How does the ANSYS fatigue module calculate the alternating stress difference range?
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In Release 11.0. ANSYS calculates the alternating stress difference range according to the method prescribed in Section VIII, Division 2 of the ASME Boiler and Pressure Vessel Code. In that method, component stress difference ranges are first calculated. These component stress difference ranges are then used to determine an equivalent stress range and an alternating stress difference range. The following example is an axisymmetric cylinder subjected to two different internal pressures. For these two loading cases, ANSYS calculated an alternating stress difference range of 46. 6. From hand calculations, the approximate stress difference range should be 45.9. Thus, the ANSYS results agree closely with the hand calculations. Hand Calculations: Load Case 1: SX = -8 SY = 45 SZ = 98 SXY = 0 SYZ = 0 SXZ = 0 Load Case 2: SX = -16 SY = 90 SZ = 196 SXY = 0 SYZ = 0 SXZ = 0 Component Stress Difference Ranges delta SX = -16 - (8) = -8 delta SY = 90 - 45 = 45 delta SZ = 196 - 98 = 98 delta SXY = 0 delta SYZ = 0 delta SXZ = 0 Equivalent Stress Range = SQRT( 1/2 *(-8-45)^2+(45-98)^2+(-8-45)^2 ) = 91.8 Alternating Stress Difference Range = 91.8/2 = 45.90 ! ANSYS INPUT/prep7 et,1,182,1,,1 mp,ex,1,10e6 mp,prxy,1,.3 rect,9.5,10.5,0,25 rect,9.5,10.5,25,50 wpoff,0,50 cyl4,0,0,9.5,0,10.5,90 wpcsys aglue,all numcmp,all lsel,s,length,,.99,1.01 lesize,all,.35 alls esize,1 mshape,0,2d mshkey,1 amesh,all lsel,s,line,,4,8,4 lsel,a,line,,10 nsll,,1 cm,press_n,node nsel,s,loc,y,-.01,.01 d,all,uy,0 nsel,s,loc,x,-.01,.01 d,all,ux,0 alls n1 = node(10.5,25,0) /solu time,1 cmsel,s,press_n sf,all,press,10 alls solve time,2 cmsel,s,press_n sf,all,press,20 alls solve /post1 set,1 nsel,s,node,,1 prnsol,s,comp prnsol,s,prin set,2 prnsol,s,comp prnsol,s,prin alls fp,1,10,30,100,300,1000,10000 fp,21,650,390,240,161,109,59 set,1 fsnode,n1,1,1 set,2 fsnode,n1,1,2 fe,1,1000 ftcalc,1,n1 !ANSYS OUTPUT ! ALTERNATING SI (SALT) = 46.605 |
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