PSI - Issue 33

7

Mauro Ricotta et al. / Procedia Structural Integrity 33 (2021) 695–703 Author name / Structural Integrity Procedia 00 (2019) 000–000

701

π 2α 2π 2α  

r

R

(5)



0

In particular, the following equation was found to well correlate with the experimental data (Ricotta et al. 2021):

1



 1

 

    

1    

K

N      1 R R  

1 c 

  

(6)

K



1c

where K 1c is the GSIF value of the pointed V-notch and R N is the notch root radius giving the transition from a full notch sensitivity (for radii larger than R N ) to an incomplete notch sensitivity (for radii smaller than R N ) and can be determined according to the following expression (Zappalorto, 2019):

1

q 1 

  

K

q

1



1 

R

0N r q 1 q 1 M     

1c



(7)

N

0 

0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 0° 90° Symbols: experimental data Solid line: Eq. (6) with  =1.5 Dashed lines: ±20% Scatterband

K 1  c / K 1c

(R/R N )

1- 

Fig. 6. Critical GSIF of SFC notched components. Comparison between the predictions based on Eq. (6) and experimental data.

4. Damage analysis The microscopic damage mechanisms frequently observed in the case of  =0° orientation angle are shown in Fig. 7a, where multiple broken fibres can be noted and a considerable presence of fibre pull-outs (see the approximately circular marks in the matrix), as also observed by Zhang et al (1993) for CF-PPS composites. Moreover, profuse crazing is evident in the matrix in the plane normal to the applied stress, close to the fibre end, that can be located a posteriori, considering the circular marks visible in the matrix. A different damage scenario was found in the case of  =90° orientation angle, as shown in Fig. 7b, where, indeed, multiple initiation and growth of hackles from the fibre tracks can be clearly observed, as usually found in the case of brittle matrices, as reported by Hayes et al (2015). Typical evidences of the damage observed close to the notch tip of V-notched specimens with  =0° are reported in Fig. 8a, which refers to R=0.25 mm and a= 2 mm, as an example. As evident, a quite extensive presence of broken fibres, fibre-matrix debonding and fibre pull-out can be observed as well as craze formation and fibrillation induced by the PPS matrix ductility, as for the plain specimens. Regarding the specimens with  =90°, matrix failure and formation of hackles were noticed, as shown in the pictures in Fig. 8b, taken from the notch tip of a V-notched specimen with R=5 mm and a = 10 mm, suggesting that the cracks propagated mainly at the fibre-matrix interface. It is also worth mentioning that for all the tested specimen geometries the same damage mechanisms were observed.