PSI - Issue 3

Jilali Nattaj et al. / Procedia Structural Integrity 3 (2017) 579–587 Author name / Structural Integrity Procedia 00 (2017) 000–000

586

8

The evolution of the damage shows that the tangent of the curve is moderate when β is close to 0 (crack initiation zone) and increases during propagation of the crack to accelerate towards the end of life of the material.

5.2. Comparison of the damage evolution of the three applied loading levels

Figure 4. Damage & reliability curves under load levels ∆σ = (248, 282, and 352) MPa determined by equations (12) and (13).

According to the figure 4 the three damage curves have the same tendency, whereas the slope is increasingly accentuated when the loading level increases. The curves are very close because of the values which are close to the stress levels applied The curves are very similar to those defined by the unified theory, shown in the figure 5 below.

Figure 5. Damage & reliability curves under load levels ∆σ = (248, 282, and 352) MPa determined by equation (4)

The graphs figures 4 and 5 show that the two damage’s approaches defined by the unified theory and the rate of reduction of the cycle’s number of breaking (RRCB) have similar results which validate our model.