PSI - Issue 37

Behzad V. Farahani et al. / Procedia Structural Integrity 37 (2022) 873–879 Behzad V. Farahani et al./ Structural Integrity Procedia 00 (2021) 000 – 000

877

5

expected discontinuities were detected in the cracked region. It was feasible to estimate the crack path by following the discontinuities. Consequently, the crack length was measured as reported in Table 1.

a)

b)

Figure 3. ESPI results, a) vertical displacement contour and b) normal strain in y -direction.

Figure 4. Crack length measurement by EPSI .

4. Stress Intensity Factor Calculation Regarding the SIF calculation, as a reference solution, ASTM (ASTM International 2015) proposes an equation to calculate the SIF range ( ∆ ) for a standard MT specimen assuming a linear elastic, isotropic and homogeneous behaviour as follows: ∆ = ∆ √ 2 2 (2) Where ∆ = − is the load range, and and are the specimen thickness and width. Moreover, = / where the crack length, , takes the value measured by the travelling microscope at the end of fatigue loading test – see Table 1 for the reference SIF value. Concerning the SIF calculation with the experimental data, a computational iterative overdeterministic algorithm was deployed as extensively described in (Farahani, Melo, Tavares, et al. 2020; Farahani et al. 2018; 2017). As an input data, the deformation field and the crack tip position must be fully defined. This approach turns the stress fields into Muskhelishvili’s equations (Muskhelishvili 1958), describing them theoretically around the crack tip. This methodology possesses the advantage of using an unlimited number of data points, minimizing errors. The algorithm