Influence of Nanoscale Inhomogeneity Incorporating Interface Effect on Crack Nucleation at Intersection of Twin and Grain Boundary in Nanocomposite

Nanocracks can generate at the intersection of the deformation twin and grain boundary (GB). A mathematical model is built to study the nanoinhomogeneity effect on nanocrack nucleation and propagation in the nanocrystalline matrix. The boundary condition at the interface between the nanoinhomogeneity and the matrix is modified by incorporating the interface effect. The influence of the nanoinhomogeneity shear modulus, the nanoinhomogeneity radius, the nanoinhomogeneity position, the interface effect, and the external stress on the nanocrack nucleation and propagation is investigated in detail. The results indicate that the stiff nanoinhomogeneity suppresses nanocrack nucleation and propagation and thereby improves the tensile ductility of nanocomposites without loss of their predominantly high strength. Both the positive interface residual tension and interface elastic constants suppress nanocrack nucleation and propagation, while the negative interface residual tension and interface elastic constants promote nanocrack nucleation and propagation. Furthermore, the effect of interface residual tension is rather significant. The interface elastic constants have a weak effect on nanocrack nucleation and propagation.

Coroas cerâmicas bi-layers: Uma revisão de literatura sobre tipos de cerâmicas, processamento cerâmico e tensão residual

INTRODUCTION: The usage of ceramic materials as a restoration strategy faces some problems, such as interferences between porcelain and zirconia, being the first one used as ceramic cover and the second one as infrastructure or coping. OBJECTIVE: review the literature on bi-layer ceramic crowns, through the types of ceramics, ceramic processing and residual stress.METHODOLOGY: Databases for this review were Bireme, Pubmed, Scielo and Virtual Libraries. Keywords were searched on Mesh. Inclusion criteria were Studies, Laboratorial and Clinical, Systematic Review and Meta-Analysis, papers and specific literature regarding the theme, in both English and Portuguese. Exclusion criteria were letter to the editor, clinical case and opinion piece, literatures that don’t face the theme and papers that analyze other odontological ceramics. Literature and papers were selected through summaries and abstracts. FINAL CONSIDERATIONS: Residual tension in bi-layers ceramics crowns with zirconia infrastructure and porcelain cover occur due to a lot of factors such as coefficient of thermal expansion, cooling speed, processing, and thickness of ceramic cover.

Straightening of low-rigid cylindrical details. Part I. Justification of the type of loading and modes at transverse straightening

For straightening of low-rigid cylindrical details like shaft and axes different types of loadings are considered which form tension different in size and in distribution. As the perspective direction, it is possible to consider correction by a bend at the influence of the distributed loading with the subsequent hardening of a billet by superficial plastic deformation based on a cross cheesing of it by flat plates. Purpose of the work was to define tension of the billet at cross correction for the choice of more effective type of loading and processing rational modes. The mathematical apparatus was used based on laws of the theory of an elastoplastic solid and Ansys Workbench software package. Novelty is the research of effective methods of loading at cross correction of cylindrical details. As a result of analytical calculations, value of the residual tension providing correction of cylindrical details was determined. Residual tension necessary for correction of cylindrical details depends on an initial deflection, material and preparation rate. Tension of cylindrical details was defined depending on a type of the application of cross loadings. Bend tension for correction of a shaft at distributed loading is less, than tension from action of cross force. For correction of a shaft with a diameter of 10 mm, 200 mm long and an initial deflection of 0.5 mm it is necessary to create bend tension equal to about 370 MPa. An effective method of loading at cross correction of cylindrical details is the bend at influence of the distributed loading. The received extreme values of bend coefficients are from 5.3 to 5.5 for all cases of shaft rigidity at correction by cross bend at distributed loading with l/L relation equal to 0.8. The developed mathematical model gives quite reliable values of the residual tension providing correction of cylindrical details. The analytical dependence for determination of the size of general deflections and definition of an effective loading type can be recommended for practical use in production for achievement of precision accuracy of low-rigid details like shaft.