Experimental Analysis of Fatigue Cracks Emanating from Corner Notches in the Presence of Variable Residual Stress Fields

Engineering structures and mechanical systems designed for high cycle fatigue applications are largely affected by the residual stresses imparted to the mechanical component by the manufacturing operations used in the fabrication process. Macroscopic residual stresses are self-equilibrating within the dimensions of the mechanical components, thus, a material region with tensile residual stresses is somewhat counterbalanced with compressive residual stresses arising in another region of the material’s component. This non-uniform distribution of residual stresses in the mechanical components and its incorporation into physics-based models for fatigue life assessment is a complex problem. The focus of the present work is to bring insight into the fatigue crack growth phenomenon in the presence of variable residual stress fields. 6061-T6 aluminum alloy was used for the manufacturing of a specimen test with a variable residual stress field produced by a cold worked operation of a drilled hole at the specimen’s center. Corner notches were machined into the specimen’s hole. A fatigue crack growth test of the specimen was carry-on in a servo-hydraulic fatigue machine. Experimental results were presented in plots of crack length versus the number of cycles and fatigue crack growth rate versus crack length. A fractography analysis was also conducted to characterize distinct features of the fatigue crack growth process in the specimen. The fracture surfaces present evidence of the highly complex nature of the residual stress distribution in the specimen test.