PSI - Issue 28

Evangelia Nektaria Palkanoglou et al. / Procedia Structural Integrity 28 (2020) 1286–1294 E. Palkanoglou et al. / Structural Integrity Procedia 00 (2019) 000–000

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larger than 0.0624 were found in a large area of the matrix material, whereas for a periodic unit cell, the corresponding values were two orders of magnitude smaller in the whole matrix area.

Fig. 4: (i) Evolution of plastic zone in CGI with for a single vermicular graphite particle for fixed ((a) and (b)) and periodic ((c) and (d)) boundary conditions Equivalent plastic strain is depicted, and graphite is removed for better visualisation. (ii) Comparison of developed stresses in the unit cell for different boundary conditions. A comparison in terms of developed stresses is shown in Fig. 4 (ii). Apparently, the average von Mises stresses in both cases climb up to 350 MPa. For the periodic unit cell, the curve exhibits a bilinear behaviour whereas for a fixed one it is smoothly nonlinear. For comparison, the developed stresses in a 4×4 array of unit cells subjected to thermal loading is also plotted, which coincides with to the periodic unit cell’s response, as expected.

Fig. 5: (i) Average value of damage variable in the inclusion for different boundary conditions. (ii) Damage distribution in inclusion for different boundary conditions and temperature levels.

Moreover, the effect of different boundary conditions on debonding was examined. As shown in Fig. 5 (i), damage was initiated at 93 °C for a fully fixed unit cell and at 215 °C in the case of PBCs. This may be attributed to the fact that a fully fixed unit cell cannot deform as freely as a periodic one; therefore, earlier plasticisation of the matrix should, in turn, lead to earlier damage. Also, damage increased in a nonlinear manner in the fully fixed unit cell compared to an almost linear curve for a periodic one. This is related to the concentration of highly damaged elements in the circumference of the inclusion for the case of a fixed unit cell, compared to a smoother distribution of damaged