PSI - Issue 61

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

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the bending strength, the nominal stress at the middle span section obtained using the maximum load value, while the stiffness modulus was determined through linear regression of the load-displacement curves with a correlation factor greater than 95% and considering the interval in the linear segment. The microhardness tests were performed using a Shimadzu HMV-G Vickers micro durometer, and 25 measurements were performed using a Vickers indenter with an applied load of 200 gf and a holding time of 15 s. 3. Results 3.1. Epoxy resin suspension viscosity and contact angle between CNF particles and resin Fig. 1 shows the results obtained for the study related to the suspension viscosity and contact angle between CNF particles and resin. From Fig.1a is possible to observe an increase in viscosity with the carbon nanofibers content, reaching the highest value for 1 wt.% of CNFs. Compared to the neat resin, the viscosity increases around 74.7% for the Ebalta resin and 27.9% for the Sicomin resin. The results obtained for the neat resins are in accordance with the suppliers' technical data sheets, while the other values obtained for the nanocomposites are in accordance with those reported by other authors (Jiménez-Suárez et al. (2012), Koziol et al. (2017), Parente et al. (2022)). In terms of contact angle versus time curves, Fig. 1 b) shows that the initial values for Ebalta resin (94º) are 34.3% higher than for Sicomin (70º). Subsequently, in both cases there is a decrease in contact angles over time, reaching values of 52º and 27º, respectively. Therefore, it is possible to conclude that the resin wets the CNFs, suggesting that cohesive forces occur between resin and carbon nanofibers in the composite.

b)

a)

Fig. 1. a) Resin suspension viscosity; b) Evolution of the contact angle with time between the carbon nanofiber specimens and resin.

3.2. Shrinkage Table 1 summarizes the shrinkage values observed for neat Sicomin resin and Sicomin resin reinforced with 0.75 wt.% of CNFs.

Table 1. Shrinkage results.

Mold height H 0 (mm) Lowest point H 1 (mm)

% Change

3.2 0.5

Without carbon nanofiber With carbon nanofiber

38.0 37.3

36.8 37.1