Fracture assessment for electron beam welded damage tolerant Ti-6Al-4V alloy by the FITNET procedure

Abstract

Fracture assessment of the cracked structures is essential to avoiding fracture failure. A number of fracture assessment procedures have been proposed for various steel structures. However, the studies about the application of available procedures for titanium alloy structures are scarcely reported. Fracture assessment for the electron beam(EB) welded thick-walled damage tolerant Ti-6Al-4V(TC4-DT) alloy is performed by the fitness-for-service(FFS) FITNET procedure. Uniaxial tensile tests and fracture assessment tests of the base metal and weld metal are carried out to obtain the input information of assessment. The standard options and advanced options of FITNET FFS procedure are used to the fracture assessment of the present material. Moreover, the predicted maximum loads of compact tensile specimen using FITNET FFS procedure are verified with the experimental data of fracture assessment tests. As a result, it is shown that the mechanical properties of weld metal are inhomogeneous along the weld depth. The mismatch ratio M is less than 10% at the weld top and middle, whereas more than 10% at the weld bottom. Failure assessment lines of standard options are close to that of advanced option, which means that the standard options are suitable for fracture assessment of the present welds. The accurate estimation of the maximum loads has been obtained by fracture assessment of standard options with error less than 6%. Furthermore, there are no potential advantages of applying higher options or mismatch options. Thus, the present welded joints can be treated as homogeneous material during the fracture assessment, and standard option 1 can be used to achieve accurate enough results. This research provides the engineering treatment methods for the fracture assessment of titanium alloy and its EB welds.