resistance (close to 80 N), but standard deviation (SD) is important
(60 N for sample L). The induced repeatability relative error (±15%) is too large to conclude that there is a clear difference in behavior from the other
samples. Such a test should be adopted at a relevant scale, using a low amount
of samples, to measure the critical stress intensity of flakes, in analogy with
the procedure suggested by Vincent et al. (2002) and to correlate this observation
with crispness, but this is out of the scope of the present work.