Noise Factors in High Speed Tensile Testing Final - NAFEMS · Noise Factors in High Speed Tensile Testing Paul Wood, University of Warwick Trevor Dutton, ... Test machine - Load frame

SIXTH FRAMEWORK PROGRAMME PRIORITY [6.2] [SUSTAINABLE SURFACE TRANSPORT]012497 DEVELOPMENT OF BEST PRACTICES AND IDENTIFICATION OF BREAKTHROUGHTECHNOLOGIES IN AUTOMOTIVE ENGINEERING SIMULATION - AUTOSIM

Summary

Noise Factors in High Speed Tensile Testing

Paul Wood, University of WarwickTrevor Dutton, Dutton Simulation Ltd

[email protected]

Issues relating to tensile testing of materials with strain rate sensitivity, with comment on specimen setup, instrumentation, data extraction and preparation of data for use in CAE models.The work presented here is intended purely as a summary of the Materials Characterisation topic of the PARD programme, running for the previous three years; more details can be found in related publications from the same authors – please see the final slide for references.


Project Aim

Develop processes to generate and validate strain rate dependent material data for use in crash simulation

Technical Deliverables

•• collaborative partnership• develop test procedures “code of practice”• data processing techniques• validation

Understanding of the factors affecting the quality and cost of data generation


Business need for strain rate dependent material data: uncertainty and high cost in strain rate material tensile datareduce time and risk in product developmentlightweight, innovative car body designslever more value from virtual testing

Background

Same material tested at 10 labs around the world at a relatively low strain rate (10/s) as part of Round Robin study c.2006


Material Input for Virtual Crash Testing - Objective

$ $ ==================== $ MAT (Material) cards $ ==================== $ *MAT_PIECEWISE_LINEAR_PLASTICITY $ Steel Type ? Grade ? Batch ? Date ? $ MID Density E Poisson'sR YielStr 1 7.85E-9 210000.0 0.3 245 $SR Param C P LC (Load curve or table ID) 0.0 0.0 600 0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 $ *DEFINE_CURVE $ $ Usage: $ 600 0 1.0 1.0 0.0 0 245 0.00024890600 249.02161 0.0012489060 263.05911 0.10724890 565.39117 0.10824890 566.07971 0.35824889 802.9360

Family of strain rate dependent flow curves

Typical material card format in commercial simulation software (LS-DYNA)


Processes to Generate and Validate Strain Rate Dependent Material Data


High Speed Test FacilityKnock-out wedge

Strain gauge mounted on specimen gauge length to measure plastic strain

Strain gauge mounted on specimen tab to measure load in specimen

Piezo load washer(also LVDT to measure actuator stroke in real time and uniaxial accelerometer mounted on Fast Jaw grip)

Specimen

Fast Jaw Grip

Fixed or static grip head


Operation of Fast Jaw Clamp System

GRIP accelerated to target velocity:Then released to grab specimenin ~5 microsecsafter knockout wedge in jaw hits spacer rod

FAST JAW GRIP start position Plastic extension

of specimen gauge length follows

Positions of strain

gauge sensors

on specimen

Fixed end


High Speed Movie of Test


High Speed Movie of Test at 15 m/s – approx 600 strain/s


Calibration of High Speed Tensile Specimen

y = 0.00053272xR2 = 0.99946476

y = 0.00052737xR2 = 0.99956864

0

1

2

3

4

5

6

7

0 2000 4000 6000 8000 10000 12000 14000

Force (static load cell) [N]

Stra

inG

auge

Sig

nal,

Gai

n 10

00 [v

]

60 mm GL25 mm GLLinear (60 mm GL)Linear (25 mm GL)

Specimen Calibrated under

Quasi-static load

Moving grip end

Strain gauge on gauge length (quarter bridge)

Strain gauges on static grip length (full bridge)

Static Force Applied to SpecimenV

olta

ge O

utpu

t Fro

m S

train

Gau

ge C

ircui

ts


Specimen Design - Force Measurement


Output from Strain Gauge Sensor on Gauge Length

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

0.037 0.0375 0.038 0.0385 0.039 0.0395 0.04 0.0405 0.041

Time [s]

Stra

in [%

]

0

10

20

30

40

50

60

70

80

90

100

Stra

in R

ate

[1/s

]


Modelling Experiment

Purpose:

Improved understanding of test machine capability

Identify large error sources•Machine system•System of measurement•Interpretation of raw data

Introduce countermeasures •Robust specimen designs•Improved testing control


Modelling Specimen, Sensors and Boundary Conditions

Static Grip Head:Rigid element one degrees of freedom X

Def

orm

ed L

engt

h (~

210

mm

)Fast Jaw Grip:Rigid element only one degree of freedom X accelerated to constant velocity of 15m/s in 5μsecs

Target marker positions identify nodes to record data

(~ strain, strain rate, displacements, velocity and stress)

x

Strain gauge force sensor elements mounted on specimen

Machine mounted force sensor spring element

(Piezo load washer)


PHYSICAL RELATED LABEL LEVEL OF IMPORTANCE

LEVEL OF MODEL COMPLEXITY

INVESTIGATE FACTOR

RANGE SETTING FOR RANDOM INPUT (+/-) CENTRED ON MEAN

Test machine - Displacement rate of moving grip VELOCITY low low fixed - velocity

Test machine - Slippage between specimen tab and grips GRIP_SLIP low high fixed - friction

Test machine - Load frame stiffness FRAME_STIF low high fixed

Loadcell - Precis ion LOCEL_PRECISE low medium fixed - FSDLoadcell - Offaxis loading LOCEL_OFFAXIS low high fixed - compensated

Geometry - Gauge length width GEO_GLWIDTH high medium 0.1Geometry - Gauge length thickness GEO_GLTHICK high low 0.04

Material - Yield stress (0.2% proof offset) MAT_YIELD high low 5 Mpa

Material - Young's modulus MAT_MOD medium low 4200

Test machine - Load train alignment between fixed and moving grips out-of-plane

BOU

NDAR

Y CO

NDI

TIO

NS

Specimen alignment - Offcentre line to load train in-plane

Specimen alignment - Rotated to load train in-plane

Instrumentation - Digital data acquis ition system

MEA

SURI

NG S

YSTE

M

Material - True stress v. strain (ordinate scaling coefficient for multi-point data)PR

OPE

RTIE

S

Strain measure - Extensometer clip gauge alignment to specimen centre lineStrain measure - Extensometer clip gauge position on gauge lengthStrain measure - Strain gauge alignment to specimen centre lineStrain measure - Strain gauge position on gauge length

medium

high

low

low

high high

high high

high

high

low

medium

low

3 deg

fixed - centred

medium

2 deg

fixed - coplanar

fixed - coplanar

0.01

5 deg

fixed - centred

low low

medium

low

fixed - quasi-static

SPEC_OFFCENT

SPEC_ROTAT

LOAD_IPLAN

1 mm

Test machine - Load train alignment between fixed and moving grips in-plane

LOAD_OPLAN

CLIPGAGE_ANG

CLIPGAGE_POS

high mediumMAT_SCALE_COEF

STRAGAGE_ANG

STRAGAGE_POS

INSTR_DAQ


Specimen Boundary Conditions (relationship to m/c interfaces)


-0.40

-0.20

-

0.20

0.40

0.60

0.80

1.00SP

EC_O

FFC

ENT

SPEC

_RO

TAT

CLI

PGA

GE_

AN

G

STR

AG

AG

E_A

NG

GEO

_WID

TH

GEO

_GLT

HIC

K

MA

T_YI

ELD

MA

T_SC

ALE

_CO

EFF

MA

T_M

OD

MA

T_YI

ELD

_X_S

CA

LE_C

OEF

F

Noise Factors (IPs)

Cor

rela

tion

Coe

ffici

ent (

R)

Sensitivity of Force at Yield to Noise Factors


Correlation between Noise Factors / Control Factors


Raw Engineering Stress Strain Data

0

900

0 5 10 15 20 25 30

Strain [%]

Stre

ss [M

Pa]

<0.001/s1.2/s closed loop (a)1.2/s closed loop (b)6.4/s closed loop (a)6.4/s closed loop (b)65/s open loop (a) 65/s open loop (b)168/s open loop

RAW TRUE DATA

0

1000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

True Plastic Strain

True

Stre

ss (

Mpa

)

0.001 /s1.2 /s1.2 /s6.4 /s6.4 /s65 /s65 /s168 /s420 /s

Generate High Speed Tensile DataDesign range of interest for crash structures is 0.001/s to 500/s (average ~ 60/s)

Data Pre-ProcessingTransform to true plastic data

Fit Material ModelCreate a set or family of strain rate curves

Format Material ModelFor input to crash simulation design software

Data Generation and Processing

DP600 strain rate flow curves with IARC fitted surface

00.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

True Plastic Strain

True

Stre

ss (M

Pa)


Low and High Speed Crush

Low and High Speed Bend

Material Validation Process for Automotive Crash Applications


Manufacture of Spot welded Box Specimens

Initiator design

Direction of roll

Initiator design

Direction of roll


Crushing on Sled Rig


Top Hat Quasi-static and Sled Impact Crush Results

Quasi-static


Numerical Investigations – Modelling Variability


Numerical Investigations – Noise Factors


Model Output - Top Hat Force versus Displacement from Stochastic and Nominal Models


Model Output - Performance Dependency


Conclusions

• A new method for high speed tensile testing has been developed at IARC, Warwick University– Test equipment commissioned– Instrumentation techniques developed– Control of significant noise factors

• Data recording and post-processing techniques have been developed to allow strain rate testing and material modelling for strain rates up to 600/s

• Validation using component tests and models has been carried out

• Further work on other materials is continuing; a current project is also addressing connections


ReferencesA number of previous publications have addressed the topics presented here in greater depth – the reader is referred to

the following:

1. P.K.C. Wood C.A. Schley, S Kenny, T. Dutton ‘Validating Material Information for Stochastic crash Simulation’, Proceedings of 5th European LS-DYNA Users’ Conference, Birmingham, 2005 – Link to Paper

2. Paul K.C. Wood, C. A. Schley, S. Kenny, I. McGregor, R. Bardenheier, T. Dutton, N. Heath. ‘Crash Performance of Materials’. Proceedings of 6th Int. Conf. on Materials for Lean Weight Vehicles. University of Warwick, 2005

3. P.K.C. Wood, C. A. Schley, S. Kenny, T. Dutton, M. Bloomfield, R. Bardenheier, J. R. D. Smith. ‘Validating performance of automotive materials at high strain rate for improved crash design’, Proceedings of 9th Int. LS-DYNA Users’ Conference. Detroit, 2006 – Link to Paper

4. Wood P.K., Schley C.A., Dutton T., McGregor I., Bardenheier. ‘Characterising performance of automotive materials at high strain rate for improved crash design’, Pub. Journal De Physique (1V), Proceedings DYMAT 8th, Int. Conf. Dijon, France, 2006

5. P. K. C. Wood, C. A. Schley, M. Buckley, J. Smith. ‘An improved test procedure for measurement of dynamic tensile mechanical properties of automotive sheet steels’, SAE World Congress Paper 2007-01-0987, Michigan, USA, April 2007

6. P. K. C. Wood, C. A. Schley, M. Buckley, B. Walker, T. Dutton. ‘Validating dynamic tensile mechanical properties of sheet steels for automotive crash applications’. Proceedings of 6th European LS DYNA Users’Conference, Gothenburg, Sweden, May 2007 – Link to Paper

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Noise Factors in High Speed Tensile Testing Final - NAFEMS · Noise Factors in High Speed Tensile Testing Paul Wood, University of Warwick Trevor Dutton, ... Test machine - Load frame