STRAIN-RATE-AND-TEMPERATURE-EFFECTS- ON-THE-FLOW … · BACKGROUND...

Austempering, A Technology for Substitution

ADI DAYS 2016 6th – 7th October Minerbe

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STRAIN RATE AND TEMPERATURE EFFECTS ON THE FLOW STRESS OF ADI

A. Ruggieroa, G. Iannittib, E. Veneric, F. Vettorec , N. Bonoraa

a University of Cassino and SL, DICeM, Cassino, Italyb TECHDYN Engineering, I-‐00199 Rome, Italy

cZanardi Fonderie S.p.A, I-‐37046 Minerbe (VR), Italy

BACKGROUND



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• Cast irons are widely used in industrial practice mainly for the production of components through the process of casting

• ADI matrix microstructure: ausferrite

• Excellent property combinations of strength, ductility, and toughness

• Valid substitute for steel for structural applications

References

[1] Böhme* and Reissig, Adv. Eng. Mat. 2015, 17, No. 8

[2] Keough and Hayrynen, SAE, 2000, paper no 248871

BACKGROUND



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• Designers show lack of confidence

• Dread of a presumed low ductility under impulsive loading

• Charpy impact test results

AIM OF THE WORK



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• To investigate the constitutive response of the ADI 1050-‐6 under different conditions of strain rate and temperature

• To analyze the strain rate effect on the ductility

• To develop a constitutive model for the design of components operating under both static and dynamic conditions

MATERIALS



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DESIGNATIONUTS (MPa)

YIELD STRESS (MPa)

ELONGATION %

HARDNESS(BR)

ADI 1050 1050 700 6 320-‐380ADI 1200 1200 850 3 340-‐420HSiADI 1450 1040 8.9 40042CrMo4 1200 800 11 -‐

[3]References

[3] J. R. Keough, K. L. Hayrynen and G. L. Pioszak, AFS Proc. 2010, Schaumburg, IL USA

EXPERIMENTAL CHARACTERIZATION



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TEST STRAIN RATE TEMPERATURE

QUASI-STATIC TENSILE 0.001/s -60°C, 25°C e +70°C

Quasi-‐static characterization • Instron 5586 (electromechanic) • Local deformation measurements (DIC) • Low temperature (liquid CO2) • Induction heating

EXPERIMENTAL CHARACTERIZATION



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Characterization at high strain rate • Direct Tension Split Hopkinson Pressure Bar • Low temperature (liquid CO2) • High frame rate camera

TEST STRAIN RATE TEMPERATURE

DYNAMIC TENSILE 600/s -60°C e 25°C

DYNAMIC TENSILE 1200/s -60°C e 25°C

8000 mm

3000 mm 3000 mm

1000 mm

A

A

A-‐A

1200 mm

specimenclamp

EXPERIMENTAL RESULTS: local strains



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Local deformation map

Remarks

• Uniform strain over the gage length up to failure. No necking

0 0.05 0.1 0.15 0.20

200

400

600

800

1000

1200

1400

1600

Deformazione

Sfor

zo (M

Pa)

T= 298 KT= 213 KT= 343 K

Stress

Strain

EXPERIMENTAL RESULTS: temperature effect



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Remarks

• At low temperatures, the work hardening rate increases, whereas the apparent yield strength seems to decrease slightly

• Same behavior at different strain rates

0 0.05 0.1 0.15 0.20

200

400

600

800

1000

1200

1400

1600

Deformazione

Sfor

zo (M

Pa)

T= 298 KT= 213 KT= 343 K

0 0.05 0.1 0.15 0.2 0.250

200

400

600

800

1000

1200

1400

1600

Deformazione

Sfor

zo (M

Pa)

HpkGS_2HpkGS_7HpkGS_11HpkGS_15

Quasistatic test Dynamic test

T=213 K

T=298 K



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Remarks

• Strain rate affects the material yield stress

• Under dynamic loading, necking occurs just before failure

T=25°C

Stress

Stress

EXPERIMENTAL RESULTS: strain rate effect on the flow stress

T=-‐60°C

EXPERIMENTAL RESULTS: strain rate effects on yield stress and ductility



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Remarks

• Absence of the knee in the initial yield stress vs. strain rate diagram

• As for the ADI 1200, the failure strain increases with the strain rate

10-4 10-3 10-2 10-1 100 101 102 103 104600

700

800

900

1000

1100

1200

1300

1400 ADI 1050 (present work) ADI1200 (Bohmer and Reissig, 2015) Linear Fit of Sheet1 B"R02"

Yie

ld s

tres

s, R

0.2%

[MP

a]

STRAIN RATE [1/s]10-4 10-3 10-2 10-1 100 101 102 103 104

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40 ADI1050 T=298K ADI1200 (Bohmer and Reissig, 2015) ADI1050 T=213K

FA

ILU

RE

STR

AIN

STRAIN RATE [1/s]

EXPERIMENTAL RESULTS: failure mode



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HpkGS5 RT 1200s-‐1

HpkGS7 RT 1200s-‐1

STRENGTH MODEL



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0 100 200 300 4000

1000

2000

3000

4000

5000

6000

7000

8000

9000

Temperatura (K)

A e

B (M

Pa)

AFit ABFit B

AS (MPa) ma B0 (MPa) mb n C

1207 160 10805 160 0.6 0.014 1.0

( ) ( )( ) ( )σ ε ε= + ⋅ + !nA T B T 1 Cln *

! "! "= − −$ %$ %

& '& '

! "= −$ %

& '

Sa

0b

TA A 1 exp

m

TB B exp

m

Modified Johnson-‐Cook

MODEL VERIFICATION



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0 0.5 1 1.5 2 2.50

5000

10000

Allungamento (mm)

Forz

a (N

)

dε/dt=1E-3 s-1, T=298 KFEM

0 0.5 1 1.5 2 2.50

5000

10000

Allungamento (mm)

Forz

a (N

)


0 0.5 10

5000

10000

Allungamento (mm)

Forz

a (N

)


0 0.5 1 1.50

5000

10000

Allungamento (mm)

Forz

a (N

)

dε/dt=600 s-1, T=213 KFEM

0 0.5 10

5000

10000

Allungamento (mm)

Forz

a (N

)

dε/dt=1200 s-1, T=213 KFEM

0 0.5 1 1.50

5000

10000

Allungamento (mm)

Forz

a (N

)

dε/dt=600 s-1, T=298 KFEM

0 0.5 1 1.50

5000

10000

Allungamento (mm)

Forz

a (N

)

dε/dt=1200 s-1, T=213 KFEM

CONCLUSIONS



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• Experimental results show an increase of up to 10% in ductility with increasing the strain rate

• Possible differences in the failure mechanism at different strain rates were observed

• Strain rate affects the initial yield stress (typical of a BCC structure)

• Absence of the knee in the initial yield stress vs strain rate diagram (typical of a FCC structure)

• Temperature affects the work hardening rate mainly (typical of a FCC structure)

• The proposed constitutive model describes with good accuracy the phenomenological behavior that the ADI 1050 shows in the ranges of strain rate and temperature analyzed

ONGOING WORK



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• To analyze further the peculiar effects of strain rate and temperature on the flow stress

✓ Micro mechanical modeling for evaluating the effects of residual stress

✓ To investigate the composite structure of the ausferrite

• To analyze the stress triaxiality effect on the ductility at different strain rates and temperatures

• To develop a damage model0 0.5 1 1.5 2

0

0.5

1

1.5

2

2.5

3

TF

Defo

rmaz

ione

a ro

ttura

Equivalent failure strain

( )σ σm eqTriaxiality factor

STRAIN-RATE-AND-TEMPERATURE-EFFECTS- ON-THE-FLOW … · BACKGROUND...

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