Stiffness degradation of SiC/Ti tubes subjected to biaxial loading

Abstract

This paper presents the results of a combined experimental and theoretical investigation of the stiffness degradation of unidirectional [0] and angle-ply [±45] s SiC/Ti tubes subjected to axial, torsional and combined axial/torsional loadings. The test program consisted of a series of axial and torsion tests, to sequentially higher load levels, on tubes fabricated using SCS 6 silicon carbide fibers and Ti-15-3 titanium matrix. At each load level, both the axial and torsional stiffnesses were measured. This procedure provided the opportunity to study the axial and torsional response at different levels of interfacial damage, matrix plasticity and combined load states. The experimentally measured axial and shear moduli, and initial yield stresses were compared with micromechanics predictions generated with different degrees of imperfect fiber/matrix bonding. No evidence of moduli degradation in the [0 4] tubes was present under tensile loading, whereas under shear loading, shear modulus degradation was observed only after occurrence of damage accompanied by pronounced plastic flow. Substantial degradation of both axial and shear moduli was observed in the [±45] s tubes under axial loading. The results suggest that the degradation of the interfacial bond in the [±45] s tubes accelerated yielding of the matrix which, in turn, contributed to further degradation in the case of the shear modulus. The results of this investigation point to the importance of damage-induced stiffness degradation and damage-accelerated yielding in SiC/Ti laminated tubes.