Relationship between fatigue notch factor and strength

Abstract

The fatigue notch sensitivity for metallic materials can be divided into two types: high and low notch sensitivity. When the stress ratio R = −1, if the specimen diameter or width D ⩾ 10 mm, material with yield/tensile ratio ( Y/ T) > 0.9 or σ 0/ σ T > 0.3 is considered as high notch sensitive, whereas low notch sensitivity is found otherwise. If D 10 mm, material with ( Y/ T) > 0.9 or σ 0/ σ T >0.45 is high notch sensitive. Otherwise, it is low notch sensitive. For the blunt notch a relationship between fatigue notch factor ( K f ) and strength is derived. For low notch sensitive materials or fatigue crack growth conditions, K f = K t 2 (4−√( Y T)) . For high notch sensitive materials or fatigue crack initiating conditions, K f = K t 1 (2−√( Y T)) . The ratios of calculated and experimental values for K f are within 0.9–1.1. The stress concentration factors ( t ∗ ) of the turning point from blunt to sharp notch are K t ∗ = ( 2Δσ 0√d ΔK th ) 3 2 and K t ∗ = ( 2Δσ 0√d ΔK th ) 2−√( Y T)) , corresponding to low and high notch sensitive materials, respectively. The calculated values are in agreement with experimental results.