Cyclic plastic zone modified critical distance theory for notch fatigue analysis of metals

Abstract

Notch fatigue strength analysis has decisive role in safe structural design and operational reliability of key components. For notched structures, the presence of the cyclic plastic zone (CPZ) is generally cause for crack initiation and growth at the notch tip, which alters notch geometries and acts as if it is wider than its physical size. Particularly, the influence of the CPZ is more significant in a low cycle fatigue regime. Accordingly, a novel approach for notch fatigue analysis is proposed by combining theory of critical distance (TCD) with CPZ concepts. Experimental data of En3B low carbon steel and 6082 aluminum alloy are introduced for model affirmation and correlation. Results indicate that the critical distance increases with the size of CPZ instead of a material constant during low cycle fatigue analysis, and the proposed model provides better correlations of predicted fatigue lives with tested results than classic TCD and Susmel and Taylor models.