2 with limited experimental data and conventional material constants, thereby to realize the calculations for the crack growth rates and to do the life predictions which are in different stress ratio under complicated loading conditions. Moreover, provides yet homologous calculation examples. Anticipate that the works will be having practical significances for fatigue - damage - fracture tests to save experimental times, fund inputs and to expand engineering applications. 2. The calculations of crack growth rate for elastic-plastic steels In references [1，2] provide the relation between the fracture life fc N2 and half-cycle of amplitude value /2 tδΔ of crack tip open displacement at crack growth stage, 2' 2 2 2 c fc fc t N = × Δ δ δ (1) But if it is expressed to adopt one-cycle of crack tip open displacement range tδΔ , it become as following form 2 2 2 2 c c fc t N B Δ × = − δ (2) And relation between the crack growth rate 2 2 / da dN and one-cycle of crack tip open displacement range tδΔ is as discussed [3~4], 2 2 2 2 / λδ t da dN B= Δ (3) Where the equations (1) and (2) can be described as the reversed beeline 2 1 C C in bidirectional combined coordinate system and bidirectional curves in the whole process( Fig.1)［5~7］, that is predigested by logarithm transacting just is showed the relation between the life and the crack tip open displacement. And the equations (3) can be described as the positive direction beeline 1 2 CC , it just is showed for the relation between the crack growth rate and the crack tip open displacement. Research and discover that in fact the relations among equations (1), (2) and (3) are consistent. Here the parameters 2λ , 2c and 2B are all material constants. 2λ and 2c are exponents of equations, 2 2 1/c =− λ , its geometrical meaning is the slope of force triangle bevel edge. Of course some key material constant in the engineering calculations must be obtained from experimentations. But actually in a number of calculation models, there are functional relationps between some parameters or between some material constants each other, so that we can use the kinds of having
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