Improving of Assessment Quality of Fatigue Analysis Using: MS, FEMFAT and FEMFAT LAB Virtual Iteration

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Improving the assessment
quality of a fatigue analysis
ALTAIR Motion solve, FEMFAT LAB
virtual iteration and FEMFAT

General Workflow
Author: FEMFAT SUPPORT 207.10.2015
Workflow of fatigue testing and analysis
based on road load data
Application & calibration
Data acquisition on proving ground
Load data analysis
Fatigue testing
Virtual iteration MBS model
Fatigue analysis

General Workflow
Acceleration
Typical responses
• Accelerations
– 1-axial
– 3-axial
• Displacements
– Draw wire displacement sensor
• Frame torsion
• Strains (directly/calibrated to
forces)
– Axle
– Ball joint
– Link
– Rod
– Spring
– Stabilizer
• Load cells
– Mount
• Wheel force transducers
Displacement
Strain – ball jointStrain – twist beam
Load cell Wheel force transducer

General Workflow
Load data analysis
Fatigue testing
Fatigue analysis

General Workflow
• FEMFAT LAB
– Load data analysis software
• Module Virtual Iteration:
– Load data generation for simulation models
based on measurement data (test track or test
bench)
• General approach
– Generate external load based on internal,
measured response
• Same approach as the iteration process in
the laboratory (test bench)
• Excellent convergence between
measurement and simulation
• Method is automated for
– MOTIONSOLVE
– ADAMS
– SIMPACK
– RECURDYN
black…measurement
red…...simulation

General Workflow
Load data analysis
Fatigue testing
Fatigue analysis

General Workflow
• MotionSolve model of front axle of a
passenger car (half axle)
• Computing internal forces for fatigue
analysis of the knuckle with
• Measurement signals from test track
• Desired (measurement)
• Damper force
• Ball joint force longitudinal
• Ball joint force lateral
• Tie rod force axial
• Spring displacement (used for model-check)
• Goal: load at wheel (4 channels)
• Vertical displacement (wheel center)
• Longitudinal force (wheel center)
• Steering torque (wheel center)
• Lateral force (tire patch)

General Workflow
Measurement signals (responses)
Damper force
Tie rod force
Ball joint forces Spring displacement
MBS: requests

General Workflow
Load data analysis
Fatigue testing
Fatigue analysis

VI Introduction
MOTION
SOLVE
(MBS)
Input un Output yn
Load
(drive)
Desired
(response)
Inverse non-linear problem
find load for given response
Response
Often simply and cheaply measureable
• Accelerations
• Displacements (relative)
• Strains
• Forces (internal)
Drive
High effort or not measureable
• Forces (external)
• WFT
• Load cell
• Strain gauges
• Displacements (absolute)

VI Introduction
MOTION
SOLVE
(MBS)
Input un Output yn
Load
(drive)
Desired
(response)
Calculation of the transfer function (MBS):
F(s) = y0(s) / u0(s) noise signal and its response
Calculation of first drive:
u1(s)= F-1(s) yDesired(s)
Calculation of further iterations:
un+1(s)=un(s)+ F-1(s) (yDesired(s) – yn(s))

VI Introduction
Iteration process
un+1 = un + F -1 ( yDesired - yn )
1. Noise
2. Response of noise
6. Response = desired 5. Response
3. Transfer function 4. Drive signal

VI Results
Results: 10. iteration, rough road

VI Results
Damper force – time domain 15th to 20th second Ball joint force lateral – time domain 15th to 20th second
Ball joint force longitudinal – time domain 15th to 20th second Tie rod force axial – time domain 15th to 20th second
black…measurement
red…...simulation

VI Results
Damper force - frequency domain Ball joint force lateral - frequency domain
Ball joint force longitudinal - frequency domain Tie rod force axial - frequency domain
Results: 10. iteration, rough road black…measurement
red…...simulation

VI Results
Spring displacement
(model check)
Spring displacement – time domain
Spring displacement – time domain 15th to 20th second Spring displacement – frequency domain
black…measurement
red…...simulation

VI Results
Results: 10. Iteration – relative damage values (signal based)
Relative damage comparison
simulation to measurement
1,02
1,03
0,99
0,970,97
0,90
0,95
1,00
1,05
1,10
Damper force Bolt force lateral Bolt force
longitudinal
Tie rod force Spring deflection
relativedamagevalue

General Workflow
Load data analysis
Fatigue testing
Fatigue analysis

Fatigue analysis
Internal forces of
MOTION SOLVE
using VI:
Rough road
Specimen
material data
FE structure & FE stresses
for each load case
Multi axial fatigue assessment
RESULT:
Damage Values

Fatigue analysis
S/N1 modified
by FEMFAT
Load Cycles
StressAmplitude
S/N material
from specimen tests
 Stress Tensors
 Material Properties
 Stress Gradient
 Mean Stress Influence
 MultiAXial Load
 Technological Influences
 Size Influence
 Temperature Influence
 PLASTic Deformations
 SPOT Joints s
 Anisotropical Behaviour
of Arc WELDs
 etc.

Fatigue analysis
 Stress Tensors
 Stress Gradient
 Mean Stress Influence
 MultiAXial Load
 Temperature Influence
 PLASTic Deformations
 etc.
Influences in FEMFAT
Finally : Component S/N curve
including all influences
FOR EACH NODE
Stress
Amplitude
Load cycles
Mean Stress
Stress
Amplitude
UTSUCS
Specimen Material Data
Mean Stress
Stress
Amplitude
UTSUCS Load cycles

Fatigue analysis
 Transformation of all stress tensors
into several planes (2D,3D)
 Filtering of interesting planes
 Generation of the load histories
of the stress components
 Rainflow counting in all selected planes
 Damage analysis
(Influence Parameter Method)
 The cutting plane with maximum damage is
assumed to be the critical plane for fatigue failure
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yzzyyyyxxy
xzzxyyxxxx
nnne
nnne
nnne
sss
sss
ssss
++×+
++×+
++×=

sa n
sm n
 a
 m


Result comparison
Crack predicted
after 60 h
Crack observed
after 97 h
Crack predicted
after 28 h
Test bench FEMFAT with WFT FEMFAT with Virtual Iteration

The future is ours to make.

Improving of Assessment Quality of Fatigue Analysis Using: MS, FEMFAT and FEMFAT LAB Virtual Iteration

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