Behavior of a surface oblique crack in fretting fatigue

Abstract

Stress intensity factors (SIFs) are obtained for a surface oblique crack under normal and tangential traction and remote extension loads. The surface oblique crack is modeled as the pseudo-dislocations. The Airy stress functions are derived for an edge dislocation in a semi-infinite plane. Stress field due to surface tractions is obtained by integrating the Flamant solution. The SIFs of Mode I and Mode II ($K_I$ and $K_{II}$) are then obtained. Finite element analysis is performed with a commercial code ABAQUS and compared with the analytical results. The analytical results are in good agreement with the previously published results for simple configurations as well as the results of FEM. From investigating the SIFs and their ranges, following results are obtained. The growth rate of a surface oblique crack decreases due to the reduction of the SIF ranges. The crack driving force depends on the obliquity, the normal traction and the ratio of crack to traction length. The range of tangential traction is directly related with the crack growth rate. The peak value of tangential traction is found to be a key parameter to accelerate the crack growth. A fretting fatigue experiment is conducted with Al 2024-T4 pad and specimen. The pad has a rectangular foot to simulate a punch pressure on the contact surface between the specimen and the pad. The pad length, the normal pressure and the bulk stress are varied for the experimental conditions. The load ratio is set to be zero during the experiments. A simple calibration method for measuring the contact forces is developed. Special specimens are designed for the calibration. The method developed use the strain values of the pad and the loading bars as correlating parameters. Linear relationships are observed between the fretting parameters, and used as in situ calibration curves during fretting fatigue experiments. Fretting fatigue cracks are monitored and analyzed by image processing. The results with 10 and 5 m...