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Computational micromechanics provides an efficient strategy to optimize composite materials by addressing the effect of different material and geometric parameters involved. In the present paper, the effective transverse elastic properties for periodic composite materials reinforced with single and clustered polygonal fibers are evaluated using the micromechanical finite element formulation subject to periodic displacement boundary conditions. The cross-sectional shapes of polygonal fibers are assumed to be triangular, square, pentagonal, hexagonal, octagonal, and circular to perform comprehensive investigation. By applying a periodic displacement constraint along the boundary of the representative unit cell of the composite to meet the requirement of straight-line constraint during the deformation of the unit cell, the computational micromechanical modeling based on homogenization technology is established for evaluating the effects of fiber shape and cluster on the overall properties. Subsequently, the micromechanical model is divided into four submodels, which are solved by means of the finite element analysis for determining the traction distributions along the cell boundary. Finally, the effective orthotropic elastic constants of composites are obtained using the solutions of the linear system of equations involving traction integrations to investigate the effects of fiber shape and cluster on the overall properties.

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper investigates the effects of clustering on the effective transverse thermal conductivity of unidirectional cement composites filled with natural hemp fibers. A typical clustering pattern with four hemp fibers embedded into cement matrix is designed as the representative two-dimensional unit cell, which is taken from the periodic cement composite under consideration, and a clustering degree parameter is introduced to adjust the distance between clustered fibers. For this heterogeneous two-component composite model, distributions of the heat flux component are obtained using finite element simulation for various clustering cases involving different global fiber volume concentrations, clustering degree parameters, and thermal conductivity of both fiber and matrix, to evaluate the effective thermal conductivity of the composite. To further reveal the effects caused by clustered fibers, a random cluster pattern of hemp fibers in the unit cell is considered for comparison with the present regular clustering pattern. Further, a simple theoretical model with specified flexible factor f is developed by matching the theoretical and numerical predictions. [ABSTRACT FROM AUTHOR]

A novel liquid polymeric precursor for boron nitride (BN), which can be directly used as an impregnant for ceramic matrix composites, was synthesized by condensation of the substituent from 2,4,6-trichloroborazine andn-propylamine. The structure and composition of the precursor were characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and chemical analysis. The preceramic polymer was composed of B3N3hexagons linked mainly with =NCH2– units and had a chemical formula of BC2.4N1.63H8.6. Pyrolysis of the cured precursor to 1,200°C in NH3yielded turbostratic BN almost without carbon impurity. Moreover, the BN displayed good anti-oxidation property in air up to 950°C. [ABSTRACT FROM PUBLISHER]