Damage modeling of graded Ti-based composites using repeated unit cell approach

In the present study, macroscopic mechanical behaviors of titanium-based functionally graded biomaterials (FGMs) under the influence of composite damage have been investigated using the repeated unit cell approach. Based on the proposed method, the FGMs were idealized to be composed of finite uniform layers, each of which is represented by one repeated unit cell. The titanium (Ti) matrix is modeled as an isotropic hardening elastic plastic solid following the incremental (J2) theory of plasticity. As the strength and fracture toughness of hydroxyappatite (HA) inclusion is very weak as compared with the Ti metal, the HA particles may be broken firstly when the composite is subjected to an excessive load. The brittle failure criterion has been implemented in the VUMAT subroutine using the finite element software ABAQUS. A uniaxial tension test along the y-axis of the unit cell has been simulated. The simulation results show that the load-bearing capability of Ti/HA FGMs will decrease rapidly with the increase in the volume fraction of HA. Due to the absence of the load bearing capability of HA, the mechanical behaviors of unit cell are similar to those of a porous structure and the applied load is entirely carried by the Ti matrix. The computational results indicate that this method is capable of predicting the failure process of Ti/HA FGMs.