PSI - Issue 80

Pavel Šandera et al. / Procedia Structural Integrity 80 (2026) 169–176 Šandera / Structural Integrity Procedia 00 (2025) 000 – 000

173 5

Fig. 3. The dependences of the roughness parameter R L on the plastic zone size R pz for both porosities.

The dependences of the roughness parameter R L on the plastic zone size R pz for both porosities are plotted in Fig. 3. The R L -values are distinctly higher for the higher porosity, which means a longer crack path leading to a higher fatigue life of porous filaments when compared to the compact ones. As also expected, the R L -values increase with the increasing R pz -values, i.e., with an increasing fatigue loading and a decreasing number of cycles to failure. The statistical frequency distributions of R L -values related to variants of the constructed fracture surface are plotted in Fig. 4 as an example for R pz = 60 μm . An approximative formula R L = π(1 + S dr )/4 is often used in the quantitative topography (e. g. Underwood and Banerjee, 1992). It is easy to see that the calculated parameters R L and S dr shown in Figs. 1 and 3 nearly satisfy this formula.

Fig. 4. The statistical frequency distributions of R L -values related to variants of the constructed fracture surface for both porosities.

The dependences of the roughness parameter S a on the plastic zone size R pz for both porosities are plotted in Fig. 5. Considering the shift of both curves, the S a -values for both porosities are practically identical, despite the extremely high data scatter. This somewhat surprising result only means that the averaged local deviations of fracture surface