PSI - Issue 42

Available online at www.sciencedirect.com Available online at www.sciencedirect.com Available online at www.sciencedirect.com

ScienceDirect

Procedia Structural Integrity 42 (2022) 110–117 Procedia Structural Integrity 00 (2019) 000–000 Procedia Structural Integrity 00 ( 019) 00–000

www.elsevier.com / locate / procedia www.elsevier.com / locate / procedia

© 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 23 European Conference on Fracture – ECF23 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) r-revie unde responsibility of 23 European Conference on F acture – ECF23 . Keywords: Split Hopkinson Pressure Bar; Dynamic Calibration; Optical Extensometer; Strain Measurement Abstract A new method for dynamic calibration of the bar instrumentation, i.e. the strain measurement, of a split Hopkinson pressure bar is proposed. To this end, the displacements at the bar / specimen interfaces are measured optically and compared with the calculated displacements from the measured strain signals of the bar instrumentation. The bar signals at di ff erent positions and the displacements are analyzed by experimental and theoretical approaches. It was found that the additional measurement of the striker velocity and the assumption of momentum conservation can be omitted by applying the new method. Furthermore, there is no need for the conventional two-step calibration, i.e. ‘bars apart’ and ‘bars together’. The proposed one-step dynamic calibration of the instrumentation with respect to strains and displacements can even be performed during an actual test with a specimen. The optical extensometer is not only used for dynamic calibration purposes but also for measuring the interface displacements of the specimen during a test. Consequently, the strains can be calculated from the very beginning of the test. © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of 23 European Conference on Fracture – ECF23 . Keywords: Split Hopkinson Pressure Bar; Dynamic Calibration; Optical Extensometer; Strain Measurement 23 European Conference on Fracture – ECF23 One-Step Dynamic Calibration of Strain Measurement in a Split Hopkinson Pressure Bar Sebastian Henschel a, ∗ , Lutz Kru¨ger a a TU Bergakademie Freiberg, Insititute of Materials Engineering, Gustav-Zeuner-Str. 5 , 09599 Freiberg, Germany Abstract A new method for dynamic calibration of the bar instrumentation, i.e. the strain measurement, of a split Hopkinson pressure bar is proposed. To this end, the displacements at the bar / specimen interfaces are measured optically and compared with the calculated displacements from the measured strain signals of the bar instrumentation. The bar signals at di ff erent positions and the displacements are analyzed by experimental and theoretical approaches. It was found that the additional measurement of the striker velocity and the assumption of momentum conservation can be omitted by applying the new method. Furthermore, there is no need for the conventional two-step calibration, i.e. ‘bars apart’ and ‘bars together’. The proposed one-step dynamic calibration of the instrumentation with respect to strains and displacements can even be performed during an actual test with a specimen. The optical extensometer is not only used for dynamic calibration purposes but also for measuring the interface displacements of the specimen during a test. Consequently, the strains can be calculated from the very beginning of the test. 23 European Conference on Fracture – ECF23 One-Step Dynamic Calibration of Strain easurement in a Split Hopkinson Pressure Bar Sebastian Henschel a, ∗ , Lutz Kru¨ger a a TU Bergakademie Freiberg, Insititute of Materials Engineering, Gustav-Zeuner-Str. 5 , 09599 Freiberg, Germany

1. Introduction 1. Introduction

In a typical split Hopkinson pressure bar (SHPB) setup, the bars are instrumented for strain measurement (Gray (2000)). The strain is not measured directly, but e.g. by the electric resistance change of foil strain gauges (SG) mounted on the bar’s surface. The change of this resistance is typically measured by a change of the output voltage of a Wheatstone bridge. Hence, the knowledge of the conversion factor K ε (see Eq. 1) from the output voltage U to the strain ε within the bar is an essential knowledge for further signal analysis: In a typical split Hopkinson pressure bar (SHPB) setup, the bars are instrumented for strain measurement (Gray (2000)). The strain is not measured directly, but e.g. by the electric resistance change of foil strain gauges (SG) mounted on the bar’s surface. The change of this resistance is typically measured by a change of the output voltage of a Wheatstone bridge. Hence, the knowledge of the conversion factor K ε (see Eq. 1) from the output voltage U to the strain ε within the bar is an essential knowledge for further signal analysis:

ε = K ε · U ε = K ε · U

(1) (1)

∗ Corresponding author. Tel.: + 49-3731-39-3452 ; fax: + 49-3731-39-3720. E-mail address: sebastian.henschel@iwt.tu-freiberg.de ∗ Corresponding author. Tel.: + 49-3731-39-3452 ; fax: + 49-3731-39-3720. E-mail address: sebastian.henschel@iwt.tu-freiberg.de

2452-3216 © 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 23 European Conference on Fracture – ECF23 10.1016/j.prostr.2022.12.013 2210-7843 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of 23 European Conference on Fracture – ECF23 . 2210-7843 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of 23 European Conference on Fracture – ECF23 .