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An insightful understanding of the formation mechanism of process-inherent defects and deformation is increasingly important for the property evaluation and structural design of ceramic matrix composites (CMCs). For this purpose, a coupled thermal–diffusive–mechanical modeling approach was proposed by considering three important phenomena that occur during the pyrolysis process for manufacturing CMCs: variations of the physical and mechanical properties of the constituents, generation and diffusive of pyrolysis gas, and multiple thermal deformations. The synergistic effects of these three phenomena on the stress, damage development, microstructural morphology, and process deformation of SiC matrix composites were investigated using finite-element simulations. This new approach was validated by comparing the simulation and experimental results. Significant volume shrinkage of the matrix during the polymer-to-ceramic transformation resulted in large tensile stresses and subsequent highly fragmented microstructure in CMCs. The pyrolysis-gas-induced expansion on the matrix under a damage state may yield a positive process deformation of CMCs at the macroscale, overcoming the effects of the volume shrinkage of the bulk matrix at the microscale. The modeling approach is expected to guide high-quality manufacturing of CMCs and comprehensive studies of structure–processing–property relationships.

In this paper, the process deformation of 2D SiC/SiC composite materials in the pyrolysis stage of precusor infiltration and pyrolysis process (PIP) is investigated experimentally and computationally through a multiscale study. The pyrolysis process of PCS was described by a kinetic model. The intrinsic properties and behaviors of pyrolysed PCS were characterized experimentally. The macroscopic properties and behaviors of 2D-SiC/SiC composite materials were obtained through the homogenization method. The proposed methodology can successfully predict the process deformation of an L-shaped 2D SiC/SiC composite structure in cyclic PIP process. It is revealed that the pyrolysis of precusor can generate significant chemical shrinkage and stiffness variation, leading to the process deformation of the entire composite structure. Unlike the precusor, the variation of properties and behaviors of composite materials are anisotropic. Furthermore, the cyclic process and the evolution of matrix composition complicate the process deformation. The behavior of composite material is dominated by pyrolysing PCS at first several cycles whereas by pyrolysed SiC at last several cycles. The fundamental understating on process deformation in this paper may benefit the design and the manufacture of SiC/SiC composite materials. [ABSTRACT FROM AUTHOR]

Special features of formation of the grain structure and mechanical properties of copper during recrystallization annealing after cold deformation with a wide range of reduction are studied. The constants of the Hall-Petch equation are determined for copper, the microstructure of which forms in the course of plastic deformation and subsequent heat treatment. The results of the study are allowed for in the process of production of claddings for jet charges. [ABSTRACT FROM AUTHOR]