MATERIALS HIENGE& ENGIEERING ELSEVIER Materials Science and Engineering A 489(2008)120-126 www.elsevier.com/locate/msea Dynamic compressive mechanical properties and a new constitutive model of 2D-C/Sic composites Liu Mingshuang, Li Yulong,", Xu Fei, Xu Zejian, Cheng Laifei a School of Aeronautics, Northwestem Polytechnical University, Xi an, 710072, China b School of Materials Science and Engineering. Northwestern Polytechnical University, Xi'an,710072, China Received 15 June 2007; received in revised form 2 December 2007; accepted 3 January 2008 Abstract The layer-directional compressive properties of 2D-C/SiC composites were investigated at strain rates ranging from 10- to 2. x 103s-I.The quasi-static experiments were performed using the electronic universal testing machine, and the dynamic experiments were conducted by the split Hopkinson pressure bar system. The results show that the dynamic compressive stress-strain curves are non-linear. The failure strength and the elasticity modulus vary linearly to the logarithm of the strain rate, and the failure strain reduces with an ing strain rate. Scatter of dynamic compressive failure strength obeys Weibull distribution and the Weibull parameter m is 5.27. The damage angle of dynamic compression is larger than that of static loading. Observed on SEM, the ruptured surface is smooth at high loading rate and more cracked fibers appear in the specimen than at lower strain rate. Based on the experimental results, a new constitutive model is proposed in this paper. C 2008 Elsevier B. V. All rights reserved. Keywords: Ceramic matrix composites( CMCs); Weibull distribution; Dynamical constitutive model; Damage angle 1. Introduction the non-linear mechanical behavior of 2D-C/SiC composites Two damage modes were emphasized that transverse microc- Carbon-fiber-reinforced Sic-matrix( C/SiC)composites fab- racks were characterized by a deterministic accumulation and ricated by the chemical vapor infiltration process(CVi)have a random development of longitudinal micro cracking, 1.e been developed and are widely used in high technology struc- fiber/matrix and bundle/matrix debonding. Baste [3]summa- tural applications, especially in aerospace field, in which the rized a methodology for the formulation and identification of ratios of stiffness/weight and strength/weight, and high temper- the constitutive laws of ceramic-matrix composites. It relied ature prop re of great int on an anisotropic damage evaluation Sarva and Nemat-Nasser Many investigations have been conducted on 2D-C/SiC com- [4] investigated the effect of the strain rate on the compres- posites. Camus et al. [1] investigated the mechanical responses sive strength of Sic under uniaxial loading. They found a of 2D-C/SiC composites subjected to uniaxial tensile and com- marked increase in the compressive strength at strain rates pressive loadings. An extended non-linear stress-strain response greater than 10-s. Futakawa et al. [5] used a tensile split and a multi-stage development of damage involving trans- Hopkinson pressure bar to investigate the Sicr/Sicm compos- verse matrix microcracking, bundle/matrix and inter-bundle ites From the results, the interface friction stress was evaluated debonding as well as thermal residual stress release were evi- by the fiber pullout length, which was measured through micro- denced In compression, after an initial stage involving closure scopic observations of fractured specimens. And it was larg of the thermal microcracks generated from processing, the in dynamic loading than that in static loading. Weeks and opposites displayed a linear-elastic behavior until fai Sun [6] investigated the rate-dependent behavior of AS4/PEEK Bouazzaoui et al. [2] used an ultrasonic method to investi (APC-2)thermoplastic composites over a wide strain rate (10-3to 102s-)and introduced two Corresponding author at: P.O. Box 118, Northwestern Polytechnical Uni- Although a wealth of literature is reported on static mechan- versity, Xi'an 710072, PR China. Tel +862988494859: fax:+862988494859. ical properties, the dynamic compressive behavior of C/Sic E-mailaddress:liyulong@nwpu.edu.cn(L.Yulong) composites has not yet been reported to our knowledge. In this 0921-5093 ter 2008 Elsevier B v. All rights reservedMaterials Science and Engineering A 489 (2008) 120–126 Dynamic compressive mechanical properties and a new constitutive model of 2D-C/SiC composites Liu Mingshuang a, Li Yulong a,∗, Xu Fei a, Xu Zejian a, Cheng Laifei b a School of Aeronautics, Northwestern Polytechnical University, Xi’an, 710072, China b School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, 710072, China Received 15 June 2007; received in revised form 2 December 2007; accepted 3 January 2008 Abstract The layer-directional compressive properties of 2D-C/SiC composites were investigated at strain rates ranging from 10−4 to 2.8 × 103 s−1. The quasi-static experiments were performed using the electronic universal testing machine, and the dynamic experiments were conducted by the split Hopkinson pressure bar system. The results show that the dynamic compressive stress–strain curves are non-linear. The failure strength and the elasticity modulus vary linearly to the logarithm of the strain rate, and the failure strain reduces with an increasing strain rate. Scatter of dynamic compressive failure strength obeys Weibull distribution and the Weibull parameter m is 5.27. The damage angle of dynamic compression is larger than that of static loading. Observed on SEM, the ruptured surface is smooth at high loading rate and more cracked fibers appear in the specimens than at lower strain rate. Based on the experimental results, a new constitutive model is proposed in this paper. © 2008 Elsevier B.V. All rights reserved. Keywords: Ceramic matrix composites (CMCs); Weibull distribution; Dynamical constitutive model; Damage angle 1. Introduction Carbon-fiber-reinforced SiC-matrix (C/SiC) composites fab￾ricated by the chemical vapor infiltration process (CVI) have been developed and are widely used in high technology struc￾tural applications, especially in aerospace field, in which the ratios of stiffness/weight and strength/weight, and high temper￾ature properties are of great interest. Many investigations have been conducted on 2D-C/SiC com￾posites. Camus et al. [1] investigated the mechanical responses of 2D-C/SiC composites subjected to uniaxial tensile and com￾pressive loadings. An extended non-linear stress–strain response and a multi-stage development of damage involving trans￾verse matrix microcracking, bundle/matrix and inter-bundle debonding as well as thermal residual stress release were evi￾denced. In compression, after an initial stage involving closure of the thermal microcracks generated from processing, the composites displayed a linear-elastic behavior until failure. Bouazzaoui et al. [2] used an ultrasonic method to investigate ∗ Corresponding author at: P.O. Box 118, Northwestern Polytechnical Uni￾versity, Xi’an 710072, PR China. Tel.: +86 2988494859; fax: +86 2988494859. E-mail address: liyulong@nwpu.edu.cn (L. Yulong). the non-linear mechanical behavior of 2D-C/SiC composites. Two damage modes were emphasized that transverse microc￾racks were characterized by a deterministic accumulation and a random development of longitudinal micro cracking, i.e. fiber/matrix and bundle/matrix debonding. Baste [3] summa￾rized a methodology for the formulation and identification of the constitutive laws of ceramic–matrix composites. It relied on an anisotropic damage evaluation. Sarva and Nemat-Nasser [4] investigated the effect of the strain rate on the compres￾sive strength of SiC under uniaxial loading. They found a marked increase in the compressive strength at strain rates greater than 102 s−1. Futakawa et al. [5] used a tensile split Hopkinson pressure bar to investigate the SiCf/SiCm compos￾ites. From the results, the interface friction stress was evaluated by the fiber pullout length, which was measured through micro￾scopic observations of fractured specimens. And it was larger in dynamic loading than that in static loading. Weeks and Sun [6] investigated the rate-dependent behavior of AS4/PEEK (APC-2) thermoplastic composites over a wide strain rate range (10−5 to 102 s−1) and introduced two rate-dependent models. Although a wealth of literature is reported on static mechan￾ical properties, the dynamic compressive behavior of C/SiC composites has not yet been reported to our knowledge. In this 0921-5093/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2008.01.014