AR Boccaccini et al. Composites Science and Technology 65(2005)325-333 impact energy may involve more complex mechanisms Republic. S. Atiq acknowledges the Government of than purely matrix microcracking, including fibre/ma- Pakistan for a fellowship trix interface debond Thus a predictive model for the ballistic impact behaviour of the present composites must take into References consideration the complex microstructure of the com- posites and the effect of interfaces. The formulation [1 Marshall DB, Davis JB. Ceramics for future power generation of such a model is beyond the scope of the present technology: fiber reinforced oxide composites. Curr Opin Solid State Mater Sci 2001: 5: 283-9. [2] Holmquist M, Lundber R, Sudre O, Razzell AG, Molliex L Considering the failure commencement load as an Benoit J, et al. Alumina/alumina composite with a porous indicator of residual strength of the composite, it was ronia interphase, processing, properties ad component testing. found that this reaches a minimum value when the im- J Eur Ceram Soc 2000: 20: 599-606 pact energy is just below that required for penetration 3] Chawla KK, Coffin C, Xu ZR. Interface eng n oxide of the projectile(Fig. 10(b)). Further increase in ballistic fibre/oxide matrix composites. Int Mater Rev 2000: 45: 165-8 4 Peters PWM, Daniels B, Clements F, Vogel WD. Mechanical impact energy after penetration of the sample by the characterisation of mullite based ceramic matrix composites at projectile results in increase of the load carrying capabil st temperatures up to 1200C. J Eur Ceram Soc 2000: 20: 531-5 ity of the composite, due to less microstructural damage [5]Kanka B. Schneider J. Aluminosilicate fiber/mullite matrix being introduced in the sample. This behaviour is in gen composites with favourable high ature properties. J Eur Ceram Soc2000:20:619-93 eral agreement with the literature on ballistic resistance [6] Kramb VA, John R, Zawada LP Notched fracture behaviour of of composite materials [31]. an oxide/oxide ceramic matrix composite. J Am Ceram Soc [7 Lewis MH, Tye A, Butler E, Al-Dawery I. Development of 4. Conclusion terfaces in oxide matrix composites. Key Eng Mater 1999: 164- 5:351-6 The work has demonstrated that the cn technic [8 Schmuecker M, Schneider H, Chawla KK, Xu ZR, Ha J-s Thermal degradation of fibre coatings in mullite-fibre- reinforced can be used to assess fracture behaviour in mullite fibre mullite composites. J Am Ceram Soc 1997: 80: 2136-40 reinforced-mullite matrix composites of complex micro- [9] Ha J-s, Chawla kK, Engdahl EE. Effect of processing and fiber structure. The fracture toughness(Kl) values deter coating on fibre matrix interaction in mullite fibre-mullite matrix mined using the Cn technique were in the range of composites. Mater Sci Eng A 1993: 161: 303-8. 1.8-3.3 MPa m". The large scatter of fracture tough [10] Holmquist MG, Lange FF Processing and properties of a porous oxide matrix com reinforced with continuous oxide fibres. J ness values is typical for this kind of materials due to Am Ceram soc2003:86:173340. the complex(heterogeneous)composite microstructure [ll] Schneider H, Okada K, Pask JA, editors. Mullite and mullite The observed fibre pull-out effect is due to a favourable ceramics. Chichester: Wiley: 1994. matrix/ fibre interfacial bond given by NdPOA coating of [2 Somiya S, Davies RF, Pask JA, editors. Ceramics transactions. Mullite and mullite matrix osites. vol. 6. Westerville the fibres OH: American Ceramic Society: 1990 Mullite fibre reinforced-mullite matrix composites, [13] Chawla KK. Ceramic matrix composites. 2nd ed. Norwell(MA), when subjected to ballistic impact loading by firing Dordrecht. The Netherlands: Kluwer Academic Press: 2003 pherical projectiles, retain some of their load bearing [14] Chawla KK, Xu ZR, Ha J-s Processing, structure and properties capacity after penetration by the projectile. This is of mullite fiber mullite matrix composites. J Eur Ceram Soc due to the fact that structural damage caused by pro- [15] Yeheskel O, Balmer ML, Cranmer DC Interfacial chemistry of jectiles remains localised preventing catastrophic fail mullite-mullite composites. Ceram Eng Sci Proc 1988: 9(7- ure. For the conditions of the present tests, :687-94 penetration by the projectile occurs at impact energy [16] Boccaccini AR, MacLaren I,Lewis MH, Ponton CBElectroph of about 4J. which indicates that there is a limiting va- retic deposition infiltration of 2-D woven SiC fibre mats with lue for the material to be useful in ballistic armour of mullite composition. J Eur Ceram Soc 1997;17:154 applications when it is used on its own(without back- [17] Kaya C,Gu X, Al-Dawery I,Butler EG.Microstructural ing layers) development of woven mullite fibre-reinforced-mullite ceramic atrix composites by infiltration processing. Sci Technol Adv Mater2002:3:35-4 [18 She J, Mechnich P, Schneider H. Schmuecker M, Kanka B Effect Acknowledgements of cyclic infiltrations on microstructure and mechanical behaviour of porous mullite/mullite composites. Mater Sci Eng A The research was partially funded from Grants of 2002:325:19-24 NATO(No. PST CLG.977558)and Royal Society 19 Ha JS, Chawla KK. Mechanical behaviour of mullite reinforced with mullite fibres. Mater Sci Eng A 1995: A203: 1271-6 (London, UK). Part of the experimental work was [20] Akatsu T, Yasuda E, Sakai M Fracture toughness and work of financially supported by Grant No. A2041003 of the fracture of toughened brittle materials in chevron notch geometry. Grant Agency of the Academy of Sciences, Czech Fract Mech Ceram 1996: 11: 245impact energy may involve more complex mechanisms than purely matrix microcracking, including fibre/ma￾trix interface debonding and localised fibre fracture. Thus a predictive model for the ballistic impact behaviour of the present composites must take into consideration the complex microstructure of the com￾posites and the effect of interfaces. The formulation of such a model is beyond the scope of the present experimental study. Considering the failure commencement load as an indicator of residual strength of the composite, it was found that this reaches a minimum value when the im￾pact energy is just below that required for penetration of the projectile (Fig. 10(b)). Further increase in ballistic impact energy after penetration of the sample by the projectile results in increase of the load carrying capabil￾ity of the composite, due to less microstructural damage being introduced in the sample. This behaviour is in gen￾eral agreement with the literature on ballistic resistance of composite materials [31]. 4. Conclusion The work has demonstrated that the CN technique can be used to assess fracture behaviour in mullite fibre reinforced–mullite matrix composites of complex micro￾structure. The fracture toughness (KIc) values deter￾mined using the CN technique were in the range of 1.8–3.3 MPa m1/2. The large scatter of fracture tough￾ness values is typical for this kind of materials due to the complex (heterogeneous) composite microstructure. The observed fibre pull-out effect is due to a favourable matrix/fibre interfacial bond given by NdPO4 coating of the fibres. Mullite fibre reinforced–mullite matrix composites, when subjected to ballistic impact loading by firing spherical projectiles, retain some of their load bearing capacity after penetration by the projectile. This is due to the fact that structural damage caused by pro￾jectiles remains localised preventing catastrophic fail￾ure. For the conditions of the present tests, penetration by the projectile occurs at impact energy of about 4 J, which indicates that there is a limiting va￾lue for the material to be useful in ballistic armour applications when it is used on its own (without back￾ing layers). Acknowledgements The research was partially funded from Grants of NATO (No. PST.CLG.977558) and Royal Society (London, UK). Part of the experimental work was financially supported by Grant No. A2041003 of the Grant Agency of the Academy of Sciences, Czech Republic. S. Atiq acknowledges the Government of Pakistan for a fellowship. References [1] Marshall DB, Davis JB. Ceramics for future power generation technology: fiber reinforced oxide composites. Curr Opin Solid State Mater Sci 2001;5:283–9. [2] Holmquist M, Lundber R, Sudre O, Razzell AG, Molliex L, Benoit J, et al. Alumina/alumina composite with a porous zirconia interphase, processing, properties ad component testing. J Eur Ceram Soc 2000;20:599–606. [3] Chawla KK, Coffin C, Xu ZR. Interface engineering in oxide fibre/oxide matrix composites. Int Mater Rev 2000;45:165–89. [4] Peters PWM, Daniels B, Clements F, Vogel WD. Mechanical characterisation of mullite based ceramic matrix composites at test temperatures up to 1200 C. J Eur Ceram Soc 2000;20:531–5. [5] Kanka B, Schneider J. Aluminosilicate fiber/mullite matrix composites with favourable high temperature properties. J Eur Ceram Soc 2000;20:619–93. [6] Kramb VA, John R, Zawada LP. Notched fracture behaviour of an oxide/oxide ceramic matrix composite. J Am Ceram Soc 1999;82:3087–96. [7] Lewis MH, Tye A, Butler E, Al-Dawery I. Development of interfaces in oxide matrix composites. Key Eng Mater 1999;164– 165:351–6. [8] Schmuecker M, Schneider H, Chawla KK, Xu ZR, Ha J-S. Thermal degradation of fibre coatings in mullite–fibre-reinforced mullite composites. J Am Ceram Soc 1997;80:2136–40. [9] Ha J-S, Chawla KK, Engdahl EE. Effect of processing and fiber coating on fibre matrix interaction in mullite fibre–mullite matrix composites. Mater Sci Eng A 1993;161:303–8. [10] Holmquist MG, Lange FF. Processing and properties of a porous oxide matrix composite reinforced with continuous oxide fibres. J Am Ceram Soc 2003;86:1733–40. [11] Schneider H, Okada K, Pask JA, editors. Mullite and mullite ceramics. Chichester: Wiley; 1994. [12] Somiya S, Davies RF, Pask JA, editors. Ceramics transactions. Mullite and mullite matrix composites, vol. 6. Westerville, OH: American Ceramic Society; 1990. [13] Chawla KK. Ceramic matrix composites. 2nd ed. Norwell (MA), Dordrecht, The Netherlands: Kluwer Academic Press; 2003. [14] Chawla KK, Xu ZR, Ha J-S. Processing, structure and properties of mullite fiber mullite matrix composites. J Eur Ceram Soc 1996;16:293–9. [15] Yeheskel O, Balmer ML, Cranmer DC. Interfacial chemistry of mullite–mullite composites. Ceram Eng Sci Proc 1988;9(7– ):687–94. [16] Boccaccini AR, MacLaren I, Lewis MH, Ponton CB. Electroph￾oretic deposition infiltration of 2-D woven SiC fibre mats with mixed sols of mullite composition. J Eur Ceram Soc 1997;17:1545–50. [17] Kaya C, Gu X, Al-Dawery I, Butler EG. Microstructural development of woven mullite fibre-reinforced–mullite ceramic matrix composites by infiltration processing. Sci Technol Adv Mater 2002;3:35–44. [18] She J, Mechnich P, Schneider H, Schmuecker M, Kanka B. Effect of cyclic infiltrations on microstructure and mechanical behaviour of porous mullite/mullite composites. Mater Sci Eng A 2002;325:19–24. [19] Ha JS, Chawla KK. Mechanical behaviour of mullite composites reinforced with mullite fibres. Mater Sci Eng A 1995;A203:1271–6. [20] Akatsu T, Yasuda E, Sakai M. Fracture toughness and work of fracture of toughened brittle materials in chevron notch geometry. Fract Mech Ceram 1996;11:245. 332 A.R. Boccaccini et al. / Composites Science and Technology 65 (2005) 325–333