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Joris Degrieck - One of the best experts on this subject based on the ideXlab platform.
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numerical study of the influence of the specimen geometry on split Hopkinson bar tensile test results
Latin American Journal of Solids and Structures, 2009Co-Authors: Patricia Verleysen, Benedict Verhegghe, Tom Verstraete, Joris DegrieckAbstract:FINITE ELEMENT SIMULATIONS OF HIGH STRAIN RATE TENSILE EXPERIMENTS ON SHEET MATERIALS USING DIFFERENT SPECIMEN GEOMETRIES ARE PRESENTED. THE SIMULATIONS COMPLEMENT AN EXPERIMENTAL STUDY, USING A SPLIT Hopkinson TENSILE BAR SET-UP, COUPLED WITH A FULL-FIELD DEFORMATION MEASUREMENT DEVICE. THE SIMULATIONS GIVE DETAILED INFORMATION ON THE STRESS STATE. DUE TO THE SMALL SIZE OF THE SPECIMENS AND THE WAY THEY ARE CONNECTED TO THE TEST DEVICE, NON-AXIAL STRESSES DEVELOP DURING LOADING. THESE STRESS COMPONENTS ARE COMMONLY NEGLECTED, BUT, AS WILL BE SHOWN, HAVE A DISTINCT INFLUENCE ON THE SPECIMEN BEHAVIOUR AND THE STRESS-STRAIN CURVE EXTRACTED FROM THE EXPERIMENT. THE VALIDITY OF THE BASIC ASSUMPTIONS OF Hopkinson EXPERIMENTS IS INVESTIGATED: THE UNIAXIALITY OF THE STRESS STATE, THE HOMOGENEITY OF THE STRAIN AND THE NEGLIGIBLENESS OF THE DEFORMATION OF THE TRANSITION ZONES. THE INFLUENCE OF DEVIATIONS FROM THESE ASSUMPTIONS ON THE MATERIAL BEHAVIOUR EXTRACTED FROM A Hopkinson EXPERIMENT IS DISCUSSED.
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Numerical study of the influence of the specimen geometry on split Hopkinson bar tensile test results
2005Co-Authors: Patricia Verleysen, Joris Degrieck, Benedict Verhegghe, B. C. De CoomanAbstract:In recent years numerous studies on the high strain rate tensile properties of sheet materials using Split Hopkinson Tensile Bar (SHTB) experiments have been reported in literature. For SHTB experiments no consensus exists on the specimen geometry to be used and its influence on the observed behaviour. However, previous studies have revealed that changes in the specimen geometry give rise to distinct differences in established mechanical behaviour. In this contribution results are presented of finite element simulations of SHTB experiments using different specimen geometries. These simulations not only confirm previously obtained experimental results, but also give complimentary and detailed information on the true distribution of the stress and the strain in the specimen, including the non-axial stresses. Attention is paid to the basic assumptions of Hopkinson experiments: the uniaxiality of the stress state and the homogeneity of the strain. It is shown that the validity of these assumption is highly geometry dependent. The influence of the deviation from these assumptions on the material behaviour extracted from a Hopkinson experiment will be discussed.
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Numerical study of the influence of the specimen geometry on split Hopkinson tensile test results
WIT transactions on engineering sciences, 2005Co-Authors: Patricia Verleysen, Joris Degrieck, Benedict Verhegghe, B. C. De CoomanAbstract:In recent years numerous studies on the high strain rate tensile properties of sheet materials using Split Hopkinson Tensile Bar (SHTB) experiments have been reported in literature. For SHTB experiments no consensus exists on the specimen geometry to be used and its influence on the observed behaviour. However, previous studies have revealed that changes in the specimen geometry give rise to distinct differences in established mechanical behaviour. In this contribution results are presented of finite element simulations of SHTB experiments using different specimen geometries. These simulations not only confirm previously obtained experimental results, but also give complimentary and detailed information on the true distribution of the stress and the strain in the specimen, including the non-axial stresses. Attention is paid to the basic assumptions of Hopkinson experiments: the uniaxiality of the stress state and the homogeneity of the strain. It is shown that the validity of these assumption is highly geometry dependent. The influence of the deviation from these assumptions on the material behaviour extracted from a Hopkinson experiment will be discussed.
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Measurement of the evolution of the axial strain distribution in Hopkinson specimens
Journal de Physique IV (Proceedings), 2003Co-Authors: Patricia Verleysen, Joris DegrieckAbstract:To investigate the dynamic properties of materials very often a split Hopkinson bar setup (or Kolsky apparatus) is used. During an experiment a specimen is subjected to a high strain rate, uni-axial compressive or tensile stress. Classical measurements provide the history of the strain, the strain rate and the stress in the specimen material during an experiment. However, at each moment, only one, mean, value for the stress, the strain and the strain rate are obtained. In this contribution a combined optical-numerical technique is presented which allows to obtain the evolution of the strain along the full length of the specimen during an experiment. Results are presented. They clearly show that the developed technique is a powerful tool to monitor the non-homogeneous deformations in a Hopkinson specimen. Attention will be paid to the influence of the specimen geometry on the strain distribution in Hopkinson specimens. Some comments will be made on classical assumptions with regard to strain homogeneity and extraction of the strain history.
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Non-homogeneous and multi-axial stress distribution in concrete specimens during split Hopkinson tensile tests
Computers & Structures, 2000Co-Authors: Patricia Verleysen, Joris DegrieckAbstract:Abstract A split Hopkinson bar set-up is often used for the dynamic testing of materials. Test execution is relatively simple, and interpretation of test results is considered to be straightforward. Classical treatment of Hopkinson bar test results is based on the assumption of a homogeneous, uniaxial stress state in the specimen. However, non-axial stress components inevitably accompany the axial stress. These stresses have a large influence on the mechanical behaviour of concrete. To investigate the dynamic tensile properties of concrete, a split Hopkinson bar set-up was built. To obtain the full understanding, numerical simulations of the behaviour of the test set-up have been performed. The results are presented in this paper.
Patricia Verleysen - One of the best experts on this subject based on the ideXlab platform.
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Challenges related to testing of composite materials at high strain rates using the split Hopkinson bar technique
EPJ Web of Conferences, 2018Co-Authors: Ahmed Elmahdy, Patricia VerleysenAbstract:The design of sample geometries and the measurement of small strains are considered the main challenges when testing composite materials at high strain rates using the split Hopkinson bar technique. The aim of this paper is to assess two types of tensile sample geometries, namely dog-bone and straight strip, in order to study the tensile behaviour of basalt fibre reinforced composites at high strain rates using the split Hopkinson bar technique. 2D Digital image correlation technique was used to study the distribution of the strain fields within the gauge section at quasi-static and dynamic strain rates. Results showed that for the current experiments and the proposed clamping techniques, both sample geometries fulfilled the requirements of a valid split Hopkinson test, and achieved uniform strain fields within the gauge section. However, classical Hopkinson analysis tends to overestimate the actual strains in the gauge section for both geometries. It is, therefore, important to use a local deformation measurement when using these 2 geometries with the proposed clamping technique.
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numerical study of the influence of the specimen geometry on split Hopkinson bar tensile test results
Latin American Journal of Solids and Structures, 2009Co-Authors: Patricia Verleysen, Benedict Verhegghe, Tom Verstraete, Joris DegrieckAbstract:FINITE ELEMENT SIMULATIONS OF HIGH STRAIN RATE TENSILE EXPERIMENTS ON SHEET MATERIALS USING DIFFERENT SPECIMEN GEOMETRIES ARE PRESENTED. THE SIMULATIONS COMPLEMENT AN EXPERIMENTAL STUDY, USING A SPLIT Hopkinson TENSILE BAR SET-UP, COUPLED WITH A FULL-FIELD DEFORMATION MEASUREMENT DEVICE. THE SIMULATIONS GIVE DETAILED INFORMATION ON THE STRESS STATE. DUE TO THE SMALL SIZE OF THE SPECIMENS AND THE WAY THEY ARE CONNECTED TO THE TEST DEVICE, NON-AXIAL STRESSES DEVELOP DURING LOADING. THESE STRESS COMPONENTS ARE COMMONLY NEGLECTED, BUT, AS WILL BE SHOWN, HAVE A DISTINCT INFLUENCE ON THE SPECIMEN BEHAVIOUR AND THE STRESS-STRAIN CURVE EXTRACTED FROM THE EXPERIMENT. THE VALIDITY OF THE BASIC ASSUMPTIONS OF Hopkinson EXPERIMENTS IS INVESTIGATED: THE UNIAXIALITY OF THE STRESS STATE, THE HOMOGENEITY OF THE STRAIN AND THE NEGLIGIBLENESS OF THE DEFORMATION OF THE TRANSITION ZONES. THE INFLUENCE OF DEVIATIONS FROM THESE ASSUMPTIONS ON THE MATERIAL BEHAVIOUR EXTRACTED FROM A Hopkinson EXPERIMENT IS DISCUSSED.
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Numerical study of the influence of the specimen geometry on split Hopkinson bar tensile test results
2005Co-Authors: Patricia Verleysen, Joris Degrieck, Benedict Verhegghe, B. C. De CoomanAbstract:In recent years numerous studies on the high strain rate tensile properties of sheet materials using Split Hopkinson Tensile Bar (SHTB) experiments have been reported in literature. For SHTB experiments no consensus exists on the specimen geometry to be used and its influence on the observed behaviour. However, previous studies have revealed that changes in the specimen geometry give rise to distinct differences in established mechanical behaviour. In this contribution results are presented of finite element simulations of SHTB experiments using different specimen geometries. These simulations not only confirm previously obtained experimental results, but also give complimentary and detailed information on the true distribution of the stress and the strain in the specimen, including the non-axial stresses. Attention is paid to the basic assumptions of Hopkinson experiments: the uniaxiality of the stress state and the homogeneity of the strain. It is shown that the validity of these assumption is highly geometry dependent. The influence of the deviation from these assumptions on the material behaviour extracted from a Hopkinson experiment will be discussed.
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Numerical study of the influence of the specimen geometry on split Hopkinson tensile test results
WIT transactions on engineering sciences, 2005Co-Authors: Patricia Verleysen, Joris Degrieck, Benedict Verhegghe, B. C. De CoomanAbstract:In recent years numerous studies on the high strain rate tensile properties of sheet materials using Split Hopkinson Tensile Bar (SHTB) experiments have been reported in literature. For SHTB experiments no consensus exists on the specimen geometry to be used and its influence on the observed behaviour. However, previous studies have revealed that changes in the specimen geometry give rise to distinct differences in established mechanical behaviour. In this contribution results are presented of finite element simulations of SHTB experiments using different specimen geometries. These simulations not only confirm previously obtained experimental results, but also give complimentary and detailed information on the true distribution of the stress and the strain in the specimen, including the non-axial stresses. Attention is paid to the basic assumptions of Hopkinson experiments: the uniaxiality of the stress state and the homogeneity of the strain. It is shown that the validity of these assumption is highly geometry dependent. The influence of the deviation from these assumptions on the material behaviour extracted from a Hopkinson experiment will be discussed.
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Measurement of the evolution of the axial strain distribution in Hopkinson specimens
Journal de Physique IV (Proceedings), 2003Co-Authors: Patricia Verleysen, Joris DegrieckAbstract:To investigate the dynamic properties of materials very often a split Hopkinson bar setup (or Kolsky apparatus) is used. During an experiment a specimen is subjected to a high strain rate, uni-axial compressive or tensile stress. Classical measurements provide the history of the strain, the strain rate and the stress in the specimen material during an experiment. However, at each moment, only one, mean, value for the stress, the strain and the strain rate are obtained. In this contribution a combined optical-numerical technique is presented which allows to obtain the evolution of the strain along the full length of the specimen during an experiment. Results are presented. They clearly show that the developed technique is a powerful tool to monitor the non-homogeneous deformations in a Hopkinson specimen. Attention will be paid to the influence of the specimen geometry on the strain distribution in Hopkinson specimens. Some comments will be made on classical assumptions with regard to strain homogeneity and extraction of the strain history.
Han Zhao - One of the best experts on this subject based on the ideXlab platform.
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A versatile split Hopkinson pressure bar using electromagnetic loading
International Journal of Impact Engineering, 2018Co-Authors: Beibei Wu, Yulong Li, Han ZhaoAbstract:Abstract This paper presents a novel electromagnetic split Hopkinson pressure bar (ESHPB), which employs the electromagnetic energy conversion technique of LC circuit to generate directly the incident stress pulse. Such a versatile technique can generate easily compressive as well as tensile incident pulses. The duration and amplitude of the incident pulse could be controlled by adjusting the capacitance and charging voltage in the LC circuit. Therefore, compressive or tensile high strain-rate tests can easily be performed using the present apparatus by simply choosing the compression bars or tension bars. The primitive shape of generated stress pulse is a half-sine function, which is well suited for testing brittle materials and soft rubber-like materials in order to reach a rather constant strain rate. Meanwhile, for the tests of metals, a pulse shaper can be used to reach a rather classical trapezoidal pulse similar to that of the classical pressure bar tests. Furthermore, it is also possible to modify the stress pulse by shaping the discharge current using a specially designed active coil array and a sequential switch. Finally, a number of different materials were tested in compression and tension using this electromagnetic split Hopkinson bar system. The same materials were also tested using the traditional split Hopkinson bars. It turns out that the results obtained by the present device are consistent with those by the traditional split Hopkinson bars. Compared with traditional pulse generation techniques by the impact of a projectile or by a sudden release of a pre-stressed section, the proposed electromagnetic energy conversion technique can be accurately triggered within several microseconds. It is, therefore, a good candidate to supply the symmetrical and synchronous loads in bidirectional or biaxial split Hopkinson bar systems in the future.
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Impact behaviour of hollow sphere agglomerates with density gradient
2009Co-Authors: Huabin Zeng, Han Zhao, Stephane Pattofatto, Yannick Girard, Valia FascioAbstract:This paper presents a study on the influence of the density gradient profile on the mechanical response of graded polymeric hollow sphere agglomerates under impact loading. Quasi-static, standard split Hopkinson pressure bar (SHPB) tests as well as higher speed direct impact Hopkinson bar tests and Taylor tests are performed on such hollow sphere agglomerates with various density gradient profiles. It is found that the density gradient profile has a rather limited effect on the energy absorption capacity from those tests. It is because the testing velocity performed (
C R Siviour - One of the best experts on this subject based on the ideXlab platform.
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beyond Hopkinson s bar
Philosophical Transactions of the Royal Society A, 2014Co-Authors: Fabrice Pierron, Haibin Zhu, C R SiviourAbstract: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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A measurement of wave propagation in the split Hopkinson pressure bar
Measurement Science and Technology, 2009Co-Authors: C R SiviourAbstract:This paper presents results from optical and analytical measurements of stress wave propagation in a rod of PMMA. The rod is loaded between the incident and transmitter bars of a split Hopkinson pressure bar. Displacements in the rod are measured using high speed photography with digital image correlation. Independent calculations of strain and displacement in the rod are made from the waves measured at the Hopkinson bar gauge stations, from which all required material parameters (apart from density) can be calculated by applying standard wave propagation theory. The paper finishes with a discussion of how these measurements will be developed in the future.
J. G. Williams - One of the best experts on this subject based on the ideXlab platform.
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Stress wave propagation effects in split Hopkinson pressure bar tests
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 1995Co-Authors: N. N. Dioh, Alojz Ivankovic, P. S. Leevers, J. G. WilliamsAbstract:Studies of the properties of materials at high strain rates by the split Hopkinson pressure bar suggest that most materials show a sharp increase in strain rate sensitivity at high rates. In this paper, analytical and numerical evidence is presented which shows that his apparent increase in the strain rate sensitivity reported in the literature may result from stress wave propagation effects present in the test. A one-dimensional analytical solution has been developed for a rate independent bi-linear material tested in a split Hopkinson pressure bar apparatus. The solution, which is based on a stress wave reverberation model, shows that there is an apparent increase in the strain rate sensitivity of the material which can only be explained in terms of large propagating plastic wave fronts in the specimen. Numerical modelling of the same test geometry for the same input material model is in excellent agreement showing conclusively that stress wave propagation effects are inevitable at high impact velocities. The assumption of uniform stress and strain distribution within a split Hopkinson pressure bar specimen is therefore incorrect at high impact velocities. The formulation of the novel numerical code used in the present work, which is based on the finite volume technique, is also presented.
