FATIGUE CRACK GROWTH CHARACTERISTIC FOR DIFFUSION BONDED LAMINATES OF TITANIUM ALLOY WITH CENTERED HOLE

To investigate the crack growth characteristics of diffusion bonded (DB) laminates of TC4 titanium alloy with ϕ6 centered hole, the reduplicated fatigue tests for 8mm thick TC4 plate, three-layer DB laminates and three-layer DB laminates with localized ϕ12 no-welded area were conducted under the constant amplitude fatigue stress inserted periodically with marker load. The crack growth (a, N) data were obtained by quantitative fractography. The analysis on the failure surface shows that the typical semi-elliptic surface crack are found for the 8mm plate; the untypical semi-elliptic surface crack for the 3-layer DB laminate; the corner quarter-elliptic crack for the localized no-welded DB laminate whose crack growth could be divided to three phase. The comparison on the da/dN-a curves of those coupons shows that the crack growth characteristic of the DB laminate has no difference with the 8mm thick plate, while the localized ϕ12 no-welded area decreases the crack growth rate and improves the damage tolerance property of the DB laminate.