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Understanding and Coping with

Material Modeling Limitations in FEA

Hubert Lobo

DatapointLabs, NY

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DatapointLabs

Researc q ality aterial testi

ISO 17025 r cti envir nment

Results in 5 ays (48 urRUS service)

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omainexpertise in material calibration

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expert material testing

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= Materials testing +CAE material parameter onversion

metal, plastic, foam, rubber, composites

over 20 CAE software codes

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data conversionmaterials +

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Modeling Limitations

Understandingmaterial model requirements

Gapsbet eenmaterial dataandmodel

Obtainingpertinent properties

Difficulties inparameter conversion (fitting)

Preparationof input files

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Unclearmodel requirements

Modeling terminology not

compatible it testing terminology

Conf sion ca ses inter retation errorCommonmistakes

Engineering/tr e/plastic stress-strain

Engineering instea of tr e yiel stress

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Gaps between model and data

Non-linear elasti it

Elasti limit well below

lassi al ield point

ignifi ant plasti

strains prior to ield

Post-yield with ne king

behavior

3

3

. . . . .

Engineering train %)

Engineering

tress

Pa)

data

Plasti Point

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Handling complex phenomena

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Strain mm/mm

Stress

Pa

UT 1-39.62-1

UT 1-39.62-2

yield point

necking starts

neck propagation

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Getting pertinent properties

Importanceofmeasuring t e right property

rtifact freedata

Properly esigne experi ents

eg.not sing crosshea isplace ent

to calc late strain

Traceabledata (ISO 17025)

NIST tracea le instr ents

Certifie traine technicians

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Getting theright samples

Spatial variation

Properties ary ith location

For ing, stretching, ol ing

Environmental variation

Ageing andconditioning

ProcessvariationDegradation fromprocessing

Recycledmaterials

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Model Fitting

Complexnon-

linear regression

Importanceof

good fits

Evaluating quality

of fitteddata

Vis al meas res

Q antitati e

meas res

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ComplexModeling

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Model limitation

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Validation

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Comparison to experiment

0

10

20

30

40

50

60

0 0.05 0.1 0.15 0.2 0.25 0.3

Str i (mm/mm)

Str

ss(

)

LS- Y Sim l ti

T sil x rim t

T 24 l

limitation

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Input file creation

Time-consumingexotic formats

Errorpronedataentry

eed todefine theundefinable Some terms not nown

Some terms ass med

Impact on simulation = unknown

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Solutions

Try tounderstand themodel completely

Measure the correct data ithprecision

andminimumnoiseMeasure the right material

Select thebest model for thedata

Ensure thebest fit ofmodel todata

Validateagainst asimpleexperiment

Createerror-free input file

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Improvements

Simple improvements an add power

Validated models represent baseline

Models an be tuned for multi-a ial loadings

Measure Calibrate Validate Tune