卖妄应动( Alternating Stress (2)r>0为同号应力循环;r<0为异号应力循环 (3)构件在静应力下,各点处的应力保持恒定,即σmnx=mi 若将静应力视作交变应力的一种特例,则其循环特征 r=+1o.=0 max max mIn
(Alternating Stress) （2）r > 0 为同号应力循环; r < 0 为异号应力循环. （3）构件在静应力下,各点处的应力保持恒定，即 s max= s min . 若将静应力视作交变应力的一种特例,则其循环特征 r = +1 0 s a = s m = s max O s max s min=0 t s
卖妄应动( Alternating Stress 例题3发动机连杆大头螺钉工作时最大拉力Fmx=583kN最小 拉力Fmn=558N,螺纹内径为d=15mm,试求an3Cm和r 解: 4×58300 nax max一 =561MPa 兀×0.01152 4×55800 0mAπ×0.01153÷5372MPa nn 561-537 0 = max =12MPa 2 MaxmIn 561+537 549MPa 2 2 0m=5n=0.957 537 max
(Alternating Stress) 例题3 发动机连杆大头螺钉工作时最大拉力Fmax =58.3kN,最小 拉力Fmin =55.8kN,螺纹内径为 d=11.5mm,试求 sa ,s m 和 r. 解: . = = = max max 2 4 58300 561MPa 0 0115 F A s . . = = = min min 2 4 55800 537 2MPa 0 0115 F A s 12MPa 2 561 537 2 max min a = − = − = s s s 549MPa 2 561 537 2 max min m = + = + = s s s 0.957 561 537 max min = = = s s r