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Artykuły w czasopismach na temat "Hopkinson pressure bars (SHPB)":
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Harrigan, John J., Bright Ahonsi, Elisavet Palamidi i Steve R. Reid. "Experimental and numerical investigations on the use of polymer Hopkinson pressure bars". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, nr 2023 (28.08.2014): 20130201. http://dx.doi.org/10.1098/rsta.2013.0201.
Streszczenie:
Split Hopkinson pressure bar (SHPB) testing has traditionally been carried out using metal bars. For testing low stiffness materials such as rubbers or low strength materials such as low density cellular solids considered primarily herein, there are many advantages to replacing the metal bars with polymer bars. An investigation of a number of aspects associated with the accuracy of SHPB testing of these materials is reported. Test data are used to provide qualitative comparisons of accuracy using different bar materials and wave-separation techniques. Sample results from SHPB tests are provided for balsa, Rohacell foam and hydroxyl-terminated polybutadiene. The techniques used are verified by finite-element (FE) analysis. Experimentally, the material properties of the bars are determined from impact tests in the form of a complex elastic modulus without curve fitting to a rheological model. For the simulations, a rheological model is used to define the bar properties by curve fitting to the experimentally derived properties. Wave propagation in a polymer bar owing to axial impact of a steel bearing ball is simulated. The results indicate that the strain histories can be used to determine accurately the viscoelastic properties of polymer bars. An FE model of the full viscoelastic SHPB set-up is then used to simulate tests on hyperelastic materials.
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Pham, Thanh Nam, Hyo Seong Choi i Jong Bong Kim. "A Numerical Investigation into the Tensile Split Hopkinson Pressure Bars Test for Sheet Metals". Applied Mechanics and Materials 421 (wrzesień 2013): 464–67. http://dx.doi.org/10.4028/www.scientific.net/amm.421.464.
Streszczenie:
Determination of theflow stress of materials at high strain rate is very important in automotive and military areas.The compressive flow stress at high strain rate can be obtained relativelyexactly by SHPB(Split Hopkinson Pressure Bars) tests. However, it is difficult to determinethe flow stressexactlyin the tensile state by using the SHPB tests. The difficulty in the tensile SHPB tests is how to fix a specimen on two bars. So, the design of a specimen and holders is needed to obtain more accurate measurement of the flow stress. In this study, the accuracy of the tensile SHPB tests results was numerically investigated. Finite element analyses of the tensile SHPB were carried out for various cases of fixing bolt location and bolting force. From the analysis results, a design guide for the fixing structure was obtained and the causes of error were investigated.
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Quinn, R. M., L. H. Zhang, M. J. Cox, D. Townsend, T. Cartwright, G. Aldrich-Smith, P. A. Hooper i J. P. Dear. "Development and Validation of a Hopkinson Bar for Hazardous Materials". Experimental Mechanics 60, nr 9 (18.08.2020): 1275–88. http://dx.doi.org/10.1007/s11340-020-00638-w.
Streszczenie:
Abstract Background There are a variety of approaches that can be employed for Hopkinson bar compression testing and there is no standard procedure. Objectives A Split-Hopkinson pressure bar (SHPB) testing technique is presented which has been specifically developed for the characterisation of hazardous materials such as radioactive metals. This new SHPB technique is validated and a comparison is made with results obtained at another laboratory. Methods Compression SHPB tests are performed on identical copper specimens using the new SHPB procedures at Imperial College London and confirmatory measurements are performed using the well-established configuration at the University of Oxford. The experiments are performed at a temperature of 20 ∘C and 200 ∘C. Imperial heat the specimens externally before being inserted into the test position (ex-situ heating) and Oxford heat the specimens whilst in contact with the pressure bars (in-situ heating). For the ex-situ case, specimen temperature homogeneity is investigated both experimentally and by simulation. Results Stress-strain curves were generally consistent at both laboratories but sometimes discrepancies fell outside of the inherent measurement uncertainty range of the equipment, with differences mainly attributed to friction, loading pulse shapes and pulse alignment techniques. Small metallic specimens are found to be thermally homogenous even during contact with the pressure bars. Conclusion A newly developed Hopkinson bar for hazardous materials is shown to be effective for characterising metals under both ambient and elevated temperature conditions.
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Kariem, Muhammad Agus, John H. Beynon i Dong Ruan. "Numerical Simulation of Double Specimens in Split Hopkinson Pressure Bar Testing". Materials Science Forum 654-656 (czerwiec 2010): 2483–86. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.2483.
Streszczenie:
The split Hopkinson pressure bar (SHPB) is the most commonly used technique to characterize the dynamic behaviour of materials at very high strain rates. However, a classic single specimen test only generates a single stress-strain curve at the average strain rate of the test. This paper proposes three arrangements on the use of double specimens in SHPB compression testing. All waves propagating along the bars have been used to analyse the dynamic behaviour of the specimens. To simulate the test and predict its dynamic performance, an axisymmetric finite element analysis using LS-DYNA was conducted for the experiment using 13 mm bar diameter. The validity of the simulations was checked with experimental data from normal SHPB testing. Based on the simulations, the modified techniques are achievable and at least two stress-strain curves of materials can be extracted without violating the requirement of a valid SHPB test.
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Baranowski, Pawel, Roman Gieleta, Jerzy Malachowski, Krzysztof Damaziak i Lukasz Mazurkiewicz. "SPLIT HOPKINSON PRESSURE BAR IMPULSE EXPERIMENTAL MEASUREMENT WITH NUMERICAL VALIDATION". Metrology and Measurement Systems 21, nr 1 (1.03.2014): 47–58. http://dx.doi.org/10.2478/mms-2014-0005.
Streszczenie:
Abstract Materials and their development process are highly dependent on proper experimental testing under wide range of loading within which high-strain rate conditions play a very significant role. For such dynamic loading Split Hopkinson Pressure Bar (SHPB) is widely used for investigating the dynamic behavior of various materials. The presented paper is focused on the SHPB impulse measurement process using experimental and numerical methods. One of the main problems occurring during tests are oscillations recorded by the strain gauges which adversely affect results. Thus, it is desired to obtain the peak shape in the incident bar of SHPB as “smooth” as possible without any distortions. Such impulse characteristics can be achieved using several shaping techniques, e.g. by placing a special shaper between two bars, which in fact was performed by the authors experimentally and subsequently was validated using computational methods.
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Nie, Hailiang, Weifeng Ma, Junjie Ren, Ke Wang, Jun Cao, Wei Dang, Tian Yao i Kang Wang. "Size Effect in the Split Hopkinson Pressure Bar Experiment". Journal of Physics: Conference Series 2160, nr 1 (1.01.2022): 012065. http://dx.doi.org/10.1088/1742-6596/2160/1/012065.
Streszczenie:
Abstract For many structures, their service environment is very strict, and the requirements for the impact resistance of materials are very high. Therefore, the dynamic testing method has important scientific significance and application value for practical engineering. Split Hopkinson pressure bar (SHPB) is one of the most common experimental methods for obtaining dynamic mechanical properties of materials. However, there is no uniform standard for the size of the bars and specimens used in the test. Theoretically, the size has little influence on the experimental results, but it has not been proved by experiments. This paper mainly studies the influence of device/specimen sizes of split Hopkinson pressure bar through experiments, it is demonstrated that the sizes of bars and specimen have little effect on experimental results.
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Adorna, Marcel, Jan Falta, Tomáš Fíla i Petr Zlámal. "PREPROCESSING OF HOPKINSON BAR EXPERIMENT DATA: FILTER ANALYSIS". Acta Polytechnica CTU Proceedings 18 (23.10.2018): 77. http://dx.doi.org/10.14311/app.2018.18.0077.
Streszczenie:
This work presents a data preprocessing procedure for signal acquired during high strain-rate loading using a custom Split Hopkinson Pressure Bar (SHPB). Before the evaluation of the experimental data, preprocessing of the measured signals including application of suitable digital or analog filter needs to be performed. Our department mainly focuses on measurements performed on advanced materials (e.g. materials with predefined structures or hybrid foams). For such measurements, it is essential to perform data preprocessing and apply suitable filter, to be able to appropriately determine deformation pulses on the measuring bars. This paper focuses foremost on spectral analysis of the measured signals, and design of optimal method of data filtering. Data from several different SHPB experiments were processed and results of different filtering methods are shown in this paper. Parameters of the best performing filter were optimized and shown to be universal for wide range of SHPB measurements.
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Zhang, Xing, Bao Cheng Li, Zhi Min Zhang i Zhi Wen Wang. "Investigation on Deformation in ZK60 at High Strain Rate". Materials Science Forum 488-489 (lipiec 2005): 527–30. http://dx.doi.org/10.4028/www.scientific.net/msf.488-489.527.
Streszczenie:
Split Hopkinson Pressure Bars (SHPB) was applied to investigate shock resistance of magnesium alloy. The deformation behaviour was reported of ZK60 magnesium alloy at high strain rate, and the relationship was established between the dynamic properties and the impact velocity. Results indicate: with impact velocity improvement, much twinned crystal and fine grain can be obtianed, this made dynamic properties enhancement of ZK60 alloy.
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Zhao, Peng Duo, Yu Wang, Jian Ye Du, Lei Zhang, Zhi Peng Du i Fang Yun Lu. "Using Split Hopkinson Pressure Bars to Perform Large Strain Compression Tests on Neoprene at Intermediate and High Strain Rates". Advanced Materials Research 631-632 (styczeń 2013): 458–62. http://dx.doi.org/10.4028/www.scientific.net/amr.631-632.458.
Streszczenie:
The strain rate sensitivity of neoprene is characterized using a modified split Hopkinson pressure bar (SHPB) system at intermediate (50 s-1, 100 s-1) and high (500 s-1, 1000 s-1) strain rates. We used two quartz piezoelectric force transducers that were sandwiched between the specimen and experimental bars respectively to directly measure the weak wave signals. A laser gap gage was employed to monitor the deformation of the sample directly. Three kinds of neoprene rubbers (Shore hardness: SHA60, SHA65, and SHA70) were tested using the modified split Hopkinson pressure bar. Experimental results show that the modified apparatus is effective and reliable for determining the compressive stress-strain responses of neoprene at intermediate and high strain rates.
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Lee, Sang Hyun, Brian Tuazon i Hyung Seop Shin. "Construction of Data Acquisition/Processing System for Precise Measurement in Split Hopkinson Pressure Bar Test". Applied Mechanics and Materials 566 (czerwiec 2014): 554–59. http://dx.doi.org/10.4028/www.scientific.net/amm.566.554.
Streszczenie:
The Split Hopkinson Pressure Bar (SHPB) testing technique has been used to derive the constitutive equations of engineering materials at high strain rate using the reflected and transmitted waves measured from the input and output bars. In this case, a precise measurement of the reflected and transmitted waves is important to determine a reliable stress-strain relation. In this study, to achieve the precise measurement of the reflected and transmitted waves in the SHPB experiment, a data acquisition scheme utilizing the LabVIEW software and a post processing program have been constructed. With the constructed system, an accurate data acquisition without a digital storage oscilloscope and a convenient post processing of the signals obtained through the SHPB test for identifying the mechanical properties have been possible. Therefore, a fast and simple generation of the strain rate - time curve and the nominal stress - nominal strain curve has been implemented by just selecting the specified regions on the reflected and transmitted wave profiles acquired. Also, the process to set the appropriate test configuration in the SHPB test for various kinds of materials has become easy with the constructed system.
Rozprawy doktorskie na temat "Hopkinson pressure bars (SHPB)":
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Chihi, Manel. "Étude des performances d’un composite carbone/époxy dopé par des nanocharges sous des sollicitations sévères". Electronic Thesis or Diss., Brest, École nationale supérieure de techniques avancées Bretagne, 2021. http://www.theses.fr/2021ENTA0017.
Streszczenie:
Ce travail de thèse a été réalisé dans un contexte de valorisation des matériaux composites à base de nanocharges. La connaissance du comportement mécanique des nanocomposites dopés par des nanocharges soumis à des sollicitations dynamiques sévères est une donnée importante pour les concepteurs des structures composites dédiées aux applications civiles et militaires. Ce comportement doit être caractérisé dans un large domaine de déformation ; pour des vitesses de déformation pouvant atteindre 10⁵s⁻¹. Une attention particulière est portée au système des barres d’Hopkinson (SHPB) en raison de son utilisation fréquente dans une telle gamme de vitesses de déformation qui correspond à la gamme de vitesses de la plupart des applications industrielles. Dans ce contexte, nous avons mené dans un premier temps une étude centrée sur l’effet des nanocharges sur le comportement dynamique et la cinétique de l’endommagement d’un composite de référence à base de fibres de carbone noyées dans une matrice époxy. Nous avons opté pour le choix de deux types de nanocharges présentant une compositions chimiques pareilles (basé sur le carbone pur) mais deux géométries différentes (quasi-1D pour les nanotubes de carbone (NTC) et 2D pour les nanofeuillets de graphène (GNP)). On a préparé les deux séries de nanocomposites NTC et GNP dans les mêmes conditions tout en utilisant des fractions massiques communes (0.5%, 1% et 2%) pour pouvoir mener une étude comparative concernant les deux systèmes. Une campagne d’essais de compression dynamique, hors-plan (OP) et dans le plan (IP) et, ainsi qu’une étude numérique ont été menées. Il a été démontré que le comportement dynamique et la cinétique d’endommagement des matériaux sont très sensibles à la vitesse de déformation et à la direction de sollicitation. Les résultats de ces essais nous ont aussi permis d’appréhender l’influence de l’ajout des nanocharges sur la réponse des matériaux. Le pourcentage de 1% GNP montre des performances optimales en rigidité, contrainte maximale et résistance à l’endommagement. Toutefois, les nanocomposites peuvent être très sensibles aux conditions environnementales, en particulier au vieillissement hygrothermique qui peut réduire leurs performances mécaniques. De ce fait, l’effet du vieillissement hygrothermique (60°C/80% HR) sur la durée de vie des nanocomposites est alors étudié expérimentalement (chargement dans le plan). Des baisses de différentes propriétés mécaniques en fonction du temps (15, 40 et 100 jours) et de la teneur en eau absorbée sont mises en évidence pour chaque fraction massique. Cependant, il a été démontré que l’introduction de nanocharges, sauf dans le cas 0.5% NTC, entraine une dégradation plus importante du composite de référenceThis thesis work was carried out in a context of valorization of composite materials based on nanofillers. The knowledge of the mechanical behavior of nanocomposites doped by nanofillers submitted to high dynamic loading is an important data for the designers of composite structures dedicated to civil and military applications. This behavior must be characterized in a wide range of deformation; for strain rates in the range of 10² to 10⁵s⁻¹. Particular attention is devoted to the Hopkinson pressure bar system (SHPB) because of its frequent use in such a wide range of deformation which corresponds to the strain rate deformation range of most industrial applications. In this context, we first conducted a study focused on the effect of nanofillers on the dynamic behavior and damage kinetics of a carbon/epoxy composite. We have chosen two types of nanofillers with similar chemical compositions (based on pure carbon) but two different geometries (quasi-1D for carbon nanotubes (CNT) and 2D for graphene nanoplatelets (GNP). The two series of nanocomposites CNT and GNP were prepared under the same conditions while using common mass fractions (0.5%, 1% and 2%) in order to conduct a comparative study of the two nanocomposite systems. A dynamic compression test (in-plane (IP) and out-of-plane (OP)) and a numerical study were conducted. It has been shown that the dynamic behavior and damage kinetics of the materials are very sensitive to the strain rate and the direction of solicitation. The results of these tests also allowed us to understand the influence of the addition of nanofillers on the response of the materials. The percentage of 1% GNP shows optimal performances in stiffness, maximum stress and resistance to damage. However, nanocomposites can be very sensitive to environmental conditions, in particular to hygrothermal aging that can reduce the mechanical performances. Therefore, the effect of hygrothermal aging (60°C/80%RH) on the lifetime of nanocomposites is studied experimentally (in-plane loading). Decreases of different mechanical properties as a function of time (15, 40 and 100 days) and absorbed water content are highlighted for each mass fraction. However, it was shown that the introduction of nanofillers, except in the case of 0.5% CNT, leads to a more significant degradation of the reference composite
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Berger-Pelletier, Hugues. "Modelling of split hopkinson pressure bars : adaptation of a compression apparatus into tension". Thesis, Université Laval, 2013. http://www.theses.ulaval.ca/2013/28977/28977.pdf.
Streszczenie:
Les Barres d’Hopkinson sont couramment utilisées pour tester les matériaux à des hauts taux de déformations. Souvent, différents systèmes de barres sont utilisés pour tester les matériaux en tension ou en compression. Par contre, il serait pratique d’utiliser un seul système, pour prendre des mesures en tension et en compression. Des études ont été faites pour convertir le système de compression existant du centre de Recherche et Développement pour la Défense Canada (RDDC) de ValCartier. Un concept a été choisi parmi 6 systèmes de tension déjà existants. Le choix a été validé avec un modèle d’éléments finis fait sur LS-Dyna. Le modèle a été calibré sur des résultats de compression fournis par le RDDC. Il fut ensuite modifié pour intégrer le nouveau concept. À cause d’un manque de ressources, les résultats de simulation sur LS-Dyna n’ont pu être comparés avec des résultats expérimentaux, puisqu’un premier prototype n’a pu être fabriqué.The Split Hopkinson Pressure Bars (SHPB) is a common method used to characterize materials at high rates of strain. First used to experiment on materials in compression, the method was adapted to do tests in tension and torsion. The compression apparatus consists of a specimen sandwiched between 2 pressure bars, called the input bar and the output bar. A third bar, the striker, is launched at the input bar. Upon impact, a compressive pulse traveling toward the specimen is generated. This load is partially transmitted into the specimen and the output bar, the rest of it being reflected back into the input bar. Using measurements of the input, transmitted and reflected pulse, it is possible to develop the stress-strain response of the material deforming at high strain rates. This is achieved using strain gages adequately placed on both pressure bars. Many researchers use a different SHPB system when it comes to tension tests. Many methods exist, but all of them are based on compressive experiments. It would therefore be convenient to only have one system, which is capable of taking measurements both in compression and tension. Based on the compressive SHPB apparatus used by the Defense, Research and Development Canada (DRDC) center in ValCartier, studies were made to convert the compressive system into a tensile setup. The goal was to modify it with minimum changes possible, in order to easily go back and forth between the two configurations. A design choice was made, considering 6 existing tension systems. To validate the decision, a finite element model was created using LS-Dyna. The modal was first aligned with the compression results provided and then modified to implement the selected design. Because of a lack of available resources, LS-Dyna simulation results were not compared with experimental data, as it was not possible to create a first prototype.
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Hughes, Foz. "The high strain-rate behaviour of polymers and nanocomposites for lightweight armour applications". Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13705.
Streszczenie:
The need for efficient, lightweight armour solutions has never been so great as it is today. Increasing numbers of personnel, both military and civilian are being placed in an expanding variety of life-threatening situations, and we must recognise the responsibility to maximise their combat survivability. One way to help protect these people is to provide them with some form of armour. Advanced polymeric materials are finding an increasing range of industrial and defence applications. These materials have the potential to improve the performance of current armour systems, whilst also reducing their cost and weight. Polymers may be reinforced with the addition of nanofillers such as carbon nanotubes or graphene, to produce nanocomposites, an exciting emerging polymer technology. Nanomaterials have been shown to exhibit extraordinary strength, far higher than that of traditional armour materials. Nanocomposites have the possibility of being remarkable materials, with high strength and light weight. The work detailed in this report is an investigation into the mechanical properties of nanocomposites along with some novel blended polymer composites. Two compressive testing techniques have been used to carry out this investigation. The intermediate strain-rate Optical Drop-Weight, and the high strain-rate Split-Hopkinson Pressure Bar. The latter required some significant modifications in order to optimise it for use with low-density polymers. Ultimately, nanocomposites were found to behave virtually indistinguishably from the monolithic polymer matrices. Yield strengths and energy absorption characteristics remained inside the ordinary experimental scatter. Blended composites, in which a long chain length polymer is combined with a chemically similar polymer with a shorter chain length, proved to be more interesting. Yield strengths of these novel materials were increased over that of either constituent material, although energy absorption remained low.
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Durand, Bastien. "Etude expérimentale du frottement entre l’acier et un matériau fragile sous haute vitesse et haute pression". Thesis, Orléans, 2013. http://www.theses.fr/2013ORLE2039/document.
Streszczenie:
L’objectif de la thèse est la caractérisation expérimentale du frottement entre l’acier et un matériau fragile. Les pressions et les vitesses de glissement qu’on cherche à atteindre sont respectivement de l’ordre de 10 à 100 MPa et l’ordre de 10 à 100 m/s. Les tribomètres classiques ne peuvent pas être utilisés car les pressions qu’on cherche à atteindre sont suffisamment élevées pour mener le matériau fragile à rupture. Pour pallier cette difficulté, le matériau doit être confiné. Un échantillon cylindrique du matériau est alors inséré dans un tube en acier qui fait à la fois office de confinement et de surface de frottement. Avec cette configuration, comme nous ne pouvons pas effectuer de mesures directes au niveau de l’interface, les paramètres de frottement sont identifiés à partir de mesures indirectes et de modèles analytique et numérique. Deux types de dispositifs ont été conçus pour effectuer à la fois des essais d’orientation en quasistatique et des essais sur barres de Hopkinson. Les essais quasi-statiques permettent une identification fiable du frottement et montrent que des pressions de 100 MPa peuvent être obtenues avec notre configuration sans dégrader le matériau fragile. En revanche, les essais sur barres de Hopkinson ne donnent pas satisfaction. Un dispositif spécifiquement adapté à la dynamique rapide a alors été conçu. Il permet d’identifier le frottement sous des pressions de 100 MPa et des vitesses de10 m/sThe aim of the thesis is the experimental characterisation of the friction between steel and a brittle material. The desired pressures and the desired sliding velocities are respectively of the order of 10-100 MPa and 10-100 m/s. Usual tribometers cannot be used because the desired pressures are high enough to fracture the brittle material. The material has to be confined to overcome this difficulty. A cylindrical sample of the material is therefore inserted into a steel tube which acts both as a confinement and a sliding surface. Such a configuration does not enable to carry on direct measurements on the interface, the friction parameters are thus identified from indirect measurements and from analytical and numerical models. Two types of set-up have been designed to carry on both quasi-static tests and tests on split Hopkinson pressure bars. Quasi-static tests enable a reliable identification of friction and show that the desired pressures can be reached with our configuration whilst retaining the brittle material integrity. Unfortunately, the results obtained with split Hopkinson pressure bars are not satisfactory. A set-up specifically adapted to dynamic situations has thus been designed. It enables identification of friction under pressure of 100 MPa and velocities of 10 m/s
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Lea, Lewis John. "Structural evolution in the dynamic plasticity of FCC metals". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273897.
Streszczenie:
Above true strain rates of $10^4$ s$^{-1}$ FCC metals exhibit a rapid increase in strength. Understanding of the physical mechanisms behind this strength transition is hindered by the number and interdependence of candidate mechanisms. Broadly, contributions to strength can be split into `instantaneous' effects and the more permanent `structural' ones. In this thesis a series of experiments are presented which are designed to separate the two types of contribution. Chapter 2 outlines the basics of dislocation plasticity, based on the seminal works of Taylor and Orowan. It then progresses on to discuss recent experimental and theoretical work on the understanding of slip as avalanche behaviour. Chapter 3 summarises traditional modelling approaches for instantaneous strength contributions which are routinely applied below $10^4$ s$^{-1}$. It then continues on to outline a number of different approaches which have been adopted to attempt to explain and model the strength transition. Chapter 4 outlines the methods used in the earliest stages of the study: Instron and split Hopkinson pressure bar methods. Both methods are well established, and cover the majority of the range of rates under study. Emphasis is made on minimising experimental sources of error, and subsequently accounting for those which are unavoidable. Finally, the specimen material is introduced and is shown to be fit for purpose. Chapter 5 presents a set of mechanical tests of specimens at strain rates between $10^4-10^5$~s$^{-1}$. The softening of the specimens with increased temperature is observed to increase with strain rate, both in absolute terms and when normalised to the 300 K measurement for each strain rate. The observations are most easily explained if the strength transition is due to an increase in early stage work hardening, however, some anomalous behaviours remain. Chapter 6 introduces a new experimental technique; direct impact Hopkinson pressure bars, required to perform experiments shown to be necessary by the results of Chapter 5. Photon Doppler velocimetry is applied to the projectiles used in experiments, removing one of the most significant flaws of the technique, and creating a more confident basis with which to perform further experimental work. Chapter 7 presents a series of `jump tests' at ambient temperatures. Specimens are deformed at strain rates ranging from $10^{-2}$ to $10^5$~s$^{-1}$ to a fixed strain of 0.1, then reloaded to yield at a strain rate of $10^{-1}$. The yield point at reload is shown to have the same rapid upturn as seen when the specimens were deforming at high rates, providing strong evidence that the increase in strength is due to changes in the underlying dislocation structure, rather than a dynamic effect, as it remains even when the high strain rate is removed. Chapter 8 continues on from the conclusions of Chapter 7. Jump tests are expanded to a variety of temperatures and strains, to provide a more complete characterisation of metal behaviour. No dramatic change in the saturation of work hardening is observed to coincide with the increase in early stage work hardening. Chapter 9 discusses discrepancies between contemporary high rate models and recent developments in the understanding of plasticity being an avalanche process. Potential consequences of incorporating avalanche plasticity into high rate models are explored. Particular attention is paid to Brown's observation that based on quasi static observations of avalanche behaviour, the formation of dislocation avalanches will begin to fail at strain rates of approximately $10^4$ s$^{-1}$. Consequences of the progressive breakdown of avalanche behaviour are discussed with respect to the experimental observations presented in earlier chapters. In Chapter 10, we will discuss the key conclusions of the work. Finally, a number of avenues are proposed for building upon the current work both theoretically and experimentally.
Części książek na temat "Hopkinson pressure bars (SHPB)":
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Govender, R. A., G. S. Langdon i G. N. Nurick. "Impact Bend Tests Using Hopkinson Pressure Bars". W Dynamic Behavior of Materials, Volume 1, 421–26. Cham: Springer International Publishing, 2013. http://dx.doi.org/10.1007/978-3-319-00771-7_51.
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Zuanetti, Bryan, Kyle Ramos, Carl Cady, Adam Golder, Chris Meredith, Dan Casem i Cynthia Bolme. "High Strain-Rate Testing of Brittle Materials Using Miniature Beryllium Split-Hopkinson Pressure Bars". W The Minerals, Metals & Materials Series, 65–73. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-22576-5_7.
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Bracq, A., G. Haugou i H. Morvan. "Constitutive Modeling of Polyamide Split Hopkinson Pressure Bars for the Design of a Pre-stretched Apparatus". W Dynamic Behavior of Materials, Volume 1, 201–5. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-95089-1_36.
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Elkarous, L., A. Nasri i R. Nasri. "Dynamic Calibration Method for Copper Crusher Gauges Based on Split Hopkinson Pressure Bars Technique and Finite Element Modeling". W Lecture Notes in Mechanical Engineering, 732–42. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-27146-6_80.
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Kruszka, Leopold, i Kamil Sobczyk. "Round-Robin Exercise for Compression Testing of Steel Alloy of Pressure Tank at High Strain Rate". W Critical Energy Infrastructure Protection. IOS Press, 2022. http://dx.doi.org/10.3233/nicsp220007.
Streszczenie:
The aim of the paper is to show a type of the round-Robin test on the example of experiments at a high strain rate using various split Hopkinson pressure bar test stands located at different locations in Warsaw – a scientific-technical center and a university. The results of the conducted experiments in the form of a circumferential stress and radial stress were shown for each analyzed SHPB test stand, using an identical research specimen. A comparison was made, and the obtained results were compared on the graphs of the stress-strain curve for various SHPB test stands and on the strain rate – strain graphs for the selected SHPB test stand.
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"The water saturation effects on dynamic tensile strength in red and buff sandstones studied with Split Hopkinson Pressure Bar (SHPB)". W Advanced Materials, Structures and Mechanical Engineering, 177–80. CRC Press, 2016. http://dx.doi.org/10.1201/b19693-36.
Streszczenia konferencji na temat "Hopkinson pressure bars (SHPB)":
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Costanzi, Marco, Gautam Sayal i Golam Newaz. "Dynamic Behavior of Monolithic and Composite Materials by Split Hopkinson Pressure Bar Testing". W ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32944.
Streszczenie:
A Split Hopkinson Pressure Bar (SHPB), an experimental apparatus for testing of solid materials at high strain rates, was in-house designed and realized by the Mechanical Engineering Dept. of WSU: it can test different types of materials and provide their dynamic mechanical properties (e.g. Young’s modulus, hardening or plasticization coefficients, yield strength). This SHPB works at strain rate levels between 1000 and 3000 s-1 and impact speeds between 6 and 9 m/s. The specimen is simply a 6 mm dia. 3 mm long cylinder. The apparatus and its software were benchmarked by means of tests on Aluminum and Titanium, whose mechanical properties are well known, and later successfully applied to non-metallic materials like Nylon, Epoxy, Carbon fiber and glass fiber reinforced composites.
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Tanabe, Yuji, Takeo Tamura, Kenji Suzuki, Jiro Kuniya i Tetsuo Shoji. "Contributory Factors to Accurate Prediction of Rate of Stress Corrosion Cracking in Boiling Water Reactor Under Unexpected Condition During Operation: Part 3—The Effect of High Loading Rate on SCC Growth Behaviour". W ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/pvp2010-26136.
Streszczenie:
The goal of the study is to reveal the effect of high loading rate on the stable SCC growth behaviour of nuclear-grade stainless steel, SUS316L. To this end, the Split-Hopkinson pressure bar (SHPB) experiments on SUS316L were performed first to establish the dynamic tensile stress-strain response at strain rates up to 700s−1. The analyses of dynamic stress intensity factors for wedge loading experiments on modified compact tension specimens during SCC test were then performed by the finite element method. The outline of the wedge loading experiments by the use of the Split-Hopkinson pressure bar is briefly mentioned in this paper as well.
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Vallee, Glenn E., i Steven D. Army. "Determination of the Temperature Dependent Dynamic Response of Elastomeric Materials Using the Split Hopkinson Pressure Bar". W ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-13262.
Streszczenie:
An effective, low cost method of determining the temperature dependent dynamic response of elastomeric materials at high strain rates using the Split Hopkinson Pressure Bar (SHPB) is developed. The test system allows the determination of the dynamic modulus at temperatures up to 150°C with control of specimen temperature within ± 3°C without the use of specialized equipment or cumbersome heating and positioning fixtures often required for temperature dependent testing. The test specimen is heated using a low cost electric resistance tape, which heats the transmitter and incident bars adjacent to the specimen. A finite element analysis is performed to predict the temperature vs. time response of the test specimen, which is verified using a simple thermocouple arrangement. The dynamic stress-strain response of a nitrile elastomer, commonly used as an impact absorber, is investigated over temperatures ranging from 20°C to 110°C at strain rates between 3000/s and 3500/s. The effect of strain rate on the dynamic modulus is not significant, but the effect of temperature is dramatic. The dynamic modulus of the nitrile is reduced by more than 60% at 110°C.
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MESPOULET, JEROME, HAKIM ABDULHAMID, MAËLLE PEYRATOUT i PAUL DECONINCK. "DYNAMIC POLYMERIC FOAM EVALUATION TO MINIMIZE BEHIND ARMOR BLUNT TRAUMA (BABT): FROM MATERIAL CHARACTERIZATION TO SIMULATION VALIDATION". W 32ND INTERNATIONAL SYMPOSIUM ON BALLISTICS. Destech Publications, Inc., 2022. http://dx.doi.org/10.12783/ballistics22/36171.
Streszczenie:
This paper deals with the characterization of the dynamic behavior and the damping capability of a polymeric foam that is implemented on soldiers’ chest. Split Hopkinson Pressure Bars (SHPB) experiments have been performed at strain rates ranging from 420 to 5100 s-1. The effect of confinement on the deviatoric behavior of the material has been investigated through unconfined and confined experiments. The damping behavior was studied with the help of ballistic tests. Steel spheres were launched on the foam with an aluminum reference backing. 3D Digital Image Correlation (DIC) with two high speed cameras was set up to monitor the back-face deformation and evaluate the dynamic damping capability of the polymeric foam. At the end, a material model was calibrated using the results of the SHPB experiments and the simulation of the ballistic tests showed a very correction with the impact experiment
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Prabhu, Rajkumar, W. Glenn Steele, M. F. Horstemeyer, Stephanie Ryland, Erin E. Colebeck, W. R. Whittington, Lakiesha N. Williams i Jun Liao. "Uncertainty Analysis of the Mechanical Response of Porcine Brain at High Strain Rate Compression". W ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53738.
Streszczenie:
The Split-Hopkinson Pressure Bar (SHPB) apparatus presents a unique capability in studying the dynamic response of a material, but it is accompanied with a moderately high noise level, giving a rather large standard deviation for the stress-strain behavior of the soft biological material being tested [1]. Compounding the errors in a SHPB setup is the uncertainty arising from sample-to-sample variability in a soft biological material. Uncertainties arise in a measured variable through a vast number of sources such as an imperfect instrument calibration process, standards used for calibration, and the influence of the measured variable due to inconsistencies in ambient temperature, pressure, humidity and vibrations.
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Mahfuz, Hassan, Wahid Al Mamun, Hisham Mohamed, Uday Vaidya, Anwarul Haque i Shaik Jeelani. "High Strain Rate Response of Resin Infusion Molded Sandwich Composites". W ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0909.
Streszczenie:
Abstract Foam core sandwich composites have been tested under high strain rate (HSR) loading in the thickness direction. The regular Split Hopkinson Pressure Bar (SHPB) has been modified by replacing the steel transmitter bar by a polycarbonate bar. This modification resulted in stronger signals from the transmitter bar, which would otherwise be very feeble especially when testing soft materials. New sets of mathematical formulations have been derived to account for the impedance mismatch between the incidence and transmitter bars. The modified equations are first verified with a known material and then used for sandwich composites. Three types of core with various densities have been tested under compression at strain rates ranging from quasi-static to 1000 S−1. The compressive failure stress has been observed to be directly proportional to the core density, as well as to the strain rate. The strain rate sensitivity was moderate, and the sandwich composites mostly failed by the collapse of the foam-cell. Delamination did not play a major role in the failure process. Details of the mathematical derivations and the analysis of the HSR behavior are presented in this paper.
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MESPOULET, JEROME, HAKIM ABDULHAMID, MAËLLE PEYRATOUT i PAUL DECONINCK. "APPLICATION OF THE BUILDING BLOCK APPROACH (BBA) FOR LIGHT WEIGHT PERSONAL ARMOUR MATERIALS CALIBRATION". W 32ND INTERNATIONAL SYMPOSIUM ON BALLISTICS. Destech Publications, Inc., 2022. http://dx.doi.org/10.12783/ballistics22/36173.
Streszczenie:
This paper presents a lightweight armor structure calibration method. The armor consists of a stacking of two materials: a ceramic tile and a backing made of UHMWPE (Ultra High Molecular Weight Polyethylene) plate. Using a building block approach, each material is characterized separately before studying the response of the resulted structure under ballistic impact. For the ceramic material, Hugoniot and spall parameters are identified using plate impact tests. Then, data from dynamic confined compression tests on SHPB (Split Hopkinson Pressure Bars) are used to complete the model. The characterization of the composite backing is realized using a dynamic press (tension), SHPB (out-of-plane compression) and gas gun (out-of-plane shear). The out-of-plane shear configuration test has been specifically designed to highlight the behavior of the composite material. Experimental data are used to calibrate a non-linear orthotropic material model with damage for the composite plate and a JH-2 material model for the ceramic. Moreover, the modelling of inter-ply interaction appears to be predominant to correctly reproduce the ballistic behavior of UHMWPE. The model of each material has been validated in a ballistic test configuration using a sphere for the composite and a rod projectile for the ceramic. Additional tests were conducted to study the ballistic response of the stacking (ceramic tile + UHMWPE) with a more realistic 7.62mm projectile
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Miller, David A., i Cameron K. Chen. "Application of Advanced Constitutive Models to the Simulation of Machining". W ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-10842.
Streszczenie:
Advanced constitutive models have long been used to describe plastic material response at high strains and high strain rates. These models include the Johnson-Cook, Zerrelli-Armstrong and Material Threshold Stress (MTS) formulations, each with a separate fidelity. The constitutive parameters for these complex models are commonly identified using laboratory techniques such as quasi-static load frames at room and elevated temperatures, Split Hopkinson Pressure Bars (SHPB) in tension and compression, gas guns, and Taylor impact cylinders. However, while the models are able to adequately describe material response under high strain and high strain rate, the loadings are all uniaxial in nature. The ability of these constitutive models and parameters to describe a different dynamic loading event, namely shear dominated machining, has not been thoroughly investigated. This work will develop numerical simulations applying multiple constitutive models with material parameters experimentally determined for fully annealed copper samples. Ultimately, the machining simulation will be compared with high fidelity experimental machining data. The utility of this research extends to the fundamental questions that surround the machining process, such as tool forces, surface damage, precision and quality.
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Thomas, Tonnia, Hassan Mahfuz, Leif A. Carlsson, Krishnan Kanny i Shaik Jeelani. "High Strain Rate Response of PVC Foams". W ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/amd-25408.
Streszczenie:
Abstract In this study, cross-linked poly-vinylchloride (PVC) closed-cell foams were examined under high strain rate compression loading using a servohydraulic testing machine and a modified Split Hopkinson Pressure Bar (SHPB) apparatus with a steel incident bar and a polycarbonate transmitter bar for strain rates up to 2000 s−1. Three foam densities were examined, viz. 75, 130, and 260 kg/m3. The stress and strain-time history and stress-strain behavior were evaluated. An increase of stress and strain was observed for all categories of foam as strain rate increased. A post impact study was also performed to evaluate the failure modes of the foam cores. A densification band of collapsed cells was the major mode of failure.
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Daniel, Isaac M., i Shiguo Rao. "Dynamic Mechanical Properties and Failure Mechanisms of PVC Foams". W ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1957.
Streszczenie:
Abstract Two closed-cell PVC foams were characterized at strain rates up to 1000 s−1. Experiments in the strain rate range between 10−4 and 1 s−1 were conducted on a servohydraulic testing machine and those in the range between 1 and 103 s−1 were conducted on a modified Split Hopkinson Pressure Bar (SHPB) apparatus. The striker and input/output pressure bars in the latter were made of polycarbonate (Lexan) instead of metal. The polycarbonate material was tested at different strain rates and found to behave linearly for strain rates up to 1000 s−1. All stress-strain curves show typically five deformation stages, initial elastic deformation, nonlinear deformation up to a peak load, softening after the peak, a plateau and finally strain hardening corresponding to material densification. The initial modulus increases slightly with strain rate and both peak and plateau stresses increase with strain rate. The softening stage becomes longer with increasing strain rate, a fact attributed to heat generation during the adiabatic deformation. Failure mechanisms at different stages of deformation were identified by loading specimens to different strain levels and observing them by scanning electron microscopy. The initial elastic behavior corresponds to bending of the cell walls; nonlinear and softening behavior correspond to buckling of the cell walls; and densification results from collapse of the cells.