PSI - Issue 79

Osman Bayrak et al. / Procedia Structural Integrity 79 (2026) 413–420

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sizes, and elastic properties of the phases were outlined in a preliminary study (Aslan & Bayrak, 2025). Same RVE, mesh configurations, and elastic properties were used in this study. In the preliminary study, it was numerically revealed that interfacial porosities play a key role in mechanical behaviour of the nanocomposites (Aslan & Bayrak, 2025), which had been pointed out before by experimental studies (Bódis et al., 2019). To the best of the knowledge, there is no known statistical data regarding the dispersion of the interfacial porosities. (Bódis et al., 2019) described dispersions of the porosities as “sparsely situated” in the interfaces. Therefore, discrete and quasi-random interfacial porosities were introduced in the FE models in this study.

Figure 1 Appearance of a pore in the interface a real microstructure (reproduced with permission from Ceramics International, 45, 4814 (Bódis et al., 2019)) (a) ; partial contact deactivation is applied in order to induce sparsely distributed pores in the interface (b)

The porosities were introduced in the form of partial debondings in the interfaces in the FE models. At first, contact between the ceramic matrix and GNPs was defined as glue contact, which coupled the degrees of freedom of the neighboring nodes of the opposing faces in the interfaces. Both experiments (Ramírez et al., 2018) and numerical studies (Aslan & Bayrak, 2025) stated that there is a bonding between graphene and Si3N4 matrix, and it can break under stress. Therefore, the glue contact was assigned a normal stress limit and a shear stress limit ( σ =467 MPa, τ =80 MPa, respectively) based on the preliminary study (Aslan & Bayrak, 2025). Before proceeding onto the fracture simulations in tensile and bending tests, a uniaxial loading-unloading process was applied on the models to induce the porosities. Matrix failure was not defined during this process. It was defined during the tensile bending test analyses. When the coupled nodes (glue contacts) in the interfaces reached the stress limits based on the formula given in Eq.1 (based on an equation given in User’s Manual of Marc ® Mentat software), those nodes were debonded from each other, transitioning to touching contact, therefore leaving porosity-like conditions in the interfaces. These debondings, as can be seen in the Figure 1, are partial, in other words discontinuous, which is the case often reported in the literature (Bódis et al., 2019). Although the dispersion of the debondings appears random, it is dependent on the orientation distribution of graphene, which was based on experiments (Tapasztó et al., 2016). Following the loading stage of this porosity-induction process, the models were unloaded, bringing it back to its initial geometrical condition with the induced debondings (porosities) maintained.