COMPARISON OF R-CURVE METHODOLOGIES FOR RANKING THE TOUGHNESS OF ALUMINUM-ALLOYS

In an effort to determine an optimum method for ranking the fracture t oughness of developmental aluminum alloys over a wide range of fractur e 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 midd le 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 i ntensity from secant compliance based crack length and stress intensit y calculated from J-integral testing were equivalent. Comparison of te st results obtained from different specimen sizes and configurations i ndicated that standard validity requirements for compact tension speci mens may be overly restrictive. Improved correlation between specimen types was obtained by plotting K-eff or K-J against physical crack ext ension as compared to effective crack extension.