Abstract

Slow, intermediate and high strain rate experiments with UT geometries are performed on aluminum AA7075-T6 sheet metal at various temperatures. The comprehensive experimental program characterizes the plasticity response at temperatures ranging from 20°C to 360°C and at strain rates ranging from 0.001/s to 150/s. The elevated temperature - elevated strain rate experiments are performed on a hydraulic tensile testing machine and a Split Hopkinson Pressure Bar system with a Load Inversion Device along with a custom-made induction heating system. A machine learning based modified Johnson-Cook plasticity model is calibrated to capture the complex strain rate and temperature effect of the observed hardening response.

Highlights

  • There is a constant quest to better understand and model the effect of strain rate and temperature driven by industrial problems including metal forming, machining, accidental loading or high-speed impact, amongst others

  • Experiments at high loading speeds are conducted on a Split Hopkinson Pressure Bar (SHPB) system with a Load Inversion Device (LID) for tensile testing

  • The deformation resistance is decomposed into a reference mixed Swift-Voce strain hardening, as well as a neural network term describing the effect of strain rate and temperature

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Summary

Introduction

There is a constant quest to better understand and model the effect of strain rate and temperature driven by industrial problems including metal forming, machining, accidental loading or high-speed impact, amongst others. Aluminium alloy AA 7xxx series has seen particular interest for impact protection systems [1] These alloys often feature minimum strain rate effect at room temperature [2] but high strain rate dependency at elevated temperatures [3]. To characterize these complex effects, many phenomenological models have been developed, most notably the Johnson-Cook (JC) model [4]. The performance of the NN model is compared to that of a classic JC model to highlight the flexibility and accuracy of the NN modelling

Material and specimens
Setup for low strain rates
Setup for intermediate strain rates
Setup for high strain rates
Constitutive modelling
Johnson-Cook type hardening law
Neural network based hardening law
Experimental Results
Modeling results
Conclusion

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