ARL-TR-7987 ● MAR 2017

US Army Research Laboratory

Identifying Opportunities in the Development 

of Ceramic Matrix Composite (CMC) Materials 

for Armor Applications

by Jeffrey J Swab and Emil J Sandoz-Rosado

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ARL-TR-7987 ● MAR 2017

US Army Research Laboratory

Identifying Opportunities in the Development 

of Ceramic Matrix Composite (CMC) Materials 

for Armor Applications

by Jeffrey J Swab and Emil J Sandoz-Rosado

Weapons and Materials Research Directorate, ARL

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Identifying Opportunities in the Development of Ceramic Matrix Composite 

(CMC) Materials for Armor Applications

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Jeffrey J Swab and Emil J Sandoz-Rosado

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14. ABSTRACT

The purpose of this effort was to summarize the history of ceramic matrix composites (CMCs) for armor and capture the 

current state of the art in fiber-reinforced CMCs and ceramic fibers to identify potential opportunities future research in CMCs 

for armor applications.

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ceramic matrix composites, CMC, ballistic performance, fiber-reinforced ceramics, ceramic fibers

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Jeffrey J Swab

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Contents

List of Figures iv

List of Tables iv

Acknowledgments v

1. Introduction 1

1.1 Background on Ceramic Matrix Composites (CMCs) for Armor 1

2. Findings 2

2.1 CMCs for Armor 2

2.2 Ballistic Test Information 4

2.3 Manufacturers of CMCs for Armor 6

2.4 Patents 7

3. Background on Commercial Fibers 8

4. Inorganic Fibers 9

4.1 Nonoxide Ceramic Fibers 9

4.2 Oxide Ceramic Fibers 12

5. Electrospun Ceramic Nanofibers 14

6. Carbon Fibers 15

7. Conclusions 17

8. References 19

List of Symbols, Abbreviations, and Acronyms 23

Distribution List 24
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List of Figures

Fig. 1 Specific strength vs. toughness of various fibers, demonstrating that 

incredibly thin electrospun PAN fibers can disruptively, 

simultaneously increase strength and toughness (Reprinted with 

permission from Yuris Dzenis)............................................................15

List of Tables

Table 1 CMC manufacturers...............................................................................6

Table 2 Patents on fiber-reinforced ceramics for armor .....................................7

Table 3 Properties and costs for first through third generation commercial 

nonoxide ceramic fibers. Table data reprinted with permission from 

Schawaller et al. 2012..........................................................................10

Table 4 Properties and costs for commercial oxide ceramic fibers ..................13
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Acknowledgments

The authors would like to acknowledge the fruitful discussion with Brian Scott, 

James Campbell, and Eric Warner of the US Army Research Laboratory (ARL),

and John La Scala from ARL who provided the initial motivation for this deep dive.
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INTENTIONALLY LEFT BLANK.
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1. Introduction

1.1 Background on Ceramic Matrix Composites (CMCs) for 

Armor

The inherent high hardness of ceramic materials such as alumina (Al2O3), silicon 

carbide (SiC), and boron carbide (B4C) make them integral components in a variety 

of protections systems for Army vehicles and personnel. Unfortunately their 

inherent sensitively to flaws (i.e., brittleness) limits this potential especially in 

regard to multi-hit ballistic performance. Attempts have been made over the past 

several decades, with varying degrees of success, to improve the performance of 

the ceramic by modifying the design of the protection system. This includes 

changes to the backing material, the adhesive used in laminated systems, the 

geometry of the ceramic as well as different methods to confine and retain the 

ceramic in a state of compression (Gooch 2002). At the same time research 

continues within the ceramics community to develop stronger and tougher ceramics 

through grain boundary engineering, microstructural tailoring, and the 

incorporation of second phase materials to create CMCs. The second phase in 

creating CMCs typically has been in the form of a platelet/particulate, whisker or 

long, continuous fiber. More recently carbon nanotubes (CNTs) have been 

examined. Fracture toughness improvements have been minimal with 

platelet/particulate or whisker additions and there are still many questions 

surrounding the impact of CNTs on toughness. However, the integration of long 

continuous fibers has significantly increased fracture toughness and resulted in new 

CMC applications in space vehicles, components for high-temperature gas turbine 

engines, and for brake systems (Krenkel 2005). The most common of these CMCs 

are comprised of carbon, SiC, Al2O3, or mullite (Al2O3-silicon dioxide [SiO2]) 

fibers, and these same materials also serve as the primary matrix material. 

As a result of these new applications CMCs are more readily available, 

manufacturing processes for both the fibers and the CMCs continue to mature, and 

new fiber and CMC materials are under development. Novel fiber technologies are 

also being developed, including boron nitride nanotubes (Niguès et al. 2014) that 

have been shown to exhibit high inter-layer friction, which is a desirable 

characteristic for a fiber. 
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2. Findings

2.1 CMCs for Armor

Over the past half century there have been several reports and papers published that 

provided a review of lightweight ceramic materials under consideration for armor 

applications (Stiglich 1968; Wong and Berman 1971; Viechnicki et al. 1989, 1991; 

Gooch 2002). These publications have focused on monolithic ceramics and how to 

maximize the benefits of these ceramics in armor systems with minimal discussion 

or information on CMCs. 

The report by Stiglich (1968) mentions only one “composite” an “Al clad B4C” and 

the only discussion about fibers is the placement of boron fibers into an epoxy sheet 

that could then be built up to make a ceramic backing material or possibly as a 

strike face material with fine thickness gradations. The status report by Wong and 

Berman (1971) contained the following single paragraph on CMCs:

Fiber-reinforced ceramic armors have also been considered and 

efforts made to determine physical, mechanical, and ballistic 

properties. Investigations at the Franklin Institute and the Air Force 

Materials Laboratory have been concerned with continuous matrices 

of Al2O3 and MgO-Al2O3 reinforced with either sapphire whiskers 

and filaments or Nichrome-type wires. Meanwhile, industry and 

other agencies including Goodyear Aerospace Corporation [Kolarik 

RV. Development of a 14.5 mm, BS-41 composite armor system. 

Goodyear Aerospace Corp. (Contract DAAG 46-68-C-0115), 28 

June 1968-18 Mar 1970 (confidential report)], and the Army 

Materials and Mechanics Research Center have evaluated various 

graphite fiber reinforced ceramics. To date, the experimental results 

have been mixed and inconclusive. Nevertheless, this class of 

materials still exhibits a high potential as a source for lightweight 

armor materials.

A chapter (Laible 1980) on ceramic composite armor makes no mention at all of 

any CMC materials, but 2 publications by Viechnicki et al. (1989, 1991) provide 

the most details and indicate that CMCs are more developmental than their 

monolithic counterparts. These 2 publications show that CMCs are of interest 

because of their potential to reduce collateral damage around the impact site, which 

can lead to improved multi-hit capabilities. (Multi-hit performance can be achieved 

with monolithic ceramics by designing the armor system using individual ceramic 

plates that are sufficiently isolated from each other to reduce damage propagation 

into adjacent plates while still providing the necessary overall protection level.) The 
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following specific ceramic composite materials are briefly discussed: titanium 

carbide containing 15% Ni; Al2O3 containing SiC whiskers; borosilicate glass 

containing a high volume (60–70%) of either a graphite or SiC fiber; titanium 

diboride (TiB2) containing either B4C or SiC particulates; and a suite of Al2O3

materials made via the LANXIDE* process, which uses the controlled oxidation of 

liquid aluminum to form an Al2O3 matrix with residual aluminum plus the addition 

of ceramic particulates, whiskers or fibers. An example of this would be a 

composite of Al2O3/aluminum with aligned SiC fibers. The LANXIDE process was 

successful in fabricating pieces containing ceramic particulates, but fiber 

reinforcement was difficult because the capillary action needed for molten 

aluminum infiltration was impeded (Scott 2016).

A study by Lillo et.al (2003) examined SiC containing a “bone-shaped” SiC 

whisker in a SiC matrix. The composite had reduced properties and ballistic 

performance, as measured by depth of penetration, was poor. The mass efficiency 

was approximately 3.8 compared to 7 for a commercially available, armor-grade 

SiC. The low properties and performance were attributed to density, which was 

about 5% lower than the commercial SiC.

Neither of the most recent reviews (Gooch 2002; David et al. 2009) mention CMCs 

for armor applications. The former review focuses on ballistic requirements, design 

factors related to the incorporation of ceramics into the armor system, and some of 

the applications of ceramic armors based on the companies who have produced the 

ceramic. The latter review discusses materials ranging from ballistic fabrics to 

ceramic armor to laminated composites and integral armor for current and future 

body armor applications. This review also discusses nanomaterials and future 

design concepts, including the use of CNTs in woven fabrics and polymers. There 

is no mention of any CMC materials being considered for this application. 

The US Department of Defense produced a composite materials handbook (MILHDBK-17, now called Composite Materials Handbook). Volume 5 of this 

handbook is dedicated to CMCs. The latest version of Volume 5 is dated 17 June 

2002 and it contains a section titled “Impact Behavior”, but unfortunately this 

section, as well as many others, is empty and labeled as “Reserved for future use.” 

An analysis of the fiber-reinforced SiC market by Garshin et al. (2012) includes a 

discussion of the potential use of fiber-reinforced CMCs in protection systems. 

They conclude that overall the volume of goods made of ceramic composite 

materials will steadily rise by 8%–10% each year, that the Liquid Silicon 

Infiltration(LSI) method has the greatest potential for producing cost-effective 

 *Lanxide Corp. Newark, Delaware.
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ceramic composites and that the main applications are where high temperatures, 

chemical attack, or abrasive loads are encountered. Garshin et al. (2012) also 

conclude that “the commercial potential of ceramic composite materials is most 

fully realized in the following applications: . . . protective equipment for individual 

and collective use.” Unfortunately, they do not provide any specifics or support for 

this portion of their conclusion.

2.2 Ballistic Test Information

A search of the technical literature uncovered very few publications that discuss 

fiber-reinforced CMCs for impact protection or provide impact performance data 

on this class of materials. Glass reinforced with SiC fibers was discussed by 

Rawlings (1994) where it was shown that the cracking features were modified by 

the SiC fiber reinforcement but that the cracking was not drastically different from 

what is observed on an impacted monolithic ceramic or glass. Danko et al. (1995)

reported impact information on a silicon nitride/hexagonal boron nitride 

(Si3N4/BN) fibrous monolithic ceramic. The material was formed following a 

patented process (Coblenz 1988) that develops a fibrous texture in conventional 

polycrystalline ceramics, but this material is not technically a fiber-reinforced 

ceramic. Specimens were tested against 2 hardened steel 7.62-mm threats—the 

Soviet armor piercing machine gun round at 1731 ft/s and the AK-47 armor piercing 

round at 2337 ft/s. Perforation was complete against both threats, but there was 

limited delamination and no cracking in the 25.4-cm radius around the hole and the 

outline of the perforation was square instead of round. The author uses these latter 

observations as an indication of a material with multi-hit capability. It is indicated 

in the Danko et al. paper that Los Alamos National Laboratory agreed to team with 

Advanced Ceramics Research, Inc. (the lead authors) to conduct further research 

on this material, but there is no published evidence of any additional research being 

conducted or that any other monolithic ceramics with a fibrous texture, have been 

examined for impact resistance.

A ceramic-coated flexible material for improved stab resistance was reported by 

von Niessen and Gadow (2002). This material was either an aramide fabric (Twaron 

CT 710, Twaron Products, Wupertal, Germany) or a mullite fiber fabric (Nextel 

720 from 3M, Minneapolis, MN, consisting of 85% Al2O3 and 15% SiO2) coated 

with a 100-μm layer of Al2O3 or titanium dioxide (TiO2) using air plasma spray 

process. The coated Twaron fabric was 5 times more stab resistant than the 

uncoated Twaron fabric.

Silicon nitride reinforced with SiC fibers was examined to provide small-scale 

impact protection for space stations against strikes by meteoroids and orbital debris 

(Tamura and Mutou 2005). The material was tested in the velocity range of 2.2 to 
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3.6 km/s using 1-mm-diameter aluminum alloy spheres. As expected the fragments 

from the composite were much smaller than the fragments from a comparable 

monolithic Si3N4. 

Corman and Luthra (2006) determined the damage tolerance of a variety of CMCs 

compared to monolithic Si3N4, by conducted low-velocity, 116 and 427 m/s, impact 

tests using 4-mm-diameter steel spheres. These tests were designed to simulate 

collisions from foreign objects in the turbine engine. The conclusion was the 

following: “None of the CMC samples tested, with impact energies ranging from 

the threshold of observable damage up to complete penetration, displayed 

catastrophic damage, and yet all tests on monolithic sintered Si3N4 showed 

catastrophic failure at both energies tested.”

Boccaccini et al. (2005) tested the impact behavior of a CMC consisting of a mullite 

matrix containing woven mullite fiber mats (Nextel 720). Tiles, without any 

backing, were impacted by glass spheres, nominally 10 mm in diameter and 

weighing 1.4 g, within a velocity range of 77.6–207.5 m/s. Results showed 

substantial localized damage that is typically observed in similar composites and 

the material retained some load-bearing capacity even after impact. The authors 

state that there is limited value of the material being used in ballistic armor 

applications without any backing material. 

The most in-depth analysis of CMCs for armor was work conducted by Heidenreich 

and colleagues (2003, 2006, 2010). In this series of manuscripts they focused on 

the development of CMCs for protection against small-caliber threats. A liquid 

silicon infiltration method (highlighted by Garshin et al. 2012), that was developed 

to produce carbon-fiber reinforced SiC for spacecraft thermal protection and highperformance brake discs, was used to fabricate carbon-fiber reinforced SiC and 

biomorphic siliconized silicon carbide (SiSiC) materials. The biomorphic materials 

are based on low-cost pyrolyzed wooden templates. Their initial testing (2003), 

against a 7.62-steel core armor-piercing round, showed the biomorphic SiSiC had 

a single hit ballistic limit of 850 m/s for an areal density of 50 kg/m2 while the 

carbon-fiber reinforced SiC exhibited better multi-hit performance since the 

amount of damage was significantly less in this material. Subsequent testing (2006)

compared the biomorphic SiSiC to commercial Al2O3 tiles against the same threat. 

The results showed that the SiSiC had a similar ballistic limit velocity. However,

the lower density of the SiSiC (~3 g/cm3) indicated that it had a ballistic 

performance comparable to commonly used monolithic SiC materials. Their final 

publication (2010) in this area focused on changing the SiC of the SiSiC for 

improved mechanical properties. These materials had a ballistic limit velocity of 

930–1056 m/s at areal densities between 36.7 and 38.3 kg/m3 but they exhibited 

brittle behavior that limits them to single-hit protection. To improve the potential 
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of multi-hit performance cut carbon fibers were incorporated into some 

compositions. This addition did not change the ballistic limit velocity, but there was 

greatly reduced fragmentation indicating potential improvement in the multi-hit 

capabilities.

2.3 Manufacturers of CMCs for Armor

Very little information on CMCs for ballistic applications is available in brochures 

or on the company websites. Table 1 from MIL-HDBK-17-5 provides a list of CMC 

manufacturers (circa 2001) and is presented here. An Internet search was conducted 

for each manufacturer to see if there was any indication that their materials are 

presently being evaluated or used for ballistic applications. None of the 

manufacturers listed have any information on their website indicated that they are 

developing or using CMC materials for impact/ballistic protection. 

Table 1 CMC manufacturers

Albany International Techniweave Hitco

Ceramic Composites, Inc. Hyper-Therm

Composite Factory, Inc. Northrop-Grumman

Composite Optics Inc. Ceramics 

(formerly a Dow Corning business unit) Refractory Composites, Inc.

General Electric Textron, Inc.

Goodrich-Aircraft wheels and brakes division Ultramet

Hexcel Synterials

Honeywell Advanced Composites 

(formerly DuPont Lanxide Composites)

Examination of a late 1980s brochure from the French company SEP shows that 

SEP was promoting 2 fiber-reinforced SiC matrix CMCs for ballistic protection. 

The 2D C/SiC CMC was labeled as SEPCARBONIX and the 2D SiC/SiC CMC 

was labeled as CERASEP. Both of these materials were designed a standalone 

components for fragmentation protections or as a support layer in a system using a 

monolithic ceramic front face to improve multi-hit performance. An Internet search 

shows that SEP is still in existence, but there is no evidence on their site that they 

are still conducting research on CMCs for protection applications. 

A 2005 brochure from the German company SGL Carbon Group is entirely focused 

on a “bullet-proof ceramics” labeled as TAVCOR. TAVCOR is a series of carbonfiber reinforced products for use as armor plating of vehicles, aircraft and ships as 

well as personnel protection systems. The brochure touts the benefits of these 

CMCs as multi-hit capability, large plate dimensions, complex geometries, low 
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weight and fewer modifications to vehicle chassis and as having “extraordinary 

ballistic properties in various applications” and “specially designed to resist 

ballistic projectiles”. The information in this brochure is not on the current SGL 

website but they are still developing a carbon fiber-reinforced SiC for ballistic 

protection. The site indicates that this material is an “innovative material solution 

for tailor-made high-performance ballistic protection” and the materials can be used 

in protection systems for military wheeled and track vehicles, helicopters, and 

ships.

Recently, Lancer Systems, LP, met with the US Army Research Laboratory (ARL)

to discuss the possible evaluation of their family of CMCs, labeled CeraComp, for 

graded lightweight composite armor. There are 3 different CMCs that make up the 

CeraComp family. All 3 have a silicon oxygen carbon (SiOC) matrix and contain 

either continuous or chopped carbon fiber or a ceramic fiber as the reinforcement. 

These materials are currently used in aerospace, industrial, semiconductor, and 

automotive areas.

2.4 Patents

Table 2 is a compilation of the patents that incorporate fiber-reinforced ceramics in 

the protection system. To the authors knowledge none of these patents have resulted 

in a CMC that is being used in an armor system.

Table 2 Patents on fiber-reinforced ceramics for armor

Patent no. Publication date Applicant Title

US5970843 October 26, 1999 Northtrop Grumman Corp Fiber-reinforced CMC armor

US6135006 October 24, 2000 Northtrop Grumman Corp Fiber-reinforced CMC armor

US7238414 July 3, 2007 SCL Carbon AG – Germany

Fiber-reinforced composite for 

protective armor, and method for 

producing the fiber-reinforced 

composition and protective 

armor

US20120055327 March 8, 2012 John Holowczak

Armor systems having CMC

layers

US4615935 October 7, 1986 The Boeing Company

Glass fiber-reinforced ceramic 

perform and method of casting it

EP0376794A1 July 4, 1990 Societe Europenne De 

Propulstion – France

Protective material with a 

ceramic multilayer structure
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3. Background on Commercial Fibers

Fibers are a critical component to most composite types due to their enhancement 

of the mechanical properties of the surrounding matrix. “High-performance” fibers 

typically have high specific i) stiffness (~200 GPa·cm3/g), ii) strength 

(~2 GPa·cm3/g), and iii) toughness (~100 J/g), all of which are critical to the 

weight-efficient augmentation of composite materials (Pilato and Michno 1994; 

Papkov et al. 2013). An independent report published in May 2016 predicts that the 

market for these particular types of fibers is expected to expand at a compound 

annual growth rate of 8.62% during 2015–2022, increasing by a total of 

$15.7 billion (Insights 2016). The growth in high-performance fibers is being 

driven by expanding demand for electric vehicles, aerospace, and defense, which 

all require lightweight structural composite materials. 

Generally speaking, organic fibers attain high performance through the orientation 

of stiff and strong covalent chain networks along a single axis, whereas the 

mechanisms for increased toughness are more complicated, and depend on the 

granular or molecular structure of the respective fiber. Commercial highperformance fibers that are used in composites are generally ultrahigh-molecularweight polyethylene (UHMWPE), aramid-based fibers such as Kevlar, PBO, glass, 

boron-based fibers, or carbon fibers. The fiber review detailed that carbon fibers 

and glass fibers dominate the structural composites markets due to their high 

stiffness and strength but low-impact resistance, while UHMWPE and Kevlar 

dominate armor and protection due to their toughness and resilience (Gillespie et 

al. 2005). 

CMCs are used in applications with vastly different operating conditions than 

traditional polymer-based composites and thus require fibers with different salient 

properties than the aforementioned polymeric fibers. CMCs are frequently 

employed in high-temperature (1000 °C+) environments such as gas turbine blades 

and thus require fibers with good thermal stability, and low creep. The production 

of ceramics requires high temperatures, prohibiting the use of organic polymeric 

fibers that degrade below 500 °C and even prohibiting the use of traditional glass 

fibers that soften or melt below 700 °C (Schawaller et al. 2012). As such, ceramic 

fibers are frequently used in current CMC applications, despite their low-impact 

resistance. Ceramic fibers have stiffness and strength comparable to polymeric 

high-performance fibers, albeit with a higher sensitivity to flaws, and thus lower 

impact resistance and toughness. Current commercially available CMCs are not 

optimized to resist the shock of ballistic impact, since both the matrix and the 

reinforcing fibers have low-impact resistance. Because CMCs are being considered 
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in this review for ballistic protection, major advancement in fiber technology in the 

past decade will be examined across both inorganic and pure carbon fibers.

4. Inorganic Fibers

4.1 Nonoxide Ceramic Fibers

Silicon carbide (SiC) fibers are one of the more common ceramic fibers used in 

CMCs. Ceramic fibers comprised of SiC are considered nonoxide, although there 

can be residual oxygen depending on the quality of the fiber, and generally they 

have superior tensile modulus and strength compared to oxide fibers (Schawaller 

et al. 2012). One drawback to nonoxide-based fibers is their susceptibility to 

oxidative degradation. There are 3 principal types of SiC fibers according to their 

chemical composition, oxygen content and silicon-to-carbon ratio (Ichikawa 2016). 

The sequential advancements in the 3 generations of fiber arise from the need to 

have higher temperature fibers capable of operation at or above 1300 °C. The first 

generation of fibers, Si-C-O (Nicalon) and Si-Ti-C-O (Tyranno Lox M) both 

contain over 10-wt% oxygen introduced during their respective curing. While their 

maximum operating temperature (1100 °C) is low for many traditional CMC 

applications, these fibers are suitable for consideration in CMCs for hard-armor 

applications. The second generation of fibers, are SiC (Hi-Nicalon) and Sr-Zr-C-O 

(Tyranno ZMI), achieving oxygen contents below 1 wt% through exotic processes 

such as electron beam irradiation curing in a helium environment, for improved 

thermal stability (1500 °C) but marginal operating temperatures due to creep from 

excess carbon (1150 °C). Third generation fibers (Hi-Nicalon Type S, Tyranno SA,

and Sylramic) achieve stoichiometric ratios of silicon-to-carbon, and thus have 

reduced creep, by pyrolizing the precursor fibers in hydrogen gas, which removes 

excess carbon. Because the major advancements in these fiber types are hightemperature operation and creep reduction and the mechanical properties of newer 

generation ceramic fibers do not shift significantly, fibers with less processing may 

have adequate performance for CMC hard armors with much less cost associated 

with manufacturing (see relative properties and costs in Table 3). Furthermore, the 

role of oxygen and amorphous material regions associated with nonstoichometric 

elemental ratios on ductility in these fibers has yet to be investigated. It is possible 

that fibers with increased oxygen or extra carbon could have better impact 

resistance than the purified fibers.
10

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Table 3 Properties and costs for first through third generation commercial nonoxide ceramic fibers. Table data reprinted with permission from 

Schawaller et al. 2012.

Trademark Manufacturer Curing

Approximate

max. production 

temp. 

(°C)

Composition 

(wt%)

SiC grain

size

(nm)

Average fiber

diameter

(mm)

Tensile strength

(GPa)

Tensile

modulus

(GPa)

Cost

(€ kg-1)

Nicalon Nippon Oxygen 1200 Si: 56.5 2 14 3.0 220 1000

NL 200/201 Carbon C:31.2

O: 12.3

Tyranno Ube Oxygen 1200 Si: 55.4 3–5 11 3.3 187 1200

LoxM Industries C:32.4

O: 10.2

Ti: 2.0

Tyranno S Ube Oxygen 1200 Si: 50.4 3–5 8.5/11 3.3 170 1000

Industries C:29.7

O: 17.9

Ti: 2.0

Hi-Nicalon Nippon Electron 1300 Si: 63.7 5–10 14 2.8 270 3250

Carbon irradiation C:35.8

O: 0.5

TyrannoZMI Ube Oxygen 1300 Si: 56.1 11 3.4 200 1400

Industries C:34.2

O: 8.7

Hi-NicalonS Nippon Electron >1500 Si: 68.9 100 12 2.6 420 7000

Carbon irradiation C:30.9

O: 0.2
11

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Table 3 Properties and costs for first through third generation commercial nonoxide ceramic fibers. Table data reprinted with permission from

Schawaller et al. 2012 (continued).

Trademark Manufacturer Curing

Approximate

max. production 

temp. 

(°C)

Composition 

(wt%)

SiC grain

size

(nm)

Average fiber

diameter

(mm)

Tensile strength

(GPa)

Tensile

modulus

(GPa)

Cost

(€ kg-1)

Tyranno Ube Oxygen >1700 Si: 67.8 200 10/7.5 2.8 380 6500

SA1/3 Industries C:31.3

O: 0.3

Al:0.6

Sylramic COI Oxygen >1700 SiC: 95.7 100 10 2.7 310 8500

Ceramics TiB2:3.0

B4C:1.0

O: 0.3

Sylramic-iBN COI Oxygen >1700 SiC/BN >100 10 3.0 400 10500

Ceramics
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4.2 Oxide Ceramic Fibers

The most prevalent commercial ceramic fiber variety is Al2O3 or mullite, which is 

a phase that contains both Al2O3 and SiO2. Oxide ceramic fibers are generally 

cheaper than nonoxide ceramic fibers, are resistant to oxidative degeneration, but 

have higher creep and lower thermal stability than nonoxide ceramic fibers (see 

relative properties and costs in Table 4) (Schawaller et al. 2012, Ichikawa 2016). 

Some oxide-based ceramic fibers have demonstrated ductility at higher 

temperature, which could be useful in integration into CMCs for hard-armor 

applications. Almeida et al. (2015) benchmarked a novel CeraFib75 oxide fiber 

with Nextel 720 by evaluating elastic and creep properties at temperatures ranging 

from 25 to 1400 °C. The primary difference in the mechanical performance of the 

2 fibers was brought on by the differing Al2O3/SiO2 composition. CeraFib75 is 

75-wt% Al2O3 and 25-wt% SiO2, while Nextel 720 is 85-wt% Al2O3 and 15-wt% 

SiO2 with the former having a larger content of mullite phases, as quantified by 

X-ray diffraction. The values for elastic modulus and strength for CeraFib75 are 

225 ± 25 GPa and 1.42 GPa, and for Nextel 720 the values are 221 ± 16 GPa and 

1.65 GPa, as obtained by quasistatic single-fiber tensile test at room temperature. 

CeraFib75 exhibits very slight softening of elastic modulus as temperature 

increases, in contrast to Nextel 720, but shows a much higher retention of strength 

at higher temperatures. At room temperature, Nextel 720 has a higher strength than 

CeraFib75 likely because of the presence of large defects in the latter fiber, a 

broader distribution of performance, which can be attributed to the relatively new 

CeraFib processing line. The superior high-temperature performance of CeraFib75 

compared to Nextel 720 as measured by tensile and creep experiments likely stems 

from the larger presence of mullite in the CeraFib 75 fiber, a phase which is more 

stable at these temperatures. The high-temperature ductility demonstrated by the 

CeraFib 75 at 1400 °C is interesting and may indicate a toughening mechanism that 

could potentially be exploited during impact.
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Table 4 Properties and costs for commercial oxide ceramic fibers

Fiber Composition 

(wt%)

Diameter 

(mm)

Density 

(g cm-3)

Tensile 

strength 

(GPa)

Tensile 

modulus 

(GPa)

Production technique/ 

structure

Approx. price

(€ kg-1)

3MNextel 720

Al2O3: 85

SiO2: 15 10–12 3.4 2.1 260 sol/gel, 59 vol%a-Al2O3 þ

41 vol% mullite

790 (1500 den)

600 (3000 den)

3MNextel Al2O3: >99 10–12 3.9 3.1 380 sol/gel, a-Al2O3 790 (1500 den)

610 600 (3000 den)

440(10000den)

3MNextel 550

Al2O3: 73

SiO2: 27 10–12 3.03 2.0 193 sol/gel, g-Al2O3 þ

SiO2 amorph.

590 (2000 den)

3MNextel 440

Al2O3: 70

SiO2: 28

B2O3:2

10–12 3.05 2.0 190 sol/gel, g-Al2O3 þ

mulliteþSiO2 amorph. 500 (2000 den)

3MNextel 312

Al2O3:62.5

SiO2: 24.5 10–12 2.7 1.7 150 sol/gel, mulliteþ amorph. or100% amorph. 260 (1800 den)

B2O3: 13

Sumitomo Al2O3: 85 10/15 3.3 1.8 210 polyaluminoxane, 640–720

Altex SiO2: 15 g-Al2O3

Nitivy Al2O3: 72 7 2.9 2.0 170 sol/gel,g-Al2O3 390 (twisted yarn,

Nitivy ALF SiO2: 28 twists: 10–15)

Mitsui Al2O3: 60–80 7–10 2.9 not available unknown, d-Al2O3 not available

Almax-B SiO2:40–20
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An oxide/oxide CMC consisting of an Al2O3 matrix reinforced with Nextel 720 

fibers was characterized using tension, fatigue, and creep experimentation from 

room temperature up to 1150 °C (Di Salvo et al. 2015). Fracture studies 

demonstrated that fiber bundle decohesion from the matrix was a limiting factor in 

the overall mechanical behavior of the material. Fiber pullout occurred with fibers 

as long as 5 mm being cleanly pulled from the matrix during tensioning, indicating 

weak bonding between the fibers and the matrix. Computed tomography (CT) scans 

of the CMC specimens indicated that there was a relatively high volume of porosity 

existing between individual fibers and fiber tows, leading to stress concentrations 

and ultimately failure. The role of fiber/matrix interface for ceramics requires a 

great deal of further study, since fiber delamination and porosity are likely to be a 

major CMC failure mechanisms during high-rate impact. 

5. Electrospun Ceramic Nanofibers

Commercial ceramic fibers (both oxide and nonoxide) are manufactured through 4 

production processes defined by how the ceramics are dispersed in preceramic 

polymer dopes: i) spinning from molecularly dispersed precursors (solution 

process), ii) spinning from colloidally dispersed precursors (sol/gel process), 

iii) spinning from dopes containing coarse ceramic particles (slurry process), and 

iv) spinning from inorganic polymers (precursor polymer process) (Schawaller et 

al. 2012). While not employed for the commercial production of ceramic fibers, 

electrospinning has emerged as a method for synthesizing ceramic fibers with 

diameters down to a few 100 nm (Chronakis 2005). Between 2002, when 

electrospinning of ceramic fibers was first reported, and a report by Sigmund and 

colleagues in 2006, more than 20 types of ceramics have been electrospun into 

nanofibers (Sigmund et al. 2006). Since then, titania (Park et al. 2010), BN (Salles 

et al. 2010), and SiC nanofibers (Lee et al. 2010) have been synthesized, with the 

latter showing mechanical properties on par with commercially available SiC fibers 

albeit with much easier manufacturability owing to the thinner diameter and greater 

compliance (Chen et al. 2015). Electrospun nanofibers are advantageous to 

standard fibers because they provide high-surface area per unit mass (better 

bonding with matrix), can have controlled morphology and surface structure. 

Electrospun polymeric nanofibers also demonstrate a simultaneous increase in 

strength and toughness as the diameter of the fibers shrink toward 100 nm, a feat 

that is impossible for standard fibers above 1 μm in diameter to achieve (for a 

comparison between standard and electrospun fibers, see Fig. 1) (Papkov et al. 

2013). While the mechanisms for toughening polymeric nanofibers through 
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electrospinning differ greatly from ceramic nanofibers, it is possible that 

mechanisms such as grain alignment and consolidation can be encouraged in 

ceramic electrospun nanofibers, leading to increased mechanical performance. 

Fig. 1 Specific strength vs. toughness of various fibers, demonstrating that incredibly thin 

electrospun PAN fibers can disruptively, simultaneously increase strength and toughness 

(Papkov et al. 2013) (Reprinted with permission from Yuris Dzenis)

6. Carbon Fibers

Commercial carbon fibers have some of the highest specific strength and stiffness 

of any high-performance fibers and are integral to lightweight structural 

composites. In particular, the implementation of carbon fiber composites into 

lightweight automobiles is a burgeoning field, with major automotive companies

such as BMW having invested significantly into carbon fiber production for 

composites in their electric vehicles in the past 5 years (Insights 2016). While the 

stiffness and strength of carbon fibers is quite high, their impact resistance is low 

because of the brittleness of carbon-carbon bonding coupled with low-intra-fibular 

interaction. As a result of low-impact resistance, carbon fibers are not suitable for 

use in soft-armor applications. Production of carbon fiber is generally from pitch 

stock (Gillespie et al. 2005) or from PAN fiber (Yusof and Ismail 2012), with the 

latter production technique accounting for 90% of global carbon fiber production. 

Creating carbon fiber from PAN precursor requires 4 pyrolysis steps: 1) oxidative 

stabilization (~200 °C), 2) carbonization (burning off other elements), 3) 
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graphitization (~3000 °C), and 4) activation (~900 °C). The resulting fiber is 

thermally stable enough to be considered for CMC armor applications, since it can 

withstand ceramic processing temperatures. Carbon fibers have not been 

considered for traditional CMC applications because of high-operational 

temperature requirements (1300 °C+).

Recent advancements in commercial carbon fiber manufacturing include coating 

the spun PAN precursor fiber (with coatings like silicone oil, fatty acids, etc.) to 

improve inter-fiber cohesion during the carbonization process yielding a stiffness 

increase from 219 to 224 GPa, and a strength increase from 2.45 to 3.25 GPa (Yusof 

and Ismail 2012). Furthermore, catalytic modification of PAN precursor with 

oxidizing agents, Lewis acid compounds, bases, metal compounds, and acids have 

resulted in more stable fibers (Yusof and Ismail 2012). More recently, stabilization 

of the carbon fibers has found to be aided by the tailored surface functionalization 

of embedded CNTs, yielding higher stiffness and strength, but lower toughness 

(Park et al. 2015). The scientific research community has focused on extracting 

superior carbon fiber performance through other synthesis routes and 

modifications. One group investigated the production of carbon fiber using very 

high-molecular weight PAN, attaining a final carbon fiber tensile stiffness of 

345 GPa and a tensile strength of 4.3 GPa owing to a more homogeneous filament 

with no core/shell structure because of its comparatively small diameter of 2.5 μm 

(Morris et al. 2016). Several studies examined the impact of nanoparticulate 

additives to aid in intra-fibrilar cohesion, with modest increases in performance 

with the addition of CNTs (Zhang et al. 2009) and graphene oxide (Wang et al. 

2016) into carbon fiber precursors. Finally, entire fibers have been synthesized from 

nanostructures, such as graphene (Xin et al. 2015), which exhibits high-thermal 

conductivity but relatively low-mechanical properties when compared to 

commercial high-performance fibers, or CNTs, which produce higher toughness 

fibers (Xin et al. 2015). 

Incidentally, the last publication that covers the mechanical performance of CNT

fiber, (Koziol et al. 2007), is coauthored by Philip Cunniff, who summarized the 

inferior ballistic performance of carbon fibers when compared to polymeric highperformance fibers (Cunniff 1999). While the quasistatic mechanical performance 

of carbon fibers is excellent, their impact resistance is low due to their brittle 

fracture behavior, mitigating their performance as a ballistic barrier. As such, 

carbon fibers should only be considered for CMC armor applications in the event 

that a technology presents itself that significantly toughens the fibers, especially 

during impact.
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7. Conclusions

The purpose of this effort was to summarize the history of CMCs for armor and 

capture the current state of the art in fiber-reinforced CMCs and ceramic fibers to 

identify potential opportunities future research in CMCs for armor applications. 

The following are the key findings:

• CMCs have been examined periodically over the past 5 decades for armor 

applications but efforts are few in number and the details are sparse.

• The limited ballistic information available indicates that use of fiberreinforced CMCs in armor systems can provide some improvement in 

multihit capabilities, but the single-shot performance is substantially 

inferior to monolithic ceramics. Platelet/particulate or whisker-reinforced 

CMCs show minimal, if any, improvement in ballistic performance.

• The primary driver of the fiber-reinforced CMCs market is the aerospace 

and automotive industries where lightweight, high-temperature structural 

components are required.

• Ceramic fibers have properties on par with high-performance polymeric 

fibers.

• No information is available on the impact behavior of ceramic fibers 

(anecdotally poor). Will this diminish the protective capability of CMCs the 

same way carbon fibers cannot be used for soft armor?

• No information is available on the required geometries or mechanical 

properties of a fiber in a CMC for hard-armor applications. Are stiffer or 

less stiff fibers favorable? Is elongation to failure of 1%–2% adequate? Are 

CMCs with more fibers (smaller fiber diameter) favorable or are fewer 

interfaces and thus reduced porosity favorable?

• Based on these findings there is little evidence at this time that any 

commercially available CMCs perform better than monolithic ceramics 

during ballistic impact. However, there are no mechanistic descriptions, 

presently available that explain why monolithic ceramics would be 

inherently better than CMCs for ballistic protection.

• The potential for improved multi-hit capability of hard armor containing 

CMCs appears significant and warrants investigation, but limitations in the 

current processing of CMCs and the impact theory to predict the 

performance of ceramics during a ballistic event prohibits a comprehensive 

ballistic evaluation.
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• The current manufacturing variability of CMCs commonly leads to the 

presence of porosity in the final component. This severely limits their 

ballistic potential but not their use in high-temperature, structural 

applications. As a result, a project focused on developing CMCs specifically 

for hard armor is required. Such a project is outside the scope of an 

internally funded ARL project, because it would require extensive funding 

and novel CMC manufacturing capabilities. However, a significant external

effort, or a meaningful partnership between ARL and a CMC industry 

leader could lead to advances in CMCs and the creation of hard armors with 

multi-hit capabilities.
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List of Symbols, Abbreviations, and Acronyms

Al2O3 alumina

ARL US Army Research Laboratory

B4C boron carbide

BN boron nitride

CMC ceramic matrix composite

CNT carbon nanotube

CT computed tomography

LSI Liquid Silicon Infiltration (method)

Si3N4 silicon nitride

SiC silicon carbide

SiO2 silicon dioxide 

SiOC silicon oxygen carbon

SiSiC siliconized silicon carbide 

TiB2 titanium diboride

TiO2 titanium dioxide

UHMWPE ultrahigh-molecular-weight polyethylene
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