Experimental measurement of tensile and torsional properties of CANSAS-II SiC fibres

Among the mechanical properties of SiC fibres, tensile properties have drawn extensive research attention. Nevertheless, data regarding shear properties, tensile-shear properties, and Poisson's ratio are still scarce. This paper focuses on investigating the shear behaviour of SiC fibres by examining their torsional properties. A specifically designed fibre torsional testing apparatus, along with a corresponding testing procedure, was put forward. By integrating this developed apparatus with a tensile testing machine, experiments were carried out on CANSAS - II fibres. These experiments included tensile tests, torsional tests, Poisson's ratio measurements, and tensile - torsional tests. The ultimate tensile/shear strength, ultimate tensile/shear strain, tensile/shear modulus, and Poisson's ratio of the fibres were accurately determined. Based on the results of the tensile-torsional tests, the relation between failure tensile stress and failure shear stress was investigated. The test results clearly demonstrate the brittle fracture characteristics of the fibres. With the increase in fibre diameter, a slight downward trend was observed in the tensile modulus, shear modulus, and Poisson's ratio. Moreover, the aggregation degree of the fibre moduli was higher than that of the strengths. Additionally, the maximum principal stress criterion, employed to describe the competitive relation between the failure tensile strength and failure shear strength, was found to be overly optimistic in cases of pure tension and pure shear.