FIGURE 3: CRACK PROPAGATION RATE VERSUS CRACK LENGTH NOTCH SHARPNESS -COLD EXPANSION EFFECT The figure 3 shows the evolution of crack propagation rate and bring out the notch sharpness effect (hole radius) and the cold expansion effect. A increase of the hole radius and of the cold expansion degree lead to a decrease of the crack propagation rate . We have to notice after cold expansion the crack propagation rate don’t go back initial value, that means the parameters of the PARIS law have changed. Radius in mm Radius 3 mm cold working Expansion degree % 1 .0 2.5 3.0 0 1.7 3.4 4.3 7.1 9.0 Time Life in kilocycles 60XX1 75 220 340 340 450 720 1208 211 95 60XX2 119 335 611 611 1040 1420 2000 321 130 Minimum of crack Propagation Rate 10 -6mm/cycle 60XX1 13.6 11.5 8.80 8.80 6.65 4.20 2.50 14.21 31.60 60XX2 8.5 7.1 4.95 4.95 2.80 2.25 1.50 9.34 30.70 TABLE 2: TIME LIFE IN KCYCLES - CRACK PROPAGATION RATE SHARPNESS AND COLD EXPANSION DEGREE (NOMINAL STRESS 28.5 MPA) 0 5 10 15 20 25 30 35 0 2 4 6 8 10 DCE % (da/dN)min mm/cycle (x 10^-6) 60XX1 60XX2 0 0,5 1 1,5 2 2,5 3 3,5 4 0 2 4 6 8 10 Degre of cold expansion Na ( tot)/ Na without expansion Beneficial effect of cold expansion Destructive effect of cold expansion 60XX1 60XX2 FIGURE 4: COLD EXPANSION EFFECT BRING OUT OF DAMAGING AFTER A TOO HIGH C.E.D 1.E-06 1.E-05 1.E-04 1.E-03 15 20 25 30 35 40 da/dN ( mm/cycle) Drilling New Crack Initiation 60XX2 Crack Length mm 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 15 20 25 30 35 40 60XX2 Crack length mm da/dN (mm/cycle) New Crack Initiation Drilling and cold working
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