Materials and Design 31 (2010) 1945–1952

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Materials and Design

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On the comparison of the ballistic performance of 10% zirconia toughenedalumina and 95% alumina ceramic target

X.F. Zhang a,*, Y.C. Li b

a School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, Jiangsu, Chinab Department of Mechanics and Mechanical Eng., University of Science and Technology of China, Hefei 230027, Anhui, China

a r t i c l e i n f o

Article history:Received 15 August 2009Accepted 22 October 2009Available online 25 October 2009

Keywords:A. Engineering ceramicsE. Impact and ballisticI. Brittle fracture

0261-3069/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.matdes.2009.10.046

* Corresponding author. Tel.: +86 2584317853; faxE-mail address: lynx@mail.njust.edu.cn (X.F. Zhan

a b s t r a c t

Ballistic performance of different type of ceramic materials subjected to high velocity impact was inves-tigated in many theoretical, experimental and numerical studies. In this study, a comparison of ballisticperformance of 95% alumina ceramic and 10% zirconia toughened alumina (ZTA) ceramic tiles was ana-lyzed theoretically and experimentally. Spherical cavity model based on the concepts of mechanics ofcompressible porous media of Galanov was used to analyze the relation of target resistance and staticmechanical properties. Experimental studies were carried out on the ballistic performance of abovetwo types of ceramic tiles based on the depth of penetration (DOP) method, when subjected to normalimpact of tungsten long rod projectiles. Typical damaged targets were presented. The residual depth ofpenetration on after-effect target was measured in all experiments, and the ballistic efficiency factor ofabove two types ceramic plates were determined. Both theoretical and experimental results show thatthe improvement on ballistic resistance was clearly observed by increasing fracture toughness in ZTAceramics.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Ceramic materials are widely used in armor systems as well asaircraft structures, fighting vehicles and tanks for the advantages oflow density, high compressive strength and hardness [1]. Responseof ceramics to projectile impact and other types of high-speedloading conditions are thus a relevant issue for these applications.Ballistic performance of many types of ceramics was investigatedin many experimental, theoretical and numerical studies. A briefreview of the progress penetration/perforation of ceramic targetscan be found in [2]. A great amount of these studies regarding cera-mic targets subjected to high velocity impact investigate thebehavior of materials under impact load. All the results show thatceramic materials have better ballistic performance than ordinaryarmor materials such as rolled homogeneous armor (RHA).

In spite of the excellent physical and mechanical properties ofceramics, the main drawbacks are their brittleness, large scatterof strength and easy crack growth. The inherent brittleness ofceramics makes special considerations necessary in designing withthese materials as armor systems. In ductile metals, localized stres-ses that exceed the yield point are usually relieved by local plasticdeformation that redistributes the stress into a wider area, pre-venting fracture. Ceramics, however, have no such yield point; they

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fail when localized stresses exceed material strength. Typically,elastic behavior is linear right up to the fracture point. Moreover,they usually have high modulus of elasticity, which results in frac-ture at relatively small strains. Considerable effort has been ex-pended aimed at increasing the ductility, or toughness, ofceramic materials. The directions that appear most promising in-volve transformation toughening and reinforcing the matrix witha dispersed phase such as fibers or whiskers, for example, phasetransformation of ZrO2 from tetragonal to monoclinic is one effi-cient way to improve the toughness of ceramic material, especiallyin alumina. Examples of such applications include cutting tools,drill bits, wear parts, structural and electronic components, elec-trodes, biomechanical devices, lightweight armor, and gas–turbinecomponents [3]. Researchers all over the world investigated themechanical properties of toughened ceramic materials, recently re-search results can be found in [4–6]. These studies have describedvarious aspects of toughening mechanisms in increasing the ductil-ity of ceramic materials, and mechanical properties improvementwere highlighted both in compression and tension. For the ballisticperformance of toughened ceramic material, ballistic evaluationwas carried based on several toughened alumina targets by Hagg[7], and the result shows that toughened ceramic material exhibitan improvement of ballistic performance in some test. At end oftheir report, they suggest that more experiments should be con-ducted to determine the reason why some specimen performedso outstandingly.

Table 1Material components of 10% ZTA ceramic and 95% alumina ceramic.

Ceramic type 10% ZTA ceramic (%) 95% Alumina ceramic (%)

Al2O3 85 95ZrO2 10 –SiO2 2 2.5CaO 2 1.5MgO 1 1

Table 2Mechanical properties of 10% ZTA ceramic and 95% alumina ceramic.

Parameters 95% Alumina ceramic 10% ZTA

Density, q0 (g/m3) 3.5437 3.7320Initial porosity, h0 0.091 0.088Static yield limit, Y (GPa) 2.20 2.15Static Young’s modulus, E0 (GPa) 190 190Dynamic Young’s modulus, E (GPa) 277 272Tensile strength, rf (GPa) 0.220 0.667Poissons’s ratio, v 0.23 0.20Surface wave speed, CR (m/s) 8900 8820

1946 X.F. Zhang, Y.C. Li / Materials and Design 31 (2010) 1945–1952

Zirconia toughened alumina (ZTA) ceramic is the most impor-tant, widely used and cost effective oxide ceramic material basedon phase transformation toughening method. It has wear and cor-rosion resistance along with high strength and toughness and typ-ical zirconia content in ZTA is between 10% and 20%. Themechanical properties of ZTA have been investigated by research-ers all over the world. Recent research progress related to ZTAmechanical properties can be found in [8–12], all the research re-sults show ZTA ceramics predominate mechanism for improve-ment of mechanical properties. Contrast with the widelyresearches on mechanical properties for ZTA, little effort has beenexpended aimed at the ballistic performance assessments. Someballistic test results were provided by Sun [13] and Zhang [14,15]which give a limited evidence of improved ballistic performanceby increasing fracture toughness of ZTA ceramics.

This paper presents a comparison of ballistic performance of10% ZTA and 95% alumina ceramic tiles. Spherical cavity modelbased on mechanics of compressible porous media of Galanovwas used to analyze the relation of target resistance and staticmechanical properties. Ballistic tests were performed on the ballis-tic efficiency of 10% ZTA and 95% alumina ceramic tiles, backed bymetal plates, against the impact of tungsten long rod projectiles(LRP). The impact velocity of LRP was varied from 1100 to1500 ms�1 and influences on the ballistic efficiency were studied.Experimental results show that the penetration resistance of alu-mina ceramics can be improved significantly by phase transforma-tion toughness method of ZrO2.

2. ZTA ceramic materials and mechanical characteristics

With the development of materials science, researchers all overthe world found various toughness methods with which to im-prove the fracture characteristics of ceramic materials. The fracturetoughness and the strength of ceramic material can be significantlyimproved by the mechanism of transformation toughening, inter-granular dispersion strengthening, or intragranular dispersionstrengthening. In transformation toughening, the secondary phaseparticles, while constrained by the ceramic matrix, expand duringphase transformation, resulting in residual stresses around eachsecondary phase particle, which have to be nullified for the crackto propagate through the transformed zone, i.e., increased fracturetoughness. An example of transformation toughening is aluminatoughened by tetragonal or monoclinic zirconia particles [16].The toughening mechanisms of ZTA ceramics are as follows [17]:

Pure zirconia is monoclinic (m) at room temperature and pres-sure. With increasing temperature the material transforms totetragonal (t), at approximately 1170 �C and then to a cubic (c)fluorite structure starting about 2370 �C with melting at 2716 �C[18,19]. Phase changing which causes volume expansion on cool-ing, c?t by approximately 2.31%; t?m by approximately 4.5%, willinduce micro-cracks in ceramic materials. This small size of micro-cracks will scatter and absorb the energy of the opening of themain crack tip when there is an impact loading on ceramic mate-rial, and this will improve the fracture toughness of ceramicmaterial.

In the present paper the 95% alumina ceramic and 10% ZTAceramic are produced by Shandong institute for the production ofindustrial ceramics design of China. A high purity alumina powderwas mixed with other oxides powder such as zirconia, magnesia.The samples were sintered then machined to plates ofU100 mm � 10 mm and U100 mm � 20 mm. The material compo-nents are shown in Table 1. Quasi-static mechanical experimenthas been conducted on above two types of ceramic [18], and themechanical properties were listed in Table 2.

Addition of ZrO2 to alumina ceramic, generally increases itstoughness, but always reduces its hardness. Improved toughnessof ceramic material is reported to have both beneficial and detri-mental effects in improving the dynamic mechanical properties[19], especially in anti-penetration process. It has a positive contri-bution of fracture toughness but reduce the penetration resistanceof ceramic target, and the combination performance of toughnessand hardness should be verified in future research. This ‘combina-tion performance’ is actually the result of two distinct effects: (a)the dynamic yield stress effects and (b) the toughness effect. Targetresistance is a combination effect of mechanical properties of cera-mic material during penetration, and it should be analyzed boththeoretically and experimentally.

3. Target resistance of toughening ceramic material

For high velocity penetration problems, various hydrodynamictheories have been developed using similar modifications of Ber-nouilli’s equation. Tate [20] represented the pressure on the axisat the interface as:

P ¼ qtU2=2þ Rt ¼ qpðV � UÞ2 þ Yp ð1Þ

The terms Rt and Yp were identified as the strength terms for thetarget and penetrator materials respectively. qt and qp are targetand penetrator densities respectively, U is the penetration velocity,and V is the ‘‘free flight” projectile velocity. In Eq. (1), qt and qp areconstant and it is assumed that once in motion the penetrator andtarget materials behave as frictionless incompressible fluids. In or-der to get a better ballistic performance (smaller penetration depthat same interface pressure), higher target resistance Rt (strengthterm for target) would then be required to get smaller value ofpenetration velocity.

Target resistance is Rt a material dependent parameter whichdetermine by target yield strength, dencity, Possion’s ratio andmodulus etc. Lots of analytical theories have been developed todetermine the target resistance Rt, and the most important one iscavity expansion theory. It assume that a pressure needed in ex-panded a cavity in target material, and cavity expansion theoryprovides an good analogy for the target resistance in high velocityimpact if dynamic properties of the target are substituted for qua-si-static properties. The theory for spherical cavity expansion in aductile target was developed many years ago by Hill [21]. The ex-tended review and detailed analysis of exiting models of cavity

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

2.8

3.2

3.6

4.0

4.4

4.8σ

f =0.1GPa

σf =0.4GPa

σf =0.7GPa

σf =1.0GPa

Rt/Y

Y /GPa

Fig. 2. The solution for the ratio of target resistance to yield strength as function ofyield strength.

0.2 0.4 0.6 0.8 1.0

2.8

3.2

3.6

4.0

4.4

4.8 Y=1.0GPa Y=2.0GPa Y=3.0GPa Y=4.0GPa

Rt /Y

σf /GPa

X.F. Zhang, Y.C. Li / Materials and Design 31 (2010) 1945–1952 1947

expansion with different rheology can be found in Satapathy[22,23]. In these models, Mohr–Coulomb law was used to charac-terize the pressure–shear behavior of a ductile material in commi-nuted (pulverized) region employing internal friction coefficient,and cavity expansion pressure essentially depends upon this coef-ficient. To estimate this coefficient a fitting experiment is neces-sary, which complicates the application of these models. Inpresent research, a cavity pressure determine method developedby Galanov [24] based on the concepts of mechanics of compress-ible porous and power material is used to analyzed the combina-tion performance of toughening and high strength.

Fig. 1 presents a geometrical scheme of spherical cavity expan-sion which shows three zones with different stress–strain states ofmaterial: (1) the region near the cavity is comminuted (pulverized)region with a < r < b; (2) next to the comminuted zone is the dila-tation and pore formation (radially cracked) region with b < r < c;(3) and beyond the ‘radially cracked’ is the elastic region with r > c.

In Galanov’s model, the target resistance Rt (pressure in cavity)is written as:

Rt ¼ �r� ab

� ��3hk

ð2Þ

where r* is the stress depends only on material properties, whichdefined as:

r� ¼ �2ð1� h�Þ3=2

3ffiffiffiffiffih�p Y ð3Þ

h� ¼ 1� ð1� h0Þ expðevÞ ð4Þ

ev ¼ er þ 2eu ¼ �r�

E1� ð1� vÞ

ffiffiffiffiffiffiffiffiffiffiffiffiffi2rf

ð�r�Þ

s !ð5Þ

The terms h* and ev are the total porosity and volumetric strain ofmaterial at boundary between dilatation region and pulverized re-gion respectively. h0 is the initial porosity of material, v and E arePossion’s ratio and Young’s modulus, Y and rf are material yieldstrength and uniaxial tensile strength respectively.

ab

� �3¼ ev �

r�

K� 3r�

E1� 1� v

2

ffiffiffiffiffiffiffiffiffi2rf

�r�

r !ð6Þ

Elastic region

Dilatation and pore formation region

Pulverized region

Cavity

c

ba

Fig. 1. Model scheme of spherical expansion in spherical coordinates.

Fig. 3. The solution for the ratio of target resistance to yield strength as function oftensile strength.

0 2 4 6 8 102.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Y =1.0GPaY =2.0GPaY =3.0GPaY =4.0GPa

Rt/Y

θ0 /%

Fig. 4. The solution for the ratio of target resistance to yield strength as function ofinitial porosity of material.

Table 3Results of calculations of properties of 10% ZTA ceramic and 95% alumina ceramic.

Ceramic material 95% Alumina ceramic 10% ZTA ceramic

�r*/GPa �3.97 �4.04h* 0.0996 0.0937hj 0.0910 0.0880ej �0.0165 �0.0167v* 0.0635 0.0573a/b 0.399 0.386Rt/GPa �5.10 �5.20

Fig. 7. Photographs of original shot of tungsten long rod projectile.

Table 4Mechanical properties of projectile and after-effect target.

Material Density(g cm�3)

Yongmodule(GPa)

Tensilestrength(MPa)

Yieldstrength(GPa)

Tungsten long rod projectile 17.2 255 160 3.060Medium steel 7.85 180 150 0.494

1948 X.F. Zhang, Y.C. Li / Materials and Design 31 (2010) 1945–1952

where K is the modulus of uniform compression and defined by:

1K¼ 1

Ksð1� hkÞþ 3

4hk

Gsð1� hkÞ3ð7Þ

Here Ks and Gs are modules of uniform compression and shearing ofporousless material, respectively.

hk ¼ ð1þ eV Þh� � eV ð8Þ

where hk is the porosity of material in comminuted region.In order to analyze the influence static of mechanical properties

to ballistic performance for ceramic materials, we first comparedtarget resistance results for yield strength Y, uniaxial tensilestrength rf and initial porosity h, respectively. As shown in Fig. 2,the influence of yield strength to target resistance Rt at different le-vel of tensile strength, from which can see the nonlinear relation

COVER PLATE

Presδ 1 δ 2

AFTER-EFFECT TARGETCERAMIC TILE

PENETRATOR

Fig. 5. Target configuration in the DOP test.

Time recoder

Ceramic target

Aluminum foil

25mm ballistic gunGunjet lock

Basement Basement

Sabot Recycling

Fig. 6. Experiment layout configuration for ballistic test.

X.F. Zhang, Y.C. Li / Materials and Design 31 (2010) 1945–1952 1949

between Rt/Y and yield strength Y. Ratio of target resistance toyield strength decreasing with increasing of yield strength, whichmeans lower value Y has larger contribution to Rt. Fig. 3 showsan approximate linear relation between tensile strength and targetresistance. Tensile strength has a significant influence to targetresistance at lower yield strength. Compared with yield strengthof ceramic material, the tensile strength has limited contributionto target resistance. Fig. 4 shows the relation of target resistanceand initial material porosity h0. It can be observed from Fig. 4 thatthe ratio of the target resistance to yield strength sensitivity de-creases with increases of initial porosity of ceramic material, espe-cially for lower yield strength. It can be concluded that ceramicmaterial yield strength Y is the main factor which determines thetarget resistance Rt. But as a brittle material, ceramic material eas-ily fractures under impact loading. As the fracture toughnessimproving (improving the tensile strength), it will change the sizeof the elastic region, the cracked region and the comminuted re-gion which ultimately affects Rt.

Using the static mechanical properties data of 95% aluminaceramic and 10% ZTA ceramic material in Table 2, we can get thedynamic parameters for cavity expansion theory based on com-pressible porous and powder ceramic material. Table 3 summa-rizes the results of calculations. It can be seen that withimproving of fracture toughness, the target resistance of 10% ZTAhigher than that of 95% alumina ceramic, and ratio of cavity sizeto pulverized region size increases in 10% ZTA.

4. Ballistic characterization

In the ballistic tests shown schematically in Fig. 5, the ceramictiles backed by after-effect metal plate target were impacted bytungsten LRP. Direct ballistic tests have been used to versify the

Epoxy resin

Fig. 8. Photograph and configuration of ce

ballistic performance of 95% alumina ceramic and 10% ZTA cera-mic. The depth of residual penetration in the after-effect targetwas measured in each case. The depth of penetration (DOP) meth-od is an efficient way to evaluate the anti-penetration ability [25],which can easily get a dimensionless factor of ballisticperformance.

Following the definition in [26], ballistics performance is as-sessed by a dimensionless factor which combines the mass effi-ciency and thickness efficiency of the material. The thicknessprotection coefficient Fs and mass protection coefficient Fm aredefined.

Fs ¼Pref � Pres � d1

d2ð9Þ

Fm ¼ðPref � Pres � d1Þ � qref

d2 � qcð10Þ

where Pres is the residual penetration depth in after-effect targetand Pref is the penetration depth in target without ceramic tiles.d1, d2 is the thickness of cover plate and ceramic tiles respectively.qref, qc is density of after-effect target and ceramic tile.

5. Comparison ballistic test to tungsten long rod projectile

5.1. Experiment layout and ceramic target

Experiments were performed in a small arms range whereintungsten LRP was fired using 25 mm ballistic gun, which is1.37 m long and with rifling twist of 7.5�. It can used to fire severalsub-types of ammunition such as armor piercing, high explosiveand tracer. In present test, the 25 mm ballistic gun was used to firelarge velocity range of armor piercing fin stabilized discarding

After-effect Target

Cover plate

Ceramic tile

ramic target with after-effect target.

Table 5Summary of depth of penetration experiments.

Ceramic Projectile velocity (ms�1) Residual penetration(mm)

Reference penetration(mm)

Thickness protectioncoefficient (Fs)

Mass protectioncoefficient (Fm)

95% alumina ceramic 1192 19 65.7* 0.8740 1.93611257 27.1 81.9* 1.0360 2.29491372 41.8 94.9* 1.0020 2.21961498 46.2 117.3* 1.3620 3.0171

10% ZTA ceramic 1173 16.5 64.3* 0.8960 1.88471273 26.3 84.5* 1.1040 2.32221397 32.3 95.1* 1.1960 2.51571520 37.3 118.8* 1.5700 3.3023

* Simulation results based on one experiment.

1200 1300 1400 1500

1.0

1.5

2.0

2.5

3.0

3.5 Fs of 95% alumina ceramic

Fs of 10% ZTA

Fm of 95% alumina ceramic

Fm of 10% ZTA

Prot

ectio

n co

effi

cien

t F

v / m/s

1950 X.F. Zhang, Y.C. Li / Materials and Design 31 (2010) 1945–1952

sabot (APFSDS), and the velocity is controlled by adjusting themass of propellant. Fig. 6 shows the experiment layout configura-tion in ballistics test. These projectiles were fired at velocities rang-ing from 1100 to 1500 ms�1. Time recording started as the LRParrived at the first aluminum foil and stopped as it arrived the sec-ond aluminum foil, then the projectile velocity can be calculatedusing V = T/Dt, where T is the distance of two aluminum foils,and Dt is the value of time recorder. The velocities were measuredto an accuracy of ±5 ms�1. The tungsten long rod projectile has adiameter of 7 mm, length of 110 mm and it weighs 51 g. Fig. 7shows photographs of the tungsten LRP.

Ceramic tiles were backed by plates of medium steel, a com-monly used grade of steel material, were used in the present exper-iments. The mechanical properties of the above steel targets andtungsten long rod projectile are given in Table 4. Physical andmechanical properties of the two types of ceramic material, usedin the current experiments, are given in Table 2. The ceramic titlesused were U100 mm in diameter with thickness of 10 and 20 mm.The sizes of the ceramic tiles have been chosen in such a way as toprovide multi-layer protection effect, which is a common require-ment in armor application. Ceramic tiles are multi-layer structureswhich have three layers and the thickness of each layer is 20, 20and 10 mm. These tiles were bonded into the after-effect targetwith size of U135 mm in diameter with 152 mm in height asshown in Fig. 8. At the entrance face of ceramic tiles there is a3 mm thickness steel plate used as cover plate to intercept theceramic debris during the impact of the projectile, and betweenthe ceramic tiles and the cover plate is 2 mm thick of rubber toconfine the ceramic tiles in axial direction. Between ceramic tilesand after-effect target in radial direction is filled with epoxy resin

1100 1200 1300 1400 15000

10

20

30

40

50

95% alumina ceramic10% ZTA

Pre

s/1

0-3m

v0 /m/s

Fig. 9. Residual penetration depth against impact velocity.

to fasten the ceramic tiles. Six screws of U5 mm were used to fixthe cover plate with the target.

6. Results and discussion

Long rod projectiles were fired in the range of 1100–1500 ms�1

to have four ballistic performance tests against targets with 10%ZTA and 95% alumina ceramic tiles. The experimental results fromTable 5 are shown graphically in Figs. 9 and 10, which shows a plotof the residual penetration Pres versus the impact velocity V for the

0

Fig. 10. Protection coefficient against impact velocity.

Fig. 11. Comparison of numerical and experimental result at impact velocity of1142 ms�1.

Fig. 12. Photo of residual penetration in after-effect target.

X.F. Zhang, Y.C. Li / Materials and Design 31 (2010) 1945–1952 1951

two types of ceramic tiles and ballistic efficiency Fs, Fm versus theimpact velocity V respectively. For each impact velocity, the depthof penetration in the medium steel without ceramic tiles was com-puted using numerical simulation technology based on one exper-iment. Fig. 11 shows the comparison of simulation andexperimental result at impact velocity of 1142 ms�1. Detail of thesimulation works can be found in Zhang [27].

Fig. 9 shows a nonlinear relation between the impact velocityand residual penetration depth in after-effect target, and as impactvelocity increasing, the residual penetration increased slowly. Thisis consistent with the hypothesis that the effective target resis-tance decreases as the impact velocity increases because the pen-etration velocity increases with impact velocity at same targetresistance, similar results were observed by Subramanian [28]. Asshown in Fig. 10, the thickness protection coefficients of two typeceramic material are both less than 1.0 at lower impact velocity(v0 � 1250 ms�1) which means that the two types of ceramic tileshave shows poor ballistic performance than that of medium steel.The thickness protection coefficient increases with the impactvelocity increasing. The mass protection coefficient Fm is alwayshigher than 1.0 in impact velocity of 1100–1500 ms�1 whichshows that ceramic materials have high value in armor protectionmaterial at the same weight.

Fig. 10 shows the residual penetration depth in the after-effectsteel target against impact velocity of the projectile for differenttype of ceramic tiles. From the results, it is observed that with im-pact velocity increasing, the residual penetration depth of the twotypes of ceramic tiles increased. The curve in the case of 10% ZTAceramic tiles increases more slowly than that of 95% alumina cera-mic, which means the penetration resistance of 10% ZTA ceramictiles is more than the penetration resistance of 95% alumina cera-mic tiles, especially to higher velocity tungsten LRP. Similarly, Hagg[7] studied the ballistic performance of toughened ceramic mate-rial at impact velocity of 1390 ms�1. This limited number of exper-iment result performed on three layer ZTA ceramic tiles give afurther evidence of improving ballistic performance by increasingfracture toughness for ceramic materials.

Due to high velocity impact, fracture ceramic material ejectedout and the diameter of the after-effect target has no differencewith that before impact. This means the ceramic tiles have strongerradial direction confine effect than that of axial direction. Fig. 12shows photographs of the residual penetration results in after-ef-fect target for 10% ZTA and 95% alumina ceramic tiles at a compa-rable impact velocity. It is again observed that the depth ofpenetration in the 95% alumina ceramic tiles is smaller than thepenetration depth in the 10% ZTA tiles of the same total thickness.

The main reasons for the enhanced penetration resistance of the10% ZTA ceramic tiles is the reduced fractures when compare to95% alumina ceramic. Due to their low density, high stiffness andbrittleness, the speed of longitudinal sound waves in ceramics isgenerally of the order of 10 km/s. The damage caused in the cera-mic structure due to the passage of the compressive shock wavedecreases the penetration resistance in ceramic structure. As thefracture toughness improving, it will change the size of the elasticregion, the cracked region and the comminuted region which ulti-mately affects the target resistance.

7. Conclusions

Comparison ballistic performance has been performed on 95%alumina ceramic tiles and 10% ZTA ceramic tiles. Combined influ-ence of yield stress, tensile strength and initial porosity to targetresistance has been analyzed based on cavity expansion theory ofGalanov. Ballistic tests were conducted on 95% alumina ceramictiles and 10% ZTA ceramic tiles based on the DOP method. Residualpenetration depth of two type ceramic tiles was studied, and bal-listic efficiency was determined. Results of the kinetic projectileexperiment show that the protection efficiency factor increaseswith projectile velocity increasing. With given thickness of theceramic tile, the protection efficiency factor of 10% ZTA ceramictiles increase more quickly than that of 95% alumina ceramic tiles.A significant increasing in ballistic performance of ZTA ceramic tilehas been observed in our experiments. However, the mechanisms

1952 X.F. Zhang, Y.C. Li / Materials and Design 31 (2010) 1945–1952

of contribution of increasing the toughness fracture to ballistic per-formance could not be identified by limited number of ballistictest. Further, well designed experiments and numerical modelswould be necessary to quantify the role of toughened ceramic inenhancing the penetration resistance of ceramic targets.

Acknowledgements

The researches are supported by the China National Natural Sci-ence Foundation (10632080) and China Postdoctoral Science Foun-dation (20060400731) and the Youth Scholarship Foundation ofNanjing University of Science & Technology. The author would liketo thank Prof. Zhonghua Du (NJUST) and Prof. Peihui Shen (NJUST)for their support and encouragement, and Dr. Xiaoning Zhao(NJUST) for his experiment assistance.

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