Abstract: Needled-punched ceramic matrix composites are promising for a wide range of applications in hot-end structures in aerospace field. However, the manufacturing defects causing in the process of pre-fabrication and deposition lead to a high degree of dispersion in their properties. It is difficult to accurately predict their mechanical behavior. A sub-regional parametric characterization method for pore defects in needle-punched ceramic matrix composites was proposed based on X-ray microscopy and 3D image reconstruction techniques. Combined with the idea of probabilistic fitting, the size and structural characteristics of the material pore defects were parametrically characterized, and it was found that the equivalent diameter of the pores in the fiber-web layer was larger than that in the unidirectional layer, but the aspect ratio was smaller than that in the unidirectional layer. The elastic properties of the materials were predicted and analyzed using ellipsoid fitting and multiscale modelling methods, and the predictions differed from the experimental results by about 3.1% with good accuracy. The discussion of pore parameters revealed that: the unidirectional layer porosity has better uniformity in the distribution direction, and the reduction of the elastic properties in the direction of the fiber bundle length is lower than that in the other directions; in comparison, the fiber-web layer has higher porosity, and it is beneficial to reduce the porosity of the fiber-web layer to further improve the overall elastic properties of the material by improving the process parameters.

Key words: needle-punched ceramic matrix composites, X-ray microscopy, characterization of pore defects, multiscale modelling, elastic properties