Patent Application
20230332864
This invention relates to the field of fragmentation launchers and particularly to the design of an explosively driven fragment launcher and a method for explosively launching a fragment at a target.
There is a requirement to ensure that armours utilised in the protection of personnel and platforms are produced to rigorous standards, further to this there is also a requirement to ensure that the munitions produced also meet the required safety and manufacturing standards including those standards relating to insensitive munitions, which set requirements on how the munition should behave when damaged, including damage caused from fragmentation. The testing of these systems needs to be completed in a controlled manner to ensure that the materials in question are rigorously tested to the appropriate standard. These assessments typically require a projectile or fragment, or fragments to be ‘fired’ or launched at a target. The target is then assessed for damage using a variety of known methods including visual inspection, X-Ray or any other destructive or non-destructive method. In these test regimes it is critical that the projectile or fragments arrives at the target at the appropriate speed or velocity, whilst also being of the appropriate shape, volume or cross sectional area, i.e. avoiding deformation or oblation. It is also important to try to minimise any collateral effects attributable to the launch method which may obfuscate the effects on the target from the projectile or fragment under test. Furthermore it is also vital that the test method and apparatus are able to achieve the desired effects consistently and repeatedly.
Existing test systems can be expensive and complex to produce in a controlled way to allow for repeatable and consistent test results. Furthermore, in order to achieve the higher velocities (>1500 ms−1) for larger size fragments (>50 g) using a device such as an explosively driven fragment launcher, the amount of explosive required, also referred to as Net Explosive Quantity (NEQ), makes it difficult to operate within the safety constraints of some test ranges or facilities. In addition increasing the amount of explosive increases the chances of producing unwanted fragmentation of the confinement casing, unless the confinement casing is made substantially thicker, which again has an impact on cost and ease of production.
As such there is a requirement for a fragment launching device, which is capable of delivering a range of velocities for a range of fragment sizes, weights or volumes, whilst also minimising the amount of explosive material required, thus increasing the safety aspects of use.
Therefore it is an aim of the present invention to provide an alternative explosively driven fragment launcher and method for explosively launching a fragment at a target.
According to a first aspect of the invention there is provided an explosively driven fragment launcher comprising a casing, having a main body for housing an explosive charge, the casing further comprising a first end provided with a launching aperture configured to hold a fragment and a second end provided with a detonation position configured to receive a detonation means for detonating the explosive charge, wherein the inner profile of the casing tapers from the main body towards the launching aperture and from the main body towards the detonation position, such that in use an explosive pressure is directed towards a fragment to be launched.
Armour systems for vehicles or personnel must be appropriately tested to ensure they meet the stringent standards and requirements placed upon them. These protection systems must be tested in numerous configurations, dependent on how they are expected to be used, for example on a person, within a vehicle or within an installation such as a bunker or as part of wider infrastructure such as buildings. This leads to tests being required on various material types as well as a plurality of variations for example thickness. Similar tests are also required for munition casings where there is a requirement to ensure that the casing can withstand impacts from projectiles or fragments without compromising the integrity of the weapon, this can extend further to storage containers or boxes for such munitions. Furthermore as well as this variety of test targets there are numerous weapons and effects which need to be simulated. For example a bullet may be used to test a specific armour however this may also be simulated through the use of a surrogate projectile. In the instance of testing armour or munitions casings it may be preferable to test using a projectile to simulate fragmentation from weapons systems, where this is the case the projectile may be referred to as a fragment. This testing requires that projectiles or fragments of a plurality of sizes, volumes and weights can be launched to specific velocities in a controlled and repeatable manner. To achieve this a fragment launcher may be used, consisting of a means to hold the fragment and a launching means. In the case of an explosively driven fragment launcher, the launching means is an explosive material contained within a body of the launcher. The explosive material is detonated such that the explosive pressure waves or gases act upon the fragment imparting energy such that the fragment or projectile is launched. The velocity of the fragment is determined by its mass and the amount of energy imparted from the explosive pressure waves or gas. As such the velocity is typically related to the amount of explosive material used, where increasing the amount of explosive material would increase the velocity of the fragment. This relationship is often described using the Gurney equations or similar.
The inventor has identified improvements to an explosively driven fragment launcher to enable cost effective and efficient delivery of high speed fragments of a plurality of sizes, shapes and weights, with relatively low amounts of explosive material, also referred to as Net Explosive Quantity (NEQ).
The explosively driven fragment launcher has an outer casing with a main body for housing an explosive charge comprising a first end and a second end. In this context the first end is that which would be directed towards and closest to, the ‘target’. The ‘target’ is simply the material which would receive the fragment or projectile after launch and may take many forms, such as a witness plate, armour panel, sheet material, munition casing or ammunition box or container, test standards including those which may be biofidelic, or any other such object. The second end is that which is directed away from and furthest from the ‘target’. The first end is provided with a launching aperture configured for holding a fragment or projectile of a plurality of shapes, sizes and weights. The aperture provides a channel from the outside of the casing to the internal volume, and is preferably positioned central to the longitudinal axis of the fragment launcher. This aperture can be any three dimensional shape, but preferably is shaped to match the dimensions and shape of the fragment. For example it may provide a recess suitable for a fragment cuboid in shape, furthermore where the cross sectional area of this cuboid is varied between fragments the aperture can also be altered to accommodate such variations in fragment size. Additionally should a cylindrical or spherical fragment or projectile be used the aperture can equally be manufactured to accommodate those three dimensional shapes, or any conceivable alternate shape. Advantageously the aperture may be manufactured such that it is conformal to the fragment, such that there is a close fit between the two. This advantageously ensures that the explosively formed gases do not bleed or leak around the fragment thus ensuring efficient transfer of energy from the explosive pressure to the fragment. The aperture can be of uniform cross section through the first end of the casing, connecting the outer external surface and inner volume of the casing. Alternatively it can have a varied cross section or profile, as an example a ‘stepped profile’ with the outermost section of the first end of the casing aperture being of a depth and cross-sectional area suitable for housing the fragment or projectile and any additional depth of outer casing toward the internal volume of the casing, being of a different cross sectional area. For example a reduced cross sectional area could be used to provide a ‘seat’ for the fragment to assist locating the fragment in the aperture, as well as providing means for further focusing of the explosively formed pressure or gases from within the casing main body behind the fragment.
Alternatively the launch aperture may be provided with an adjustable holding mechanism, such as a chuck, such that the size of launch aperture can be adjusted to accommodate fragments of different cross sections. The chuck may reduce the cross sectional area using any known common configuration, for example for a cylindrical geometry the chuck would provide the ability to hold fragments of different diameter. The chuck may be adjusted using a tool or key which interfaces with the chuck mechanism, alternatively a ‘tool free’ adjustment mechanism may be built in which allows for adjustment by hand. The mechanism adjusts the clamping elements such as to provide an aperture for the fragment of variable cross section. The chuck advantageously allows for an adjustable fragment holder which provides sufficiently conformal fitting such as to hold the fragment, whilst still allowing efficient launch of the fragment.
Alternatively, instead of modifying the launch aperture to be complementary to the fragment, the inventor has shown that fragments can be manufactured such as to have a standard outer shape or cross section but may contain a fragment of an alternative shape, size or volume within it. For example, a standard sized disc “blank” may be used to create a fragment of a given shape and thickness, by cutting, machining or perforating the desired fragment shape, for example a cuboid, into the surface of the disc. Sufficient material is removed such that prior to use the disc is partially perforated such that the fragment remains attached to the disc, but in use the same said perforations provide a weakness such that the explosive pressure or gases causes the desired fragment to part, in this example the cuboid, from the disc and is therefore launched. This advantageously allows for the launch aperture to be manufactured to standard dimensions simplifying the manufacturing process of the launcher, whilst still providing the ability to launch fragments of a range of preselected masses, shapes and sizes.
The second end of the casing is provided with a detonation position configured to receive detonation means. The detonation position provides a channel from the outside of the casing to the internal volume configured to receive a detonation means, and is preferably positioned central to the longitudinal axis of the fragment launcher. This channel can be varied in size or shape or both, for example for a channel with a circular cross-sectional area when viewing the invention in plan view, the diameter could be varied to accommodate detonation means of differing diameters. Alternatively for a channel with a square cross-sectional area, this area could as equally be varied. Furthermore the detonation position can be manufactured to receive a detonation means with a plurality of fixing methods. For example the detonation means may be mounted using a friction fit where the detonation means is a tight fit with the detonation position. Alternatively the detonation means may be fixed by threaded means, where both the casing and detonation means are threaded such that they can be fixedly attached, this advantageously provides a robust connection able to withstand the blast pressures generated in use. The detonation means can be chosen from any of the well know methods within the art and may also include devices referred to as initiators. These may be electrical or non-electrical detonation means designed to safely initiate an explosive.
The main body of the casing is the remaining casing between the first end and second end, and is configured such as to have an internal volume suitable for receiving an explosive charge. This explosive charge can be any explosive materials known to the art, but preferably a malleable or mouldable explosive such as plastic explosive. It is the detonation of this explosive charge which in turn creates the explosive pressure and gases which are directed toward and launch the fragment from the launch aperture.
The casing internal volume tapers from the main body internal wall towards the launching aperture at the first end. This tapering advantageously allows for the directing of the explosive pressure toward fragment via the launch aperture. This tapering may be stepped or preferably smooth to provide predictable performance of the propagation of the explosive wave pressures or gases within the casing. The tapering may be formed by known manufacturing techniques such as milling, machining or casting or advanced or additive manufacture. The tapering may take any shape, for example, when viewed in cross-section through the plan view of the invention, it may reduce linearly or non-linearly, taking a convex or concave profile. The position of the start of the tapering of the internal section is determined by profile or angle of such profile and as such can be varied to provide a plurality of internal shapes or curvatures to the tapering. The tapering of the main body towards the first end is terminated by the fragment launch aperture. Furthermore the casing internal volume tapers from the main body internal wall towards the detonation position at the second end. This tapering may be stepped or preferably smooth to provide predictable performance of the movement of the explosive pressure or shock wave through the explosive material within the casing. The tapering towards the second end also advantageously allows for the shaping of the explosive material, held within the main body of the casing, which in turn creates a shaped detonation charge, which advantageously directs the explosive shock wave and gases towards the launch aperture. The tapering may be formed by known manufacturing techniques such as milling, machining or casting or advanced or additive manufacture. The tapering may take any shape, for example, when viewed in cross section through the plan view of the invention, it may reduce linearly or non-linearly, taking a convex or concave profile. The position of the start of the tapering of the internal section is determined by the required profile or angle of such profile and as such can be varied to provide a plurality of internal shapes or curvatures to the tapering. The tapering of the main body towards the second end is terminated by the detonation position.
The outer casing should be of suitable thickness to safely contain the explosive material when in use, but may be varied, for example to minimise cost, for example to produce a single use device. Alternatively the casing may provide suitable containment to the explosive such that it may be reused. The outer casing may be made of any suitable material which provides sufficient strength suitable for the confinement of the internally held explosive charge when in use. The material selected must also be able to be manufactured to have the desired internal tapering, fragment launch aperture at the first end and detonation position at the second end. A typical material may be a metal or alloy for example steel, but other materials such as plastics or composites may also prove suitable. The casing may be formed using any known manufacturing or machining technique such as forming, milling or turning, additionally it may be formed by additive or advanced manufacturing processes.
In certain embodiments of the invention the first end comprises a cap removably attached to the main body. The cap may be configured such that it contains the launch aperture, additionally it may also be configured to contain all or part of the internal tapering from the main body towards the launch aperture. The cap may be configured to any predetermined proportion of the main body casing. Advantageously this provides access to the internal volume of the invention whilst additionally providing a simple means to modify the launch aperture both in terms of shape or size, with a further advantage of providing a means to modify a proportion of, or all of the tapering from the main body to the launch aperture. The material of the cap may be selected to be the same material as the outer casing, alternatively it may also be selected from any suitable alternative material to that of the main casing. A typical material may be a metal or alloy for example steel, but other materials such as plastics or composites may also prove suitable. The cap may be removably attached using any known means suitable to the materials of the cap and outer casing, such as fasteners, clamps, brackets, in addition to other known fixing methods such as friction fitting or use of a bonding material or media.
In further embodiments of the invention the second end comprises a cap removably attached to the main body. The cap may be configured such that it contains the detonation position, additionally it may also be configured to contain all or part of the internal tapering from the main body towards the detonation position. The cap may be configured to any predetermined proportion of the main body casing. Advantageously this provides access to the internal volume of the invention whilst additionally providing a simple means to modify the detonation position both in terms of shape or size, with a further advantage of providing a means to modify a proportion of, or all of the tapering from the main body to the launch aperture. The material of the cap may be selected to be the same material as the outer casing, alternatively it may also be selected from any suitable alternative material to that of the main casing. A typical material may be a metal or alloy for example steel, but other materials such as plastics or composites may also prove suitable. The cap may be removably attached using any known means suitable to the materials of the cap and outer casing, such as fasteners, clamps, brackets, in addition to other known fixing methods such as friction fitting or use of a bonding material or media.
In certain embodiments of the invention the cap(s) is or are removably attached to the main body section by threaded means. The threaded means can be manufactured using any known machining or manufacturing technique. Advantageously the threading means provides for a simple method for both attaching and removing the removably attached cap(s). An additional advantage is that in use, the threaded means is able to withstand the forces of the blast pressure wave ensuring that the explosively driven fragment launcher remains intact, further improving the safety of device.
In certain embodiments of the invention there is a spacer with a first and second end, configured to reduce the internal volume of the main body section, wherein there is a channel between the first and second end of said spacer. Within this context the first end is that which is closest to the launch aperture and the second end is that which is closest the detonation position. The spacer may be selected from a preselected set of sizes, shapes or volumes and is placed internal to the main body casing such as to vary and reduce the internal volume of the main body casing. This advantageously allows for a configurable explosively driven fragment launcher wherein by varying the internal volume the amount of explosive charge is also varied, resulting in an explosive pressure wave which can be optimised to the fragment size or mass as well as to the required fragment velocity. An additional advantage is that the configurability is provided within the same physical main body casing without the requirement of having to manufacture multiple casings of different size or internal volume thus reducing both manufacturing complexity as well as cost. The inventor has further identified that the use of spacer internal to the main body casing, as opposed to simply reducing the volume of explosive charge and leaving a void, improves the transfer energy to the fragment from the explosive blast wave, thus making a more reliable and predictable fragment launching device whilst also achieving higher velocities then otherwise might be possible. The channel between the first and second end of the spacer is configured to allow for the explosive gas or pressure wave to travel unobstructed towards the first end of the device, namely that containing the launch aperture, additionally helping to concentrate the gases or shockwave. As well as the spacer size or volume being able to be varied, advantageously the channel size may also be varied, for example if the spacer is viewed in cross-section the cross-sectional area of the channel could be varied, allowing further control of the explosive gases or shock wave. The spacer may be positioned within the main body of the casing at any position between the casing first end and the casing second end. Preferably the spacer is positioned internal to the main body casing at the first end, such that the first end of the spacer is adjacent the launch aperture. This advantageously allows for the explosive material to be placed between the spacer second end and the main casing second end. Even more preferably the spacer may be placed adjacent the main casing second end adjacent the detonation position. Advantageously this allows for the explosive material or fill to be adjacent the launch aperture. When in this position the channel within the spacer may also be further configured to accept or propagate an initiation shock wave from the detonation means or provide a detonation position for the detonation means. The spacer can be made of any suitable material and advantageously can be selected to be the same or different to that of the main body casing. The material can be selected such that the spacer is reusable such that in use, it is able to withstand the forces and pressures associated with the explosive blast, alternatively it may be selected such that the material breaks or fails, such that the spacer is a single use item. A typical material for the spacer may be a metal or alloy for example steel, but other materials such as plastics or composites may also prove suitable. Plastic is a general term which includes a variety of polymeric materials. The material may be selected from any of these known materials. The use of a plastic material advantageously allows for a simple and cost effective manufacturing process to be used. Additionally plastic materials lend themselves to be shaped easily allowing for various shapes and sizes to be produced to suit the requirement of the invention. The shaping of the spacer may be formed using any known manufacturing or machining technique such as forming, milling or turning, additionally it may be formed by additive or advanced manufacturing processes, which include techniques commonly referred to as ‘3D printing’.
In certain embodiments the plastic material may be Acrylonitrile Butadiene Styrene (ABS). The inventor has shown that this material is simple to manufacture to the desired shape of the spacer, for example using additive manufacture, is cost effective and furthermore withstands the forces experienced when in use.
In further embodiments of the invention the first and second end of the spacer are shaped substantially to match the internal tapering of the main body. The inventor has identified that this shaping advantageously increases the efficiency, reliability and repeatability of the fragment launcher.
In this context ‘shaped to match’ means that either or both the first and second end of the spacer are shaped so as to be complimentary to the first or second end of the internal tapering of the main body casing. In certain embodiments of the invention the spacer first end may be shaped to substantially match the inner tapering of the casing first end, such that if the spacer was inserted in the casing internal volume within the first end, the spacer would be conformal to any tapering towards the launch aperture. Preferably the spacer may have the second end shaped to substantially match the internal tapering of the second end of the main body casing, such that if the spacer was inserted in the casing internal volume it would be conformal to any tapering towards the detonation position. Even more preferably the spacer may have the second end shaped to substantially match the internal tapering of the second end of the main body casing, such that if the spacer was inserted in the casing internal volume it would be conformal to any tapering towards the detonation position, and furthermore the spacer first end is also shaped to be complementary to the shape of the second end of the spacer. The inventor has shown that this advantageously allows for efficient energy transfer through the explosive charge towards the launch aperture. The shaping of the spacer may be formed using any known manufacturing or machining technique such as forming, milling or turning, additionally it may be formed by additive or advanced manufacturing processes which include techniques commonly referred to as ‘3D printing’.
In further embodiments of the invention the internal tapering of the main body casing towards the detonation position is between 10 and 70 degrees to the longitudinal axis of the casing. This range of angles should also be considered to include those angles within typical manufacturing tolerances. Positive angles are measured clockwise from the longitudinal axis of the invention which is at zero degrees. The inventor has shown this range of angles advantageously allow for efficient transfer of energy or gases from the explosive material to the fragment, such that for a reduced explosive fill the required velocities may be achieved for a given fragment mass.
In further embodiments of the invention the internal tapering of the main body casing towards the launching aperture is between 10 and 70 degrees to the longitudinal axis of the casing. This range of angles should also be considered to include those angles within typical manufacturing tolerances. The inventor has shown this range of angles advantageously allow for efficient transfer of energy or gases from the explosive material to the fragment, such that for a reduced explosive fill the required velocities may be achieved for a given fragment mass.
In certain embodiments of the invention the angle of the internal tapering of the main body casing towards the launching aperture is complementary to that of the internal tapering of the main body casing towards the detonator position. This advantageously allows for efficient energy transfer to the fragment, whilst additionally providing the benefit of simplifying manufacture.
In further embodiments of the invention the angle of the internal tapering is 30 degrees to the longitudinal axis of the casing. This angle should also be considered to include those angles within typical manufacturing tolerances. The inventor has shown that this angle advantageously provides for the efficient transfer of energy, both in terms of the propagation of the explosive shock wave through the explosive material but also in then focusing or imparting said energy onto the fragment in the launch aperture.
In certain embodiments the explosively driven fragment launcher the outer casing is cylindrical, the internal tapering of the main body towards the launching aperture and from the main body towards the detonation position is conical. This geometry has been shown to be advantageous in producing a predictable and repeatable performance. It has been further shown to provide a launcher with the required performance in an easy to manufacture form.
In further embodiments of the invention there is an explosive charge within the main body of the casing. This advantageously means that the launcher can be provided ‘ready to use’ and such that the explosive filling is undertaken in the correct controlled environment by an appropriate person or authority.
According to a second aspect of the invention there is provided a method of explosively launching a fragment comprising the steps of, providing an explosively driven fragment launcher in accordance with the first aspect of the invention, providing an explosive charge, position the explosively driven fragment launcher a predetermined distance from the target with the launching aperture aimed at said target, inserting a fragment of predetermined size into the launching aperture, inserting a detonation means into the detonation position, initiating the detonation means such that an explosive pressure wave is initiated, such that the fragment is explosively launched at the target. This method advantageously achieves repeatable launch velocities for a given fragment size or mass, utilising lower amounts of explosive when compared to other methods for launching fragments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013913.5 | Sep 2020 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2021/000096 | 8/31/2021 | WO |
