Issue 49

M. J. Adinoyi et alii, Frattura ed Integrità Strutturale, 49 (2019) 487-506; DOI: 10.3221/IGF-ESIS.49.46

increases, resulting in dislocations-dislocation interaction [8]. This interaction will result in cyclic hardening, translating to positive mean stress. Thus, the abrupt rise in the mean stress at higher number of cycles can be attributed to increase in dislocation density. The ε m behavior for the alloy can then be summarized as follows: for ε a less than 0.6%, the ε m is compressive but rises to become tensile if the fatigue life exceeds three thousand cycles or when applied strain amplitude is above 0.6%.

0.30% 0.40% 0.50% 0.60% 0.70%

600

(a)

400

200

0

-200

-400

Minimum & Maximum Stresses (MPa)

-600

1,E+00

1,E+02

1,E+04

1,E+06

Number of fatigue cycles

50

(b)

25

0

0.30% 0.40%

-25

0.50% 0.60%

Mean stress (MPa)

0.70%

-50

1,E+00

1,E+02

1,E+04

1,E+06

Number of fatigue cycles

Figure 6 : Variation of (a) the maximum and minimum stresses with the number of fatigue cycles, (b) Mean stress with number of fatigue cycles.

D AMAGE A SSESSMENT THROUGH R ESIDUAL S TIFFNESS AND E STIMATED S TRAIN C OMPONENTS

P

lastic strain is an important parameter for the assessment of fatigue damage in fatigue loading. However, the current alloy exhibits no discernible plastic deformation for the majority of the strain amplitudes investigated. Thus, it is devised to evaluate damage through the trend analysis of the residual stiffness, ௦ . The residual stiffness is analogous

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