PSI- Issue 9

Amal Saoud et al. / Procedia Structural Integrity 9 (2018) 235–242 Amal Saous/ Structural Integrity Procedia 00 (2018) 000–000

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The critical value of G II , G IIc , is then found by measuring the critical load Pc needed to fracture a specimen containing a crack of length ac, and using the slope of the compliance curve at this same value of a :

3 0 C ma C  

(2)

Where m and C 0 are determined by linear regression of the experimental curve C as a function of a 3 G

IIC becomes:

2 2

3

mP a

(3)

G



IIc

2

B

We set the mean value of the Mode II initiation fracture toughness G IIC and determined using respectively the formula cited previously in (3) in Tab. 4. Knowing that a material subjected to stresses contains stored elastic energy stored, during material cracking, there is an energy release.

Table 4: Mode II initiation fracture toughness

G IIc THUYA N/m

G IIc Eucalyptus Grandis N/m

a (mm)

Average

Standard deviation

Average

Standard deviation

4 6 8

113.95 221.99 174.65 237.20 267.06

33.37 37.14

395.07 569.00 571.19 482.24 563.15

75.86

192.70 120.18

9.20

10 12

11.87 62.51

77.25 52.25

In Fig 5. We observe for the first species namely Thuya a dispersion for each value of a, except for the values of 8 and 10mm this dispersion is less visible. We also observe that the crack propagation is stable from the ratio a / w = 0.3 Hence the quasi-stability of our prototype, we can conclude that for values greater than a/ W = 0.3 G IIC is a characteristic of this species. For the Eucalyptus Grandis we notice a minor dispersion, but we can see that the propagation of the crack is stable from the ratio a / w = 0.2 Hence the stability of our prototype, we can conclude that for all the values a / W, G IIC is a characteristic of Eucalyptus Grandis.

0 100 200 300 400

G IIC in N/m

0 2 4 6 8 10 12 14

Length of Notch in mm

Fig 5: Evolution of the energy restitution rate G IIc of Thuya