Damage analysis of particulate biocomposites using finite element technique

Abstract

Particle reinforced polymer biocomposite (PRPB) has been incorporated into numerous different designs and utilized for many patients in bone replacement. Further application of this and related composites will involve exploring their potential in major weight-bearing applications. A recent review of biomechanics highlights the important role of damage in governing mechanical properties of biomaterials. Developing a new biocomposite with desired mechanical properties is usually accomplished by an experimental trial-an-error approach. Although some empirical and numerical approaches have been developed, there is no method so far by which damage phenomenon and mechanical properties of biocomposite can be satisfactorily predicted. Conventional computation methods neglect the gradual degradation of material and are no longer suitable for designing this category of material. This calls for a novel simulation methodology that can predict the mechanical properties and damage process of PRPB. The objective of this project is to develop a scientific approach for predicting the mechanical properties and the failure process of PRPBs by simulating the damage mechanism of PRPB at mesoscopic level. In a tertiary phase representative volume element, particle-matrix debonding and matrix damage have been taken into account to model the damage mechanism. After validation of the results from the mesoscopic studies, the damage constitutive and evolution equations for mechanistic structural analyses can be established. Several kinds of unit cell models together with superelement techniques have been incorporated in a finite element code ABAQUS. Moreover, the effects of damage on the matrix and the interphase of PRPB have been depicted by user-defined material subroutines written in FORTRAN. With a newly designed three-dimensional unit cell model, three new different schemes have been initially proposed in this project to predict the flexural properties of hydroxyapatite-reinforced poly-1-lactide acid (HA/PLLA) biocomposite. The computational results are in good agreement with the Chow's empirical formula and the experimental data. Using a hybrid micro-macro modelling technique, the three-phase cell model has also been applied to predict the elasto-plastic properties of hydroxyapatite-reinforced polyetheretherketone (HA/PEEK) biocomposite. Ductile damage evolution in the matrix has been adopted and a failure criterion was established using the damage law. In comparison of the results with the experimental ones, the hybrid micro-macro modelling technique is applicable for modelling the mechanical properties of PRPB. Owing to the complexity of the analyses mentioned above, a multi-level superelement technique has been proposed for predicting macro-elastic properties with the computational time and memory space greatly reduced. To demonstrate the applicability of this technique, a superelement model has been constructed in describing the porous material. A dual-parameter damage analytical model has been derived on the basis of the micro-analytical results. Using a case of tensile loading of a notched cylindrical bar, this technique has been proven reliable in predicting macroscopic response of engineering structures. In addition, superelements and conventional elements have also been used together to successfully solve non-linear problems for the prediction of elasto-plastic properties of PRPB. Hydroxyapatite-reinforced polydimethacrylate biocomposite is a tooth restoration dental material. It is amongst the first attempt, the damage mechanism of this biocomposite has been revealed and modelled quantitatively taking into consideration the effect of water sorption. By combining this with the hybrid micro-macro modelling technique, the method to simulate the stress and displacement of an idealised restoration-tooth structure under both polymerisation shrinkage and water sorption has been developed. This project has been conducted, in the first instance, to incorporate the concept of damage mechanics to develop a hybrid micro-macro technique that can be applied to simulate the local damage mechanism, the constitutive behaviours, and the structural properties of PRPBs. The deliverables of the project not only provided a means for designing PRPBs, but also opened a door for further extending the damage theory in analyzing biomaterials and their structures.