ABSTRACT:

Fatigue behavior of 2024-T3 aluminum alloy is caracterized for the role of compressive portion of constant or variable amplitude loading conditions which include single or periodic single peak compression overloads. It is found that the compressive load cycles have a remarkable effect on crack propagation as well as crack initiation. Particularly, it is noticeable that, under high baseline load ratio without crack closure, the non-propagation crack arrested by single peak tension overload recommenced to propagate by following single peak compression overload. Such results are discussed in terms of crack opening level, reversed plastic zone size, residual deformation on the crack surfaces and so on.

1. INTRODUCTION

Conversely, the effect on fatigue crack propagation is generally considered to be minimal, since the creek is expected to be fully closed during the compressive portion of the cycle, necessitating a stress intensity of zero at the crack tip (Hudson et aI, 1974). Similarly, it is found that compressive overload cycles In general have little effect under variable amplitude loading, except when they immediately follow a tensile overload where they act to reduce the post-overload retardation (Schijve et aI, 1962; Stephens et al,1976). In such tests, however, the crack growth rates were analyzed with respect to not the effective stress Intensity range (11 K. If) but the nominal stress intensity range (11 K) which rely on only the tensile portion of the load cycle, so that one of the most Important effects of compressive portion of the cycle, I.e., reduction of crack opening level were neglected. On the other hand, some studies show compression stresses have a strong effect on the crack opening level and increase crack growth rate in both stages of near- threshold and steady- state crack propagation (Newman, 1984; Yu et al. 1984; Kurihara, 1986).

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