FATIGUE CRACK GROWTH MECHANISMS OF LONG AND SMALL CRACKS IN STRUCTURAL MATERIALS

Fatigue crack growth mechanisms of long and small cracks were investigated in cast and wrought aluminum and titanium alloys with various microstructures (as-cast A535, 6061-T61, mill-annealed Ti-6Al-4V). The effects of microstructure and bulk residual stresses on the fatigue crack growth response of each material were evaluated. Bulk residual stresses were introduced in the testing specimens through quenching. Long crack growth data was generated on compact tension specimens and small crack growth testing was performed on surface flaw tension specimens at low stress ratio, R=0.1. Fatigue crack growth mechanisms with and without crack closure as well as low and high residual stress levels were identified. Corrective techniques compensating for residual stresses and closure on fatigue crack growth data will be presented and discussed.