A pulseshaped split hopkinson pressure bar shpb, modified for lowimpedance material testing, was used to ensure that the samples deformed under dynamic equilibrium and at a nearly constant strainrate. A detailed experimental study was conducted in designing cylindrical pulse shapers for testing various types of materials using split hopkinson pressure bar shpb test setup. Tests were conducted three times to confirm the repeatability of experimental. Split hopkinson pressure bar for soft materials 123 soft materials, have been utilized in the hopkinson bar experiments on polymeric foams and rubbers 11, 50. A kolsky bar experiment is the most commonly high strain rate. The split hopkinson pressure bar shpb has been in use for many years to measure the compression response, principally of metals, but also more recently for much softer materials such as polymers. For instance, application of polymeric bars 2,7, 8 or hollow metallic transmission bar 9 in the split hopkinson pressure bar shpb experiments has been proposed with the purpose of reducing. High strain rate tests were conducted using a split hopkinson pressure bar system built for the purpose. Kolsky bars can be constructed to conduct experiments in tension or compression, both of which are studied in this paper. As this foam cures at room temperature and in ambient air conditions, the liquid mixture was sprayed at the samples surface and pressed carefully into the entire cellular structure. Among various dynamic testing techniques, the split. Split hopkinson pressure bar shpb testing has traditionally been carried.
Splithopkinson pressure bar test and numerical simulation. Department of aerospace and mechanical engineering, the university of arizona, 1 n mountain avenue, tucson, az 857210119, usa. Characterization and constitutive modeling of polymeric. Crushing of the polymeric foam cores is the main method in which blast energy is absorbed during underwater blast scenarios. Characterization of anisotropic polymeric foam under. Brief introduction of split hopkinson pressure bar shpb alt. In order to experimentally obtain valid dynamic material properties of polymeric foams with split hopkinson bars, necessary modifications on the technique are necessary. The system uses the friction between the specimen and the pressure bars to apply the. Numerical analysis on usability of shpb to characterize. Inderscience publishers linking academia, business and. Split hopkinson pressure bar experiments on polymeric foams article in international journal of vehicle design 3723 january 2005 with 91 reads how we measure reads. Experimental stressstrain curves for aluminium aa1050o for different values of strainrate. Technical points of the strain field measurement on the basis of high speed. Polymeric foams are used for impact protection due to their ability to absorb large amounts of strain energy.
It can be imagined that the resolution of the measured. Hopkinson pressure bar shpb, originally developed by. For this purpose, a bevelled end is cemented to the input bar and the output bar are rotatable to be parallel to the inclined plane of the bevelled end. The split hopkinson pressure bar shpb technique is most commonly used in this situation as it covers a broad range of high strain rates. A split hopkinson bar method for testing materials with. Intermediate strain rate tests were conducted in a servohydraulic machine. Split hopkinson pressure bar testing of soft materials, asm handbook, vol 8, mechanical testing and evaluation, asm int. A tensile split hopkinson bar for testing particulate polymer composites under elevated rates of loading a. Splithopkinson pressure bar testing of soft materials mechanical.
Split hopkinson pressure bar shpb tests were performed only on the three grades of san foam used in the underwater panels. Strain rate dependent compressive response of open cell. This was performed in order to understand the extent of energy absorption, and the benefits of using a graded density foam core in underwater blast. High strain rate tests 10 3 s 1 were conducted in a split hopkinson kolsky pressure bar shpb. Jiang international journal of vehicle design ijvd, vol. The highstrainrate compressive behavior of an epoxy syntactic foam is examined in this study.
The splithopkinson pressure bar technique is named for bertram hopkinson ref 7 who. The challenges in split hopkinson bar testing technique modified for. Split hopkinson pressure bar shpb experiment input bar specimen output bar two force measurements ain time h r 0,t ain. High strain rate tests were conducted under strain control using a split hopkinson pressure bar shpb system made of polymeric polycarbonate bars. Dynamic stress equilibrating process in a rubber specimen during a split hopkinson pressure bar experiment, experimental. Using the split hopkinson pressure bar to validate material models.
To test weak materials such as foams at high strain rates, the use of a split hopkinson pressure bar shpb setup made of low impedance bars, which are mostly viscoelastic, is indispensable. Dynamic mechanical behaviour of polymer materials intechopen. The detailed experimental technique and analyses are well documented and there have. Nylon hopkinson bar methods and the associated data processing are briefly recalled in section 2. Fe analysis of critical testing parameters in kolsky bar. A novel approach to studying these processes is to compare finite element. Especially for a flexible polymer, the extremely low wave impedance and considerable deformation strain result in the challenge for dynamic. Polymers free fulltext studying a flexible polyurethane. Split hopkinson pressure bar experiments on polymeric foams. Pulse shaping is necessary to ensure valid testing conditions. Elastomeric polyurethane foams incorporated with nanosized. High rate compressive behaviour of a dilatant polymeric foam. The polycarbonate material has an impedance that is closer to that of foam than metals and results in lower noise to signal ratios and longer loading pulses.
Characterization and constitutive modeling of polymeric foams under static and. However, the disadvantage of using polymeric bars is their low heat. This paper carries out a split hopkinson pressure bar shpb test on the steel fiber and highstrength concrete, two main components of the sfrhsc, aiming to disclose the failure features and dynamic compressive strength of the sfrhsc under dynamic conditions. Testing of polymeric foams at high and medium strain.
Split hopkinson pressure bar experiments on polymeric foams by b. High strain rate tests were conducted using a split hopkinson pressure bar kolsky bar system made of polycarbonate bars having an impedance compatible to that of the foam material. This shpb system was made of polymeric polycarbonate bars. Using the split hopkinson pressure bar to validate. A viscoelastic polymeric split hopkinson pressure bar shpb was used as a means of determining the dynamic characteristics of lowimpedance or soft materials. Split hopkinson bar techniques for characterizing soft. A polymeric split hopkinson pressure bar instrumented with. Accurate average stressstrain relations can be obtained when soft large diameter polymeric pressure bars. Split hopkinson pressure bar an overview sciencedirect topics. Split hopkinson bar experiments are fundamental test arrangements to determine elastic, plastic, and fracture properties of materials under high strain rates. Characterization of polymeric foams under multiaxial. The polycarbonate material has an impedance that is closer to that of foam than metals.
The present work introduces and all polymeric split hopkinson bar apshb experiment, which overcomes these limitations. Here we describe a dynamic stress relaxation experiment using a specially configured split hopkinson pressure bar with a corresponding timescale of microseconds. The present investigation aims at testing polymeric foam under impact loading using large diameter nylon hopkinson bars and optical field measurements. Polymeric foams are an essential part of personal protection equipment, such as helmets and body armor. A tensile split hopkinson bar for testing particulate. The hopkinson pressure bar was first suggested by bertram hopkinson in 1914 as a way to measure stress pulse propagation in a metal bar. Classic splithopkinson pressure bar testing mechanical testing. Split hopkinson pressure bar an overview sciencedirect. In brief, the kolsky bar, sometimes referred to as the split hopkinson pressure bar, is an experimental apparatus used to study the mechanical properties of materials at high strain rates. Hopkinson bar is an effective experimental device to study the dynamic mechanical properties of materials under onedimensional stress state. Split hopkinson pressure bar for soft materials 119 in both rtv630 rubber and epoxy foam cases, it is not possible to use the average deformation to represent the pointwise deformation in specimen. The relevance of the present method for establishing mechanical response of polymeric foam is also demonstrated. In this work, the compressive response of an open cell polyurethane foam currently used as liner in the advanced combat helmet is examined across strain rates.
They conducted plate impact experiments to measure the pressuretime curves by a. The split hopkinson pressure bar shpb has been in use for many years to. Split hopkinson pressure bar techniques for characterizing soft. Impact testing of polymeric foam using hopkinson bars and. Dynamic compression testing on polymeric foams jstor. These mechanisms are observed insitu during compression experiments using highspeed photography, and linked back to stressstrain responses of the materials. Since the split hopkinson pressure bar was first adapted for tensile loading, extensive research has been completed. A novel approach to studying these processes is to compare finiteelement. So, it can be used in the shb experiment to test the soft polymer materials. Design, testing, and applications, springer 388 pages. Split hopkinson pressure bar techniques for characterizing.
A traditional load frame is used to investigate the quasistatic behavior, and two different modifications of a. The split hopkinson pressure bar shpb is a mature method and a commonly used apparatus to accurately test the dynamic compression properties of various materials at strain rates ranging from 100s to 0s. Attempts to apply the split hopkinson bar in measurement on more compliant materials, such as plastics, rubbers and foams, suffer from limitations on the maximum achievable strain and from high noisetosignal ratios. Pulse shaping techniques for testing elasticplastic. The splithopkinson pressure bar shpb test is one of the most versatile methods for determining the. Dynamic compressive response and failure behavior of an. Department of aerospace and mechanical engineering, the university of arizona, 1 n mountain. Characterization and constitutive modeling of polymeric foams under static and dynamic loading. Split hopkinson pressure bar shpb technique is the most important test method to characterize dynamic stressstrain relations of various materials at different strain rates, and this technique requires uniform deformation of specimen during the experiment.
In this paper, an optical field measurement along with large diameter nylon hopkinson bars is highlighted in the experimental setup for the polymeric foam characterization. The system was analyzed and calibrated to account for the viscoelastic response of its bars. Hopkinson bar experiment typical system characteristics. This data has been used to investigate a common foam constitutive model, and shows that strain rate effects become more pronounced at rates above approximately s. Proper modifications are required when a split hopkinson pressure bar shpb is used to determine the dynamic compressive properties of polymeric foams. Dynamic mechanical properties of polyvinyl alcohol. Highrateloading experiments provide the critically needed data required for the development of. Among various dynamic testing techniques, the split hopkinson pressure bar shpb, originally developed by kolsky 7, is the only method that provides the.
A modified split hopkinson pressure bar shpb device was used to. Dynamic compression testing on polymeric foams request pdf. Split hopkinson pressure bar experiments on polymeric. Dynamic characterization of compliant materials using an. This paper provides the necessary information for conducting a hopkinson bar experiment and analyzing the experimental data. It is thus critical to understand their dynamic response and to accurately determine their elastic modulus, yield stress and strength under high strain rates 1. This paper presents a new method based on the split hopkinson pressure bar shpb to perform impact combined shearcompression test for cellular materials. A pulse shaping technique was used with a split hopkinson pressure bar to ensure homogeneous deformation in the foam specimens under dynamic compression. Deformation to fracture evolution of a flexible polymer.
To avoid these uncertainties in experimental data, magnesium bars and. Split hopkinson pressure bar testing of soft materials. A polymeric split hopkinson pressure bar apparatus was used to achieve strain rates from 500 to 2500s. Experimental and numerical investigations on the use of polymer. The split hopkinson pressure bar was designed to produce uniform deformation, high strain rate, uniaxial conditions. Effect of aspect ratio of cylindrical pulse shapers on force equilibrium in hopkinson pressure bar experiments. Polymeric foam, impact testing, hopkinson bars, highspeed imaging, digital image correlation. High strain rate tests were conducted using a split hopkinson pressure bar system built for the purpose using polymeric polycarbonate bars. The dynamic compressive stressstrain behavior of a rigid polyurethane foam with four values of density 78, 154, 299, and 445 kgm 3 has been determined in the strainrate range of 5000 s. Determination of dynamic elastic modulus of polymeric. In a conventional bar system the signals that immediately follow the accumulation of sample strain are typically overwritten by reflected waves within the input and output bars. A finite element model of the hopkinson bar experiment is developed in threedimensions and is used in detailed numerical analyses. A split hopkinson pressure bar technique for measuring the. Quasistatic and intermediate strain rate tests were conducted in a servohydraulic testing machine.
Split hopkinson pressure bar for soft materials 141 figure 21. The implications of these experiments on opencell, porous metals, and closed and opencell polymer foams are described. Compressive response of polymeric foams under quasistatic. There are also novel methods of measuring the strains directly on the. A pulseshaped split hopkinson pressure bar shpb, modified for lowimpedance material testing, was used to ensure that the samples deformed under dynamic equilibrium and. Later, in 1949 herbert kolsky refined hopkinsons technique by using two hopkinson bars in series, now known as the splithopkinson bar, to measure stress and strain. It can directly test the stress and strain of samples under dynamic impact state. Crushing of the polymeric foam cores is the main method in which blast energy is absorbed. Hopkinson bar experiments as a method to determine impact.
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