Stainless Steel Spheres Research Articles

The Quantification of Physiologically Relevant Cross-Shear Wear Phenomena on Orthopaedic Bearing Materials Using the MAX-Shear Wear Testing System

Background: The occurrence of multi-directional sliding motion between total knee replacement bearing surfaces is theorized to be a primary wear and failure mechanism of ultra-high molecular weight poly(ethylene) (UHMWPE). To better quantify the tribologic mechanisms of this cross-shear wear, the MAX-Shear wear-testing system was developed to evaluate candidate biomaterials under controlled conditions of cross-shear wear. Method of approach: A computer controlled traveling x-y stage under a 3 degree-of-freedom statically loaded pin is used to implement the complex multi-directional motion pathways observed during TKR wear simulation. A MHz collection of dynamic x-y friction was available on all six environmentally controlled stations. The functionality of this testing platform was proven in a 100,000 cycle, 11.6 MPa, wear test using 15.0 mm diameter polished stainless steel spheres against flat GUR4150 UHMWPE. A five-pointed star wear pattern was used to incorporate the physiologically relevant cross-shear sliding conditions of stop/start, 50mm∕s entraining velocity and five crossing angles of 72°. Using normalized volumetric reconstruction of the resulting surface damage, a direct quantitative relationship between linear and cross-shear surface damage intensity was obtained. Results: Cross-shear surface damage volume loss was found to be 2.94 (±0.88) times that associated with linear sliding under identical tribologic conditions. SEM analysis of linear wear damage showed consistent fibril orientation along the direction of sliding while cross-shear wear damage showed multi-directional fibril orientations and increased surface roughness. Significant increases in discrete crossing-point friction coefficients were recorded throughout testing. Conclusions: This scientific approach to quantifying the tribologic effects of cross-shear provides fundamental wear mechanism data that are critical in evaluating potential biomaterials for use as in vivo bearings. Relevant multi-axis, cross-shear wear testing is necessary to provide quantifiable measures of complex biomaterials wear phenomena.

TH-C-T-617-04: Measurements and Monte Carlo Simulations of Dose Perturbations Due to Metallic Implants in Proton Radiotherapy

Purpose: To quantify the doseperturbation behind implanted metallic appliances and fiducials in protonradiotherapy.Method and Materials:Doseperturbations from stainless steel spheres of 6.4–15.9 mm diameter were investigated in proton therapy beams. Passive lateral spreading was combined with collimation to produce 17.8‐cm diameter fields. Penetration ranges were varied between 40 and 160 mm. Dose profiles were measured in planes perpendicular to the proton beam axis, at distances of 0–150 mm behind the implants, using radiographic film exposed to 0.4–0.5 mGy. The experiments were modeled in detail with Monte Carlo simulations that included hadron and electron transport physics. 120×106proton histories were simulated, corresponding to 8% or less statistical uncertainty. Results: Edge effects are most prominent at the highest proton beam energies and produce concentric perturbations of +/−10–40% for the implants considered here. Thick implants (w.r.t. the beam range) may stop the protons, leaving a zero dose shadow behind it. For thin and intermediate implants, the range loss in the implant produces a cone of dose enhancement of up to 20% directly behind the implant due to in increase in the stopping power values. In an air cavity, shadows reduce the dose by up to 60% at 15 cm distance downstream from the implant. The Monte Carlo simulations agree with the measurements to better than 8% in all cases and typically to within 4%. Additional simulations will be presented for implants of gold and tantalum, ranging in size from 0.8 to 3 mm. Conclusion: We have identified several representative cases in which implants produce significant doseperturbations. In such cases, a treatment plan should include suitable simulations or measurements to ensure that the implants do not result in cold spots in the tumor or hot spots in normal tissue.

Mechanical evaluation of a respiratory device

This article aims to characterize the mechanical behaviour of the Flutter VRP 1, a respiratory physiotherapy device designed to aid sputum clearance of the airways of patients. The device resembles a smoking pipe with a conical cavity containing a stainless steel sphere which floats up and down while the patient comes with a forced expiration through it. The sphere's oscillatory movement is function of the air flow rate and angular orientation of the device. When the sphere's oscillatory frequency matches the natural frequency of the patient's chestwall + abdomen system, it will produce resonance which, in turn, will enhance sputum clearance. A dynamical model of the Flutter was formulated and an experimental setup was assembled in order to study the oscillatory frequency of the sphere under different conditions of air flow rate, fluid pressure, angular orientation and sphere's material and weight. Interesting results presented by this article point to eventual mechanical optimization of the device and show information that could be beneficial to the professional of the respiratory physiotherapy.

Enhanced temperature uniformity by tetrahedral laser heating

Temperature profile on a spherical sample that is heated by laser beams in various geometries while processed in vacuum is analyzed. Sample heating by one or four laser beams was considered. An analytical expression was derived for directional sample heating cases. It suggests an enhanced temperature uniformity over the samples when heated with four diffuse laser beams arranged in a tetrahedral geometry. This was experimentally verified by heating a spherical stainless steel sample by laser beams. Both the calculated and experimentally determined temperature variations over the sample suggest that use of diffuse four beams arranged in tetrahedral geometry would be effective in reducing temperature variation to within 1 K. The enhancement in the temperature uniformity for four diffuse beams arranged in a tetrahedral geometry by a factor of 50 over a single focused beam is promising to accurately measure of thermophysical properties. This drastic improvement in temperature uniformity might even enable atomic diffusion measurements in the undercooled liquid states of the bulk glass forming alloys since Marangoni and gravity driven convection will be substantially reduced.

Microhardness and high-velocity impact resistance of HfB2/SiC and ZrB2/SiC composites

The results of Vickers microhardness and high-velocity impact tests on monolithic ZrB2/SiC and HfB2/SiC ultra-high temperature ceramic (UHTC) composites are presented. The UHTC materials exhibit fracture behavior typical of ceramics under indentation and impact loading. The materials are relatively hard with microhardness values of about 15 to 20 GPa. Cracks were observed to extend from the corners of indentations. Impacts of stainless steel and tungsten carbide spheres, with diameters in the 500 to 800 micron range and velocities of 200 to 300 m/s, produced minimal plastic deformation but significant radial and ring cracking at the impact sites. Impacts of micron-scale iron particles traveling at 1 to 3 km/s produced essentially no surface damage.

Effect of Particle Coating on Fluidized-Bed Heat Transfer

Heat-transfer coefficients from a fluidized suspension to immersed stainless steel spheres and an aluminum cylinder were studied in a laboratory-scale bubbling fluidized bed using coated and uncoated silica sand particles from a 90-MWth circulating fluidized bed (CFB), as well as a 30-MWth bubbling fluidized bed (BFB). The experiments were carried out for gas-velocity-to-minimum-fluidization-velocity ratios (u/umf) from 1 to 3.5 and mean particle diameters of 350 and 635 μm. The heat-transfer coefficients for the coated particles were lower than those for the uncoated particles in all cases, with the difference between uncoated and coated sand particles being more significant for the CFB material than for the BFB sand.

Prediction and measurement of residual stresses in quenched stainless-steel spheres

A finite element (FE) technique has been used to predict the residual and thermal stresses which occur during water quenching of solid stainless-steel (SS) spherical balls. The variations of residual stresses at different positions and cross-sections, e.g. the radial, axial and tangential directions, have been examined. Also, the influence of heat transfer coefficient, the initial temperature and the hardening assumption on residual stress results has been investigated. The results show that high compressive residual stresses occur along the cooling surface. Moving away from the surface, these residual stresses begin to decrease and reverse their sign, and near the centre are tensile. Preliminary quenching experiments have been carried out using spheres of type 316L stainless steel. The temperature during quenching was recorded and compared with finite element simulations. The surface residual stresses were determined using the incremental centre-hole measurement technique. Neutron diffraction (ND) was used to determine the residual stresses in the centre of the sphere. The paper compares these measurements with the finite element results as well as comparing the measured cooling temperature history with simulation. Overall there is good agreement between the predicted and measured stresses.

Avaliação experimental do coeficiente global de transferência de calor em leito fixo percolado com água

Many experiments were performed in a fixed bed heat exchanger, packed with stainless steel spheres, percolated by water and heated through the wall. Wall and center temperatures were measured for several experimental conditions: 3 mm d p 2 = 0.99). Additionally, it was observed that the temperatures near the wall are more influenced by the water flow rate than those at the center of the fixed bed

Microparticle detachment from surfaces exposed to turbulent air flow: Effects of flow and particle deposition characteristics

This work presents the results of experiments conducted to provide quantitative information on particle detachment from surfaces. The effects of certain, controllable factors on the detachment of 70 μm -diameter stainless-steel spheres from a glass surface exposed to accelerated air flow in a wind tunnel were studied. Changes in the free-stream velocity required to detach 50% of the particles, the threshold velocity for detachment, were measured for variations in the controlled factors. These factors were air relative humidity, residence time between particle deposition onto the substrate and flow application, mean flow acceleration, deposition density, final free-stream velocity, and final flow Reynolds number. Results reveal that deposition density was the most effective factor that enhanced detachment at all relative humidities. Residence time was found to be the most effective factor that suppressed detachment at high relative humidity. The threshold velocity increased with increasing relative humidity and was lower for turbulent flow versus laminar flow. Within the uncertainty limits, the mean flow acceleration in the transient period was found not to affect the threshold velocity in the range from 0.014 to 0.34 m/s 2 . The final free-stream velocity also did not affect the threshold velocity, provided it was greater than the threshold. A set of experimental conditions that lead to a relatively small uncertainty is presented.

Creating Highly Triaxial Residual Stresses and Relaxation of the Stress Field due to Thermal Ageing

This paper presents results from an experimental and numerical study about the creation of highly triaxial residual stresses by rapid spray water quenching of solid stainless steel spheres and cylinders and the subsequent change in residual stresses due to creep. Finite element (FE) simulations predicted highly compressive residual stresses around the surface of the specimens and tensile near the centre. Neutron diffraction (ND) was used to measure the internal residual stress distribution in quenched specimens. These measurements were in good agreement with FE predictions. Simulations of creep relaxation and damage accumulation were also carried out in stainless steel specimens which had previously been water quenched and subsequently allowed to thermally age at 550°C for 3200 h.

Synthesis of a Novel Magnetic Resin and the Study of Equilibrium in Cation Exchange with Amino Acids

Magnetic cation-exchange resins usually consist of small polymeric particles with a magnetic material dispersed within their structure. Because the mass-transfer kinetics through these solid particles depends on their size, very small diameter particles are desirable. Nevertheless, faster kinetics can also be obtained by using particles consisting of spherical magnetic cores covered with a thin layer of polymeric adsorbent material. In the present work, we describe the synthesis of a novel type of ion-exchange resin, in which the magnetic core was a single spherical stainless steel particle and the covering layer was poly(styrene-co-divinylbenzene). To check their ion-exchange characteristics, the equilibrium adsorption of the amino acids methionine, phenylalanine, and tryptophan on magnetic and nonmagnetic resins was investigated. The experimental results are explained in terms of a model that considers that the surface of the ion exchangers is heterogeneous, with two different types of adsorption sites ...

Effect of energy density on properties and marginal integrity of posterior resin composite restorations

Objectives. The purpose of this study was to determine the minimal extent of cure required by the base of a Class 2 resin composite restoration ( Z250, 3M ESPE, St Paul, MN, USA) that allows it to support the rest of the restoration and maintain its marginal seal under simulated clinical conditions. Methods. Resin composite (Z250, 3M ESPE, St Paul, MN, USA) was placed incrementally or in bulk into Class 2 preparations in extracted human molar teeth and exposed to various light-curing energy densities. The restorations were subjected to 1000 thermal cycles (5–55 °C) and 500,000 fatigue cycles from 18 to 85 N using a stainless-steel sphere. Marginal integrity was evaluated using visual rating (ridit analysis) and microleakage. Degree of conversion (DC) and Knoop hardness (KHN) were determined at the occlusal and gingival surfaces using a reusable tooth template with identical preparation dimensions. Percentage of maximum DC and KHN were determined. Mechanical properties were tested in resin composite bars having similar KHN values as the resin composite at the gingival margins. Results. Energy density had a significant effect on gingival marginal defects as determined by ridit analysis but not on microleakage. Water had a significant dissolving effect on gingival margin integrity at very low degrees of conversion and energy densities (4000 mJ/cm 2). There was no overall significant effect of thermal–mechanical stressing on gingival marginal defects or microleakage. Significance. Based on ridit analysis, a recommended lower limit of gingival margin acceptability in the bulk-filled Z250 resin composite restoration was created by 80% of maximum conversion, 73% of maximum hardness and approximately 70% of maximum flexural strength and modulus in the gingival marginal area.

Deformation behavior of stainless steel particles under compressive load

Spherical stainless steel particles with diameters of 0.040–0.185 mm plastically deform immediately on compressive loading. The load–displacement relationship was observed to be approximately linear in the range of displacement within 5% of the particle size.

Oblique incidence hypervelocity impacts on rock

The behaviour of granite rock under normal incidence hypervelocity impact in the laboratory has been studied using impacts of 2-mm diameter stainless-steel spheres at between 1 and 6 km s(-1). It was found that, at normal incidence, there is a strong dependence of crater size with impact speed (v). Crater mass was found to depend on v((2.3+/-0.4)), i.e. compatible with scaling with impact energy. However, crater depth and diameter have different and dissimilar dependences on impact speed, such that the crater shape (depth/diameter) is not a constant, but decreases as impact speed increases, being 0.26 at 1 km s(-1) and falling linearly to 0.16 at 6 km s(-1). In addition, a second data set with the same projectile and target combination was taken at a mean impact speed of 5.4 +/- 0.2 km s(-1), with the angle of incidence of impact ranging from 0degrees (normal incidence) to 85degrees (glancing incidence). The oblique incidence data show that crater depth and excavated mass start to decrease immediately when non-normal incidence occurs. Crater length and width initially decrease at a slower rate, with little decrease apparent until the angle of impact exceeds 50degrees from the normal. At the highest angles of incidence (85degrees, glancing incidence), there is a sudden change in crater shape, with crater length no longer decreasing as impact angle increases. It was found that for oblique impacts, excavated crater mass scales linearly with cos theta and not with the square of costheta as indicated in earlier work. This is similar to the scaling observed in other brittle and ductile materials. Finally, when used to predict populations of non-circular craters on large Solar system bodies, the results yield estimates (3 per cent) close to the observed rate (5 per cent) on Venus, Mars and the Moon.

Dynamic self-assembly of rings of charged metallic spheres.

This Letter describes dynamic self-assembly in a system of stainless steel spheres ( approximately 1 mm in diameter) rolling on a flat dielectric surface under the influence of an external magnetic field that rotates parallel to the plane of the surface. As the spheres move, they charge triboelectrically. Self-assembly is mediated by two types of electrostatic interactions among these charges: (i) attraction between negatively charged regions of the surface and positively charged spheres and (ii) repulsion between the like-charged spheres. The spheres organize into highly ordered rings as a result of these electrostatic interactions.

Laboratory measurements of sound scattering from a buried sphere above and below the critical angle (L)

Laboratory measurements of low frequency (1–10 kHz) evanescent wave field scattering from a sphere buried in water-saturated sand was examined. A 60 cm stainless steel sphere was buried just below a sand–water interface and the acoustic backscattering cross section was measured for above and below critical angle geometries. The below critical angle insonification results clearly show significant levels of backscatter from the buried sphere due to evanescent wave insonification at the lower end of the spectrum (1–3.5 kHz). These measurements compare favorably with first principle estimates of the backscattered target strength and with a T-matrix-based numerical model.

Calorimetric measurements of optical signals in electrostatic discharge studies

A method based on calorimetry and an instrument are described for the absolute measurement of the energy contained in optical radiation, especially in the optical signatures of electrostatic discharge. The optical emission of a spark gap, comprised of two stainless-steel spheres, was collected by an optical condenser system and focused on the calorimeter sensor. The system was calibrated using a set of light-emitting diodes and tested using either single-pulse discharge or a continuously operating optical source. The calorimeter system detectivity, in terms of output voltage related to the input energy, was determined to be 4.3 /spl times/ 10/sup 7/ V/spl middot/J/sup -1/ and its detection limit was 2.3 /spl times/ 10/sup -13/ J. The system has application for nonintrusive characterization of optical emissions associated with discharge events.

Aerodynamic levitation of stainless steel spheres in Argon plasma jet Part II: Heat transfer

Aerodynamic levitation of stainless steel spheres in Argon plasma jet Part II: Heat transfer

Target damage from highly oblique hypervelocity impacts of steel spheres against thin laminated targets

Target hole sizes and geometries were measured for a series of highly oblique hypervelocity impacts of steel spheres against thin laminated targets. The impact velocity was nominally 4.6 km/s for most of the experiments with a few tests conducted at 7.3 km/s. Impact obliquity ranged from 60° to 80° from the normal to the target plane. Projectiles were stainless steel spheres with masses of 222 g, 25 g, and 1 g. Targets were laminated MX-2600 silica phenolic bonded to a 2024-T3 substrate. Target thickness, t, was varied to give thickness to projectile diameter, d, ratios of t/d = 0.6 and 0.3 for each projectile. CTH Eulerian wavecode calculations of selected tests were performed to improve our understanding of the experimental results.

Blast cleaning of gas turbine components: deposit removal and substrate deformation

The effectiveness of glass and stainless steel spheres in the blast cleaning of stationary gas turbine components was evaluated as a function of particle size, speed, impact angle, and standoff distance. The overall objective was to maximize the rate of deposit removal while minimizing substrate deformation. It was found that deposit erosion and substrate deformation were strong functions of particle stream power, particle kinetic energy, and impact angle. The erosion of deposits on compressor and turbine stage components exhibited brittle characteristics, while substrate deformation was ductile. For this reason, an impact angle of 90° to the surface was optimal. Substrate deformation increased with average particle kinetic energy, independent of stream power. Deposit removal with glass media increased with stream power. Blasting with the stainless steel media, which was softer than the substrate, prevented deformation while still removing deposits.