Crack Paths 2006

appropriate C T specimen is given, which is in good agreement with the experimental

results. The difference between the both SN-curves for C Tand C T Nspecimen reflects

the initiation cycles Ni. The slope of the SN-curve for the cracked specimen is 3.54,

whereas the slope of the SN-curve for the notched specimen is 3.64.

ENAW-7075-T651

CT (NASGRO)

CT (experiments)

C T N(experiments)

Pa ]

[ M

CT(w=72mm,t=10,5mm) N(U=2 m) a0 = 17 mm, C A

14160202468,0E+00

1,0E+02

1,0E+04

1,0E+06

1,0E+08

cycles

Figure 4. SN-curves for cracked and notched specimen under constant amplitude

loading (CA)

In order to investigate the influence of overloads SN-curves have been determined from

experiments, at which in a constant baseline level loading overloads with different

overload ratios Rol = F a,ol/Fmax have been interspersed.

CT(NASGRO)

E NAW-7075-T651

CT (experiments)

C T N(experiments)

Pa ]

[ M

CT (w =72mm,t=10,5mm) N(U= )

aF0EL=IX17/2m8 m

1024602468,0E+00

1,0E+02

1,0E+04

1,0E+06

1,0E+08

cycles

Figure 5. SN-curves for cracked and notched specimen under spectrum loading

(FELIX/28)

The SN-curve of the notched specimen is almost not affected using the overload

ratios of 1.5 and 2.0 and if the overload is applied at the first cycle. I.e. the crack

initiation phase is not influenced as well. But for higher overload ratios a larger effect is