DE3145057C1 - Piezoelectric device for igniting detonators - Google Patents

Description

The present invention relates to a piezoelectric pre direction for projectiles loaded with explosives is intended to ignite the electrical detonator that this Explosives initiated.

The invention also relates to an explosive loaded projectile containing such a device.

A piezoelectric device for igniting a electrical detonator, which is used in a ballistic pro jectile or guided missile containing explosives ini tied. This device contains a ferroelectric Material that is electrically connected to the detonator. This ferroelectric material is so in the projectile housed that there was a mechanical impact on the projectile Experienced stress. This creates mechanical stress an electrical voltage that ignites the detonator causes.

The ge of a piezoelectric device of this type delivered electrical energy is however relatively low. A such device is therefore very much only for the ignition sensitive initial explosives.

Now it is for security and reliability reasons beneficial, little sensitive initial explosives or directly secondary explosives which is an electrical energy on the order of 0.1 to 0.5 J over a period of time require 0.5 to 1 µs to be able to ignite.

The objective mentioned is the subject of the present invention.

The piezoelectric device incorporating the invention contains a ferro electrically connected to the detonator electrical material built into the projectile in this way is that when it hits the floor it is a mechanical bean experience experience.

According to the invention, this piezoelectric device is thereby  characterized in that they are stacked several Includes sheets of ferroelectric material that are electrical are connected in parallel, this plate stack elek trisch on the one hand with a capacitor that is able under the influence of mechanical stress, the the stack experienced during the bullet hit, generated to store electrical energy and on the other hand with one High voltage switch is electrically connected, which in turn is electrically connected to the detonator, this switch at a certain threshold the stored in the capacitor energy works.

When serving, the stacked plates depolarized one after the other from ferroelectric material. The thus delivered electrical energy is ge in the capacitor saves. The stored energy reaches the Functional threshold of the high voltage switch, this will be Energy is transferred to the detonator, causing the ignition of the Explosives.

Due to the use of a stack of parallel ones ferroelectric plates, you get a very cheap upper area-thickness ratio, so that the obtained electrical Energy can reach 0.1 to 0.5 J, which is enough to make little sensitive initial explosives or secondary explosives to ignite.

In addition, due to the use of a stack ferroelek trischer plates the width of the Vorrich invention very low, which means that they can be installed in classic projectiles or guided missiles.

According to an advantageous embodiment of the invention Means are provided to attach the ferroelek limit the voltage applied to the material, which is below that of the coercive field strength of said forming material.  

It is achieved that the whole of the ferroelectric Slabs of the stack under the impact of the shock wave is completely depolarized from each other.

According to a preferred embodiment of the invention the ferroelectric plates from a ferroelectric measure material that turns from a ferroelectric into an anti-ferro electrical condition. In this case there are means provided to apply the voltage applied to the plates to a Limit value below that of the tension of the first Transition from an anti-ferroelectric to a ferroelek trical state.

Under these conditions it is also ensured that all ferroelectric plates under the influence of Shock wave can be depolarized one after the other.

The invention also relates to one loaded with explosives Projectile that has an ogive that has a recess on the inside contains, in which a piezoelectric according to the invention direction is installed. This ogive contains one on the floor impact compressible wall, with a plunger between the bottom of the ogive and the plate stack made of ferroelectric Material is provided.

A feature of the present invention is that the distance between the bottom of the recess of the ogive and the pestle as well as the one between this pestle and the stack of Plates made of ferroelectric material is calculated so that with a bullet impact speed between 500 and 1000 m / s the impact pressure induced by the ram in the stack is between 10 and 20 kbar.

Further peculiarities and advantages of the invention are known from the following description can be seen.

In the accompanying drawings, the examples of which are not based on the are limited to:  

• -, Figure 1 is a view in longitudinal section of the pre derteils a ballistic projectile which includes a he invention modern piezoelectric device.
• - 2 indicates the Figure is a schematic of the electrical circuit of the inventive apparatus again.
• - Figure 3 shows the electrical circuit diagram of the stacked ferroelectric plates of the device.
• - shows the Fig 4, the curves of the measured to the capacitor terminals of the device as a function of time for various materials fer roelektrische voltage again..

In the embodiment of Fig. 1, the ballistic projectile comprising a nose cone 1, whose bottom is a screwed onto the projectile body 2 1. The ogive 1 has a recess 3 from the inside, which is aligned with the XX'-axis of the projectile. The bottom 4 of this recess 3 is approximately frustoconical. In the vicinity of this bottom 4 , the wall 5 of the ogive 1 has a constriction 6 , as a result of which this wall 5 can be pressed together when the ogive 1 serves in the direction of the XX ′ axis.

Inside the recess 3 , a plunger 7 and a stack of disc-shaped plates 8 , 9 , 10 , 11 and 12 are provided along the XX'-axis of ferroelectric material. The plunger 7 has a frustoconical front part 13 which is at a certain distance j _{1 from} the bottom 4 of the recess 3 . This plunger 7 , on the other hand, has a truncated cone-shaped lower part 14 , the distance to the first plate 8 of the stack is j ₂ .

The plunger 7 and the stack of ferroelectric plates 8 to 12 are accommodated in a sleeve 15 , which in turn is fastened in the recess 3 of the ogive 1 .

From Fig. 1 it can be seen that the part 15 a of this sleeve 15 , in which the plunger 7 is installed, with part of the wall 5 of the ogive 1 in the vicinity of the constriction 6 has no loading.

The plunger 7 is connected to this part 15 a of the sleeve 15 via a ring 16 made of plastic, which is sheared off when the ogive 1 is opened.

The stacked plates 8 to 12 made of ferroelectric material are electrically connected to each other and to the support plate 17 of an electrode 18 , which is also arranged along the XX'-axis. This electrode 18 and the plates 8 to 12 are electrically opposite the sleeve 15 , the ogive 1 and the projectile body 2 by synthetic resin - such as. B. epoxy resin - isolated. This resin 19 laterally surrounds the plates 8 to 12 and the electrode 18 .

From FIGS. 1 and 3 shows that the ferroelek trical plates are electrically connected in parallel with 8 to 12 by means of conductors 20, 21. The conductors 20 are embedded in the synthetic resin 19 and connected to the negative output electrode. The conductors 21 are in electrical contact with the sleeve 15 , which is the positive electrode.

The stacked ferroelectric plates 8 to 12 are electrically connected (see FIG. 2) to a capacitor 22 , which can store the successive releases of these plates 8 to 12 under the influence of the shock waves that occur when the ogive 1 strikes.

The electrical circuit of the device according to the invention also contains a high-voltage switch - for. B. a spark gap 23 with dielectric breakdown - which is electrically connected to the plates 8 to 12 and the capacitor 22 . This spark gap responds as soon as the voltage reaches a certain threshold, and gives the energy stored in the capacitor 22 to the detonator 25 z. B. from the wire detonator type.

In the embodiment of FIG. 2, the plates 8 to 12 and the capacitor 22 are also electrically by a rectifier element 24 - z. B. a diode - connected to each other.

Any ferroelectric can be used for the stacked plates 8 to 12 , provided that it can be depolarized under electrical voltage. In order to make this depolarization possible, this voltage must be below the value of the coercive field strength of the ferroelectric material.

The best results are obtained when using plates made of ferroelectric material, which can change from a ferroelectric state to an antiferroelectric state under the action of impact. So that the depolarization of the material can take place, the voltage supplied by the compressed material must remain below the value of the voltage which corresponds to the first transition from an anti-ferroelectric (AF) to a ferroelectric (F) state. The energy yield is at a maximum if the pressure acting on the stack of plates 8 to 12 when the projectile hits is limited to a value of 10 to 20 kbar at an impact speed between 500 and 1000 m / s.

These pressure ratios are obtained by regulating the aforementioned distances j ₁ and j ₂ and by choosing a suitable shock impedance for the ferroelectric material of the plates 8 to 12 .

If the ferroelectric material is from a ferroelek transition into an anti-ferroelectric state sintered ceramics obtained by synthesis can correspond to the following formulas:

• a) the materials of the type Pb (Zr _1-x Ti _x ) O ₃ with 0.03 <x <0.08 with the following phase sequence with temperature increase AF (anti-ferroelectric) → F (ferroelectric) → P (paraelectric).
  example
  Pb (Zr _0.965 Ti _0.035 ) O₃ + 1% Nb₂O₅;
  P _b (Zr _0.95 Ti _0.05 ) O₃ + 0.8% WO₃;
• b) the ternary compounds Pb (Zr, Sn, Ti) O₃, which have the phase sequence when the temperature rises: F → AF → P.
  example
  Pb _0.99 Nb _0.02 [(Zr _0.73 Sn _0.27 ) _0.93 Ti _0.07 ] _0.98 O₃
• c) the compounds of the general formula
  Pb (Hf _1-y Zr _y ) _1-x Ti _x O₃
  example
  Pb (Hf _0.3 Zr _0.7 ) _0.915 Ti _0.085 O₃ + 1% La₂O₃
• d) the compounds of the general formula
  Pb _1-y La _y (Zr _1-x Ti _x ) O₃.

These materials have the property that they are under Effect of an electrical field due to the phase change AF → F can be polarized. The electrical transition field AF → F (3.5 kV / mm and more) is far stronger than the coercive force. The polarized material stays in one big one Temperature range ferroelectric. Depolarization takes place under a flat shock wave due to irreversible phase changes tion F → AF, even under the influence of an electric field of (case of the stack).

Finally, all of these materials have a high value for P _r ² / 2E (P _r remanent polarization, E dielectric constant), which theoretically represents the stored electrical energy.

To make this stack, other ferroelek tric materials are used provided that they have a strong coercive force and a low Dielek possess tricity constant so that they are at least part can be depolarized if the voltage at the  Clamping their electrodes increases (case of certain ceramics PZT or piezoelectric polymer). Did actually leads to an increase in the electric field stabilization of the ferroelectric state of the Materials, especially if this field is the coercive has field strength or is stronger. To make this difficult You can avoid the thickness of the last place Reinforcing materials in the stack.

The thickness of the ferroelectric plates 8 to 12 is selected taking into account the value of the dielectric constant and that of the maximum voltage to be reached at the terminals of the capacitor 22 . Each of the plates 8 to 12 can e.g. B. have a diameter of 10 mm and a thickness of 0.5 mm.

The device according to the invention works as follows:
When the ogive 1 hits its wall 5 is pressed together. The bottom 4 of this ogive 1 is supported on the plunger 7 , whereby the ring 16 is sheared off. The plunger 7 then slides along the XX'-axis and induces a shock wave in the first ferroelectric plate 8 .

Thanks to the distances j ₁ and j ₂ , the impact pressure is 10 to 20 kbar at impact speeds that are usually between 500 and 1000 m / s.

Thanks to the frustoconical design of the bottom 4 of the ogive 1 and the front part 13 of the plunger 7 , the device works properly when the angle of incidence, based on the XX'-axis, is between 0 and 60 °.

The shock wave generated on impact spreads in the five ferroelectric plates 8 to 12 and depolarizes them one after the other. In this way, the first plate 8 charges the capacitor 22 to a voltage V ₁ , just like the other four ferroelectric plates 9 to 12 . The second plate 9 charged with the voltage V ₁ is in turn depolarized and charges the capacitor 22 , the voltage of which reaches V ₂ and so on. After approximately one microsecond, the maximum voltage is reached at the terminals of the capacitor 22 , the capacitance of which, B. is 30 nF.

The rectifier element 24 located between the capacitor 22 and the ferroelectric plates 8 to 12 prevents the dielectric losses and the repolarization of the depolarized plates 8 to 12 .

The spark gap 23 is short-circuited as soon as the electrical voltage reaches a z. B. reached maximum threshold set to 3000 V. The capacitor 22 ent then instantly charges via the detonator 25 , where it is caused by the ignition of the explosive.

In the example considered, the electrical energy supplied by the stacked plates 8 to 12 reaches 100 to 150 mJ. This energy can be increased up to 500 mJ by using more powerful ferroelectric materials and / or a larger number of stacked plates.

Thanks to the fact that such electrical energy values achieved, it is possible to initial little sensitive detonate explosives or even secondary explosives. One can therefore check the ignition safety of the ballistic pro significantly increase jectile or guided missiles.

So with the help of a stack electrically parallel switched ferroelectric plates very high electrical Energy achieved with very little space will.

Fig. 4 shows, by way of example, the curves of the voltage T in volts as a function of the time t in microseconds, the values at the terminals of the 32 nF capacitor 22 being measured in the following cases

• a) Case of a stack of 5 ferroelectric disks dated Type "metastable" with phase change,
• b) case of a stack of 5 ferroelectric disks, of where the last two are twice as thick as the three first,  
• c) case of a stack of five ferroelectric slices ben with a coercive force of the order of magnitude of 2000 V / mm.

The invention is of course not limited to the examples just described, and you can use them numerous changes can be made without the Would exceed the scope of this invention.

Thus, instead of being constant, the thickness of the ferroelectric plates 8 to 12 can increase in the direction of propagation of the shock wave. This arrangement also allows the value of the electrical energy obtained to be increased.

In the case of a shaped charge floor are the ferroelek trical plates preferably annular, so that they are a have axial opening that the disturbance of the shaped charge beam limited.

The spark gap 23 can be replaced by any other high-voltage switch or by an avalanche-like semiconductor element.

Claims (10)

1. Piezoelectric device for explosives charged projectiles, which is used to ignite an electrical detonator that initiates this explosive, this device contains a ferroelectric material that is electrically connected to the detonator and installed in the projectile so that it hits the projectile experiences a mechanical stress, characterized in that it contains a stack of several plates ( 8 , 9 , 10 , 11 , 12 ) made of ferroelectric material which are electrically connected in parallel, this stack being electrically connected to a capacitor ( 22 ) which is able to store the energy generated under the action of the mechanical stress acting on the stack upon projectile impact, this stack also being electrically connected to a high-voltage switch ( 23 ), which in turn is in electrical contact with the detonator ( 25 ) is standing, the switch ( 23 ) comes into operation as soon as the energy stored in the capacitor ( 22 ) reaches a certain threshold. 2. Device according to claim 1, characterized in that means are provided to limit the voltage applied to the plates ( 8 , 9 , 10 , 11 , 12 ) made of ferroelectric material to a value which is lower than that of the coercive force of the material from which these plates are formed. 3. Device according to claim 1, characterized in that the plates ( 8 , 9 , 10 , 11 , 12 ) consist of a ferroelectric which can change from a ferroelectric to an anti-ferroelectric state, and in that means are provided to limit the voltage applied to these plates to a value lower than the voltage of the first transition from an anti-ferroelectric to a ferroelectric state. 4. The device according to claim 3, characterized in that said ferroelectric material was selected from sintered ceramics of the following composition: Pb (Zr _1-x Ti _x ) O₃
Pb (Zr, Sn, Ti) O₃
Pb (Hf _1-y Zr _y ) _1-x Ti _x O₃
Pb _1-y La _y (Zr _1-x Ti _x ) O₃whereby the proportions of the elements are chosen so that these materials represent metastable ferroelectrics. 5. The device according to claim 4, characterized in that the ferroelectric material consists of Pb (Zr _1-x Ti _x ) O ₃ with 0.03 <x <0.08. 6. Device according to one of claims 1 to 5, characterized in that the electrical circuit between the stack of plates ( 8 , 9 , 10 , 11 , 12 ) made of ferroelectric material contains a rectifier ( 24 ). 7. Device according to one of claims 1 to 6, characterized in that the thickness of the plates made of ferroelectric material ( 8 , 9 , 10 , 11 , 12 ) increases in Rich direction of the shock wave acting on the stack upon projectile impact. 8. Device according to one of claims 1 to 7, determined for a shaped charge floor, characterized in that each of the plates made of ferroelectric material has an opening centered on the projectile axis is. 9. Projectile loaded with explosives, which has an ogive ( 1 ) which has an inner recess ( 3 ) in which a piezoelectric device according to the invention is built, the ogive having a wall ( 5 ) which is compressible when the projectile hits and a plunger ( 7 ) between the bottom ( 4 ) of the recess ( 3 ) of the ogive and the stack of plates ( 8 , 9 , 10 , 11 , 12 ) made of ferroelectric material, characterized in that the distance (j ₁ ) between the bottom ( 4 ) of the recess ( 3 ) of the ogive and the plunger ( 7 ) and the space (j ₂ ) between the plunger ( 7 ) and the stack of plates ( 8 , 9 , 10 , 11 , 12 ) made of ferroelectric Material are calculated so that at impact speeds of the projectile from 500 to 1000 m / s, the impact pressure induced by the plunger ( 7 ) in the stack is between 10 and 20 kbar. 10. Projectile according to claim 9, characterized in that the stack of plates ( 8 , 9 , 10 , 11 , 12 ) made of ferroelectric material and the plunger ( 7 ) are arranged axially in a sleeve ( 15 ) which in the savings ( 3 ) the ogive ( 1 ) is provided, the part ( 15 a) of this sleeve, which lies opposite the deformable wall ( 5 ) of the ogive, is separated from it by an intermediate space and the plunger ( 7 ) with said ge Part ( 15 a) of the sleeve via a mechanical Ver connector ( 16 ) is firmly connected, which is destroyed in the projectile impact under the action of the thrust force exerted on the plunger ( 7 ) by the bottom ( 4 ) of the ogive.