3.3. Mechanical properties
The mechanical properties investigated were the rupture force of husk (HFR) and that of shell (SFR), and the slope of force-deformation curve of husk (HSL) and that of shell (SSL).
Fig. 5 shows that HFR quickly decreases from 75.7 N to 53.3 N during the immature stage. After that, HFR reduces slowly and linearly to 46.5 N at the end of the mature stage, then continues to decrease to 36.6 N at the end of the over-mature stage. While the young coconut fruit is developing towards over-maturity, husk consisting of spongy tissue and embedded fibres (Jarimopas and Ruttanadat, 2007) gradually loses moisture (Jarimopas and Kusol, 2007) leaving empty spaces in the tissue. Accordingly, when more mature and drier husk is compressed it deforms more easily and needs less force to rupture.