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A study has been made of the effect of an externally imposed, low-frequency modulation ([less than or equal to] 100 Hz) on the action of a fluid in machining. It is shown that in conventional machining, fluid action in terms of lubrication is essentially confined to the edges of the chip-tool contact along the tool rake face, with little or no change in the friction condition over much of this face. However, the effectiveness of the lubricating action is significantly enhanced when a controlled low-frequency modulation of sufficient amplitude, such as to break the chip-tool contact, is imposed in the direction of cutting. Measurements show that the friction coefficient between tool and chip is reduced by a factor of up to three in the presence of such a modulation. The extent of the secondary deformation zone in the chip material close to the rake face is also significantly reduced. Direct observations of the tool rake face show that when the modulation is applied, the fluid penetrates into much of the intimate contact region between chip and tool. Keywords: Machining, Modulation, Friction, Lubrication

Taylor's theory of crystal plasticity is reformulated for dislocations in a couple stress medium. The divergence between Taylor's approach and an approach that includes the effects of couple stresses on dislocation interactions is demonstrated. It is shown that dislocations separated by a distance that is comparable to a characteristic material length scale, have mutual interaction somewhat weaker than that predicted by classical elasticity.

An experimental technique is described for measuring the temperature field in a workpiece during surface grinding. The technique involves measurement of the radiation emitted by a side of the workpiece immediately adjoining the wheel-workpiece contact region using a Charge-Coupled Device (CCD) based Infra-Red imaging system. By using an appropriate calibration procedure, measured radiation values are converted to temperatures. Novel aspects of the experimental technique are full-field measurement of temperature at high spatial and temporal resolution, high sensitivity and non-intrusive measurement. The repeatability of temperature measurement is found to be very good. The experiments have provided an accurate estimate of the surface and sub-surface temperatures in the workpiece. Furthermore, by grinding along a taper with a continuously increasing depth of cut, the effect of material removal rate on temperature field has been characterized. Measurements of the temperature field in taper grinding have been found to correlate well with those made in conventional constant depth grinding thereby, establishing taper grinding as a viable, accelerated test for studying grinding temperatures. Full-field measurements of workpiece temperature should facilitate study of thermal damage and multi-scale validation of thermal models in grinding.

Polishing is a finishing process in which a smooth work surface is produced by rubbing it against a polishing block with an abrasive slurry interspersed between them. A model has been developed to estimate the temperature rise of the work surface in polishing. In this model, the forces acting on an abrasive particle are derived from a mechanistic analysis of abrasive-workpiece contacts. The heat generated at a contact is taken as the product of the friction force and the relative sliding velocity between the abrasive and the work surface. For calculating the heat flux transferred into the workpiece, each of the abrasive-workpiece contacts is modeled as a hardness indentation of the work material by a conical indenter. The moving heat source analyses of Jaeger and Blok are then applied to estimate the fraction of the heat flux flowing into the workpiece, and the maximum and average temperature rise of the work surface. Calculations of the work surface temperature rise are made for the polishing of steel, soda-lime glass, and ceramics. These show that the work surface temperature rise in polishing is quite small, typically much less than 200 [degrees] C, and substantially less than in grinding. The low values calculated for the work surface temperature rise are shown to be consistent with many observations pertaining to the mechanical state of polished surfaces. The effect of polishing process variables on the work surface temperature rise is analyzed.

Commercial electrical conductor wires are currently produced from aluminum alloys by multi-step deformation processing involving rolling and drawing. These processes typically require 10 to 20 steps of deformation, since the plastic strain or reduction that can be imposed in a single step is limited by material workability and process mechanics. Here, we demonstrate a fundamentally different, single-step approach to produce flat wire aluminum products using machining-based deformation that also ensures adequate material workability in the formed product. Two process routes are proposed: (1) chip formation by free-machining (FM), with a post-machining, light drawing reduction (<20%) to achieve desired finish and (2) constrained chip formation by large strain extrusion machining (LSEM). Using commercially pure aluminum conductor alloys (Al 1100 and EC1350) as representative material systems, we demonstrate key features of the machining-based processing, including (a) single-step processing to achieve flat wire geometries, (b) surface finish (Ra = 0.2 to 1.0 µm) comparable to that of commercial wire products made by drawing/rolling, (c) deformation control independent of wire size, and (d) hardness increases of 50-150% over that of annealed wires, while retaining high electrical conductivity (>56% IACS). The wire microstructure, which can also be varied via the large-strain deformation parameters, is correlated with mechanical and electrical properties. Implications for commercial manufacture of flat wire products are discussed. [ABSTRACT FROM AUTHOR]

Superfinishing is an abrasive finishing process in which a smooth work surface is produced by simultaneously loading a bonded abrasive stone against a rotating workpiece surface and oscillating (reciprocating) the stone. The surface topography of a 600 grit aluminum oxide stone used for superfinishing is quantitatively described using scanning phase-shift interferometry. A bounded three-parameter lognormal distribution is found to provide a more accurate representation of cutting edge height distribution than a bounded normal distribution, especially in fining the upper tail end of data. Moreover, the stone surface characteristics are nearly constant throughout stone life suggesting that superfinishing is a self-dressing process. This stone surface geometry is used to develop a contact mechanics model of the superfinishing process. The model estimates the number of cutting edges, involved in material removal, the load distribution on these edges, and the resulting surface roughness of the superfinished surface. The effect of contact pressure on these estimated values has been studied. Only a very small percentage (less than O. 16 percent) of the cutting edges, which are comprised of the large cutting edges occurring in the tail end of distribution, are actively engaged in material removal. Further, the arithmetic average surface roughness, [R.sub.a], is found to be related to the average depth of penetration while the peak-to-valley surface roughness, [R.sub.t] or [R.sub.tm], is related to the maximum depth of penetration. The prediction of surface roughness made with this model is found to agree reasonbly well with experimental results for superfinishing of hardened steel surfaces. [S0742-4787(00)00302-7]

The deformation field, material flow, and mechanics of chip separation in cutting of metals with superimposed low-frequency modulation (

A novel, hand-held Reference Point Indentation (RPI) instrument, measures how well the bone of living patients and large animals resists indentation. The results presented here are reported in terms of Bone Material Strength, which is a normalized measure of how well the bone resists indentation, and is inversely related to the indentation distance into the bone. We present examples of the instrument's use in: (1) laboratory experiments on bone, including experiments through a layer of soft tissue, (2) three human clinical trials, two ongoing in Barcelona and at the Mayo Clinic, and one completed in Portland, OR, and (3) two ongoing horse clinical trials, one at Purdue University and another at Alamo Pintado Stables in California. The instrument is capable of measuring consistent values when testing through soft tissue such as skin and periosteum, and does so handheld, an improvement over previous Reference Point Indentation instruments. Measurements conducted on horses showed reproducible results when testing the horse through tissue or on bare bone. In the human clinical trials, reasonable and consistent values were obtained, suggesting the Osteoprobe ® is capable of measuring Bone Material Strength in vivo, but larger studies are needed to determine the efficacy of the instrument's use in medical diagnosis.