Streamlining Stress and Fatigue Evaluation of...

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



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



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



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



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



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



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



How Do You Manage YourDurability Process

The Modal Stress Recovery (MSR)Toolkit

n Streamlines stress and fatigue evaluation



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



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?



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



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



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



Modal Stress Recovery Example 4/5n Compute and store stress/strain components

at selected nodes

Modal Stress Recovery Example 5/5n Plot nodal stresses



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



FE-Fatigue Example 2/10n Run ADAMS analysis

FE-Fatigue Example 3/10n Export stress shape function to partial FES file



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



FE-Fatigue Example 6/10n Specify analysis type

FE-Fatigue Example 7/10n Use output from previous ADAMS run as

loading input



FE-Fatigue Example 8/10n Select material from database

FE-Fatigue Example 9/10n Run Fatigue Analysis



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



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



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



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

Date post:	25-Apr-2018
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