Mechanical length scales and their link to fatigue crack growth kinetics in beta-annealed Ti-6Al-4V

摘要

Correlations among microstructure, crack-tip fields and fatigue fracture are studied in beta-annealed Ti-6Al-4V. By means of digital image correlation, the area integral of the opening strain (ε_(int)) over the cyclic plastic zone was obtained, which was proportional to ΔK~m, where m is the Paris exponent, so that da/dN ∝ ε_(int). Analysis shows that m = 2(2 + (1 + n')~(-1)) where ri is the cyclic hardening exponent (0 <= n'<= 1). This predicts 5 <= m <= 6, in agreement with experiments, and strongly suggests that fatigue fracture of beta-annealed Ti-6A1-4V can be described using non-local strain parameters.