Low Loading Levels Research Articles

High-performance lubricants in powder compaction: An overview of their benefits

In powder metallurgy, compaction is a key step of the process which determines important properties of the parts produced (e.g., density, part weight, surface finish). It follows that compaction must be efficient, stable, and repetitive. Traditional powder metallurgy lubricants include EBS wax, which has been used for decades. New research has uncovered much better products which offer several benefits, including a better lubrication performance. This enables powder mixes to offer comparable ejection performance at lower loading levels. In turn, the performance of the process is improved, due to a more stable die fill and higher apparent density. For parts producers, these benefits can generate additional value through a better quality, a more stable operation and a reduction of scrap rates, which more than compensates the higher costs of these new materials.

Communication—Enhanced Dielectric Constant of Polymer Composites via Regulating Thermal Reduction Treatment Time of Graphene Oxide

The addition of graphene can change the distribution of conductive pathways in the polymer composites and further affect the dielectric properties. In this work, a facile and environmentally friendly method was proposed to enhance dielectric properties by manipulating the reduction extent of reduced graphene oxide (RGO) in polyvinylidene fluoride (PVDF) matrix just through altering the thermal reduction treatment time. Measurement results showed that the electrical percolation occurred as thermal reduction treatment time increased and the conduction mechanism changed into approximate free electron model. RGO/PVDF composites with tailorable dielectric properties were realized with a low filler loading level.

Проблемы стимулирования инновационного развития нефтедобывающих и нефтеперерабатывающих предприятий

The development of corporate forms of management in oil production and oil refining is impossible without the introduction of the latest technical and technological developments that increase the efficiency of production that deepen the processes of processing and further use of oil products, which is currently imposed by the high wear of fixed assets; low level of loading of production capacities; the lack of incentives for the introduction of innovation and the use of NTP achievements, etc. In order to ensure the further innovative development of corporate forms of management in oil production and oil refining, it is necessary to develop a system of stimulation of it, which allows the use of earned funds, both to promote employees and to finance measures that ensure innovative development.

Fatigue crack growth of deformed pearlitic rail steels under multiaxial loading

A new non-standard experiment is developed to measure fatigue crack propagation in the shear crack growth mechanism occurring in rail and crossing parts. Pre-cracked tubular specimens are loaded under cyclic Mode-II and static compressive Mode-I stresses to reproduce those shear crack growth conditions. To investigate the influence of severe plastic deformation as found in the top of rails in track, specimens are pre-deformed using high pressure torsion. For the pearlitic rail steel, the crack path and crack growth behavior changes distinctively with material pre-deformation: In the undeformed material cracks bifurcate under the Mode-II loading and turn into a Mode-I dominated mixed-mode. After severe plastic deformation, the crack propagates in Mode-II at significantly lower load levels without bifurcating. A detailed analysis of the fracture surfaces as well as the correlation of the crack path and microstructural alignment confirm these findings. Therefore, the proposed experimental procedure could provide Mode-II fatigue crack growth data required to predict crack propagation within rolling contact fatigue in rails and crossings.

Creep characteristics and constitutive model of bio-based concrete in aqueous environment

Bio-based materials generally have high porosity, which are prone to biodegradation during the long-term application, especially in a humid environment. To better understand the impact of the aqueous environment on creep performance of bio-based concrete, the effects of the loading method (single-stage and multi-stage), axial force (50 kN, 100 kN, 150 kN), and water pressure (1 MPa, 2 MPa, 3 MPa) on the long-term creep characteristics of bio-based apricot shell concrete are investigated in this study, with a creep duration of up to 1051 h. The results show that water pressure has a significant effect on the creep properties of apricot shell concrete. The creep strain and creep rate of apricot shell concrete gradually decrease with the increase of water pressure, which attributes to the water confining pressure that restrains the propagation of micro-cracks and consequently reduces the creep strain. Moreover, the creep strain and creep rate of apricot shell concrete increase with the increase of axial force. The creep behavior of bio-based apricot shell concrete in low load level is well described by a proposed Burgers piecewise creep model, which is recommended to express the long-term creep behavior of bio-based apricot shell concrete in the aqueous environment.

Intelligent Scheduling Method Supporting Stadium Sharing

At present, the fast-paced work and life make people under great pressure, and people’s enthusiasm for fitness is getting higher and higher, which is in contradiction with the shortage of existing stadiums. So it is considerably significant to open shared stadiums near where citizens live for booking. Therefore, how to allow citizens to book a suitable stadium according to their own needs through mobile phones or computers is an urgent problem to be solved. The booking of the shared stadium can be regarded as a mobile edge computing (MEC) scenario, and the problem can be transformed into task scheduling research under MEC through intelligent scheduling method. When using edge computing (EC) technology for service calculation, the mobile terminal needs to offload the service to the edge computing server. After the server completes the calculation, the calculation results will be sent back to the mobile terminal. Therefore, the calculation time and system energy consumption in the calculation process can be further reduced through task scheduling to improve user satisfaction. In this study, joint scheduling of service caching and task algorithm is proposed to reduce the latency of booking shared stadium request and improve user experience. The simulation results show that the proposed algorithm with edge cooperation idea can achieve lower average system latency at lower load level and can significantly reduce the cloud offloading ratio under low and middle pressure. In addition, the proposed algorithm uses the secondary transfer of more tasks to reduce the pressure of local task running. Finally, the quality of experience (QoE) satisfaction rate under low pressure is guaranteed.

Experimental Investigation and Numerical Simulation of C-Shape Thin-Walled Steel Profile Joints

The versatility of steel, its high resistance in relation to its low mass, as well as the easily accessible technology in the context of using recyclable materials and the low negative impact on the environment represent important arguments in using thin-walled steel profiles to make structures for buildings with a low height regime. This paper presents the results of an experimental program that investigated the behavior of three types of joints in a T-shape form made of thin-walled steel profiles to make shear wall panels or truss beam floors. Due to the small dimensions of the C-profiles of 89 × 41 × 12 × 1 mm, and of the technology of their joining, manufacturers prefer the hinged connections of elements with self-drilling screws. The purpose of the research presented in this paper is to assess the maximum capacity of the joints, the elastic and post-elastic behavior until failure, and also the mechanisms failure. The types of joints analyzed are commonly used in the production of structural systems for houses. The experimental program, which consisted of testing 5 specimens for each type of joint in tension (shear on screws), showed different behavior in terms of load-displacement. The experimental, tested models were analyzed by finite element simulations in an ANSYS nonlinear static structure with 3D solid models. The materials were defined by a bilinear true stress–strain curve obtained after some experimental tensile tests of the steel. The results of the experimental tests showed that the main failure mechanism is a yielding of the holes where the screws were mounted and a shearing of the profile walls. Adding an additional screw on each side increases the capacity of the joints, but not until a yield loss is obtained. In conclusion, it is shown that the solution is suitable for a low level of loading in a static manner; however, additional studies are necessary in order to develop and verify other solutions, thus improving the strength of the connection.

Experimental and analytical study of bond between basalt FRP bars and geopolymer concrete

This paper presents an experimental and analytical study of the bond behaviour of basalt fibre reinforced polymer (BFRP) bars in geopolymer concrete (GPC). Pull-out tests were conducted on ribbed BFRP bars embedded in GPC cubes considering different bar diameters (6, 8 and 10 mm) and embedment lengths (5db, 10db and 15db) to investigate their effects on bond behaviour in terms of bond-slip response, bond strength and failure mechanisms. Results indicate that the chemical adhesion is low, and the bond is mainly dependent on mechanical interlocking which stopped when pullout occurred by local crushing of the GPC with the BFRP ribs remaining undamaged, suggesting high rib shear strength. A theoretical bilinear model was used to describe the local bond-slip relationship and the bond interface properties. There exists nonlinear bond stress distribution, especially for longer embedment lengths and lower load levels with a bond stress concentration factor of 3.9. A parametric study was performed to estimate the influences of bar diameter, embedment length and elastic modulus on maximum pull-out load, based on which the load transfer mechanisms between BFRP bars and GPC were explored, and a formula for predicting the bond strength was proposed in comparison with experimental data.

Porphyrin Photoabsorption and Fluorescence Variation with Adsorptive Loading on Gold Nanoparticles.

Here, we report the photophysical structure–property relationship of porphyrins adsorbed on gold nanoparticles. The number of porphyrin–alkanethiolate adsorbates per particle was adjusted by a post-synthetic thiol/thiolate exchange reaction on 1-dodecanethiolate–protected gold nanoparticles. Even with a low loading level of adsorbates (<10% of all thiolate sites on gold nanoparticles), the shoulder absorption at the Soret band was intensified, indicating the formation of aggregates of porphyrin adsorbates on the nanoparticles. Steady-state fluorescence quantum yields could be adjusted by the bulkiness of substituents at the meso-positions of the porphyrin or the methylene linker chain length, regardless of the porphyrin loading level and the nanoparticle diameter.

Effect of Low-Level Cyclic Loading on Bond Behavior of a Steel Bar in Concrete with Pre-Existing Damage.

Understanding the bond behavior of steel rebar in concrete is important in order to determine the performance of a reinforced concrete structure. Although numerous studies have been carried out by many researchers to develop a robust model for numerical analysis, no consensus has been reached as the bond behavior depends on hysteresis. In this study, the bond behavior of a steel bar in concrete with pre-existing damage is investigated under low-level cyclic loading. Based on the experimental bond stress and slip curve, a numerical model for finite element analysis to simulate the effect of low-level cyclic loading is proposed. The results from the numerical analysis show good agreement with the experimental data, including accumulated damage on stiffness and strength throughout entire load cycles.

Application of Ultrasonic Atomization on a Micro Jet Engine Using Biofuel for Improving Performance

Jet engines are commonly used in aeronautical applications, and are one of the types of gas turbine engines. The circulation of air releases heat energy to expand the volume of hot fluids and impact the turbine wheel to generate power of hot gases. The present study investigates the potential of using ultrasonic atomization technology to assist in the combustion process. An experimental rig was set up to determine the performance of jet engines using ultrasonic droplets. A gas analyzer was used to measure various greenhouse emissions of exhaust gas. The performance of the engine was tested under three load levels (high, medium, low), starting from 10 psi at a steady state, to the minimum value. A significant result was tested for a low value of nitrogen monoxide at the three levels of load, and a specific result was tested for an efficiency value of 2% at the three levels of load. Carbon dioxide was found to decrease at the low load level. The use of an ultrasonic atomization device to assist in the combustion process was useful in achieving engine efficiency of 1% and a reduction of 25% in carbon dioxide exhaust gas.

Evaluation of fatigue performance of cement-treated composites based on residual strength through discrete element method

Fatigue damage is the process of material fatigue failure caused by cyclic loading, and the development of damage degrades the material properties. This paper aims to investigate the fatigue degradation law of cement-treated base (CTB) materials using a discrete element method (DEM) simulation technique. A fatigue evolution model was adopted to characterize the time-dependent fatigue damage under cyclic loading. Virtual semi-circular bending (SCB) fatigue and residual strength tests at different fatigue stages were performed on mesoscale DEM model to evaluate the fatigue damage of CTB material. With residual strength variable, the fatigue damage model was established to reveal the accumulation of damage. The results show that the residual strength evolution nearly appears an exponential correlation with the fatigue stages. In the first stage, the strength degradation is stable and appears as approximately linear. At about 80% of the fatigue life, the degradation rate is significantly accelerated. The residual strength degradation rate is related to the initial stress level and decreases with the increase of stress ratio. At the same fatigue life stage, the greater residual strength attenuation will be generated with a lower load level. The fatigue damage evolution model indicates the fatigue damage accumulation approximately linearly in the early stage and rapidly in the late stage. The late fatigue stage has the main contribution to fatigue failure. The degradation law demonstrates the lower the load level is, the more the damage accumulation at the same fatigue life stage will be, and the corresponding critical damage is greater. Moreover, based on the strength degradation law, a prediction model is established to evaluate the residual fatigue life of pavement base material.

A Simple Two-Stage AC-AC Circuit Topology Employed as High-Frequency Controller for Domestic Induction Heating System

The induction heating process at a domestic level is getting attention nowadays as this power converting topology ensures clean, reliable, flexible, and fast operation. The low input frequency is converted to required regulated high output frequency with indirect and direct power converting approaches. The circuit and control complexity and high conversion losses associated with indirect power converting approaches lower their uses for domestic induction systems. The direct ac-ac power conversion approach is one of the viable solutions for low and medium power level loads, especially for domestic induction heating loads. The circuit complexity, cost, and conversion losses of the direct power converting systems depend on the number of the controlled switching devices as each controlled switch requires one gate driving circuit and one isolated dc supply. Simplified pulse width modulation (PWM) switching control also lower their control effort. Therefore, in this article, a simplified direct ac-ac power converting approach is introduced for a high-frequency domestic induction heating system. Here, the regulation of the high output frequency is achieved by simply cascading the single-phase full-bridge rectifier with a full-bridge inverter with a simple control strategy. The characteristics of the developed topology are validated through simulation results of the Simulink-based platform and practical results of the developed practical setup.

Biaxial Cyclic Loading of Woven Fabrics

For the purpose of this paper, investigations were carried out on specifically designed fabrics with different structural parameters. The biaxial cyclic loading of fabrics and its consequences were investigated. The weave structures with the smallest weave units (plain weave, basket weave 2/2, rib weave 1/1 (2+2) and rib weave 2/2 (1+1) with the same warp and weft density (24 ends/cm and 24 picks/cm) were selected. Biaxial cyclic loadings of fabrics were performed on a newly developed patented device. The influence of the low level of cyclic loadings of fabrics on the change of tensile properties in warp and weft direction was investigated. The results showed that the low level of biaxial cyclic loading can lead to a permanent linear deformation of fabrics. Despite the fact that the forces that cyclically strain the fabric in two directions amount to 10% of the breaking elongation, after a certain number of cycles there is an irreversible deformation and reduction of breaking forces, but sometimes they can result in an increase in breaking forces. It was found that the tensile elongation of fabrics is affected both by thread crimping and by the structural properties of fabrics resulting from changes in the weave.

Ratcheting Examination of 1045 Notched Steel Plates under Low-High and High-Low Sequences

Abstract The present study examines the ratcheting response of 1045 notched steel plates undergoing uniaxial step-loading cycles. Loading steps were applied with different Low-High and High-Low sequences. Ratcheting tests were conducted on notched samples, and average local strains were measured with the use of strain gauges mounted in the vicinity of notch roots. Measured ratcheting strains near notch roots were found as high as 10 times those of tests conducted on unnotched samples. The magnitude of applied cyclic load as well as notch diameter influenced local ratcheting strain at the vicinity of the notch root. The lower nominal load level over the first step in the Low-High sequence substantially promoted ratcheting magnitude over subsequent loading steps with higher load magnitudes. In the High-Low loading sequence, the previous load step with higher magnitude retarded the local accumulated plastic strain of the subsequent step with a lower load level. The plastic zone at the notch root was affected over the loading steps. Microhardness tests were conducted at several positions within a small area of 1.5 by 4 mm near the notch root to map the plastic zone and its progress after each loading step. Microhardness data collected at the notch region verified an enlarged plastic zone over the Low-High loading sequence, while the plastic zone for the High-Low loading sequence was estimated about 50 % smaller in size. Cracking at the notch root and fracture surface taken within the plastic zone were examined through optical and scanning electron microscopies.

Population HIV viral load metrics for community health.

Evidence linking HIV-1 RNA viral load and downstream HIV incidence is strong on both an individual and population level. The risk of HIV acquisition is higher from people with HIV who have high viral load levels compared with low viral load levels. In North American settings, rates of HIV incidence have tracked with viral suppression levels in people who have been diagnosed with HIV (ie, community viral load).1 Universal HIV test-and-treat trials done in sub-Saharan Africa between 2012 and 2018 show that expanding universal HIV testing and antiretroviral therapy (ART) delivery can substantially reduce population viral load, with concomitant reductions in HIV incidence.

Effect of early age loading on the subsequent mechanical and permeability properties of concrete and its mechanism analysis

Modern construction methods often result in concrete structures bearing loads at an early age, which is different from the stress condition under the standard curing in the laboratory. This study experimentally examined effects of different ages and external loads on subsequent mechanical and permeability properties of concrete, and investigated the mechanism of effect from the perspective of internal structure changes. The results show when the early age loading reaches 40% of the current concrete strength, the original internal structure of specimens will be severely damaged, reflecting significant increase in the proportion of mesopores and macropores and obvious connectivity cracks, thus making the mechanical and permeability properties deteriorate, and the earlier the applied load, the greater of this deterioration. However, when loading at 10%, the original internal structure cannot be changed greatly due to the low load level, and some parts of the original pores are even compacted rather than expanded which has little effect on subsequent mechanical and permeability properties of concrete.

Bi-objective dynamic multiprocessor open shop scheduling for maintenance and healthcare diagnostics

This paper addresses a bi-objective dynamic multiprocessor open shop scheduling problem in which the simultaneous objectives of minimizing both the mean weighted flow time and the makespan are considered. This problem is commonly encountered in maintenance and healthcare diagnostic systems. Since it is NP-hard for both objectives, efficient heuristics are needed to quickly generate a set of non-dominated solutions that a decision maker would choose from. For this sake, two metaheuristic approaches based on the non-dominated sorting genetic algorithm (NSGA-II) and the multi-objective grey wolf optimizer (MOGWO) are developed in this paper. Both metaheuristics are hybridized with simulated annealing (SA) local search. Parameter tuning computational experiments are conducted first on a set of 30 small instances from the literature for which Pareto optimal solutions are known. Then, computational experiments on large randomly generated instances are conducted. Computational results for small instances show that the NSGA-II is capable of generating non-dominated solutions that are very close to the optimal Pareto front. Results also reveal that the performance of the NSGA-II is better in most of the cases compared to the MOGWO under different settings of the studied problem for both small and large instances. However, for large instances with large number of workstations and jobs, low loading level and high percentage of busy machines at the beginning of the schedule, the difference in performance between both metaheuristics is minor.

Assessment of the Mechanism of Adhesive Destruction Coatings

Information on deformation of coatings at different loading levels during peeling is given. It is shown that the deformations of the organosilicon coating appear already at the initial stages of loading, and the obtained data correlate with the data on acoustic emission. For a polyvinyl acetate coating at low loading levels, equal to 0.3-0.4 R, the release of acoustic signal energy is not observed. The absence of signals with a large amplitude at loading levels up to 0.7-0.8 R indicates the development of plastic deformations in the contact zone of the coating with the substrate. It was found that early localization of bond breaking in the contact zone, leading to the formation of a fracture focus, occurs in organosilicon coatings KO-168. For PVAC coatings, an abrupt growth of cracks is characteristic, which is preceded by its slow growth. The pseudoplastic mechanism of destruction of PVAC coatings has been established. The influence of the nature of the substrate on the change in the nature of the peeling of the coatings is considered.

Effects of mean load on interlaminar fracture behavior of carbon-epoxy prepreg fabric laminates under Mode I fatigue loading

Mode I delamination fatigue crack growth behavior was investigated in a carbon-epoxy prepreg fabric laminate by evaluating the mean load effects. The fatigue crack growth rate was determined as a function of the maximum Mode I strain energy release rate considering an exponential fitting function according to the Compliance Based Beam Method (CBBM). Classical data reduction techniques were combined with the proposed method, indicating less scatter on results and satisfying basic assumptions of smoothness and continuity for the fatigue crack growth process. The delamination growth rate curve proved to be strongly affected by the applied mean load as the fatigue onset delamination. The number of cycles to onset is higher for lower load levels and, considering the stable propagation region, a higher delamination growth rate was reported for higher load levels. The fractographic analysis has confirmed the effects of cyclic loading and the mean load levels on fracture surfaces. For a higher mean load, failure mechanisms expose static aspects and substantial presence of microcracks at fiber imprints, while, under lower mean load were noticed significant wear and plasticity and featureless fiber tracks.