FIELD OF INVENTION
The present invention generally relates to a molding process to obtain a helmet and more specifically, relates to a macromatrix pre-thermoforming molding process to obtain a rifle protection helmet shell therefrom.
BACKGROUND OF THE INVENTION
Head protection is one of the most vital aspects for soldiers in times of warfare and combat. During World War I, M1 “Steel Pot” metal helmets were used by soldiers to protect themselves against lethal projectiles and they later came to be known as first generation combat helmets. Since then, a lot of research and development has been done on the evolution of light weight ballistic helmets for soldiers.
Around 1960, US army took an initiative to replace the then existing M1 steel pot helmets with a more light weighted, higher protection helmet with better comfort configuration for their soldiers. This led to the development of Personnel Armor System for Ground Troops (PASGT) helmets made up of resin coated aramid (aromatic polyamides) fabric. This evolution then moved on to the development of advanced combat helmets and enhanced combat helmets in order to lighten its weight even more and exhibit higher protection levels.
Modern age combat helmets these day offer not only better protection from lethal projectiles but also provide enhanced capabilities based on cutting edge latest technologies like night vision device, laser sight, communication setup etc. Across the globe, military and law enforcement agencies are looking for a contemporary helmet to better protect soldiers from lethal threats, like rifle projectiles.
OBJECTIVES OF THE INVENTION
The main objective of present invention is to solve the problems stated above and subsequently disclose pre-processing techniques and molding methodology to obtain a uniform performance helmet shell.
Another objective of the present invention is to develop layer by layer construction of helmet shell based on layout design of helmet, including selection of materials.
As per another objective of present invention, ballistic testing and performance analysis of helmet shells obtained from the macro-matrix pre-thermoforming is disclosed.
Other objectives of the present invention shall be clear to a person skilled in the art once the below description is read along with the associated figures, tables and claims.
BRIEF DESCRIPTION OF FIGURES
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may have been referred by embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
These and other features, benefits, and advantages of the present invention will become apparent by reference to the following figures, with like reference numbers referring to like structures across the views, wherein:
Fig. 1 illustrates thickening due to shear angle changes;
Fig. 2 illustrates variation in thickness variation with shear angle;
Fig. 3 illustrates stress waves generated after a ballistic impact;
Fig. 4 illustrates characteristics of ballistic impact energy absorption in composite armor;
Fig. 5 illustrates a helmet shell under maximum load in final cycle; and
Fig. 6 illustrates resistance to penetration data against a 7.62 x 39 mild steel core ammunition or ballistic
DETAILED DESCRIPTION OF EMBODIMENTS
While the present invention is described herein by way of example using embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments of drawing or drawings described, and are not intended to represent the scale of the various components. Further, some components that may form a part of the invention may not be illustrated in certain figures, for ease of illustration, and such omissions do not limit the embodiments outlined in any way. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the present invention as defined by the appended claim. As used throughout this description, the word “may” is used in a permissive sense (i.e. meaning having the potential to), rather than the mandatory sense, (i.e. meaning must). Further, the words “a” or “an” mean “at least one” and the word “plurality” means “one or more” unless otherwise mentioned. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as “including”, “comprising”, “having”, “containing” or “involving” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term “comprising” is considered synonymous with the terms “including” or “containing” for applicable legal purposes. Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention.
In this disclosure, whenever a composition or an element or a group of elements is preceded with the transitional phrase “comprising”, it is understood that we also contemplate the same composition, element or group of elements with transitional phrases “consisting of”, “consisting”, “selected from the group of consisting of, “including”, or “is” preceding the recitation of the composition, element or group of elements and vice versa.
The present invention is described hereinafter by various embodiments with reference to the accompanying drawings, wherein reference numerals used in the accompanying drawings correspond to the like elements throughout the description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.
The present invention generally relates to a molding process to obtain a helmet and more specifically, relates to a macromatrix pre-thermoforming molding process to obtain a rifle protection helmet shell therefrom. The present invention discloses the development of advanced ballistic helmets which meet challenging needs, such as, to protect the wearer from high energy rifle ammunitions such as 7.62 x 51 mm M80 NATO ball or 7.62 x 39 mm AK47 hard steel core, mild steel core, lead core and from several other small arms and ammunitions, including non-ballistic blunt impacts.
One of the biggest challenges in this present technology is molding a section consisting of numerous plies into a compound-curved helmet shape. This typically results in significant wrinkling and folding of the layers, further resulting in non-uniform thickness, and low and uneven pressure in the molded helmet shell structure. This phenomenon has been researched extensively with woven and non-woven fabrics both.
As per the above, a person skilled in the art would acknowledge that while pressing a cross-ply material to form a complex curve, the angle between the warp and weft fibers (i.e., the shear angle) changes. This change in shear angle is the main mechanism by which the fabric conforms to the mold geometry. The crown section of the helmet is the zone where shear angle is 90 degrees. Moving down along the diagonal, the shear angle starts changing considerably which results in trellising, causing thickening of the lower section also with low pressure. This observation aptly explains the occurrence of wrinkles and folds, and consequent poor structurability in the helmet shell, which further results in poor performance against high energy ballistic threats such as rifle ammunitions.
As illustrated in Fig. 1, as the shear angle declines from 90°, the helmet shell starts to show thickening along the diagonal and reduction in area. The thickening of helmet shell can be estimated by calculating a unit area of a portion of composite material changes as its shear angle (?) decreases from 90°.
If the original area (Astart) of the composite is a², where a is the length of each side, then the following equations describe the relationship between the starting laminate thickness (tstart) and the ending laminate thickness (tend):

Astart = a² [1]
Vstart = a² x tstart [2]
Aend = a² x sin? [3]
Vend = a² x sin?tend [4]
Vstart = Vend [5]
a²·tstart = a² x sin?tend [6]
tend = tstart/(sin?) [7]
This relationship is also illustrated in Fig. 1, wherein V represents the volume a unit of material.
As can also be seen from Fig. 2, the in-plane shear is known as trellising. The composite material used in this process has a limit at which point they will start folding and wrinkling. To minimize the folding and wrinkling along with low pressure, the methodology as per present invention given below is adopted.
Macro-matrix pre-thermoforming process, as per an embodiment of the present invention, has shown the potential ability to reduce wrinkling in helmet shells, irrespective of their shape and designs, allowing significant depth, consequently resulting in minimum folds and wrinkles on the finished helmet shell.
The present invention has a completely novel approach to achieving uniform thickness with minimum wrinkles in helmet shell, which is also corroborated by follow-up testing and investigation of the protective performance of rifle helmets, based on various physical and perforation resistance characteristics.
As per an embodiment of the present invention, designing of a ballistic helmet depends on, but is not limited to, selection of lightweight composite materials, helmet shell layup from the selected high-performance composite materials, developing pre-molded shell by using layering of materials in right location and orientation, pre-molding the shells using specially designed molds, and final molding with standard processing parameters.
A person skilled in the art would appreciate that the composite materials for molding helmet shells are selected for minimizing the weight and thickness of the helmet shell, while maintaining highest performance. Therefore, based on current materials, various materials were selected for the present invention.
As per a preferred embodiment, first step to the macro-matrix pre-thermoforming molding process as per present invention is to stack selected plies of, but not limited to, engineered textiles or fabrics or aromatic polyamide or high and ultra-high molecular weight polyethylene or woven and non-woven unidirectional fabric, or prepreg composite or glass and carbon composites or structural composite or nano composite material, in a specifically designed layout, including but not limited to, full layers or slit and non-slit layers or polygons or strips or uniform and non-uniform geometrical shapes and other shape plies.
The above is done in a calculative sequence in order to obtain a uniformly molded helmet shell. These layers or pieces come with or without thermoplastic or thermoset polymeric, elastomeric, resin matrix, with and without added nano particles, which acts as a medium to adhere the multiple layers together, simultaneously giving structural rigidity to the molded shell and desired shape, such as but not limited to a full cut or high cut or mid cut or PASGT or any other shape of helmet.
The mold, consisting of minimum two or more halves made of metal or alloy or polymer or composite material, is pre-heated by oil, air, steam or electric heaters before placing the stack of plies to the temperature in the range of 100 – 150 °C. The temperature of oil is generally 10°C above the forming temperature to reduce the effect of the die cooling.
The stack of layers is laid flat on the mold top or bottom or side surfaces. In this step, it is important to properly place or hold or press or control or release the stack of plies so that the helmet shell shape is formed properly.
The mold halves are then moved from the top or bottom or sides in a longitudinal or across or angular direction, onto the stack of plies, until molding pressure is generated, so as to form the stack of materials in the shape of required helmet shell. This forming may occur in between the upper or sides or lower surfaces of the mold.
The stack or plurality of plies then moves as mold halves traverses downward or upward or sideward or in an angular direction. During this process, pressure is increased gradually. As the pressure increases to, for example, 10MPa, and the stack of plies moves across the clamping surface, the pressure gradually further increases from, for example, 10 to 100 MPa or some time even more than that.
A person skilled in the art would acknowledge that at his point, some portion of the stack that engages more on clamping surface will move-in less due to a higher frictional force holding this section. Therefore, proper indexing of the plies is crucial, and has to be done as per the present invention. A clean smooth surface on the plies also helps to ensure even movement of the plies.
As the mold halves is moved through the material which consist of several plies, the rate of pressure increases and follows a predetermined profile, which is controlled by a downstream pressure regulator. Once the mold halves reach its fully traversed position, they need to be held at the same pressure for about 10-50 minutes to start the curing process material. Cold water or oil or air is then circulated to bring down the mold temperature to, for example, plus (+) 50°C to minus (-) 50°C.
Once the helmet shell has completely consolidated and cured, pressure from the mold is to be relieved, and then the respective mold half traverse back to its position so that the finished helmet shell can be removed from the mold cavity.
Based on physical examination of the molded helmet shells made by above mentioned methodology of the present invention, it is observed that the sample helmet shells molded right from the initial stage were having extremely low wrinkling and thickness uniformity, as was desired.
Further modification in the pre-thermoforming process and layout design may be made to minimize wrinkles and thickness variation up to next level. The modifications i.e., in layout or design or sequence and changes in layout orientation, mold halves transverse rate, pressure and temperature as well as the consistent clamping force, as per present invention, avoids the slippage of layers to increase the acceptability rate up to 99%, which was previously 95%.
MECHANISM OF ENERGY DISSIPATION IN MULTI LAYERED COMPOSITE ARMOR:
One of the main purposes of the present invention is to disclose an approach towards the development of helmet shell to provide protection against high velocity rifle threats. The present invention therefore includes step by step manufacturing process, as discussed above, to obtain a helmet shell which may later be tested to characterize its performance, based on the concept of energy dissipation in ballistic helmet shell.
As is illustrated in Fig. 3, when the helmet or armor is impacted by a projectile, transverse and longitudinal waves are generated. These longitudinal and transverse waves travel along the reinforcing fibers, until they encounter an obstacle like a fabric verge or a fabric overlap. On the occurrence of this encounter, a significant amount of energy transmits to other successive layers, and this continues until the entire amount of energy in the form of compressive waves are dissipated by composite armor. On the other hand, some amount of residual energy in the form of tensile waves is also absorbed by the first end point or the obstacle itself, in the form of re-bounce, as shown in Fig. 3.
The kinetic energy carried by stress waves is dissipated through several mechanisms, including but not limited to, Back Face Deformation (BFD), fibre fracture, inter-yarn friction, delamination of layers and friction between the projectile and the fabric, until it is totally absorbed by multiple layers of an armor. The failure or perforation in composite armor happens when the kinetic energy absorbed by armor exceeds the critical value of tensile stress of the fibers, as illustrated in Fig. 4. However, if the projectile velocity becomes zero (complete absorption of kinetic energy) before the penetration, then the projectile has been successfully resisted to penetration by the armor and the amount of energy with which projectile has been fired is said to be completely dissipated or absorbed by the armor material. Thus, fabric reinforcement properties against ballistic impacts, as exhibited by the present invention, plays a vital role in ballistic impact energy absorption.
In the approach of making ballistic helmets as per present invention, through the pre-thermoforming process, which effectively reduces wrinkles in the molded helmet shell, increases the performance of fibers due to strain induced crystallization phenomenon, significantly thereby enhancing the capability of tensioned fibers to absorb the energy of high velocity rifle projectiles.
PHYSICAL AND RESISTANCE TO PENETRATION CHARACTERISTICS:
The molded helmet shells obtained using above mentioned method, as per present invention, are tested for ballistic penetration resistance, as well as on physical parameters, such as structural rigidity test. Tests of the ballistic penetration resistance of the helmet shell were conducted by checking the resistance to penetration (V0) against 7.62 x 39 mild steel core projectiles at the velocity of 720±20 m/s. Back face deformation against pre-thermoformed helmet shells is recorded by placing the test specimen over pre-conditioned clay filled head form of size large using depth caliper.
PHYSICAL (STRUCTURAL RIGIDITY) CHARACTERISTICS:
The structural rigidity characteristic of helmet shell represents their elastic behavior under compression loading. In this testing, specimens of helmet shells as per present invention were taken and tested in the direction of ear-to-ear. Samples were kept on the test table of universal testing machine using the flat anvil and then the pre-test width of the samples were measured, followed by repeated 45 load cycles of 1000 N. Consequently, the width of helmet is again measured under the loading condition after that samples were removed from test table and kept ambient for 24±1 hours. Again, residual deformation was measured by checking the helmet sample width. Fig. 5 illustrates the helmet shell under maximum load in final cycle.
The structural rigidity results for the pre-thermoformed helmet shell is tabulated as below:

Sample description Pre-thermoform moulded helmet shell
Sample Dimensions
(LxWxH) 248x225x160
Helmet shell size Large
Maximum testing load (N) 1000
Number of load cycles 45
Pre-test max. helmet width (ear to ear) (mm) 225
Helmet width under final loading cycle (mm) 224
Helmet width after final loading cycle (mm) 224
Helmet width After 24 ± 1 Hrs (mm) 224
Permanent deformation (%) 0.4

Thus, it is clear to a person skilled in the art from above that a higher structural rigidity is observed in pre-thermoformed helmet shells of present invention. This also confirms the strengthening of the fibers due to strain induced crystallization in the helmet shells.
BALLISTIC CHARACTERISTICS:
Fig. 6 illustrates the resistance to penetration (V0) data of the pre-thermoformed helmet shells as per present invention. The observation of performance characteristics of pre-thermoformed helmet shells may be co-related with the above-mentioned challenges and mechanism of energy dissipation in multi layered composite armor section along with test data of physical as well as ballistics characteristics with respect to effect of wrinkling and folding in molded helmet shells.
The strengthening of fibers in the present pre-thermoformed helmet shell due to strain induced crystallization allows the fabric layers to absorb more energy on ballistic impacts. Since the present invention obtains even more higher crystallinity after the pre-thermoforming process, the helmet shells as per present invention thereby provides even more absorption of ballistic impacts.
Also, based on the test data obtained from physical as well as ballistic testing against rifle ammunition, it can be derived that pre-thermoforming process plays a vital role to form helmet shells with improved structurability, as 30 samples helmets validated wherein 0% perforation rate was observed in the pre-thermoformed helmet shells out of 270 shots of 7.62 x 39 mild steel core bullets were performed at the velocity of minimum 650-750 m/s.
Also, recorded values of Back Face Deformation (BFD) against rifle ammunition in pre-thermoformed helmet shells exhibit similar trends as the maximum BFD value in pre-thermoformed helmet samples of present invention is 22 mm, whereas the minimum reported BFD was 0 mm. Similarly, in structural rigidity test, the performance of pre-thermoformed helmet shells was found better, wherein tested ear-to-ear permanent deformation recorded was 0.4%.
The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention, and provides the best mode of practicing the invention presently contemplated by the inventor. While there is provided herein a full and complete disclosure of the preferred embodiments of this invention, it is not desired to limit the invention to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like.
Accordingly, the invention is anticipated to hold on to all other such alternatives, modifications, and variations that fall within the scope of the present invention and appended claims.

We Claim:

1. A macro-matrix pre-thermoforming molding process to obtain rifle protection helmet shell, wherein the molding process comprises the steps of:
a. a plurality or stack of plies is pre-heated in a mold by oil, air, steam or electric heaters;
b. the plurality or stack of plies’ layers are laid flat on the mold at its top or bottom or or side surfaces;
c. said mold halves are moved from the top, bottom or sides in longitudinal or across or angular direction onto the plurality or stack of plies, until molding pressure is generated, thereby forming the plurality or stack of materials in the shape of required helmet shell;
d. the plurality or stack of plies moves as mold halves traverses downward or upward or sideward or in angular direction, whereby pressure is increased gradually and the stack of plies moves across the molding surface to gradually increase pressure further;
e. mold halves are then moved through the material which consist of plurality of plies, whereby rate of pressure increases with the movement of mold halves, following a predetermined profile controllable by a downstream pressure regulator;
f. the mold halves then reach its fully traversed position, whereby it has to be held at the same pressure for few minutes to start the curing process material; and
g. cold water or oil or air is then circulated in the mold halves, bringing down the mold temperature prior to removal of the helmet shell.

2. The macro-matrix pre-thermoforming molding process as claimed in claim 1, wherein the plurality or stack of plies is pre-heated in a mold by oil, air, steam or electric heaters in the range of 100 – 150 °C.
3. A rifle protection helmet obtained by macro-matrix pre-thermoforming process, wherein wrinkles in the molded helmet shell are reduced, thereby increasing the performance of fibers due to strain induced crystallization, and further enhancing the capability of tensioned fibers to absorb energy of high velocity rifle projectiles.
4. The rifle protection helmet as claimed in claim 3, wherein the helmet is made up of engineered textiles or fabrics or aromatic polyamide or High and Ultra high molecular weight polyethylene or woven/non-woven unidirectional fabric or prepreg composite or glass and carbon composites or structural composite or nano composite material in specifically designed layout.
5. The rifle protection helmet as claimed in claim 4, wherein the layout comprises full layers or slit and non-slit layers or polygons or strips or uniform and non-uniform geometrical shapes.
6. The rifle protection helmet as claimed in claim 5, wherein the plurality of layers or pieces may comprise thermoplastic or thermoset polymeric or elastomeric or resin matrix, and may also be with or without added nano particles.
7. The rifle protection helmet as claimed in claim 3, wherein said helmet is molded in a mold comprising at least two or more halves made of metal or alloy or polymer or composite material, further having heating and cooling provision.

8. The rifle protection helmet as claimed in claim 3, wherein said helmet may be obtained by cutting in plurality of standard and non-standard shapes such as a full cut, mid cut, high cut, PASGT or MICH.
9. The rifle protection helmet as claimed in claim 3, wherein said helmet may have a weight range of 1000-2500 grams.
10. The rifle protection helmet as claimed in claim 3, wherein said helmet may have a thickness range of 10-25 millimeters.
11. The rifle protection helmet as claimed in claim 3, wherein said helmet may resist minimum nine (09) shots of 7.62 x 39 mm AK 47 mild steel core bullet at a minimum velocity of 650-750 m/s.
12. The rifle protection helmet as claimed in claim 11, wherein said helmet has uniform protection all around the helmet surface, without using any additional armored plate or insert or applique or any other add-on material.
13. The rifle protection helmet as claimed in claim 3, wherein said helmet may resist a 7.62 x 51 mm M80 NATO ball NIJ 0101.06 (Level III) or 7.62 x 39 mm AK47 hard steel core, lead core and .30 caliber (level IV) NIJ 0101.06.
14. The rifle protection helmet as claimed in claim 13, wherein said helmet may resist other small arms and ammunitions, including RCCs, FSP and spherical fragments.
15. The rifle protection helmet as claimed in claim 3, wherein said helmet has V50 fragment protection for more than 1200 m/s against 1.1g fragment simulating projectile in accordance with MIL 662F, STANAG 2920 and other various global and national standards at hot (+70 degree centigrade), cold (-50 degree centigrade), water immersion up to 24 hours, dry conditions and all other temperature and environmental conditions.

16. The rifle protection helmet as claimed in claim 3, wherein said helmet provides resultant Back Face Deformation (BFD) in clay from 0 to 25mm.
17. The rifle protection helmet as claimed in claim 3, wherein said helmet protects user or wearer from non-ballistic blunt impacts.
18. The rifle protection helmet as claimed in claim 17, wherein said helmet protects user or wearer from non-ballistic blunt impacts with reported value of acceleration due to gravity being 50-150 g when tested as per DOT FMVSS 218 or STANAG 2902 and other various global and national standards at hot (+70 degree centigrade), cold (-50 degree centigrade), water immersion up to 24 hours, dry conditions and all other temperature and environmental conditions.
19. The rifle protection helmet as claimed in claim 3, wherein said helmet has no perforation on the surface in order to maintain uniform ballistic protection.
20. The rifle protection helmet as claimed in claim 3, wherein said helmet comprises a modular retention system without perforating the helmet shell, ensuring uniform protection with complete stability of helmet provided by a twist fit mechanism and complying the requirement of EN 397, taking the anchorage load up to 200 kg.
21. The rifle protection helmet as claimed in claim 3, wherein said helmet has flame resistance characteristics in accordance with STANAG 2902 or EN 397 and other various global and national standards and standards of rigidity.
22. The rifle protection helmet as claimed in claim 3, wherein said helmet has compression resistance characteristics in accordance with STANAG 2902 or AR-PD 10-02 and other various global and national standards.

23. The rifle protection helmet as claimed in claim 3, wherein said helmet has resistance against high temperature from 50 to 80 degree Celsius.
24. The rifle protection helmet as claimed in claim 3, wherein said helmet has resistance against cold temperature from 5 to -50 degree Celsius.
25. The rifle protection helmet as claimed in claim 3, wherein said helmet has resistance against normal and sea water immersion for a minimum of 24 hours.
26. The rifle protection helmet as claimed in claim 3, wherein said helmet has resistance against fungal growth in accordance with MIL 810 G or JSS55555 and other various global and national standards.
27. The rifle protection helmet as claimed in claim 3, wherein said helmet has resistance against chemical agent in accordance with MIL 64159 B and other various global and national standards.
28. The rifle protection helmet as claimed in claim 3, wherein said helmet has provision to mount tactical accessories such as MIL 1913 picatinny rail, NVG shroud, counterweight system, ballistic visor, flashlight, laser, camera and other advanced and conventional accessories.
29. The rifle protection helmet as claimed in claim 28, wherein the accessories may be mounted on the helmet without making any perforation or any using any external fastening system.