Hammer test

Ansbreiteprobe, /. (Metal.) flattening test, hammering test. 

The sensitiveness of an explosive to impact is measured by determining the minimum height from which a given weight must be dropped in order to initiate detonation. Many forms of fall hammer test have been devised, the most important point of the various designs being the means adopted for retaining the explosive. A simple and practical method, used at Ardeer for many years, is shown in Fig. 6.7. In this the explosive is put... 

Fall hammer test. A test of the sensitiveness of explosives to impact using a weight which falls vertically (see p. 69). 

DSC showed that exothermic decomposition (-1200 J/g) begins at about 110°C. A falling hammer test indicated shock induced decomposition. Considerable caution is advised when employing this useful reagent. 

Impact sensitivity varies widely from one chemical to another. Since it is not possible to test many chemicals with wide sensitivity ranges by a conventional drop hammer test, we have begun the trial use of a drop ball tester which allows us to change the weight of falling objects over a wide range 101. ... 

Takayuki Abe, Touru Hirayama, Tadao Yoshida, "Evaluation of Reactivity and Hazards of Oxidizing Agents (V), Drop Hammer Test of Oxidizing Agent and Red Phosphorus Mixture", Anzen Kogaku (J. of Japan Society for Safety Engineering), 26, 205(1987)... 

This equipment is modified from the 5kg drop hammer test equipment called for by Japanese Industrial Standards (JIS). A 5kg drop hammer was removed from the original equipment which was modified to attach 2kg and 5kg steel ball bearings. The front view of this equipment is shown in Figure 3.10. 

Some errors are unavoidable in impact sensitivity tests like the drop hammer test and drop ball test Important questions involve the precision and accuracy of acquired results. During the World War II in U.S.A., statistical investigations on drop hammer tests were carried out mainly by Professor Dixon 211 at the Bruceton Laboratory to achieve greater accuracy in determining impact sensitivity with the fewest trials. 

In the case of the drop hammer test using the up and down method, the drop height is decreased at certain intervals when the sample explodes or correspondingly is increased at certain intervals when the sample dose not explode. This procedure is carried out through several iterations. As the result of these trials, test heights are concentrated near the 50% explosion height, and it becomes possible to estimate the 50% explosion height. 

Methods A to E are drop hammer tests and F to I are drop ball tests. The order of amounts of energy necessary for explosion to occur is ... 

The drop hammer test was the most popular sensitivity test for explosives, but some problems existed with this evaluation. First, the range of sensitivity in this test is narrow therefore the sensitivity of many explosive materials or materials which have the potential to explode cannot be evaluated. Highly sensitive materials could not be distinguished because neither high now low sensitivity explosive materials could be... 

M4. Procedure This test is not done when the drop hammer test or the small gap test indicated high sensitivity on the part of the tested substance. A 5.0 g sample of the substance is placed in a 10 or 15ml sample tube. If the density of the substance is high, 10 ml Fig. 3.81 Cross-section of projector... 

Comparing the results of the small gap test and other sensitivity tests The data from conventional sensitivity tests for explosive materials and the sensitivities determined in the small gap test are shown in Fig. 3.118 - 3.120. The drop hammer test was the most popular test. The results are from the 50% explosion test carried out in USA. Fig.3.118 compares the experimental results with a 2.5 kg or 5 kg hammer in the type 12 drop hammer test machine at Los Alamos National Laboratory in the USA and the results from the small gap test A good correlation between these data 0 is obtained. Fig.3.119 compares the results in the small gap test and the results in the conventional test carried out at two laboratories in the USA. The open circles are data from the NSWC (National Surface Weapon Center), and the filled circles are data from the LANL (Los Alamos National Laboratory). 

The materials requiring less than 3 mm of critical gap width in the small gap test cannot be measured in a BAM friction test. More sensitive materials can be measured in both tests and show a reasonable correlation. But the correlation between the results of the drop hammer test and the friction test is not always good for the mixtures of oxidizer and fuel. Examples of this are shown in Fig.3.121. In these examples the samples demonstrate high blow sensitivities but low friction sensitivities or low blow sensitivities but high friction sensitivities. The interpretation of the results seems to indicate four possibilities. 

Regretfully, only two small gap tests of these mixtures were carried out The results of ammonium perchlorate - aluminiun powder - sulfur and potassium perchlorate -aluminium powder — titanium powder, are shown in Fig.3.97. The mixture of potassium perchlorate—aluminium powder is found to be highly sensitive. Considering the results of small gap test it seems reasonable that the class identified by the drop hammer test or the friction test should be 2 - 3 grade. 

For mixtures with median sensitivity, it is difficult to determine whether explosion happens or not in the drop hammer test. Variable initiator tests using the ballistic mortar(Sec. 3.3) are better. 

Most of mixtures of oxidizer and red phosphorus possess very high sensitivity. The results of drop hammer tests for this kind of mixture is shown in Sec.3.3. In the range of experiments, the mixtures of red phosphorus with bromite, chlorite and sodium peroxide possess very high sensitivity. 

Fig. 6.1 Drophammer in accordance with the BAM (a) and detailed sketch of the drop-hammer test with the two steel rollers, a hollow steel collar and a centring ring for fixation (b).

The h50 o/j value is directly correlated to the impact sensitivity and corresponds to the drop-height in cm, for which 50 % of the samples explode in a drop hammer test using a 2.5 kg mass (Tab. 8.1). In the equation above, y0, a, b and c are constants with the following values ... 

Ger for Falling Hammer Test). See IMPACT SENSITIVITY OR SHOCK SENSITIVITY TEST in Vol 1, p XVII and FI (Figure of Insensitiveness Test> described on p XII... 

Table 29. Drop hammer test with a 2 kg hammer, non-explosive height in cm for 50 trials...

Table 28. The classification of the sensitivity of fundamental two component compositions Table 29. Drop hammer test with a 2 kg hammer, nonexplosive height in cm for 50 trials Table 30. Friction test by Yamada s friction machine, non-explosive weight in kg for 50 trials...

Energetic materials can be made to react violently by relatively minor insults such as dropping a hammer a few feet [3,44-46]. This low velocity initiation (LVI) process can be unpredictable and is difficult to understand. LVI is often studied using a drop-hammer apparatus to determine a minimum height needed for a 50% chance of LVI of a particular energetic material (H50). The peak stress in a drop-hammer test is thought to be 1 GPa lasting for -250 i.s... 

In the experimental realm, several areas can be identified for future work. To better understand sensitivity, we need a better idea of what happens when energetic materials are subjected to mild insults. For example, more studies of what happens in a drop-hammer test seem warranted. These might include sub-critical experiments such as the studies of Sharma and co-workers [63,205] who analyzed the chemical composition and molecular structure of samples after subthreshold drop hammer impact, or real time IR imaging of hot spot formation such as the studies of Woody and co-workers [55,56]. For some reason, sub-critical experiments seem not very popular in the energetic materials community perhaps missing out on the big explosion is not satisfying enough. 

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