Damage analysis on a graded porous biocomposite structure under flexural load using FEM

A multi-level finite element (FE) method was developed to firstly study the mechanical responses and progressive damage behaviors of graded porous structures made of hydroxyapatite particle reinforced polymer biocomposite (HA/PEEK) under flexure load. In order to bridge the mechanical properties of the base material, damage and failure criteria of the building blocks for the graded porous structure, and macroscopic response of the structure, three-level FE models from micro-, mesoto macro-scale were established. A graded porous biocomposite implant was considered as a continuum structure with a solid section and a porous section with a gradient change in porosity from 29.5 to 80.9% in six equal steps. The macro-scale FE model of the implant was then constructed from the meso-scale unit cubic-shaped cell model, which was made of beam elements with a fixed length but a gradient change in their cross-section areas depending on the porosity level. The base material of the structure, HA/PEEK, was obtained from our previous work through a micro-scale unit cell model consisting of the particle and polymer matrix for predicting its stress–strain relation with dependence on variation of HA volume fraction. By adoption of the proposed method, a virtual three-point bending test was simulated to predict force–displacement relations of the implant and its damage initiation and propagation in both graded and uniform porous structures under flexural load. The trend of the predicted results agreed with those reported in open literature.