3 important significances of correlations, can derive a number of beneficial formulas, obtain some calculation methods on the strengths, crack propagation rates and life predictions. For example between the material constant 2B and other constants are having functional relations as formulas below, ) )/( ) ( 2(2 02 2 02 2 2 2 2 a a N N B c c fc − − = − λ δ ( 0) = mσ (4) ) )/( ( ) 2 2 (1 02 2 02 2 - 2 2 2 2 a a N N B c c fc m fc − × − ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − = λ δ δ δ , ( 0) ≠ mσ (5) Where fc 2δ in (4~5) are critical value of the crack tip open displacement, c fc δ δ = 2 , the 2B is defined as comprehensive material constants. Its physical meaning is a concept of power, is a maximal increment value, and also is given out energy in one cycle made specimens to failure. Its geometrical meaning is a maximal micro-trapezia area to approximate to beeline, and is also an intercept between 4 3O O− (Fig.1). And slope of micro-trapezium bevel edge just is corresponding to the exponent 2λof formula (4, 5). c a2 is a critical crack size, 02 a is initial (or precrack) crack size. 02 N is initial life, 0 02 = N ; c N2 is a critical life. mδ is a mean value of the crack tip open displacement, )/2 ( min max δ δ δ = + m , here max δ and min δ are the maximal and minimal values of the crack tip open displacement. Moreover if its unit of the parameter 2B is calculated by ‘mm’, then the value of 2B must be again multiplied by 1000. For the sake of safety, the comprehensive constant 2B should be calculated as following form, ) )/( ( ) 2 2 (1 02 02 2 - 2 2 2 2 a a N N B pv eff fc m eff eff − × − ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − = λ δ δ δ (6) Where eff B2 is also an effective comprehensive material constant, its physical meaning is a given out effective energy in one cycle made specimens before failure. Here pv pv eff a a N N v − = − ) )/( ( 02 02 2 , pv v is defined to be the virtual rate, ) *( / v v m cycle pv = [6,8]. ) *,( / 3 10 ~3 10-7 -8 v m cycle v pv × = ≈ × . eff a is an effective size during steady growth course. pv N is a virtual life. 2eff δ is an effective value of crack tip open displacement, that is the parameters during steady growth course, they must be all obtained from experiment. Here suppose that
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