Issue 49
M. J. Adinoyi et alii, Frattura ed Integrità Strutturale, 49 (2019) 487-506; DOI: 10.3221/IGF-ESIS.49.46
600
600
400
400
(b) ε a
= 0.3%
(a)
200
200
0
0.3% 0.4% 0.5% 0.6% 0.7%
0
-200
-200
2nd cycle half-life cycle 100,000 cycle
Stress (MPa)
-400 Stress (MPa)
-400
-600
-600
-0,8
-0,4
0
0,4
0,8
-0,8
-0,4
0
0,4
0,8
Strain (%)
Strain (%)
600
600
400
400
(d) ε a
= 0.5%
(c) ε a
= 0.4%
200
200
0
0
2nd cycle half-life cycle 6000 cycle
-200
-200
2nd cycle half-life cycle 20000 cycle
Stress (MPa)
Stress (MPa)
-400
-400
-600
-600
-0,8
-0,4
0
0,4
0,8
-0,8
-0,4
0
0,4
0,8
Strain (%)
Strain (%)
600
600
400
400
(f) ε a
= 0.7%
(e) ε a
= 0.6%
200
200
0
0
-200
-200
2nd cycle half-life cycle 900 cycle
2nd cycle half-life cycle 2048 cycle
Stress (MPa)
Stress (MPa)
-400
-400
-600
-600
-0,8
-0,4
0
0,4
0,8
-0,8
-0,4
0
0,4
0,8
Strain (%)
Strain (%)
Figure 1 : Representative hysteresis loop evolution for all investigated strain amplitudes; (a) stabilized cycles; (b)-(f) for selected cycles.
Fig. 6(b) displays the mean stress ( ε m ) evolution with the number of cycles for the alloy. For a major part of the cycling, negative mean stress evolved at applied strain amplitudes of 0.3% to 0.6%. However, there is a tendency for the mean stress to rise abruptly with increasing number of cycles at lower applied strain amplitudes. In contrast, strain amplitude of 0.7% produces tensile mean stress of about 10 MPa for the entire fatigue life. Mean stress development indicates the asymmetry of cyclic stress. It is clear from the illustrations in Fig. 6(b) that mean stress evolution for the present alloy is dependent on both applied strain amplitude and number of cycles. This may be due to its microstructure and strengthening mechanism. The evolution of tensile mean stress with the number of cycles for the alloy may suggest that, the density of dislocation
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