Research

[1] Patent: Helmet Impact Liner System, US 20130291289

 

US Patent No. 0291289 describes a lining system inside the helmet that protects the user from large impulses and helps to prevent brain injuries. Head injuries such as concussion used to be quite common in contact sports such as football, but recently, technology has improved to help better protect athletes. Additionally, concussions can occur in military personnel that have been shot in the head while wearing a helmet. While the helmet can stop the bullet, the impact can still cause injury due to the high impulse subjected on the user. The lining system described in this patent serves to absorb energy and distribute it evenly so that the risk of injury to the wearer is less than that if they are using another helmet. Additionally, the configuration of the lining system is important in distributing the energy [1]. The lining is attached to the inside of the helmet and cushions the users head and also makes it more comfortable to wear. The structures which absorb the energy function using compression [1]. This patent is relevant to our current project in that we can use a similar system to manage the distribution of energy absorbed from a bullet and protect the wearer from injury.

 

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[2] Article: Thermoforming and Structural Analysis of Combat Helmets

 

Simulation and manufacturing of military helmets are incredibly important in determining the effectiveness of a helmet design. In order to perform a simulation of a helmet, the material properties must be determined. Additionally, the tests performed on a material sample must also be representative of the manufacturing of the material samples used in the making of the helmet [2]. In this journal article, the following tests and standards used were used to gather the material properties for Ultra High Molecular Weight Polyethylene [2]:

1. bias-extension test, ASTM D 1774-93

2. cantilever bend test, ASTM D 1388

3. peel test, ASTM D 1876-01

4. lap shear test, AS/NSZ 3572.19:1997

5. tensile test, ASTM D 882-02

6. flexural test, ASTM D 790

7. short beam shear test, ASTM D 2344

When manufacturing a helmet using this material, UHMWP must be shaped in the form of a helmet correctly to eliminate defects that could alter the material properties [2]. To prevent defects, flat stacks of UHMWPE plies should be preheated and then formed into the shape of the helmet to eliminate splices in the plies [2]. Additionally, wrinkles can occur in the stacked plies, which again alters the material properties. This defect can be avoided by applying heat to the plies of UHMWPE so that they melt and become viscous essentially glue themselves together with the absence of trapped air [2]. This eliminates any air bubbles and other trapped gasses that can cause wrinkles. The information gathered from this article will surely help in obtaining the correct testing procedures and manufacturing processes to produce an effective material.

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[3] Patent: Varying Thickness Helmet For Reducted Weight And Increased Protection, US 20090313736A1

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This patent provides detailed explanations on structuring the material properties of a helmet based on area hit rate and threat assessments to the user. By utilizing multiple projectile defeat mechanisms, helmet thickness and weight could be reduced without compromising overall protection. It also goes further in-depth on optimizing helmet thickness to present enemies with a smaller “kill zone”. Through usage of 3D threat models, the thickness of the helmet would be varied throughout the entire helmet. Areas where a soldier would likely take a direct hit would have a thickness requirement that stops the incoming projectile. Larger projectiles or higher threats would require the thickness to be sized according to likely shooting angles, where the requirement would be to deflect or cause the projectile to glance off of the surface of the helmet. Low threat areas on the helmet such as the top and rear would have reduced thickness to lower overall weight. Higher threat areas require projectile defeating mechanisms that stop or deflect expected projectile threats. The patent helps to maintain overall helmet protection while maintaining the same weight or even reduced weight which is the goal of the group’s experiments.

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[4] Article: Soldiers’ Satisfaction With Their Ballistic Helmets

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The journal article [4] articulates a survey done on soldiers currently deployed and veterans. The journal notes users’ satisfaction with their ACH helmets compared to PASGT helmets. Satisfaction can range from comfort, weight and fit to maintainability and overall impression. Results show that more users are satisfied with the ACH helmet than the PASGT helmet. The ACH helmet had over 60 percent satisfaction across all five categories whereas the highest rate of satisfaction for the PASGT helmet is only 30 percent. Most notable of the survey is the issues with the 2 helmets. The ACH’s most prominent problems were identified to be loose screws, loose straps, loose pads, heat retention and spare part availability. The PASGT’s issues were much more abundant, which involved causing headaches, heavy weight, uncomfortable, poor fit, caused cuts and skin irritation and various others. This is article provides invaluable information for the project as it can help create improvements for a better product for soldiers as well as avoid making the same mistakes predecessors have made.

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[5] Patent: Rifle Rated Ballistic Helmet, US 2011/0203024 A1

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In this patent, a new rifle rated ballistic helmet is introduced. The lightweight helmet that is resistant to penetration by rifle bullet. The 80% of the helmet shell has the outer layer consist of hexagon shape plates: the base of the shell to the crown is covered by plates. Other 20% of the helmet shell area is not covered by plates due to a concern about weight addition; the goal for total weight helmet does not exceed 6.85 pounds. The hexagon shape plates are made of Ultra High Molecular Weight Polyethylene (UHMWPE): the UHMWPE fibers are molded in a thermoplastic resin matrix. The hexagon shape is chosen to achieve interlocking geometry shape for the plates. The plates are 0.6 cm thick and diameter of hexagon can be from 1.0 inches to 2.0 inches. The group is designing a combat helmet named HUK helmet that will have a weight close to the current helmet, but better strength. HUK helmet will be designed with two different materials, Kevlar molded in UHMWPE. The idea of a layer consist of hexagon plates can help the group to improve layering the composites on the shell. Also, the group can consider molding kevlar in thermoplastic resin matrix to compare the strength and weight per cubic inches to kevlar in UHMWPE. This can give the group variety of sample types to explore and strengthen the result data. The hexagon diameter used in the patent can also be considered as a reference start point to build the group’s sample plates. Moreover, covering entire area of the shell can be reconsidered with covering area that is more likely to be aimed and hit in other words the top part of a helmet has a less change to be hit.

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[6] Article: Finite element analysis of the Advanced Combat Helmet

 

In this journal article, ballistic performance of Advanced Combat Helmet (ACH) is evaluated by the U.S. military. Finite element analysis (FEA) contains the simulations and experiments and the results from FEA are compared to the existing test data in literature. From the simulation and experimental data it is shown that ACH responses under 9 mm bullet and 1.1 g fragment simulating projectile [6], however, ACH is deficient under impact of .223 rifle impact by an experiment conducted in an open field. The comparison of simulation results to experimental data showed that the developed ACH model was capable of prediction the ACH responses under ballistic impacts of 9-mm bullet and 1.1g fragment simulating projectile.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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The picture above is showing how the experimental test set up by following NIJ standard The test is conducted with V50 ballistic limit, which is specified by the Army’s Standard MIL-H-44099 A. The material properties for the helmets are taken from the literature and FEA is done with this properties. Throughout the simulation and open field experiment the permanent deformation of the ACH is observed and varied depending on impact locations: the front part of the helmet had the smallest impact size. The group can verify what part of the helmet has the smallest impact area and apply this information with covering that area of the helmet with more layers of the composite samples made of kevlar and UHMWPE. Also, it can be learned NIJ test setup, an open field setup, and V50 ballistic limit. This article can be useful for the group by providing what material properties are needed for FEA and plan for what testings are required in order to achieve all necessary material properties. Moreover, the group project HUK helmet will be proved its better performance by comparing the data to the ACH data in the article.

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[7] Patent: Armor Panel, US 5789327

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US Patent No. 5789327 initially addresses how one method of making body armor resist bullets by simply increasing the amount of material used, however, there are drawbacks.  One of the major issues is that it increases the weight of the jacket, which will increase the fatigue put onto the user. Wearing the vest over long periods can cause the user to sweat and can double the weight of the vest due to the sweat being absorbed by the ballistic cloth [8].  Reducing the weight will also make the jacket much more comfortable and the user will wear it more often than just when they need it the most, which could ultimately save a life when it might not be expected. Another downside of simply increasing the number of layers used means the cost of the product also increases, so finding another material could benefit both the producer and consumer.  The patent's invention uses an elastomeric adhesive material with oriented polymer chains to bond the ballistic-resistant cloth layers together. Using this method, it produces a sample that requires less than half the thickness, is much lighter, and also buoyant, making it all around more user friendly. Based on the finding from this patent, incorporating a material such as the polyethylene, between Kevlar layers could create a more convenient and combat-ready helmet.     

 

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[8] Article: The effect of target thickness on the ballistic performance of ultra high molecular weight polyethylene composite

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The journal article [8] explains an experiment that analyzed the ballistic performance of Dyneema polyethylene of varying thicknesses up to 100 mm with both 12.7 mm and 20 mm fragment simulating projectiles.  One of the first forms of information found in this article found that the Dyneema performed better than Kevlar under various testing. The article also addressed how the polyethylene commonly failed.  When the panel is under 10 mm, it was found to have large deflection and bulging, while failure comes mainly from fiber tension [8]. When the test panel becomes larger, the penetration becomes a two stage process. First, the sample experienced shear plugging from the initial penetration and then transitioned into bulging of a rear section. This gives a good idea of the kind of failure that would be experienced when utilizing the polyethylene in the helmet.  Since the HUK Helmet will be dealing with thin layers of the Dyneema, it would be expected to experience one of these forms of failure, as opposed to the two stage process. Implementing the layers of Kevlar will hopefully reduce the large deflection in the Dyneema, and ideally combining them will produce a material that provides an optimal combination of ballistic resistance and light weight.

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[9] Patent: Helmet Shell Fabric Layer and Method of Making the Same

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US Patent No. 4596056 filed in 1986 gives an idea as to a pattern by which to position fabric that is to be then molded with a subsequent material to form the helmet. The patents lays out possible shapes of individual pieces of fabric that can be combined to ultimately form a helmet shell. This is particularly important as it will allow the group the option to reference this type of methodology for forming the final helmet, if we choose to construct a helmet using a mold. The pattern laid out in the patent ensures the individual fabric pieces would not overlap, if done properly and in turn would conserve the fabric in general. It also allows for increased precision and the minimal overlap of material will ensure a consistent thickness during layering. Right now this patent would be useful because moving forward the group knows it can use this methodology to prototype a helmet using UHMWPE and kevlar but in parallel is looking into alternative methods of construction. This helps us to move forward and have an idea for a plan of molding a helmet with patterning and combining individual kevlar sheets.

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[10] Article: Dynamic and Fatigue Performances of Composite Materials

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This article highlights some research that will be useful as the group moves forward into some of our planned material testing. Particularly since we are working in composites it is important to understand the methodology behind what the article highlights as low-cost manufacturing which is definitely a concern of the group given the scope of the project. Particularly as we do move forward the results will drive the project and costs associated with moving forward given what we learn at each step will add up. In some of the research presented in this article and with charpy testing kevlar composite were affected relatively greater with low masses striking at high velocity, which is something the group will have to investigate further given that we do intend to make a helmet ballistic protective helmet. It also highlights previous research, which measured impact energy of kevlar epoxy at about 694 kJ/m2, a value we will definitely take into account during testing setup. The result was obtained using a standard impact test using a notch and it is important to note the the compression side during testing experienced some yielding but did not fracture completely, which is a consideration for the group.

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Citations:

[1] Szalkowski, Ron, Schmidt, Joshua, “Helmet Impact Liner System.” United States Patent Publication Number US 2013/0291289, Publication Date November 7. 2013

[2] Cartwright BK, Lex Mulcahy NN, Chhor AO, et al. Thermoforming and Structural Analysis of Combat Helmets. ASME. J. Manuf. Sci. Eng. 2015;137(5):051011-051011-9. doi:10.1115/1.4031154.

[3] Kocher, Robert W., Simon, David E., "Varying Thickness Helmet For Reducted Weight And Increased  Protection" United States Patent Publication Number US 2009/0313736 A1, Publication Date December 24, 2009 

[4] Ivins, Brian J, et al. "How Satisfied Are Soldiers with Their Ballistic Helmets? A Comparison of Soldiers' Opinions about the Advanced Combat Helmet and the Personal Armor System for Ground Troops Helmet." Military Medicine, vol. 172, no. 6, June 2007, pp. 586-591. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=mnh&AN=17615837&site=ehost-live&scope=site.     

[5] Morgan, Arthur C.,"Rifle Rated Ballistic Helmet". Patent US 2011/0203024 A1, issued Aug 25, 2011.

[6] Palta, Emre, Fang, Hongbing & Weggel, David C., "Finite element analysis of the Advanced Combat Helmet under various ballistic impacts." Interntional Journal of Impact Engineering Vol. 112 (2018): pp. 125-143. DOI: https://doi.org/10.1016/j.ijimpeng.2017.10.010.

[7] Rousseau, Wm. Richard. “Armor Panel”. Patent 5,789,327, issued Aug. 4, 1998.  

[8] Nguyen, Long H. et la. “The effect of target thickness on the ballistic performance of ultra high molecular weight polyethylene composite.” International Journal of Impact Engineering Vol. 75 (2015): pp. 174-183. DOI: https://doi.org/10.1016/j.ijimpeng.2014.07.008

[9] White, Milton R., "Helmet Shell Fabric Layer and Method of Making the Same". Patent 4,908,877A, issued Mar, 20 1990.

[10] Lee, Dai Gil Suh, Nam Pyo. (2006). Axiomatic Design and Fabrication of Composite Structures - Applications in Robots, Machine Tools, and Automobiles - 10.1 Introduction. Oxford University Press.