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Austempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

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STRAIN RATE AND TEMPERATURE EFFECTS ON THE FLOW STRESS OF ADIA. Ruggieroa, G. Iannittib, E. Veneric, F. Vettorec , N. Bonoraaa University of Cassino and SL, DICeM, Cassino, Italyb TECHDYN Engineering, I-00199 Rome, ItalycZanardi Fonderie S.p.A, I-37046 Minerbe (VR), Italy

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BACKGROUNDAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

2Cast irons are widely used in industrial practice mainly for the production of components through the process of castingADI matrix microstructure: ausferriteExcellent property combinations of strength, ductility, and toughnessValid substitute for steel for structural applications

References[1] Bhme* and Reissig, Adv. Eng. Mat. 2015, 17, No. 8[2] Keough and Hayrynen, SAE, 2000, paper no 248871

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BACKGROUNDAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

3Designers show lack of confidenceDread of a presumed low ductility under impulsive loadingCharpy impact test results

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AIM OF THE WORKAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

4To investigate the constitutive response of the ADI 1050-6 under different conditions of strain rate and temperatureTo analyze the strain rate effect on the ductilityTo develop a constitutive model for the design of components operating under both static and dynamic conditions

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MATERIALSAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

5DESIGNATIONUTS (MPa)YIELD STRESS (MPa)ELONGATION %HARDNESS(BR)ADI 105010507006320-380ADI 120012008503340-420HSiADI145010408.940042CrMo4120080011-

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

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EXPERIMENTAL CHARACTERIZATIONAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

6TESTSTRAIN RATETEMPERATUREQUASI-STATIC TENSILE0.001/s-60C, 25C e +70C

Quasi-static characterizationInstron 5586 (electromechanic)Local deformation measurements (DIC)Low temperature (liquid CO2)Induction heating

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EXPERIMENTAL CHARACTERIZATIONAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

7Characterization at high strain rateDirect Tension Split Hopkinson Pressure BarLow temperature (liquid CO2)High frame rate cameraTESTSTRAIN RATETEMPERATUREDYNAMIC TENSILE600/s-60C e 25CDYNAMIC TENSILE1200/s-60C e 25C

8000 mm3000 mm3000 mm1000 mm

AAA-A1200 mm

specimen

clamp

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EXPERIMENTAL RESULTS: local strainsAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

8Local deformation map

RemarksUniform strain over the gage length up to failure. No necking

StressStrain

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EXPERIMENTAL RESULTS: temperature effectAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

9RemarksAt low temperatures, the work hardening rate increases, whereas the apparent yield strength seems to decrease slightly Same behavior at different strain rates

Quasistatic testDynamic testT=213 KT=298 K

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Austempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

10RemarksStrain rate affects the material yield stressUnder dynamic loading, necking occurs just before failure

T=25C

StressStressEXPERIMENTAL RESULTS: strain rate effect on the flow stressT=-60C

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EXPERIMENTAL RESULTS: strain rate effects on yield stress and ductilityAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

11RemarksAbsence of the knee in the initial yield stress vs. strain rate diagramAs for the ADI 1200, the failure strain increases with the strain rate

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EXPERIMENTAL RESULTS: failure modeAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

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HpkGS5 RT 1200s-1

HpkGS7 RT 1200s-1

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STRENGTH MODELAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

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AS (MPa)ma B0 (MPa)mbnC1207160108051600.60.0141.0

Modified Johnson-Cook

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MODEL VERIFICATIONAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

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CONCLUSIONSAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

15Experimental results show an increase of up to 10% in ductility with increasing the strain ratePossible 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

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ONGOING WORKAustempering, A Technology for SubstitutionADI DAYS 2016 6th 7th October Minerbe

16To 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 ausferriteTo analyze the stress triaxiality effect on the ductility at different strain rates and temperaturesTo develop a damage model

Equivalent failure strain

Triaxiality factor

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