Abstract:

On the basis of the modified strip yield model for considering thickness effects and strain hardening, a fatigue crack closure analytical model is presented. The main objective is to study the influence of thickness on crack closure behavior. The tensile stresses on the plastic zone and the yield stress in compression are defined and found to be multiplied by a function in tension for considering the thickness and hardening effects and a factor in compression for considering material Bauschinger effect, respectively. A plastic constraint factor is correspondingly defined with the plastic zone length ratio in this model. Crack closure coefficients and crack opening stress ratios with different thicknesses and stress ratios are calculated and compared with some other results. It is noted that the relation between crack closure coefficients or crack opening stress ratios and plastic constraint factor α when stress ratio R is given can be determined by prescribed functions. Consequently, the crack growth rate under constant amplitude loading can be rewritten as a comprehensive equation with different thicknesses and stress ratios.

Key words: tr iaxial str ess constr aint, closur e model, fatigue, cr ack pr opaga tion r ate