COMPOSITES SCIENCE AND TECHNOLOGY ELSEⅤIER Composites Science and Technology 62(2002 www.elsevier.com/locate/compscitech The transverse thermal conductivity of 2D-SiCr/sic composites G.E. Youngblood a ,*. David J Senora, R.H. Jones. Samuel Graham Pacific Northwest National Laboratory, PO Box 999, MSIN K2-44, Richland, WA99352, US.A Sandia National Laboratories. Livermore. CA 94550. USA Received 21 June 2001; received in revised form 7 February 2002: accepted 7 February 2002 Abstract The Hasselman-Johnson(H-)model for predicting the effective transverse thermal conductivity(Kefr) of a 2D-SiCr/Sic com- posite with a fiber-matrix thermal barrier was assessed experimentally and by comparison to numerical FEM predictions. Agree- ment within 5% was predicted for composites with simple unidirectional or cross-ply architectures with fiber volume fractions of 0.5 or less and with fiber-to-matrix conductivity ratios less than 10. For a woven 2D-SiCdSic composite, inhomogeneous fiber packing d numerous direct fiber-fiber contacts would introduce deviations from model predictions. However, the analytic model should be very appropriate to examine the degradation in Kefr in 2D-woven composites due to neutron irradiation or due to other mechanical or environmental treatments. To test this possibility, expected effects of irradiation on Ker were predicted by the H-J model for a hypothetical 2D-SiCrSic composite made with a high conductivity fiber and a cvi-Sic matrix. Before irradiation, redicted Kefr for this composite would range from 34 down to 26 W/m K)at 200 and 1000C, respectively. After irradiation to saturation doses at 200 or 1000C, the respective Kefr-values are predicted to decrease to 6 or 10 w/(m-K).C 2002 Elsevier Science Ltd. All rights reserved Keywords: A. Ceramic-matrix composites(CMCs); B Modeling: B. Thermal conductivity; C Computational simulatio 1. ntroduction for possible applications in advanced nuclear fission Silicon carbide(SiC) exhibits favorable mechanical A major issue to be considered when using SiC/ SiC in ld chemical properties at high temperatures for many a high-temperature neutron radiation environment, or applications. Desirable properties of SiC that also make in other non-radiation environments where components it attractive for use in fusion reactor applications in a or structures are subjected to a high heat flux, is the neutron radiation environment are its dimensional sta- expected in-service behavior of its effective transverse bility in the 800-1000oC temperature range, low thermal conductivity, Keff. Knowledge about the expec induced radioactivity and low afterheat [1]. However, ted range of Kefr is necessary to optimize SiC/SiC con the brittle nature of SiC limits its use as a structural figurations for their intended uses. Several modeling material. As compared to monolithic SiC, continuous studies have shown how Kefr depends upon constituent fiber-reinforced SiC-matrix composites (SiCr/SiC) exhi- fiber and matrix thermal conductivity values, and their bit improved toughness with a high, non-catastrophic volume fractions and distributions [6-8]. However strain-to-failure [2]. For these reasons, SiC in the form many experimental measurements have indicated that of SiCr/SiC is being considered as a structural material interfaces between fibers and matrices in a composite for first wall or breeder blanket applications in introduce a thermal barrier that may affect Keff [9-12] advanced fusion power plant concepts in the US [3] Furthermore, Kefr may be affected by physical changes and in international programs [4, 5]. In the US, the of the interface and even the surrounding atmosphere DOE-sponsored Nuclear Energy Research Initiative As with mechanical behavior, to attain desired thermal (NERD) program also is examining SiC composites behavior of SiC SiC proper attention needs to be given to the design of the interphase and to the control of Corresponding author. Tel:+1-509. interfacial thermal effects Classical composite models recently have been up- dated to include the effect of interfacial thermal barrier 0266-3538/02/S. see front matter C 2002 Elsevier Science Ltd. All rights reserved. PII:S0266-3538(02)00069-6The transverse thermal conductivity of 2D-SiCf/SiC composites G.E. Youngblooda,*,David J. Senora ,R.H. Jonesa ,Samuel Grahamb a Pacific Northwest National Laboratory, PO Box 999, MSIN K2-44, Richland, WA 99352, USA bSandia National Laboratories, Livermore, CA 94550, USA Received 21 June 2001; received in revised form 7 February 2002; accepted 7 February 2002 Abstract The Hasselman–Johnson (H–J) model for predicting the effective transverse thermal conductivity (Keff) of a 2D-SiCf/SiC com￾posite with a fiber-matrix thermal barrier was assessed experimentally and by comparison to numerical FEM predictions. Agree￾ment within 5% was predicted for composites with simple unidirectional or cross-ply architectures with fiber volume fractions of 0.5 or less and with fiber-to-matrix conductivity ratios less than 10. For a woven 2D-SiCf/SiC composite,inhomogeneous fiber packing and numerous direct fiber–fiber contacts would introduce deviations from model predictions. However,the analytic model should be very appropriate to examine the degradation in Keff in 2D-woven composites due to neutron irradiation or due to other mechanical or environmental treatments. To test this possibility,expected effects of irradiation on Keff were predicted by the H–J model for a hypothetical 2D-SiCf/SiC composite made with a high conductivity fiber and a CVI-SiC matrix. Before irradiation, predicted Keff for this composite would range from 34 down to 26 W/(m K) at 200 and 1000
C,respectively. After irradiation to saturation doses at 200 or 1000
C,the respective Keff-values are predicted to decrease to 6 or 10 W/(m–K). # 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Ceramic-matrix composites (CMCs); B. Modeling; B. Thermal conductivity; C. Computational simulation 1. Introduction Silicon carbide (SiC) exhibits favorable mechanical and chemical properties at high temperatures for many applications. Desirable properties of SiC that also make it attractive for use in fusion reactor applications in a neutron radiation environment are its dimensional sta￾bility in the 800–1000
C temperature range,low induced radioactivity and low afterheat [1]. However, the brittle nature of SiC limits its use as a structural material. As compared to monolithic SiC,continuous fiber-reinforced SiC-matrix composites (SiCf/SiC) exhi￾bit improved toughness with a high,non-catastrophic strain-to-failure [2]. For these reasons,SiC in the form of SiCf/SiC is being considered as a structural material for first wall or breeder blanket applications in advanced fusion power plant concepts in the US [3] and in international programs [4,5]. In the US, the DOE-sponsored Nuclear Energy Research Initiative (NERI) program also is examining SiC composites for possible applications in advanced nuclear fission reactors. A major issue to be considered when using SiCf/SiC in a high-temperature neutron radiation environment,or in other non-radiation environments where components or structures are subjected to a high heat flux,is the expected in-service behavior of its effective transverse thermal conductivity, Keff. Knowledge about the expec￾ted range of Keff is necessary to optimize SiCf/SiC con- figurations for their intended uses. Several modeling studies have shown how Keff depends upon constituent fiber and matrix thermal conductivity values,and their volume fractions and distributions [6–8]. However, many experimental measurements have indicated that interfaces between fibers and matrices in a composite introduce a thermal barrier that may affect Keff [9–12]. Furthermore, Keff may be affected by physical changes of the interface and even the surrounding atmosphere. As with mechanical behavior,to attain desired thermal behavior of SiCf/SiC proper attention needs to be given to the design of the interphase and to the control of interfacial thermal effects. Classical composite models recently have been up￾dated to include the effect of interfacial thermal barriers 0266-3538/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(02)00069-6 Composites Science and Technology 62 (2002) 1127–1139 www.elsevier.com/locate/compscitech * Corresponding author. Tel.: +1-509-375-2314; fax: +1-509-375- 2186. E-mail address: ge.youngblood@pnl.gov (G.E. Youngblood)