7 It must point that the equations (10), (16), (20) and (21) can also only apply to work stress 1 / << s σ σ ( s σ σ 0.5 ≤ ). 2.2 Calculations for crack growth rate under work stress s σ σ=> condition On the other hand, for work stress s σ σ=> condition, it must be changed to use as following calculating equations. Here there are also two kinds of methods (1) The calculation methods used by the stress σ It also can directly use the stress σto calculate the tδ and tδΔ [10]. Here the crack tip open displacement tδ and tδΔ are as bellows [10] E a y t s s 2 2( / 1) 0.5 + = σ σ πσ δ ( )m (22) ,( ) ( /2 1) 02 2 m E a y s s t + Δ Δ = σ σ πσ δ (23) ) ( / ( /2 1) 2 2 2 2 2 2 m cycle E a y B dN da s s eff ， λ σ σ πσ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + Δ = = (24) [ ] { } pv meff s s eff v a E B × + = − 2 / 2 2 ( ( / 1) 2 λ σ σ πσ ( 0) = mσ (25) [ ] pv s meff meff s s eff v a a a E B × ⎪⎭ ⎪ ⎬ ⎫ ⎪⎩ ⎪ ⎨ ⎧ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + × − + = − 2 2 2 min 2 max 2 2 ) ( / 1 2 2( ( / 1) λ σ σ σ σ σ πσ ( 0) ≠ mσ (26) ( ) ( / 1) m E a s s eff meff ， + = σ σ πσ δ (27) Where c eff δ δ (0.3 ~ 0.35) = . (2) The calculation methods combined by stress and strain Its method is that the comprehensive material constant eff B2 to adopt the eff δ to express, and the crack tip open displacement to adopt the stress σto express, its form as follow
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