PSI - Issue 74

Marta Kianicová et al. / Procedia Structural Integrity 74 (2025) 38–43 Mara Kianicová / St ru ctur al Integrity Procedia 00 (2025) 000 – 000

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Fig. 2 Colored topological height maps of fatigue fracture surfaces of a) compact and b) porous filaments fractured after several tens of thousands loading cycles.

3.2. Roughness parameters of fracture surfaces Determination of roughness parameters is important for a quanti tative assessment of crack -tip shielding and extension of crack path caused by pore - crack interactions. We selected the following three commonly used parameters according to ISO 25178: S a - the arithmetical mean height, S v - the maximum pit depth and S dr - developed interfacial area ratio. The definition of these parameters is described in Appendix A. These parameters were determined for fatigue fracture surfaces of 4 compound and 4 porous fibers fractured under CTPB tests in the range of fatigue life in between 10 2 and 10 6 cycles. The dependences of all measured parameters S dr , S a and S v on the fatigue life are shown in Figs. 3, 4 and 5, where their arithmetic mean values and standard deviations are plotted. Observe that the mean values of porous fibers are higher than those of compact ones. Considering the high data scatter, one can say that they decrease with increasing number of cycles to failure, at least in the low-cycle fatigue range N f ϵ (10 2 ; 10 5 ). Their possible increase in the high-cycle fatigue range, indicated by only one experimental point, should be verified by further experimental data. In general, the analysis of fracture surface roughness of fibers fractured by CTPB tests confirmed a higher roughness of porous filaments (compared to compact ones), thus indicating their higher resistance to fatigue fracture. A statistical assessment of complete S-N curves determined in the CTPB tests is currently under progress and will be published elsewhere.

Fig. 3 The dependence of the parameter S dr on fatigue life of compact and porous filaments