Effect of Crack Tip Stress Concentration Factor on Fracture Resistance in Vacuum Environment

: An investigation was carried out to characterize the effect of crack tip stress concentration factor (Kt) on fracture resistance of various aluminum alloys and a steel in vacuum environment. The materials investigated were peakaged 7075-T651, overaged 7075-T7351, 5083-H131, fully sensitized Al 5083 (175 C/240 hrs), 2024-T351, and AISI 4340 steel. Fracture mechanics wedge-opening-load (WOL) specimens were used in the current study. The test environment was vacuum so that the baseline fracture resistance of the material without the influence of environment could be determined. The results indicate: (1) in all alloys, the fracture resistance is highest for blunt-notches (smaller Kt), and is lowest for fatigue-sharpened precracked notches (larger Kt); (2) the fracture resistance decreases linearly as Kt increases; (3) at similar Kt levels, AISI 4340 steel exhibits fracture resistance about twice higher than those of the aluminum alloys; (4) the peakaged 7075-T651 and overaged 7075-T7351 have comparable fracture resistance; (5) the fracture resistance of 2024-T351 alloy is higher than 7075 alloys; (6) the fracture resistances of as-received 5083-H131 (5083R) and sensitized 5083S (175 C/240 hrs) are comparable in all Kt, except at the smallest Kt = 3 where the fracture resistance of 5083R is higher; and (7) the fracture paths are transgranular and the fracture mode is ductile void coalescence in all cases, irrespective of the stress concentration factor.