Lower Volume Loss Research Articles

Macro- and microtopographical examination and quantification of CAD-CAM composite resin 2- and 3-body wear

Statement of problemThe selection of an appropriate restorative material based on wear behavior is important for the long-term success of a dental restoration. For computer-aided design and computer-aided manufacturing (CAD-CAM) composite resins, information about their wear resistance and wear mechanism is scarce. PurposeThe purpose of this in vitro study was to compare the 2- and 3-body wear of CAD-CAM composite resins with that of lithium disilicate ceramic and to develop analysis software. Material and methodsFlat specimens were prepared from the following CAD-CAM composite resins: Cerasmart (CS), SHOFU Block HC (SH), Katana Avencia (KA), Brilliant Crios (BC), an experimental composite resin (EXP), and lithium disilicate ceramic IPS e.max CAD (REF). The specimens underwent 2-body wear (50 N, 5/55°C, 400 000 cycles) opposed by human enamel antagonists. Specimen wheels were prepared with each material on each wheel for 3-body wear with a millet slurry (15 N, 15% slip, 200 000 cycles). All specimens were digitized by using a dedicated laser scanner. Analysis software was developed to calculate macrotopographical examination of volume loss. The microtopography of the surfaces was examined by using scanning electron microscopy. For data analysis, the Kruskal-Wallis test with the Tukey-Kramer post hoc test and the 1-sample Wilcoxon test were used (α=.05). ResultsAfter 2-body wear simulation, SH and KA presented higher volume loss than the other CAD-CAM materials. For 3-body wear, REF had lower volume loss than CS, SH, or BC. In addition, BC led to higher volume loss than EXP. The patterns of 2- and 3-body wear were different. ConclusionsThe ceramic showed good global wear resistance. The volume loss of the CAD-CAM composite resins differed and depended on the material. The 2- and 3-body wear test methods tended to differ with regard to volume loss. Examination of the worn surfaces revealed different mechanisms acting in 2- and 3-body wear test.

Efficacy of different strategies to treat root dentin eroded by liquid or gaseous hydrochloric acid associated with brushing abrasion

ObjectiveThis study aims to evaluate how casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) associated with Nd:YAG or Diode laser affects dentin exposed to hydrochloric acid (HCl) with or without tooth brushing. DesignOne hundred and sixty human root dentin blocks were selected after they were initially eroded with liquid HCl (pH 1.2) 3x for one day. The blocks were divided into the following groups: G1– liquid HCl (HCl-l), G2– HCl-l + brushing, G3– gaseous HCl (HCl-g), and G4– HCl-g + brushing. Each group was randomly assigned to the following treatments (n = 10): A) Control (no treatment), B) CPP-ACP, C) CPP-ACP associated with Nd:YAG laser (λ = 1064 nm) (40 mJ, 10 Hz, 0.4 W, 15 s), and D) CPP-ACP associated with Diode laser (λ = 980 nm) (0.5 W, 200 μs, 15 s). The treatment with CPP-ACP (G2, G3 and G4) was applied on the dentine surface for 5 min. Erosion (6x/day/20 s) and erosion (6x/day/20 s) with abrasion (2x/10 s) were performed for five days. Dentin volume loss was determined by 3D confocal laser microscopy. Data were analyzed with two-way ANOVA and Tukey's tests. ResultsG1 - CPP-ACP (10.77 ± 1.66) and CPP-ACP associated with Diode laser (9.98 ± 0.89) showed lower volume loss in relation Control group (12.86 ± 0.63) (p < 0.05). G2 - CPP-ACP associated with Diode laser (12.41 ± 1.08) elicited lower volume loss as compared to the Control (14.42 ± 1.24) (p < 0.05). As for G3 and G4, all treatments showed similar volume loss. ConclusionCPP-ACP and CPP-ACP associated with Diode laser could control dental tissue loss in dentin eroded by liquid HCl. Moreover, CPP-ACP associated with Diode laser could effectively decrease dental tissue loss in dentin exposed to liquid HCl and brushing.

Novel bilayer Zn[sbnd]Ni/Ni[sbnd]Co[sbnd]SiC nanocomposite coating with exceptional corrosion and wear properties by pulse electrodeposition

This work reports the development of a novel bilayered ZnNi/NiCoSiC nanocomposite coating on mild steel (MS) by electrodeposition. The top Ni-Co-SiC nanocomposite layer, when deposited directly on MS (monolayer) shows a hardness of 734 HV and a corrosion current density of ∼28μA/cm2 in 3.5 wt% NaCl. However, the lack of adherence of the coating with MS results in poor wear and scratch resistance. Mild steel is anodic to NiCoSiC nanocomposite and any kind of discontinuity in the coating may lead to severe galvanic corrosion. This problem has been successfully overcome with the incorporation of an anodic (with respect to mild steel)Zn12%Ni under-layerin between the electrodeposited NiCoSiC nanocomposite coating and MS, which is adherent to both the materials. This bilayer coating has a hardness of 760 HV and corrosion current density of ∼19μA/cm2 in 3.5 wt% NaCl which are slightly better than that of the monolayer. Further, the bilayer coating assembly exhibits exceptionally low volume loss under wear (∼350 mm3) compared to bare mild steel (∼1700 mm3). This ZnNi/NiCoSiC nanocomposite bilayercoating has the potential to emerge as hard, wear resistant and anti-corrosive coating which is essential in the field of heavy duty machines.

Tribological behaviour of a 3Y-TZP/Ta ceramic-metal biocomposite against ultrahigh molecular weight polyethylene (UHMWPE)

This study aims to evaluate the tribological behaviour of 3Y-TZP/Ta (20vol%) ceramic-metal composites and 3Y-TZP monolithic ceramic prepared by spark plasma sintering (SPS) against ultrahigh molecular weight polyethylene (UHMWPE). According to the results of pin (UHMWPE)-on-flat wear test under dry conditions, the UHMWPE – 3Y-TZP/Ta system exhibited lower volume loss and friction coefficient than the UHMWPE – monolithic ceramic combination due to the presence of an autolubricating layer that provides sufficient lubrication for reducing the friction. Owing to the lubrication of the liquid media, under wet conditions obtained using simulated body fluid (SBF), similar behaviour is observed in both cases. Additionally, the ceramic and biocomposite materials were subjected to a low temperature degradation (LTD) process (often referred to as “ageing”) to evaluate the changes in the tribological behaviour after this treatment. In this particular case, the wear properties of the UHMWPE-biocomposite system were found to be less influenced by ageing in contrast to the case of the UHMWPE-zirconia monolithic material. In addition to their exceptional mechanical performance, 3Y-TZP/Ta composites also showed high resistance to low temperature degradation and good tribological properties, making them promising candidates for biomedical applications, especially for orthopaedic implants.

EFFECT OF THIXOFORMING ON THE WEAR PROPERTIES OF AL-SI-CU ALUMINUM ALLOY

In this study a hypoeutectic Al-6Si-3Cu aluminium alloy was synthesized using two different routes: the thixoforming process and the conventional mould casting process. The microstructural features, hardness and wear behavior of thixoformed alloy have been evaluated and compared with that of as-cast alloy. Cooling slope method was used to produce the non-dendritic microstructure feedstock for thixoforming. Thixoforming was carried out at 50% liquid fraction. The dry sliding wear behaviour of the produced alloys was investigated under two loads; namely, 10 and 50 N and 1m/s sliding speed for 9 km sliding distance. The thixoformed alloy exhibited globular primary phase morphology with fine and uniform distributed Si and intermetallic particles. On the contrary, dendritic primary phase, coarse flaky silicon particles and segregated microstructure has been observed in conventional cast alloy. Thixoformed alloy exhibited improvement in the wear resistance in comparison to the conventional cast alloy, which may be attributed to the microstructural enhancement resulting in improved hardness. The thixoformed samples displayed lower volume loss of ~16.20 mm3 and ~42.40 mm3 at loads of 10 and 50 N respectively compared with that of conventional cast samples. On the basis of observations and analyses on the wear rates and worn surfaces, the wear mechanism of the alloys was dominantly controlled by abrasive, adhesive and minor delamination.

Fluxes and production efficiency of irrigated wheat ecosystem under edaphic constraints of western Maharashtra plateau: a micrometeorological investigation

Energy fluxes and canopy microclimate of wheat grown on the edaphically stressed shallow basaltic soil at Baramati, India were studied during 2014-15.The crop was grown with optimum irrigation, applied at frequent intervals, resulting in a low seasonal Bowen ratio (H/LE: Sensible heat flux/Latent heat flux) value of 0.23. The diurnal average flux rate for H during various phenophases varied between 2.2 and 16.2 Wm-2 and had a seasonal mean of 11.0 Wm-2. LE exchange rates varied between 44.2 and 56.8 Wm-2 and the seasonal mean was 49.0 Wm-2.Evapo-transpiration (ET) of wheat in the location under standard growing condition was estimated at 312 mm.However, the crop could actually evapotranspire water in the range of 187-248 mm,as measured through an eddy covariance based protocol, even though it received about 410 mm of water through irrigation and rainfall. Canopy condition were interpreted through hyperspectra based indices, viz. NDVI and LSWI which indicated atleast two instances of stress, one around maximum tillering and the other between anthesis and dough stages.Net primary production and yield during the 105 day long growing season were 558 g C m-2 and 3.3 t ha-1, respectively and the productivity gap could be minimized by addressing the major edaphic limitations, i.e. low soil volume and high seepage losses.

Estimation of blood loss is inaccurate and unreliable

To determine the characteristics associated with improved accuracy or reliability of estimating operative blood loss. Operating room personnel at a tertiary care hospital evaluated 3 operative simulations and provided estimations of blood loss. The simulations utilized precise, known volumes of porcine blood and saline on tapes, sponges, and in suction containers. Low volume (50mL), mid volume (300mL), and high volume (900mL) blood loss scenarios were used in this simulation. Information collected included the blood loss estimation, the participant's occupation, years of experience in the operating room, confidence level in estimating blood loss, and their opinion as to which group would provide the most accurate estimation. Sixty practitioners participated: 17 anesthesia providers, 22 surgeons, and 21 nurses and technicians. Overall, estimations were significantly inaccurate: scenario 1, mean error 52%; scenario 2, mean error 61%; scenario 3, mean error 85%. Ninety-five percent of participants provided estimations that had >25% error in at least 1 scenario. Only 27% demonstrated consistency in over or under-estimating the blood loss. There was no association between specialty, years of experience, or confidence in ability with consistency or accuracy of estimating blood loss. This study demonstrates that visual estimation of operative blood loss is unreliable and inaccurate. No provider specialty, level of experience, or self-assessment of ability was associated with improved estimation. Blood loss estimations are not a reliable metric to judge physician performance or patient outcomes. Consideration should be given to alternative reporting of operative blood loss to better direct perioperative care.

Tribological Characteristic of Titanium Alloy Surface Layers Produced by Diode Laser Gas Nitriding

AbstractIn order to improve the tribological properties of titanium alloy Ti6Al4V composite surface layers Ti/TiN were produced during laser surface gas nitriding by means of a novel high power direct diode laser with unique characteristics of the laser beam and a rectangular beam spot. Microstructure, surface topography and microhardness distribution across the surface layers were analyzed. Ball-on-disk tests were performed to evaluate and compare the wear and friction characteristics of surface layers nitrided at different process parameters, base metal of titanium alloy Ti6Al4V and also the commercially pure titanium. Results showed that under dry sliding condition the commercially pure titanium samples have the highest coefficient of friction about 0.45, compared to 0.36 of titanium alloy Ti6Al4V and 0.1-0.13 in a case of the laser gas nitrided surface layers. The volume loss of Ti6Al4V samples under such conditions is twice lower than in a case of pure titanium. On the other hand the composite surface layer characterized by the highest wear resistance showed almost 21 times lower volume loss during the ball-on-disk test, compared to Ti6Al4V samples.

Antisynthetase syndrome: Pulmonary computed tomography findings of adult patients with antibodies to aminoacyl-tRNA synthetases

ObjectivesTo describe the pulmonary CT findings in patients with anti-ARS-antibody-positive interstitial lung disease (anti-ARS-ILD) MethodsThe CT findings of 64 patients with anti-ARS-ILD were retrospectively reviewed. The images were retrospectively reviewed independently by 2 chest radiologists, and the final decision on the CT findings was made by a third chest radiologist. ResultsThere were 16 male and 48 female patients, aged 54.2±13.4 years. Sixteen patients had anti Jo-1, 24 had anti-EJ, 9 had anti-PL-7, 7 had anti-PL-12, 5 had anti-KS, and 3 had anti-OJ antibodies. Overall, 63 patients (98.4%) had CT findings predominantly in the lower lobe; 61 patients (95.3%) showed peripheral opacities, and 47 patients (73.4%) showed peribronchovascular opacities. Ground-glass attenuation, consolidation, and reticulation showed similar distribution patterns. Regarding detailed CT findings, 89.1% of patients had lower volume loss, 76.6% had interlobular septal thickening, and 67.2% had thickening of bronchovascular bundles. The final radiologic diagnoses were as follows: inconsistent with usual interstitial pneumonia (UIP) in 63 patients (98.4%), which included nonspecific interstitial pneumonia (NSIP) in 35 patients (55.6%), organizing pneumonia (OP) in 4 patients (6.3%), and OP with fibrosis in 22 patients (34.9%). ConclusionsThe characteristic CT findings of patients with anti-ARS-ILD were areas of ground-glass attenuation and reticulation, predominantly distributed as lower and peribronchovascular lesions, which is compatible with NSIP. One-third of patients showed OP with fibrosis.

410 Association between better renal function preservation and lower volume loss between robotic partial nephrectomy and laparoscopic partial nephrectomy: A propensity score matched analysis

410 Association between better renal function preservation and lower volume loss between robotic partial nephrectomy and laparoscopic partial nephrectomy: A propensity score matched analysis

Paired comparison of methylene blue- and amotosalen-treated plasma and cryoprecipitate.

Cryoprecipitate is used in the treatment of patients with acquired hypofibrinogenaemia. Studies have not directly compared cryoprecipitate produced following pathogen inactivation (PI) of fresh-frozen plasma (FFP) using different systems. The effects of methylene blue (MB) and amotosalen (AS) PI systems on the quality of FFP and cryoprecipitate were investigated in a paired study. Seven group A and 7 group O pools of plasma were prepared and split into individual units and rapidly frozen to produce FFP. Units of FFP were thawed and either PI treated with MB or amotosalen, or left untreated (control). Samples of FFP along with the corresponding cryoprecipitate were tested for a range of coagulation factors, thrombin generation (TGT) and rotational thromboelastometry (ROTEM). AS-FFP showed a smaller decrease following treatment for most coagulation factors analysed than MB-FFP, except fibrinogen (antigen) and factor VII, partly due to lower volume losses. There was no significant difference between treatment methods for fibrinogen content of cryoprecipitate with treated units meeting current UK specification, or TGT and ROTEM parameters studied. MB-cryo contained a significantly higher content of FVIII and lower content of FXIII when compared to AS-cryo, with no difference in fibrinogen activity.

The effect of transmitted Er:YAG laser energy through a dental ceramic on different types of resin cements.

The laser debonding procedure of adhesively luted all-ceramic restorations is based on the ablation of resin cement due to the transmitted laser energy through the ceramic. The purpose of this study was to determine the effect of Er:YAG laser irradiation transmitted through a dental ceramic on five different resin cements. Five different resin cements were evaluated in this study: G-Cem LinkAce, Multilink Automix, Variolink II, Panavia F, and Rely X Unicem U100. Disc shaped resin cement specimens (n = 10) were fabricated for each group. A ceramic disc was placed between the resin cement discs and the tip of the handpiece of Er:YAG laser device. The resin cement discs were irradiated through the ceramic and the volume of the resin cement discs were measured using a micro-CT system before and after Er:YAG laser irradiation. The volume loss of the resin cement discs was calculated and analyzed with one-way ANOVA and Tukey-HSD tests. The highest volume loss was determined in G-Cem (1.1 ± 0.6 mm3 ) and Multilink (1.3 ± 0.1 mm3 ) (P < 0.05) groups, and the lowest volume loss was determined in Rely X (0.3 ± 0.07 mm3 ), Variolink (0.4 ± 0.2 mm3 ), and Panavia (0.6 ± 0.2 mm3 ) groups (P < 0.05). All resin cements were affected by the laser irradiation resulting in the volume loss of the cement; however, there are significant differences among different resin cements. All the resin cements tested in this study were effected by the Er:YAG laser irradiation and there were significant differences among the resin cements with regard to ablation volume. Lasers Surg. Med. 47:602-607, 2015. © 2015 Wiley Periodicals, Inc.

From days to decades: numerical modelling of freshwater lens response to climate change stressors on small low-lying islands

Abstract. Freshwater lenses on small islands are vulnerable to many climate change-related stressors, which can act over relatively long time periods, on the order of decades (e.g., sea level rise, changes in recharge), or short time periods, such as days (storm surge overwash). This study evaluates the response of the freshwater lens on a small low-lying island to various stressors. To account for the varying temporal and spatial scales of the stressors, two different density-dependent flow and solute transport codes are used: SEAWAT (saturated) and HydroGeoSphere (unsaturated/saturated). The study site is Andros Island in the Bahamas, which is characteristic of other low-lying carbonate islands in the Caribbean and Pacific regions. In addition to projected sea level rise and reduced recharge under future climate change, Andros Island experienced a storm surge overwash event during Hurricane Francis in 2004, which contaminated the main wellfield. Simulations of reduced recharge result in a greater loss of freshwater lens volume (up to 19%), while sea level rise contributes a lower volume loss (up to 5%) due to the flux-controlled conceptualization of Andros Island, which limits the impact of sea level rise. Reduced recharge and sea level rise were simulated as incremental instantaneous shifts. The lens responds relatively quickly to these stressors, within 0.5 to 3 years, with response time increasing as the magnitude of the stressor increases. Simulations of the storm surge overwash indicate that the freshwater lens recovers over time; however, prompt remedial action can restore the lens to potable concentrations up to 1 month sooner.

Strain Estimation of Folds, Orbiculites and Quartz Phenocrysts in the Ambaji Basin of the South Delhi Terrane, Aravalli-Delhi Mobile Belt, NW India and its Tectonic Implication

Abstract Ambaji basin in the south Delhi terrane of Aravalli-Delhi Mobile Belt consists of greenschist facies rocks which are intruded by 850-750 Ma Ambaji granites and several phases of quartz and pegmatite veins. The basin is tectonically juxtaposed against the Balaram-Kui-Surpagla-Kengora Granulite Complex. In this paper the deformation structures of the Ambaji basin has been studied and strain has been measured using different markers like folds, orbiculites and quartz phenocrysts and its tectonic implication has been discussed. Strain due to folding has been expressed in terms of shortening that has been estimated using wavelength / arc length ratio. Since the folds belong to Class 1C geometry, the arc length of the parent Class 1B fold has been calculated after removing the homogeneous strain component from Class 1C fold. The above technique was verified by drawing a Class 1B fold and modifying to Class 1C by homogeneous strain in Macromedia FreeHand MX software. Further, this was cross checked by measuring strain in two strain ellipses that represent respectively shortening in Class 1B and Class 1C folds. The shortening was estimated to be ca. 65% and 55% during F1 and F2 folding respectively. In order to know the finite strain in the folded rocks the deformed orbiculites in the metabasalt and quartz phenocrysts in the metarhyolite and granites have been analysed by Normalized Fry techniques. An apparent flattening strain with about 10 to 23 % volume loss has been estimated; correlation between inclinations of the longer axis of strain ellipse with strain suggests layer parallel shear to be the primary cause of folding. It has been suggested that buckling associated with moderate shortening and low volume loss are responsible for the deformation in the low grade rocks of Ambaji basin during evolution of South Delhi Terrane.

Properties of Zn–Bi composite coatings prepared by ionic co-discharge deposition

Zn–Bi composite was synthesized by ionic co-discharge deposition and its properties were investigated. The results show that the Zn–Bi composite with the incorporation of Bi has a finer grain size than the pure Zn coating and improves the mechanical properties. The microhardness is increased by approximately two times simply by adding a small amount of Bi electrolyte into a Zn bath solution. A lower volume loss of the Zn–Bi composite coating compared with the pure Zn coating also indicates that the Zn–Bi coating has a better wear resistance.

Tribocorrosion properties of different type titanium alloys in simulated body fluid

Body fluids and relative motion between implant and bone lead to synergistic degradation reactions, which cause failed implantation or adverse tissue reactions for implant materials used in human body. Because of their good chemical biocompatibility as well as acceptable mechanical properties, titanium (CP Ti) and its alloys are widely used in implant applications. β-type Ti alloys including alloying elements such as Nb, Zr and Mo have become more popular among the extensively used α- and (α+β)-type Ti alloys due to their low elastic modulus, comparable mechanical properties and high biocompatibility. This paper was mainly aimed to investigate the electrochemical and tribological properties of β-type Ti alloys. Also, traditionally used α-type Ti (α- CP Ti) and (α+β) type Ti-6Al-4V (α/β- Ti64) alloys were included for comparing the same set of the results. The XRD and SEM investigations and hardness measurements were utilized to analyze the structure, surface morphology and mechanical behavior of the alloys. Simulated body fluid (SBF) was used as corrosive environment. Tribocorrosion tests were carried out at open circuit potential (OCP), cathodic and three different anodic potentials under reciprocating sliding condition. Potentiodynamic scans were obtained with and without wear test. Friction coefficient, current density and volume loss were measured and calculated. The relative motion accelerated the material loss in corrosive environment due to the combined effect of electrochemical reaction and tribological action. All Ti alloys had almost the same sensitivity to the potentiodynamic corrosion. The ratio of depassivation/repassivation affected wear performance of titanium and its alloys during tribocorrosion tests. The rate of chemical reaction was higher in β-type Ti-15Mo (β- Ti15) and Ti-45Nb (β- Ti45) alloys as compared to others. The (α+β) type Ti-6Al-4V (α/β- Ti64) and β type Ti-13Nb-13Zr (β- Ti1313) showed lower volume loss and lower friction coefficient values during tribocorrosion tests than others. The corrosion resistance of the β- Ti64 alloy exhibited better corrosion resistance than β- Ti1313 alloy. However, considering the implants applications, the β- Ti1313 alloy may be a good candidate with relatively low elastic modulus and without toxic alloying elements.

Cost-effectiveness analysis in minimally invasive spine surgery.

Medical care has been evolving with the increased influence of a value-based health care system. As a result, more emphasis is being placed on ensuring cost-effectiveness and utility in the services provided to patients. This study looks at this development in respect to minimally invasive spine surgery (MISS) costs. A literature review using PubMed, the Cost-Effectiveness Analysis (CEA) Registry, and the National Health Service Economic Evaluation Database (NHS EED) was performed. Papers were included in the study if they reported costs associated with minimally invasive spine surgery (MISS). If there was no mention of cost, CEA, cost-utility analysis (CUA), quality-adjusted life year (QALY), quality, or outcomes mentioned, then the article was excluded. Fourteen studies reporting costs associated with MISS in 12,425 patients (3675 undergoing minimally invasive procedures and 8750 undergoing open procedures) were identified through PubMed, the CEA Registry, and NHS EED. The percent cost difference between minimally invasive and open approaches ranged from 2.54% to 33.68%-all indicating cost saving with a minimally invasive surgical approach. Average length of stay (LOS) for minimally invasive surgery ranged from 0.93 days to 5.1 days compared with 1.53 days to 12 days for an open approach. All studies reporting EBL reported lower volume loss in an MISS approach (range 10-392.5 ml) than in an open approach (range 55-535.5 ml). There are currently an insufficient number of studies published reporting the costs of MISS. Of the studies published, none have followed a standardized method of reporting and analyzing cost data. Preliminary findings analyzing the 14 studies showed both cost saving and better outcomes in MISS compared with an open approach. However, more Level I CEA/CUA studies including cost/QALY evaluations with specifics of the techniques utilized need to be reported in a standardized manner to make more accurate conclusions on the cost effectiveness of minimally invasive spine surgery.

Optimal Design of LCL Harmonic Filters for Three-Phase PFC Rectifiers

Inductive components such as line filter inductors or transformers occupy a significant amount of space in today's power electronic systems, and furthermore, considerable losses occur in these components. A main application of inductive components is EMI filters, as, e.g., employed for the attenuation of switching frequency harmonics of power factor correction (PFC) rectifier systems. In this paper, a design procedure for the mains side LCL filter of an active three-phase rectifier is introduced. The procedure is based on a generic optimization approach, which guarantees a low volume and/or low losses. Different designs are calculated to show the tradeoff between filter volume and filter losses. The design procedure is verified by experimental measurements. Furthermore, an overall system optimization, i.e., an optimization of the complete three-phase PFC rectifier, is given.

Effect of electrical current on the tribological behavior of the Cu-WS2-G composites in air and vacuum

As the traditional graphite-based composites cannot meet the requirement of rapid developing modern industry, novel sliding electrical contact materials with high self-lubricating performance in multiple environments are eagerly required. Herein a copper-based composite with WS2 and graphite as solid lubricant are fabricated by powder metallurgy hot-pressed method. The friction and wear behaviors of the composites with and without current are investigated under the condition with sliding velocity of 10 m/s and normal load of 2.5 N/cm2 in both air and vacuum. Morphologies of the worn surfaces are observed by optical microscope and compositions of the lubricating films are analyzed by XPS. Surface profile curves and roughness of the worn surfaces are obtained by 2205 surface profiler. The results of wear tests show that the friction coefficient and wear volume loss of the composites with current are greater than that without current in both air and vacuum due to the adverse effects of electrical current which damaged the lubricating film partially and roughed the worn surfaces. XPS results demonstrate that the lubricating film formed in air is composed of oxides of Cu, WS2, elemental S and graphite, while the lubricating film formed in vacuum is composed of Cu, WS2 and graphite. Because of the synergetic lubricating action of oxides of Cu, WS2 and graphite, the composites show low friction coefficient and wear volume loss in air condition. Owing to the fact that graphite loses its lubricity which makes WS2 become the only lubricant, severe adhesive and abrasive wear occur and result in a high value of wear rate in vacuum condition. The formation of the lubricating film on the contact interface between the brush and ring is one of the factors which can greatly affect the wear performance of the brushes. The low contact voltage drop of the composites in vacuum condition is attributed to the high content of Cu in the surface film. This study fabricated a kind of new sliding electrical contact self-lubricating composite with dual-lubricant which can work well in both air and vacuum environments and provides a comprehensive analysis on the lubrication mechanisms of the composite.

A High-Torque-Density Permanent-Magnet Free Motor for in-Wheel Electric Vehicle Application

A motor for in-wheel electric vehicle (EV) requires high efficiency and specific torque. In view of this, permanent-magnet brushless dc (PM BLDC) motor is most commonly employed for this application. However, due to the increasing cost of PMs, machines that do not use PMs are attracting interest. Switched reluctance motor (SRM), with its simple and robust construction, along with fault tolerant operation, is a viable option for in-wheel EV application. However, the SRM has low specific torque as compared with BLDC. Therefore, design improvements are required to make SRM a viable alternative to BLDC motor. In this paper, a new 12/26 pole SRM with high specific torque is proposed for in-wheel EV application. This machine has segmented-rotor-type construction. Also, concentrated-winding arrangement is used, ensuring low end-winding volume and copper loss. The developed machine also has high efficiency. In order to verify the design, the prototype of the machine is fabricated, and experimental results are presented.