Issue 51

B. Zaoui et alii, Frattura ed Integrità Strutturale, 51 (2020) 174-188; DOI: 10.3221/IGF-ESIS.51.14

Effect of crack propagation (Crack sizes) Under the same simulation conditions of the previous study, the effect of the elaboration temperature of the composite, on the crack propagation, initiated in the matrix perpendicular to the main axis of the fiber, is analyzed. To do this, this crack propagates in the direction of the fiber (Fig. 5a, b and c). The results obtained showed that, in mode I, the crack propagates only in the matrix. In this case, the stress intensity factor increases with the advance of the crack and with the increase of the elaboration temperature of the composite .The normal compressive residual stresses induced in the fiber cause the crack lips to close (Fig. 5a).The negative values of the stress intensity factor are characteristic of this closure. This crack does not propagates in mixed modes (mode II and III) only if its heads tends towards the interface (fiber-matrix interface), in this zone of the composite, the stress intensity factors values in these modes (mode II and III) reach their maximum values in the matrix and in the fiber (Fig. 5b and 5c).In other words, in this zone the crack propagates in mixed mode I, II and III; far from this zone, this crack develop in mode I in the matrix and in modes II and III in the fiber (Fig. 5a, b and c).The crack crossing the fiber by shearing its lips (modes II and III). The crack propagation kinetics in the composite is all the stronger as the fibers are jointly bonded to the matrix at high temperatures.

-75 -50 -25 0 25 50 75 100

a)

10 20 30 40 50 60 70 80 90 100 K II ( MPa.mm 1/2 )

b)

Matrix

Fiber

Matrix

Fiber

I ( MPa.mm 1/2 )

 T = 400°C  T = 600°C  T = 800°C

 T= 400°C  T= 600°C  T= 800°C

0,000 0,005 0,010 0,015 0,020 0,025 -200 -175 -150 -125 -100

0,000 0,005 0,010 0,015 0,020 0,025 -40 -30 -20 -10 0

K

a (mm)

a (mm)

0 2 4 6 8

c)

Matrix

Fiber

-8 -6 -4 -2 III ( MPa.mm 1/2 )

 T = 400°C  T = 600°C  T = 800°C

K

0,000 0,005 0,010 0,015 0,020 0,025 -14 -12 -10

a (mm)

Figure 6: Variation of the stress intensity factor of the crack oriented at 45 ° according to its size and the composite elaboration temperature. a) in mode I, b) in mode II, c) in mode III.

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