Non-parametric identification of the non-homogeneous stress in high strain-rate uni-axial experiments

Aloui, Souheila; Othman, Ramzi; Poitou, Arnaud; Guégan, Pierrick; El-Borgi, Sami

doi:10.1016/j.mechrescom.2008.04.005

Cited by 28 publications

(32 citation statements)

References 10 publications

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“…The resulting equations only involve end forces (or moments) and acceleration and can be used to produce stress-strain curves without the need to formulate a model a priori. This can be referred to as a non-parametric approach as quoted from [40,41]. But let us now imagine that neither F 1 nor F 2 is measured.…”

Section: Extension To More General Cases: the Virtual Fields Methods (mentioning

confidence: 99%

Beyond Hopkinson's bar

Pierron

Zhu

Siviour

2014

Phil. Trans. R. Soc. A.

122

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In order to perform experimental identification of high strain rate material models, engineers have only a very limited toolbox based on test procedures developed decades ago. The best example is the so-called split Hopkinson pressure bar based on the bar concept introduced 100 years ago by Bertram Hopkinson to measure blast pulses. The recent advent of full-field deformation measurements using imaging techniques has allowed novel approaches to be developed and exciting new testing procedures to be imagined for the first time. One can use this full-field information in conjunction with efficient numerical inverse identification tools such as the virtual fields method (VFM) to identify material parameters at high rates. The underpinning novelty is to exploit the inertial effects developed in high strain rate loading. This paper presents results from a new inertial impact test to obtain stress–strain curves at high strain rates (here, up to 3000 s −1 ). A quasi-isotropic composite specimen is equipped with a grid and images are recorded with the new HPV-X camera from Shimadzu at 5 Mfps and the SIMX16 camera from Specialised Imaging at 1 Mfps. Deformation, strain and acceleration fields are then input into the VFM to identify the stiffness parameters with unprecedented quality.

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Section: Extension To More General Cases: the Virtual Fields Methods (mentioning

confidence: 99%

Beyond Hopkinson's bar

Pierron

Zhu

Siviour

2014

Phil. Trans. R. Soc. A.

122

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“…To identify the constitutive parameters, a non-parametric approach was proposed by Othman et al [39,40] consisting in calculating the average stress in any transverse slice of a rectangular specimen loaded uniaxially in a Kolsky bar from a measured force at the boundary, the full-field acceleration maps and the cross-sectional area of the specimen. The stress-strain curve can then be obtained using the full-field strain maps.…”

Section: The Virtual Fields Methodsmentioning

confidence: 99%

Exploration of Saint-Venant’s Principle in Inertial High Strain Rate Testing of Materials

Zhu

Pierron

2015

Exp Mech

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Current high strain rate testing procedures of materials are limited by poor instrumentation which leads to the requirement for stringent assumptions to enable data processing and constitutive model identification. This is the case for instance for the well known Split Hopkinson Pressure Bar (SHPB) apparatus which relies on strain gauge measurements away from the deforming sample. This paper is a step forward in the exploration of novel tests based on time and space resolved kinematic measurements obtained through ultra-high speed imaging. The underpinning idea is to use acceleration fields obtained from temporal differentiation of the full-field deformation maps measured through techniques like Digital Image Correlation (DIC) or the grid method. This information is then used for inverse identification with the Virtual fields Method. The feasibility of this new methodology has been verified in the recent past on a few examples. The present paper is a new contribution towards the advancement of this idea. Here, inertial impact tests are considered. They consist of firing a small steel ball impactor at rectangular free standing quasi-isotropic composite specimens. One of the main contributions of the work is to investigate the issue of through-thickness heterogeneity of the kinematic fields through both numerical simulations (3D finite element model) and actual tests. The results show that the parasitic effects arising from non-uniform through-the-thickness loading can successfully be mitigated by the use of longer specimens, making use of Saint-Venant's principle in dynamics.

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“…Recently, Aloui et al (2008) and Othman et al (2010) proposed a non-parametric method which assumes a uni-axial stress state in the specimen. Moreover, the method necessitates the knowledge of one force at one boundary of the specimen and the whole twodimensional displacement field.…”

Section: Introductionmentioning

confidence: 99%

Semi-analytic inverse method for rubber testing at high strain rates

Aloui

Othman

Verron

et al. 2013

Mechanics Research Communications

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Keywords:High strain rate Soft material Stress heterogeneity Elastomer Hopkinson bar Because of their low mechanical wave speed, high strain rate testing of rubber is highly difficult. Indeed, stress and strain homogeneity is hard to achieve. In this paper, a semi-analytic inverse solution is proposed. This solution is based on a uni-axial stress state assumption in the specimen. Moreover, a new-Hookean law is assumed for rubber. The new method is successfully applied to a high strain rate test on a synthetic rubber.

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Non-parametric identification of the non-homogeneous stress in high strain-rate uni-axial experiments

Cited by 28 publications

References 10 publications

Beyond Hopkinson's bar

Beyond Hopkinson's bar

Exploration of Saint-Venant’s Principle in Inertial High Strain Rate Testing of Materials

Semi-analytic inverse method for rubber testing at high strain rates

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