Meyer R., Koehler J., Homburg A. Explosives. Wiley-VCH, 2002 / Explosives 5th ed by Koehler, Meyer, and Homburg (2002)

Strength

Arbeitsvermögen; force

Also W Bulk Strength, Weight Strength.

The performance potential of an explosive cannot be described by a single parameter. It is determined by the amount of gas liberated per unit weight, the energy evolved in the process (W Heat of Explosion), and by the propagation rate of the explosive (detonation velocity W Detonation). If an explosive is to be detonated in a borehole, the relevant parameter is its “strength”; here the criterion of the performance is not so much a high detonation rate as a high gas yield and a high heat of explosion. If, on the other hand, a strong disintegration effect in the nearest vicinity of the detonation is required, the most important parameters are the detonation rate and the density (W Brisance).

A number of conventional tests and calculation methods exist for determining the comparative performance of different explosives. The determinations of the detonation rate and density require no conventions, since they are both specific physical parameter.

Lead block test and ballistic mortar test

Practical tests for comparative strength determination are the lead block test and the declination of a ballistic mortar. In both cases relatively small amounts of the explosive (of the order of 10 g) are initiated by a blasting cap. In the lead block test, the magnitude measured is the volume of the pear-shaped bulge made in the block borehole by the sample introduced into it; in the ballistic mortar test the magnitude which is measured is the deflection angle; this angle is taken as a measure of the recoil force of a heavy steel weight suspended as a pendulum bob, after the exploding cartridge has fired a steel projectile out of a hole made in the bob. The performance of the explosive being tested is reported as the percentage of that of W Blasting Gelatin, which is conventionally taken as 100% (For further details W Ballistic Mortar). In both cases the explosive is enclosed in a confined space, so that, for all practical purposes, the parameter measured is the work of decomposition of an explosive in a borehole. The disadvantage of both methods is that the quantity of the sample used in the test (exactly or approximately 10 g) is quite small, and for this reason accurate comparative data can be obtained only with more sensitive explosives; less sensitive materials require a longer detonation development distance (W Detonation), within which a considerable proportion of the 10-g sample does not fully react. Practical methods for determining the performance of explosives requiring much larger samples (up to 500 g) include the following.

Jumping mortar test

Two halves with finely ground surfaces fitting exactly onto one another form a mortar with a borehole. One of the halves is embedded in the ground at a 45° angle, while the other half is projected like a shot, when the explosive charge is detonated in the hole; the distance to which it has been thrown is then determined. A disadvantage of the method is that when high-brisance explosives are tested, the surfaces must be reground after each shot. The method gives excellent results with weaker W Permitted Explosives.

Vessel mortar test

This test is also based on the determination of the range distance of a heavy projectile. The explosive is suspended in a thick-walled vessel, and an accurately fitting cap of the vessels is projected. This apparatus is stronger, and the weight of the charge may be made as large as 500 g.

Large lead block test

The device consists of a lead block with linear dimensions three times as large as normal. The block has been used to obtain information about slurries; the method is too expensive for practical work, since more than one ton of lead must be cast for each shot.

The crater method

This method is based on the comparison of the sizes (volumes) of the funnels produced in the ground by underground explosions. It is used for explosives with a large critical diameter only if no other method is available, since it is inaccurate and the scatter is large.

W Aquarium Test

The sample is exploded under water (in a natural water reservoir or in a man-made pool), and the pressure of the resulting impact wave is measured with the aid of lead or copper membranes.

W Specific Energy

For calculations of performance parameters of explosives W Thermodynamic Calculation of Decomposition Reactions. As far as the strength of propellants and explosives is concerned, the most relevant thermodynamically calculable parameter is the W Specific Energy. This is the amount of energy which is released when the gases in the body of the explosive (assumed to be compressed in their initial state) are allowed to expand at the explosion temperature while performing

Fig. 22. Specific energy and relative weight strength in relation to lead block test values.

useful work. In order to illustrate the working performance obtainable from explosive materials, this magnitude is conventionally reported in meter-tons per kilogram; in this book, it is also given in joules (J).

The calculated values of the specific energy agree well with the performance data obtained by conventional tests. This is particularly true of the tests in which larger samples are employed, but the apparatus required for such tests is nor always available, and the tests themselves are relatively expensive.

The following empirical formula relating the specific energy to the relative weight strength is valid in most cases:

weight strength (%) = 0.0746 Vspec. energy (in mt/kg)

The relationship between the size of the lead block excavation and the specific energy is not linear. The true relationship may be seen in Fig. 22 (representation of experimental results).

The relationship between weight strength and the coefficient d’utilisation pratique (c.u.p) used in France (W Lead Block Test) can be given by the empirical formula weight strength (%) = 0.645 V(%) c.u.p. and

(%) c.u.p. = 1.55 V(%) weight strength.

Strontium Nitrate

Strontiumnitrat; nitrate de strontium

Sr(NO3)2

colorless crystals molecular weight: 211.7 oxygen balance: +37.8% nitrogen content: 13.23%

Strontium nitrate is used in pyrotechnics as a flame-coloring oxidizer for red-colored fireworks.

Styphnic Acid

trinitroresorcinol; 2,4,6-trinitro-1,3-dihydroxybenzene; Trinitroresorcin; trinitroresorcinol;´ acide styphnique; Trizin; TNR

yellow-brown to red-brown crystals empirical formula: C6H3N3O8 molecular weight: 245.1

energy of formation: – 493.1 kcal/kg = –2063.1 kJ/kg enthalpy of formation: –510.0 kcal/kg = –2133.8 kJ/kg oxygen balance: –35.9%

nitrogen content: 17.15%

volume of explosion gases: 814 l/kg heat of explosion

(H2O liq.): 706 kcal/kg = 2952 kJ/kg (H2O gas): 679 kcal/kg = 2843 kJ/kg specific energy: 89 mt/kg = 874 kJ/kg

density: 1.83 g/cm3

melting point: 176 °C = 349 °F lead block test: 284 cm3/10 g

Supercord 40 and Supercord 100

Trade names of W Detonating Cords containing 40 and 100 g PETN/m distributed in Germany and exported by DYNAMIT NOBEL. It is covered with red-colored plastic. It is used for the initiations of ANFO blasting agents and for W Contour Blasting.

Surface Treatment

Oberflächenbehandlung; traitement de surface

When gunpowder burns in the chamber of a weapon, the internalballistic energy of the powder charge is best exploited if the gas pressure is kept constant almost up to the emergence of the projectile from the barrel, despite the fact that the gas volume keeps growing larger during that reriod, owing to the movement of the projectile. It follows that gas evolution from the powder charge should be slow at first, while towards the end of the combustion process, it must be quicker (“progressive burning”). This is achieved mainly by imparting a suitable shape to the powder granule (in a seven-hole powder, the surface area increases during combustion, and the combustion is therefore progressive); progressive combustion is also enhanced to a considerable extent by surface treatment, i.e., by allowing phlegmatizing, combustionretarding substances (such as Centralit, dibutyl phthalate, camphor, dinitrotoluene, etc.) to soak into the powder. A careful surface treatment is an excellent way of keeping the maximum pressure peak of the combustion curve low.

Susan Test*)

The Susan Sensitivity Test is a projectile impact test. The explosive to be tested is loaded into a projectile shown in Fig. 23 and thrown against a steel target. The reaction on impact is recorded by measuring the shock wave pressure by a gauge 10ft (3.1 m) away. The percentage of the reaction (0 = no reaction; 40 = fast burning reactions; 70 = fully reacted TNT; 100 = detonation) is plotted against the projectile velocity (0 to 1600 ft/s = 488 m/s). W Plastic Explosives with rubberlike binders give better results than cast RDX/TNT mixtures.

*Information, results, and figure obtained from Brigitta M. Dobratz, Properties of Chemical Explosives and Explosive Simulants, publication UCEL-51319, University of California, Livermore.

Fig. 23. The Susan projectile.

Fig. 24. Test results.

Sympathetic Propagation

W Detonation, Sympathetic Detonation

Taliani Test

An improved version of the manometric test developed by Obermüller in 1904. The method was considerably modified, first by Goujan and, very recently, by Brissaud. In all modifications of the method, the test tube containing the sample preheated to the desired temperature is evacuated, and the increase in pressure produced by the gaseous decomposition products is measured with a mercury manometer. The test is usually terminated when the pressure has attained 100 mm Hg. The test temperature are:

The sample must be thoroughly dried before the test; the result would otherwise also include all other components which increase the pressure on being heated, such as water and organic solvents. Since the result is also affected by the nitroglycerine content of the propellant sample, the test can only be used in order to compare propellants of the same kind with one another. This, in addition to the high testing temperature, makes the applicability of the Taliani test for propellants questionable. Another disadvantage is the necessity for thorough drying, since in the course of the drying operation the test sample is altered in an undesirable manner, and the experimental stability data may show better values than its true stability. The latter disadvantage does not apply to nitrocellulose testing.

Tamping

Verdämmen; bourrage

Synonymous with W Stemming

Tamping Pole

Ladestock; bourroir

A wooden or plastic pole used to compact explosive charges for stemming.