12 Multi-mode Model and Calculation Method for Fatigue Damage …
167
a
b
Fig. 12.6 V-notched Al-alloy specimen at R = −1: a emergence of a “quasi-crack”, b growth of a
“quasi-crack”
σ B = 288 MPa, HCF fatigue limit σ u = 130 MPa, VHCF fatigue limit ˜
σ u = 60 MPa,
β VH = 0.3.
In the series of tests, the bi-curved notched specimen shape was used. In the waist,
it has a quasi-flat shape of 6.18 mm width and 3 mm thick. The notch was 1 mm
depth with the tip curvature radius of 0.5 mm and the angle of cleavage of 60 degrees.
Figures 12.6 and 12.7 show the calculation results for VHCF mode. In Fig. 12.7
the results of real and computational experiments on constructing fatigue curves for
specimens with a side notch are presented. The curves in the figures approximate the
experimental points for R = –1 (Fig. 12.7a) and R = 0.01 (Fig. 12.7b).
In Fig. 12.7, slight differences are observed between the calculated and experimental points. This can be explained as follows. The exponential exponent β VH of
the fatigue curve for aluminium weakly depends on the cycle asymmetry coefficient
R [23, 37], but in the accepted calculating scheme with SWT criterion, this exponent
is considered constant. Figure 12.6 shows the lines of the effective stress level σ VH
for the specimen with a notch in two states: before the fatigue quasi-crack initiation
and at the moment when it has passed approximately halfway to macro-destruction.
167
a
b
Fig. 12.6 V-notched Al-alloy specimen at R = −1: a emergence of a “quasi-crack”, b growth of a
“quasi-crack”
σ B = 288 MPa, HCF fatigue limit σ u = 130 MPa, VHCF fatigue limit ˜
σ u = 60 MPa,
β VH = 0.3.
In the series of tests, the bi-curved notched specimen shape was used. In the waist,
it has a quasi-flat shape of 6.18 mm width and 3 mm thick. The notch was 1 mm
depth with the tip curvature radius of 0.5 mm and the angle of cleavage of 60 degrees.
Figures 12.6 and 12.7 show the calculation results for VHCF mode. In Fig. 12.7
the results of real and computational experiments on constructing fatigue curves for
specimens with a side notch are presented. The curves in the figures approximate the
experimental points for R = –1 (Fig. 12.7a) and R = 0.01 (Fig. 12.7b).
In Fig. 12.7, slight differences are observed between the calculated and experimental points. This can be explained as follows. The exponential exponent β VH of
the fatigue curve for aluminium weakly depends on the cycle asymmetry coefficient
R [23, 37], but in the accepted calculating scheme with SWT criterion, this exponent
is considered constant. Figure 12.6 shows the lines of the effective stress level σ VH
for the specimen with a notch in two states: before the fatigue quasi-crack initiation
and at the moment when it has passed approximately halfway to macro-destruction.