PSI - Issue 71

Poshadri Chathri et al. / Procedia Structural Integrity 71 (2025) 309–316

312

a

b

Fig. 3.a. Variations in the Cross-Sectional Shape of Pits (Cor, 1999) b. Dogbone specimen ASTM E8/E8M-13a (ASTM E8, 2010)

Table 3: Aspect ratios of pits.

Diameter(2C)

Depth(a)

Aspect ratio(a/2C)

1.89 1.14 0.73

1.29 1.71 1.28

0.69 1.56 1.76

2. Validation of the simulations A number of 3D stress finite element analysis were performed in ABAQUS® on the 3D-dogbone specimen with and without pits based on the uniform displacement till the failure of the model. 2.1. Meshing: For the original specimen, a structured mesh was generated due to its simple geometry, with a global mesh size of 1 and edge seeding of 0.5 in the gauge area, using C3D8R (8-node linear brick, reduced integration, hourglass control) . In contrast, for spherical and various shaped pits with more complex geometries, a tetrahedral mesh was applied, with a global size of 1 and edge refinement of 0.1 at the pits, utilizing C3D10M (10-node modified quadratic tetrahedron), as shown in Figure 4c. Linear elements were used for the model without pits because the geometry was simple and could be accurately represented using first-order elements to capture the results. For spherical and different shaped pits, quadratic elements were used to capture the complex stress distribution around curved and localized features. Although different element types were used, the comparison remains valid as all models' overall stress trends and mechanistic responses are consistent. One end of the model is constrained by creating a reference point and fixing all degrees of freedom, while the opposite end (y- direction) is subjected to a displacement through a reference point. 2.3. Tension test without pits specimen Using input parameters from the reference paper by Liu et al. (2023) the simulation yielded the following results: yield stress of 372.35 MPa, ultimate tensile strength of 934.04 MPa, and strain percentage of 76.7%. These simulation results closely align with the findings reported in the reference study (Liu et al., 2023). 2.4. Tension test with random pitting To observe the variation of mechanical properties with pits, four random pits were created with a depth of 1.71 mm and a diameter of 1.14 mm, as shown in Figure. 4 a-b. The simulations in Figure. 5a-b show that the material with pits has a yield stress of 356.85 MPa, ultimate tensile strength of 798.086 MPa, and a strain percentage of 72.9%. Compared to the without pits specimen, yield strength decreased by 3.8%, while ultimate strength decreased by 14.68%, and strain reduced by approximately 4.9%. In Figure. 5c, there is good agreement between the reference paper and the simulation. The with-pitting simulations show a reduction in yield strength, ultimate strength, and percentage strain compared to both the reference paper and the no-pits condition. The presence of pits reduces the effective cross-sectional area of the material, which lowers its ability to bear mechanical loads, Pits act as stress concentrators, amplifying the local stress around their edges. This