Search

The initiation and propagation of stage-I cracks determine the magnitude of the life in copper single crystals as the transition to stage-II behavior heralds the advent of fracture. The behavior of initiation and propagation of stage-I cracks under strain control is well understood. However, the PSB behavior and consequently the behavior of the stage-I cracks under load control is significantly different and requires an understanding before a unified methodology for predicting fatigue lives of copper single crystals based on the physics of the kinetics of stage-I crack growth can be developed. Stage-I cracks are found to nucleate in PSBs under load control. However, unlike in strain control, these cracks are almost exclusively found in micro PSBs. The cracks then grow along the PSBs with the occasional crack ‘skipping’ on a secondary slip system to an adjacent PSB. These cracks also show a tendency, similar to that in strain control, to ‘rob’ adjacent PSBs of strain and halt the growth of cracks in those PSBs. The extent of this ‘strain robbing’ region under load control is not known. The growth kinetics of the population of the cracks can be modeled as a function of the cumulative strain and leads to a Coffin Manson equation for predicting the fatigue life. It is seen that this Coffin Manson equation provides a lower bound for the fatigue life of the copper single crystals. [Copyright &y& Elsevier]