Search

High resolution EBSD studies on a deformed copper polycrystal have been carried out to quantify the microstructural residual stress distributions, and those of stress state including triaxiality of importance in defect nucleation studies. Crystal plasticity analysis of a representative, similarly textured, model polycrystal has been carried out showing that the experimental distributions of microstructural residual stress components, effective stress, hydrostatic stress and stress triaxiality are well captured. The crystal model enables point-wise microstructural Schmid factors to be calculated both globally (ie with respect to the macroscopic remote loading) and locally from full knowledge of the grain-level stress state. Significant differences are demonstrated such that global Schmid analysis tends to overestimate slip activity and the frequency of high Schmid factors, indicating that the local microstructural heterogeneity is significant and caution is necessary in interpreting polycrystal behaviour using global Schmid factors. A stored energy criterion for fatigue crack nucleation indicates that preferential sites for fatigue crack nucleation are local to grain boundaries (as opposed to triple junctions), and that hard-soft grain interfaces where high GND densities develop are preferable.

Objectives It is proposed that a non-uniform rational B-spline (NURBS) based solid geometric model of a ceramic crown would be a flexible and quick approach to virtually simulate root canal access cavities. The computation of strain components orthogonal to surface flaws generated during the drilling would be an appropriate way of comparing different access cavity configurations. Methods A μCT scan is used to develop a full 3D NURBS geometric solid model of a ceramic crown. Three different access cavity configurations are created virtually in the geometric model and there are then imported into proprietary finite element software. A linear analysis of the each crown is carried out under appropriate in vivo loading and the results are post-processed to carry out a quantitative comparison of the three configurations Results The geometric model is shown to be a flexible and quick way of simulation access cavities. Preliminary indications are that post processed strain results from the finite element analysis are good comparators of competing access cavity configurations. Significance The generation of geometric solid models of dental crowns from μCT scans is a flexible and efficient methodology to simulate a number of access cavity configurations. Furthermore, advanced post-processing of the primary finite element analysis results is worthwhile as preliminary results indicate that improved quantitative comparisons between different access cavity configurations are possible.

The Sih, Paris and Irwin analytical solution for cracks in anisotropic elastic media has been developed for an hcp Ti single crystal and shown to lead to crack tip normal stresses which are independent of crystal orientation but other stress components which are dependent. Detailed finite element studies confirm that the stress intensity remains independent of crystal orientation but ceases to do so in an edge-cracked bi-crystal. The incorporation of crystallographic slip demonstrates that single-crystal crack tip stresses largely remain independent of crystal orientation but that the plastic zone size and shape depends greatly upon it. Significant differences result in both the magnitude and extent of the plasticity at the crack tip with crystallographic orientation which can be quite different to that predicted using Mises plasticity. For an edge crack terminating in a bi-crystal, the slip fields which result depend upon both crystal mis-orientation and morphology.