Wear of Composites by Abrasives of Varying Hardness

The relationship between the wear of three composite resins and the hardness of the abrasive was studied by a two-body abrasion test. The wear rates of the composites increased linearly with abrasive hardness from 530 to 2080 KHN. Measurement of the slope of the wear rate versus abrasive hardness over this range provided a sensitive method for ranking the composites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68031/2/10.1177_00220345790580031201.pd

Wear of Fluorapatite Single Crystals: III. Classification of Surface Failure

Modes of surface failure observed for natural fluorapatite single crystals under sliding were classified and related to wear and frictional behavior. The basal surfaces exhibited brittle or ductile failure depending on the combination of load and slider design. The transition occurred at penetrations of 0.3 to 0.5 μm.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67122/2/10.1177_00220345720510026101.pd

In vitro Wear of Microfilled and Visible Light-cured Composites

Wear of microfilled composites, a visible light-cured composite, and a conventional composite were characterized by two-body abrasion and single-pass sliding. There were differences in abrasion rates among the materials. Tangential forces, wear track widths, and surface failure modes were different among materials. Wear characteristics are combinations of these properties.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67083/2/10.1177_00220345790580111301.pd

Wear of Fluorapatite Single Crystals : V. Influence of Environment on Frictional Behavior and Surface Failure

The influence of environment on the frictional behavior and surface failure of fluorapatite single crystals was evaluated for sliding in air, water, and dimethylformamide. The coefficient of friction was independent of environment. The ductile-to-brittle transition, however, occurred at a lower load in water than in air.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68110/2/10.1177_00220345730520050501.pd

Penetration of Commercial and Dental Waxes

Penetration of commercial and dental waxes was studied. Measurements indicated that resistance of paraffin and dental inlay waxes to penetration was closely related to the temperature at which solid-solid transformations occurred. Annealed waxes were more resistant to penetration than unannealed waxes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67386/2/10.1177_00220345740530023701.pd

Analytical Formulation of the Jacobian Matrix for Non-linear Calculation of the Forced Response of Turbine Blade Assemblies with Wedge Friction Dampers

A fundamental issue in turbomachinery design is the dynamical stress assessment of turbine blades. In order to reduce stress peaks in the turbine blades at engine orders corresponding to blade natural frequencies, friction dampers are employed. Blade response calculation requires the solution of a set of non-linear equations originated by the introduction of friction damping. Such a set of non-linear equations is solved using the iterative numerical Newton-Raphson method. However, calculation of the Jacobian matrix of the system using classical numerical finite difference schemes makes frequency domain solver prohibitively expensive for structures with many contact points. Large computation time results from the evaluation of partial derivatives of the non-linear equations with respect to the displacements. In this work a methodology to compute efficiently the Jacobian matrix of a dynamic system having wedge dampers is presented. It is exact and completely analytical. The proposed methods have been successfully applied to a real intermediate pressure turbine (IPT) blade under cyclic symmetry boundary conditions with underplatform wedge dampers. Its implementation showed to be very effective, and allowed to achieve relevant time savings without loss of precision

Stress Analysis of a Tooth Restored with a Post and Core

An idealized axisymmetric finite element model of a second premolar restored with a post and core was used to study the distribution and magnitude of stresses as a function of the following parameters : the diameter of the post, the length and the shape of the post, and finally the interface characteristics between post and cement. Emphasis was directed toward the cement layer interposed between the post and the tooth. Bonding between the post and the cement appeared to be the most important parameter to achieve optimal mechanical behavior of the tooth-prosthesis combination.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66564/2/10.1177_00220345830620061501.pd

Frictional Behavior and Surface Failure of Human Enamel

The frictional behavior and surface failure of human enamel under sliding in water was examined. A large plowing component of friction was observed. For normal loads of up to 1kg, ductile behavior of the wear scar was apparent. Intermittent cracks were obrerved that appeared to propagate around the enamel rods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67266/2/10.1177_00220345730520063001.pd

Wear of Fluorapatite Single Crystals : II. Frictional Behavior

The frictional behavior of natural fluorapatite single crystals under sliding was evaluated. Strain rate did not influence the coefficient of friction. Low and high regimes of friction were related to the amount of penetration; higher values of friction were associated with deeper penetration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67389/2/10.1177_00220345720510026001.pd

Rotational Viscometry of a Zinc Phosphate and a Zinc Polyacrylate Cement

The rheological properties of a zinc phosphate and a zinc polyacrylate cement were investigated using a rotational viscometer. The effects of time, temperature, shear rate, and spindle geometry on the measured viscosities were evaluated. Results indicated that both cements exhibited Newtonian behavior.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66697/2/10.1177_00220345770560071001.pd