CYCLIC NEAR-TIP FIELDS FOR FATIGUE CRACKS ALONG METAL-METAL AND METAL-CERAMIC INTERFACES

Finite element analyses were conducted with the objective of determini ng the cyclic near-tip fields ahead of a stationary tensile fatigue cr ack lying along the interface between two dissimilar solids. The model systems analyzed are (i) a metal-metal bimaterial whose components ha ve the same elastic properties but different plastic deformation chara cteristics, and (ii) a metal-ceramic bimaterial. In both cases, monoto nic loading to the peak tensile load results in a predominantly mode I field ahead of the crack. However, unloading in one or both component s of the bimaterial with prior plastic deformation generates mixed-mod e conditions at the crack tip. The mode mixity persists during a signi ficant portion of the next loading phase and is gradually removed upon reloading to the peak stress. The cyclic plastic zone size directly a head of the fatigue crack is approximately one-fifth the size of the m onotonic plastic zone. The residual compressive stresses within the cy clic plastic zone are computed. The implications of reversed yielding and mixed-mode near-tip fields to constant-amplitude and variable-ampl itude fatigue fracture are discussed.