no consistency in the identified values. These results suggest that the cost function is not sensitive enough to the hardening modulus. This limited sensitivity to the hardening modulus was expected based on the results of the finite element validation. Notably, for specimen 3 no values for the yield stress or hardening modulus could be identified. 29.5 Conclusions In this manuscript, the virtual fields method was used to inversely identify the elasto-plastic parameters of aluminum 6082T6, an aircraft grade aluminum, from an inertial impact test. The feasibility of this novel protocol was shown using simulated finite element data. The virtual fields method was implemented to recover the plastic parameters input in the finite element model. As a proof of concept, a short test campaign was performed impacting four samples of aluminum 6082-T6 at a speed of 50ms 1. The material parameters identified using the virtual fields method are in line with published results on the high strain rate response of aluminum [7, 8]. Although it is also possible to identify the parameters using finite element updating, it is worthwhile to remember that the virtual fields method is at least an order of magnitude less computationally expensive than finite element model updating since there is no need for a finite element computation to evaluate the cost function. In the future additional testing campaigns will be performed to more thoroughly examine the source of the camera noise in the final 85 frames, and to increase the strain rate by impacting at higher speeds. Other materials with more significant hardening will also be investigated. Acknowledgements This material is based on research sponsored by the Air Force Research Laboratory, under agreement number FA8655-13-13041. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Air Force Research Laboratory or the U.S. Government. Ms. Sarah Dreuilhe acknowledges the support of EPSRC for partial funding through a Doctoral Training Grant. Dr. Frances Davis and Prof. Fabrice Pierron acknowledge support from EPSRC through grant EP/L026910/1. Prof. Fabrice Pierron also expresses gratitude to the Wolfson Foundation for support through a Royal Society Wolfson Research Merit Award. References 1. Pierron, F., et al.: Beyond Hopkinson’s bar. Philos. Trans. R. Soc. A Math. Phys. Eng. Sci. 372(2023), 1471–2962 (2014) 2. Moulart, R., et al.: Full-field strain measurement and identification of composites moduli at high strain rate with the virtual fields method. Exp. Mech. 51(4), 509–536 (2011) 3. Pierron, F., Gre´diac, M.: The Virtual Fields Method. Springer, New York (2012) 4. Devivier, C., Pierron, F.: Grid method GUI: a tool to process grid images. http://gridmethod.tk/GMGUI_r.php. Accessed 14 Mar 2016 5. Garcia, D.: Robust smoothing of gridded data in one and higher dimensions with missing values. Comput. Stat. Data Anal. 54(4), 1167–1178 (2010) 6. Garcia, D.: A fast all-in-one method for automated post-processing of PIV data. Exp. Fluids 50(5), 1247–1259 (2011) 7. Moc´ko, W., et al.: Compressive viscoplastic response of 6082‐T6 and 7075‐T6 aluminium alloys under wide range of strain rate at room temperature: experiments and modelling. Strain 48(6), 498–509 (2012) 8. Vignjevic, R., et al.: Effects of orientation on the strength of the aluminum alloy 7010-T6 during shock loading: experiment and simulation. J. Appl. Phys. 92(8), 4342–4348 (2002) Table 29.2 Identified plastic parameters for the four specimens tested Specimen no. Yield stress, σ0 (MPa) Hardening modulus, H (MPa) 1 272 358 2 275 303 3 – – 4 266 521 29 Image-Based Inertial Impact Tests on an Aluminum Alloy 223
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