EXPERIMENTAL AND THEORETICAL-STUDY ON NUMERICAL DENSITY EVOLUTION OF SHORT FATIGUE CRACKS

Fatigue testing was performed using a kind of triangular shaped specim en to obtain the characteristics of numerical density evolution for sh ort cracks at the primary stage of fatigue damage. The material concer ned is a structural alloy steel. The experimental results show that th e numerical density of short cracks reaches the maximum value when cra ck length is slightly less than the average grain diameter, indicating grain boundary is the main barrier for short crack extension. Based o n the experimental observations and related theory, the expressions fo r growth velocity and nucleation rate of short cracks have been propos ed. With the solution to phase space conservation equation, the theore tical results of numerical density evolution for short cracks were obt ained, which were in agreement with our experimental measurements.