Image sharpness measurement in scanning electron microscopy—part II

A method for qualitative and quantitative analysis of scanning electron microscope (SEM) images forthe determination of sharpness is presented in this paper. Described is a procedure for qualitative analysis based on a software program called SEM Monitor that can be applied to research or industrial SEMs for day-to-day performance monitoring. The idea is based on the fact that, as the electron beam scans the sample, the low-frequency changes in the video signal show information about the larger features and the high-frequency changes give data on finer details. The image contains information about the primary electron beam and about all the parts contributing to the signal formation in the SEM. If everything else is kept unchanged, with a suitable sample, the geometric parameters of the primary electron beam can be mathematically determined. An image of a sample, which has fine details at a given magnification, is sharper if there are more high frequency changes in it. In the SEM, a better focused electron beam yields a sharper image, and this sharpness can be measured. The method described is based on calculations in the frequency domain and can also be used to check and optimize two basic parameters of the primary electron beam, the focus, and the astigmatism.     

Is the wear factor in total joint replacements dependent on the nominal contact stress in ultra-high molecular weight polyethylene contacts?

The exact dependence of wear factor on contact stress, load and apparent contact area is much disputed in the literature. This study attempts to solve this dispute. Pin-on-plate studies of ultra high molecular weight polyethylene against stainless steel were conducted under different combinations of load (33-250 N), nominal stress (0.56-12.73 MPa) and face diameter, as well as two tests where both stress and load were kept constant, while the diameter was changed. For these tests the centre of the pin face was bored out to create four different average pin diameters with similar face areas. Diameter and load were found to have no significant effect on the wear factor, while the wear factor decreased with increasing contact stress according to the relation K = 2 x 10(-6) sigma(-0.84).     

Design,development, and calibration of a force-moment measurement system for wheel–rail contact mechanics in roller rigs

A force measurement system, referred to as “dynamometer”, for accurately acquiring the contact forces and moment in a single-wheel roller rig using piezo-electric load cells is designed and developed. Accurate determination of the wheel–rail contact forces and moments is an essential requirement for studying the wheel–rail contact mechanics. The dynamometer is placed in the load-path between the wheel–rail interface and the ground, enabling it to measure the forces and moments at the interface. A series of tests are performed to determine the quasi-static and dynamic characteristics of the dynamometer. Additionally, finite element analysis and multi-body dynamic modeling are used to establish flexural modes and dynamic interface between the components. The simulation and test results indicate that the dynamometer is able to accurately and reliably measure the contact forces and moments at the wheel–rail interface.     

Chemical changes in asbestos-based friction materials during performance — a review

The importance of chemical changes to the performance of asbestos based friction materials is discussed. The available information is reviewed in three sections: Composite Materials, Polymers, and Inorganic Materials. The relevance of the information is discussed and conclusions drawn regarding the scope for research into this area.     

On the thermal aspect of fretting wear—temperature measurement in the subsurface layer

In fretting wear, the kinetics of the oxide film formation as well as the microstructure and the mechanical properties of the subsurface layer depend significantly on the temperature field produced in the fretted zone. Information reported in the open literature indicates contradicting values for the temperature produced at the interface. In the present study, an experimental method for direct measurement of the temperature profile in the subsurface layer has, therefore, been developed and verified. This method overcomes the limitations and the uncertainties inherent in methods of measurement used before. An error analysis indicated that the temperature gradient can be measured within ± 2.5%. The extent of the temperature measurement zone has been estimated by the theory of thermal constriction resistance and found to be in good agreement with some available experimental data.     

Can extra-articular strains be used to measure facet contact forces in the lumbar spine? An in-vitro biomechanical study

Experimental measurement of the load-bearing patterns of the facet joints in the lumbar spine remains a challenge, thereby limiting the assessment of facet joint function under various surgical conditions and the validation of computational models. The extra-articular strain (EAS) technique, a non-invasive measurement of the contact load, has been used for unilateral facet joints but does not incorporate strain coupling, i.e. ipsilateral EASs due to forces on the contralateral facet joint. The objectives of the present study were to establish a bilateral model for facet contact force measurement using the EAS technique and to determine its effectiveness in measuring these facet joint contact forces during three-dimensional flexibility tests in the lumbar spine. Specific goals were to assess the accuracy and repeatability of the technique and to assess the effect of soft-tissue artefacts. In the accuracy and repeatability tests, ten uniaxial strain gauges were bonded to the external surface of the inferior facets of L3 of ten fresh lumbar spine specimens. Two pressure-sensitive sensors (Tekscan) were inserted into the joints after the capsules were cut. Facet contact forces were measured with the EAS and Tekscan techniques for each specimen in flexion, extension, axial rotation, and lateral bending under a +/- 7.5 N m pure moment. Four of the ten specimens were tested five times in axial rotation and extension for repeatability. These same specimens were disarticulated and known forces were applied across the facet joint using a manual probe (direct accuracy) and a materials-testing system (disarticulated accuracy). In soft-tissue artefact tests, a separate set of six lumbar spine specimens was used to document the virtual facet joint contact forces during a flexibility test following removal of the superior facet processes. Linear strain coupling was observed in all specimens. The average peak facet joint contact forces during flexibility testing was greatest in axial rotation (71 +/- 25 N), followed by extension (27 +/- 35 N) and lateral bending (25 +/- 28 N), and they were most repeatable in axial rotation (coefficient of variation, 5 per cent). The EAS accuracy was about 20 per cent in the direct accuracy assessment and about 30 per cent in the disarticulated accuracy test. The latter was very similar to the Tekscan accuracy in the same test. Virtual facet loads (r.m.s.) were small in axial rotation (12 N) and lateral bending (20 N), but relatively large in flexion (34 N) and extension (35 N). The results suggested that the bilateral EAS model could be used to determine the facet joint contact forces in axial rotation but may result in considerable error in flexion, extension, and lateral bending.     

An experimental study on real–time analysis of two–phase peristaltic slug flows in dialysis machines

Two–phase flows appear in many industrial and biomedical applications. One of the most vital biomedical applications of two–phase flows is in hemodialysis machines due to air embolism and heparin injection. Since these flows have a very complex and intermittent nature, studying their dynamics is a very challenging and fundamental problem. The purpose of this article is to present an experimental study on the dynamics of two–phase peristaltic slug flows. The measurement strategy is based on the image processing technology. The characteristic parameters of the two–phase pulsatile slug flows, including the slug length, as well as the translational velocity and frequency of the slug motion, are measured, and the effect of the liquid flow rate and liquid superficial velocity is investigated. The results show that the average and maximum slug velocities, and also the dominant amplitude of the slug velocity increase with the flow rate and liquid superficial velocity, while it is not possible to clearly predict a correlation between the liquid superficial velocity and the slug length. The measurement strategy presented in this article can be used in the control and alarm systems of smart dialysis machines.     

Structure—phase transformations in contacting surface layers of coated steel during slipping friction with lubricant

Two approaches are used in simulating the thermal impact during the slipping friction of steel with lubricant, when high pressure is created and travels as an expansion—compression wave to the surface layers. This results in polymorphic transformation and anomalously fast diffusional mass transfer below the kinetic-transformation temperature. The pressure and diffusion coefficients are calculated.     

An integrated solution—KAGFM for mass customization in customer-oriented product design under cloud manufacturing environment

In hot strip rolling process, rolling schedule is a key technology which directly influences strip product quality. Rolling schedule optimization is actually a problem of load distribution. To make a better rule of the load distribution of aluminum hot tandem rolling, multi-objective optimization algorithm is used to optimize rolling schedule. Preventing slipping, power margin and minimum energy consumption are selected as the optimization objectives. To make a precision calculation of rolling schedule, an adaptive neural network which is based on classification system is applied to improve the prediction ability for the rolling force, and its on-line training system reduces the prediction errors caused by different rolling conditions. The improved differential evolution algorithm is used to search the Pareto front, and it obtains a good approximation of the Pareto-front and decreases computation time. Load distribution strategies focused on different objectives are generated from the Pareto front to meet the requirements of industrial spots. The experiment result shows the algorithm covers the front quickly and distributes well. Comparing with the original schedule, the proposed method reduces the probability of slippage and energy consumption.     

Nanotribology Application in the Coining Industry (I)—Turn off Stamping Oil Sprayer during Coining

The most common tribological cases involve two solid surfaces repeatedly contacting each other. During coining, however, a pair of dies strikes each blank that has been stamped only once. The requirements of the surface physical and chemical properties for coining are different compared to the common tribological conditions. For example, a low-viscosity stamping oil is used during coining in the United States Mint, as well as other industries. Under coining tonnage this small amount of liquid on die surfaces may promote microcrack propagation. In this case, lubrication does not prolong die life but shortens it.

In this work, the lubrication mechanism during coining was studied. A lubricant layer was applied on blank surfaces before coining. Based on the special stamping condition, blank surfaces must meet several tribological requirements. According to these requirements, a new technology was employed and the use of a new lubricant was implemented. As a result, fatigue die life was increased almost three times on high-volume production lines and coin surface quality was improved.     

Jet properties and mixing chamber flow in a high-pressure abrasive slurry jet: part I—measurement of jet and chamber conditions

Techniques to enhance the performance of a high-pressure abrasive slurry jet micro-machining process (HASJM) were investigated by altering the conditions within the jet. The slurry flow rate was controlled using six inlet tubes (cross-sectional areas of 0.2, 0.46, 1.27, 1.77, 3.08, and 4.51 mm²), and was found to have a large effect on the conditions within the mixing chamber. The tubes permitted the use of high-concentration slurry solutions, which resulted in increased machining rates and the ability to machine glass targets without cracking by using a minimum particle concentration of 17 wt%. Slurry tubes producing large slurry flow rates caused the mixing chamber to flood, resulting in a much lower jet velocity. The size of the smallest slurry tube size that caused the mixing chamber to flood was dependent on the pump operating pressure, and varying from 1.27 mm² at 134 MPa, to 1.5 mm² at 233 MPa. Mixing chamber flooding significantly reduced the erosion rate of the jet and increased the machining time, as discussed in the second part of this two-part paper. Mixing chamber pressures were found to be low enough to cause boiling, which increased the jet diameter and the width of features that could be machined without a mask.     

Formation of silicon nanocrystals in Si—SiO<Subscript>2</Subscript>—<Emphasis Type="Italic">α</Emphasis>-Si—SiO<Subscript>2</Subscript> heterostructures during high-temperature annealing: Experiment and simulation

Experiments and simulations are performed to study the formation of silicon nanocrystals (Si-NCs) in multilayer structures with alternating ultrathin layers of SiO₂ and amorphous hydrogenized silicon (α-Si:H) during high-temperature annealing. The effect of annealing on the transformation of the structure of the α-Si:H layers is studied by methods of high-resolution transmission electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. The conditions and kinetics of Si-NC formation are analyzed by the Monte Carlo technique. The type of the resultant crystalline silicon clusters is found to depend on the thickness and porosity of the original amorphous silicon layer located between SiO₂ layers. It is shown that an increase in the thickness of the α-Si layer in the case of low porosity leads to the formation of a percolation silicon cluster instead of individual Si nanocrystals.