Crack-Tip Chemistry and Fracture Mechanics-Based Model of the Crack Growth Rate/Stress Intensity Relationship for Ni + P

摘要

A crack-tip chemistry model capable of describing the K/sub ISCC/ and stages I and II crack growth rate kinetics of Ni + P has been developed. This model incorporates the electrochemistry in the crack, IR drop effects, corrosion rate effects along the crack wall, material yield strength and plastic flow properties, and crack geometry parameters. The model predicts that cracking proceeds with a well defined threshold followed by a stage I with a rapid increase in crack growth rate and a stage II in which the crack growth rate is independent of the stress intensity; however, the threshold is underpredicted. A discussion of crack-tip shielding and critical strain effects on these calculations is presented. A critical fracture strain concept can account for the difference in the calculated and measured K/sub ISCC/. Crack growth rates in the stage II regime are underpredicted by a factor of 5. Mechanical fracture occurring simultaneously with anodic dissolution could account for this difference, but direct evidence for such a process is not available. (ERA citation 11:040957)