PSI - Issue 57

Nesrine Majed et al. / Procedia Structural Integrity 57 (2024) 502–509

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Nesrine Majed et al. / Structural Integrity Procedia 00 (2019) 000 – 000

4. Affected depth approach (AD approach) This approach is proposed and validated by Nasr et al. (2018) for materials containing surface defects and subjected to periodic loadings. It is based on the concept of affected depth. To apply this approach, we have to determine the value of the affected depth . It is defined as the depth from the tip of the defect to the inside of the specimen in which the Crossland equivalent stress is equal to (equation 2) as shown in figure 5.b. This depth is independent of the defect size and is computed by numerical simulation as given in the following model: ( ) ≤ (2) where = τ − is the fully reversed torsion fatigue limit of the defect-free material, and is the parameter identified from one experimental fatigue limit of the defective material by numerical simulation. The proposed method for evaluating the fatigue limit of material with defects under tensile or torsional loadings is illustrated in figure 3. Once the affected depth is determined, the Crossland equivalent stress at the depth ( ) is computed. This value is then compared to . If ( ) is greater or less than , the calculation is repeated with another applied loading P that is lower or higher than the initial applied loading. The defective fatigue limit is determined when the ( ) is equal to . A simplified model is used based on loading and geometric symmetries. It is used to determine the stress distribution in the vicinity of the defect is a semi cylinder containing hemi-spherical pore. Due to symmetry of the problem only ¼ of the numerical specimen is considered. One of the sections of the EF model is loaded using a distributed load, on the other facets a plane support link is applied to ensure symmetry as shown in figure 2.

Fig. 2. Completed and simplified models with load

and boundary conditions for tension loading.

Figure 3. Iterative calculation to search for fatigue limit of a sample containing defect.