Paul D. Funkenbusch

Sensitivities of Medial Meniscal Motion and Deformation to Material Properties of Articular Cartilage, Meniscus and Meniscal Attachments Using Design of Experiments Methods

This study investigated the role of the material properties assumed for articular cartilage, meniscus and meniscal attachments on the fit of a finite element model (FEM) to experimental data for meniscal motion and deformation due to an anterior tibial loading of 45 N in the anterior cruciate ligament-deficient knee. Taguchi style L18 orthogonal arrays were used to identify the most significant factors for further examination. A central composite design was then employed to develop a mathematical model for predicting the fit of the FEM to the experimental data as a function of the material properties and to identify the material property selections that optimize the fit. The cartilage was modeled as isotropic elastic material, the meniscus was modeled as transversely isotropic elastic material, and meniscal horn and the peripheral attachments were modeled as noncompressive and nonlinear in tension spring elements. The ability of the FEM to reproduce the experimentally measured meniscal motion and deformation was most strongly dependent on the initial strain of the meniscal horn attachments (epsilon(1H)), the linear modulus of the meniscal peripheral attachments (E(P)) and the ratio of meniscal moduli in the circumferential and transverse directions (E(theta)E(R)). Our study also successfully identified values for these critical material properties (epsilon(1H) = -5%, E(P) = 5.6 MPa, E(theta)E(R) = 20) to minimize the error in the FEM analysis of experimental results. This study illustrates the most important material properties for future experimental studies, and suggests that modeling work of meniscus, while retaining transverse isotropy, should also focus on the potential influence of nonlinear properties and inhomogeneity.

Ductile two-phase alloys: prediction of strengthening at high strains

When alloys containing two ductile phases are heavily deformed, composite-like microstructures develop and strengths well in excess of either of the phases in single phase form may be exhibited as a result of microstructure/dislocation density effects. In this paper a previously-published model for such strengthening is reviewed, and its application in a predictive capacity discussed. Flow stressvs fabrication strain data for the two components in single phase form and for one two-phase alloy are necessary for this purpose. The model may then be applied to predict strength for any other two-phase alloy as a function of composition, fabrication strain, and interphase spacing. The approach is illustrated using existing data for several alloy systems. For Ag-Fe and Cu-Nb alloys (with very limited mutual solubility) strengths can be predicted within 15 to 20 pct of the experimental values over the entire range of strains and volume fractions for which data are available. In systems where the potential for precipitation hardening exists (e.g., Cu-Fe) thermal history is important. When such hardening becomes a significant factor, the model cannot be used in its present form due to uncertainty over how to “add” the strengthening from this effect. Such hardening may, however, be useful in further improving the properties of these materials.

Solidification of YBa2Cu3O7−δ from the melt

Abstract Nucleation and growth of 123 from the melt via a peritectic reaction into domains of aligned platelets is studied. Analysis of the microstructure of well-formed domains indicates that there is no orientation difference between adjacent platelets within a domain, suggesting that a domain grows from a single nucleus. The platelet boundaries are found to be filled-in with secondary phases that correspond to the liquid phase at high temperature, suggesting that constitutional supercooling effects may be operative. Samples quenched from temperatures considerably below the peritectic temperature contain only a few crystals, indicating the presence of a large nucleation barrier. The above observations, coupled with extensive microstructural examination of quenched solid-liquid interfaces, suggest that the 211 size, distribution and volume fraction not only control the growth rate of 123 along the fast growth ab -plane (by supply of yttrium), but also the growth rate along the slow growth c -direction since the nucleation barrier is reduced at 211/123 intersections. At high cooling rates there is a distinct change in the nucleation and growth processes. Structures characteristic of sympathetic or autonucleation and spherulitic growth are observed. These structures are distinct from the single crystal nature of well-formed domains. The growth mechanism which results in the formation of 123 domains and the final microstructure within a single domain, also explains the observed non-weak-link characteristics for current flow along the a , b - and c -directions, as determined by direct transport and magnetization measurements.

Mechanical properties of highly aligned YBa2Cu3O7−δ effect of Y2BaCuOx particles

Abstract The elastic modulus and hardness of highly aligned YBa 2 Cu 3 O 7−δ obtained by melt processing was determined using a highly spatially resolved mechanical properties microprobe. Ultra-low load indentation measurements on the (001) cleavage plane of aligned 123, indicated a Youngs modulus of 143 ± 4 GPa and a hardness of 10.0 ± 1.9 GPa. For measurements on a plane perpendicular to the cleavage plane, values of 182 ± 4 GPa for the modulus and 10.8 ± 1.7 GPa for the hardness were obtained. A lower modulus in the c -direction is perhaps a result of the layer-like structure of 123, with weak coupling between the layers. Measurements on the trapped single crystal 211 particles yielded a modulus of 213 ± 5 GPa and a hardness of 14.4 ± 2 GPa. Considerations of the thermal and elastic mismatch effects between the 211 particles and the 123 matrix, the large thermal expansion anisotropy of aligned 123, and microstructural examination of polished and fracture surfaces of the aligned samples indicate that the 211 particles perhaps serve to enhance the fracture resistance behavior of 123 by energy dissipation due to interfacial delamination and crack bridging.

Effect of subgingival depth of implant placement on the dimensional accuracy of the implant impression: An in vitro study

STATEMENT OF PROBLEM In some instances, an implant needs to be placed deep subgingivally, which may result in a less accurate impression of the implant. PURPOSE.: The purpose of this study was to evaluate the effect of subgingival depth of implant placement on the accuracy of implant impressions. MATERIAL AND METHODS A stone master model was fabricated with 5 implant analogs (RN synOcta analog), embedded parallel to each other, at the center (E) and the 4 corners (A, B, C, and D). The vertical position of the shoulders of the implants was intentionally different among the implants: A and E were flush with the top surface of the model; B was 2 mm below, and C and D were 4 mm below the surface. The horizontal distances of implants A, B, C, and D from E were measured with a measuring microscope. A cross-shaped metal measuring bar was then fabricated and connected to E, with the arms of the casting designed to be 2 mm above the top surface of the model and incorporating a reference mark. With the measuring bar connected to E, the vertical distances from the apical surface of A, B, C, and D to the measuring reference marks were measured with a digital micrometer. The body of the impression coping for implant D was modified by adding 4 mm of additional impression coping, while standard impression copings were used for all other implants. Open tray impressions were made using medium-body polyether material (Impregum Penta) or a combination of putty and light-body vinyl polysiloxane (VPS) material (Elite HD+) (n=15). Then casts were poured with type IV dental stone. The vertical and horizontal distances of the casts were measured with the methods outlined above for the master model. The distortion values that were determined as differences between the measurements of the master model and those of the casts were collected for statistical analysis. Two-way and 1-way repeated measures ANOVA followed by Tukeys HSD test were performed to compare the distortion values (alpha=.05). RESULTS For vertical measurements, 2-way repeated measures ANOVA showed no significant depth (P=.36), material (P=.24), or interaction effects (P=.06). However, it showed significant depth effect for horizontal measurements (P=.01). Within the polyether group, 1-way repeated measures ANOVA showed significant differences in horizontal measurements among the implants with different depths (P=.03). The post hoc Tukeys test showed that the impression of 4-mm-deep implants with normal impression copings (C) was significantly less accurate than impressions of 0-mm-deep implants (A) (P=.02). Within the VPS group, there was no significant difference among the implants with different depths (P=.09). CONCLUSIONS There was no effect of implant depth on the accuracy of the VPS group. However, for the polyether group, the impression of an implant placed 4 mm subgingivally showed a greater horizontal distortion compared to an implant placed more coronally. Adding a 4-mm extension to the retentive part of the impression coping eliminated this difference.

Surface microroughness of optical glasses under deterministic microgrinding

Deterministic microgrinding of precision optical components with rigid, computer-controlled machining centers and high-speed tool spindles is now possible on a commercial scale. Platforms such as the Opticam systems at the Center for Optics Manufacturing produce convex and concave spherical surfaces with radii from 5 mm to ∞, i.e., planar, and work diameters from 10 to 150 mm. Aspherical surfaces are also being manufactured. The resulting specular surfaces have a typical rms microroughness of 20 nm, 1 μm of subsurface damage, and a figure error of less than 1 wave peak to valley. Surface roughness under deterministic microgrinding conditions (fixed infeed rate) with bound abrasive diamond ring tools with various degrees of bond hardness is correlated to a material length scale, identified as a ductility index, involving the hardness and fracture toughness of glasses. This result is in contrast to loose abrasive grinding (fixed nominal pressure), in which surface microroughness is determined by the elastic stiffness and the hardness of the glass. We summarize measurements of fracture toughness and microhardness by microindentation for crown and flint optical glasses, and fused silica. The microindentation fracture toughness in nondensifying optical glasses is in good agreement with bulk fracture toughness measurement methods.

Anisotropic hardness and fracture toughness of highly aligned YBa2Cu3O7−δ

The hardness and fracture toughness of aligned YBa2Cu3O7−δ obtained by melt processing was found to be highly anisotropic. Indentation measurements show that the (001), (100), and (010) planes are the preferred fracture planes in this material and that the critical stress intensity factor for propagating a crack on the (001) basal plane is the lowest, i.e., Kc001<Kc100 or Kc010. Indentation crack length measurements on the (001) basal plane with the impression diagonals oriented parallel to the [100] and the [010] directions, indicate that the fracture toughness of these planes is K100/010air∼0.7 MPa m1/2. The hardness in this orientation was found to be 6.7 GPa. Measurements on a plane perpendicular to the basal plane resulted in a lower hardness of ∼3.8 GPa. This reduction in hardness is influenced by the extensive preferential cleavage of the (001) basal plane boundaries. The extremely low values of the fracture toughness suggest that considerable toughening would have to be achieved in melt‐textured 1...

Fabrication of highly aligned YBa2Cu3O7−δ-Ag melt-textured composites

Abstract Liquid phase processing techniques with slow cooling through the peritectic transformation have been utilized to fabricate bulk aligned 123-Ag composites. Coarse (∼30–40 μm) and fine (∼5–10 μm) particles of silver are distributed between and within the 123 grains. Although the processing temperatures employed are much higher than the melting point of silver, particles of silver are retained behind the advancing solid-liquid interface. The peritectic reaction occurs at the solid-liquid interface and the rate of the reaction is limited by diffusion between the two solid phases, hence the transformation invariably results in some unreacted phases. Ellipsoidal, Y 2 BaCuO itx particles varying in size from 10–25 μm are trapped within the 123 phase. In addition, regions of CuO and BaCuO 2 are present in the sample as separate phases. Silver particles are also dispersed in these insulating regions of the microstructure. The 123-Ag composites have superior mechanical properties compared to melt-textured stoichiometric 123 samples. A detailed study describing the effects of processing on the microstructureof these aligned composites is reported.

Wear and self-sharpening of vitrified bond diamond wheels during sapphire grinding

Abstract Vitrified bond diamond wheels were tested during grinding of single crystal sapphire on a precision CNC grinding platform. Self-sharpening, evidenced by the occurrence of cyclic behavior in the machine deflection (grinding force), was observed for wheels made with one bond/diamond composition. These wheels could remove large volumes of sapphire without re-dressing. The self-sharpening effect was reproducible but showed considerable variability in terms of the detailed cycle shape. Wheel failure eventually occurred due to a loss of the self-sharpening action (overloading) or stall-out of the spindle. Process conditions producing increased wheel wear enhanced the self-sharpening action.

In vitro comparison of the cutting efficiency and temperature production of 10 different rotary cutting instruments. Part I: Turbine

STATEMENT OF PROBLEM Standards to test the cutting efficiency of dental rotary cutting instruments are either nonexistent or inappropriate, and knowledge of the factors that affect their cutting performance is limited. Therefore, rotary cutting instruments for crown preparation are generally marketed with weak or unsupported claims of superior performance. PURPOSE The purpose of this study was to examine the cutting behavior of a wide selection of rotary cutting instruments under carefully controlled and reproducible conditions with an air-turbine handpiece. MATERIAL AND METHODS Ten groups of rotary cutting instruments (n=30) designed for tooth preparation were selected: 9 diamond rotary cutting instruments (7 multi-use, 2 disposable) and 1 carbide bur. One bur per group was imaged with a scanning electron microscope (SEM) at different magnifications. Macor blocks (n=75) were used as a substrate, and 4 cuts were made on each specimen, using a new rotary cutting instrument each time, for a total of 300 cuts. The cuts were performed with an air-turbine handpiece (Midwest Quiet Air). A computer-controlled, custom-made testing apparatus was used to monitor all sensors and control the cutting action. The data were analyzed to compare the correlation of rotary cutting instrument type, grit, amount of pressure, cutting rate, revolutions per minute (rpm), temperature, and type of handpiece, using 1-way ANOVA and Tukeys Studentized Range test (alpha=.05). RESULTS Compared to the baseline temperature, all rotary cutting instruments showed a reduction of temperature in the simulated pulp chamber. The Great White Ultra (carbide bur) showed a significantly higher rate of advancement (0.15 mm/s) and lower applied load (106.46 g) and rpm (304,375.97). CONCLUSIONS Tooth preparation with an adequate water flow does not cause harmful temperature changes in the pulp chamber, regardless of rotary cutting instrument type. The tested carbide bur showed greater cutting efficiency than all diamond rotary cutting instruments.