A Thesis Presented to - AURA - Alfred University

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A Thesis Presented to The Faculty of Alfred University

An investigation into the viablility of ceramic foam and ultra high molecular weight polyethylene composite for ballistic arrest

By Joseph Rice

In partial fulfillment of the requirements for

the Alfred University Honors Program 4/29/2021

Under the Supervision of:

Chair:

Dr. Tim Keenan, Assistant Professor, Biomaterials Engineering

Committee Members:

Dr. William Carty, Emeritus Professor, Materials Science & Engineering

Dr. Roger Loucks, Professor, Physics and Astronomy

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Acknowledgments

I would like to thank my advisor, Dr. Keenan for the help and guidance throughout this project. I would also like to thank Andy Norris for helping provide the ceramic foam for test material and Dr. Pilgrim for supplying the polyethylene. Jim Thiebaud and Dr. Stohr also deserve a thank you for their help with mechanical testing and SEM guidance.

Finally, my most appreaciated support came from my family who always encouraged me to push myself but not at the expense of my sanity.

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LIST OF TABLES

Page Table I. NIJ Armor classifications and threats ... 8 Table II. PSZ filter parameters [7] ... 13 Table III. Test Velocities and Kinetic energies of 124gr 9mm and 40gr 22LR ... 20 Table IV. Information regarding sample 3 ballistic testing including ID, caliber, velocity,

KE and physical observations ... 21 Table V. Information regarding sample 3 ballistic testing including ID, caliber, velocity,

KE and physical observations ... 23

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LIST OF FIGURES

Page Figure 1. .223 rifle round vs 9mm pistol round. ... 12 Figure 2. Figure 2. Filter used in sample 1, reference scale in inches. ... 15 Figure 3. Steps of Sample 1 processing, showing placement of filter into crucibles (1),

addition of powder to filter (2), sample immediately after removal from

furnace (3), Sample after cooling (4) . ... 15 Figure 4. Steps of sample 2 processing showing starting filer set up (1), placement of

loaded filter into furnace (2), bottom side of sample after 8 hour dwell (3), final removed sample (4) ... 17 Figure 5. Steps of sample 3 processing including powder loading the filter (1),

placement into furnace (2), and removal/cooling (3). ... 18 Figure 6. Sample 4 processing steps illustrating cylinder preparation (1 and 2),

placement of pressing cylinder into furnace (3) and exploded view of die (4).

... 19 Figure 7. Shot ID and entry placement show from the strike face of sample 3 (left) and

shot exit location (right).. ... 22 Figure 8. Shot ID and entry placement show from the strike face of sample 2 (left) and

shot exit locations (right).. ... 23 Figure 9. Expanded view of exit channel (Sample 3, shot 2) ... 25 Figure 10. Captured .22LR projectiles from sample 3, shot 4 (left) and sample 2, shot 2

(right) ... 25 Figure 11. Clear indent with estimated axis measurement (left), distorted indent with

estimated axis estimates (right)... ... 27 Figure 12. Channel of sample 2, shot 2, showing entry on the left and final resting bullet

on the right ... 28 Figure 13. . Optical microscope image of interior polyethylene particle ... 29

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Figure 14. SEM imaging of sample 1 at 250x (left), 1000x (middle) and 2500x (right) . 29 Figure 15. SEM imaging of sample 4 at 75x (left), 1000x (middle) and 2500x (right) ... 30

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ABSTRACT

Modern developments in small arms ammunitions and capabilities have led to an increased focus on personal body armor. Traditionally, ceramic faced armor with aramid backings has been a top choice for protection from small arms, due to its ability to stop a variety of rifle rounds. Recently however, ultra-high molecular weight laminate armors constructed from materials such as dyneema® have begun to be adopted due to their extreme weight savings. However, these armors are extremely expensive and are not capable of stopping higher level threats such as armor piercing ammunition. In an effort to explore an alternative method for body armor creation, a zirconia ceramic filter was combined with ultra-high molecular weight polyethylene (UHMWPE) powder. This idea looked to experiment with the viability of combining the properties of a hard ceramic and high-strength polymer into a single, interconnected composite. Four sample iterations were created using various times at temperature, pore densities, sizes, and pressures.

Ballistic testing was conducted to assess whether this composite possessed any realistic ability to arrest projectiles. Only 2 of the 7 projectiles were stopped, but upon further assessment, some of the interactions that lead to the capture of projections were observed.

Hardness testing and SEM imaging were conducted in order to better understand the failures of the composite.

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INTRODUCTION

Background

Body armor has been the natural response to the development of offensive weapons for thousands of years. However, with the implementation of firearms as the primary weapon of war, personal armor fell out of fashion. This was due to the unique nature of high velocity threats and a lack of the materials and knowledge needed to defeat such threats. Recently though, body armor has become a staple for modern soldiers because of the leaps in materials and technology involved. Police, security forces, and military personnel require varying degrees of protection, ergonomics, and weight parameters for modern armor, which now involves a diverse group of materials and techniques.

Understanding threats

Within the United States, the National Institute of Justice (NIJ) develops the testing and rating procedures used for qualification of body armor. NIJ testing covers both ballistic resistance (NIJ Standard-0101.06) and stab resistance (NIJ Standard-0115.00) [2]. For the purposes of this thesis, only ballistic resistance will be explored. NIJ Standard-0101.06 divides armor classification into five types (IIA, II, IIIA, III and IV) by ascending ballistic performance. Table I contains the five armor classifications and the summarized threats they are rated to stop. This table also contains the maximum possible energy needed to be stopped based on NIJ weight and velocity requirements.

Table I. NIJ Standard-0101.06 classifications and threats

Classification Threats Maximum possible energy (J)

IIA 9mm; .40 S&W 762.8 Joules

II 9mm; .357 Magnum 1,010 Joules

IIIA .357 SIG; .44 Magnum 1,357 Joules

III 7.62x51mm (M80) 3,518 Joules

IV .30 caliber AP (M2 AP) 4,250 Joules

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9 Type IIA

Type IIA armor is tested both new and conditioned using 9mm Full Metal

Jacketed Round Nose (FMJ RN) bullets with a grain weight of 124gr (8.0 g) and velocity of 373 m/s ±9.1 m/s as well as .40 S&W FMJ bullets with a grain weight of 180gr (11.7 g) and velocity of 352 m/s ± 9.1 m/s.

Type II

Type II armor is tested both new and conditioned using 9mm FMJ RN bullets with a grain weight of 124gr (8.0 g) and velocity of 398 m/s ±9.1 m/s as well as .357 Magnum Jacketed Soft Point (JSP) bullets having a grain weight of 158gr (10.2 g) and velocity of 436 m/s ±9.1 m/s.

Type IIIA

Type IIIA armor is tested both new and conditioned with .357 SIG FMJ Flat Nose (FN) bullets with a grain weight of 125gr (8.1 g) and velocity of 448 m/s ±9.1m/s as well as .44 Magnum Semi Jacketed Hollow Point (SJHP) bullets with grains weight of 240gr (15.6 g) and velocity of 408 m/s ± 9.1 m/s.

Type III

Type III hard armor plates are tested only in the conditioned state while Type III flexible armor is tested both new and conditioned. Both are tested using 7.62 mm FMJ steel jacketed bullets (US Military M80) with a grain weight of 147gr (9.6 g) and velocity of 847 m/s ± 9.1 m/s.

Type IV

Type IV armor plates are tested only in the conditioned state while Type IV flexible armor is tested both new and conditioned. Both are tested using .30 caliber armor piercing (AP) bullets (US Military M2 AP) with grain weight of 166gr (10.8) and

velocity of 878 m/s ± 9.1m/s.

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10 Understanding Injury Mechanisms

The human body is very poorly equipped to deal with penetrative injuries. It is believed that 1 J is the low limit for lethality during penetrative attacks, but it is militarily accepted that 80 J is needed for a small penetrative projectile to cause incapacitation [1].

During high velocity ballistic impacts, a temporary wound channel is created resulting is large amounts of soft tissue damage due to cavitation. Cavitation results from turbulent flow in the wake of the projectile. An area of expanding low pressure vapor forms behind the projectile during penetration which then quickly collapses. This is particularly deadly within the thoracic cavity where the heart, lungs, and central nervous system reside, whereas extremities are able to tolerate these impacts better due to the elasticity of skin and muscle tissue [3]. As a result, most modern armor is designed to protect the wearer from the catastrophic damage that would ensue following a high velocity impact to the thorax.

Unlike penetrative injuries, the human body is well equipped to deal with blunt force trauma. As an example, a baseball can be thrown around 40 m/s, with a mass of 0.145kg. With a kinetic energy of 116 J, this would fall well within the military value of 80 J needed for a penetrative projectile to cause incapacitation. However, because a baseball does not have penetrative potential at such a low velocity, it will not cause catastrophic damage to the unsuspecting batter. Blunt force trauma can still present an issue however when designing armor. Described by the NIJ as Backface Signature (BFS), or the greatest extent of non-penetrative indentation into a backing material after amor impact. NIJ certification dictates that backface signature cannot exceed 44mm into the clay analogue backing [2]. It is within this threshold that the armor has successfully prevented significant injury to the wearer.

Behind Armor Blunt Trauma (BABT) has increased in threat as larger calibers with higher energies are fielded, alongside unconventional threats such as explosive ordinances. Another cause of this increase has been armor designers desire to reduce the weight and thickness of armor systems. Although this has clear benefits for alleviating the effect of carrying heavy, bulky armor, it may also increase the likelihood that armor cannot properly dissipate or absorb the energy from the impact. Although penetrative

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injury is prevented, the energy deposited into the body wall though the backing of the armor can still cause serious blunt force trauma. This trauma can cause serious injury within the thoracic region to the heart, lungs, pleural cavity, and chest wall which can result in death [4]. Simply preventing the penetration of the projectile is only part of an armor systems function, whereas preventing significant injury to the wearer is the ultimate goal.

Understanding Armor systems

Armor systems have had a multitude of materials and construction methods over the past 100 years. However, it is the more recently developed armor systems that have become a staple for police and military personnel. There are two basic armor types; one being flexible armor, otherwise known as textile based armor or soft armor; and one being hard armor, otherwise known as plate armor. Each has their own unique uses and capabilities.

Soft armor will be touched on briefly, as the purpose of this thesis is to explore an alternative hard armor. Soft armor is known as flexible textile-based armor because it is constructed from a weave of small yarns which is able to flex and conform to the wearer.

These weaves are layered upon one another to create a multilayer construction. These yarns are made from high tensile strength materials such as the aramids Kevlar® or Twaron® or Polyethylene fibers Spectra® or Dyneema® [5]. Upon impact, the projectile accelerates the weave to a similar velocity. If the energy is not sufficient to cause the failure of the fibers, then the subsequent layers also accelerate, dissipating the energy of the projectile. Above a specific velocity however, the yarns will fail. In this case very little energy is taken from the projectile and penetration occurs [1]. It is for this reason that soft armor is only capable of stopping lesser threats, normally constituting NIJ level II, IIA and IIIA threats. Another important consideration to make is the kinetic energy density (KED) of the threat. The kinetic energy density of a threat is described as the amount of energy per unit area of the projectile [1]. As the KED increases, the difficulty of stopping the projectile also increases. Rifles bullets generally have high KED’s while pistol threats generally have lower KED. Figure 5 illustrates the visual difference

between a rifle caliber and pistol caliber. It is visually apparent that the rifle caliber has a

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much smaller contact area than the pistol caliber. The rifle round also travels at a much higher velocity, 960 m/s vs 380m/s. As a general rule, these factors make stopping rifle threats much more difficult than stopping pistol threats.

Figure 1: .223 rifle round on the left vs 9mm pistol round on the right

Hard armor is commonly used by military personnel, military vehicles, and has begun to gain some popularity with law enforcement as the weight decreases and ergonomics increase. Hard armor is required in situations where the KED is too high, typically above 30 J/mm and the number of woven layers needed to arrest the projectile would become unreasonable for soft armor. In cases of high KED, a “disruptor-absorber”

structure currently provides the best protection from high energy threats with hard cored penetrators [1]. This structure provides a two-step method towards preventing penetration from these projectiles. The first step is disruption. The incoming projectile will first come into contact with a hard strike face material. Ceramics are the most common choice due to their high hardness. Relatively high purity alumina (98%), silicon carbide, or boron carbide function as the first contact material. The purpose of the strike face is not to extract large amounts of energy from the projectile, but rather act to decrease the KED of the projectile. Due to the high hardness of the ceramic face, the projectile either

fragments or deforms, known as mushrooming. The second stage is then absorption.

Because the strike face was able to deform the incoming projectile and increase its KED,

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a similar approach can be taken as soft armor. Polymer composites such as aramid in a polymer resin matrix or pressure consolidated polyethylene laminates are common backings. These backings that were unable to prevent penetration on their own are then able to absorb the energy of the projectile due to its dispersion over a larger surface area.

Materials and Methods

Materials:

The polyethylene chosen was GUR 4120. Of the 3 samples obtained, GUR 4120 had the highest molecular weight at 5.0*10⁶g/mol, and a shore hardness D, 15 s value of 60 [6]. After reviewing the thesis completed by Timothy Morrissey, GUR 4120 was expected to provide an “excellent property spectrum” as described by the manufacturer. It also appeared that GUR 4120 had been affected the least in initial heating tests where other samples had begun to oxidize and significantly change color.

The ceramic foam of choice was provided by Ask chemicals LLC. The foams provided were denoted PSZ. Primary components were 97% zirconia and 3% magnesia.

Table II contains typical values for various parameters of the filters. Because armor ceramics are specific in their construction and composition, the closest analogue was determined to be the Zirconia filters [7]. Although these filters were not expected to function as efficiently as tradition SiC or alumina armors, they were expected to suffice as test subjects to determine the viability of synthesis.

Table II: PSZ filter parameters [7]

Typical Values

Zirconia composition (%) 96--97

Magnesia composition (%) 2.8—3.0

Modulus of rupture (Room temp)(psi) 250

Bulk density (g/cm³) 0.84—1.12

Porosity (%) 80--85

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Sample Creation

Sample 1

The first sample functioned as proof of concept for incorporating the powder into the foam matrix. The ceramic foam was disc shaped with a diameter of approximately 2 inches and a height of approximately 0.6 inches. This filter also has a pore density of 15 pores per inch (ppi). The UHMWPE used was GUR 4120. Figure 2 includes an image of the filter for reference. Figure 3 illustrates the steps taken. All samples were heated using a benchtop muffle furnace (Thermo Scientific, North Carolina).

1. The filter was placed into 2 crucibles in an abundance of caution to prevent a spill into the furnace.

2. Powder was carefully poured into the crucible containing the filter. Once the powder reached the top on the filter, it was hand tapped 15 times in order to settle the powder into the matrix. More powder was added, and the process repeated until the filter would no longer accept powder.

3. The sample was placed into the furnace at 160°C for 240 minutes. Higher temperatures such as 190°C risked the oxidation and degradation of the sample, especially at dwell times longer than 120 minutes [6] It can be seen that the sample had a clear surface when it was removed from the furnace. The surface was somewhat sticky with a putty-like consistency.

4. The sample was allowed to cool at room temperature. The color quickly changed to a milky white and the material became hard. The crucible around the sample needed to be broken in order to remove it.

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Figure 2. Filter used in sample 1, reference scale in inches.

Figure 3. Steps of Sample 1 processing, showing placement of filter into crucibles (1), addition of powder to filter (2), sample immediately after removal from furnace (3),

Sample after cooling (4)

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16 Sample 2

The second sample was created with a larger disk (diameter 4” and height 0.8’).

This filter had a lower pore density of 10 ppi and included a side wall around the perimeter of the filter. GUR 4120 was again the polyethylene used. Steps taken for this process are illustrated in figure 4.

1. It was determined that there was no risk of spill over from sample 1. The sample 2 filter was wrapped with aluminum foil and powder was tapped and loaded following the procedure of sample 1 (15 hand taps and loaded until powder is no longer accepted).

2. The powder loaded sample was placed into the furnace at 160°C for 8 hours.

When removed the top appeared clear and sticky similar to sample 1. Small amount of yellow discoloration had occurred.

3. The aluminum foil was removed, and it was observed that the bottom of the sample was still white and relatively soft, like a dense foam. It is believed that the size of the sample and the contact with the bottom of the kiln did not allow the bottom of the sample to reach temperature for long enough.

4. The sample was flipped with the white face up and placed back into the furnace at 160°C. The sample remained for 4 hours and was removed. The top face had turned clear while more yellow discoloring was observed. After cooling at room temperature, both faces felt hardened.

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Figure 4. Steps of sample 2 processing showing starting filer set up (1), placement of loaded filter into furnace (2), bottom side of sample after 8-hour dwell (3), final removed sample (4).

Sample 3

The third and largest sample was prepared using a roughly rectangular filter with dimensions of approximately 4” by 8.5” and a width of 1”. This filter had a pore concentration of 15ppi and like sample 2, had walls along the perimeter. Figure 5 illustrates the processing steps taken.

1. The sample was placed in aluminum foil like sample 2. Powder was loaded in the same fashion as samples 1 and 2. No noticeable difference in powder loading was observed between sample 2 and 3 due to pore concentration.

2. The sample was placed into the furnace at 160°C for 7 hours. The sample was then removed, and the bottom layer of aluminum foil was removed. It was again clear that the bottom was white and foam-like. The sample was flipped and placed back into the furnace for 7 hours.

3. The sample was removed and allowed to air cool. Some yellow discoloration occurred along the edges of the sample. However, the surface was primarily clear and sticky as in sample 1. After air cooling both sides were hard to the touch.

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Figure 5. Steps of sample 3 processing including powder loading the filter (1), placement into furnace (2), and removal/cooling (3).

Sample 4

Sample 4 was created using a filter of the same dimensions as sample 1. The filter used had a diameter of approximately 2” and height of 0.6”. The filter also had the same pore density as sample 1 at 15ppi. The purpose of this sample was to experiment with application of pressure using a Carver hydraulic benchtop manual press (Carver, Indiana).

Sample 4 creation is illustrated in figure 6 and the steps described below.

1. An aluminum cylinder is created with two layers of aluminum foil. Once the bottom of the cylinder is capped, 0.5” of GUR 4120 powder is added to the bottom. The filter is then placed on top of the powder layer.

2. Using the same add and tap method as the other samples, powder is then added to the cylinder until there is a 0.5” powder layer on top of the filter. Looking at image 4 of figure 6, it can be seen that there is room for 0.5” of powder on either end of the filter.

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3. The aluminum cylinder is capped to prevent the die from seizing due to any material spill. The cylinder and all die components are placed into the furnace at 160°C for 5 hours.

4. The die components are removed after the 5-hour period and are placed immediately onto the press. Pressure was applied slowly with expectation of reaching 1000 psi. However, at 250 psi, cracking became audible. To preserve the ceramic filter, pressure was released at 250 psi. The cylinder was removed from the die set up and the aluminum foil was removed. The pressed sample appeared uniformly white and opaque.

Figure 6. Sample 4 processing steps illustrating cylinder preparation (1 and 2), placement of pressing cylinder into furnace (3) and exploded view of die (4).

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Results and Analysis

Ballistic testing

Ballistic testing was conducted on samples 2 and 3 according to NIJ testing protocol distances. The samples were placed 16 ft. from the muzzle and velocity measurement was taken 6.6 ft. from the muzzle [2]. All velocity measurements were conducted using a ProChrono Plus chronograph (Competition Electronics Inc, Illinois). In order to prevent loss of energy due to tumbling or excessive movement of the samples during testing, they were placed against a closed cell polyurethane block. Two different rounds were used, 9mm 124gr FMJ, and .22LR 40gr round nose. The 9mm was fired from a Glock 43x with a barrel length of 3.41” and the .22LR was fired from a Ruger 10/22 having a barrel length of 18.5”. It should also be noted that the temperature was 35°F, outside of standard NIJ testing protocol. 5 shots were fired prior to testing of each caliber and the velocities were recorded. This can be seen in table III.

Table III. Test Velocities and Kinetic energies of 124gr 9mm and 40gr 22LR.

Sample 3 ballistic testing.

Testing of Sample 3 was conducted first. The sample was shot 5 times. Each time it was inspected and replaced onto the foam backing. Each shot velocity was also measured.

Figure 7 illustrates the placement of each shot and Table IV contains information regarding each of the shots.

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Table IV: Information regarding sample 3 ballistic testing including ID, caliber, velocity, KE and physical observations

Shot ID Caliber Velocity (m/s) Kinetic Energy

Observation

Shot 1 9mm 331 460 Direct Pass through

Shot 2 .22LR 298 115 Direct pass Through

Shot 3 .22LR 301 118 Entered form the side, was diverted out the side of the sample

Shot 4 .22LR 312 127 Entered in the side, was stopped.

Small cracking occurred on surface

Shot 5 9mm 334 469 Entered in the side, penetrated

approximately 50% of the sample (2”) before diverging out the side.

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Figure 7. Shot ID and entry placement show from the strike face of sample 3 (left) and shot exit location (right).

Sample 2 ballistic testing

Sample 2 testing was conducted second. Due to the limited size of the sample, only 2 shots were placed. Each shot velocity was recorded. Table V contains observations and data regarding the shots. Figure 8 illustrates the shot placement onto the sample.

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Table V: Information regarding sample 3 ballistic testing including ID, caliber, velocity, KE and physical observations

Shot ID Caliber Velocity (m/s) Kinetic Energy

Observation

Shot 1 9mm 332 463 Direct Pass through

Shot 2 .22LR 310 125 Entered from the side, was contained.

Blew out material from the side so the bullet was visible.

Figure 8. Shot ID and entry placement show from the strike face of sample 2 (left) and shot exit locations (right).

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Of the 7 total shots fired, 2 were stopped within the material. The shots that directly passed through the material followed a similar failure pattern. Figure 9 illustrates a closer view of the exit channel of sample 3. The surface polyethylene on the impact side of the sample contained a hole that was shaped consistently with the projectile.

However, the exit side of the channel was roughly conical in shape, with material blow out of a larger radius than the intruding projectile. This constitutes a distribution of energy onto a larger of area. For the .22LR, the entry is 5.7mm while the exit was on average 20mm. This shows that the kinetic energy distribution was lessened from 4.5 J/mm² to 0.37 J/mm². This lessening of KED is also visible on the captured projectiles shown in figure 10. Each of the .22LR rounds where mushroomed and their largest diameter expanded roughly twice in size, .22” to .4”. This expansions of KED and distribution of energy is precisely how armor needs to perform to stop incoming projectiles. However, there projectiles were not stopped unless they entered along the width, which extended the distance needed to penetrate.

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Figure 9. Expanded view of exit channel (Sample 3, shot 2)

Figure 10. Captured .22LR projectiles from sample 3, shot 4 (left) and sample 2, shot 2 (right)

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26 Hardness testing

Because the harness of the polyethylene contributes to the effectiveness of the armor, harness testing was performed. To test the hardness of the polyethylene, Vickers hardness tests were performed to better understand the effects of pressure or heat work on the samples as well as obtain a metric for comparison. Testing was conducted using a LECO V-100-A2 hardness tester (LECO, Michigan). Repeated attempts were made at 1, 5, and 10 kg loads to achieve a good indent on the pressurized sample (sample 4). However, no good indents were observed. Indents were also unachievable on the interior of the ballistic samples 2 and 3. There were two primary concerns with why indents were unachievable. One being that the material had a loosely connected network resulting in a foam-like structure. In this case the indents would be much too large and distorted to read.

The second concern was material spring back was distorting or fully retreating the indent making it impossible to measure [8]. This hypothesis coincides well with why the projectile channels had completely closed on themselves or had much smaller diameter than the bullet. This can be seen in figure 9, where the channel is irregular and partially closed after penetration. However, indentation was successful on the surface of sample 2.

Multiple surface locations were indented and then viewed using a Wild Heerbrugg M3Z optical microscope (Wild Heerbrugg, Switzerland) in conjunction with a SPOT Insight 2Ms Mosiac Camera and SPOT software (version 4.6). The diameter of the indent was measured along both axis, as seen in figure 11. Figure 11 also illustrates some of the difficulty associated with this method. Some indents such as the one on the right of figure 11, had clear edges and lengths, while others had much more rounded edges and unclear dimensions, such as the indent on the right of figure 11. Table VI contains the dimensions of 4 indents, taken at various locations on sample 2, and their related Vickers hardness values as calculated using equation 1. It is clear that the hardness across the surface is uneven with a standard deviation of 2.47. Typical values of Vickers hardness for UHMWPE is 6.4 – 8.3 [9], which does coincide somewhat well with the values measured.

It is for this reason that the surface is believed to have reached melt and crystallized properly. Because readings could not be obtained regarding the interior material or

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pressurized sample, it is believed that melt was not achieved, and proper crystallization did not occur.

𝐻𝑉 = 1.854(𝐹/𝑑²) (1)

Where HV is unitless Vickers hardness, F is the load in kg, and d is the diagonal length in mm.

Table VI. Indent ID with average diagonal length and STD Dev and Vickers hardness values calculated from 2 measured diagonals.

Figure 11. Clear indent with estimated axis measurement (left), distorted indent with estimated axis estimates (right).

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28 SEM/optical observations

Optical

Using the same optical microscope used to measure the indents, various images were taken to better understand the interactions of the composite. Figure 12 illustrates that the material close to the edges, and thereby exposed to more heat, appeared glassy shown by arrow 1. Material deeper with the sample was whiter in color and did not contain the transparency seen on edge material. Figure 14 shows that when viewed in greater detail, small fibers protrude from the surface of interior polyethylene particles. It is believed that because this material was shielded from receiving proper heat, it was unable to form the smooth crystalline phase seen along the surface. This theory also coincides with the hardness testing, which seemed to show that only the surface had reached a measurable hardness value, while the interior had not.

Figure 12. Channel of sample 2, shot 2, showing entry on the left and final resting bullet on the right

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Figure 13. Optical microscope image of interior polyethylene particle

SEM imaging

Scanning electron microscope (SEM) imaging was conducted using a Joel, JSM- 7800F Field Emission Scanning Electron Microscope (Tokyo, Japan). Figure 15 shows the ceramic, polyethylene interface of sample 1. A separation between the main body of polyethylene and ceramic is noticeable at 250x magnification. At 1000x and 2500x, it can be seen that the polyethylene does appear to have mildly bonded to the ceramic face.

Figure 14. SEM imaging of sample 1 at 250x (left), 1000x (middle) and 2500x (right)

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Figure 16 illustrates SEM images of sample 4. Because this sample was pressured to 250 psi, it was expected that the interface would be better joined. An opposite effect was observed. At 75x, the ceramic appears loosely imbedded in the polyethylene. At 2500x magnification, there is clearly no bonding visible. It is unknown why this would occur.

However, it is possible that because the ceramic began to break at 250 psi, it separated itself from the polyethylene during failure. The ceramic in figure 16 is fractured in multiple locations and had not been subjected to any mechanical testing. This leaves the applied pressure as the primary expected reason that the ceramic had broken apart. It is especially apparent that the materials were not bonded within the 2500x frame. There is obvious separation between the material and no blending is observed like in figure 14.

Figure 15. SEM imaging of sample 4 at 75x (left), 1000x (middle) and 2500x (right)

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I. SUMMARY AND CONCLUSIONS

Armor that is capable of stopping a projectile through deformation and energy capture is a necessity for modern soldiers and police. Ceramic and UHMWPE have been proven to be effective materials for use in body armor. They do however have limitations, such as weight, bulk, and price. A zirconia ceramic filter was infilled with UHMWPE powder in an attempt to explore an alternative armor composite. It is clear that the armor in its current state is not an effective method of stopping ballistic threats. Ballistic testing showed that rounds could only be stopped along the width of the samples, while direct attacks simply passed through. However, some redeeming qualities were observed such at the dispersion of energy over larger areas and the deformation of the projectile. Optical and SEM analysis highlighted some areas for improvement, such as the ceramic-polyethylene interface. Hardness testing also highlighted the irregularity of the crystallinity of the polyethylene, and the need for better processing steps.

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II. FUTURE WORK

Because the composite illustrated some of the qualities needed for effective armor, further testing of improved synthesis methods should be considered. The powder placed into the filter did not receive the proper heat needed to crystallize except for on the surface. This flaw left the inside weak as observed by the hardness testing. Applied pressure also created difficulties when the ceramic broke at relatively low pressure. A primary concern would be obtaining ceramic filters closer to body armor ceramics, i.e., SiC, high purity alumina, BN. Once a higher hardness ceramic is chosen, experimentation with improved infilling processes could be conducted. This may include application vacuum or use of an extrusion die to fill the ceramic filter.

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III. REFERENCES

[References are examples and do not match thesis text above]

[1] Horsfall, I. (2012). Key issues in body armour: threats, materials and design.

Advances in Military Textiles and Personal Equipment, 3–20.

[2] National Institute of Justice, February 22 (2018), Body Armor Performance Standards ,nij.ojp.gov:

https://nij.ojp.gov/topics/articles/body-armor-performance-standards

[3] Penn-Barwell, J. G., Brown, K. V., & Fries, C. A. (2015). High velocity gunshot injuries to the extremities: management on and off the battlefield. Current reviews in musculoskeletal medicine, 8(3), 312–317.

https://doi.org/10.1007/s12178-015-9289-4

[4] Cannon , L. , 2001 . Behind armour blunt trauma—an emerging problem . Journal of the Royal Army Medical Corps , 147 ( 1 ), pp. 87 – 96 .

[5] M. Grujicic, G. Arakere, T. He, W.C. Bell, B.A. Cheeseman, C.-F. Yen, B. Scott.

(2008) A ballistic material model for cross-plied unidirectional ultra-high molecular-weight polyethylene fiber-reinforced armor-grade

composites,Materials Science and Engineering: A,Volume 498, Issues 1–2, Pages 231-241.

[6] Morrissey, T , 2011. Ultra high molecular weight polyethylene thin sheet test sample production. Bachelor thesis, Alfred University, Pages 4-19.

[7] A. Norris, Ask Chemicals LLC, 4/20/2021, Private Communication.

[8] Theibud, James, Alfred University, 4/12/2021, Private Communication.

[9] Dielectric Manufacturing. (2020, May 28). Material properties of uhmw

polyethylene. Retrieved April 26, 2021, from https://dielectricmfg.com/knowledge- base/uhmw/