Issue 48

K. Kimakh et alii, Frattura ed Integrità Strutturale, 48 (2019) 429-441; DOI: 10.3221/IGF-ESIS.48.41 437 where area is the equivalent default size in μm, α is a parameter that depends on the material function of the Vickers hardness and R is the stress ratio. Equivalent defect size from surface roughness profile In our case, the formulation proposed were considered to predict the fatigue limit of our material as a function of the surface roughness generated by the chosen cutting conditions. To evaluate the equivalent defect size, we considered the real profiles of specimens observed by an optical microscope instead of the roughness profiles obtained by the surface roughness tester. Actually, the samples were cutted longitudinally to highlight the surface roughness profile. So they were polished to eliminate the traces generated by the cut-off machines. Fig. 7 shows the surface state profiles observed by optical microscope of different surface roughness with two different magnifications (x100 and x200). (a) (b) (c) (d) Figure 8 : Roughness profile observations. (a) Specimen with Ra=3.12µm, (b) Specimen with Ra=2.26 µm, (c) Specimen with Ra=1.24µm and (d) Specimen with Ra=0.5 µm. x 100 x 100 x 200 x 200 x 200 x 100 x 200 x 100