**3. Results and discussion**

### **3.1 Determination of** *β* **under mode II**

The CSTBD specimen has been used by many researchers to study mode I and mode II brittle fracture in different materials. However, the experimental results obtained in the past part from this specimen indicate that the mode II is β = 22° [34] and β = 25° [11].

Depending on the crack length and the disc radius already chosen, the numerical calculation reported in this figure (**Figure 6**) shows that the stress (σ) is equal to zero near to angle 22, this result is similar for all compositions, so this angle verifies the pure mode II. Therefore, the results of the FE analysis have been obtained shows

**Figure 6.** *Variation of σθθ for each compositions.*

**Figure 7.** *The image of correlation.*

that the angle 22°C verifies the pure mode II. The value of this angle is in the interval of 20° and 30°. A very good agreement is shown between the theoretical predictions and the experimental results. Applying the load, the same crack propagation is carried out in the numerical and experimental element.
