Asynchronous Load Research Articles

Study on the behavior of small cracks in PA38-T6 (6060-T6) aluminum alloy under multiaxial fatigue loadings

This study investigated the effects of multiaxial cyclic loading on the initiation and propagation of fatigue cracks in an industrial-grade aluminum alloy. Four different loading cases, including 90° out-of-phase and asynchronous loading, were used under the control of strain. The study used cellulose acetate film replication and SEM fractography techniques to increase the understanding of the evolution of fatigue damage on specimen surfaces. The material exhibited a shear damage mechanism with a significant amount of small cracks coalescence. It was explained why, despite a high agreement with the assumptions of the critical plane approach, the predicted fatigue life was overestimated at high loading levels. A correlation between the crack initiation period and overall fatigue life, regardless of loading case, was presented, which has a potential for practical applications.

Load identification in a plate-beam lattice from interior dynamic data

We consider the inverse problem of determining transverse dynamic loads acting on a clamped plate stiffened by two sets of orthogonal beams. Under the assumption of infinitesimal deformation, in the sense that linear elasticity applies, homogeneous isotropic material and negligible beam torsional stiffness, we show that the measurement of the transverse response of the system in an open subset of the mid-plane, and for an arbitrarily small interval of time, is sufficient for the unique determination of the spatial component of the load. The uniqueness result holds for multiple asynchronous loads and suggests a reconstruction procedure, which is used for a numerical validation of the method.

Experimental determination of static characteristics of loads in nodes of a 6 kv power supply system

Subject of research: static characteristics of nodes of 6 kV power supply systems with asynchronous load.
 Purpose of research: experimental determination of static characteristics by active and reactive power, calculation of the reserve coefficient by static stability of a node with asynchronous load.
 Object of research: power supply systems with a complex load, which includes asynchronous motors.
 Main results of research: the results of an active experiment to determine the static characteristics of the load node are presented. The measurements were carried out using devices that record the quality of electricity. Voltage regulation was carried out by the RPN device, the current transformers on the input switch were selected as the connection point of the device. Static characteristics of active and reactive power were constructed using interpolation and extrapolation tools. The critical voltage of the load node is determined. The coefficient of static stability margin is determined.

Decoupling electroplasticity by temporal coordination design of pulse current loading and straining

Multi-mechanism coupled electroplasticity (EP) has not been fully elucidated yet due to the difficulty in eliminating thermal effect, although isothermal, air-cooled, and cryogenic methods are usually used, there are different heating histories from electrically-assisted deformation. The 0–7% pre-strained Ti–6Al–4V alloy is taken as the case material. Based on the two different characteristics of the time-accumulation of thermal effect and the instantaneous nature of the athermal effect, a comparative study is conducted by designing two temporal coordination methods of pulse current and straining, viz., asynchronous loading with high-energy current (ALHC) and synchronous loading with low-energy current (SLLC), where the thermal and athermal effects are highlighted by different loading times, loading and unloading moments of pulse current of different magnitudes. Under ALHC condition, the decreasing yield strength and increasing elongation of the 7% pre-deformed material are observed with increasing current density and loading times, and stress reduction up to 20.7% for yield strength and ductility recovery of maximal 99.1% for elongation are obtained for 14.0 A/mm2 and loading three times. Moreover, stage B of the work hardening rate related to dislocation de-pinning disappears, and the TEM shows an annealing effect that the tangled dislocations are annihilated and rearranged by climbing. Thus, the Joule heat-based thermal effect dominates this condition. Under SLLC condition, the loading and unloading of pulse current of 2.81 A/mm2 in the plastic stage result in an instantaneous drop and rebound in flow stress and work hardening rate (stage B exists), respectively, and are accompanied by the negligible instantaneous temperature rise, while loading at the elastic stage, the overall flow stress and work hardening rate is decreased. It is concluded that the athermal effect can lower the dislocation phonon drag effect and the deformation activation energy, and change the athermal atomic state and dislocation slip mode, which dominates the varied flow stress and elongation. A dislocation dynamics-based physical model is developed by taking into account phonon drag, diffusion activation energy, and deformation activation energy to account for the thermal and athermal effects on dislocations, providing a self-consistent explanation of the above behaviors and mechanisms of the flow stress and ductility under ALHC and SLLC conditions.

Fretting fatigue crack propagation under out-of-phase loading conditions using extended maximum tangential stress criterion

In this paper, a numerical crack growth analysis is conducted by using the Maximum Tangential Stress (MTS) criterion and its extension, which considers the contact stress between the crack surfaces. Moreover, fretting fatigue is a multiaxial non-proportional loading problem, and most components are subjected to asynchronous loads. Therefore, this paper mostly focuses on the influence of loading phase difference (Φ) on the crack propagation behavior. Meanwhile, for the fretting fatigue problem, as there is a relationship between the crack initiation and propagation, the effect of initiation characteristics, including crack initiation position and direction is studied under different loading phase differences using Linear Elastic Fracture Mechanics (LEFM) theory. It is observed that the predicted crack path and lifetime by using the extended MTS criterion and Paris’ law is in good agreement with the experimental results in the literature. It is found that the phase difference has a strong effect on the crack propagation behavior. Furthermore, we found that the crack initiation position has a greater influence on crack propagation behavior than the crack initiation direction.

A Research on the Load Calculation Method in Designing the Traction Power Supply for Integrated Subway – MCR

This paper presents a load calculation method in the design of a traction power supply for integrated subways. Integrated subways have a large carrying capacity and the ability to balance between meeting travel needs and satisfying conditions such as high quality service, cost optimization for railway infrastructure construction, and installation of traction power systems. In an integrated model, the calculation of the traction power supply design is much more complicated than in other stand-alone models. This paper presents the research results on the load calculation method of a traction power supply for the operation of the system. The results show the feasibility of the method when applied to an asynchronous loading system and met the standards of IEEE P1653.2, EN 50328, and IEC 60146-1 in the design of the power supply for permitted overloads according to class VI.

The Design Method of Traction Power Supplies in Integrated Metro Systems

Integrated subway systems have emerged as a new trend that provides the highest quality service at the lowest investment cost by combining the advantages of the two largest passenger transport capabilities during peak hours. Under the integrated model, designing the traction power supply is much more complex than for other independent systems. This article presents the results of a study on the method of calculating the design load of the power supply for the transport operation of the system. Matlab R2017b/Railway Systems is a reliable software for simulating and analyzing some necessary data, and the research results show the feasibility of the method when applied to the case of asynchronous load on the system. The results meet the power supply design standards according to IEEE P1653.2, EN 50328, and IEC 60146-1 overload allowances for class VI, and voltage standards according to EN 50163, UIC 600, and IEC 60850.

VanityX: An Agile 3D Rendering Platform Supporting Mixed Reality

VanityX is a prototype, low-level, real-time 3D rendering and computing platform. Unlike most XR solutions, which integrate several commercial and/or open-source products, such as game engines, XR libraries, runtime, and services, VanityX is a platform ready to adapt to any business domain including anthropology and medicine. The design, architecture, and implementation are presented, which are based on CPU and GPU asymmetric multiprocessing with explicit synchronization and collaboration of parallel tasks and a predictable transfer of pipeline resources between processors. The VanityX API is based on DirectX 12 and native programming languages C++20 and HLSL 6, which, in conjunction with explicit parallel processing, the asynchronous loading and explicit managing of graphic resources, and effective algorithms, results in great performance and resource utilization close to metal. Surface-based rendering, direct volume rendering (DVR), and mixed reality (MR) on the HoloLens 2 immersive headset are currently supported. Our MR applications are directly compiled and deployed to HoloLens 2 allowing for better programming experiences and software engineering practices such as testing, debugging, and profiling. The VanityX server provides various computational and rendering services to its clients running on HoloLens 2. The use and test cases are in many business domains including anthropology and medicine. Our future research challenges will primarily, via the MetaverseMed project, focus on opening new opportunities for implementing innovative MR-based scenarios in medical procedures, especially in education, diagnostics, and surgical operations.

Perspectiva de estudiantes de posgrado sobre la enseñanza dialógica virtual de la escritura

The aim of this study is to characterize the gra¬duate student perspectives on a virtual dialogic teaching initiative oriented to the revision of dissertation chapters written by the students themselves. Within an exploratory qualitative study in-depth interviews are taken with 12 stu-dents from three seminar editions. The analy¬sis shows three relevant categories regarding online dialogic teaching of writing: time ma¬nagement, synchronous exchange and digital technologies. There are three senses of the tem¬poral dimension: times relative to the seminar schedule, to the student daily life, and to the in¬tellectual process of writing practices. Further-more, a combination of heavy asynchronous load with synchronous encounters is valued. Re¬garding the technologies, the students generate environments that take advantages of devices’ technological potential based on the physical environment possibilities and also value the pedagogical relevance of the applications. The category properties show some changes of gra¬duate writing, and its dialogic teaching in the digital world.

Fatigue Life Assessment of Metals under Multiaxial Asynchronous Loading by Means of the Refined Equivalent Deformation Criterion

As is well-known, non-proportional fatigue loading, such as asynchronous one, can have significant detrimental effects on the fatigue behavior of metallic materials by reducing the fatigue strength/fatigue limit and by leading to a fatigue damage accumulation increased with respect to that under proportional loading. In the present paper, the novel refined equivalent deformation (RED) criterion is applied for the first time to estimate the fatigue lifetime of materials, sensitive to non-proportionality, subjected to asynchronous loading under low-cycle fatigue regime. The present criterion is complete since it considers: (i) the strain path orientation, (ii) the degree of non-proportionality, and (iii) the changing of material cyclic properties under non-proportional loading. To evaluate its accuracy, this criterion is applied to examine two different metals (a 304 stainless steel and a 355 structural steel) whose experimental data under multiaxial asynchronous loading are available in the literature. More precisely, the parameters of the criterion are firstly determined by using experimental strain paths, and then the computed refined equivalent deformation amplitude is used to represent the experimental data with a satisfactory accuracy. Finally, a comparison with the results obtained through two other criteria available in the literature is performed, highlighting the good prediction of the present RED criterion.

Parameter Identification of Asynchronous Load Nodes

Asynchronous loads (AL), because of their low negative-sequence resistance, produce the effect of reduced unbalance at their connection points. Therefore, proper modeling of unbalanced load flows in power supply systems requires properly accounting for AL. Adequate models of the induction motor can be realized in the phase frame of reference. The effective use of such models is possible only if accurate data on the parameters of induction motor equivalent circuits for positive and negative sequences are available. Our analysis shows that the techniques used to determine these parameters on the basis of reference data can yield markedly disparate results. It is possible to overcome this difficulty by applying parameter identification methods that use the phase frame of reference. The paper proposes a technique for parameter identification of models of individual induction motors and asynchronous load nodes. The results of computer-aided simulation allow us to conclude that by using parameter identification, we can obtain an equivalent model of an asynchronous load node, and such a model provides high accuracy for both balanced and unbalanced load flow analysis. By varying load flow parameters, we demonstrate that the model proves valid over a wide range of their values. We have proposed a technique for the identification of asynchronous load nodes with such asynchronous loads, including electrical drives equipped with static frequency converters. With the aid of the AL identification models proposed in this paper, it is possible to solve the following practical tasks of management of electric power systems: increasing the accuracy of modeling their operating conditions; making informed decisions when taking measures to reduce unbalance in power grids while accounting for the balancing adjustment effect of AL.

Analysis and Comparison of Performance of Interline Power Flow Controller with Various Control Algorithms under Various Power Stability Problems

The Interline Power Flow Controller (IPFC) is a voltage source converter based Flexible AC Transmission System (FACTS) controller for series compensation and power flow management among a substation's multiline transmission systems. Individual Voltage Source Converters (VSC) can inject reactive voltage that can be adjusted to manage active power flow in a line. This VSC is used to convert DC voltage to AC voltage and the voltage is kept constant in the entire process. In this article, a circuit model for IPFC is constructed, and a simulation of an interline power flow controller is performed, with control performed utilizing a variety of algorithms, including adaptive weighted feedback, gravitational search, BAT, and ANT colony optimization. The system's performance was evaluated in a variety of scenarios, including fault incidence, synchronous load connection, and asynchronous load connection. The design of system and analysis of system has been carried out using MATLAB Simulink in terms of various parameters at point of common coupling like voltage, current, power and power factor.

Application of machine learning methods in multiaxial fatigue life prediction

AbstractThis paper compares the results of multiaxial fatigue life estimation using machine learning methods and classical fatigue models. The fatigue life of PA38‐T6 aluminum alloy under uniaxial, proportional, and non‐proportional loading, including asynchronous loading, is studied. Machine learning methods are trained only on basic loadings, namely, axial, torsional, and 90° out‐of‐phase. The results obtained with the machine learning algorithms, dense neural networks, support vector regression (with linear and radial basis functions), decision tree, random forest, and XGBoost algorithms, are comparable to the results of classical models like Ellyin–Gołoś, Fatemi–Socie, and Ince–Glinka. The best results are achieved for dense neural networks. In that case, they are often slightly more accurate than those obtained using classical methods.

Crack coalescence mechanism of flaw pairs under biaxial loading conditions using additively printed models and photoelastic experiments

Revelation of the mechanism of crack coalescence is critical in understanding the failure of solids. However, specifying the mechanism of crack coalescence is challenging because the stress distribution in a complicated fracture system is complex. A visualization method using 3D printing models and photoelastic techniques was introduced to directly reveal and quantify the evolution of stress concentration at the flaw tips of flaw pairs under different biaxial loading schemes. The results indicate that the evolution of shear stress concentration at the flaw tips along the dip angle of the flaw plays a primary role in crack initiation from the flaw tips. A synchronous loading scheme significantly constrains the development of shear stress concentration at flaw tips; thus, cracks can rarely initiate. In an asynchronous loading condition, shear cracks are primarily observed emerging from the flaw tips due to the variation of shear stress concentration on the flaw tips. The propagation of shear cracks is the main cause of crack coalescence in the bridging region. This phenomenon is more significant in the scenario of a positive bridging angle.

Verification of the Tanaka non-proportional isotropic cyclic hardening model under asynchronous loading

Non-proportional cyclic loading path induces intrinsic strain hardening to the low stacking fault energy materials. The hardening is manifested in increased stress response which underestimation leads to non-conservative life prediction. This study aims to verify the Tanaka non-proportional isotropic cyclic hardening model under a wide spectrum of multiaxial asynchronous loadings. The Tanaka model is coupled with the Chaboche kinematic hardening model for stress path estimation. Modeling results are compared with fatigue experiments for two non-alloyed steel grades, E235 and E355. The Tanaka model improves the performance of the Chaboche model and exhibits its applicability to asynchronous loading.

The Influence of Buckling Mode and Buckling Stability Coefficient of Rigid-Frame Bridge during Construction in Cold Region

The study aims to further standardize the construction process, improve the construction quality, and ensure the stability of infrastructure construction. The continuous rigid-frame bridge is taken as the research object, the finite element model of the bridge body is established by using the beam element, and the overall stability of the rigid-frame bridge is analyzed in the construction and completion stages. Moreover, the stability coefficient and buckling mode are established under different working conditions in each stage, the linear stability variation law is summarized, and the geometric nonlinear stability analysis method is established through the specific data. The nonlinear stability safety factor and buckling mode are obtained, and the influence of wind load and initial defects on the stability of continuous rigid-frame bridge is further explored. The results show that with the increase of the bridge height, the overall stability factor of the bridge is decreasing, and the safety factor of the single-limb thin-walled hollow pier is relatively larger than that of the double-limb thin-walled hollow pier. During the construction, the asymmetric self-weight load caused by the asynchronous load and cantilever pouring has the greatest impact on the stability of the bridge. The stability safety factor of the geometric nonlinear stability analysis method constructed is 0.3% and 1.27% lower than the ideal state, respectively. The stability safety factor of the wind load and the initial defect is 12.65% lower than the ideal state, and the stability safety factor is greatly reduced. The results have important reference significance to ensure the construction safety and overall stability of the bridge.

Modeling of non-proportional multiaxial fatigue under synchronous and asynchronous sinusoidal loading conditions

Multi-axial asynchronous loading presents a unique challenge in fatigue analysis of structural components. A comprehensive investigation is carried out into asynchronous multi-axial fatigue through the framework of path dependent maximum range cycle counting methods (PDMR). Through the investigation two key aspects of asynchronous loading: 1) Unclear cycle definition, and 2) Non-proportionality across different frequency ratios are addressed. The PDMR framework enables a uniform cycle definition and superior correlation of synchronous and asynchronous experimental data. Systematic analysis across a various asynchronous loading is carried out to provide insight into the damage they cause.

Fatigue fracture surface metrology of thin-walled tubular austenitic steel specimens after asynchronous loadings

This paper aims to study the effect of asynchronous axial-torsional strain-controlled loading histories on fracture surface behavior of thin-walled tubular X5CrNi18-10 (304/304L) austenitic steel specimens. Tests under pure axial loading and pure torsional loading are also conducted to better segregate the effect of multiaxiality. The fractures surface topographies were examined through the profiles over the entire surface with the support of an optical measurement system. Then, features of the post-failure fractures were related to the loading conditions and the fatigue life. The outcomes indicate that the multiaxial loading path significantly affects the surface topography. Overall, fracture surface parameters increase for higher fatigue lives. Based on the dialectic relationship, a fatigue damage model able to estimate the fatigue lifetime under asynchronous axial-torsional loading histories has been successfully developed. The fracture surface topology parameters collected from both sides of the same specimen lead to comparable results which reinforces the applicability of the proposed approach.

Fretting fatigue crack initiation behaviour in heterogeneous materials under out-of-phase loading

Fretting fatigue commonly exists at the junction of contacting bodies that are subjected to oscillating force. Meanwhile, the presence of fretting will affect the fatigue lifetime dramatically, especially when the material is heterogeneous as cracks initiate at defects such as inclusions, micro-voids and micro-cracks. Fretting fatigue is a multi-axial non-proportional loading problem, in which most components and assemblies undergo asynchronous loads. Thus, investigating the influence of phase angle (Φ) in heterogeneous materials is quite meaningful. In this study, different locations of micro-voids in three different loading phase angles are taken into consideration. The critical plane approach and quadrant method are adopted to predict the crack initiation lifetime and crack orientation. It is found that the existence of micro-voids significantly affects the damage parameter, when Φ equals 180°, and plays a relatively small effect when Φ equals 90°. In addition, the crack initiation lifetime varies with the location of micro-voids since the location of micro-voids has different effects on the damage parameters.

Design of a High Performance Resonant Controller for Improved Stability and Robustness of Islanded Three-Phase Microgrids

Islanded microgrids face difficulties due to the presence of nonlinearity, asynchronous load, and unknown load dynamics. Moreover, conventional control schemes in the islanded microgrids show slow dynamic response, significant voltage-current oscillations, frequency change, low output power quality, and less reference tracking capability. In this regard, a robust and high performance controller is required against the instability issues related to various load conditions and sudden load changes in the solar photovoltaic (PV)-based solar photovoltaic (PV) based islanded microgrids. This paper presents the design and implementation of a second-order high performance resonant controller for robustness and improving the stability of a solar PV based three-phase islanded microgrid (TPMG) under varying system conditions. The design of the proposed controller is based on a backstepping scheme where control Lyapunov functions are used to find transfer functions. The transfer functions that are obtained by this approach are the transfer functions of a resonant controller with proportional-integral controllers. The performance of the proposed controller is investigated in MATLAB/Simulink. The simulation results demonstrate the robustness of the proposed controller in terms of stability, dynamic responses, voltage-current oscillations, total harmonic distortion, and reference tracking of the TPMG. Moreover, the performance of the proposed controller is illustrated against various load dynamics and sudden load changes. A laboratory-scale experiment verifies the simulation results of the proposed controller.