PSI - Issue 61

J.M. Parente et al. / Procedia Structural Integrity 61 (2024) 285–290 J.M. Parente et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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For example, while the difference between the mold height (H0) and the lowest point (H1) for neat resin is 3.2%, this value is only 0.5% for the nano-reinforced resin. Therefore, it is possible to conclude that the presence of CNFs reduces the shrinkage effect by 84.4%. This behavior is similar to that obtained by Koziol et al. (2017), but opposite to that observed by the authors in another study involving graphene and the same resin (Parente et al. (2022)). 3.3 Effect of cure temperature on the bending properties The effect of cure temperature can be found in Fig. 2. It is possible to observe that, for all the materials studied, an increase in the cure temperature decreases the flexural strength, but with more expressive values for the Sicomin resin. Considering a cure temperature of 40ºC, for example, neat Sicomin resin has a flexural strength of 91.4 MPa, but when it decreases to 5ºC there is an increase of 38.4%. The same comparison for neat Ebalta resin leads to values of 92.3 MPa and 27.8%, respectively.

150

4

6

a)

b)

c)

130

110

3

5

90

CNF Neat resin

CNF Neat resin

CNF Neat resin

Bending strain [%]

70

2

4

Bending stress [MPa]

Bending stiffnes [GPa]

0 1020304050

0 1020304050

0 1020304050

Temperature [ºC]

Temperature [ºC]

Temperature [ºC]

6

4

150

f)

d)

e)

130

5

3

110

90

CNF Neat resin

CNF Neat resin

CNF Neat resin

Bending strain [%]

4

2

70

Bending stiffnes [GPa]

0 1020304050

0 1020304050

0 1020304050

Bending stress [MPa]

Temperature [ºC]

Temperature [ºC]

Temperature [ºC]

Fig. 2. Effect of cure temperature for: a) Bending stress and Ebalta resin; b) Bending stiffness and Ebalta resin; c) Bending strain and Ebalta resin; d) Bending stress and Sicomin resin; e) Bending stiffness and Sicomin resin; f) Bending strain and Sicomin resin.

Furthermore, when both resins are reinforced with CNFs, they exhibit slightly higher flexural strength than the neat resins. In this case, considering the temperature of 5°C where the highest flexural strength is observed, the difference between the values obtained for neat and nano-reinforced Ebalta resin is 3.9%, while for Sicomin it is 5.9%. Finally, regarding bending stiffness, the effect of cure temperature is similar to that described for bending strength, while for the flexural strain an increase in temperature increases the ductility of all materials.

3.4 Microhardness

The microhardness values are shown in Fig. 3, where it is noted that the resin containing CNFs presents a decrease in microhardness with an increase in the cure temperature of around 4.9%. The same effect also occurs for the neat