Increase Of Holding Time Research Articles

FIFA 11+ Warm-up

In an effort to reduce soccer injury rates, the Fédération Internationale de Football Association (FIFA) developed the 11+ warm-up. Widespread uptake of this program remains a challenge despite its effectiveness, but may be increased if positive impacts on physical performance as well as injury risk factors such as neuromuscular control are shown. Effects of the program on physical performance measures and movement control have not been investigated in young female soccer athletes. PURPOSE: To determine the effect of the FIFA 11+ program, compared to a standard warm-up, on movement control, agility, vertical jump (VJ), and core stability in young female athletes after a 5 month indoor soccer season. METHODS: Forty-seven girls from the U10 and U11 divisions of a developmental soccer club were randomized by team to the intervention group (IG) or the control group (CG). IG teams were taught the 11+ warm-up, consisting of 15 exercises broken into 3 sections: 1) slower running drills, 2) strength and plyometric exercises, and 3) faster sprints. The CG continued with their previously planned warm-up. Teams practiced and played 2-3x/week. Blinded assessors conducted pre- and post-season testing of movement control (Landing Error Scoring System), and physical performance (T-test, VJ, and static plank). Two-way Repeated Measures ANOVA analyses were used to compare movement control and physical performance of the groups over time. RESULTS: The IG demonstrated a significantly greater increase in static plank hold time compared to the CG (26.1 ± 38.5 vs. 2.1 ± 37.1 seconds, p=.047). All athletes, regardless of group, improved their LESS score (pre- 6.8 ± 1.6; post-season 6.2 ± 1.4, p=.005) and agility T-test time (pre- 14.2 ± 1.2; post-season 13.8 ± 1.0 seconds, p=.001). No differences were found for the VJ. CONCLUSIONS: The 11+ program, performed over a 5 month indoor soccer season by 9-11 year old soccer players, resulted in improved core stability compared to a regular warm-up, but this did not translate into a significantly greater change in LESS score in the IG. The 11+ program may not be more effective than other dynamic warm-ups at improving neuromuscular control and agility. However, time and space limitations inherent in the indoor soccer environment may have negatively impacted the program’s ability to reach its full potential.

A Transient Liquid Phase Sintering Bonding Process Using Nickel-Tin Mixed Powder for the New Generation of High-Temperature Power Devices

A transient liquid phase sintering (TLPS) bonding process, Ni-Sn TLPS bonding was developed for the new generation of power semiconductor packaging. A model Ni/Ni-Sn/Ni sandwiched structure was assembled by using 30Ni-70Sn mixed powder as the reactive system. The results show that the bonding layer is composed of Ni3Sn4 and residual fine Ni particles with a small amount of Ni3Sn2 at 340°C for 240 min, which has a heat-resistant temperature higher than 790°C. The microstructural evolution and thermal characteristic of the bonding layer for various times at 300°C and 340°C were also studied, respectively. This reveals that, after isothermally holding for 240 min at 300°C and for 180 min at 340°C, Sn has been completely transformed into Ni-Sn intermetallic compounds (IMCs) and the bonding layer is mainly composed of Ni3Sn4 and residual Ni particles. The analysis result for the mechanical properties of the joint shows that the hardness of the bonding layer at 340°C for 240 min is uniform and that the average value reaches 3.66 GPa, which is close to that of the Ni3Sn4 block material. The shear test shows that, as the holding time increases from 60 min to 180 min at 340°C, because of the existence of Sn, the disparity of shear strength between room temperature and 350°C is large. But when the holding time is 180 min or longer, Sn has been completely transformed into Ni-Sn IMCs. Their performances are very similar whether at room temperature or 350°C.

Prediction of the Hot Flow Stress Behavior of AA6063 Including Mg2Si Dissolution

A constitutive model that includes the effect of Mg2Si dissolution during pre-deformation heating and holding has been developed for the prediction of the hot flow stress behavior of AA6063 aluminum alloy. The deformation behavior of homogenized AA6063 aluminum alloy was studied by performing compression tests on a Gleeble 3500 thermomechanical simulator at temperatures ranging from 400 to 550 °C and strain rates from 0.01 to 10 s−1. A one-dimensional model of particle dissolution in spherical coordinate system was developed to determine the Mg-Si solute content during pre-deformation heating and holding. Using the Mg solute content determined from the particle dissolution model, the flow stress during the deformation of AA6063 aluminum alloy at specific temperatures and strain rates was predicted using a modified hyperbolic sine equation. The constitutive model developed was found to be in good agreement with experimental measurements in this study as well as other experimental and model results published in the literature. A 14% increase in flow stress of the alloy was observed for an increase in hold time from 60 to 1500 s at 450 °C. This is due to increased deformation resistance of the alloy as the Mg-Si solute content increases. The modified hyperbolic sine equation developed in this study clearly shows that accounting for Mg-Si solute content improves the ability to accurately predict the flow stress behavior of AA6063 aluminum alloy.

Microstructural evolution during the brazing of Al2O3 ceramic to kovar alloy by sputtering Ti/Mo films on the ceramic surface

Alumina (Al2O3) ceramics were metallized by magnetron sputtering Ti/Mo bilayer films on the surface with a subsequent high temperature sintering and were brazed to Kovar alloy (Fe-Ni-Co) using Ag-Cu eutectic alloy. The Ti/Mo metallization film and the brazing seam microstructures were investigated and the correlation between the Al2O3/Kovar joining strength and the microstructures of the brazing seam was discussed. The results show that the joining strength is related to the thickness of the Ti/Mo adhension layer which depends on the holding time during brazing. The mutual diffusion of the elements at the interface firstly increases the thickness of the adhension layer as the holding time increases and the Mo film acts as a barrier layer to block the diffusion of Ti atoms into the seam. The optimal brazing joining strength of 72.6±5.0MPa could be achieved at a brazing temperature of 810°C for 14min However, if the holding time is further prolonged, Mo atoms will diffuse into the (Ni, Cu) solid solution, resulting in the diffusion of Ti atoms and the adhension layer becoming indistinguishable. Therefore, the intermetallic Ni3Ti forms in the seam and the titanium oxide changes from TiO to Ti2O3 or Ti3O5, which leads to the joint strength decreasing.

Temperature‐dependent uniaxial ratchetting of ultra‐high molecular weight polyethylene

AbstractUniaxial stress‐controlled cyclic tests were performed on the ultra‐high molecular weight polyethylene (UHMWPE) polymer at different temperatures. The effects of stress level, stress rate, peak/valley stress hold and loading history on the ratchetting of the UHMWPE were discussed at different temperatures, and the temperature‐dependence of ratchetting was addressed. It is concluded from the experimental observations that the ratchetting of the UHMWPE depends greatly on the test temperature, and the ratchetting strain increases with the increasing temperature from −20 to 37 °C, but decreases when the temperature is equal to or higher than 60 °C in some cases. The ratchetting is also time‐dependent and increases with the increase of peak stress hold time and the decrease of stress rate. The ratchetting presents apparent loading history dependence, and previous cyclic history with higher stress level remarkably restrains the occurrence of ratchetting in the subsequent cyclic loading cases with lower stress levels, but previous cyclic history with lower stress level hardly influences the ratchetting in the subsequent cyclic loading cases with higher stress levels.

Scheduling at an auction logistics centre with physical internet

Auction logistics centre (ALC) performs transshipment operation on auction products from their inbound-from-supplier transporters to their outbound-to-client transporters with goods trading functions. Major third-party trading service providers have solved technological problems of dealing with millions of simultaneous biddings. But logistics that fulfils the massive and lumpy auction demands in the centre is still challengeable. The lack of process visibility and synchronised schedule has made the congestion on material flow, especially for the trolley loading and auction trading stages. Space resource is wasted and auction products deteriorate as holding time increases. This paper aims to provide a first demonstration of scheduling for auctions of perishable goods using Physical Internet (PI). PI-enabled scheduling is vital to facilitate the decision-making process while ensuring required throughput time with large trading volumes. A PI-ALC is created to automate the flow of information and enable the flexible implementation of scheduling. Following the hybrid flowshop classification, a timely operation scheduling model is developed. A heuristic-based solution approach is proposed to minimise either makespan or value loss using a set of dispatching rules. Simulation experiments show that the dispatching–picking mechanisms have statistically significant interaction impacts on both performance criteria. Decision-makers should strike a balance between minimising makespan and value loss based upon the growth in the frozen buffer size. Finally, the sensitivity analyses justify that schedulers can flexibly select dispatching rules under various demand patterns and operation time windows, as well as system configurations and trolley sizes.

Effect of Holding Time on Microstructure and Properties of Transient Liquid-Phase-Bonded Joints of a Single Crystal Alloy

Experimental investigations have been done to verify the effects of hold time during transient liquid-phase bonding on joint microstructure and mechanical properties of a nickel-based single crystal superalloy. The superalloy was bonded at 1473-1513 K for 0.25-12 h in vacuum environment. A set of parameters, 1513 K for 10 h, was determined as the optimum bonding condition. SEM results revealed that the joint without the completion of isothermal solidification is comprised of four different distinct regions, namely, rapid solidification zone (RSZ), isothermal solidification zone (ISZ), diffusion zone, and base metal. EBSD data indicated that the ISZ across the centerline of the bond has an undifferentiated crystallographic orientation being the same as the base metal. At increasing hold times at 1513 K, RSZ and also borides would disappear and result in an improvement of mechanical properties. Mechanical property tests at elevated temperatures have been done to determine the joints’ quality. High-temperature creep rupture strength (for 100 h at 1373 K) and tensile strength (at 1273 K) of the joints could both attain 90% of those of the base metal.

Microstructure Evolution of Mg-Gd-Y-Zn-Zr Magnesium Alloy During Partial Remelting

The article deals with the research on the microstructure evolution of Mg-Gd-Y-Zn-Zr magnesium alloy through partial remelting process. It aims at finding out what effects the microstructure of semi-solid Mg-Gd-Y-Zn-Zr alloy will result in under different remelting temperatures and holding times. Based on the results, if to raise the remelting temperature and to prolong the holding time, the size of solid grain will tend to expand and its spheroidization degree also begins to show improvement. In addition, the grain shows tendency of coarsening when the holding time increases. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.6483

Effect of Boric Acid on the Properties of Magnesium Slag Powder

This paper studies about the boric acid affect on magnesium slag powder properties. The certain content of 0.05% to 3.0%(weight ratio) boric acid and magnesium slag was sufficiently mixed, the mixed powder is putted into a 20 × 20 × 20mm mold, and using 13 tf pressure to press the powder. The molded sample was placed in a muffle furnace, sintering at different temperatures (1000 °C ~ 1200 °C) and different holding times (1h ~ 6h), when holding time is reached, the sample was cooled naturally. Samples were analyzed. The sintered samples using XRD to study phase analysis and using EDS to research elemental composition and doing SEM for microstructure analysis. The results showed that: the main components of magnesium slag CaO, MgO, Fe2O3, Al2O3, β-C2S, γ-C2S and so on. Magnesium slag with certain content of boric acid, with the sintering temperature, the acid content and the holding time increases, the conversion rate of the β-dicalcium silicate change into γ-dicalcium silicate in magnesium slag is decreases. Without adding boric acid the suppress square material magnesium slags are mess into powder, magnesium slag joined with certain content of boric acid still be a square material, and suppression of the sample becomes more dense.

Effects of Melt Holding Time on as Cast Microstructure and Tensile Properties of Sr-Modified AS31Alloy

Melt holding time has important influences on the modification effect of Sr modified AS31 alloy. Effects of different melt holding time (30min, 60min, 90min and 120min) at 700°C on as cast microstructure and tensile properties both at ambient temperature and elevated temperature of Sr-modified AS31 alloy were studied. There exist polyhedral shape, fine fibers shape and a few Chinese script Mg2Si particles in Sr-modified AS31 alloys. And the average grain size is smallest in Sr-modified AS31 alloys with holding time at 700°C for 30min. The ultimate strength, yield strength and elongation at both ambient temperature and 150°C decrease gradually when the melt holding time increases from 30min to 120min. In the process of smelting of Sr-modified AS31. The burning loss of Sr element becomes more serious with the prolongation of melt holding time, which contributes to the modification effect reducing.

Springback evaluation in hot v-bending of Ti-6Al-4V alloy sheets

In this paper, v-bending of Ti-6Al-4V alloy sheet was conducted from room temperature to 850 °C at a fixed velocity of 0.1 mm/s. Punches with punch radii of 1, 2, 4, and 6 mm, as well as several holding times were used. V-bending and springback behaviors were numerically analyzed with an isotropic hardening model that considered rate-dependent effects. Using a punch radius of 1 mm always leads to negative springback in the temperature range of 550–750 °C. This behavior occurs because an arc formed in the transition side near the end of bending and flattened at the end of bending, leading to an internal bending moment which causes specimen to bow inward after unloading. At a punch radius of 2 mm, positive springback occurs at 300–650 °C, while negative springback occurs at 700–750 °C. At punch radii of 4 and 6 mm, positive springback occurs at 600–750 °C, and the angle decreases as temperature increases. At 850 °C, negative springback occurs at a punch radius of 4 mm due to the decrease in yield strength. At a punch radius of 1 mm, cracking occurs at room temperature and 500 °C, while at 2 mm, it occurs only at room temperature. This discrepancy is ascribed to the greater plastic deformation caused by the smaller punch. As holding time increases, the shape of the deformed specimen more closely matches the desired shape.

Evolution of strain-induced precipitates in a model austenitic Fe–30Ni–Nb steel and their effect on the flow behaviour

The present work investigated the evolution of strain-induced NbC precipitates in a model austenitic Fe–30Ni–Nb steel deformed at 925°C to a strain of 0.2 during post-deformation holding between 3 and 1000s and their effect on the reloading flow stress. The precipitate particles preferentially nucleated on the nodes of the periodic dislocation networks constituting microband walls. Holding for 10s resulted in the formation of fine, largely coherent NbC particles with a mean diameter of ∼5nm, which displayed a cube-on-cube orientation relationship with austenite and caused the maximum increase in the reloading steady-state flow stress. A further increase in the holding time from 30 to 1000s led to the formation of semi-coherent, gradually coarser and more widely spaced particles with a mean diameter of 8nm and above, which led to a gradual decrease in the reloading steady-state flow stress. The holding time increase resulted in progressive disintegration of the dislocation substructure and dislocation annihilation through static recovery processes, which was also reflected by the measured softening fractions. The precipitate particle shape changed during post-deformation annealing from elliptical to faceted octahedral and subsequently to tetra-kai-decahedral.

Effect of hold time on the mechanical fatigue failure behavior of lead-free solder joint under high temperature

In this paper, effect of hold time on the low cycle mechanical fatigue failure behavior of Sn3.0Ag0.5Cu solder joint was investigated. Fatigue tests were conducted utilizing trapezoid waveform with four hold times (0, 2, 5, 10 s) under 348 K. The results show that samples tested under waveform with hold time has the faster maximum stress drop rate comparing to that without hold time. Accordingly, the fatigue life of solder joint is declined with increasing hold time. However, there exists a threshold value, and when the hold time exceeds this value, the fatigue life changes little. Stress relaxation occurs during the hold time, which is completed in a short time under high temperature. Deformation of the solder joint is not uniform, which is concentrated in the solder matrix near the substrate. Micro crack initiates at the corner of the solder joint and propagates in the strain concentrated zone with a direction parallel to the applied load. In addition, Creep voids are observed from the fracture morphology of solder joints tested with hold time, which nucleate at the slip bands and the dendrite boundary tensile ledges. Moreover, the fracture morphology appears an inter-granular rupture mode. However, for solder joints tested without hold time, the rupture mode is trans-granular with some dimples dispersed on the morphology.

Crack growth behavior of 9Cr−1Mo (P91) steel under creep–fatigue conditions

Several components operated at high temperature are also subjected to cyclic loading making crack growth behavior under creep–fatigue conditions a significant concern during design and during service. This is especially the case for components designed for long term service. Creep–fatigue crack growth tests were conducted on a modified 9Cr–1Mo (P91) steel at 625°C under constant load amplitude conditions with various hold times using compact type specimens. The crack growth rates per cycle increased significantly with increase in hold time when crack growth data were plotted with the cyclic stress intensity factor, ΔK. It is shown that the creep–fatigue interactions during crack growth for various hold times are represented better by the (Ct)avg parameter implying that the P91 steel behaves in a creep-ductile manner. The test results are also used for assessing the newly developed American Society for Testing and Materials (ASTM) test standard, E2760-10 for creep–fatigue testing.

Effects of Thermalrate Treatment Technique on Microstructure and Mechanical Properties of Hypoeutectic Al–Si Alloys

In this study, effects of thermalrate treatment (TRT) technique on microstructure and mechanical properties of hypoeutectic Al–Si alloys with addition of Ti were studied. The superheating temperatures of the melt were ascertained based on the DSC result. The results show that when the alloy castings in sand mold were treated with TRT technique at the superheating temperature of 930 °C, α-Al changes into smaller equiaxial crystals from coarse dendrites, and hardness of the alloy increases by 12.7 %, compared to that of the alloy treated with conventional casting technique. In addition, the supercooling increases to 8.5 °C and the characteristic temperatures of eutectic solidification are all the lowest with TRT technique at the superheating temperature of 930 °C. As holding time increases at the pouring temperature of 730 °C in TRT at the superheating temperature of 930 °C, the effects on microstructure and mechanical properties of the alloy casting in sand mold decrease. TRT technique plays a limited role in the alloy casting in permanent mold.

Textural Characteristics of Coconut Shell-Based Activated Carbons with Steam Activation

Activated carbons were prepared from coconut shells by using carbonization at 600 °C for 2 h followed by water steam activation. Effects of activation temperature, hold time and water steam amount on the yield, BET surface area and micropore volume of activated carbons were evaluated. The pore structure of the activated carbon was characterized by N2 adsorption at 77K. Surface area, micropore volume and pore size distribution (PSD) of the carbons were determined by the Brunauer–Emmett–Teller (BET) equation, Dubinin–Astakhov (DA) and the Non-Local Density Functional Theory (NLDFT) methods, respectively. The results show that activated carbons with specific surface area of 1500 m2/g and pore size lower than 2 nm can be produced at 900 °C for 1~2 h. Hold time could be reduced by increasing steam amount and activation temperature, but micropore was enlarged and yield was decreased. Increasing hold time could produce more micropores when steam amount and activation temperature were more appropriate. Pore size distribution shows that activated carbons are microporous dominant.

Effects of Process Conditions on Crack Healing in 30Cr2Ni4MoV Steel during Hot Forging

Internal cracks in 30Cr2Ni4MoV steel were produced by compressing cylindrical sample with drilled hole. In order to consider the effects of deformation degree, temperature, strain rate and holding time on the crack healing, the hot compression tests were performed on Gleeble-1500 thermo-simulation machine under different process conditions. By in situ observation under optical microscope and scanning electron microscope, effects of process condition on crack healing and the behaviours of crack healing were revealed successfully: (1) the result of crack healing improves as the melt temperature, reduction and holding time increase, (2) the effect of crack healing decreases as the strain rate increases. By the energy dispersive spectroscopy, it is also found that the chemical composition of the healed crack area is different from that of the matrix.

Influence of accelerated aging on nanomechanical properties, creep behaviour and adhesive forces of PDMS

In the present study, the nanoindentation creep behaviour of untreated and ultraviolet (UV) treated polydimethylsiloxane (PDMS) samples was investigated, accompanied with adhesion analysis and Fourier transform infrared spectroscopy (FTIR) characterisation. Different hold times, in the range of 5–2000 s (at 10 μN of applied load), were incorporated into each nanoindentation measurement. The increase in hold time results in an increase in change in depth of the indenter in both samples. The error in hardness/modulus due to creep can be neglected for hold times of ∼400 s or more for untreated PDMS and ∼200 s or more for UV treated PDMS. The FTIR obtained data revealed surface deterioration, while the bulk nanomechanical properties were almost identical. A decrease in adhesive energy in the case of UV treated PDMS was observed, indicating that adhesive forces play a significant role at the nanometre scale in the indentation tests (real contact area determination during nanoindentation measurements).

Failure characteristics and life prediction for thermally cycled thermal barrier coatings

The effect of high temperature hold time at 1050°C on thermal fatigue properties and failure characteristics of electron beam-physical vapor deposited (EB-PVD) thermal barrier coated samples (TBCs) was investigated in this work. To clarify this effect, the microstructure, especially that near the interface after certain thermal cycles was characterized by scanning electron microscopy (SEM). Results revealed that with increasing hold time at high temperature, fatigue life first increased then decreased and the failure mode diverted from the interfacial failure mode to one that consisted of both the interfacial failure mode and failure within the TBC. Failure was determined by strain energy density in the ceramic coating and the TGO, the fracture toughness of the ceramic coating, the TGO and the interface, and their correlations with microstructure defects near the interface. Based on analysis of the failure mechanism and the microstructure evolution near the interface, and by combining the simulation modeling of the thermal cycling response, a damage accumulation life prediction model was developed in terms of the TGO thickness. This model, which considered the evolution of the fatigue stress due to the increase in TGO thickness, was able to predict thermal fatigue life of the TBCs/nickel based superalloy system under different thermal cycling histories.

Study on Microstructure of ZnO Lighting Arrester with High Voltage Gradient

To obtain ZnO arrester with high voltage gradient and small size, through the optimizing foundamental formula of arrester and changing sintering temperature and holding time, the electrical properties and microstructure of varistors were studied. The density of varistors was determined by using the mass - volume method , voltage gradient and leakage current of ZnO arrester were measured with Ⅱ Surge Arrester Tester DC parameters, microstructure of varistor ceramics were studied by means XRD and SEM. The experimental results show that with increasement of the sintering temperature, the density of varistors increases, and the voltage gradient continues to decrease and leakage current almost keeps unchangable. As the holding time increases, while as the voltage gradient continues to decrease, and leakage current almost unchanges.