Direct Measurement of Transverse Compressive Properties of Polyacrylonitrile-Based Single Carbon Fibers

Evaluating the properties of single carbon fibers is crucial, as it provides parameters not only for optimizing carbon fiber production processes but also for enhancing composite material properties. In recent years, significant advancement have been made in the evaluations of the transverse compressive properties of single fibers. However, compressive testing methods for fibers in the fine size range remain limited at the commercial scale. The direct measurement of the transverse compressive properties of three domestic high-strength polyacrylonitrile-based single carbon fibers (T300 grade, T700 grade, and T800 grade) with diameters of ~5.5~6.5 μm was made possible through the use of a micro-compression tester. Transverse compressive moduli of 5.19 GPa (0.050), 5.42 GPa (0.104), and 6.63 GPa (0.120) were obtained for domestic T300-, T700- and T800-grade carbon fibers, respectively. In addition, transverse compressive strengths of 2.35 GPa (0.033), 2.65 GPa (0.041), and 2.82 GPa (0.121) were obtained for domestic T300-, T700- and T800-grade carbon fibers, respectively. It is noted that minor deviations in fiber geometry from an ideal circular cross-section may influence absolute modulus and strength values. These fibers exhibit strong anisotropy in the longitudinal and transverse directions from the fiber axis. A correlation between the transverse compressive modulus and strength was found for these fibers. These results provide critical parameters for the optimization of carbon fiber-reinforced composite designs (e.g., enhancing impact resistance in aerospace structures), offering substantial practical value to the field of materials science.