As the constant loss is known the efficiency can be predetermined at any load. Split hopkinson bar is an inexpensive device for performing high strainrate experiments. The hopkinson pressure bar was first suggested by bertram hopkinson in 1914 as a way to measure stress pulse propagation in a metal bar. The influence of strain rate over domains involving the thermal activation and the viscous drag behaviour of the dislocations is discussed.
The strain rate is found to be controlled by the stress and strain of the deforming specimen, geometry the length and diameter of. Baron model of social and emotional intelligence esi. A method commonly used to achieve this reduction in hopkinson bar tests is to curve the end of the striker bar as shown in figure 9. Theory the efficiency of the dc machine can be accurately determined by the regenerative method, normally known as hopkinsons test. Spectral analysis of wave propagation through a polymeric.
Building on the experience of hopkinson and davies 1948 and kolsky 1949 had independently devised the split hopkinson pressure bar shpb technique that is now commonly used for characterizing the dynamic. The driving theory tough ten 40% of learner drivers can. Test ptate bar incident bar transmitter bar free end,f 8 ft 7t 8 ft gr ep test plate bat bar 3 ifigure 1. Hopkinson pressure bar, is schematically shown in fig. Theoretical and experimental pressurevelocity data for striker bar of length. Beginning with raw voltages from two strain gages along with the incidenttransmitted bars mechanical and geometrical properties, the user can visually analyze forces. One of these two machines is operated as a generator to supply the mechanical power to the motor. Hopkinsons test is another useful method of testing the efficiency of a dc machine.
Limitations of the hopkinson pressure bar for high. The input to the motor is given by the supply mains. Theory the efficiency of the dc machine can be accurately determined by the regenerative method, normally known as hopkinson s test. It is a full load test and it requires two identical machines which are coupled to each other. Identification of constitutive model parameters in.
Torsion test techniques include lathe torsion testing machines, a torsional hydraulic actuator, impact torsion techniques and hopkinson torsion bar systems. The hopkinson bar technique is named after bertram hopkinson who, in 1914, studied the shape and evolution of stress pulses as a function of time as they propagated down a long rod. Split hopkinson pressure bar an overview sciencedirect topics. H output bar out t output bar specimen one force measurement output bar only l out out out c t l 2. High rate characterization of low impedance materials using a. Impacttension compression test by using a splithopkinson bar. Rocklike materials are composites that can be regarded as a mixture composed of elastic, plastic, and viscous components. One is acting as a motor and another one as a generator. In this method, the dc machine generator or motor is run as a motor at noload and losses of the machine are determined. Aug 03, 2018 hopkinsons test is another useful method of testing the efficiency of a dc machine. 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. Comparisons and contrasts to the differences invoked when using a tensile hopkinson bar in terms of loading technique, sample design, and stressstate stability, are discussed. 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. However, other hopkinson bar schemes have been devised to load samples in uniaxial tension, torsion, and to test fracture toughness of notched samples.
The specimen strain rate in the split hopkinson bar shb test has been formulated based on a onedimensional assumption. A typical shpb test system generally consists of a striker which is propelled by a gas gun, input bar, output bar, shock absorber and a data acquisition system, as shown in fig. Application of the split hopkinson resonant bar test for. Length of output bar duration of the experiment strategy.
Beyond hopkinsons bar philosophical transactions of the. The specimen is sandwiched between the transmission and incident bar. They exhibit viscoelasticplastic behavior under a highstrainrate loading according to element model theory. Xbar theory motivating intermediate projections ling 322 read syntax, ch. Electrical machines lab 1 griet eee 6 control the speed of a motor. Classic splithopkinson pressure bar testing mechanical. It has only been the last decade or so, however, that. Using the split hopkinson pressure bar to validate. Advancements in the split hopkinson bar test by michael adam kaiser abstract the split hopkinson bar test is the most commonly used method for determining material properties at high rates of strain.
By kevin young a thesis submitted to the faculty of graduate studies through the department of mechanical, automotive and materials engineering in partial fulfillment of the requirements for the degree of master of applied science at the university of windsor. Dynamic tensile strength enhancement of concrete in split hopkinson pressure bar test show all authors. Development of a tensile split hopkinson pressure bar testing facility. Using split hopkinson pressure bars to perform large strain compression tests on polyurea at low, intermediate and high strain rates jongmin shima, dirk mohra,b, aimpact and crashworthiness laboratory, department of mechanical engineering, massachusetts institute of technology, cambridge, ma 029, usa b solid mechanics laboratory cnrsumr 7649, department of mechanics, e. The development and use of a torsional split hopkinson bar testing apparatus for determining the mechanical properties of materials at high rates of strain is described. The technique was applied to investigate dynamic response in pure iron. Thus, this method is an economical and convenient method of testing of dc machines. Two types of ofhc copper were selected as specimen materials.
Split hopkinson pressure bar graphical analysis tool. Dynamic rock tests using split hopkinson kolsky bar. Hopkinson s test hopkinson s test is also known as regenerative test, back to back test and heat run test. This test overcomes the drawback of swinburnes test, which does not take any account of the stray load losses occurring in dc machines under loaded condition. Hopkinson bar technique v 0 striker split hopkinson pressure bar shpb experiment input bar specimen output bar two force measurements ain time h r 0,t ain hh0h,ttime ll inin,t2,t ain time h r t h l t l st l in 2l st c. Pdf design and characteristics of a split hopkinson pressure bar. Split hopkinson bar, which can test materials at strain rates as high as 2000 s1. Tittmann 2 proposed the use of additional mass in resonant bar tests to reduce resonance frequencies. The use of the direct impact hopkinson pressure bar. Our decision to begin this lecture series on modern social theory with the question what is theory. Hopkinson bar technique ut specimen v 0 striker direct impact experiment. The theory of a propagating wave through an iron wire by transferring the energy of a dropping weight was described.
Evolution of specimen strain rate in split hopkinson bar. The validity and applicability of the assumption made in the 1d hopkinson bar theory are discussed. A new impacttensioncompression testing technique based on a onedimensional elasticstresswave theory has been developed. Using split hopkinson pressure bars to perform large strain. Uncertainty analysis of kolsky bar strain gage output. Yongjian mao 1,2, yulong li, feifei shi1 1 school of aeronautics, northwestern polytechnical university, xian 710072, p. In the middle, the apparatus is the same as a conventional shtb system. Split hopkinson pressure bar shpb has become a frequently used technique to measure the uniaxial compressive stressstrain relation of various engineering materials at high strainrates.
To observe the plastic wave propagation, an experimental setup is designed with a shpb facility and a high speed digital camera. The method is based on threepoint bending tests at high loading rates, performed in an experimental device which is a modification of the classical split hopkinson pressure bar. Design customization and development of split hopkinson. The effects of alignment and bar curvature on response of polymeric test specimens have since been confirmed both experimentally and with the aid of dyna simulations using the portergould constitutive model.
Now there is an another method to determine the efficiency of a dc machines called as regenerative method or hopkinsons test method. On the plastic wave propagation along the specimen length. A matlabsimulinkbased method for modelling and simulation. Design of a split hopkinson bar apparatus for use with fiber. Advancements in the split hopkinson bar test vtechworks. Using split hopkinson pressure bars to perform large. Di erent designs have been used to load material specimens in compression or in tension. Conventional hopkinson bar analysis is invalid due to the viscoelastic nature of the polymeric bar material. The kolsky bar, also known as the split hopkinson bar chen and song, 2011, is an experimental apparatus used to test materials at high strain rates, usually in the order of 102 to 104 1s. Development of a hopkinson bar apparatus for testing soft.
Once the losses of the machine are known, its efficiency at any desired load can be determined in advance. At this point, the test carries on as in the standard hopkinson bar. The traditional kolsky bar or split hopkinson pressure bar consists of two long hardened steel bars aligned endtoend with the sample sandwiched in between the bars. We present a procedure for measuring the dynamic fractureinitiation toughness of materials. The hopkinson pressure bar is a measurement tool that has been used for a variety of applications, including measurement of high. In this method, speed control is possible from rated speed to low speeds. Some fundamental issues, such as stress wave dispersion effect, loss of contact, pulse shaping effect are still needed to thoroughly understand in hopkinson pressure bar loaded fracture experimental techniques. This paper presents an analytical solution for stress wave propagation in viscoelasticplastic rocklike materials under a highstrainrate loading and verifies. Build a compression split hopkinson bar apparatus to validate theory and prove. Regenerative or hopkinsons test in the previous post we have seen how to determine the efficiency of dc machines using the method swinburns test. Design details the split hiopkinson bar apparatus primarily consist of two major subsystems. The splithopkinson pressure bar shpb test is one of the most versatile methods. One of the machines is made to act as a motor driving the other as generator which supplies electric power to motor. Because this sample geometry is the same as the split hopkinson pressure bar test used primarily for largestrain, dynamic impact experiments, we call this technique the.
The specimen used can be made of solid bars or thinwalled tubes. A new impacttensioncompression testing technique based on a one dimensional elasticstresswave theory has been developed. Hopkinson bar testing of cellular materials a thesis submitted to the university of manchester for the degree of doctor of philosophy in the faculty of engineering and physical science 2010 elisavet palamidi school of mechanical, aerospace and civil engineering. Effect of stress wave dispersion on hopkinson pressure bar. Composite materials shawn lang a thesis submitted in. Numerical simulations of the kolsky compression bar test. One of these two machines is operated as a generator to supply the mechanical power to the motor and the other is operated as a motor to drive the generator. The main advantages of the swinburnes test are as follows. Elementary planewave propagation theory can be used for evaluating the. These techniques can provide a strain rate range between 10 2 and 10 4 s. The shtb apparatus consists of four bars, one dynamic strain recording set and a camera pack. With the impact of a striker at the free end of the input bar, a compressive longitudinal incident wave. Dynamic rock tests using split hopkinson kolsky bar system. Dynamic compressive and splitting tensile tests on mortar.
Dynamic tensile strength enhancement of concrete in split. A matlabsimulinkbased method for modelling and simulation of split hopkinson bar test. Articles 6 addressed a common design theory for any customization of shpb design that could result in acceptable calibration curves and stress wave shapes. It is this split hopkinson pressure bar set up that has been widely used in many research studies to characterize materials at dynamic loadings. Coupled with the loading device, a highspeed photography system was used to measure the crack mouth opening displacement. China 2 institute of structural mechanics, china academy of engineering physics, mianyang 621900, p. Determination of dc machine efficiency by backtoback test hopkinson test introduction. The apparatus is capable of generating a smooth torsional pulse with a risetime of approximately 20 microseconds and can be used to generate shear stressstrain. The splithopkinson pressure bar, named after bertram hopkinson, sometimes also called a kolsky bar, is an apparatus for testing the dynamic stress strain response of materials. The modern shpb system is widely used in the laboratory studies on stress waves in various types of solids such as metals, rocks, concrete, and so on.
In hopkinson test, two identical shunt machines are required which are coupled both mechanically and electrically in parallel. The stress, strain, and strain rate of a specimen during impact were evaluated with the aid of a stresswave. Stress wave propagation in viscoelasticplastic rocklike. Figure 1a shows a schematic of the basic compression apparatus.
This apparatus consists of four long pressure bars, i. The split hopkinson pressure bar shpb is also called the davies bar or the kolsky bar after those who developed the modern shpb system on the basis of the original hopkinson bar. A modified split hopkinson torsional bar system for. Experiment ends before leftward traveling wave in output bar reaches strain gage. For viscoelastic bars, accurately determining this propagation coef. While it is recognized that the koslkyhopkinson technique or split hopkinson pressure bar technique can generate data up to the upper strainrate limit of the thermalactivated regime, it is necessary to use a direct impact hopkinson pressure bar. The strain rate is found to be controlled by the stress and strain of the deforming specimen, geometry the length and diameter of specimen, impedance of bar, and impact velocity.
A polymeric hopkinson bar was developed enabling nonmetallic materials, such as polycarbonate and rubber, to be tested at strain rates from 500s. The experimental results of the loading wave agreed well with the theoretical prediction. The power required to test a large machine is small. A test is carried out by striking the end of the incident bar with a projectile fired from an air gun that sends an elastic wave down the bar, which then rapidly deforms the sample. In the shb test, the reflected pulse monitored in the input bar represents the specimen strain rate. The development and use of a torsional split hopkinson bar. While some emphasized that sociological theory or social theory is a i w hati st he or y. Hopkinsons test hopkinsons test is also known as regenerative test, back to back test and heat run test. The theory governing the specifics of hopkinson bar testing has been around for decades. Swinburnes test is the simplest indirect method of testing dc machines.
In 1914, his son bertram hopkinson 30 continued his work by using a long elastic bar to determine the pressures produced by the impact of a bullet or by a detonation of an explosive. High rate characterization of low impedance materials. Although there is no universal standard design for the split hopkinson pressure bar test apparatus, all split hopkinson pressure bars share common design elements 4. The split hopkinson bar shb,24,25 which is also called the kolsky bar, has been used extensively for measuring the uniaxial stressstrain curves of various materials at high strain rates 102 to 104 s 1. Determination of dynamic fractureinitiation toughness using. Pdf specimen size and shape effect in split hopkinson pressure. Evolution of specimen strain rate in split hopkinson bar test. Comparison of finite element results and split hopkinson pressure bar test results shows that the dynamic tensile strength enhancement of concrete materials is strongly influenced by the inertial effect. The split hopkinson bar test is the most commonly used method for determining material properties at high rates of strain.
This is a regenerative test in which two identical dc shunt machines are coupled mechanically and tested simultaneously. The strain rate is found to be controlled by the stress and strain of the. Shpb is suitable for high strain rate test in strain rate range of 102 to 104 s1. With the impact of a striker at the free end of the input bar, a compressive longitudinal incident wave was created and then travels along the bar. Schematic of split hopkinson bar the theory of uniaxial wave propagation through elastic media leads to the following relations. The accuracy of an shpb test is based on the assumption of uniaxial and uniform stress distribution within the specimen, which, however, is not always satisfied in an actual shpb test due to the existence of. Pdf the results from an experimental and computational study on the effects of specimen size and shape on split. However, as the strain gage data has discrete point, there will likely be a small di erence. Conventional hopkinson bar analysis is invalid due.