Advances in Ceramic Armor X

A collection of 14 papers from the Armor Ceramics symposium held during The American Ceramic Society’s 38th International Conference on Advanced Ceramics and Composites, held in Daytona Beach, Florida, January 26-31, 2014.

• Language: English
• Publisher: Wiley
• Release date: Jan 28, 2015
• ISBN: 9781119040606

Book preview

Preface

I had the pleasure of being the lead organizer for the 12th Armor Ceramics Symposium in 2014 at the 38th International Conference on Advanced Ceramics and Composites. I am very grateful for the guidance and support that was provided by Jeff Swab, Andy Wereszczak, Jim McCauley, and the organizing committee in putting this symposium together. Consistent with the history of this symposium, we strived to create a program that would foster discussion and collaboration between researchers from around the world in academia, government, and industry on various scientific issues associated with the topic of armor ceramics.

The 2014 symposium consisted of approximately 55 invited, contributing, and poster presentations from the international scientific community in the areas of synthesis & processing, manufacturing, materials characterization, testing & evaluation, quasi-static & dynamic behavior, modeling, and application. In addition, because of their importance for the foreseeable future, this symposium also had special focused topic sessions on Adhesive Bonding of Ceramics and Boron Carbide. Based on feedback from attendees, the 2014 symposium was a success, and the manuscripts contained in these proceedings are from some of the presentations that comprised the 12th edition of the Armor Ceramics Symposium.

On behalf of Jeff Swab and the organizing committee, I would like to thank all of the presenters, authors, session chairs, and manuscript reviewers for their efforts in making this symposium and the associated proceedings a success. I would also especially like to thank Andy Wereszczak, Todd Beaudet, Vlad Domnich, Mike Golt, Steve Kilczewski, Jim McCauley, Bob Pavlacka, and Jared Wright for stepping up to host and chair the symposium when we were unable to due to remnant effects of Sequestration. Last, but not least, I would like to recognize Marilyn Stoltz and Greg Geiger of The American Ceramic Society, for their support and tireless efforts without which the success of this symposium would not be possible.

JERRY C. LASALVIA

Symposium Chair, Armor Ceramics

Introduction

This issue of the Ceramic Engineering and Science Proceedings (CESP) is one of seven issues published from manuscripts submitted and approved for the proceedings of the 38th International Conference on Advanced Ceramics and Composites (ICACC), held January 26-31, 2014 in Daytona Beach, Florida. ICACC is the most prominent international meeting in the area of advanced structural, functional, and nanoscopic ceramics, composites, and other emerging ceramic materials and technologies. This prestigious conference has been organized by The American Ceramic Society's (ACerS) Engineering Ceramics Division (ECD) since 1977.

The 38th ICACC hosted more than 1,000 attendees from 40 countries and approximately 800 presentations. The topics ranged from ceramic nanomaterials to structural reliability of ceramic components which demonstrated the linkage between materials science developments at the atomic level and macro level structural applications. Papers addressed material, model, and component development and investigated the interrelations between the processing, properties, and microstruc-ture of ceramic materials.

The conference was organized into the following 19 symposia and sessions.

The proceedings papers from this conference are published in the below seven issues of the 2014 CESP; Volume 35, Issues 2-8, as listed below.

Mechanical Properties and Performance of Engineering Ceramics and Composites IX, CESP Volume 35, Issue 2 (includes papers from Symposium 1)

Advances in Solid Oxide Fuel Cells X, CESP Volume 35, Issue 3 (includes papers from Symposium 3)

Advances in Ceramic Armor X, CESP Volume 35, Issue 4 (includes papers from Symposium 4)

Advances in Bioceramics and Porous Ceramics VII, CESP Volume 35, Issue 5 (includes papers from Symposia 5 and 9)

Advanced Processing and Manufacturing Technologies for Nanostructured and Multifunctional Materials, CESP Volume 35, Issue 6 (includes papers from Symposia 7 and 8)

Ceramic Materials for Energy Applications IV, CESP Volume 35, Issue 7 (includes papers from Symposia 6 and 13)

Developments in Strategic Materials and Computational Design V, CESP Volume 35, Issue 8 (includes papers from Symposia 2, 10, 11, and 12 and from Focused Sessions 1, 2, 3, and 4); the 3rd Global Pacific Rim Engineering Ceramics Summit; and the 3rd Annual Global Young Investigator Forum

The organization of the Daytona Beach meeting and the publication of these proceedings were possible thanks to the professional staff of ACerS and the tireless dedication of many ECD members. We would especially like to express our sincere thanks to the symposia organizers, session chairs, presenters and conference attendees, for their efforts and enthusiastic participation in the vibrant and cutting-edge conference.

ACerS and the ECD invite you to attend the 39th International Conference on Advanced Ceramics and Composites (http://www.ceramics.org/daytona2015) January 25-30, 2015 in Daytona Beach, Florida.

To purchase additional CESP issues as well as other ceramic publications, visit the ACerS-Wiley Publications home page at www.wiley.com/go/ceramics.

ANDREW GYEKENYESI

Ohio Aerospace Institute, NASA Glenn Research Center, USA

MICHAEL HALBIG

NASA Glenn Research Center, USA

Volume Editors

July 2014

TESTING METHOD FOR CERAMIC ARMOR AND BARE CERAMIC TILES

Erik Carton, Geert Roebroeks

Group Explosions, Ballistics and Protection, TNO

P.O. Box 45, Rijswijk, The Netherlands

ABSTRACT

TNO has developed an alternative, more configuration independent ceramic test method than the standard Depth-of-Penetration test method. In this test ceramic tiles and ceramic based armor are evaluated as target without a semi-infinite backing layer. An energy approach is chosen to evaluate and rank the target materials penetration resistance. By measuring the armor material's energy absorption, subtracting the residual projectile energy after penetration from the projectile energy before impact, an objective performance parameter for the ceramic or ceramic based armor is obtained. However, this parameter is still related to the specific projectile used in the test. The presented alternative testing method for ceramic based armor uses a high speed camera technique to determine residual velocity of target material fragments and of projectile remains. The residual mass of the projectile is determined, capturing the penetrated projectile (and ceramic fragments) in a water basin. Analysis of the projectile remains after the impact event, provides valuable information on the two projectile to target interaction stages, dwell and penetration. The test method and analysis method are described in this paper. Results on ceramic and ceramic based armor are presented and discussed.

INTRODUCTION

Ceramic materials are used in armor applications for decades now (ever since the Vietnam War). Their unique combination of mechanical properties like high hardness, compressive strength, stiffness and relative low density are frequently mentioned to rationalize the use of ceramics in armor. However, even after decades of use the relation between mechanical properties and ballistic (protection) efficiency is not fully understood. This may be explained by also considering some other relevant mechanical properties of ceramic materials like their modest tensile strength and a brittle fracture behavior. This combination of mechanical properties results in an early failure and negligible energy dissipation during fracturing of ceramic materials. It is the main reason ceramics are not used stand-alone in armor applications. Ceramics need to be supported using a backing material that is ductile and capable to absorb (residual kinetic) energy. Often metal sheets or polymer fiber materials (like fabrics and composite) are used as backing material in armor systems. Hence, armor ceramics are often tested in combination with a backing material that influences the projectile-target interaction, which complicates the search for a unique relation between a mechanical property of the ceramic with its ballistic efficiency [1]. To complicate things further, the projectile-target interaction not only depends on intrinsic material properties of the ceramic and its backing material. Many researchers have shown that extrinsic properties, like tile dimensions, pre-stress and confinement also have a large influence on the ballistic behavior of a ceramic armor system [2–5].

Several test methods for ceramic materials and ceramic-based armor have been developed and used [14]. In this article first the Depth-of-Penetration test method is analyzed. Then the current view on projectile ceramic interaction is discussed followed by an explanation of the alternative test method proposed in this work. Finally, some test results using the alternative test method are provided and conclusions are drawn.

Depth of Penetration test method

In the eighties, Rosenberg [6] introduced a ballistic test method for ceramic materials in which the tiles were supported by a semi-infinite backing material like aluminum alloy or RHA blocks. The thickness of the backing materials were such that the residual projectile after perforation of the ceramic strike face is stopped in the backing material without any deflection of the rear of the block. The depth-of-penetration (DoP) of the projectile is determined for each shot and compared to the DoP of the projectile in the block without a ceramic strike face. Comparing both DoP values several efficiency factors can be determined based of the volume and/or mass reduction due to the ceramic strike face at hand. Figure 1 shows the result of DoP-tests of 4 armor ceramic types for a range of tile thicknesses. Two armor grade Alumina's and two armor grade SiC types were used. The static material properties (like density, Vickers hardness, sound velocity and toughness (Kic as obtained from hardness indents) of both Alumina types were similar as well as those for the two SiC types. The DoP-tests have been performed using 7.62 AP8 projectiles at 930 m/s with the (100x100 mm) tiles glued to an aluminum alloy (AA7075-T6) backing block using an elastic flexible adhesive (Sicaflex 226) with a thickness ranging from 0.3 to 0.6 mm. In Figure 1 is shown that the two Alumina tile types behave identical in the DoP tests. The same applies to the SiC types indicating a good correlation between the (identical) material properties and the ballistic efficiency of the ceramic materials [7]. The SiC tiles show a better ballistic efficiency compared to Alumina, as for the same thickness the SiC tiles show a lower depth of penetration. A second result in Figure 1 is the limitation of the maximal tile thickness that can be used for the DoP test using 7.62 AP8 projectiles. This WC-Co (cemented carbide) cored projectile represents the heaviest threat of this caliber and also the impact velocity used represents a close ranged shot (barrel exit velocity). Nontheless, the maximal tile thickness that results in a measurable DoP in the backing block is limited to 7 mm for the SiC-tiles and 9 mm for the Alumina tiles. In fact the range is even smaller as the DoP values below 5 mm are not formed by penetration of the residual projectile, but rather by surface damage due to the high local pressure and movement (rotation) of ceramic fragments crushed between the (deforming and eroding) projectile and the backing block. A possibility to increase the range in measurable tile thicknesses is to make use of heavier threats like (0.50 AP rounds), however this drives up the costs of materials and measurement of DoP as much thicker backing blocks have to be used. Also the minimal lateral tile dimensions will increase, which is not always possible if new ceramic types are to be tested. Too small lateral tile dimensions have shown to influence the DoP results by Hazell [2] who found an increase in DoP of squared SiC tiles with dimensions below 70 mm using 7.62 APM2 projectiles.

Figure 1 Depth of Penetration results for two Alumina and two SiC tile types [7].

In Figure 1 only the average DoP values of the tiles are shown. Figure 2 shows a plot of individual DoP test results for a range of Alumina based ceramic tiles. Such data can also be found in many of the published DoP test results by others [8–10]. The DoP results for an ceramic tile is shown to vary as much as 40% on average. An ARL report [11] mentioned that the variation in DoP can be as much as a factor of 8. Such a large variation in test results, requires many tests to get any statistical useful results and prevents small differences between ceramic materials to be determined. Although variations in mechanical properties of the ceramic samples could in principle explain these variations, commercially available armor grade ceramic tiles are mass-produced using strict process control and quality assurance, resulting in modest variations in mechanical properties. The tile shape however is often less well controlled. The sintering process and subsequent cooling to room temperature causes residual stress in the tiles, which often result in out-of plane bending of the tiles. This leads to non-uniform support conditions for ceramic tiles. However, the main reason for the wide spread in test result seems to be connected to the test method itself. The impact of the hard and brittle armor piercing (AP) core of the projectile on the ceramic strike-face results in deformation and erosion of its originally ogive or conical nose. It is well known that the shape of the projectile nose influences the penetration of a rigid projectile in a ductile material; for the same mass and velocity a blunt projectile will penetrate less deep in a ductile target. The brittle core material of an impacting AP round will fracture and erode by the initiation and growth of many small cracks. It results in a unique nose shape of the residual projectile. Even if it has lost a similar amount on kinetic energy during the interaction with the ceramic strike face, hence the same residual kinetic energy for penetration of the backing material is available, the variations in nose shape will lead to variations in penetration