variation and life prediction of biaxial/multiaxial fatigue components
This project's inspiration is to increase the understanding of fatigue life
dependency of service components on geometrical variation. In particular,
the project has used laboratory specimens data and numerical simulation
to investigate the contribution of the subsurface stress or strain conditions
to the fatigue life. This involved the development and the testing of biaxialy
loaded fatigue specimens employing several geometries and thickness variations.
The experimental results were correlated using detailed numerical simulation
and the outcome was used to investigate the contribution of the subsurface
strain conditions to the fatigue life and included further development in
subsurface damage analysis. A simple life prediction procedure has been
developed that aspires to be independent of both multiaxial stress or strain
states, and variation in the component's geometry.
1) Multiaxial strains are calculated through a subsurface finite element
2) These values are used to calculate the lives at each point using life-strain
3) The contribution to the total fatigue damage under the surface depends
on its distance from surface and strain gradient.
4) Contributions of each subsurface point is weighted and summed to estimate
the total life along that path.
Test fixtures simply support a rhombic plate specimen at its corners by
the use of four rollers that are placed and free to rotate inside holders.
The applied uniaxial cyclic reversed load is converted into rotation of
the rollers that, in turn, apply an anticlastic bending on the specimen
corners. Biaxial fatigue cracks initiate from a centre slot.
To investigate the stress and strain distribution near the crack, a fairly
complex mesh model was used that consists of nodes arranged in such an order
that enabled results to be obtained for several paths into the thickness
and at different planes.