However, even in this case, it would be helpful to receive not only a local stiffness or Young's modulus, but also a local fatigue notch factor [K.sub.f].
Arising from a determination of the local component density p by means of ultrasonic Sampling Phased Array with a possible resolution of about 6 mm, it is thus possible to derive a virtual Young's modulus [E.sub.f] and a fatigue notch factor [K.sub.fs] for the shrinkages to estimate the local fatigue strength arithmetically.
Based on the results determined so far for the fatigue strength of the sound material and the specimens with shrinkages as well as on the correlation between virtual Young's modulus [E.sub.f], density [rho] and the fatigue notch factor of the shrinkages [K.sub.fs], a fatigue design concept was developed, depicted in Figure 17 as a flow chart including also results based on X-ray analysis and shrinkage classification .
Based on the density measurement, a load simulation with the sound Young's modulus E, a determination of the fatigue notch factor for the shrinkages [K.sub.fs] and a final assessment of the fatigue strength are performed, based upon on the safety factor [S.sub.Sh] and the reference S-N curve for [P.sub.S] = 50 %.
In the developed fatigue design concept, local density information, determined by ultrasonic Sampling Phased Array, the virtual Young's modulus Ef and the fatigue notch factor of the shrinkages [K.sub.fs] were combined with a safety factor [S.sub.Sh] to estimate the local component fatigue strength arithmetically.
The fatigue notch factor, [K.sub.f], is defined in the present study as the ratio of fatigue strength of unwelded ([S.sub.uw]) and welded ([S.sub.w]) specimens at a given fatigue life, A, and temperature.
The resulting fatigue notch factor curves for welded specimens as a function of fatigue life at different temperatures are presented in Fig.
The fatigue notch factor ranged from 1.4 to 1.8 regardless of the testing temperature.
As for the fatigue notch factor decreasing slightly with life at 50[degrees]C, no physical meaning can be extracted because the displayed trend is not based on mechanical analysis but by data fitting.
The fatigue notch factor for the welded specimen varied between 1.4 and 1.8.