The variability of Material Property Measurements · The variability of Material Property Measurements The importance of proper yield stress-strain curves ... Source: ASM Atlas of

21. Mai 2004 (c) 2004 CPM GmbH,Herzogenrath,Germany

ICFG Workshop Simulation, Schanghai 2004

The variability ofMaterial Property Measurements

The importance of proper yield stress-strain curvesfor simulation results

G. H. Arfmann, M. TwicklerCPM GmbH, Herzogenrath



The variability of Material Property Measurements

• Simulation applications- Geometry, Material flow- Stresses, Tool failure- Grain distribution

• Material data requirements to do a proper simulation- Complete set of data- Method of measurement- accurate measurement

• Methods to measure yield stress – strain curves• Problems of standardization

- Curves from different origin and the Influence on results• Conclusions




• Diagnostic offailures duringprocess design

Failure of a punchWrong preformdesign















Failure of a punchWrong progressiondesign







































• Hammer forging

Analysis of theTemperaturedistribution after 18blows




• Hammer forging

Analysis of theTemperaturedistribution after 18blows




• Prediction of grainsize distributionduring forging

Correct modeling of allboundary conditions:- Temperature- Machine- Material- ……..


































To get a good simulation result we need

a good understanding of the process and the relevant models to be usedin simulation

the best available data to describe the physical behavior of the material

etc ..

The most important data are YS-Strain curves.




Stress Strain Curve datahas to be

- complete, covering the range of temperature,strain rate, strain etc. of the application- reliable, not depending where it is comingfrom- precise- ……




Stress Strain Curve

QualitySourceDocumentation




Stress Strain CurveQualitySource (Type of Test)Documentation

Tension testCompression TestTorque Test




Stress Strain CurveQualitySource (different locations)Documentation

Compression Testnon reliable data form different

sourcesBased on a study of NPL, UK




Stress Strain CurveQualitySourceDocumentation

Influence on geometry





Influence on localdeformation





Influence on materialflow





Different sources

Source: BFI/VDEh





Different sources

Source: DGM





Different sources

Source: Umformtechnik, Lange





Different sources

Source: VDI





Different sources

Source: ASM Atlas of Stress-Strain Curves





Different sources

Source: Hensel/Spittel





Different sources have different approaches todo the testing, procession anddocumentation.

Results from different sources are different.





MaterialHistoryTest parameter

Data




Stress Strain CurveQualitySourceDocumentation (of Data)

YS – Strain curveCold





YS – Strain curveWarm





YS – Strain curve

Decomposition todescribe the curve by amath. Regressionanalysis





Most of the sources use mathematical modelsto describe the YS-Strain curves.

This is a manipulation which might end upnegative on the quality.





YS – Strain curveFailure caused by

mathematical description




Stress Strain CurveQualitySourceDocumentation of Data

Material data should be made available in it'smeasured quality (corrected because of failurescaused by the measurement method only)!




Stress Strain CurveQuality of dataSourceDocumentation

Material data should be investigated alongscientifically agreed best practice standards !These still have to be developed.




Stress – Strain CurveQualitySourceDocumentation

Example of a good approach

Tooling inside a furnaceDrawing courtesy of CPM Materialdatenzentrum






Servo-hydraulic press

Photo courtesy of Servotest






Filtering of dataDrawing courtesy of CPM Materialdatenzentrum






Storing the data




Stress Strain Curve Results

Quality Standards of best practice must bedeveloped!

Source Sources today use varying methodswith different quality

Documentation Beside other important things thedata should be provided in themeasured form without anymathematical regressions done.Such regressions etc should be done inthe application at the responsibility ofthe user




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Documents

The variability of Material Property Measurements · The variability of Material Property Measurements The importance of proper yield stress-strain curves ... Source: ASM Atlas of