GB2242008A

GB2242008A - A munition containing confined explosive charge

Info

Publication number: GB2242008A
Application number: GB8823816A
Authority: GB
Inventors: Guy Couturier; Andre Winaver
Original assignee: Thomson Brandt Armements SA
Current assignee: Thomson Brandt Armements SA
Priority date: 1987-10-13
Filing date: 1988-10-11
Publication date: 1991-09-18
Anticipated expiration: 2008-10-11
Also published as: IT1235718B; GB2242008B; IT8867860A0; GB8823816D0; FR2656085B1; SE8803610D0; DE3834754A1; SE8803610L; FR2656085A1

Abstract

A munition (1) containing a confined explosive (12), is protected against a significant temperature increase such as that which would result from a fire. The envelope (10) of the munition (1) is provided with a zone (2, 3, 6) rendered so fragile that, during a temperature increase, the pressure buildup due to the decomposition of the explosive (12) produces an opening in the envelope (10), thus achieving a mechanical deconfinement of the explosive (12). In addition, the explosive (12) is chosen so that the kinetics of the decomposition-detonation be sufficiently slow for the mechanism of deconfinement to be effective before the explosion. In particular, an explosive of the composite type with a flexible binder is suitable. The fragile zone may be a solder join (2) between two parts of the envelope, fusible nut/bolt attachments, or fusible threaded inserts for attaching cheek (11) to envelope (10). Also, the cheek (11) may be attached by a crimp which is calibrated to fail at a safe internal pressure. <IMAGE>

Description

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present invention relates to munitions containing confined explosives, such as bombs. It applies more particularly to their protection against a significant temperature increa- se as would result from a fire.

During a fire occuring, for example, in a munition compartment, there is a significant temperature increase which is transm.itted to the munitions. The explosive contained in a munition, as is known, breaks down under the action of heat the material initially solid becomes progressively gaseous as the internal temperature and pressure increase, up to a certain point where the compound becomes detonating. The temperature at which decomposition begins and that at which detonation occurs depend on the explosive being considered.

Various methods are already known that aim at protecting explosive munitions from the effects of fire. One of these methods 'Consists in retarding the temperature increase of the explosive and consequently the detonation by equipping the munitions with thermal protections. These protections may be placed outside or inside the munition. When they are placed outside thev impair the streamline of the munition. Moreover, they are fragile. When the thermal protections are placed in- side the munition, they occupy a volume that could be available for the explosive and the munition suffers a decrease in efficiency.

9 is Another approach consists in trying to avoid the detonation by deconfining the explosive, i.e., by opening at least partially the cavity that contains the explosive. Various means triggered by the temperature increase, in particular pyrotechnic means, are known as, for example, the thermally triggered striking devices. When, in case of fire for example, the explosive is thus deconfined, the surface thereof which is in open air burns and it is assumed that if the opening thus created has a sufficient area, the probability of detonation is highly decreased.

However, this solution, as the previous one, takes a certain volume inside or outside the munition. In addition, its efficiency is not certain.

An object of the present invention is accordingly an explosive munition allowing to avoid the above mentioned disadvantages.

Thus, according to the present invention there is provided a munition comprising an envelope and an explosive charge confined in said envelope, said envelope comprising a fragile zone which becomes fragile with an increase in temperature and which-is capable of separating under the action of an internal pressure build up produced by the charge itself in response to the increase in temperature, thereby causing the opening of said envelope and the deconfinement of said explosive charge, said explosive being such that its kinetics of decomposition detonation is sufficiently slow to allow said deconfinement to take place before the explosion.

In particular, an explosive of the composite type with a flexible binder is suitable.

1 1 1 .#. 3.

Other objectsq features and advantages of the present in- vention will become apparent from the following detailed des-- cription given as a non-limitative example with reference to the accompanying drawings, in which: -- - Figure 1 is a schematic sectional view cf a munition in which the present invention is embodied; - Figures 2 to 7 are schematic views of various einbodionents of the fragile zone of the envelope of a munition in which the present invention is embodied.

In the Figures, like reference numerals denotes like elements.

Referring to Figure 1, there is shown in schematic sectional view an explosive munition in which the present inven- tion is embodied.

The munition, denoted as a whole by 1, is for example a bomb. It has a longitudinal axis ZZ and comprises essentially an envelope 10 and an explosive charge 12 confined in this envelope. The envelope 10 has a shape generally streamlined and it is closed at the rear end, for example by a cheek 11.

The envelope 10 of the munition includes at least a fragile zcne allowing the opening of the envelope in view of the deconfinement of the explosive during a temperature increase, under the action of the pressure buildup. The fragility of the zone in question must furthermore be compatible with the structural strength required for the operational conditions c'$ the munition (handling, acceleration during flight, vibratcry environment and resistance to impact).

i,:

% 4 r- The explosive 12 used is an explosive whose kinetics of decomposi t ion-detonat ion, i.e., the evolution of the explosive with time from the beginning of the - decomposition to the detonatici, is sufficiently slow for the deconfinement process to have time to take place in the case of a temperature increase. It is preferably a composite explosive with a flexible binder, -"or example rubber.

A first embodiment of the envelope is shown in Figure 2. It consists in constructing at least one p:)rtion of the envelope 10 by means of a separate part, for example the rear portion 13 of this envelope. This portion 13 and the remaining portion of the envelope 10 are assembled by means of a solder whose melting temperature is lower than the detonation temperature of the explosive and preferably clcse to the temperature at which the generation of gases by decomposition of the explosive charge begins.

Referring] now to Figure 2, there is shzwn an enlarged view of a zone 2 ringed with a dashed line in Figure 1, in which there can be se-en again the envelope 10 and the rear portion 13 of this envelope, as well as the layer 21 of solder assembling these two parts.

As an example, for the type of explosive mentioned above, the melting temperature of the solder is between 150 and 1800C.

Under the action of a significant temperature increase, for one, the mechanical strength of the solder decreases and, for another, the pressure builds up inside the envelope 10 until the portion 13 separates from the rest of the envelope. The explosive 12 can then be ejected and burn outside the envelope, without detonating.

In a particular embodiment, it is possible to provide in the envelope several zones thermally fragile such as that shown in Figure 2.

A second embodiment of a fragile zone:3nsists in using ;: 1 W 1 :. 5 1 mechanical devices for attaching the cheek 11 to the envelope 10 that are thernotriggering, i.e., they cease performing! their attachment function from a certain temperature upwards.

Referring now to Figure 3, there is shown an enlargLdview of a zone 3 ringed with a dashed line in Figure It-i.e., the rear end of the envelope 10, a portion of the cheek 11 and the axis of a bolt 31 and a nut 32 that ensure the attachment of parts 10 and 11 to each other.

The nut 32 is apparent outside the cheek 11 and it may include, as shown in Figure 4, a central insert 33 made of a material melting at a predetermined temperature, in which is formed the thread 34.

In a particular embodiment, the nut 32 is prefragmented. Its cohesion is then ensured by a ring 35 made of thermoplas- tic material that, above a predetermined temperature softens and no longer ensures the cohesion of the nut. Figures 5a and 5b show the nut 32 as seen in elevation and in sectional view, respectively, with its ring 35 and the axis 30.

Referring now to Figure 6, there is shown an enlarged view of a zone 6 ringed with a dashed line in Figure 1, showing another embodiment of the fragile zone.

In this Figure, there can be seen again the envelope10 and the cheek 11 that, as an example, has a sligthly different shape. The parts 10 and 11 are attached to each other by means of a bolt 61 with the axis 60.

In the envelope 10, there is disposed an insert 62 in which is formed the thread receiving the bolt 61, this insert being made of a material melting at the predetermined temperature.

The behaviour of the devices described with reference to any of Figures 3 to 6, during a significant temperature increase, is similar to that described with reference to Figure 2, namely, at this time, the mechanical strength of the enve- j,, 1 w 6 - lope decreases whereas the internal pressure increases, until the cheek and the explosive charge are ejected. - Other means of attachment of one portion of the munition, for example the rear cheek, are possible provided they have a calibrated mechanical strength to limit the internal pressure to a value that does not allow the detonation (for example, to about 300 bars).

Referring now to Figure 7, there is shown an enlarged view of such a further embodiment, for example of the zone 6.

In this Figure, there can be seen again the rear end of the envelope 10 and the cheek 11, but here the latter is crimped in the envelope 10, the crimp having a tear strength calibrated as indicated above.

A particular embodiment (not shown) of this type of attachment consists in using, for attaching the cheek, threads having a shear strength calibrated in the same manner.

The embodimentsof -he present invention as described above have, of course. been described only as non-limitative examples. Thus. in particular, in the various embodiments described. the fragile zone of the envelope has a geometry such that it allows the ejection of the explosive charge. It is understood that the case where the geometry of the fragile zone leads to an opening whose size is insufficient to allow the ejection, is within the scope of this invention.

Claims

1. A munition comprising an envelope and an explosive charge confined in said envelope,said envelope comprising a fragile zone which becomes fragile w--tIi an increase in temperature and which is capable of separating under the action of an internal pressure build up produced by the charge Itself in the Increase in temperature, thereby of said envelone and the response to causing the opening deconfinement of said explosive charge, said explosive being such that its kinetics of decompositiondetonation is sufficiently slow to allow said deconfinement to take place before the explosion.

2. A munition according to claim 1, wherein said explosive is of the composite type with a flexible binder.

3. A munition according to claim 2, wherein said binder is rubberlike.

4. A munition according to claim 1.. wherein the geometry of said fragile zone is such that said explosive charge can be ejected.

5. A munition according to any preceding claim, wherein said envelope includes at least two parts,, one of said parts forming the rear portion ofsaid munition, said rear portion being attached to the rest of the envelope by means of a solder whose melting temperature is lower than the detonation temperature of said explosive.

6. A munition according to any of claims 1 to 4, wherein said envelope comprises at least two partsi, one of said parts forming the rear portion of the munition, said rear portion being attached to the rest of the envelope by means of threaded attachment means at least partially fusible at a temperature lower than the detonation temperature of said explosive.

7. A munition according to claim 1, wherein said fragile zone of the envelope has a mechanical strength calibrated so as to limit the internal pressure to a predetermined value.

8. A munition according to claim 7, wherein said envelope comprises at least two parts, one of said forming the rear portion of the munition, said rear portion being attached to the rest of the envelope by means of a crimp whose shear strength is calibrated.

9. A munition substantially as described hereinbefore with reference to the accompanying drawings and as illustrated in Figure 1, or in Figure 1 and any one or more of Figures 2 to 7 of the accompanying drawings.

Published 1991 at The Patent office. Concept House, Cardilr Road. Newport. Gwent NP9 IRH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. CwmgeWach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.

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