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1、Fatigue:Stress-Life,Workshop A12-1,August 26,2005Inventory#002266WSA12.1-2,Goals,Goal:In this workshop our goal is to perform a Stress-Life analysis of the connecting rod model(ConRod.x_t)shown here.Specifically,we will analyze two load environments:1)Constant Amplitude Load of 4500 N,Fully Reversed
2、 and 2)Random Load of 4500N.,August 26,2005Inventory#002266WSA12.1-3,.Start Page,From the launcher start Simulation.Choose“Geometry From File.“and browse to the file“ConRod.x_t”.When DS starts,close the Template menu by clicking the X in the corner of the window.,August 26,2005Inventory#002266WSA12.
3、1-4,Preprocessing,Change the working unit system to metric(m,kg,Pa).“Units Metric(m,kg,Pa,C,s)”Verify the material is set to“Structural Steel”.Highlight the“Part 1”in the geometry branch.If not,click in the“Material”field and“browse”.,1.,2.,3.,August 26,2005Inventory#002266WSA12.1-5,.Preprocessing,S
4、elect the“Structural Steel”material and then click OK.,4.,August 26,2005Inventory#002266WSA12.1-6,.Preprocessing,Apply the following boundary conditions(see next page):,August 26,2005Inventory#002266WSA12.1-7,.Preprocessing,Highlight the Environment branch.Highlight the connecting rod surface shownI
5、nsert a force load.“RMB Insert Force”From the detail window change to“Components”and“Z=-4500 N”.,6.,5.,7.,8.,August 26,2005Inventory#002266WSA12.1-8,.Preprocessing,Highlight the Environment branch.Highlight the connecting rod surfaces shownInsert a cylindrical support.“RMB Insert Cylindrical Support
6、”From the Details of“Cylindrical Support”window:Set Radial=“Fixed”,Axial=“Free”,Tangential=“Free”,10.,9.,11.,12.,August 26,2005Inventory#002266WSA12.1-9,.Preprocessing,Highlight the Environment branch.Highlight the connecting rod surface shown Insert a fixed support.“RMB Insert Fixed Support”,14.,13
7、.,15.,August 26,2005Inventory#002266WSA12.1-10,Add results to Solution:Highlight the solution branch.RMB Insert Stress Equivalent(von Mises).RMB Insert Deformation Total.,Solution Setup,16.,August 26,2005Inventory#002266WSA12.1-11,Insert fatigue tool:Highlight the solution branch.RMB Insert Fatigue
8、Fatigue Tool.,.Solution Setup,20.,19.,August 26,2005Inventory#002266WSA12.1-12,From the Details of“Fatigue Tool”window:Specify a Fatigue Strength Factor(Kf)of.8(material data represents a polished specimen and the in-service component is cast).Specify fully reversed loading to create alternating str
9、ess cycles.Specify a stress-life fatigue analysis(No mean stress theory needs to be specified since no mean stress will exist fully reversed loading).Specify that Von Mises stress will be used to compare against fatigue material data.,.Solution Setup,August 26,2005Inventory#002266WSA12.1-13,Add resu
10、lts to the Fatigue Tool:Insert“Safety Factor”:RMB Insert Fatigue Safety Factor.From the Details of“Safety Factor”window:Set the Design Life to 1e6 cycles.,.Solution Setup,26.,August 26,2005Inventory#002266WSA12.1-14,Add results to the Fatigue Tool(cont.):Insert“Fatigue Sensitivity”:RMB Insert Fatigu
11、e Fatigue SensitivityFrom the Details of“Fatigue Sensitivity”window:Specify a minimum base load variation of 50%(an alternating stress of 2250N)and a maximum base load variation of 200%(an alternating stress of 9000N).,.Solution Setup,28.,August 26,2005Inventory#002266WSA12.1-15,Add results to the F
12、atigue Tool(cont.):Insert“Biaxiality Indication”:RMB Insert Fatigue Biaxiality IndicationSolve,.Solution Setup,29.,August 26,2005Inventory#002266WSA12.1-16,View ResultsHighlight and plot the“Total Deformation”result.,Results,August 26,2005Inventory#002266WSA12.1-17,Highlight and plot the“Equivalent
13、Stress”result.,.Results,August 26,2005Inventory#002266WSA12.1-18,Highlight and plot the“Safety Factor”result for a design life of 1e6 cycles.,.Results,August 26,2005Inventory#002266WSA12.1-19,Highlight and plot the“Fatigue Sensitivity”result for a minimum base load variation of 50%and a maximum base
14、 load variation of 200%.,.Results,August 26,2005Inventory#002266WSA12.1-20,Find the sensitivity of available life with respect to loading for a maximum base load variation of 400%.Note,must resolve to obtain the new Fatigue Sensitivity results.,.Results,August 26,2005Inventory#002266WSA12.1-21,Highl
15、ight and plot the“Biaxiality Indication”result.Note,the stress state near the critical location is not far from uniaxial(.1.2),which gives an added measure of confidence since the material properties are uniaxial.Recall,a biaxiality of zero corresponds to uniaxial stress,a value of 1 corresponds to
16、pure shear,and a value of 1 corresponds to a pure biaxial state.,.Results,August 26,2005Inventory#002266WSA12.1-22,Insert a second fatigue tool to analyze a random load of 4500N.Assume that we have strain gauge results that were collected experimentally from the component and that we know that a str
17、ain gauge reading of 200 corresponds to an applied load of 4500N:Highlight the solution branch.RMB Insert Fatigue Fatigue Tool.,Solution Setup,31.,30.,August 26,2005Inventory#002266WSA12.1-23,From the Details of“Fatigue Tool 2”window:Specify a Fatigue Strength Factor(Kf)of.8(material data represents
18、 a polished specimen and the in-service component is cast).Specify fatigue loading as coming from a scale history and select scale history file containing strain gauge results over time(browse and open the“SAEBracketHistory.dat”file).Define the scale factor to be.005(we must normalize the load histo
19、ry so that the FEM load matches the scale factors in the load history file):,.Solution Setup,August 26,2005Inventory#002266WSA12.1-24,From the Details of“Fatigue Tool”window(cont.):Specify Goodman theory to account for mean-stress effects.Specify that a signed Von Mises stress will be used to compar
20、e against fatigue material data(use signed since Goodman theory treats negative and positive mean stresses differently).Specify a bin size of 32(Rainflow and Damage matrices will be of dimension 32x32).,.Solution Setup,August 26,2005Inventory#002266WSA12.1-25,Add results to the Fatigue Tool 2:Insert
21、“Life”:RMB Insert Fatigue Life Insert“Safety Factor”:RMB Insert Fatigue Safety FactorFrom the Details of“Safety Factor”window:Set the Design Life to 1000 cycles.,.Solution Setup,39.,40.,38.,August 26,2005Inventory#002266WSA12.1-26,Add results to the Fatigue Tool(cont.):Insert“Fatigue Sensitivity”:RM
22、B Insert Fatigue Fatigue SensitivityFrom the Details of“Fatigue Sensitivity”window:Specify a minimum base load variation of 50%(an alternating stress of 2250N)and a maximum base load variation of 200%(an alternating stress of 9000N).,.Solution Setup,41.,42.,August 26,2005Inventory#002266WSA12.1-27,A
23、dd results to the Fatigue Tool(cont.):Insert“Biaxiality Indication”:RMB Insert Fatigue Biaxiality Indication Insert“Rainflow Matrix”:RMB Insert Fatigue Rainflow Matrix,.Solution Setup,43.,44.,August 26,2005Inventory#002266WSA12.1-28,Add results to the Fatigue Tool(cont.):Insert“Damage Matrix”:RMB In
24、sert Fatigue Damage MatrixFrom the Details of“Damage Matrix”window:Set the Design Life to 1000 cycles.Solve,.Solution Setup,45.,46.,August 26,2005Inventory#002266WSA12.1-29,View ResultsHighlight and plot the“Life”result.,Results,August 26,2005Inventory#002266WSA12.1-30,Highlight and plot the“Safety
25、Factor”result for a design life of 1000 cycles.,.Results,If the loading history corresponded to the loading experienced by the part over a months time,the damage and FS will be at a design life of 1000 months.Note that although a life of only 77 loading blocks is calculated,the needed scale factor(s
26、ince FS 1000=.60)is only.60 to reach a life of 1000 blocks.,Note,the“scale factor”is the scale factor for the loading to make it meet the life of 1000 months.,August 26,2005Inventory#002266WSA12.1-31,Highlight and plot the“Fatigue Sensitivity”result for a minimum base load variation of 50%and a maxi
27、mum base load variation of 200%.,.Results,August 26,2005Inventory#002266WSA12.1-32,Highlight and plot the“Biaxiality Indication”result.,.Results,August 26,2005Inventory#002266WSA12.1-33,Highlight and plot the“Rainflow Matrix”result.,.Results,Here,one can see from the rainflow matrix that the majorit
28、y of the cycle counts are for low mean stress and low stress amplitude(range).,August 26,2005Inventory#002266WSA12.1-34,Highlight and plot the“Damage Matrix”result.,.Results,Although,from the previous slide,one saw that most of the counts were for the low mean and range bins,these do not cause the most damage at the critical location,as shown in this damage matrix.Instead,themedium stress amplitude cycles cause the most damage at the critical location.,
