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• Influence of micronotch size on fatigue life is quantified by a new model. • Average crack arrest cycle decreases with the equivalent micronotch size. • Post-arrest behavior is characterized by crack coalescence and the alternation of slip system. • A high crack propagation rate is correlated with the dominate slip system of prismatic . • Micronotch size has little effect on the long crack propagation rate. The influence of the micronotch size on the small fatigue-crack behavior of CP-Ti was investigated in this study. With an increase in the equivalent micronotch size, the fatigue life and average crack-arrest cycle decreased. Microstructural analysis revealed that crack arrest results from high-angle grain boundaries, and the post-arrest behavior is mainly characterized by the connection of main and secondary cracks, or the alternation of the slip system. A high crack propagation rate is correlated with prismatic < a > slip. The activation of other slip modes may decrease the crack propagation rate. The micronotch size affected the distribution of the crack growth regions but had little influence on the long crack propagation rate. [ABSTRACT FROM AUTHOR]