Issue34

V. Di Cocco et alii, Frattura ed Integrità Strutturale, 34 (2015) 415-421; DOI: 10.3221/IGF-ESIS.34.46 418 with a lower slope if compared to stage II) and to the final rupture stage, respectively. For R = 0.50, stage II observed for R = 0.10 seems to “disappear” and a plateau is still evident for a crack growth rate of about 10 -8 m/cycle (stage II, Fig 4b). Finally, for R = 0.75, the classic three crack propagation stages are obtained and no “plateau” with constant crack growth rate is evident. 0 200 400 600 800 1000 1200 1400 35 45 55 65 75 85 95 Counts 2θ [°] Unloaded Under load Figure 3 : Investigated Cu-Zn-Al SMA spectra in unloaded and loaded conditions. 1.0E‐09 1.0E‐08 1.0E‐07 1.0E‐06 1 10 da/dN [m/cycle] ΔK [MPa∙√m] R=0.10 III II I IV V 1.0E‐09 1.0E‐08 1.0E‐07 1.0E‐06 1 10 da/dN [m/cycle] ΔK [MPa∙√m] R=0.50 III II I IV a) b) 1.0E‐09 1.0E‐08 1.0E‐07 1.0E‐06 1 10 da/dN [m/cycle] ΔK [MPa∙√m] R=0.75 I II III c) Figure 4 : Fatigue crack propagation da/dN-ΔK curves: a) R=0.10, b) R=0.50 and c) R=0.75.