The Experts below are selected from a list of 9432 Experts worldwide ranked by ideXlab platform

Amos Gilat - One of the best experts on this subject based on the ideXlab platform.

  • full field strain measurement in compression and tensile split Hopkinson Bar experiments
    Experimental Mechanics, 2009
    Co-Authors: Amos Gilat, T E Schmidt, Andrew Walker
    Abstract:

    The 3D image correlation technique is used for full field measurement of strain (and strain rate) in compression and tensile split Hopkinson Bar experiments using commercial image correlation software and two digital high-speed cameras that provide a synchronized stereo view of the specimen. Using an array of 128 × 80 (compression tests) and 258 × 48 (tensile tests) pixels, the cameras record about 110,000 frames per second. A random dot pattern is applied to the surface of the specimens. The image correlation algorithm uses the dot pattern to define a field of overlapping virtual gage boxes, and the 3-D coordinates of the center of each gage box are determined at each frame. The coordinates are then used for calculating the strains throughout the surface of the specimen. The strains determined with the image correlation method are compared with those determined from analyzing the elastic waves in the Bars, and with strains measured with strain gages placed on the specimens. The system is used to study the response of OFE C10100 copper. In compression tests, the image correlation shows a nearly uniform deformation which agrees with the average strain that is determined from the waves in the Bars and the strains measured with strain gages that are placed directly on the specimen. In tensile tests, the specimen geometry and properties affect the outcome from the experiment. The full field strain measurement provides means for examining the validity and accuracy of the tests. In tests where the deforming section of the specimen is well defined and the deformation is uniform, the strains measured with the image correlation technique agree with the average strain that is determined from the split Hopkinson Bar wave records. If significant deformation is taking place outside the gage section, and when necking develops, the strains determined from the waves are not valid, but the image correlation method provides the accurate full field strain history.

  • Torsional split Hopkinson Bar tests at strain rates above 104s−1
    Experimental Mechanics, 2000
    Co-Authors: Amos Gilat, C. S. Cheng
    Abstract:

    The torsional split Hopkinson Bar is used for testing materials at strain rates above 104s−1. This strain rate, which is an order of magnitude higher than is typical with this technique, is obtained by using very short specimens. Strain rates of 6.4×104s−1 have been achieved with specimens having a gage length of 0.1524 mm. Results from tests on 1100 aluminum show an increase in rate sensitivity as the strain rate increases.

  • Elevated temperature testing with the torsional split Hopkinson Bar
    Experimental Mechanics, 1994
    Co-Authors: Amos Gilat
    Abstract:

    The torsional split-Hopkinson-Bar technique is modified for high-strain-rate testing at elevated temperatures by heating the specimen rapidly and keeping the rest of the apparatus at room temperature. Tests have been conducted with specimens made of several materials (Haynes-188, 1020 steel, and 1151 steel) at temperatures ranging from 650°C to 1060°C and strain rates on the order of 1000 s−1.

  • A direct-tension split Hopkinson Bar for high strain-rate testing
    Experimental Mechanics, 1991
    Co-Authors: George H. Staab, Amos Gilat
    Abstract:

    A direct-tension split-Hopkinson-Bar apparatus is introduced. In this apparatus the specimen is loaded by a tensile wave that is generated by the release of a stored load in a section of the input Bar. The system can be used for experiments with test durations of up to 500 μs. The effect of specimen geometry (length to diameter ratio) is investigated. Consistent results are obtained when the ratio is larger than about 1.60. Results from tests with 6061-T651 aluminum are in agreement with published data.

Patricia Verleysen - One of the best experts on this subject based on the ideXlab platform.

  • Challenges related to testing of composite materials at high strain rates using the split Hopkinson Bar technique
    EPJ Web of Conferences, 2018
    Co-Authors: Ahmed Elmahdy, Patricia Verleysen
    Abstract:

    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.

  • Calibration of dynamic piezoelectric force transducers using the Hopkinson Bar technique
    2012
    Co-Authors: Diederik Van Nuffel, Jan Peirs, Ives De Baere, Patricia Verleysen, Joris Degrieck, Wim Van Paepegem
    Abstract:

    This work describes an easy and flexible technique for calibration of dynamic piezoelectric force transducers. A Hopkinson Bar test setup is hereby used to generate the rapidly rising force loads necessary for calibration of these kinds of devices. Strain gauges are the key transducers in this test setup for measuring the load magnitude, rise time and duration. The knowledge of these variables makes successful calibration possible.

  • experimental investigation of the deformation of Hopkinson Bar specimens
    International Journal of Impact Engineering, 2004
    Co-Authors: Patricia Verleysen, Joris Degrieck
    Abstract:

    Split Hopkinson Bar (SHB) experiments are often used to study the strain rate dependent mechanical properties of materials. During a SHB experiment a small sample of the material under study is subjected to a high strain rate, uni-axial, tensile, compressive or torsion load. From the classical measurements the time history of the mean stress, strain rate and strain in the specimen can be derived. For some applications, more detailed information concerning the variation of the deformation in the specimen is necessary. In this contribution a technique is presented which makes it possible to obtain the deformation along the length of the specimen. The deformation of a line grid attached to the specimen is recorded during an experiment by means of a streak camera. An advanced and innovative numerical technique, based on a combination of geometric moire and phase shifting, is developed to extract the time history of the deformation along the axis of the specimen from the picture of the deforming grid automatically. Large specimen deformations are allowed, and the technique proved to give highly accurate results. In this contribution results are presented of a SHB experiment on a steel sheet specimen. Some remarks are formulated concerning the generally assumed homogeneity of the deformation in the specimen, and the deformation obtained with the classical measurement techniques.

  • IMPROVED SIGNAL PROCESSING FOR SPLIT Hopkinson Bar TESTS ON (QUASI‐) BRITTLE MATERIALS
    Experimental Techniques, 2000
    Co-Authors: Patricia Verleysen, Joris Degrieck
    Abstract:

    The split Hopkinson Bar test has proven to be a very valuable technique for the determination of the dynamic characteristics for a wide range of materials. However, when testing (quasi-)brittle materials, the processing of the recorded signals has to be adapted. As shown in this contribution, when shifting the waves recorded in the Bars towards the specimen, dispersion effects can no longer be neglected and attention has to be paid to the determination of the exact time shift. After all, the neglect of dispersion effects and an inaccurate time shift cause errors in the zone of small deformations, and this zone is of major importance for (quasi-)-brittle materials.

Ian W. Hall - One of the best experts on this subject based on the ideXlab platform.

  • dynamics of metal foam deformation during taylor cylinder Hopkinson Bar impact experiment
    Composite Structures, 2003
    Co-Authors: Sergey L. Lopatnikov, Bazle A. Gama, John W. Gillespie, Carl Krauthauser, Mustafa Guden, Md Jahirul Haque, Ian W. Hall
    Abstract:

    Abstract Analytical solutions for dynamic deformation of foam materials during the Taylor cylinder–Hopkinson Bar impact experiment were obtained. It was shown that shock wave of foam collapse appears during the fast impact. The results of this experiment can be used in estimating the average material properties of the foam under dynamic loading conditions. Results show that the un-deformed and change in length of foam specimens are in good agreement between theory and experiment, as well as numerical analysis.

  • Dynamics of metal foam deformation during Taylor cylinder–Hopkinson Bar impact experiment
    Composite Structures, 2003
    Co-Authors: Sergey L. Lopatnikov, Bazle A. Gama, John W. Gillespie, Md. Jahirul Haque, Carl Krauthauser, Mustafa Guden, Ian W. Hall
    Abstract:

    Analytical solutions for dynamic deformation of foam materials during the Taylor cylinder–Hopkinson Bar impact experiment were obtained. It was shown that shock wave of foam collapse appears during the fast impact. The results of this experiment can be used in estimating the average material properties of the foam under dynamic loading conditions. Results show that the un-deformed and change in length of foam specimens are in good agreement between theory and experiment, as well as numerical analysis

Sergey L. Lopatnikov - One of the best experts on this subject based on the ideXlab platform.

  • Hopkinson Bar experimental technique: A critical review
    Applied Mechanics Reviews, 2004
    Co-Authors: Bazle A. Gama, Sergey L. Lopatnikov, John W. Gillespie
    Abstract:

    A critical review of three classic papers by B Hopkinson, RM Davies, and H Kolsky, and the state-of-the-art in Hopkinson Bar experimental techniques is presented. The validity and applicability of the assumption made in the 1D Hopkinson Bar theory are discussed. Fundamentals of the Hopkinson Bar experimental procedure are outlined including Bar calibration, specimen design, pulse shaping, and data analysis following the essential dispersion correction methodology. Additional data tables necessary for dispersion correction are provided to cover a wide range of Poisson’s ratio. In addition to the elastic-plastic metals, methodologies for soft and hard materials are also discussed. This paper provides the necessary information for conducting a Hopkinson Bar experiment and analyzing the experimental data. This review article cites 61 references.

  • dynamics of metal foam deformation during taylor cylinder Hopkinson Bar impact experiment
    Composite Structures, 2003
    Co-Authors: Sergey L. Lopatnikov, Bazle A. Gama, John W. Gillespie, Carl Krauthauser, Mustafa Guden, Md Jahirul Haque, Ian W. Hall
    Abstract:

    Abstract Analytical solutions for dynamic deformation of foam materials during the Taylor cylinder–Hopkinson Bar impact experiment were obtained. It was shown that shock wave of foam collapse appears during the fast impact. The results of this experiment can be used in estimating the average material properties of the foam under dynamic loading conditions. Results show that the un-deformed and change in length of foam specimens are in good agreement between theory and experiment, as well as numerical analysis.

  • Dynamics of metal foam deformation during Taylor cylinder–Hopkinson Bar impact experiment
    Composite Structures, 2003
    Co-Authors: Sergey L. Lopatnikov, Bazle A. Gama, John W. Gillespie, Md. Jahirul Haque, Carl Krauthauser, Mustafa Guden, Ian W. Hall
    Abstract:

    Analytical solutions for dynamic deformation of foam materials during the Taylor cylinder–Hopkinson Bar impact experiment were obtained. It was shown that shock wave of foam collapse appears during the fast impact. The results of this experiment can be used in estimating the average material properties of the foam under dynamic loading conditions. Results show that the un-deformed and change in length of foam specimens are in good agreement between theory and experiment, as well as numerical analysis

Joris Degrieck - One of the best experts on this subject based on the ideXlab platform.

  • Calibration of dynamic piezoelectric force transducers using the Hopkinson Bar technique
    2012
    Co-Authors: Diederik Van Nuffel, Jan Peirs, Ives De Baere, Patricia Verleysen, Joris Degrieck, Wim Van Paepegem
    Abstract:

    This work describes an easy and flexible technique for calibration of dynamic piezoelectric force transducers. A Hopkinson Bar test setup is hereby used to generate the rapidly rising force loads necessary for calibration of these kinds of devices. Strain gauges are the key transducers in this test setup for measuring the load magnitude, rise time and duration. The knowledge of these variables makes successful calibration possible.

  • experimental investigation of the deformation of Hopkinson Bar specimens
    International Journal of Impact Engineering, 2004
    Co-Authors: Patricia Verleysen, Joris Degrieck
    Abstract:

    Split Hopkinson Bar (SHB) experiments are often used to study the strain rate dependent mechanical properties of materials. During a SHB experiment a small sample of the material under study is subjected to a high strain rate, uni-axial, tensile, compressive or torsion load. From the classical measurements the time history of the mean stress, strain rate and strain in the specimen can be derived. For some applications, more detailed information concerning the variation of the deformation in the specimen is necessary. In this contribution a technique is presented which makes it possible to obtain the deformation along the length of the specimen. The deformation of a line grid attached to the specimen is recorded during an experiment by means of a streak camera. An advanced and innovative numerical technique, based on a combination of geometric moire and phase shifting, is developed to extract the time history of the deformation along the axis of the specimen from the picture of the deforming grid automatically. Large specimen deformations are allowed, and the technique proved to give highly accurate results. In this contribution results are presented of a SHB experiment on a steel sheet specimen. Some remarks are formulated concerning the generally assumed homogeneity of the deformation in the specimen, and the deformation obtained with the classical measurement techniques.

  • IMPROVED SIGNAL PROCESSING FOR SPLIT Hopkinson Bar TESTS ON (QUASI‐) BRITTLE MATERIALS
    Experimental Techniques, 2000
    Co-Authors: Patricia Verleysen, Joris Degrieck
    Abstract:

    The split Hopkinson Bar test has proven to be a very valuable technique for the determination of the dynamic characteristics for a wide range of materials. However, when testing (quasi-)brittle materials, the processing of the recorded signals has to be adapted. As shown in this contribution, when shifting the waves recorded in the Bars towards the specimen, dispersion effects can no longer be neglected and attention has to be paid to the determination of the exact time shift. After all, the neglect of dispersion effects and an inaccurate time shift cause errors in the zone of small deformations, and this zone is of major importance for (quasi-)-brittle materials.