scholarly journals Explosion waves and shock waves Part II—The shock wave and explosion products sent out by blasting detonators

1935 ◽  
Vol 148 (865) ◽  
pp. 604-622 ◽  
Keyword(s):  
Picric Acid ◽  
Point Of View ◽  
Hopkinson Pressure Bar ◽  
Similar Measure ◽  
Explosion Products ◽  
Lead Plate ◽  
Logical Method ◽  
Metal Casing ◽  
Set Up ◽  
Pressure Bar

The detonation of a cartridge of a high explosive is started by firing a detonator, which consists of a small metal cylinder containing a compound or mixture which is itself readily detonated when it is heated. The manner in which detonators thus function is not thoroughly understood, and the methods used for measuring their "efficiency" are, in consequence, diverse. By some methods only the total blow given by the detonator, or its crushing and shattering effect, is measured; the nail test and sand test are the crudest forms. The lead plate test gives a similar measure, and the efficiency of a detonator is judged not only by the depth of the impression produced, but also by the number and appearance of radial grooves in the lead plate produced by the disrupted metal casing. More precise physical methods have been adopted, such as the Hopkinson pressure-bar , which gives a measure of the time of action of the impulsive blow. A more logical method of measurement of efficiency would appear to be a examine the ease with which the detonator will set up detonation in a standard explosive or in a series of standard explosives. Such a method is the Esop test , in which measurement is made of the maximum amount of olive or cotton seed oil which can be mixed with picric acid without preventing its detonation by the detonator embedded in the mixture. Of the same type is the gap test , in which the detonator and a standard explosive are separated and the maximum distance is measured at which detonation of the explosive can be established. The efficiency of a detonator is of considerable technical importance. The more rapidly a detonator can set up detonation in a cartridge of explosive the greater will be the proportion of the cartridge which will detonate and the greater therefore will be the efficiency of the explosive, though once detonation is effectively set up it will be independent of the strength of detonator used. The use of an inefficient detonator may result in portions of cartridges remaining undetonated and becoming a source of danger during the subsequent handling of the material that has been blasted. With the desensitized explosives that are used in coal mines the efficiency of the detonator may influence the safety of the explosive from the point of view of its ability to ignite firedamp. The present investigation has been carried out for that reason.

scholarly journals Experimental and numerical investigations on the use of polymer Hopkinson pressure bars

2014 ◽  
Vol 372 (2023) ◽  
pp. 20130201 ◽  
Author(s):  
John J. Harrigan ◽  
Bright Ahonsi ◽  
Elisavet Palamidi ◽  
Steve R. Reid
Keyword(s):  
Curve Fitting ◽  
Rheological Model ◽  
Split Hopkinson Pressure Bar ◽  
Fe Model ◽  
Hopkinson Pressure Bar ◽  
Hyperelastic Materials ◽  
Wave Separation ◽  
Derived Properties ◽  
Set Up ◽  
Pressure Bar

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.

Dynamic Progressive Collapse of Closed Cell Aluminum Foam

2006 ◽  
Author(s):  
Bazle A. Gama ◽  
Sergey L. Lopatnikov ◽  
John W. Gillespie
Keyword(s):  
Aluminum Foam ◽  
Progressive Collapse ◽  
Direct Impact ◽  
Hopkinson Pressure Bar ◽  
Closed Cell ◽  
Before And After ◽  
Set Up ◽  
Collapse Behavior ◽  
Multiple Impact ◽  
Pressure Bar

Progressive collapse behavior of closed cell aluminum foam under multiple-impact loading is presented. A direct impact Hopkinson pressure bar set up is developed to impact aluminum foam cylinders with a striker bar at a constant impact velocity. The total length of the specimen before and after impact is measured. The incident bar response is recorded, and average stress in the specimen is calculated. The incremental plastic strain and maximum strain rate is calculated from basic test parameters. It has been shown that by conducting direct impact experiments at variable impact velocities, it is possible to determine the dynamic behavior of closed cell metal foams at constant strain rates.

The Revolutionizing of the Revolution

2017 ◽  
Author(s):  
R. R. Palmer
Keyword(s):  
French Revolution ◽  
Point Of View ◽  
Strict Sense ◽  
French Government ◽  
Thing In Itself ◽  
Set Up ◽  
The Moment ◽  
The French Revolution ◽  
The Revolution

In 1792, the French Revolution became a thing in itself, an uncontrollable force that might eventually spend itself but which no one could direct or guide. The governments set up in Paris in the following years all faced the problem of holding together against forces more revolutionary than themselves. This chapter distinguishes two such forces for analytical purposes. There was a popular upheaval, an upsurge from below, sans-culottisme, which occurred only in France. Second, there was the “international” revolutionary agitation, which was not international in any strict sense, but only concurrent within the boundaries of various states as then organized. From the French point of view these were the “foreign” revolutionaries or sympathizers. The most radical of the “foreign” revolutionaries were seldom more than advanced political democrats. Repeatedly, however, from 1792 to 1799, these two forces tended to converge into one force in opposition to the French government of the moment.

Analysis of the Impact of the Frequency Range of the Tensometer Bridge and Projectile Geometry on the Results of Measurements by the Split Hopkinson Pressure Bar Method

2013 ◽  
Vol 20 (4) ◽  
pp. 555-564 ◽  
Author(s):  
Wojciech Moćko
Keyword(s):  
Test Bench ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Deformation ◽  
Spectral Width ◽  
Hopkinson Pressure Bar ◽  
Computing Environment ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact ◽  
Bench Model

Abstract The paper presents the results of the analysis of the striker shape impact on the shape of the mechanical elastic wave generated in the Hopkinson bar. The influence of the tensometer amplifier bandwidth on the stress-strain characteristics obtained in this method was analyzed too. For the purposes of analyzing under the computing environment ABAQUS / Explicit the test bench model was created, and then the analysis of the process of dynamic deformation of the specimen with specific mechanical parameters was carried out. Based on those tests, it was found that the geometry of the end of the striker has an effect on the form of the loading wave and the spectral width of the signal of that wave. Reduction of the striker end diameter reduces unwanted oscillations, however, adversely affects the time of strain rate stabilization. It was determined for the assumed test bench configuration that a tensometric measurement system with a bandwidth equal to 50 kHz is sufficient

scholarly journals On Kaufmann's theory of the impact of the pianoforte hammer

1920 ◽  
Vol 97 (682) ◽  
pp. 99-110 ◽  
Keyword(s):  
Initial Conditions ◽  
Practical Importance ◽  
Prima Facie ◽  
Point Of View ◽  
Infinite Length ◽  
Modes Of Vibration ◽  
Rigorous Treatment ◽  
The Subject ◽  
Set Up ◽  
The Impact

The theory of the vibrations of the pianoforte string put forward by Kaufmann in a well-known paper has figured prominently in recent discussions on the acoustics of this instrument. It proceeds on lines radically different from those adopted by Helmholtz in his classical treatment of the subject. While recognising that the elasticity of the pianoforte hammer is not a negligible factor, Kaufmann set out to simplify the mathematical analysis by ignoring its effect altogether, and treating the hammer as a particle possessing only inertia without spring. The motion of the string following the impact of the hammer is found from the initial conditions and from the functional solutions of the equation of wave-propagation on the string. On this basis he gave a rigorous treatment of two cases: (1) a particle impinging on a stretched string of infinite length, and (2) a particle impinging on the centre of a finite string, neither of which cases is of much interest from an acoustical point of view. The case of practical importance treated by him is that in which a particle impinges on the string near one end. For this case, he gave only an approximate theory from which the duration of contact, the motion of the point struck, and the form of the vibration-curves for various points of the string could be found. There can be no doubt of the importance of Kaufmann’s work, and it naturally becomes necessary to extend and revise his theory in various directions. In several respects, the theory awaits fuller development, especially as regards the harmonic analysis of the modes of vibration set up by impact, and the detailed discussion of the influence of the elasticity of the hammer and of varying velocities of impact. Apart from these points, the question arises whether the approximate method used by Kaufmann is sufficiently accurate for practical purposes, and whether it may be regarded as applicable when, as in the pianoforte, the point struck is distant one-eighth or one-ninth of the length of the string from one end. Kaufmann’s treatment is practically based on the assumption that the part of the string between the end and the point struck remains straight as long as the hammer and string remain in contact. Primâ facie , it is clear that this assumption would introduce error when the part of the string under reference is an appreciable fraction of the whole. For the effect of the impact would obviously be to excite the vibrations of this portion of the string, which continue so long as the hammer is in contact, and would also influence the mode of vibration of the string as a whole when the hammer loses contact. A mathematical theory which is not subject to this error, and which is applicable for any position of the striking point, thus seems called for.

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