Higher Number Of Passes Research Articles

Inhomogeneity in strain, microstructure and mechanical properties of AA1050 alloy during twist extrusion

In this study, inhomogeneity in the distribution of effective strain, microstructure and mechanical properties of AA1050 during twist extrusion (TE) are investigated. The samples are deformed up to 8 passes without rotation between passes. It is found that flow stress of the material increases by the number of passes. The observed percentage of the increase is more significant after two passes deformation. By increasing the number of passes to 4, smaller enhancement in flow stress occurs. As the number of passes increases to 8, a pronounced enhancement in strength is observed and fraction of high angle grain boundaries significantly increases. Microstructural analysis indicates that regardless of the number of passes, no development of cells and subgrains is observed in the central region of the specimens. In contrast, distinguished cell structure forms at the surface even by applying the first 2 passes of TE. In addition, inhomogeneity in strain, microstructure and mechanical properties are more significant at higher number of passes.

Effect of homogenization (microfluidization) process parameters in mechanical production of micro- and nanofibrillated cellulose on its rheological and morphological properties

The rheological properties of microfibrillated cellulose (MFC)/nanofibrillated cellulose (NFC) suspensions have an important role during processing and mixing. In this work, the process parameters for MFC/NFC production within a microfluidizer (i.e., the size of interaction chamber and number of passes) were varied to investigate the influences on morphology, zeta potential, chemical properties and rheological features including viscosity, creep, strain recovery and yield stress behavior. The stability and appropriate viscosity of the fiber suspensions can be controlled by optimizing the processing conditions, resulting in a reduction in fiber diameter and most negative zeta potential value. The viscosity increased with higher amount of fibrillation by using a smaller chamber or higher number of passes, but intermediate plateau values are characteristic for temporary aggregation and breaking-up of the fiber network. The creep response and yield stress have been described by parameters of the Burger model and Herschel–Bulkley model, respectively, showing a more prominent effect on yield stress of chamber size than number of passes. The network formation leads to lower creep compliance and step-like strain recovery. The transition from gel-like to liquid-like behavior as characterized by the dynamic yield point at a specific strain, is almost independent of the processing conditions. Most important, the total number of passes applied in production can be directly related to the rotational Peclet number, which combines rheological and morphological data.

Physiological and Technical Demands of No Dribble Game Drill in Young Basketball Players.

This study assessed the physiological and technical demands of no dribble game drill (NDGD) in comparison with a regular drill (RD). Twenty-three young basketball players performed RDs and NDGDs in a random order. All basketball rules were followed for RDs, whereas dribbling was not permitted for NDGDs. The independent variable was the drill condition, and the dependent variables were percentage of maximal heart rate (%HRmax), rate of perceived exertion (RPE), Edwards training load (TL), and the following technical actions (TAs): pass (total, correct, wrong, and percent of correct passes), shot (total, scored, missed, and percent of made shots), interception, steal, turnover, and rebound. Wilcoxon signed-rank tests were applied to assess differences between NDGD and RD conditions for each dependent variable, and the level of statistical significance was set at p ≤ 0.05. Results showed higher values for %HRmax (p = 0.007), Edwards TL (p = 0.006), and RPE (p = 0.027) in NDGD compared with RD condition. Technical action analysis revealed higher values in NDGD than RD for total (p = 0.000), correct (p = 0.000), and wrong pass (p = 0.005), and interception (p = 0.001), whereas no significant differences were found for the other TAs. The main finding of this study was that NDGD condition elicited a greater physiological demand and a higher number of passes and interceptions than the RD one. Basketball coaches should consider the NDGD as a viable method to increase the physiological load of their training sessions and to teach passing skills in a game-based situation.

Technical Performance Analysis of Iran Premier League Soccer Players in 2012-2013 Season

Background and purpose of study : analysis of IRAN premier league soccer players’ technical performance in season 2012-2013, using a computerized match analysis system (Borhan Mobin Development Management Co, IRAN). Material and methods: in this study, data were obtained from 120 players, who performed in competitions 90 minutes. The players were classified into 3 positional roles: defenders, midfielders and forwards. Technical performance variables analysis included: total passes, total successful passes, pass accuracy, total shots; total shots to target, shot accuracy, ball interception and ball losses. The data were statistically analyzed by one-way ANOVA, Kruskal-Wallis, Mann-Whitney U and Tukey post hoc test. Results : The findings of this study showed that players performed about 45 passes per competition. Midfielders and defenders had significantly higher number of passes than forwards. Pass accuracy was about 67% and there were no significant differences between positional roles. Also, the players performed about 0.8 shots per competition, forwards and midfielders had significantly higher number of shots than defenders. Shot accuracy was about 31%; midfielders and forwards had significantly higher shot accuracy than defenders. Forwards showed significantly lower ball interception and higher ball losses than other positions. Conclusion : The result of this study showed that there were significant differences between some technical actions in positional roles. Therefore, coaches can use this information for individualization of training according to playing positions and for optimization of training in the amateur game.

Wear properties of Al–Al2O3/TiB2 surface hybrid composite layer prepared by friction stir process

In this study, surface hybrid composite was fabricated on Al6061 base sheets using friction stir processing (FSP). Samples were subjected to various numbers of FSP passes from one to four with Al2O3/TiB2 powder. Influence of number of FSP passes was studied on distribution of Al2O3/TiB2 particles in aluminium matrix, microstructure, hardness, and wear properties of specimens. The results showed that increase in the number of passes causes a more uniform dispersion of composite particles and thus, decreases particles clustering. In addition, an increase in the number of FSP passes was found to decrease the matrix grain size of the surface hybrid composite. It was observed that the hardness increased as the number of passes increased due to presence and pinning effect of hard Al2O3/TiB2 particles. Also, at higher number of passes, the surface hybrid composite wear resistance was increased.

High aspect ratio cutting of metals using water jet guided laser

We report on high aspect ratio cutting of aluminum, titanium, and steel using a water jet guided laser system equipped with a frequency doubled Nd:YAG laser. The influence of the laser power, pulse repetition rate, and number of passes on the cutting depth is investigated. High cutting depth can be achieved with high laser powers, low pulse repetition rates, and a high number of passes. The maximum cutting depth is determined to 8 mm in aluminum, 4.7 mm in titanium, and 1.5 mm in steel, respectively. The effective cutting velocity of 8 mm aluminum with 40 W laser power, in a multi pass process is determined to 0.1 mm/s. The kerf width is independent of both the chosen process parameters and the cutting depth, being in the range between 100 and 120 μm. This results in high aspect ratios of up to 12.5 in steel, 39.2 in titanium, and 66.7 in aluminum.

Nanofibrillation of pulp fibers by twin-screw extrusion

The effect of the fibrillation process through a twin-screw extruder (TSE) on properties of pulp fibers was studied, considering the degree of both fibrillation and degradation of the fibers. Never-dried refined bleached kraft pulp (NBKP) was passed through a TSE several times at a high concentration of 28 wt%. The output of fibrillated fibers had a solid content up to ca. 50 wt%, and the material was in powder form. Characterizations of the morphology, dewatering speed, sedimentation, laser light scattering, scanning electron microscopy of cellulose suspensions, and light transmittance of resin-impregnated films showed that the fibrillation degree of the pulp was enhanced with a higher number of passes. However, the results from thermogravimetry, intrinsic viscosity, and X-ray diffraction analyses indicated that some degradation occurred during the fibrillation process in the TSE. In addition, the mechanical properties of the fibrillated pulp sheets reflected the effects of treatment on the fibrillation and degradation of the cellulose. For never-dried refined NBKP pulp, the best compromise in terms of fibrillation and degradation degree is between 3 and 14 passes, depending on the envisaged properties and applications. The possibility of nanocellulose production at the reported high solid contents is of great interest for industry.

Rolling of 316L Stainless Steel with Rough Rolls to Potentially Obtain Superficial Nanograins

316L stainless steel plates of 5-mm thickness, normalized at 900 °C, were cold rolled with different reductions and number of passes using rolls with three different surface roughnesses: grain heights of 0.17 and 0.33 mm and rhomboid-shaped grains of 1.5-mm height. Subsequently, the rolled samples were annealed at 275 °C for 1 h in an effort to achieve superficial nanograins. The plates laminated using low-roughness rolls had continuous superficial microcrystallization when they were rolled for at least 26 passes. For samples made with rougher rolls, the recrystallized superficial grains formed on the surface (sized ~10-15 μm) were smaller than those below the surface; this behavior was caused by the major deformation induced by repeated indentations. The superficial recrystallization of the sample also tended to be more continuous for higher number of passes; micrographs of the penetration profiles of indentation in the samples rolled with high-roughness rolls revealed that a sample rolled 24 times had not yet reached the steady surface topology. As a conclusion, in order to successfully form superficial nanograins, very low-roughness rolls must be used as well as a small absolute reduction per pass, followed by annealing. These rolling conditions generate a continuous field of highly superficial deformations, which act as nucleation centers for nanograins during annealing.

Structural and mechanical behaviour of severe plastically deformed high purity aluminium sheets processed by constrained groove pressing technique

High purity aluminium sheets (∼99.9%) are subjected to intense plastic straining by constrained groove pressing method successfully up to 5passes thereby imparting an effective plastic strain of 5.8. Transmission electron microscopy studies of constrained groove pressed sheets divulged significant grain refinement and the average grain sizes obtained after five pass is estimated to be ∼0.9μm. In addition to that, microstructural evolution of constrained groove pressed sheets is characterized by X-ray diffraction peak profile analysis employing Williamson–Hall method and the results obtained fairly concur with electron microscopy findings. The tensile behaviour evolution with increased straining indicates substantial improvement of yield strength by ∼5.3times from 17MPa to 90MPa during first pass corroborated to grain refinement observed. Marginal increase in strengths is noticed during second pass followed by minor drop in strengths attributed to predominance of dislocation recovery is noticed in subsequent passes. Quantitative assessment of degree of deformation homogeneity using microhardness profiles reveal relatively better strain homogeneity at higher number of passes.

Influence of process parameters on the morphology, rheological and dielectric properties of three-roll-milled multiwalled carbon nanotube/epoxy suspensions

The influence of process parameters on the morphology, rheological and dielectric properties of multiwalled carbon nanotubes (MWCNT)/epoxy suspensions processed by three-roll milling has been investigated. Two apron roll speeds, 180 rpm (low) and 270 rpm (high); two different number of passes, 1 (low) and 5 (high); and two MWCNT loadings 0.01 (low) and 0.1 wt.% (high) were examined. Results obtained from rheological and dielectric measurements indicate that milling at the lower roll speed of 180 rpm leads to better enhancement of rheological and dielectric properties compared to milling at 270 rpm. The results also indicate that a higher number of passes is more favorable for improved rheological and dielectric properties. The relationship between the microstructure and the properties of the suspensions has been explained using the exfoliation-rupture MWCNT agglomerate dispersion mechanism. Milling at 180 rpm was observed to promote exfoliation of MWCNT agglomerates, whereas milling at 270 rpm promoted rupture. Agglomerate statistics carried out on micrographs of the suspensions provided circumstantial evidence that milling at the lower speed indeed promoted exfoliation over rupture, while milling at the higher speed promoted rupture. This technique of combining rheological and dielectric measurements could be an invaluable tool for monitoring MWCNT agglomerate dispersion changes, and hence tuning nanocomposite properties.

Encapsulation of ascorbic acid in liposomes prepared with milk fat globule membrane-derived phospholipids

The production of nanoliposomes is considered to be an effective technology for the encapsulation and controlled release of nutraceuticals and bioactive compounds, as well as for enhancing their stability and bioavailability. Although liposomes are generally prepared with phospholipids from soy or egg, in recent years, there has been a growing interest in the health benefits and functional properties of milk fat globule membrane-derived phospholipids, as these ingredients have become commercially available. The objective of this work was to characterize nanoliposomes prepared with milk phospholipids using microfluidization, and to evaluate their encapsulation behavior using ascorbic acid as a model biomolecule. Liposomes prepared by microfluidization with milk phospholipids showed an apparent diameter of about 100 nm. The incorporation efficiencies for ascorbic acid increased as the concentration of phospholipid-rich powder increased from 5 % to 10 % (w/w). However, from 10 % to 16 % (w/w), the incorporation efficiency reached a plateau value of 26 %. There appeared to be a change in liposome structure from unilamellar to multivesicular/multilamellar vesicles with high levels of phospholipids (16 %) and a high number of passes through the microfluidizer. Storage studies showed less stable dispersions when stored at pH 3 compared with pH 7. After 7 weeks at 4 °C, liposomes stored at pH 3 and pH 7 retained 67 % of the ascorbic acid originally encapsulated, while only 30 % remained when the dispersions were stored at 25 °C. The present work demonstrated that, using microfluidization, it was possible to obtain small, unilamellar milk phospholipids liposomes stable at neutral pH protecting ascorbic acid for at least 7 weeks.

PMO-199 Comparative study of sample adequacy of 25G vs 22G needle in endoscopic ultrasound (EUS) guided fine needle aspirate (FNA) of solid lesions

IntroductionOptimal needle size in achieving greatest diagnostic yield from EUS- guided FNA remains unclear.AimWe prospectively compared sample adequacy and safety of FNA of solid lesions between 25G and 22G (CookTM)...

Improving surface hardness of austenitic stainless steel using waterjet peening process

The present study addresses the effect of multiple jet passes and other parameters namely feedrate and pressure in waterjet peening (WJP) of austenitic stainless steel 304. An analysis of surface integrity was used to evaluate the performance of different parameters in the WJP process. An increase in the number of jet passes as well as pressure leads to a higher roughness and more erosion of the surface. However, the feedrate shows a reverse effect on the surface roughness and erosion. The surface microstructures also show the mechanism of material removal process involving initial and evolved damages. The subsurface hardness shows that treating the surface with a higher number of passes and pressure produces a higher increase of hardness and also a deeper hardening layer. But, a reverse effect on the subsurface hardness was found for the feedrate. Furthermore, cross-sectional microstructures show a higher density of slip bands in the deformed grains of the specimen treated with a higher number of jet passes and pressure. However, the amount of slip bands in the deformed grains is lower with increasing feedrate.

The effect of impurity level on ultrafine-grained microstructures and their stability in low stacking fault energy silver

The effect of impurity content on the evolution of microstructure in low stacking fault energy silver processed by severe plastic deformation (SPD) was studied. The SPD-processing was carried out on 4N5 and 4N purity Ag samples by equal-channel angular pressing (ECAP) up to 16 passes. It was found that, although the minimum grain size and the maximum dislocation density were not affected by the different impurity atom content, there is a lower degree of twinning in the less pure material for high number of passes. The small increase of impurity level from 4N5 to 4N in Ag resulted in a significantly better thermal stability at room temperature for the ultrafine-grained microstructures obtained by ECAP.

Nano grained AZ31 alloy achieved by equal channel angular rolling process

Equal channel angular rolling (ECAR) is a severe plastic deformation process which is carried out on large, thin sheets. The grain size could be significantly decreased by this process. The main purpose of this study is to investigate the possibility of grain refinement of AZ31 magnesium alloy sheet by this process to nanometer. The effect of the number of ECAR passes on texture evolution of AZ31 magnesium alloy was investigated. ECAR temperature was controlled to maximize the grain refinement efficiency along with preventing cracking. The initial microstructure of as-received AZ31 sheet showed an average grain size of about 21 μm. The amount of grain refinement increased with increasing the pass number. After 10 passes of the process, significant grain refinement occurred and the field emission scanning electron microscopic (FESEM) micrographs showed that the size of grains were decreased significantly to about 14–70 nm. These grains were formed at the grain boundaries and inside some of the previous larger micrometer grains. Observation of optical microstructures and X-ray diffraction patterns (XRD) showed the formation of twins after ECAR process. Micro-hardness of material was studied at room temperature. There was a continuous enhancement of hardness by increasing the pass number of ECAR process. At the 8th pass, hardness values increased by 53%. At final passes hardness reduced slightly, which was attributed to saturation of strain in high number of passes.

Enhancing sensitivity of biconical tapered fiber sensors with multiple passes through the taper

A single biconical fiber taper is a simple and low-cost yet powerful sensor. With a distinct strength in refractive index RI sensing, biconical tapered fiber sensors can find their place in handheld sensor platforms, especially as biosensors that are greatly needed in health care, environmental protection, food safety, and biodefense. We report doubling of sensitivity for these sensors with two passes through the tapered region, which becomes possible through the use of sensitive and high-dynamic-range photodetectors. In a proof-of-principle experiment, we measured transmission through the taper when it was immersed in isopropyl alcohol-water mixtures of varying concentrations, in which a thin gold layer at the tip of the fiber acted as a mirror enabling two passes through the tapered region. This improved the sensitivity from 0.43 dB/vol % in the single-pass case to 0.78 dB/vol % with two passes through the taper. The refractive index detection limit was estimated to be 1.210 5 RI units RIU and 0.610 5 RIU in the single- and double-pass schemes, respectively. We predict that further enhance- ment of sensitivity may be achieved with a higher number of passes through the taper. © 2010 Society of Photo-Optical Instrumentation

Analysis of Polypropylene Deformation in a 135° ECAE Die: Experiments and Three-Dimensional Finite Element Simulations

Plastic deformation of polypropylene (PP) resulting from equal channel angular extrusion (ECAE) process was investigated in a 135° die. A phenomenological elastic-viscoplastic constitutive model was identified and coupled with the three-dimensional finite element (FE) method in order to predict the different processing parameters governing the deformation behaviour of PP during the extrusion. An optimal agreement between FE results and experimental data was obtained for a friction coefficient of 0.2. A detailed three-dimensional FE analysis of stress-strain field distribution was then carried out. The effects of both the number of extrusion passes and the processing routes were experimentally highlighted. The results show that the pressing force decreases with the increase of the number of extrusion passes and reaches its saturation state rapidly for routes A and C while, for routes BA and BC, it requires a high number of passes.

Effect of severe plastic deformation on tensile properties and impact toughness of two-phase Zn–40Al alloy

Tensile properties and impact toughness of the severe plastically deformed Zn–40Al alloy were investigated. The material billets were subjected to equal-channel angular extrusion (ECAE). After processing, elongation to failure increased significantly with the increasing number of ECAE passes. ECAE also increased the strength levels after one pass, however, they were reduced with the higher number of passes. The observed softening of the alloy upon multiple ECAE passes was shown to be due to the deformation-induced homogenization and the continuous change in the composition of the constituting phases with the number of passes. In addition, the volume fraction of the hard phase decreased due to dissolution and/or breakage. The impact toughness of the alloy was improved by multi-pass ECAE due to the significant increase in ductility. These findings demonstrate that multi-pass ECAE effectively transforms brittle Zn–Al cast alloys into tougher materials with ductile fracture behavior.

Analysis of the Efficacy of Possessions in Boys' 16-And-Under Basketball Teams: Differences between Winning and Losing Teams

The purpose of this study was to analyze the ball possessions of winning and losing basketball teams in formative years (16 years and under). The sample was 3,897 ball possessions from 24 games of the boys' 16-and-under finals of the Andalusion Championship, Spain. The variables studied were game outcome, participation, and the initiation and end of each ball possession. Winning teams used more fast breaks and fewer set offenses in their ball possessions. Winning teams had shorter ball possessions and more passes and participating players. Dynamic game styles are necessary in youth basketball, focusing on continuously off-balancing the opponent through fast breaks and a high number of passes in set offenses.

Modelling texture evolution in equal channel angular extrusion of bcc materials: effects of processing route and initial texture

A modelling investigation of texture evolution in equal channel angular extrusion (ECAE) of bcc materials with a 90° die via routes A, BA, BC and C is performed using a visco-plastic self-consistent model and assuming idealized simple shear deformation at the intersection plane of the die channels. For each route, the effect of initial texture on texture evolution is examined by simulations from a random, sheet or wire initial texture. The characteristic orientation fibres as found in a single pass are also evident in the multi-pass textures, but the orientation distributions along the fibres are more complete in route A than in the other routes. The initial texture effect persists in the cross shear routes, more so in route A than BC and then BA, up to four to five passes, and afterwards the effect is insignificant and mainly on the texture strength. In route C, however, the initial texture effect remains for every pass studied due to the cyclic shear reversal in every two passes and thus there is retention of the initial texture after even-numbered passes, but as discussed this may not be true in actual ECAE deformation. It is suggested that choice of processing route is the more effective means of controlling texture at a high number of passes. The significance of these texture results is demonstrated by plastic anisotropy seen in texture-based yield loci. The predicted slip activities of the {110}⟨ 111⟩ and {112} ⟨111⟩ slip systems are discussed.