2016 Volume 65 Issue 8 Pages 573-579
Torsional-tensile, dynamic torsional pendulum oscillation and static rotary tests of carbon mono-filament were carried out. Two high performance carbon fibers，a PAN-based and a pitch-based, were chosen for these tests. From static rotational behavior of carbon and glass series connected filament, shear stress-strain diagram of carbon fiber is determined. On the diagram, the PAN-based carbon fiber exhibits a very linear shear stress-shear strain relationship up to the torsional fracture. On the other hand, the pitch-based carbon fiber shows the linear relationship up to a point. Beyond the point, increasing shear strain, slope of the τ/γ (torsional stiffness) is decreased. However, for each carbon fiber, it does not show any plastic torsional deformation, that is, it is perfectly elastic until fracture. In other words, the torsional deformation is completely recovered when the torque is reduced at every torsional deformation stage. The mono-filament of carbon fiber is tensioned until fracture with fixing torsional strain. The torsional-tensile strength of the PAN-based carbon fiber shows that increasing torsional strain, the tensile strength decrease by insensible degrees with the small torsional strain and rapidly decrease coming up to the torsional fracture strain. The torsional-tensile strength of the pitch-based carbon fiber does not change until a torsional strain, and after then decreased rapidly. Tensile rigidity is gradually decreased, increasing torsional strain, and decreased sharply at closing torsional fracture strain. The ratios of anisotropic measure of strength by the tensile strength to the torsional strength are smaller than the ratios of elasticity by the tensile modulus to the torsional modulus. This torsional-tensile test method is useful in order to evaluate strength and structural anisotropy of fiber materials.
