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RESEARCH PAPER

Exploratory Tests on a Biaxial Compression Hopkinson Bar Set-up B. Durand 1

&

P. Quillery 1 & A. Zouari 2 & H. Zhao 1,3

Received: 11 March 2019 / Accepted: 8 September 2020 # Society for Experimental Mechanics 2020

Abstract Background Multiaxial dynamic loadings occur in many industrial cases and multiaxial dynamic test development is thus a crucial issue. Objective To meet this challenge, a biaxial compression Hopkinson bar set-up is designed. Methods The set-up consists of a striker, an input bar, an internal output bar and a co-axial external output tube (surrounding the internal bar). The internal output bar measures the axial loading of the cross sample whereas the external output bar measures the transverse one via a mechanism. This mechanism uses two intermediate parts with inclined sliding surfaces. Results Gauges on the bars enable for force measurements in the set-up, and the sample displacement field is obtained by digital image correlation. Simple compression tests on cuboid samples inserted between the input bar and the internal output bar give the sample material behavior. Then, to determine the friction at the mechanism sliding surfaces, identical samples are inserted between the input bar and the external output bar, and are compressed. Conclusions Finally, the consistency of the measurements obtained during a biaxial compression test on a cross sample can be checked from the previously measured parameters and from numerical simulations. Keywords Biaxial compression dynamic test . Hopkinson bars

Introduction Multiaxial dynamic loadings usually occur in many industrial cases such as automotive impacts [1], high-speed forming [2] or high-speed machining [3]. Multiaxial dynamic test development is therefore a crucial issue. Unfortunately, most of the dynamic tests are uniaxial. For instance, the very common Hopkinson bar test (which enables for accurate measurements at high strain rates) uses the uniaxial compression loading generated by the impact of a projectile. In order to perform multiaxial tests, many set-ups have thus been designed to obtain multiaxial loadings from an initial uniaxial loading device. For example, a radial pressure can be applied to a cylindrical sample mounted on Hopkinson bars

* B. Durand [email protected] 1

Laboratoire de Mécanique et Technologie, Université Paris-Saclay, ENS Paris-Saclay, CNRS, LMT, 91190 Gif-sur-Yvette, France

2

MINES ParisTech, 75006 Paris, France

3

Sorbonne Universités, UFR 919, 4 Place Jussieu, cedex 05, F-75252 Paris, France

thanks to a confinement device. One can use a pressure vessel that enables for a controlled quasi-static pressure to be applied from a fluid [4]. Inserting the cylindrical sample inside a rigid tube can generate a dynamic radial loading even though the ratio between the radial pressure and the axial stress strongly depends on the sample material, in particular on its Poisson’s ratio [5]. Using a confinement tube made of a perfect plastic behavior material makes it possible to maintain a c