Characterization and analysis of torsion property of carbon fiber bundle combined with epoxy resin

This study established a torsion testing method for carbon fiber bundle combined epoxy resin and investigated torsional properties of several kinds of carbon fiber with different epoxy matrix. Torsion strength and modulus were calculated to characterize the torsional properties. The effects of testing conditions including aspect ratio of sample, testing speed and resin content in bundle on measured torsional results were ascertained for choosing appropriate conditions. Scanning electron microscope (SEM) observation on fractured sample and single fiber pull‐out test were carried out to illustrate the relationship between torsion property and the properties of carbon fiber, matrix, and interface. The experimental results show that the proposed method can obtain torsion strength and modulus with good data reliability using optimized testing conditions. Higher elongation of carbon fiber leads to larger torsion strength. SEM shows that low‐elongation carbon fiber tends to fail easier with brittle failure mode. Torsion modulus strongly depends on modulus of resin matrix, rather than tensile modulus of carbon fiber. Moreover, better interfacial adhesion between fiber and matrix results in large torsion strength when matrix elongation is at equivalent level. POLYM. COMPOS., 39:E2529–E2539, 2018. © 2018 Society of Plastics Engineers