Experimental study of crack growth in thin sheet 2024-T3 aluminum under tension-torsion loading

To assess the viability of using a critical COD criterion for flaws in 2024 -T3 aluminum experiencing tension stresses (S-P) and torsion stresses (S-T) , the enclosed work presents (a) a complete set of measurements for critica l COD during crack growth under nominal tension-torsion loading, (b) the ev olution of crack path with crack growth and (c) crack surface shape as a fu nction of loading. Data from this work will provide an important experiment al database for use in assessing the predictive capability of advanced, thr ee-dimensional, crack growth simulation tools. Results for COD during crack growth under tension-torsion loading indicates that the measured critical COD for tension-torsion loading is constant during crack growth. In additio n, the value of COD measured using image correlation methods is approximate ly 8% larger than observed for in-plane tension-shear, with much of the inc rease apparently due to specimen deformations in the crack tip vicinity. In addition, crack path evolution data for the range of S-T/S-P considered in this work show that the crack experiences both tunneling and slant fractur e during loading, with tunneling rapidly decreasing (a) as crack growth pro gresses for all S-T/S-P values or (b) as S-T/S-P increases. Furthermore, re sults indicate that tearing during tension-torsion loading always occurs in a manner so that the crack surfaces tend to interfere during growth. Final ly, crack surface shape data indicates that, with the exception of a small secondary transition, the direction of crack growth remains stable along a straight line oriented along the initial fatigue crack direction for the ra nge of S-T/S-P being considered.