CHAPTER 7
CONCLUSIONS
The goal was to estimate the fatigue life of single crystal nickel-base superal-
loys, based on fatigue crack driving force parameter, for which a numerical model
was developed to compute mixed mode SIFs at the crack tip. The results obtained
can be summarized as
1. An analytical method has been developed for the calculation of all the three
modes of stress intensity factors as a function of crystallographic orientation
for an orthotropic material, which can be applied to any anisotropic material,
if all the material constants are known. No prior assumption of plane stress
or plane strain was made in developing this theory.
2. Mode I, (KI), was ah--.- found to be greater for [10T] than for the [121]
orientation. For an orthotropic material, K, was found to be non-zero at
crack closure due to the coupling of the nodal displacements, whereas for an
isotropic material, it was zero.
3. The magnitude of K1i for [121] was found to be alvb--- greater than that for
[101] orientation, but the difference was not much.
4. Mode III SIF (Kill) existed because of the coupling of displacements at
the crack tip due to anisotropy. K111 for [101] was found to be much bigger
than that for [121] orientation for the Brazilian disk specimen. This p .1i -
an important role in calculation of effective K to predict the living of an
anisotropic material.
5. The K, and K111 values calculated were much higher for [101] orientation,
than those for [121] orientation. Therefore a high value of K.rs can be
expected for the [101] direction than that for the [121] direction, if we ignore