and with the same CNT array width.
The tests were performed with the objective of achieving
toughness improvements on CNT fibres as a function of various
parameters. The tests were carried out for: (i) three different
diameter values and similar superficial twist angles; (ii) three
different twist angles and (iii) three different tightening levels on
the micro slip-knots.
The measured stress-strain curves for specimens with fibre diameters
varying between 31 mm and 41 mm are shown in Fig. 5aec
and the corresponding Young's modulus, specific strength and
toughness are summarized in the first three columns of Table 1.
Three different tightening levels were investigated, while the twist
angle per unit length was kept constant at 24.5. Other fibre spinning
parameters such as twist rate, draw rate, array width are also
included in the Table. As previously, the stress-strain curves for the
knotted fibres displayed long plateau regions extending to high
strain values (300%e400%) where energy dissipation takes place.
As a consequence, in the presence of knots the toughness values
increased by more than an order of magnitude, between 15 and 30
times the original values, reaching a highest value of 102.6 J/g. Note