Enhancement of Fatigue Crack Growth and Fracture Resistance in Ti-6Al-4V and Ti-6Al-6V-2Sn Through Microstructural Modification

1977 ◽  
Vol 99 (4) ◽  
pp. 313-318 ◽  
Author(s):  
G. R. Yoder ◽  
L. A. Cooley ◽  
T. W. Crooker
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Yield Strength ◽  
Crack Propagation ◽  
Plane Strain ◽  
Plane Strain Fracture Toughness ◽  
Propagation Resistance ◽  
Crack Propagation Resistance ◽  
Strain Fracture ◽  
Mill Anneal

Significant enhancement in fatigue crack propagation resistance and plane strain fracture toughness was obtained in commercial purity Ti-6Al-4V and Ti-6Al-6V-2Sn through microstructural modification. Alloys studied were in the form of 25.4 mm-thick plate with interstitial oxygen contents of 0.20 and 0.17 weight percent, respectively. Heat treatments were chosen to provide widely varied microstructures; these included a mill anneal, recrystallization anneal and a beta anneal. The most beneficial heat treatment for improving these crack tolerance properties was found to be the beta anneal. However, the beta anneal resulted in yield strength reductions of 9 to 14 percent, from levels associated with the original mill anneal. The recrystallization anneal provided significant enhancement of plane strain fracture toughness and marginal improvement in fatigue crack propagation resistance with negligible loss of yield strength.

Plane-Strain Fracture Toughness of High-Strength Aluminum Alloys

1965 ◽  
Vol 87 (4) ◽  
pp. 904-916 ◽  
Author(s):  
C. M. Carman ◽  
D. F. Armiento ◽  
H. Markus
Keyword(s):  
Fracture Toughness ◽  
Aluminum Alloys ◽  
Yield Strength ◽  
Plane Strain ◽  
Process Zone ◽  
Inverse Function ◽  
High Strength ◽  
Plane Strain Fracture Toughness ◽  
Strain Fracture ◽  
Impurity Elements

The plane-strain fracture toughness of precipitation-hardening aluminum alloys of 7000 and 2000 series and a strain-hardening alloy 5456 have been determined at both room temperature and −320 F using circumferentially notched rounds. These results show that the plane-strain fracture toughness is an inverse function of the yield strength and that at equivalent yield-strength levels the 7000 series of alloys is tougher than the 2000 series of alloys. Plane strain-fracture toughness values were determined using “pop-in” technique employing both the center crack and single-edge-notch specimens. Comparable values were obtained in all examples tested. The effects of impurity elements, iron and silicon, on the fracture toughness of 7075-T6 aluminum alloy were investigated using a special low iron-and-silicon melt of 7075-T6 material. Reduction of these impurity elements resulted in a 30 to 45 percent upgrading of the plane-strain fracture toughness of this alloy. These data have been interpreted in terms of the process zone size, dT, using electron microfractography as an indication of this parameter. The plane strain-fracture toughness values have been used to calculate the breaking stress of part-through-cracked panel. These calculations have been confirmed experimentally for two alloys. Such data have direct applicability in the design of structures.

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