L Mingshuang et al. Materials Science and Engineering A 489(2008)120-126 4 ∽∽2历 sxs 50 perimental data(10s) 00010020.03004005006 Tr le stral True strain Os n=3 100 experimental data(85(s) ntal data(2800s) tutive moedl 00B0040050.06 00100200B0040.050.06007008 True strain True strain Fig. 11. The comparative charts of the constitutive model vs. experimental data of 2D-C/SiC composites at different strain rates. strain rate, high stress is needed to make the cracks spread, as (4) Based on the experimental results of 2D-C/SiC composites, the time of stress reaction is very short and the accumulation a new constitutive model is proposed and it agrees with the ergy is not enough to make the composite materials failure exPerimen tal data very well. As a result, the dynamic compressive strength is larger than the static one Acknowledgements The correlative exponents of Eqs. (3)and (7) for the elastic modulus E and parameter n are 0.968 and 0.9816, respectively, This project was supported by the National Natural Science which fit the results very well. Based on the deformation mecha- Foundation of China(No 90405016), China Aviation Science nism of the 2D-C/SiC composites, the rate-dependent non-linear Foundation(No 2006ZF53060) and the 111 project(B07050 feature should result from the inner damages and their evolution. to the Northwestern Polytechnical University in Xi'an Therefore it is rational to consider the factor of damage in the constitutive model References 4. Conclusions [1] G. Camus, L Guillaumat, S. Baste, Compos. Sci. Technol. 56(1996) 1363-1372 (1)The mechanical properties of the 2D-C/SiC composites [2] R.E.L. Bouazzaoui, S Baste, G. Camus, Compos. Sci. Technol. 56(1996) are rate-dependent. The failure strength and elastic mod 1373-1382 ulus increase and failure strain decreases with an increasing [3]S Baste, Compos. Sci. Technol. 61(2001)2285-2297 strain rate [4 S Sarva, S Nemat-Nasser, Mater Sci Eng. A317(2001)140-144. (2) The specimens of 2D-C/SiC composites fail by shearing M. Futakawa, Y. Tannabe, T. Wakui, et al., Int J. Impact Eng. 25(2001) under compression, and a larger shear fracture angle, 55 [6] C.A. Weeks, C.T. Sun, Compos. Sci. Technol. 58(1998)603-611 are observed at the higher strain rate of 850s-, comparing [71 M.V. Hosur, M. Adya, U.K. Vaidya, A. Mayer, S. Jeelani, Compos.Struct. with 500 at 10-4s- More cracked fibers are also observed 59(2003)507-523. at the fracture surface under higher strain rates. [8] Q.. Yuan, Y.L. Li, HJ. Li, S.P. Li, L.J. Guo, J. Inorg. Mater. 22(2007) 311-314 (in Chinese) (3)The elastic modulus of the 2D-C/SiC composites varies (9) G Ravichandran, G. Subhash, J Am. Ceram Soc. 77(1994)263-267 linearly to the logarithm of strain rates. [10] W N.J. Sharpe, K.G. Hoge, Exp Mech. 12(1972)570.L. Mingshuang et al. / Materials Science and Engineering A 489 (2008) 120–126 125 Fig. 11. The comparative charts of the constitutive model vs. experimental data of 2D-C/SiC composites at different strain rates. strain rate, high stress is needed to make the cracks spread, as the time of stress reaction is very short and the accumulation energy is not enough to make the composite materials failure. As a result, the dynamic compressive strength is larger than the static one. The correlative exponents of Eqs. (3) and (7) for the elastic modulus E and parameter n are 0.968 and 0.9816, respectively, which fit the results very well. Based on the deformation mecha￾nism of the 2D-C/SiC composites, the rate-dependent non-linear feature should result from the inner damages and their evolution. Therefore, it is rational to consider the factor of damage in the constitutive model. 4. Conclusions (1) The mechanical properties of the 2D-C/SiC composites are rate-dependent. The failure strength and elastic mod￾ulus increase and failure strain decreases with an increasing strain rate. (2) The specimens of 2D-C/SiC composites fail by shearing under compression, and a larger shear fracture angle, 55◦ are observed at the higher strain rate of 850 s−1, comparing with 50◦ at 10−4 s−1. More cracked fibers are also observed at the fracture surface under higher strain rates. (3) The elastic modulus of the 2D-C/SiC composites varies linearly to the logarithm of strain rates. (4) Based on the experimental results of 2D-C/SiC composites, a new constitutive model is proposed and it agrees with the experimental data very well. Acknowledgements This project was supported by the National Natural Science Foundation of China (No. 90405016), China Aviation Science Foundation (No. 2006ZF53060) and the 111 project (B07050) to the Northwestern Polytechnical University in Xi’an. References [1] G. Camus, L. Guillaumat, S. Baste, Compos. Sci. Technol. 56 (1996) 1363–1372. [2] R.E.I. Bouazzaoui, S. Baste, G. Camus, Compos. Sci. Technol. 56 (1996) 1373–1382. [3] S. Baste, Compos. Sci. Technol. 61 (2001) 2285–2297. [4] S. Sarva, S. Nemat-Nasser, Mater. Sci. Eng. A317 (2001) 140–144. [5] M. Futakawa, Y. Tannabe, T. Wakui, et al., Int. J. Impact Eng. 25 (2001) 29–40. [6] C.A. Weeks, C.T. Sun, Compos. Sci. Technol. 58 (1998) 603–611. [7] M.V. Hosur, M. Adya, U.K. Vaidya, A. Mayer, S. Jeelani, Compos. Struct. 59 (2003) 507–523. [8] Q.L. Yuan, Y.L. Li, H.J. Li, S.P. Li, L.J. Guo, J. Inorg. Mater. 22 (2007) 311–314 (in Chinese). [9] G. Ravichandran, G. Subhash, J. Am. Ceram. Soc. 77 (1994) 263–267. [10] W.N.J. Sharpe, K.G. Hoge, Exp. Mech. 12 (1972) 570