PSI - Issue 14

K. Chawla et al. / Procedia Structural Integrity 14 (2019) 571–576 K.Chawla et al. Structural Integrity Procedia 00 (2018) 000 – 000

574

4

2.3. Fibre bridging In Fig. 2(a) and 2(b) the representative images of unreinforced and reinforced laminate test samples, recorded during the experiments, are shown. Photographs clearly show fibre bridging in both cases, the higher for the later case. Filler embedded toughened matrix absorbs more energy during crack growth which results in the increased fracture resistance. The fibre bridging although smaller in magnitude is also observed in the neat epoxy laminate case which is attributed to the stack of transverse threads (in the woven unidirectional glass fibre fabric) coming across the crack path as shown in Fig. 2(a).

(b)

(a)

Fig. 2.Fibre bridging observed in (a) neat epoxy laminate and (b) short-fiber reinforced laminate.

3. Results and discussions Representative plots of strain energy release rate ( G I ) with crack growth are plotted in Fig. 3 for various initial crack lengths. Fig. 3(a) shows that the G I values at crack initiation is ~ 620 J/m 2 ( G Ii ). After fracture initiation, a steep rise in G I is observed owing to the fiber bridging due to transverse woven threads present along the crack path. After reaching the peak values, the plots show stabilized zone with the nearly same G I values. This indicates steady state crack propagation. Critical energy release rate, G IC , obtained from this stabilized zone is noted to be 836 ±12.87 J/m2. Fig. 3(b) shows G I vs. crack growth curves for the reinforced laminate case. From the plots it is evident that the fracture toughness values correspond to the crack initiation and the steady state region are higher when compared to the neat epoxy laminate counterparts. In addition, the G I shows increasing trend following crack initiation. This is attributed to the additional bridging induced by the short fibres during crack propagation. In current investigation the G IC values are determined from the initial data of the stable crack growth region. The G IC value for the reinforced matrix case is observed to have increased by ~ 26% when compared to the neat epoxy laminate case. The average values of the G Ii and G IC are tabulated in Table 1.