A small-angle X-ray scattering study and molecular dynamics simulation of microvoid evolution during the tensile deformation of carbon fibers

Small angle X-ray scattering and molecular dynamics simulation were used to study the microvoid evolution in carbon fibers (CFs) during tensile deformation. The stress–strain relation and the parameters of microvoids, such as the length, diameter, orientation angle and relative volume were measured. The results demonstrated that during the tensile deformation of CFs, (1) the microvoid volume increased gradually; (2) the microvoid orientation angle with respect to the fiber axis decreased; (3) the mean microvoid length statistically decreased; (4) the short range structure did not change while the bond length of partial C–C increased and the medium and long range structure became disordered; (5) the angle of partial C–C–C shifted to the small angle; (6) the increase of bond lengths and decrease of bond angles mainly appeared at stress concentration areas which were the key damage points. It was indicated that reasonable control of small microvoid growth and stress release could improve the performance of CFs.