• Research paper •

### Uniaxial tensile stress-strain behavior and strength of plain woven C/SiC composite

Yang Chengpeng,Jiao Guiqiong,Wang Bo

• Received:2009-12-07 Revised:2010-04-16 Online:2011-03-25 Published:2011-03-25
• Contact: Jiao Guiqiong

Abstract: Fiber reinforced ceramic matrix composites (CMCs) are widely investigated in recent years in order to obtain their damage mechanisms, failure modes and mechanical properties. A well-accepted fact is that the interface between the fibers and the ceramic matrix has great effects on the mechanical behavior of CMCs. The tough and nonlinear stress-strain behavior of CMCs can mainly be attributed to matrix cracking and interface debonding. Therefore, how these two factors affect the stress-strain relationship and the final strength of CMCs needs to be deeply studied. In this paper, the damage evolution and the tensile stress-strain behavior of 2D-C/SiC composite were investigated under monotonic and stepwise incremental loadings and unloadings. The strain is measured by 25 mm extensometer. The experimental results show that the stress-strain behavior of the material is obviously nonlinear; the unloading modulus decreases while the inelastic strain increases with increasing of the unloading stress; the relational curves of residual strain and unloading modulus versus the applied stress have analogous form with the tensile stress-strain curve; the fracture of the composite is quasi-brittle, i.e. catastrophic. Based on the shear-lag theory and the rule of mixture, a concise constitutive equation and a tensile strength calculation model of the damaged material were established. The simulated stress-strain curve is in good agreement with the experimental data when the applied stress is lower than 100 MPa. The difference between the theoretical curve and the experimental data when the applied stress is higher than 100 MPa mainly comes from the local strain concentrations within the seriously damaged zone, because large crack openings usually appear in this region from the experimental view. The analysis results reveal that the residual strain mainly depends on the crack opening displacement and the crack spacing, while the unloading modulus is significantly dependent on the interface debonding rate. Moreover, the uniaxial tensile behavior of 2D-C/SiC composite is mostly dominated by the longitudinal fiber bundles; the contributions of transverse fibers to the material's modulus and strength are obviously small. In the strength model, the failure criteria proposed by Tsai-Hill was applied to obtain the off-axes strength, and then the curved fiber bundle in the real material structure was equivalent to the straight. Furthermore, the rule of mixture was modified and the expression for strength calculation was presented. And, the predicted tension strength ranges from 210.5 MPa to 265.6 MPa for the 2D-C/SiC composite with 0.15 \mu m thick carbon interphase, which is also in good agreement with the experimental data.

Key words: micromechanical model

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