Inelastic Deformation of Titanium Matrix Composites Under Multiaxial Loading

A theoretical model capable of predicting the thermomechanical response of continuously reinforced, titanium matrix composite (TMC) laminates, subjected to multiaxial loading has been developed. The model is based on micromechanics and employs classical lamination theory to determine inelastic response. The constitutive relationships for each lamina are determined from a micromechanics analysis that is performed numerically using the finite element method. Matrix viscoplasticity, thermal stresses, and damage to the fiber/ matrix interfacial zone are explicitly included in the model. The representative cell of the micromechanical model is considered to be in a state of generalized plane strain, enabling a quasi two-dimensional analysis to be performed. Constant strain triangular elements are formulated with elasto-viscoplastic constitutive equations. Interfacial debonding is incorporated into the model through interface elements that are based on a constitutive model that includes normal and tangential debonding. Theoretical predictions are compared with the results of an experimental program conducted on SCS-6/Ti-15-3 unidirectional, [0 4 ], and angle-ply, [′45] s , tubular specimens. Multiaxial loading included increments of axial tension, compression, torque, and internal pressure. Loadings were chosen in an effort to distinguish inelastic deformation due to damage from matrix plasticity and separate time-dependent effects from time-independent effects. Results show that fiber/matrix debonding can be a major factor in the effective stress-strain response and that significant room temperature creep can occur at relatively low applied stress levels.