Fracture mechanics at very high load and different type of
loads

Abstract: In this report, data from fatigue crack growth programmes NASGRO and
Franc2D is analyzed. Results are correlated with reports written on Volvo
Aero, simulations performed in NASCRAC, another crack growth programme, and
also another degree project previously performed at Volvo. For some case
real test data will be used for comparison. To evaluate the function of
these programmes is essential since Volvo in the future will rely on them
to a high extent.
The different crack geometries used during the execution of this project
are through, surface and corner cracks. Since Franc2D is an entirely two
dimensional programme there were no possibilities to simulate surface or
corner cracks with it and hence these crack geometries were only applied in
NASGRO.
Cases used in this project originate from parts found in turbines, built by
Volvo Aero to the European Ariane rocket. However, presented results may
also be used to draw general conclusions concerning the functionality of
the programmes. This report may in many aspects be used as a handbook which
helps the user to choose certain parameters before a simulation is
initiated.
A variety of simulations, originating from several cases, indicated that
NASGRO and Franc2D handle stresses in two different ways. In NASGRO no
height need to be stated for a case because the stress is used along the
crack extension. In Franc2D which is a mesh based programme however, the
height must be stated and the stress is applied at the top of geometry. Two
different approaches and the case simulated should decide which approach is
most truthful.
For the through crack both programmes give satisfying results and many
results correlate well with both older results as well as expectations.
Results were also received for surface and corner cracks, some good, but in
many aspects these geometries need further development. Franc3D, which
operates in a similar manner to Franc2D but is based on three dimensions,
could be used in future simulations concerning surface and corner cracks.
The elastic-plastic module in NASGRO was also used in this project but a
range of simulations indicated that it does not work well enough for cases
presented in this project.