Skip over navigation

 

Mechanisms Associated With Damage Tolerance in Ti Alloys

Shmuel Osovski (University of North Texas), Ankit Srivastava (University of North Texas), Alan Needleman (University of North Texas), James Williams (University of North Texas)

Crack initiation and growth: methods, applications, and challenges

Tue 4:20 - 5:40

Sayles Auditorium

The aircraft industry is in constant pursuit of ways to enhance the maintainability and inspectability of airborne structures. Titanium alloys are frequently used for critical applications because they enable these goals to be met. The fracture toughness and other damage tolerant properties of high strength titanium alloys are strongly affected by processing and heat treatment that give rise to a variety of microstructures. It has been observed experimentally that + titanium alloys in which the  phase occurs in thin layers surrounding the  matrix leads to enhanced damage tolerance. The work presented here is aimed at providing guidelines to optimize such microstructures with regard to the  layer to  matrix size ratio, the grain size and the matrix () strength. We present three dimensional analyses of ductile crack in growing in + titanium under mode I loading under small scale yielding conditions. The material is modeled using an elastic-viscoplastic constitutive relation for a progressively cavitating solid. Both the grain boundary  layer and the  matrix are allowed to accumulate damage through void nucleation, growth and coalescence. The  phase is shown to undergo the most damage leading to enhanced damage tolerance due to crack deflection consistent with the experimental observations. The variation of fracture toughness and fracture surface morphology with  layer thickness and with material properties are presented and compared with experimental observations.