PSI - Issue 68

A.H. Jabbari et al. / Procedia Structural Integrity 68 (2025) 874–879 Jabbari et al. / Structural Integrity Procedia 00 (2025) 000–000

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As illustrated in Fig. 2, because of symmetrical specimen geometries just halves of the (a) CT specimens and (b) DCB specimens were modeled in 2D. The ratio of the crack length to the net width (see Fig. 1) should be 0.33 for DCB specimens (ANSI/NACE TM0177, 2016). To ensure the comparability of the results, this ratio was also considered for CT specimens. Moreover, since the given geometry of the CT specimen is valid for the specimen thickness of 13 mm, the identical thickness was considered for the DCB specimen. As different wedge thicknesses (see Fig. 1) were considered, different displacements at the loading lines were achieved. Without any plastic deformation around the inserted wedge, the applied displacement would equal the difference between the wedge thickness and the notch width. Plane-strain quadrilateral (CPE8R) elements were used for meshing the geometries. An overall element size of 0.2 mm was selected based on a prior mesh sensitivity analysis. Around the crack tip, the element size decreased to < 0.1 mm. The stress intensity factor (SIF), the equivalent contact force between the wedge and the specimen, and the effective position of this force were determined after inserting the wedge.

Fig. 2. Finite element models used for simulating the loading of (a) CT specimen and of (b) DCB specimen. The regions with refined mesh around the crack tips are magnified. In order to validate the results of the simulations, the SIF determined for the DCB specimen with elastic material behavior was compared with the stress intensity factor K I (ANSI/NACE TM0177, 2016), calculated as:

Fa (2 √ 3+2.38 B # h 3

h a )

(1)

K I =

In Equation 1, F is the load applied between the wedge and the DCB specimen, a is the crack length, h is the height of each DCB arm (here 12.7 mm), and B is the thickness of the specimen (here 13 mm). Fig. 3 compares the SIF calculated using Equation 1 and simulated using the FE software. The maximum difference is less than 5 %, which is acceptable according to NACE TM0177 (ANSI/NACE TM0177, 2016).

250

0 Stress intensity factor (MPam 0.5 ) 50 100 150 200 0,5 0

FEM-DCB Theory-DCB

1

1,5

2

2,5

3

Applied displacement (mm)

Fig. 3. Comparison of SIF from calculation and FE simulation.