Contact area

Depth sensing indentation is a powerful experimental technique for determining mechanical properties of materials. In this work a computational routine was developed based on Oliver-Pharr method for measuring a more precise values of elastic modulus using a Fischerscope H100-depth sensing indentation apparatus, with a Vickers indenter. This computational routine aims also to measure Vickers hardness, as the equipment does not have software for this purpose. From indentation data it was possible to determine initial unloading stiffness, contact depth, projected contact area, reduced modulus, elastic modulus and Vickers hardness of materials. The validity of the routine was verified analyzing two coatings and nine bulk specimens with different elastic-plastic behaviors. It was verified that the elastic moduli determined through the software of the equipment resulted in great discrepancies when low loads were applied. A good estimate of the elastic moduli of the tested materials is given by the developed routine. For several testing loads, the diagonals determined by means of analytical procedure were compared with the same diagonals measured by image analysis. A good estimate of the Vickers hardness of the above-mentioned materials is given by the developed routine using different testing loads.

The nanoporous nature of the inkjet printed silver nanoparticles entail low hardness and surface effective contact area for being compatible with pads that are suitable for wire-bonding in electronic packaging. Electroless nickel plating is a selective metal deposition technique which can brings the required thickness and hardness for further pads processing. Here, a 1.7 µm thick nickel layer is deposited on top of 600 nm thick printed and sintered silver nanoparticles using Kapton polyimide as substrate. Prior to plating, a special attention was put on tuning microstructures of printed silver pads by sintering nanoparticles at various temperature ramps (0.1, 10 and 50°C/s) up to 200°C. Results show that fast sintering exhibits the lowest electrical resistivity which is suitable in printed interconnects. However, wire-bonding on nickel pads is best achieved when low sintering ramp is used. This slow sintering presents the highest adhesion strength at the nickel/silver interface since the pores dimensions were restricted to the nanoscale. The validation of the optimized bonding process came from the low electrical contact resistance between plated nickel and the bonded gold wire, and from the wire-pull test which is in accordance with the MIL-STD 883 standard. The actual results show that a compromise has to be found when emphasis is on patterning low resistive interconnects or stiff pads for wire-bonding applications. This compromise is tailored by the sintering engineering.

Human urokinase-type plasminogen activator receptor (uPAR/CD87) is expressed at the invasive interface of the tumor-stromal microenvironment in many human cancers and interacts with a wide array of extracellular molecules. An anti-uPAR antibody (ATN615) was prepared using hybridoma technology. This antibody binds to uPAR in vitro with high affinity (K d ∼ 1 nM) and does not interfere with uPA binding to uPAR. Here we report the crystal structure of the Fab fragment of ATN615 at 1.77 Å and the analysis of ATN615-suPAR-ATF structure that was previously determined, emphasizing the ATN615-suPAR interaction. The complementarity determining regions (CDRs) of ATN615 consist of a high percentage of aromatic residues, and form a relatively flat and undulating surface. The ATN615 Fab fragment recognizes domain 3 of suPAR. The antibody-antigen recognition involves 11 suPAR residues and 12 Fab residues from five CDRs. Structural data suggest that Pro188, Asn190, Gly191, and Arg192 residues of uPAR are the key residues for the antibody recognition, while Pro189 and Arg192 render specificity of ATN615 for human uPAR. Interestingly, this antibodyantigen interface has a small contact area, mainly polar interaction with little hydrophobic character, yet has high binding strength. Furthermore, several solvent molecules (assigned as polyethylene glycols) were clearly visible in the binding interface between antibody and antigen, suggesting that solvent molecules may be important for the maximal binding between suPAR and ATN615 Fab. ATN615 undergoes small but noticeable changes in its CDR region upon antigen binding.

The distribution of various evolutionary lineages of Apis mellifera subspecies in Africa is still controversial. We sampled honeybees from eight coastal locations and three Saharan oases in Libya and analyzed mtDNA variability with restriction fragment length polymorphisms and the sequence of the tRNAleu-cox2 intergenic region. Haplotypes belonging to the oriental O evolutionary lineage, including four which are newly described, were detected in all investigated locations. Haplotypes belonging to the European M lineage were rarely detected, probably reflecting the effect of sporadic importations. Honeybees belonging to the A lineage were detected in Al Aziziyah and Zlitan close to the Tunisian border. The distribution of the O lineage extends westward up to the border between Libya and Tunisia, a contact area between the O and A lineages. Various Libyan honeybee populations in Saharan oases are characterized by novel and unique haplotypes (O4, O5, O5 0 and O5 00 ). These might be natural relic populations that became isolated when the North African Sahara desert was still grassland (0.126-0.168 Myr ago).

Thermal conductivity of particulate beds is an important property for many industrial handling processes as well as for storage of particulate materials. This paper presents a new theoretical model that is based on heat transfer between particles in three modes: heat conduction through contact area, heat conduction through voids and radiation through voids. The model is further adjusted in order to obtain effective thermal conductivity of a particulate bed by using empirical augmentation factors for the heat transfer coefficient of each one of the heat transfer mechanisms. Comparison of the results predicted by the semi-empirical model to our experimental results show good agreement. The theoretical model was investigated to examine the effect of various parameters (such as: particle elasticity and surface roughness, particle and gas thermal conductivity and particle diameter), on the effective thermal conductivity of various particulate beds. Our results show the significant effect of the contact area (that is a clear function of the compression load) between particles on the effective thermal conductivity.

A predictive model for estimating thermal contact conductance between two nominally flat metallic rough surfaces has been developed and experimentally validated. The predictive model consists of two complementary parts, the first of which is a surface deformation analysis to calculate the actual area of contact for each contact spot, while the second accounts for the effects of constriction resistance and gas gap conductance between the contacting surfaces. A surface characterization technique is developed which generates an equivalent 3-D surface profile from multiple 2-D profiles and determines the unique wavelengths of importance for the surface deformation and constriction resistance models. For given surface profiles and material properties of two contacting surfaces, and a specified contact pressure, the surface characterization technique filters out non-essential wavelengths on the surface, after which the surface deformation analysis calculates the deformation and contact area of each contacting asperity by considering three different modes of deformation, namely, elastic, elastic-plastic, and plastic. The constriction resistance model is then used to calculate the constriction resistance for each contacting asperity based on the area of contact and radius of curvature of the asperity. The constriction resistance values for all the contacting asperities are then used to calculate the total thermal contact conductance. An experimental facility has also been constructed to measure thermal contact conductance of interfaces to verify the results of the predictive model. Good agreement has been found between the model predictions and experimental measurements, validating the modeling approach.

Tractive force and train movement stability dependence on division of forces involved in wheel/rail contact area are the main subjects of this article. The influence of wheel/rail contact properties in the vehicle dynamics and adhesion fields is investigated. Current tendency all over the world is to reduce the conicity of wheels with the aim of increasing the speed of trains. Wave-length of moving wheel-set in track for worn wheel-set tyre is twice less than for new wheel running profile.

This study was conducted to predict contact area (A) of bias-ply tire based on contact area index (CAI), inflation pressure (P) and vertical load (W). For this purpose, contact area of four bias-ply tires with different contact area index were measured at three levels of inflation pressure and four levels of vertical load. Results of contact area measurement for bias-ply tires No. 1, 2 and 3 were utilized to determine regression model and three-variable linear regression model A = 113.33-0.0023 CAI-2108.6 P + 33.429 W with R = 0.901 was P 2 obtained. Also, results of contact area measurement for bias-ply tire No. 4 were used to verify model. The paired samples t-test results indicated that the contact area values predicted by model were more than the contact area values measured by test apparatus. To check the discrepancies between the contact area values predicted by model with the contact area values measured by test apparatus, RMSE and MRPD were calculated. The amounts of RMSE and MRPD were 30.4 cm and 33.1%, respectively. Amounts of RMSE and MRPD confirmed 2 that the three-variable linear regression model may be used to predict contact area of bias-ply tire based on contact area index, inflation pressure and vertical load. On the other hand, to calculate actual contact area values or contact area values measured by test apparatus (A) based on contact area values predicted by model M (A) the linear regression model A = 0.920 A-20.08 with R = 0.916 can be strongly recommended. P M P 2

Triboelectric charge accumulation both poses problems and offers opportunities for dry particulate processing. It generates hazards in many industrial systems, but is exploited in several important applications, including electrophotographic toner charging and triboelectric separation. However, the charging of continuous particulate flows on solid surfaces is poorly understood, and design of devices to optimise triboelectric behaviour is often qualitative or based on trial and error. This study attempts to identify the main charging mechanisms for a continuous particulate flow on a flat surface. The proposed charging models incorporate contact time, velocity and mode of contact. A model incorporating contact area effects arising from sliding and rolling contact is consistent with experimental data, as long as a charge limit is imposed on bouncing particles. A mechanism for this charge limit, involving separation discharge, is proposed. The effect of delocalised image charge on the system is estimated and found to be negligible. Some general design principles are proposed for triboelectric optimisation of particle processing devices.Triboelectrification produces hazards and offers opportunities for dry particle processing. Charging mechanisms for a continuous particulate flow on a flat surface are identified and modelled, for sliding, rolling and bouncing contact. These models are then validated using existing experimental data. Some general design principles are proposed for triboelectric optimisation of particle processing devices.

The novel wafer-level packaging (WLP) process described in this paper allows quasi-hermetic capping of optical devices on wafer-level yielding miniaturized glass cavity windows on top of the optical area, at the same time leaving the contact area accessible for standard electrical connections i.e. wire bond. These smaller chip-size optical cavity packages are used within standard chip-on-board (COB) assemblies for high performance optical applications providing high yield and utmost reliability. In this paper the process flow of generating optical cavity glass wafers as well as of the wafer-level capping process is demonstrated and reliability data on wafer-level and package-level are discussed.

Anisotropic conductive film (ACF) composed of an adhesive resin and fine conductive fillers such as metallic particles or metal-coated polymer balls are key materials for fine pitch chip-on-film (COF) and chip-on-glass (COG) LCD packaging technologies.

Using the finite element technique, the stress characteristics within the mandible are evaluated during a dynamic simulation of the implant insertion process. Implantation scenarios considered are implant thread forming (S1), cutting (S2) and the combination of forming and cutting (S3). Ultimately, the outcome of this study will provide an improved understanding of the failure mechanism consequential to the stress distribution characteristics in the mandible during the implantation process. Material and Methods: Parameters considered herein include bone cavity diameters of 3.9mm (for S2), 4.25mm (for S1) and a tapered cavity of diameters linearly varying from 3.9 to 4.25mm (for S3). The bone-implant system is modelled using three-dimensional tetrahedral elements. Idealised bone and implant interaction properties are assumed. The stress profiles in the mandible are examined for all bone cavity diameters. Results and Conclusion: The stress levels within the cancellous and cortical bone for S1 are significantly reduced when compared to scenarios S2 and S3. For S3, during the initial insertion steps, the stress is marginally less than that for S2. Close to the end of the insertion process, the stress level within the cancellous bone in S3 is approximately half way between that of S1 and S2. Generally for all scenarios, as the insertion depth increases the stress increases less significantly in the cortical bone than in the cancellous bone. Overall, different implant surface contact areas are the major contributors to the different stress characteristics of each scenario.

The current international standard for spectacle frames recommends that frames weighing up to 25 g should have a minimum nose-pad contact area of 200 mm 2 and that those weighing over 25 g should have a minimum contact area of 250 mm 2. It is shown that these recommendations are being almost universally ignored for frames with separate pads on arms. The information on frame materials in manufacturersÕ literature is woefully inadequate but, from the information available, there was little difference in weight between stainless steel frames and those from unnamed materials.

Scuffing failure was induced in samples of SAE 4340 steel which had been quenched and annealed at several temperatures. Examination of worn areas using grazing-incidence X-ray diffraction revealed an austenitic phase at volume fractions of up to 60%. No dependence of austenite fraction on depth was observed for depths of up to 5.0 m. No clear trend in austenite fraction after scuffing as a function of tempering temperature was found. One wear test was interrupted precisely during scuffing, and the worn areas of that sample showed 15% austenite. A fully scuffed sample of the same tempering temperature contained 60% austenite, while analysis of original material and contact areas prior to scuffing initiation revealed no austenite.

A microelectrode array was designed to minimize the pain sensation of electroporation for enhancing transdermal drug delivery. The influence of the size of the electrode -skin contact area and of the distance between electrodes on the pain sensation was tested on human volunteers. The pain level decreased with the dimension of electrode -skin contact area and with inter-electrode distance. When both reached about 0.5 mm, the pain level was not perceptible even at the threshold of transdermal electroporation level of sixty electric pulses at 150 V, 1 ms at 1 -10 Hz. An array of 11 Â11 alternately connected electrodes with 0.6 Â 0.6 mm dimension was fabricated. The electric thresholds for effective drug delivery, using toluidine blue O as a marker on mouse skin, was found to be the same for microelectrode arrays as for larger electrodes and wider interelectrode distances. In vivo transdermal electroporation using microelectrode array with 180 pulses of 150 V, 0.2 ms at 1 Hz, followed by 30 min methotrexate (MTX) occlusion increased more than 4 fold the systemic MTX level in mice. The results demonstrated the potential of painless delivery of significant amounts of chemotherapeutic agents through skin with the new electrode arrays in a clinical setting. D

Direct measurements of the pull-off (adhesion) forces between pharmaceutical particles (beclomethasone dipropionate, a peptide type material, and lactose) with irregular geometry and rough polymeric surfaces (series of polypropylene coatings, polycarbonate, and acrylonitrile-butadiene-styrene) were carried out using the atomic force microscope (AFM). These measurements showed that roughness of the interacting surfaces is the significant factor affecting experimentally measured pull-off forces. A broad distribution of pull-off force values was noted in the measurements, caused by a varying adhesive contact area for a particle located on rough substrate. The possibility of multiple points of contact between irregularly shaped pharmaceutical particles and substrate surfaces is demonstrated with nanoindentations of the particle in a fluoropolymer film. Force-distance curves showing the 'sawtooth' pattern are additional evidence that particles make contact with substrates at more than one point. Reduced adhesion of 10 to 14 micron diameter lactose and peptide material particles to the polypropylene coatings with a roughness of 194 nm was found in this study. Similar pull-off force versus roughness relationships are also reported for the model spherical particles, silanized glass particle with a size of 10 microns and polystyrene particle with a diameter of 9 microns, in contact with polypropylene coatings of varying roughness characteristics.

A computerised, real time, thin-"lm pressure transducer method is used to measure tibiofemoral contact area in total knee arthroplasty (TKA) devices that is easier and more reliable and reproducible as compared to the Fuji pressure-sensitive "lm technique. Many authors have suggested that contact areas and pressures within TKA devices can be a predictor of wear and failure of the ultra-high molecular weight polyethylene (UHMWPE) tibial insert. In this study, two contact area measurement techniques (Fuji pressure-sensitive Film and K-scan sensor system) were compared using a custom TKA testing jig designed for freedom of movement so that in any loading con"guration the component found and seated in its own`homea position. The K-scan system was used to measure contact areas of one TKA design at several angles from 0 to 1103 #exion with loads equating to 4, 4.5, and 5 times body weight. For comparison, four ranges of Fuji "lm were used to measure areas at the same #exion angles but at 5 times body weight only. Contact areas measured with the Fuji "lms were 11}36% (p(0.05) lower than those measured by the K-scan sensor. : S 0 0 2 1 -9 2 9 0 ( 9 9 ) 0 0 0 7 2 -X

In recent years it has been observed that the substrate surface temperature during thermal spray deposition has a profound effect on the morphology of the impacted droplet (splat) and consequently on the microstructure and properties of the deposits. In this set of two papers (one for metal and one for ceramic), the substrate temperature effects have been studied in an integrated manner relating the initial splat formation to microstructure development and eventually to the properties of the deposit. Isolated impacted splats have been obtained on polished steel substrates at two different temperatures (high and low) and these have been analyzed quantitatively for their shape factors and thicknesses. The deposits have been formed nominally at these two different temperatures and their microstructures and properties have been analyzed. The results confirm that there exists a threshold transition temperature for the substrate surface beyond which the splat morphology changes from a fragmented (splashed) to a more contiguous (disk-shaped) morphology. In the case of zirconia this temperature appears to be in the range of about 250 -300°C, which is roughly 10% of the melting temperature of zirconia. It has been further observed that the splat-substrate and inter-splat contact is significantly improved at higher temperatures, leading to reduced porosity, increased thermal conductivity and strength. These results are assimilated to develop an integrated structure -property relationship and preliminary arguments are presented as to the reason for such transitions.

In this study, the attrition wear, also called occlusal-contact-area wear, of human enamel was measured quantitatively with a computerized three-dimensional measuring technique over a period of four years. Tooth replicas from a clinical trial were used. A running-in wearperiod after restorative treatment, followed by steady-state wear, was suggested. The average steady-wear rate on occlusal contact areas was about 29 pm per year for molars and about 15 pm per year for premolars.

The removal ability of gutter brushes for road sweeping for various debris types and different sweeping parameters is studied through experimental tests. The brushing test rig used comprises two commercial gutter brushes, a concrete test bed, and an asphalt test road with a gutter of 0.25 cm width and 10°slope. The brush-surface contact area is determined by sweeping sand on the concrete test bed. Sweeping problems are identified and discussed, and sweeping criteria for the different debris types are suggested. Also, optimum sweeping parameters are proposed for each debris type. In addition, debris removal mechanisms are discussed and analysed. The results indicate that for large heavy debris such as stones and gravel, it is not difficult to achieve large removal forces, because the steel bristles are relatively stiff. Conversely, high removal forces are not needed for particles of millimetre or micron sizes, but bristle curvature has to be appropriate to remove particles from road concavities. Finally, it is found that mud, especially dry mud on a rough surface, is the hardest debris to sweep, requiring a brush with a large tilt angle and a very large penetration to produce large removal forces.

A physical model of the human-javelin system has been developed together with a mathematical model of javelin flight including its transverse elastic vibrations. Three kinds of parametric identifications were distinguished: geometrical, mass and aerodynamic. Numerical calculations were made for different initial velocities and throwing angles. The results obtained have been presented graphically.

The morphological features of lift-off footprints on the aluminium metallization pads were investigated to gain an understanding of the effects of bonding parameters on formation of initial bonds during thermosonic gold ball bonding. The obtained results showed that metallurgical bonding initiated at the peripheral areas of the contact area situated along the direction of ultrasonic vibration. Those areas extended inwards with an increase in ultrasonic power. Both the external bonded area and central non-bonded area increased with increasing bonding force. Based on the evolution of footprints, the bonding models were proposed, and the effects of the bonding parameters on the formation of initial bonds were discussed.

Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes has renewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titanium against various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titanium alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainless steel, silicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate were lower at the higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the highest to the lowest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to their relative fracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counterfaces and suggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which adhere to the ceramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactions along with the fracture toughness dependency helped explain the high wear on the ceramic sliders.

Extraction techniques are surface dependent processes since their kinetic directly depends on the contact area between the sample and the extractant phase. The dispersion of the extractant (liquid or solid) increases this area improving the extraction efficiency. In this article, the dispersion of the sorbent at the very low milligram level is achieved by effervescence thanks to the in situ generation of carbon dioxide. For this purpose a special tablet containing the effervescence precursors (sodium carbonate as carbon dioxide source and sodium dihydrogen phosphate as proton donor) and the sorbent (OASIS-HLB) is fabricated. All the microextraction process takes place in a 10 mL-glass syringe and the solid, enriched with the extracted analytes, is recovered by filtration. Acetonitrile was selected to elute the retained analytes. The extraction mode is characterized and optimized using the determination of five nitroaromatic compounds in water. The absolute recoveries of the analytes were in the range 61-85% while relative recoveries close to 100% in all cases, which demonstrates the absence of matrix effect on the extraction. These values permit the determination of these analytes at the microgram per liter range with good precision (relative standard deviations lower than 6.1%) using ultra performance liquid chromatography (UPLC) combined with ultraviolet (UV) detection as instrumental technique.

... 1. Introduction. Peanut-induced anaphylaxis remains the dominant and most severe of the immediate hypersensitivity reactions to foods because of its persistency and the life threatening nature (Sampson & McCaskill, 1985). ...

This report briefly reviews the measurements and interpretation of adhesion forces between microscopic probes and substrates having micro-and nano-scaled roughness characteristics. The measurements were recently conducted at Michigan Technological University using atomic force microscopy. The laboratory study concentrated on both rigid and deformable materials, with the probes larger than the size of roughness features of interacting surfaces. For such systems, a detailed surface characterization, in terms of roughness parameters, asperity size and shape and spacing between asperities, as well as analysis of deformation of materials, is required. Analysis of the experimental data can be done using theoretical models suitable for rough surfaces, which would allow one to normalize the measured forces. Alternatively, loading of the probe during adhesion force measurements can be managed properly to control deformations of the nano-scaled surface irregularities. Controlling the deformation reduces and even eliminates the effects of nano-roughness on the probe-substrate contact area, promoting conditions described by the contact mechanics models for the sphere-smooth substrate system.

This study is aimed to search the angle optimization of scraping/doctor knife in the drum dryers. Electrical measurements were made via a digital ohmmeter to calculate the real contact area between the drum and doctor knife. It was seen that the electrical resistance was decreased with the increment of drum's load. It's also seen that, the contact resistance between the couple was increased with the increment of temperature. This is an experimental practice; AISI 4140 for a drum material, HSS for a doctor knife were used. So as to increase the hardness and to reduce the resistance, the drum was coated with the harder chromium, and then it was ground for the enhancement of the surface quality.

Due to the smoothness of the surfaces in surface micromachining, large adhesion forces between fabricated structures and the substrate are encountered. Four major adhesion mechanisms have been analysed: capillary forces, hydrogen bridging, electrostatic forces and van der Waals forces. Once contact is made adhesion forces can be stronger than the restoring elastic forces and even short, thick beams will continue to stick to the substrate. Contact, resulting from drying liquid after release etching, has been successfully reduced. In order to make a fail-safe device stiction during its operational life-time should be anticipated. Electrostatic forces and acceleration forces caused by shocks encountered by the device can be large enough to bring structures into contact with the substrate. In order to avoid in-use stiction adhesion forces should therefore be minimized. This is possible by coating the device with weakly adhesive materials, by using bumps and side-wall spacers and by increasing the surface roughness at the interface. Capillary condensation should also be taken into account as this can lead to large increases in the contact area of roughened surfaces. N Tas et al

This paper introduces a touch screen technology based on infrared optical. This technology has apparent advantages in the large-size applications, which is simple, low cost, high feasibility. In the system, the detection of ambient light and the adaptive control of IR LED can effectively enhance the adaptability of the touch screen in complex light environment via the MCU. In image processing, the image of foreground and background are segmented by Otsu's method with a coefficient. Integral projection is adopted to recognize the contact area. The result shows that the performance of the system fully meets the requirements of real time and accuracy.

The motivation for this study was to find an adequate substitute for lactose as carrier in dry powder inhalers and to overcome some drawbacks inherent to lactose. Mannitol appears to be the ideal replacement of lactose because it lacks the risk of transmitting the transmissible spongiform encephalopathy, mannitol does not carry reducing groups, that may cause chemical interactions with drugs such as proteins, and is highly crystalline even upon spray drying. Spray drying in turn is a dedicated technology to prepare carrier particles for dry powder inhalers. Typically spherical particles are generated constituting comparable interparticle forces to every drug particle attached to their surface. This study shows, that mannitol particles of different surface roughness can be prepared by spray drying at different outlet temperatures, providing the opportunity of tailoring the contact area respectively the interparticle interactions between the drug and the carrier. The emergence of different surface roughness was attributed to different crystallization mechanisms. Surface roughness was quantified by confocal laser-scanning microscopy. Quantitative Raman spectroscopy revealed, that the spray dried products consist mainly of the thermodynamically stable modification I°besides small amounts (5 to 15%) of the metastable modification II, irrespective of the drying temperature and the crystallization mechanisms taking place. This renders mannitol a most suitable substitute of lactose for the use in dry powder inhalers.

This paper reviews contact modeling with an emphasis on the forces of contact and their relationship to the geometrical, material and mechanical properties of the contacting bodies. Single asperity contact models are treated first. These models include simple Hertz contacts for spheres, cylinders, and ellipsoids. Further generalizations include the effects of friction, plasticity, adhesion, and higher-order terms which describe the local surface topography. Contact with a rough surface is generally represented by a multiasperity contact model. Included is the well-known Greenwood-Williamson contact model, as well as a myriad of other models, many of which represent various modifications of the basic theory. Also presented in this review is a description of wavy surface contact models, with and without the effects of friction. These models inherently account for the coupling between each of the contacting areas. A brief review of experimental investigations is also included. Finally some recent work, which addresses the dynamics and associated instabilities of sliding contact, is presented and the implications discussed.

The use of Nitrile Butadiene Rubber NBR as seal in machines has increased in recent years. NBR is considered as the standard material for sealing and NBR owes its many applications to a range of special mechanical properties. However, the non-linear mechanical properties and incompressible behaviour of NBR make the analysis of NBR very difficult. The most common technical cause of hand pump failures was the wear of the piston seals. Contact surface of the piston seals and the piston seal contact area are the key of calculating and determining friction force and seal wear rate of hand pump NBR rubber piston seal.

The paper describes a two-dimensional computational model for simulating surface initiated crack growth in the lubricated contact area that leads to surface pitting of mechanical components. The model assumes size and orientation of the initial crack which is subjected to contact loading conditions, accounting for the elasto-hydrodynamic-lubrication effects and tangential loading due to sliding. The influence of a lubricating fluid, driven into the crack by hydraulic mechanism, is also considered. The minimum strain energy density criterion is used to analyze crack propagation with the aim of the finite element analysis. The model is applied to a real pitting problem of a gear. The results for pit sizes correlate well with those observed in experimental testing.

En este artículo presentamos cuatro figuras dentro del conjunto del abrigo de La Vacada cuyas características estilísticas y convenciones gráficas permite descartar su pertenencia al arte levantino. Sugerimos la posibilidad de que estas representaciones pudieran adscribirse a época protohistórica ya avanzada con evidentes influencias helenístico-romanas, enfatizando el contexto geográfico y cultural indígena, tanto celtibérico como ibérico, al que se asocian. Se analizan algunos fragmentos cerámicos decorados numantinos e ibéricos como paralelos de las figuras estudiadas.

Aircraft propulsion applications require low-friction and wear resistant surfaces that operate under high contact loads in severe environments. Recent research on supertough and low friction nanocomposite coatings produced with hybrid plasma deposition processes was demonstrated to have a high potential for such demanding applications. However, industrially scalable hybrid plasma technologies are needed for their commercial realization. The Large area Filtered Arc Deposition (LAFAD) process provides atomically smooth coatings at high deposition rates over large surface areas. The LAFAD technology allows functionally graded, multilayer, super-lattice and nanocomposite architectures of multi-elemental coatings via electro-magnetic mixing of two plasma flows composed of different metal ion vapors. Further advancement can be realized through a combinatorial process using a hybrid filtered arc-magnetron deposition system. In the present study, multilayer and nanostructured TiCrCN/TiCr + TiBC composite cermet coatings were deposited by the hybrid filtered arc-magnetron process. Filtered plasma streams from arc evaporated Ti and Cr targets, and two unbalanced magnetron sputtered B 4 C targets, were directed to the substrates in the presence of reactive gases. A multiphase nanocomposite coating architecture was designed to provide the optimal combination of corrosion and wear resistance of advanced steels (Pyrowear 675) used in aerospace bearing and gear applications. Coatings were characterized using SEM/EDS, XPS and RBS for morphology and chemistry, XRD and TEM for structural analyses, wafer curvature and nanoindentation for stress and mechanical properties, and Rockwell and scratch indentions for adhesion. Coating properties were evaluated for a variety of coating architectures. Thermodynamic modeling was used for estimation of phase composition of the top TiBC coating segment. Correlations between coating chemistry, structure and mechanical properties are discussed.

A common decay scenario in old and new buildings was simulated: the effects on masonry structures of salt efflorescence or subefflorescence produced by the rise of saline solution. Eight different types of masonry wall each made up of a combination of different construction materials (brick, calcarenite and four types of mortar were combined as follows: pure lime mortar, mortar + air entraining agent, mortar + pozzolana, mortar + air entraining agent + pozzolana) have been tested. These materials have different textures (strong anisotropy in brick, irregular-shaped pores in calcarenite, retraction fissures or rounded pores in mortars which also show a reduction of porosity along the contact area with the stone), different hydric behaviours (under total immersion brick + mortar specimens absorb water faster than calcarenite + mortar specimens) and different pore size distribution (brick shows unimodal pore distribution, whereas calcarenite and mortars are bimodal). In the salt weathering test, mortars interlayered with masonry blocks did not act as sacrificial layers. In fact, they allowed salts to rise through them and crystallize on the brick or calcarenite pieces causing the masonry structure to decay. Only the addition of an air-entraining agent partially hindered the capillary rise of the salt-laden solutions.

Dry and brine-saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory. Experiments were conducted by increasing vertical effective stress up to 50 MPa to study the changes in physical properties of mudstones during burial. The results suggest that the physical properties (porosity, density, acoustic velocity, etc.) of mudstones vary greatly with increasing effective stress, clay mineralogy and fluid content. Kaolinite aggregates are much more compressible than those composed of smectite. Brine-saturated clay mixtures are much more compressible than dry clay mixtures. Brine may soften and lubricate the clay matrix compared to dry clays, resulting in higher compressibility in the brine-saturated state. The lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays. The extremely fine-grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse-grained kaolinite. At 20 MPa effective stress, corresponding to about 2 km burial depth with hydrostatic pore pressure, brine-saturated pure kaolinite compacted to 20% porosity, while pure smectite retained 41% porosity. Brinesaturated clay mixtures show higher V p and lower V s than dry clay mixtures. A pronounced difference in V s was observed among the brinesaturated clay mixtures. The lowest V s as a function of vertical effective stress was found for pure smectite. For a given porosity value, smectitic clays have higher velocities and elastic moduli than the kaolinitic clays. The V p /V s ratio is significantly higher in smectite than in kaolinite aggregates. Treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties, which are strongly affected by the clay mineralogy, grain size, the amount of other minerals present and fluid content. Our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth (o2 km, 80 1C), above depths where significant chemical compaction takes place. r

The electrical contact resistance at the interface between two materials is often an unknown when modelling certain processes, such as the anodes and cathodes in Hall-Héroult cells or the spot welding of sheet metal. In this paper, a 2D axisymmetric weakly coupled thermoelectro-mechanical finite element methodology built in the commercial code ANSYS is presented. It allows the generation of Joule heat directly at the interface, the precise representation of the contact areas as well as the testing of different contact resistance models. Using existing experimental results of industrial carbon and steel cylinders in contact at different temperatures, a novel phenomenological constitutive law for electrical contact resistance was developed. This experiment was repeated at room temperature with Alcoa-Lauralco carbon and cast iron cylinders, and the 2D finite element model was used to validate and calibrate the constitutive law. An excellent agreement was found between the model predictions and the new experimental data. #