ADI DAYS - Andrew Ruggiero

Austempering, A Technology for Substitution
ADI DAYS 2016 6th – 7th October Minerbe
1
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, Italy
b TECHDYN Engineering, I-00199 Rome, Italy
cZanardi Fonderie S.p.A, I-37046 Minerbe (VR), Italy

BACKGROUND
2
• 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
3
• Designers show lack of confidence
• Dread of a presumed low ductility
under impulsive loading
• Charpy impact test results

AIM OF THE WORK
4
• 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
5
DESIGNATION
UTS
(MPa)
YIELD
STRESS
(MPa)
ELONGATION
%
HARDNE
SS
(BR)
ADI 1050 1050 700 6 320-380
ADI 1200 1200 850 3 340-420
HSiADI 1450 1040 8.9 400
42CrMo4 1200 800 11 -
[3]
References
[3] J. R. Keough, K. L. Hayrynen and G. L. Pioszak, AFS Proc. 2010, Schaumburg, IL USA

EXPERIMENTAL CHARACTERIZATION
6
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
7
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
8
Local deformation map
Remarks
• Uniform strain over the gage length up to failure. No necking
0 0.05 0.1 0.15 0.2
0
200
400
600
800
1000
1200
1400
1600
Deformazione
Sforzo(MPa)
T= 298 K
T= 213 K
T= 343 K
Stress
Strain

EXPERIMENTAL RESULTS: temperature effect
9
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 0.2
0
200
400
600
800
1000
1200
1400
1600
Deformazione
Sforzo(MPa)
T= 298 K
T= 213 K
T= 343 K
0 0.05 0.1 0.15 0.2 0.25
0
200
400
600
800
1000
1200
1400
1600
Deformazione
Sforzo(MPa)
HpkGS_2
HpkGS_7
HpkGS_11
HpkGS_15
Quasistatic test Dynamic test
T=213 K
T=298 K

10
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
11
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
104
600
700
800
900
1000
1100
1200
1300
1400
ADI 1050 (present work)
ADI1200 (Bohmer and Reissig, 2015)
Linear Fit of Sheet1 B"R02"
Yieldstress,R0.2%
[MPa]
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
FAILURESTRAIN
STRAIN RATE [1/s]

EXPERIMENTAL RESULTS: failure mode
12
HpkGS5 RT 1200s-1
HpkGS7 RT 1200s-1

STRENGTH MODEL
13
0 100 200 300 400
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Temperatura (K)
AeB(MPa)
A
Fit A
B
Fit B
AS (MPa) ma B0 (MPa) mb n C
1207 160 10805 160 0.6 0.014 1.0
            &n
A T B T 1 Cln *
  
    
  
 
  
 
S
a
0
b
T
A A 1 exp
m
T
B B exp
m
Modified Johnson-Cook

MODEL VERIFICATION
14
0 0.5 1 1.5 2 2.5
0
5000
10000
Allungamento (mm)
Forza(N)
d/dt=1E-3 s-1
, T=298 K
FEM
0 0.5 1 1.5 2 2.5
0
5000
10000
Allungamento (mm)
Forza(N)
d/dt=1E-3 s-1
, T=213 K
FEM
0 0.5 1
0
5000
10000
Allungamento (mm)
Forza(N)
d/dt=1E-3 s-1
, T=313 K
FEM
0 0.5 1 1.5
0
5000
10000
Allungamento (mm)
Forza(N)
d/dt=600 s-1
, T=213 K
FEM
0 0.5 1
0
5000
10000
Allungamento (mm)
Forza(N)
d/dt=1200 s-1
, T=213 K
FEM
0 0.5 1 1.5
0
5000
10000
Allungamento (mm)
Forza(N)
d/dt=600 s-1
, T=298 K
FEM
0 0.5 1 1.5
0
5000
10000
Allungamento (mm)
Forza(N)
d/dt=1200 s-1
, T=213 K
FEM

CONCLUSIONS
15
• 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
16
• 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 model
0 0.5 1 1.5 2
0
0.5
1
1.5
2
2.5
3
TF
DeformazionearotturaEquivalentfailurestrain
  m eqTriaxiality factor

ADI DAYS - Andrew Ruggiero

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