| dc.description.abstract | An absolute and relative stability of fixation determine the optimum direct primary and indirect secondary bone healing process through bone remodelling and osseointegration. Clinically, under compression, shear and torsional loading condition, the stability of implant fixation is affected by insufficient, over supplied and inconsistent stress shielding transfer (SST) between implant-bone interfaces. At worst, SST mechanism may trigger the implant fixation failure, implant pins or screw loosening and anatomical bone fracture that initiated from bone damage by pre-drilled technique which enhance bone microcracks interface. The micromechanics elastic interaction of microcrack penetration into Haversian system initiated by pre-drilled microcrack is presently unexplained based on fracture mechanics principles. Therefore, this research aims to investigate the Type-7 single microcrack penetration into Haversian system for primary and secondary bone formation specific to diaphysis cortical bone transverse and longitudinal fracture. Linear elastic fracture mechanics (LEFM), elastic plastic fracture mechanics (EPFM) and Kachanov theory of elliptical hole and microcracks interaction are used to establish primary and secondary bone fracture model using finite element (FE) analysis. The FE algorithms were developed in ANSYS APDL environment to establish Mode I and Mode II Type-7 crack penetration model for all cortices in transverse and longitudinal direction by incorporating crack tip stress singularity approach using displacement extrapolation method (DEM) and stress energy release rate (SERR) using J-integral method. Both approaches are numerically analysed and verified with good theoretical agreement by Brown & Srawley (0.2%), Gross & Brown (0.4%) and Tada (1.6%) analytical formulation for single edge crack in finite body. Sensitivity and statistical analysis also show a significant correlation (p < 0.05) between measured parameters for all cortices. Type-7 penetration model is further enhanced for primary bone cracking evaluation. Both DEM and J-integral method have accurately determined the Mode I (KITS(A,P,M,L), KILS(A,P,M,L)) and Mode II (KIITS(A,P,M,L), KIILS(A,P,M,L)) SIFs but it seems the only J-integral able to evaluate the influence of different Young‟s modulus in primary bone cracking. Thus, for secondary bone cracking, only J-integral analysis is further enhanced to evaluate the inhomogeneity of Haversian system interaction to drive the transverse and longitudinal Type-7 microcrack penetration through interstitial matrix, cement line and osteon induced by Haversian canal stress traction. The quantification of stress amplification σSA, stress shielding σSS and stress traction <pHC> are evaluated and verified by analytical formulations and Kachanov theory of elliptical crack and microcrack interaction. The results show that in transverse (KITS/K0) >1 and longitudinal (KILS/K0) >1, σSA is dominated in interstitial matrix area. Transition of σSA to σSS is occurred upon the cement line penetration and in osteon to Haversian canal penetration, the penetration is driven by σSS at (KITS/K0) <1 and (KILS/K0) <1. However, both transverse and longitudinal Type-7 direction experienced different intensity and energy release rate of σSA to σSS upon cement line penetration in relative to crack-to-width ratio (a/W). In conclusion, the Haversian system interaction model has successfully demonstrated the Type-7 microcrack penetration for primary and secondary bone formation. | en_US |
