Effect Of Rest Time Research Articles

Effects of Rest Time and Curing Regime on Short- and Long-Term Strength of Class C Fly Ash-Based Alkali-Activated Mortars.

This study investigated how different rest times affect the strength development of fly-ash-based alkali-activated mortar (AAM) over a period of 90 days. Two types of fly ash with varying calcium oxide contents of 37 and 21% were used. The rest times ranged from 2 to 36 h, and three curing methods (ambient, oven, and steam) were tested. The results showed that the rest time significantly influenced the compressive strength of the AAM. The optimal rest time was found to be between 12 and 30 h depending on the curing method and fly ash type. Beyond this range, there were only minor changes in strength. One type of fly ash (FA21) showed higher strength with longer rest times up to 30 h, while the other type (FA37) had the highest strength within a rest time range of from 12 to 24 h. Over the 90-day period, the specimens cured under ambient, oven, and steam conditions at 55 °C (131 °F) experienced increasing strength, but those steam-cured at 80 °C (176 °F) showed a decrease in strength. Analysis revealed the formation of hydration products in FA37, while FA21 showed a reduction in peaks for its main compounds. Additionally, XRD analysis revealed the formation of hydration products (CSH and CASH) in FA37, while FA21 displayed a reduction in peaks for its main compounds. EDS analysis indicated the presence of partially unreacted FA particles, highlighting the impact of curing methods on dissolving FA particles and the formation of geopolymer products (NASH and CNASH) responsible for compressive strength development.

Investigation of Lithium Plating-Stripping Process in Li-Ion Batteries at Low Temperature Using an Electrochemical Model

Lithium plating leads to severe capacity fading and possible safety problems in lithium-ion batteries. Thus, non-destructive detection methods for lithium plating are critical for safe and reliable operation of lithium-ion batteries. In this paper, an electrochemical model incorporated with lithium plating and stripping reactions is established to investigate the lithium plating-stripping process at low temperature. The model is validated at different current rates and temperatures and can successfully predict the characteristic voltage plateau during the rest period after low temperature charging. Modeling analysis helps to develop detection method for lithium plating via differential analysis on the voltage plateau. Distinct local minima can be found in the differential voltage curves of the batteries with plated lithium. The time when the local minima occurs in the differential voltage curves exhibits a linear relationship with the amount of reversible lithium, and thus can be applied as a quantitative indicator for detection of lithium plating. The detection of lithium plating based on differential voltage analysis is further extended to the discharge voltage profiles of the batteries after low temperature charging, considering the effects of rest time.

Effects of rest time after Li plating on safety behavior—ARC tests with commercial high-energy 18650 Li-ion cells

During charging at low temperatures, metallic Lithium can be deposited on the surface of graphite anodes of Li-ion cells. This Li plating does not only lead to fast capacity fade, it can also impair the safety behavior. The present study observes the effect of rest periods between Li plating and subsequent accelerated rate calorimetry (ARC) tests. As an example, commercial 3.25Ah 18650-type cells with graphite anodes and NCA cathodes are cycled at 0°C to provoke Li plating. It is found that the rest period at 25°C between Li plating and the ARC tests has a significant influence on the onset temperature of exothermic reactions (TSH), the onset temperature of thermal runaway (TTR), the maximum temperature, the self-heating rate, and on damage patterns of 18650 cells. The results are discussed in terms of chemical intercalation of Li plating into adjacent graphite particles during the rest period. The exponential increase of capacity recovery and TSH as a function of time suggests a reaction of 1st order for the relaxation process.

Effect of Rest Time in Sprint Training in Young Soccer Players

Effect of Rest Time in Sprint Training in Young Soccer Players

Effects of rest time on discharge response and equivalent circuit model for a lead-acid battery

This work carries out a detailed investigation on the effects of rest time on the discharge response and the parameters of the Thevenin's equivalent circuit model for a lead acid battery. Traditional methods for battery modeling require a long rest time before a discharging test so that a steady state is reached for the open circuit voltage. In a recent work, we developed an algebraic method for parameter identification of circuit models for batteries by applying discharging tests after variable and possibly very short rest time. This new method opens a door to the understanding of the effects of rest time on battery behavior, which may be used for better simulation, analysis and design of battery powered systems for improved battery efficiency and state of health. As we used the new method to extract circuit parameters after different rest times, we observed some unexpected results on the relationship between the rest time and circuit parameters. The initial voltages on the capacitors can be negative and becomes more negative as the rest time is increased. We also observed that the time constants increase with rest time. Relationships between rest time and other parameters are also reported in this paper.

Calendar and PHEV cycle life aging of high-energy, lithium-ion cells containing blended spinel and layered-oxide cathodes

One hundred seven commercially available, off-the-shelf, 1.2-Ah cells were tested for calendar life and CS cycle- and CD cycle-life using the new USABC PHEV Battery Test Manual. Here, the effects of temperature on calendar life, on CS cycle life, and on CD cycle life; the effects of SOC on calendar life and on CS cycle life; and the effects of rest time on CD cycle life were investigated. The results indicated that the test procedures caused performance decline in the cells in an expected manner, calendar < CS cycling < CD cycling. In some cases, the kinetic law changed with test type, from linear-with-time to about t 2. Additionally, temperature was found to stress the cells more than SOC, causing increased changes in performance with increasing temperature.

Micro-Friction and Adhesion Measurements for Si Wafer and TiB 2 Thin Film

An apparatus was specifically developed for micro-friction and adhesion measurements. The force measurement range is 10–2000 μN with a horizontal speed of 10–400 μm/s. The apparatus was tested using a 0.7-mm diameter steel ball as the upper specimen to measure the micro friction and adhesion behaviour of a Si (100) wafer and a TiB 2 film. The effects of rest time, speed, and load were studied. The results show that the maximum static and sliding friction forces of both the Si (100) wafer and the TiB 2 film increase with the load. At low speeds, the influence of speed on the friction force is significant. The adhesion forces of the Si (100) wafer and the TiB 2 film increase with rest time, reaching stable values after about 3000 s. The TiB 2 film has significantly less adhesion and micro friction forces than the Si (100) wafer.

Stress overshoots of organoclay nanocomposites in transient shear flow

Forward and reverse stress growth experiments have been conducted on polypropylene/organoclay nanocomposites containing the same clay loading but characterized by different microstructures. Stress overshoots have been observed for the initial start-up experiments and for the following reverse start-up experiments after a certain rest time. The amplitude of these overshoots increased with the applied shear rate and rest time, but the overshoots occurred at the same strain of about 1.7. The overshoots are related to the structure of the nanocomposites, in particular the magnitude of the overshoots increased with the degree of the clay exfoliation in the matrix. Two models, initially developed for colloidal suspensions and fiber suspensions, have been used to describe the observed phenomena. The overshoots are fairly well predicted by the first (structure network) model and explained by the competing effects of the structure breakdown under flow and reorganization during rest time. However, the model predicts that the shear stress following the overshoot decreases and reaches steady-state too rapidly. The second model developed for ellipsoid suspensions describes quite well the stress overshoots for the initial forward flow, but no effect of rest time is predicted. A modified version has been proposed by adding a molecular diffusivity contribution in the Folgar–Tucker equation. The effect of the particle disorientation is qualitatively predicted, but the kinetics is too slow compared to that deduced from experiments.

Effect of Resting Time of Pigs and Pre-Chilling Time of Thighs on the Veining Defect of Parma Dry-Cured Ham

INTRODUCTIONThe veining defect is usually localized under the skin on the medial side of the ham andit can affect a wide surface of the cut, causing its rejection from the dry-curing process.The defect appears some hours after pig death and becomes particularly visible during hamtrimming. Scientific investigation into this defect has only recently begun, highlightinga relationship between the leanness of the carcass and the visibility of the subcutaneousnetwork of veins; the latter becoming more evident with increasing meat leanness (Russo

Effect of Rest Time on Isometric Muscle Fatigue Measured by Biomechanical Impedance

Muscle fatigue has been studied in various fields. As it accompanied the change of its mechanical characteristics, we had studied the relation between muscle fatigue and its biomechanical characteristics (visco-elasticities) by using biomechanical impedances in case of the isometric contraction with continuous load. It was confirmed, as a result, that the condition of muscle fatigue was estimated from its visco-elasticities. In this study, we adopted the isometric contraction with intermittent load to examine how the rest time affected muscle fatigue. Three sets of 5 minutes 15% MVC (Maximum Voluntary Contraction) load were applied with 1 or 4 minutes interval on an antebrachial flexor muscle. The advancement and the recovery of muscle fatigue were observed in both loaded and unloaded situation. Longer rest decreased the fatiguing speed and caused an obvious recovery. Visco-elasticities were less sensitive to muscle fatigue at its early stage than MFs, which were calculated from surface EMGs.

Adhesion and friction studies of microelectromechanical systems/nanoelectromechanical systems materials using a novel microtriboapparatus

Adhesion and friction impacts the reliability of microelectromechanical systems/nanoelectromechanical systems (MEMS/NEMS) devices. It is essential to study the adhesion and friction properties of the materials that are commonly used in these devices. A novel microtriboapparatus, capable of adopting MEMS components, has been used to perform tribological studies. Calibration of sensors, piezos, and cantilever was performed in this study. The adhesion and friction properties of single-crystal silicon, diamondlike carbon (DLC) films, and hexadecane thiol (HDT) self-assembled monolayers were investigated, and the effect of rest time, velocity, relative humidity, and temperature was studied. The relevant adhesion and friction mechanisms are also discussed. It is found that solid films of DLC and HDT can apparently reduce the adhesion and friction of Si(100). In the case of Si(100), rest time, velocity, relative humidity, and temperature dependence is found, whereas DLC and HDT are insensitive or less sensitive to these parameters. This study suggests that DLC and HDT films can be used as antiadhesion coatings for MEMS/NEMS at different environments and operating conditions.

Nanotribological characterization of molecularly thick lubricant films for applications to MEMS/NEMS by AFM

Molecularly thick perfluoropolyether (PFPE) films are considered to be good protective films for micro/nanoelectromechanical systems (MEMS/NEMS) to reduce stiction, friction, and improve their durability. Understanding the nanotribological performance and mechanisms of these films are quite important for efficient lubrication for MEMS/NEMS devices. These devices are used in various operating environments and their effect on friction, adhesion and durability needs to be clarified. For this purpose, mobile and chemically bonded PFPE films were deposited by dip coating technique. The friction and adhesion properties of these films were characterized by atomic force microscopy (AFM). The effect of rest time, velocity, relative humidity, and temperature on nanotribological properties of these films was studied. Durability of these films was also measured by repeated cycling tests. The adhesion, friction mechanisms of PFPE at molecular scale, and the mechanisms of the effect of operating environment and durability are subject of this paper. This study found that adsorption of water, formation of meniscus and its change during sliding, viscosity, and surface chemistry properties play a big role on the friction, adhesion, and durability of the lubricant films.

Influence of Mixing Conditions and Rest Time on Capillary Flow Behavior of Wheat Flour Dough

ABSTRACTThe capillary flow properties of wheat flour dough were evaluated as a function of mixing time (3–60 min) and rest time (0 or 120 min) after mixing. The description of experimental flow properties was conducted using the classical Bagley approach. Long mixing times were more efficient in decreasing the resistance to elongational flow than in decreasing the resistance to shear flow. The effects of rest time on the rheological properties were estimated by calculating the percent changes in values during resting and appeared to depend on the mechanical history of dough (mixing conditions). The observed changes in rheological properties were related to possible changes in dough structure. Exponential models were used to describe the changes in farinograph consistency (R2 = 0.981) and extensional viscosity (R2 = 0.744 to 0.949) as a function of the mechanical energy input during mixing.

Effect of rest time after application of single overload cycle on fatigue life : Kumar, Rl, Kumar, A. and Singh, K. Eng. Fract. Mech. (1996) 54 (1), 147–153

Research on the basic fatigue formula, the criterion for omitting small loads, the rule for cumulative fatigue damage, and models for predicting the fatigue crack initiation (FCI) life and probability distribution under variable-amplitude loading are comprehensively studied and summarized in the present paper. First, the formula for FCI life is given as a function of the equivalent stress amplitude, and the procedures for investigating overload effects are introduced. Using the above formula to analyze test results of the overload effect on FCI life yields the formula for FCI life containing the overload effect factor, z, which can be adopted to characterize the load interaction effect when Miner's rule is used to compute the cumulative fatigue damage. Fatigue test results and analysis of the underload effect show that the FCI threshold in the FCI life formula can be taken as the criterion for omitting small loads in life prediction and in compilation of the load spectrum. Then, the fatigue damage function is defined, the cumulative fatigue damage can be computed and the FCI life of structure members under variable-amplitude loading can be obtained by using Miner's rule. Procedures for predicting the probability distribution of FCI life or fatigue life are described and examples are introduced. Furthermore, factors affecting the value of z and the applicability of Miner's rule are briefly discussed. Finally, further areas for fatigue research are tentatively proposed. Most interest should be focused on research into generally applicable life prediction models and the approach for fatigue reliability assessment of structure details made of the metals with continuous strain-hardening characteristics, which have been widely adopted in aeronautical engineering, under service load and environments.

Effect of rest time after application of single overload cycle on fatigue life

Effect of rest time after application of single overload cycle on fatigue life

Effect of rest time after application of single overload cycle on fatigue life

Experiments on IS-1020 steel for single tensile overload applied at 12 mm crack length with and without rest time were carried out. The observed retardation effects are presented here and suggested that overload retardation is primarily due to residual compressive stress generated in the crack tip region. On the basis of these experimental results some power laws are developed to predict the decreased number of delay cycles ( N D ) with rest time. The life of the specimen decreased by increasing the rest time after overload. As the magnitude of overload increased the decrease in life is larger for same rest time as compared to lesser overload.