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Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 1
StreamliningStress and Fatigue Evaluation
of Mechanical SystemsMichael Hoffmann
Diego Minen
Analysis versus Testing“Everybody believes the test results exceptthe test engineer.Nobody believes the analysis results exceptthe analyst.”
“We need to get analysis and testing on thesame page”
Mike Racicot, Total Vehicle Analysis Engineer,GM
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 2
Partnership Goalsn Integrate Physical and Virtual Testing to
Create the Analytical Design and ValidationProcessu Agree on and support standard interfacesu EDM - Seamless Integration of Component or
Subsystem Physical Test Results into theFunctional Digital Vehicle
u VTL - Consistent Setup, Test and Analysisbetween Simulated and Physical Testing
u Expertise in Integrating Solutions for AnalyticalDesign and Validation Processes
n Bring a New Level of Productivity to Designand Development Processes
Integrated Durability ProcessTest TrackTest Track
Full VehicleFull VehicleTest LabTest Lab
ComponentComponentTest LabTest Lab
n Seamless transitionu from test track to test labsu from virtual to real
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 3
Finite Element Programm
ADAMS/Durability
Software Components of aDurability Solution
ADAMS/FullSim
FE-Fatigue
ADAMS/Driveline
ADAMS/Engine
ADAMS/Car
ADAMS/EDM
ADAMS/Flex
Virtual Test Lab
ADAMS/Tire FTire
ADAMS/Durabilityn Reference data from DAC or
RPC III files and interpolateduring simulations
n Save REQUEST data toDAC or RPC III files
n Export ADAMS results toDAC or RPC III files
n View header informationand/or data in DAC or RPCIII files
n Plot DAC or RPC III timehistory data and comparewith ADAMS results
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 4
FE-Fatigue
FE stress/strainsView model andstress/strains in
Pre/Post Processor
FE-Fatigue
Load and Materialinformation Post process fatigue
results
ADAMS/Tire FTire
0 0.02 0.04 0.06 0.08 0.11000
2000
3000
4000
5000
wheel load [N]
simulation
measurement
n Tire model for NVH and durabilityapplications
200 mm10 mm
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 5
Empirical Dynamic Model (EDM)
K&C
TiresShock Absorbers
Elastomers
Dynamic K&C
Virtual Prototype
Empirical Dynamic Model
n Physical Testing Generates Data for ModelCreationu Black Box, Characteristic, and Concept Model
Virtual Prototype
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 6
Random Displacement Command
Measured Force and Displacement
VFd
Model Build
Predicted Results
Empirical Dynamic Modeln Support of EDM
u ADAMS/Viewu ADAMS/Caru ADAMS/Pre
Using EDM
Conventional Damper Model
Damper Loads During a PotholeEvent
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Michael Hoffmann, Diego Minen 7
Virtual Test Labn Dynamic Models of MTS Systems
u Mechanical, Hydraulic, and Control Systems
n Interface to Functional Digital Vehiclen Common Pre and Post-processing Utilitiesn Common Drive Files for Physical and Virtual Testsn Predictive Analysis for Validation Pathn Knowledge of Test Lab engineers can be introduced
much earlier in the design process
VTL Application Table
Full RPC Iteration andDrive File Creation
VTL/RPC –Model ofController andHydraulics
RPC Response File
Validation with TraditionalInstrumentation or SWIFT
VTL – Elasticityand Kinematicsof Test Rig
ActuatorDisplacements
Fatigue PredictionNo VTL ModelSpindle Loads
ApplicationsTest Rig ModelInput
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 8
How Do You Manage YourDurability Process
The Modal Stress Recovery (MSR)Toolkit
n Streamlines stress and fatigue evaluation
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 9
Common Process for StressComputation
n Parameter studies where objectives includecomponent stresses require switchingbetween FEA and Mechanical SystemSimulationu no integrated processu parameter studies and optimization on a system
level is too cumbersome
Generate Mode Shapes
with FEA
Obtain Stress Histories
with FEA
Obtain Load Histories
with MSS
Generate Mode & Stress
Shapes with FEA
Obtain Load & Stress
Historieswithin ADAMS
Integrated Process for StressComputation
n The MSR Toolkit allowsu Stress computation
within the ADAMSenvironment
u Parameter studies andoptimization on asystem level
n No constant switchingbetween FEA and MSS
n FEA is touched onlyonce
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 10
Integrated Process for StressComputation (cont.)
n Step One:u Mesh components
n Step Two:u Run FEA to generate mode and
stress shapes-> data is written to the MNF-file
n Step Three:u Run ADAMS to obtain the component
load histories (in terms of ModalCoordinates)
n Step Four:u Run ADAMS/PPT to
l compute and plot nodal stressesl display and animate components’
stress contours
Data Handling Issues in FatigueAnalysis
n Car body is subjected to morethan 50 load channels(suspension connection points)
n Traditional approach requires50 unit load cases to beanalyzed with FEA
n Issues: Not automated, error prone
Assign load channelsto unit load cases
units ?polarity?
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 11
Generate Mode & Stress
Shapes with FEA
Integrated Process for FatigueComputation
n The MSR and FatigueToolkitu Minimizes data transfer
between FEA, ADAMS,and FE-Fatigue
u Generates consistentset of information
n Possible user error isminimized
n Durability process isautomated
Generatestressshapes
in nCodeformat
ObtainLoad
Histories
DisplayDamageContours
ADAMS environment
Calculate damagedistribution with
FE-Fatigue from nCode
FES DAC UNI
Integrated Process for FatigueComputation (cont.)
n Step One:u Mesh components
n Step Two:u Run FEA to generate mode and stress shapes
-> data is written to the MNF-filen Step Three:
u Extract the stress shapes from the MNF-file tonCode’s FES-file
n Step Four:u Run ADAMS to obtain the component load
histories (in terms of Modal Coordinates) andwrite the modal coordinates into DAC file
n Step Five:u Run FE-Fatigue to calculate fatigue damage on
all nodesn Step Six:
u Run ADAMS/PPT to display components’damage contours
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 12
Example Process:Modal Stress Recoveryn Computes and plots Stress Components and
VonMises Invariantn Displays color contours, most critical node and
time step of occurrance
Modal Stress Recovery Example 1/5n Start ADAMS and load MSR-Fatigue Plug-In
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 13
Modal Stress Recovery Example 2/5n Run ADAMS analysis
Modal Stress Recovery Example 3/5n Animate Stresses on flex bodies
Stresses are computed for display purposes only, not stored as result sets
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 14
Modal Stress Recovery Example 4/5n Compute and store stress/strain components
at selected nodes
Modal Stress Recovery Example 5/5n Plot nodal stresses
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 15
Example Process:Durability Analysis with FE-Fatiguen Computes and displays nCode FLP results within
ADAMS/PPT
FE-Fatigue Example 1/10n Start ADAMS and load MSR-Fatigue Plug-In
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 16
FE-Fatigue Example 2/10n Run ADAMS analysis
FE-Fatigue Example 3/10n Export stress shape function to partial FES file
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 17
FE-Fatigue Example 4/10n Export load histories (in terms of Modal
Coordinates) to DAC files
FE-Fatigue Example 5/10n Start nCode software, set working directory,
and select FE-Fatigue task
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 18
FE-Fatigue Example 6/10n Specify analysis type
FE-Fatigue Example 7/10n Use output from previous ADAMS run as
loading input
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 19
FE-Fatigue Example 8/10n Select material from database
FE-Fatigue Example 9/10n Run Fatigue Analysis
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 20
FE-Fatigue Example 10/10n Display Damage Contours in ADAMS/PPT
Supported Configurationsn ADAMS 11.0n Operating systems
u Windows NT 4.0 and Windows 2000u IRIX 6.5 32 and 64 bit
n NASTRAN 70.5 and 70.7n ANSYS 5.6 and 5.7n FE-Fatigue 2.0
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 21
Summaryn The MSR and Fatigue Toolkit allows stress
and fatigue evaluation within an integratedenvironment
n Switching between different tools is reducedto a minimum
n Process improvement in terms of efficiencyand quality
n The Modal Stress Recovery Toolkit isavailable free of charge for allADAMS/Durability usersu preview of 12.0 functionality
Integrated Durability ProcessTest TrackTest Track
Full VehicleFull VehicleTest LabTest Lab
ComponentComponentTest LabTest Lab
n Seamless transitionu from test track to test labsu from virtual to real
n nCode, MDI, and MTS are available toaccelerate the integration process
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 22
Appendix
n Principles of Modal Stress Recovery
{ } [ ] { }p⋅Φ= σσ
[ ] { } { }[ ]SP+= σσσ φφφ ,...,1
Assuming that the reduction of the full set of Mode Shapes of the Flexible
Body to a sub-set is correct and comprehensive of all the required effects,
the Stress Distribution related to the body deformation can be calculated as:
ortho-normalized Modal Stress Matrix
{ }1σφ …P+S (P=number of Normal Constrained Modes S = number of Static Correction Modes)
{ }1uφ …P+S (P=number of Normal Constrained Modes S = number of Static Correction Modes)
{ }p Vector of Modal Coordinates{ }σ Stress Component Matrix
Principles of Modal Stress Recovery
Stress Mode Shapes Method
Streamlining Stress and Fatigue Evaluation
Michael Hoffmann, Diego Minen 23
Principles of Modal Stress Recoveryn FE Calculation
u Component Mode Synthesis, Craig Bamptonl Normal Modesl Static Correction Modesl Residual Vectors for Distributed/Inertial/Thermal Loads
u Modal Stress (and/or) Strain Tensorsu .mnf file gene\ration
n Flexible Bodies in ADAMSu Correct Mechanism Dynamicsu Correct Internal Deformations in the Flexible Componentu Correct Boundary Loads and Constraintsu Modal Coordinates
n Stress/Strain Computationu Combining Modal Coordinates with Modal Precomputed (Stress/Strain)
Tensorsu Post Processing in the most popular FE graphic programs and in ADAMS
l Stress/Strain Time Historyl Stress/Strain Animation
Material Young Modulus(N/m2 )
D(m)
d (m)
r (m)
s(m)
M (N m)
Steel
2.1E11
5.0E-2
3.85E-2
2E-3
1.0E-2
1
Stress
(N/m2)
Kt
ANSYSNode408
887 580
2.192
ANSYSNode4040
404 870
ADAMSNode408
873 400
2.164
ADAMSNode4040
403 600
Principles of Modal Stress Recovery -Example
ANSYS ADAMS