Variable Loading Tests Research Articles

Fabrication of novel Hydrogel/Epoxy resin composites with Soft-Hard combined Bi-Continuous aqueous load-bearing electrolytes and application in structural energy storage devices

Structural electrolytes with both mechanical and electrochemical properties are of great significance in structural energy storage devices. In this paper, we succeeded to synthesize a novel epoxy resin/hydrogel bicontinuous phase structure electrolyte for the first time by the ingenious design of the hydrophobic curing agent and the substitution of hydrogel for water, and filled the application of bicontinuous electrolyte in aqueous electrochemical energy storage system. The fine structure composition of electrolyte was divided and analyzed in detail by X-ray micro-CT technology. The epoxy resin phase is composed of a reasonable distribution of skeleton structures of various sizes, the largest of which is able to support heavy weights. And a large number of tiny skeletons are distributed to connect the skeletons of different sizes, which improves the three-dimensional interconnection of the epoxy resin phase and makes it excellent mechanical properties (Tensile strength 11.91 Mpa). The large size PVA gel phase constitutes the main pathway for conducting ions. Furthermore, the large-diameter gel phases are coupled in three dimensions with a huge number of micro-diameter gel phases, increasing the number of micro-ion transport channels and decreasing the distance of ion transport with good ionic conductivity (0.15 mS cm−1). Using carbon cloth coated in slurry as the electrode, an integrated structural energy storage bearing device was created in situ using layer brush technology, which exhibited exceptional electrochemical performance during in-situ variable load tests. We have successfully solved the construction of aqueous bicontinuous phase structure electrolyte, which made the application of various water chemistry systems in structural energy storage possible.

Fibrin clot fracture under cyclic fatigue and variable rate loading

Fibrin clot is a vital class of fibrous materials, governing the mechanical response of blood clots. Fracture behavior of fibrin clots under complex physiological load is relevant for hemostasis and thrombosis. But how they fracture under cyclic and variable rate loading has not been reported. Here we conduct cyclic fatigue and monotonic variable rate loading tests on fibrin clots to characterize their fracture properties in terms of fatigue threshold and rate-dependent fracture toughness. We demonstrate that the fracture behavior of fibrin clots is sensitive to the amplitude of cyclic load and the loading rate. The cyclic fatigue tests show the fatigue threshold of fibrin clots at 1.66 J/m2, compared to the overall fracture toughness 15.8 J/m2. Furthermore, we rationalize the fatigue threshold using a semi-empirical model parameterized by 3D morphometric quantification to account for the hierarchical molecular structure of fibrin fibers. The variable loading tests reveal rate dependence of the overall fracture toughness of fibrin clots. Our analysis with a viscoelastic fracture model suggests the viscoelastic origin of the rate-dependent fracture toughness. The toughening mechanism of fibrin clots is further compared with biological tissues and hydrogels. This study advances the understanding and modeling of fatigue and fracture of blood clots and would motivate further investigation on the mechanics of fibrous materials. Statement of significanceFibrin clot is a soft fibrous gel, exhibiting nonlinear mechanical responses under complex physiological loads. It is the main load-bearing constituent of blood clots where red blood cells, platelets and other cells are trapped. How the fibrin clot fractures under complex mechanical loads is critical for hemostasis and thrombosis. We study the fracture behavior of fibrin clots under cyclic fatigue and monotonic variable rate loads. We characterize the fatigue-threshold and viscous energy dissipation of fibrin clots. We compare the toughness enhancement of fibrin clots with hydrogels. The findings offer new insights into the fatigue and fracture of blood clots and fibrous materials, which could improve design guidelines for bioengineered materials.

Experimental studies on dynamic performance of 250-kW alkaline electrolytic system

Alkaline water electrolysis is a mature hydrogen production technology and an important means for future large-scale green hydrogen production and electrical energy storage, while enhancing and optimizing its dynamic characteristic speed is the urgent problem to achieve this goal. In this study, the dynamic response characteristics of the system current, voltage, temperature, hydrogen to oxygen (HTO) and pressure parameters are experimentally investigated at two levels (start-stop and variable load processes) and three-time scales (hours, minutes and seconds) based on the 250-kW industrial alkaline water electrolysis system. The experimental study of cold start (25 °C)→full load (90 °C)→hot shutdown (75 °C)→hot start (70 °C)→full load (90 °C)→cold shutdown (30 °C) revealed that the response time of start-stop process is hourly and temperature is the main limiting factor. The response time of HTO is on the order of minutes based on the variable load test: full load (3500 A, 1.7 MPa)→minimum load (1400 A, 1.7 MPa)→full load (3500 A, 1.7 MPa)→minimum load (800 A, 0.6 MPa). The response of HTO to parameter changes has severe time delay and inertia links, and the latter with significantly longer response time. The response time for different current step is in the order of seconds. This experimental study points out the dynamic performance level of industrial-scale alkaline water electrolysis system at the present stage and provides directions for the optimization of dynamic performance indexes, which is an important guideline for designing control strategies that integrate with renewable energy sources.

Electrohydraulic proportional position and pressure loading control utilizing a state perception and processing method

A new multifunctional proportional control triaxial stress loading apparatus is presented in this study, which can apply an output force on coal rock to simulate the conditions of triaxial stress loading, aiming at solving the problems of excessive consideration of static indices in the design and the incompleteness of the simulation and test verification system for the test parts at the performance analysis stage. This apparatus mainly combines the configuration of a triaxial stress loading system which can meet the stress loading requirements under different operating conditions, with the effective integration of multiple pressure loading operations based on the electrohydraulic proportional control method. In this context, a pressure and position combined control strategy based on the sliding mode is proposed to control the vertical and longitudinal loading hydraulic cylinders. Then, a co-simulation mode including the triaxial stress loading hydraulic system is established to verify the control strategy, system response characteristics and selection of the controller parameters. Furthermore, a multifunctional stress loading experimental platform is developed, and the stress loading characteristics with the proposed strategy are tested and analyzed. The results show that the triaxial stress loading hydraulic system can meet the response characteristics, the fluctuating deviation of the constant loading test can be restricted to 8.5%, the tracking error of the variable loading test is small, the minimum response time of instantaneous loading can reach 2.8 s, and the stress loading effect is noticeable. The experimental platform fully indicates that the stress loading system with the state perception and processing method as the core can meet a variety of verification indices of constant, variable and instantaneous loading tests. This research provides technical support for the smooth, synchronous control and intelligent operation of various types of hydraulic actuator machines.

Influence of post-sintering sizing process on the tribological behaviour of self-lubricating iron-based composite

This paper aims to investigate the effect of post-sintering sizing process on the tribological performance of self-lubricating iron-based composites. Hollow cylindrical specimens were produced by powder metallurgy. Sizing was performed by repressing the as-sintered specimens in a hydraulic press die at three different pressures: 160, 320, and 480 MPa. The tribological characterization was carried out by reciprocating dry sliding tests using a ball-on-cylinder configuration. Variable load tests were performed to evaluate the scuffing resistance, whereas constant load tests were used to assess the wear rate and friction coefficient of the composites. The results show a gradual sealing effect of porosity and lubricants reservoirs and the hardening of the surface metallic matrix (up to 98%). The scuffing resistance was reduced by 72% at higher sizing pressures due to the lower availability of solid lubricants on the surface to maintain the tribolayer. The improved surface finishing and metallic matrix hardness reduced up to 70% of the tribosystem's wear rate at 320 MPa of sizing pressure. Furthermore, a detrimental effect on the wear resistance was noticed for the specimen sized at a higher sizing pressure (480 MPa), showing the importance of optimizing the sizing pressure to improve the tribological behaviour of sintered self-lubricating composites.

Intelligent Diagnosis of Rolling Bearing Fault Based on Improved Convolutional Neural Network and LightGBM

Aiming at the problems of weak generalization ability and long training time in most fault diagnosis models based on deep learning, such as support vector machines and random forest algorithms, one intelligent diagnosis method of rolling bearing fault based on the improved convolution neural network and light gradient boosting machine is proposed. At first, the convolution layer is used to extract the features of the original signal. Second, the generalization ability of the model is improved by replacing the full connection layer with the global average pooling layer. Then, the extracted features are classified by a light gradient boosting machine. Finally, the verification experiment is carried out, and the experimental result shows that the average training and diagnosis time of the model is only 39.73 s and 0.09 s, respectively, and the average classification accuracy of the model is 99.72% and 95.62%, respectively, on the same and variable load test sets, which indicates that the diagnostic efficiency and classification accuracy of the proposed model are better than those of other comparison models.

Enhanced Stray-Load Loss Measurements Through a Zigzag Variable Load Test Approach

This article proposes an enhanced procedure for executing the standard variable load test that allows obtaining high correlation factors for indirectly measured stray-load loss during efficiency tests of induction motors. This helps to achieve the minimum values required by the international standards to consider the variable load test well executed, avoiding unwelcome test repetitions and leading to significant amount of time saved. With the machine at steady-state temperature, the enhanced procedure consists of alternatively applying load levels higher and lower than the rated load, so that the stator winding temperature zigzags around the rated value. Hence, multiple readings can be performed for each load point, having the machine in isothermal conditions. This allows averaging many measurements of the same load point to mitigate the impact of instrumentation and reading errors. The article includes load tests conducted on different induction motor sizes and pole counts, applying both the standard variable load test procedure and the proposed approach. The experimental results show that the proposed technique allows achieving higher correlation factors on the stray-load losses than the standard procedure.

Application of Operating Deflection Shapes to the Vibration-Based Mechanical Condition Monitoring of Power Transformer Windings

Operating deflection shapes (ODSs) are used for visualizing the vibration patterns of a structure. In this study, ODSs are applied to diagnose the mechanical condition of power transformer windings. First, a synchronous calibration measuring system is developed to simultaneously acquire tank vibration signals and excitation voltage signals. To perform the synchronous calibration, the phase of the excitation voltage signals is set as the reference. Next, the no-load test, load test, and variable load test are conducted on a 50-kVA transformer. The histogram of oriented gradient (HOG) and Pearson correlation coefficient (CC) are proposed to describe the differences between the different ODSs. Experimental results show that the ODSs are insensitive to the operating voltage and current, but sensitive to the clamping pressure of the windings. Field results further verify the significant change in the ODS after winding deformation. Finally, the partial ODS, which is suitable for practical transformers, is proposed to locate winding mechanical defects in power transformers. The proposed method can improve the efficiency and accuracy of the vibration-based mechanical condition monitoring of power transformers.

Power output reliability between Garmin® Vector meter and Lode Excalibur Sport® cycle ergometer

Power output can be used to control training load. However, it is important to know if different power meters are reliable, because variations in their measures have direct repercussions on the training program. The aim of this study was to verify the reliability of the power output during two different pedaling protocols (incremental and variable tests) obtained with GARMIN Vector pedals and to compare it with the gold standard LODE Excalibur cycle ergometer. Fourteen male cyclists (30 (6) years of age, maximal power 423 (23) W) performed a maximal test (initial load 100 W with 25 W/min increments) and a variable load test (100–400 W) with the LODE Excalibur cycle ergometer instrumented with GARMIN Vector pedals (coupled on the LODE Excalibur cranks). Student’s t test, intraclass correlation coefficient (ICC), and Bland-Altman analysis were used to evaluate meters’ differences and reliability, respectively. All measures performed in the incremental test (100–400 W) and two measures (100 W, 150 W) of the variable load test showed no power output measurements’ reliability between the GARMIN Vector pedals and the LODE Excalibur cycle ergometer (p < 0.05). The high non-systematic errors in power output measured by the GARMIN Vector pedals (low repeatability) can generate problems when using this equipment for the training periodization in cycling.

Stress-Strain Response Determination during Incremental Step Tests and Variable Loadings on Flat Specimens

For stress-strain response simulations and damage prediction of cyclically loaded mechanical components, it is crucial to determine both the stress-strain and durability curves of the materials sued. Round and flat specimens can be used for this purpose, either following standard recommendations for their geometry or by designing a special geometry which enables special requirements, such as initial cracks of various shapes, attachment of an extensometer, special grips for raised temperatures, and so on. However, especially in the case of flat specimens having a slender shape, buckling can occur before the stress or strain values reach a sufficient magnitude in compression. To avoid this, an anti-buckling support can be attached to the specimen, which prevents the occurrence of buckling. In turn, friction occurs between the specimen and the anti-buckling support, which affects the measurement of the stress. If a special sensor is attached under the anti-buckling support, the friction force can be measured and subtracted from the stress signal, leaving only the stress-strain response of the material under investigation. In this study, two materials were investigated during incremental step and variable loading tests: The aluminium alloy AlMgSi0.5 and a biodegradable polylactide.

Load Test of 3-MW HTS Motor for Ship Propulsion

This paper describes the test facility and load test program for a 3-MW high-temperature superconducting (HTS) motor for ship propulsion. The test facility was used to conduct a constant-load test and a variable-load test. The program consisted of the constant-load test, the variable-load test, and the inspection after tests. During the constant-load test, the motor efficiency was measured at various rotor speeds and torques, and the 100-h cumulative endurance test at 3 MW was completed successful. The variable-load test is composed of three different modes that simulated an emergency maneuver of full astern to stop the ship and avoid a collision, and they have been verified. After the series of tests, the HTS motor was taken apart and an inspection confirmed that there was no problem with the HTS field coils or other main parts. This program demonstrated the reliability of the 3-MW HTS motor for ship propulsion.

Spectrum loading effects on the running-in of lubricated bronze and surface-treated titanium against alloy steel

Lubricated bearing surfaces like those in engine connecting rods commonly experience transient loading in service. These transients can affect friction, wear rate, and regime of lubrication. It was therefore of interest to investigate the effects of periodically-varying loads on candidate bearing materials under non-steady-state conditions and running-in. Light weight titanium alloys could be used for bearing components in fuel-efficient vehicles if their sliding friction and wear characteristics were improved. Candidate surface treatments and coatings for Ti–6Al–4V alloy were tribo-tested under diesel oil lubrication with time-varying loads. A variable load bearing test (VLBT) apparatus was built for that purpose. Baseline tests of a bearing bronze (CDA 932) against alloy steel (AISI 8620) showed that wear during a variable load test was greater than that for the same duration test under a constant load equal to the average of the spectrum loads. Spectrum loading effects on the running-in and steady-state friction and wear behavior of bronze and several Ti alloy surface treatments and coatings are discussed. Results indicate that the progression of observable wear and surface damage may be difficult to quantify under the nearly full-film lubrication regimes as are found in engine bearings. Implications for screening candidate materials and coatings for lightweight engine bearings are discussed.

Emissions characteristics of spark ignition engine operating on lower–higher molecular mass alcohol blended gasoline fuels

Abstract An experimental investigation of emissions characteristics of lower–higher molecular mass alcohol blended gasoline fuels is presented in this paper. The alcohol component of the blends consisted of methanol, ethanol, propanol, butanol and pentanol. Apparatuses used in the present study were a single cylinder spark ignition engine, a hydraulic dynamometer and an exhaust analyzer. The variables that were continuously measured include engine rotational speed (min −1 ), CO, CO 2 , HC and NO emissions. During variable load tests, the results indicate that CO and HC levels in the engine exhaust are reduced with the operation on alcohol gasoline blends. NO emissions with alcohol gasoline blends are higher than with gasoline.

Fueling Kubota RTV900 Utility Vehicles with D2 and B20: Results of In-Use and Laboratory Studies

In-use and laboratory studies were conducted comparing NOX emissions, fuel efficiency, engine wear, engine torque, and engine power for Kubota RTV900 general purpose utility vehicles fueled with Number 2 low-sulfur petroleum diesel (D2) (eight vehicles) and a 20% biodiesel blend (B20) (eight vehicles). These utility vehicles were equipped with Tier IV compliant, 3-cylinder, indirect-injection (IDI) compression-ignition engines (16.1 kW @ 3200 rpm). During the in-use study there were no significant (p < 0.05) differences between fuels for corrected NOX emissions, fuel efficiency, or engine wear metals. However, during the second winter of the study, fuel gelling and filter plugging occurred in the B20 vehicles when the feedstock was switched from soybean oil to beef tallow. For the laboratory study, an identical Kubota D902-E3B engine was mounted on a stationary stand and tested. During these tests, fueling with B20 resulted in significantly (p < 0.05) lower NOX emissions at idle speed (1300 rpm); there were no significant differences in specific NOX emissions during variable-load dynamometer testing. There were no significant differences between D2 and B20 in fuel efficiency for the idle or variable-load tests. Fueling with B20 resulted in small but statistically significant decreases in torque and power at two (2900 and 3000 rpm) of the five load speeds during the variable-load tests. Based on these results, the researchers concluded that B20 is a suitable alternative fuel for Kubota RTV900 and similar utility vehicles. Use of an anti-gel additive is recommended for winter operation of beef tallow-based B20.

Mechanical testing of hydraulic fluids

The antiwear properties of hydraulic fluids are important because hydraulic pump and motor wear is costly. While international hydraulic fluid performance standards continue to be developed, e. g., the ISO/TC28/SC4 committee's draft ISO DIS 11158 ‘Specifications for mineral oil hydraulic fluids’, the normal hydraulic fluid performance specifications represent minimum requirements. Performance specifications for nonmineral oil hydraulic fluids are also being developed. Typically, both the user and the fluid manufacturer possess insufficient objective information about the antiwear properties of special fluids, e. g., environmentally acceptable hydraulic fluids (EAHF) or fire-resistant hydraulic fluids (FRHF) for use in hydraulic equipment such as axial-piston pumps, vane pumps or radial-piston motors. Manufacturer's specifications must therefore be determined. The required lubrication properties can be determined by either laboratory pump tests or a field trial, often at the customer's expense. The lubrication properties of a hydraulic fluid should ideally be determined under conditions that are equivalent to field practice. This paper will discuss the use of the vane pump test and the FZG gear test to gauge ‘recommended’ hydraulic fluid performance; many non-mineral hydraulic fluids, such as environmentally acceptable hydraulic fluids, fire-resistant fluids or synthetic hydraulic fluids, cannot be used in axial-piston systems based only on results obtained with these tests, and additional testing is always required. Proposals are made for testing of such fluids on a variable-load test rig. These tests are done with axial-piston pumps, or other similar displacement systems, and are intended to determine the industrial suitability of non-mineral hydraulic fluids.

Evaluation of an empirical traction equation for forestry tires

Variable load test data were used to evaluate the applicability of an existing forestry tire traction model for a new forestry tire and a worn tire of the same size with and without tire chains in a range of soil conditions. The clay and sandy soils ranged in moisture content from 17 to 28%. Soil bulk density varied between 1.1 and 1.4g cm −3 with cone index values between 297 and 1418 kPa for a depth of 140 mm. Two of the clay soils had surface cover or vegetation, the other clay soil and the sandy soil had no surface cover. Tractive performance data were collected in soil bins using a single tire test vehicle with the tire running at 20% slip. A non-linear curve fitting technique was used to optimize the model by fitting it to collected input torque data by modifying the coefficients of the traction model equations. Generally, this procedure resulted in improved prediction of input torque, gross traction ratio and net traction ratio. The predicted tractive performance using the optimized coefficients showed that the model worked reasonably well on bare, uniform soils with the new tire. The model was flexible and could be modified to predict tractive performance of the worn tire with and without chains on the bare homogeneous soils. The model was not adequate for predicting tractive performance on less uniform soils with a surface cover for any of the tire treatments.

変動荷重ΔＫ減少試験法による疲労き裂伝ぱ機構の研究

In order to predict the most reliable fatigue life under variable loading conditions such as survice environments, a new fatigue test method was developed, and by using it the fatigue crack propagation properties were studied for HT80, SM50B and SUS 304 steels.The test results show that, although no crack closure occurred in both the variable and constant loading tests, the crack propagation rate under the variable loading test condition was much faster than that under the constant loading test condition for all tested alloys especially at low ΔK regions.The maximum acceleration of the crack propagation was dependent of the variable loading amplitude. When the variable load was frequently applied, the crack propagation rate became proportional to second power of ΔK.From these results, it can be said that the new fatigue test method is one of the best methods to predict the most reliable fatigue life under variable loading conditions.

Fatigue crack initiation from notch root (local-strain damage accumulation process on crack initiation)

Local deformation (i.e. local-strain behavior) at the notch root in a crack initiation process in annealed 0.48% carbon steel was investigated by the real-time fine-grid method. The fatigue crack initiation cycle was controlled by local-strain damage accumulation. For a quantitative expression of cumulative fatigue damage, we propose a new parameter, the “average local-strain accumulation value,” Δ \\ ̄ ge 1 , which is defined by the integration of local-strain histories until crack initiation. The relationship between average local-strain accumulation range, Δ \\ ̄ ge 1 , and crack initiation cycles, N c , showed a line whose slope was nearly −0.5 on a log-log coordinate graph. This line we term the “local-strain damage accumulation curve.” The mean stress effect in cases of R = −1, 0 on this line ( Δ \\ ̄ ge 1 vs N c ) was very small or negligible. From the results of variable-loading tests, the linear cumulative damage law based on the local-strain value was also confirmed.