An experimental investigation of the effects of small surface scratches on the fatigue behavior of AI-Li alloys has been carried out. Small scratches were generated onto the specimen surface which were then subjected to fatigue testing. These scratches were characterized by three different parameters, scratch angle, scratch tip radius of curvature, and scratch depth. These parameters have exhibited an important influence on the fatigue life of the scratched samples. In particular, it was found that the fatigue life decreased sharply as the scratch depth increased. In addition, the scratch surface and fracture surfaces were examined under a scanning electron microscope. The observations helped in the assessment and identification of the mechanisms responsible for failure. NOMENCLATURE d = scratch depth AK = stress intensity range Kth = stress intensity threshold K,= fatigue stress factor K , = stress concentration factor N , = number of cycles to failure p = tip root radius

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Abbreviations aCrack length on non-scratched surface a'Crack length on scratched surface da/dN Crack growth rate Stress intensity factor due to compressive residual stress ΔΚ Stress intensity factor "tr Transition length from tensile to shear mode Abstract-The fatigue crack growth in Aluminum 2024-T3 alloy specimens whose surface were scratched has been investigated. The results in such specimens indicated an increased fatigue crack growth rate. Whereas, in scratched-shot peened specimens, crack growth rates were nearly equal those in as-received material. This useful influence occurred at low ΔΚ. However, as ΔΚ increased growth rates gradually increased and finally, merged with those of scratched specimens. When a through width scratch was combined with a through thickness scratch, crack growth rates exhibited characteristics of small crack behavior.