Impact machines

Petrin. The earliest reference to its prepn and use appears to be in German patents (Ref 1). Ref 15 gives its heat of explosion as 1204cal/g, and its impact sensitivity as 5 to 10 inches on the PicArsn impact machine (or roughly equivalent to Tetryl)... 

More recently, explosives have been tested for impact sensitivity by an impact machine in which 40 mg of explosive on sandpaper are placed between an anvil and a steel cylinder. A 2.5 kg weight is dropped from different heights and the sound produced serves to indicate a go or no go . The result from 25 drops is calculated to give a height at which the probability of explosion is 50%. Results from a compilation104 are presented in Table 12 and show that the relative values of TNT and picric acid are reversed from the previous table. TNT is relatively more sensitive on the Type 12 impact machine than in the FI impact test. TATB is so insensitive that it fails to explode at the maximum drop height of the machine. 

In what follows we will describe some impact machines and impact tests, ie the apparatus and methods for measuring impact sensitivity. We will then present and discuss impact sensitivity data for common explosives obtained with these machines by different laboratories. Then we will briefly consider how impact sensitivity tests have contributed to the development of the theory of initiation of explosives. Finally, we will examine impact testing from a theoretical point of view... 

Impact Machines and Impact Tests. One frequently hears the remark that there are as many types of impact machines as there are explosives test laboratories. This is somewhat misleading. In reality, all laboratories use essentially similar equipment but test procedures, and test data analyses differ. Basically an impact machine is an apparatus that drops a steel weight from a pre-determined height onto a plunger or striker resting on top of the test sample which is placed on a steel anvil... 

Brief mention of impact machines is made under Physical Tests in Vol 1, p XVII. Because there are many literature references to the following impact machines, and not because they are inherently better than any others, we will now describe the following Explosives Research Laboratory (ERL), Rotter, Bureau of Mines (BOM) Picatinny Arsenal (PicnArsn)... 

Fig 2. Drop Weight Impact Machine, ERL Model, type 12 tools... 

In addition to the impact machines just described, the search for a perfect impact machine has resulted in the development of many designs, most of which are not very different from each other, but are claimed to be improvements in the state of the art by their inventors. Below we list, in chronological order, references to and very brief descriptions of some of these machines... 

W. J. Powell et al, Ball and Disk Impact Machine, TransRoySoc A241, 287 (1948)... 

To understand what follows we must briefly digress and describe three impact machines constantly alluded to in the Russian literature-the so-called Kholevo No 1, No 2 No 3. Kholevo No 1 is quite similar to Kast s impact machine (see section on Impact Machines). The explosive sample is placed between a striker an anvil which are contained within a sleeve. Since striker anvil fit rather loosely into the sleeve there is a small air gap into which the explosive... 

An interesting consequence of the above considerations is the prediction that f-impact energy curves should be greatly flattened in impact machines having small diameter strikers. This prediction is based on the expectation that Pcr does not depend on h or... 

We have already alluded to the applicability of A B s impact model to the Weller impact machine. Below we examine the applicability of their ideas to other impact machines that also create rapid shear in the explosive samples. Let us consider the following tabulation (Table 11 of A B) where all the P s refer to compression stresses in the explosive... 

Kast, H (1869—1927). A Ger scientist who specialized in expls, and was for many years associated with the Chemisch-Technische Reichsaustalt. He designed an apparatus for the detn of brisance of expls (brisance meter), and developed a formula for theoretical calculations of brisance. Kast also developed an impact machine (Kast Stauchapparat) that was... 

PETN and RDX in a special vacuum impact machine. Their.results showed that gases developed on impact approximate mote closely those developed on thermal decomposition chan those on deton. The results are in harmony with the hypothesis of a thermal origin of impact-initiated explns and with the slow initial burning velocities observed with the rotating drum camera... 

In addition, there are a few more impact machines which are more relevant for the study of mechanism of initiation of ignition or explosion of HEMs on impact rather than their impact sensitivity. A lot of research in this direction has been carried out at the Cavendish Laboratory, Cambridge University, UK by Bowden, Yoffe, Field and their coworkers [53-59]. 

Eyster R.F, Davis, OSRD Rept 5744(1945) (One type of Drop-Weight Impact Machine developed in the US during WWII) 3) Ohart (1946), 48-9, 96, 131-32, 210 380-81 4) Anon, 11 Picatinny Arsenal Testing Manual", No 2—2 (1951), p 3 5) Glossary of... 

D) E.H. Eyster R.F. Davis, " Physical Testing of Explosives Part II, Sen sitivity Studies with the Drop-Weight Impact Machine", OSRD Rept 5744 (Dec 1945)... 

I). E.H. Eyster L.C. Smith, "Studies of the ERL Type 12 Drop-Weight Impact Machine at NOL", NOL Memo 10003(1949)... 

K) P.E. Braid R.C. Langille, " A New Type of Impact Machine for Evaluating Sensitiveness of Explosives , CanJTech 33, 28... 

Table 4.3 Figure of Insensitiveness (F of I )for some primary and secondary high explosives calculated from the results of the Rotter Impact Machine (5 kg falling weight on to 30 mg samples)...

Explosive substances can therefore be classified into three main groups using the results of the impact and friction sensitivity tests. These classes are very sensitive , sensitive and comparatively insensitive . By using the results of the tests carried out on the Rotter Impact Machine, explosive materials can be categorized into these three classifications as shown in Figure 4.2. 

Refs 1)W.H.Andersen R.F.Chaiken, Detonability of Solid Composite Propellants , Tech Memorandum of Aerojet-General Corp No809 (Jan 1959), Contract NOrd 17012, Task II and NOrd 18487 [A fundamental investigation of the factors involved in the detonation and abnormal (accelerating) deflagration of solid composite propints is described] 2)T.G.O.Berg, "Study of Susceptibility of Solid Composite Propellants to Explosion or Detonation , Aerojet-General Corp, Final Report No 0253-05(01)FP (April 1963) Contract NOrd 18487(FBM/Task 4) (A study of sensitivity to initiation of proplnts and expls by a modified Impact Machine)... 

Mercuric 5-Nitrotetrazole is a powerful primary expl It detonates at 7cm (2.5kg wt) on the Naval Surface Weapons Center impact machine, is sensitive to friction, and has an expin temp of 210°. All operations should be carried out behind a safety screen with the minimum exposure, by experienced personnel... 

The specimen is mounted in a grip, shown in Fig. 20.10, and placed in a standard impact machine. One adherend is struck with a pendulum hammer traveling at 11 ft/s, and the energy of impact is reported in pounds per square inch of bonded area. It is often difficult to achieve reproducible results with impact testing, and as a result, the test is not widely used in production situations. Impact data indicate that as the thickness of the adhesive film increases, its apparent strength also increases.11 This suggests that a portion of the energy required to rupture the bond is absorbed by the adhesive layer and is independent of adhesion. 

Impact resistance Relative susceptibility of plastics to fracture by shock, e.g., as indicated by the energy expended by a standard pendulum type impact machine in breaking a standard specimen in one blow. 

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