Fretting induced plasticity in blade /disk contacts

Guofeng Gao, Purdue University

Abstract

Finite element analyses of fretting contacts were developed for different pad geometries and material combinations. A better understanding of the surface tractions and life predictions for crack nucleation and propagation is achieved by including the effects of plasticity and the representative crack in the finite element modeling. Pure elastic finite element results were validated with the existing elastic solution suite based on Singular Integral Equations (SIEs). The elastic-perfectly-plastic analysis of a rigid cylindrical pad on an isotropic half-space was compared with the results in the literature. Different shapes of rigid indenters were examined and the results were compared with those from the SIEs. Fretting contacts with similar and dissimilar isotropic materials were studied. The effects of plasticity on fretting life were highlighted by comparing the results from pure elastic analyses and elastic-plastic analyses. Finite element modelings involving SCN materials with different rotations of material principle axes were also investigated. The crack nucleation life was calculated with the Modified Manson-McKnight model. This model, modified by stressed area approach, usually generates significantly conservative estimates when pure elastic stress results are used. When plasticity is taken into account, the life prediction accuracy for crack nucleation was proven to be improved tremendously. A representative crack was incorporated into the FEM model at the trailing edge of contact to study its effects on surface tractions and crack propagation life. The originally smooth pressure distribution has a singularity at the edge of contact and the contact size expands due to the crack growth. The crack propagation life was evaluated by using the modified crack closure method and the Paris law.

Degree

Ph.D.

Advisors

Farris, Purdue University.

Subject Area

Aerospace materials

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