Volume 24, Issue 6 (November 1996)
Comparison of R-Curve Methodologies for Ranking the Toughness of Aluminum Alloys
In an effort to determine an optimum method for ranking the fracture toughness of developmental aluminum alloys over a wide range of fracture toughness/strength combinations, five labs performed R-curve testing on aluminum alloy 2024-T3. Middle crack tension and compact tension R-curve specimens were excised from a previously tested 1.5-m wide middle crack tension test specimen. The crack resistance curves generated with the small specimens were compared to the R-curves from 1.5-m wide specimens. The experimental program indicated that effective stress intensity from secant compliance based crack length and stress intensity calculated from J-integral testing were equivalent. Comparison of test results obtained from different specimen sizes and configurations indicated that standard validity requirements for compact tension specimens may be overly restrictive. Improved correlation between specimen types was obtained by plotting Keff or KJ against physical crack extension as compared to effective crack extension.