Relation Between Fatigue Crack Growth Law and Reversible Plastic Zone Size in Fe-3% Si Alloy

Abstract

Fatigue crack growth laws were investigated in connection with the reversible plastic zone size at a crack tip by the rotating bending test of a Fe- 3%Si alloy. The main results obtained are as follows: (1) The crack growth rate is expressed by the following two equations. (a) Under a small scale yielding. dl/dN=C₁ΔK^m (l:crack length, C₁ and m:constants). (b) Under a high stress level, dl/dN=C₂σⁿl (σ:stress amplitude, C₂ and n:constants). (2) On the other hand, regardless of the scale of yielding, dl/dN=C₃r_prev (r_prev:reversible plastic zone size at crack tip, C₃:constant). (3) From the relation in (2), the physical backgrounds of the two crack growth laws in (1) and the presence of a non-propagating crack can be explained.