PSI - Issue 51

M. Vaško et al. / Procedia Structural Integrity 51 (2023) 173–178

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M. Vaško et al. / Structural Integrity Procedia 00 (2022) 000–000

3. Charpy impact test results Table 3 shows the average results from the experiment carried out on specimens with a long fibre arranged unidirectionally. Each series consisted of at least five samples. Part of the obtained data was also processed and analysed using algorithms programmed in the MATLAB software package (MATLAB (2021)).

Table 3. Specification of individual series of specimens and impact test results Series Notch presence Direction of loading Energy [kJ/m^2] A No Perpendicular 455 B Yes Perpendicular 295 C No Direct 420 D Yes Direct 460

The results showed the effect of loading orientation on the impact toughness of the specimens. The influence of a notch on the results was not observed in the specimens loaded directly on the stacking sequence of laminas. Actually, the notched specimens achieved higher impact toughness than specimens without the notch. In the article (Caminero et al. (2018)), it was demonstrated that the application of a long fibre leads to an approximately tenfold increase in the value of the impact toughness of the specimens. It follows that the presence of a long fibre has a significant impact on the achieved results. In the case of specimens loaded directly to stacking of laminas, the layering path of the reinforcing long fibre was not affected in any way, i.e. laminas with long fibre were without notch (Fig. 3).

Fig. 3. The reinforcing layers were without a notch in the case of direct loading.

Delamination occurred in several places of the specimen (around the notch and in the place of the zero axis). If delamination occurred in the vicinity of the notch, then exclusively at the boundary of reinforced and unreinforced laminas (Fig. 4).

Fig. 4. Specimens delaminated during direct loading.

A decrease in impact toughness by 35% was observed in the case of perpendicular loading to stacking of laminas. The explanation for such a drastic decrease is the application of the notch and the resulting inappropriate arrangement of the filaments of the matrix and the fibre in the structure. Due to this, a stress concentrator occurs in the area of the notch (Fig. 5).