[工学]【系列】过程设备设计第四章-44-45.ppt

4.5.2 Low cycle fatigue curve s s b s a s F F E O B D F C F eq s s s F m E m F m s s s E a E eq F a E s s s Fig. 4-66 Adjustment by mean stress 4.5.2 Low cycle fatigue curve Ajustment by mean stress and calculation of equivalent alternating stress amplitude sa with mean stress not equal to zero sa with mean stress equal to zero (1) （4-98） 4.5.2 Low cycle fatigue curve (2) （4-99） 4.5.2 Low cycle fatigue curve s m ax = s m + s a a s m s s s - = P C B A s ’ a s ’ a e s O s s 2 s s Fig. 4-67 Stress vs. strain for s s s s s 2 max 4.5.2 Low cycle fatigue curve s s max = s m + s a 0 = m s P F F E C D B A s ’ a s ’ a e O s s - 2 s s s s Fig. 4-68 Stress vs. strain for σa+σm≥2σs 4.5.2 Low cycle fatigue curve (3) ，no need to adjust . Adjustment of low cycle fatigue curve （4-100） 4.5.2 Low cycle fatigue curve 10 4 Stress amplitude S a (MPa) 10 2 10 3 10 5 10 6 10 10 5 10 4 10 3 10 2 Cycle number N Mean stress=0 After adjustment by mean st ress Fig. 4 - 69 Figure curve after adjustment by mean stress 4.5.3 Fatigue Analysis of Pressure Vessels 4.5.3 Fatigue Analysis of Pressure Vessels (1) Calculation of alternating stress amplitude ; (2) Calculation of the allowable cycle number N using design fatigue curves; (3) Comparison of the expected working cycle number n with the allowable cycle number N. If nN, re-design again. 4.5.3 Fatigue Analysis of Pressure Vessels Fig. 4-70 Design fatigue curve Cycle number N Allowable stress amplitude Sa MPa 注 (1) E=210×103 MPa (2) 对抗拉強度介于552~896 MPa用內插法 4.5.3 Fatigue Analysis of Pressure Vessels Vessels not required for fatigue analysis Fatigue analysis is not mandatory if and the total of the expected number of cycles of types ① plus ② plus ③ plus ④ does not exceed 1000 cycles. 4.5.4 Factors to Fatigue Life 4.5.4 Factors