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ABSTRACT: A wide experimental study on dynamic behaviour of concrete has been carried out by means of the Hopkinson Bar Bundle. In order
to study the effect of the internal relative humidity on the tensile behaviour of concrete loaded at different strain-rates,
some specimens have been subjected to three different curing conditions and then tested under quasi-static, soft and hard
impact loads. A physical approach is also proposed to explain the observed variation in strength.
Une large campagne d'essais dynamiques a été réalisée en traction à l'aide du système de multibarres de Hopkinson. L'étude
est axée en particulier sur l'effet de l'humidité relative interne par rapport au comportement dynamique en traction à différentes
vitesses de déformation. Les échantillons ont été soumis à trois différentes conditions de maturation. Une approche physique
est aussi proposée afin d'expliquer la variation de la résistance du béton.
Materials and Structures 04/2012; 34(1):21-26. · 1.28 Impact Factor
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ABSTRACT: Reliable material models for concrete behaviour at higher strain rates are necessary for the design and assessment of concrete structures subject to impact and blast. This information should be obtained from experiments performed on large-size concrete specimens (up to 200 mm side cubes) with aggregates of realistic maximum size (16?32 mm). Such type of experiments, based on Hopkinson bar techniques, are conducted and described in this study. Several normal concrete grades and steel-fibre-reinforced concretes have been tested, and full stress?strain curves have been obtained for strain rates up to 10/s. The results, presented in terms of the dynamic increase factor, show clearly the increase of strength of the material with increasing strain rates, more accentuated in tension than in compression, and the influence of the specimen and aggregate size.
Magazine of Concrete Research. 04/2009; 61:221-230.
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ABSTRACT: A new testing methodology based on the Hopkinson bar principle is proposed for studying globally and locally the mechanical properties of plain concrete at a high strain rate. A Hopkinson bar bundle measures the local mechanical characteristics over the cross section of a large specimen of plain concrete subjected to impact loading. With this method, more accurate measurements of the stress-strain diagram are obtained, especially during the fracturing phase of the concrete specimen.
Experimental Mechanics 01/1999; 39(2):137-141. · 1.52 Impact Factor
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ABSTRACT: A testing programme in a large range of strain rate (10-6 to 10 s-1) including those of seismic and impact loading, has been performed in tension on cubic specimens of plain concrete with aggregate of 5, 12 and 25 mm size, using hydraulic and large Hopkinson bar equipment. A new testing equipment consisting of large aluminum Hopkinson bar bundles has been implemented for a more precise measurements of the mechanical properties in particular of the softening branch of the stress strain diagram. The new Hopkinson bar bundle test allowed in particular to measure: the place(s) and time(s) of fracture initiation(s) and propagation over the specimen cross section; the residual resisting cross section during fracture propagation. Keywords: concrete, fracture, testing methodology, Hopkinson bar, high strain-rate.
Concrete under severe conditions; 01/1998
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Advances in Fracture Research; 01/1997
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2nd International Symposium on Impact Engineering; 01/1996
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ISATA; 01/1996
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2nd International Symposium on Impact Engineering; 01/1996
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01/1996
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12/1973
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ABSTRACT: A major part of this work was to establish a new data base for AISI type 316H austenitic steel, related to its sensitivity to strain-rate history, and evaluate the observed mechanical response using one of the many modern approaches to constitutive modelling. The phenomenological description of the material was a series of interrupted tensile loading with strain-rate change from quasi-static to dynamic. These data clearly showed that the material strength, although strain-rate sensitive, is not affected by the strain-rate history, indicating that a mechanical equation of state could be applied. The Bodner-Partom constitutive theory is first calibrated by the monotonic stress-strain curves collected at steady constant strain rates, then used to predict the response under various types of interrupted strain-rate change tests.
Nuclear Engineering and Design.
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ABSTRACT: A sound foundation of stress and/or strain criteria for the mechanical design of fast breeder reactor structures capable of bearing extreme dynamic loading conditions, passes through the experimental determination of dynamic mechanical properties of materials in end-of-life conditions with respect to the damaging processes to which the structures are submitted.Calculation codes must be implemented by constitutive equations describing the dynamic mechanical response of the materials, without the knowledge of which any calculation code is liable to important inaccuracies which provoke the use of high safety coefficients and, often, the uncertainty as to the effective capability of the structures to withstand the accidental loads.The results of a screening programme of dynamic tensile tests performed on AISI 304 and AISI 316 austenitic stainless steels using small specimens (7 mm2) showed that the dynamic response of such steels at temperatures of 400 and 550°C is not univocal, passing from a substantial dynamic hardening behaviour to a dynamic softening behaviour, probably due to residual microstructural differences caused by the transformation processes.From the discussion of the results obtained, follows the development of a testing programme on small (up to 20 mm2 cross section) and large specimens (up to 5000 mm2 cross section) focused on: (i) developing and calibrating dynamic constitutive equations founded on basic physical aspects, for uniaxial and multiaxial loading conditions under particular deformation and loading histories; (ii) verifying in dynamics the existing yielding criteria, hardening rules and failure theories; (iii) investigating by means of a high-load apparatus (5 MN) the influence of near real-size thickness, welding, defects and notches, on dynamic strength and deformation capability of large reactor structures.
Nuclear Engineering and Design.
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ABSTRACT: Le comportement d'un acier inoxydable de type 316 H soumis à une traction interrompue avec un changement de vitesse de déformation, ainsi que la validité d'une équation mécanique d'état, ont été déterminés par des essais expérimentaux à 300, 400, 550 et 650°C. Les effets de vieillissement dynamique aux plus hautes températures sont aussi examinés. The behaviour of a stainless steel type AISI 316 H under interrupted strain-rate change tensile tests, as well as the validity of a mechanical equation of state for this material, are determined experimentally at 300, 400, 550 and 650°C. The effects of dynamic strain aging at the highest temperatures are also examined.
http://dx.doi.org/10.1051/jphyscol:1985562.
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ABSTRACT: L'idée est discutée d'employer deux grands faisceaux de barres d'Hopkinson, disposées de façon spéculaire, pour l'observation de la distribution instantanée de la contrainte et de la déformation sur la section résistante des grandes éprouvettes de béton, chargées en dynamique rapide. The idea is discussed of using two specular bundles of Hopkinson's bars for the experimental observation of the instantaneous distribution of stress and strain over the cross-section of large concrete specimens with real size aggregate, subjected to high loading rates.
http://dx.doi.org/10.1051/jp4:1994817.
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ABSTRACT: Constitutive equations are usually calibrated only trough the experimental results obtained by means of uniaxial tests because of the lack of adequate biaxial experimental data especially at high strain rate conditions. These data are however important for the validation of analytical models and also for the predictions of mechanical behaviour of real structures subjected to multiaxial loading by numerical simulations. In this paper some developments are shown concerning biaxial cruciform specimens and different experimental machines allowing biaxial tests in a large range of strain rates. This experimental campaign has also allowed study of the influence of changing the strain paths. Diagrams of equivalent stress versus straining direction and also equivalent plastic fracture strain versus straining direction are shown.
http://dx.doi.org/10.1051/jp4:2000927.
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ABSTRACT: The strain-rate sensitivity of concrete in tension has been investigated employing Hopkinson bar techniques. The devices used have allowed the successful testing of large specimens with real size aggregates. Full stress-strain curves, including the softening branch, have been obtained for several strain rates. The use of bar bundles for holding the specimens has further provided insight on the fracturing mechanism inside the specimen, revealing amply the crack multi-activation process under dynamic loading. Such data are considered essential in the impact and blast resistant design of concrete structures..
http://dx.doi.org/10.1051/jp4:2006134100.
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ABSTRACT: On décrit une barre de pression pour grandes charges caractérisée par deux impulsions symétriques engendrées aux deux extrémités de la barre, et la méthode à utiliser pour l'interprétation des signaux. On donne les premiers résultats obtenus avec des éprouvettes de grandes dimensions en utilisant des techniques optiques de mesure. A high load pressure bar characterized by symmetric pulses coming from the two ends is described together with a method for interpretation of signals. First results obtained by testing large specimens using optical techniques are reported.
http://dx.doi.org/10.1051/jphyscol:1985563.
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ABSTRACT: High strain rate mechanical properties are a major concern for each steel manufacturer, especially with respect to thin sheet steel used in the automotive branch. We began to study this topic by starting a project with the following goals : acquiring reliable experimental data, understanding in depth the energy absorption in thin sheet steel and finding the right constitutive material equation. The first part of the project has been presented in [1]. In this paper we present data computation and comparison with the existing material model theories to exploit the experimental data. Les propriétés mécaniques à haute vitesse sont actuellement un problème crucial pour les sidérurgistes, particulièrement sur le marché automobile. Nous avons commencé à étudier ce domaine en mettant sur pied un projet qui avait pour but non seulement d'obtenir des données expérimentales fiables, mais aussi de comprendre les phénomènes d'absorption d'énergie dans l'acier et de trouver une loi de comportement correcte. La première partie de ce projet a été présentée [1] , mais une partie importante du travail qui comprend le traitement des données et la comparaison avec les théories existantes est présentée ici.
http://dx.doi.org/10.1051/jp4:19973105.
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ABSTRACT: The growing use of high strength steels in the automotive industry, to improve the crashworthiness and the light-weighting of the car body, requires the knowledge of their behaviour over a large range of strain-rates. The accuracy of the results in medium and high strain-rate tests is often strongly influenced by the experimental techniques used for the mechanical characterization of materials. Moreover, the precision of the constitutive law in reproducing the actual behaviour of the materials has important consequences in the correctness of design and assessment of car body structures subjected to impact loading. The paper presents the experimental techniques used to carry out dynamic tensile tests on thin sheet specimens. The research includes several Advanced High Strength Steels as Dual-Phase steels, TRansformation Induced Plasticity steels, etc. The tests have been carried out in the three strain-rate regimes (1–5, 10–50 and 500 s−1). The comparison of the dynamic stress-strain curves of three DP steels is presented and discussed.
http://dx.doi.org/10.1051/dymat/2009018.
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ABSTRACT: The specimen size of concrete specimens should be large enough to be representative of the material. In this paper it is shown how the bundle bars method allows the dynamic mechanical characterisation by using the uniaxial elastic wave propagation theory used in the Hokinson bar technique. Pour le béton, la taille des echantillons à tester doit être assez large pour être representative du materiau. Pour cette raison, les tests à grandes vitesses de déformation n'ont pu être réalisés auparavant par la méthode des barres de Hopkinson. La méthode suggérée dans cette étude permet de passer outre cette difficulté. La barre est divisée en un faisceau de barreaux (multibarre) ce qui permet d'avoir la propagation uniaxiale des ondes et une sollicitation homogène sur la section transversale du materiau.
http://dx.doi.org/10.1051/jp4:19973154.
