By using monotonic and cyclic loading tests, the Poisson curves along the fiber bundles directions of a 2D-C/SiC composite were obtained during various axial tensile and compressive loading processes. And the effects of axial damage evolution process on the Poisson effect of composite were studied. The results show that composite shows significant negative Poisson’s ratio behaviors with increasing tensile damage during loading process, but the Poisson’s ratio behaviors become almost linear and positive when the damage evolution process stops. In addition, the Poisson effect becomes weaker with increasing damage degree within composite. The SEM (scanning electron microscope) analysis results of fractured surfaces on tensile specimens indicate that, during tensile damage evolution process, the matrix cracks and interface debondings occurring along the loading direction will generate vertical extension deformation on composite, which is large enough to cover up the transverse elastic Poisson contraction caused by applied tensile load, so 2D-C/SiC composite shows significant negative Poisson’ ratio behaviors. And the weaker Poisson effect of composite is mainly caused by the increasing discontinuity of composite, which is caused essentially by increasing cracking damage during tensile damage evolution process.
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