Stress-Corrosion-Cracking Characterization Procedures and Interpretations to Failure—Safe Use of Titanium Alloys

Abstract

Ratio analysis diagram (RAD) interpretive procedures have been evolved recently to provide generalized engineering solutions for fracture toughness assessments of structural titanium alloys. Failure-safe design also requires consideration of possible sub-critical crack propagation (slow fracture) due to stress-corrosion cracking (SCC). Procedures for incorporation of SCC characterizations into the RAD system have now been developed. These procedures serve the dual purpose of providing simplified interpretations of critical flaw size-stress instability conditions by consideration of resistance of the material to both fast fracture and SCC. The failure conditions are expressed in terms of KI /σys ratios which provide an index of the general level of critical flaw sizes. The combination RAD also features limit lines that indicate: (a) the highest level of KIscc /σys ratios for which accurate plane strain interpretation to flaw size-stress conditions for SCC can be made for 1-in-thick plate, and (b) the highest level of SCC resistance measured in extensive surveys of plate material of this thickness.