COLLECTIVE EVOLUTION CHARACTERISTICS AND COMPUTER-SIMULATION OF SHORTFATIGUE CRACKS

Fatigue testing was conducted using a kind of triangular isostress spe cimen to obtain the short-fatigue-crack behaviour of a weld low-carbon steel. The experimental results show that short cracks continuously i nitiate at slip bands within ferrite grain domains and the crack numbe r per unit area gradually increases with increasing number of fatigue cycles. The dispersed short cracks possess an orientation preference, which is associated with the crystalline orientation of the relevant s lip system. Based on the observed collective characteristics, computer modelling was carried out to simulate the evolution process of initia tion, propagation and coalescence of short cracks. The simulation prov ides progressive displays which imitate the appearance of experimental observations. The results of simulation indicate that the crack path possesses a stable value of fractal dimension whereas the critical val ue of percolation covers a wide datum band, suggesting that the collec tive evolution process of short cracks is sensitive to the pattern of crack site distribution.