Dagmar Links BEHR GmbH & Co, Stuttgart, Germany … of parts and components starting in concept...
Transcript of Dagmar Links BEHR GmbH & Co, Stuttgart, Germany … of parts and components starting in concept...
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Lack of material data for FEA from an automotive suppliers point of view
Dagmar Links
BEHR GmbH & Co, Stuttgart, Germany
Summary:Questions of material data (aluminum, plastics) for thin walled cooling and climarisation parts
Industry Sector RTD Thematic Area DateLand Transport Education and Dissemination 14.06.02
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Introduction of BEHR GmbH & Co
Use of FEA in the company
Overwiev: parts simulated with FEA
Material data aluminum
Material data plastics
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BEHR GmbHOne of the leading original equipment manufacturers
Subsidiaries andaffiliated companies
Licensees
India
Japan
Czech Republic
Egypt
South Africa
SpainUSA
Brazil
Sweden
Italy
GermanyFrance
MalaysiaThailand
South Korea
• Vehicle air conditioning
• Engine cooling
• Passenger cars, commercial vehicles
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General contractor for thermal management Integration levels from component supply to system partner
Cockpit Module
Front-end Module Complete VehicleThermal Manage-ment System
CompleteA/C System
Complete EngineCooling System
A/C Unit
Cooling Module
Components
InstallationIntegration
Physical Integration
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Concept Design Development
FEA and associated software in BEHR development cycleOptimization of parts and components starting in concept phase
FE model(Concept)
Geometry model(Design)
FE model(detailed)
Geometry model(detailed)
Dimensioning Optimization Check up Simulation
FEA
CAD
Model BuildingFeasability studies
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FEA and associated software in BEHR development cycle
PERMAS (since 1988)
• linear statics
• contact analysis
• eigenvalues
• frequency response
• time history
• optimization
• heat transfer
• non linear material
MEDINA (since 1994)
• Pre- und Postprocessing
LMS Gateway (since 1998)
• correlation with modal analysis tests
• pre test, generation of test model
• sensitivities
LMS FALANCS (since 2000)
• fatigue analysis
Interfaces
• CATIA (direct)
• VDAFS, IGES, STEP,...
• UNIVERSAL (ASCII standard for FEM data)
• NASTRAN (interface FEM/EMA)
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BEHR parts and assembliesFEA simulation with PERMAS
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FEA of BEHR parts and assembliesTechnical barriers
• Light weight and thin walled structures
• Different materials: steel, aluminum, fiber reinforced plastic
• Different parts fit together in complex fabrication processes
• Different material suppliers from all over the world
• Wide range of temperature
• Local failure of parts depends from global component behaviour
• Material data depend on fabrication process
Target is prediction of failure
Urgent need of various material data, standard data and test correlated from parts
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Aluminum
Description of parts
Questions of material data
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Aluminum: Cooling liquid coolers and charge air coolersDescription of parts
• Aluminum core(tubes and fins), header, Plastic tank
• Header is crimped corrugating along the bumps• Tank foot with bumps on the outside
Crimp Cutout
Rib
Bump Header Bead
Tank Foot
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Aluminun: Charge air coolerTypical failure in the header bead under pulsating internal pressure and temperature
Stress peakin header bead
Crackstarting
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Aluminum: Header/tube connections of coolersExamples for stress and strain peaks
Bending of tubes:Stress peak in brazed material
Plastic strain in tube under internal pressure
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AluminumSummary of material questions
• Temperature dependent material data needed
• Difference between data from material as delivered and brazed
• Youngth Modulus from cheap tension tests is not ok
• Is there a reliable correlation between material as delivered and brazed?
• Wide scatter of all data, sensitivities
• Combination of yield curve + E-Modulus from different test sources ?
• Durability behaviour under temperature
PERMAS and others
• Reliable measurements on tube material with thickness < 2 mm is not possible, we have thickness of 0.35 mm
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Material data aluminumHigh scatter of yield and failure
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Material data aluminumExamples for behaviour under temperature
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Material data aluminumExamples for difference of delivered and brazed material
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Material data aluminumDetermination of Youngth Modulus by standard tension tests is not possible
Tension Test
Strain [ % ]
Stre
ss [ M
Pa ]
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Material data aluminumDynamic determination of youngth modulus needed
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Material data aluminumValidity of theory doubtful
• Derive E-modulus and yield curve from different testfor input of non linear analysis ?
• Derive yield curve of aluminumunder higher temperature ?
• Correlation of logarithmic (true) strain and true(Cauchy)stressvalid ?
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Material data aluminumDurability behaviour under temperature
oper
atio
n pr
essu
re
pmax
pmin
time t
creep
fatigue
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Plastics
Description of parts
Questions of material data
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Plastics: Cooling module Deformation of parts under internal pressure
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Plastics: Housings of climatisation unitsDynamic analysis
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PlasticsSummary of material questions
• Environment dependent material data needed
• Difference between supplieres ideal data and parts
• Material data dependent from fabrication
• Overlapping of different dependencies ?
• Durability behaviour ?
• Wide scatter of all dataPERMAS RA
and others
• Damping effects ?
• Material data dependent from load
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Material data plasticsBehaviour under temperature and humidity
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Material data plasticsExample for behaviour under temperature and humidity
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Material data plasticsExample for difference between ideal and real life data
• Test samples taken from expansion tank
• Material supplieres data taken from ideal DIN test samples are always much better
• Safe excess charges are needed
Ideal DIN sample
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Material data plasticsMaterial data depending from load
• Correlation of FEA modal analysis and modal analysis test with hammer
• Good MAC for important global modes
• Natural frequencies differ about 30 %
• Reason: dynamic youngth modulus
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Material data plasticsExample for strain rate dependent material (example PP TV)
2) 50 mm/min
1) 5 mm/min
3) Trend(Excel)
1. E = 2500 Mpa2. E = 2900 Mpa3. E = 5300 Mpa
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Material data plasticsExample for strain rate dependent material (example PP)
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Material data plasticsMaterial data dependent from injection molding process
• Stiffness depends from flow direction
• Only 30 % of tensile strength in real life weldlines
• Correct would be molding simulation before FE simulation
Weld line at end of flow process
Weld line during flow process
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Material data plasticsWhat is durability ?
• DIN standard for fatigue tests does not exist (in Germany)
• Overlap with creep, even at ambient temperature ?• Looking at interesting number of load cycles plastic won‘t really break !• Result of alternating load will always change during test !
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Material data plasticsDamping influenced by temperature
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Material data plasticsExample for dependencies
Frequency
Friction
Damping
Amplitude
Strain rate
Stiffness
Temperatature
Humidity
Time, creep
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Stainless steel
Is the problem solved ?
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Stainless steelSummary of fatigue information from different sources
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Lack of material dataBarrier for uptake of FEA
FEA analysis in industry is service - ‚not possible‘ is impossible !
Analyses with inexact input are done !FEA results and reality may differ !Precise statement ‚Work/Does not work‘ is not possible resp. a lie !Parts sometimes are oversized or fail ! FEA is comparison only, not prediction ! Loss of confidence in FEA !
High financial efforts in gaining data needed for Input of FEAEvaluation of results
Time and people needed to Get material dataDo (long time) test correlation
FEA engineers have to be allround experts !
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Thank you!