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Influence of laser parameters on tensile shear strength of copper welds
摘要： The electrification of the power train in the automotive industry leads to the requirement of electrical connectors with high ampacities. These connectors are often realized using ultrasonic bonding technology. Substitution of ultrasonic welding by laser welding allows an increase of ribbon cross section by a factor of 5 and thus a similar increase of the maximum transferred current. The increased cross section leads to higher loads (at least by a factor of 5) applied to the weld seam during the process. To minimize the heat input, the weld seam strength in shear direction shall be maximized. The influence of different laser parameters on the ultimate tensile shear stress in lap joint configuration is investigated, based on representative specimen geometries (10 × 0.3 mm2). The variable parameters are: laser wavelength (IR around 1050 nm + frequency doubled 515 nm), focal diameters (42–300 μm), different temper conditions of the base material, process parameters (laser power 0.6–4 kW and feed rate 50–800 mm/s), and welding strategies (single pass welding, spatial beam modulation). The material used is Cu-ETP (>99.9% Cu). For all the investigated parameters, the observed failure mode is “fracture in the fusion zone.” The ultimate tensile shear stress for all experiments is around 188 N/mm2 even for parameter changes in the order of one magnitude. This is in contrast to the assumed relation between laser parameters and the mechanical properties. This contrast will be discussed.
关键词： load-carrying capacity,ductile welds,wobbling,fiber laser welding,shear strength
更新于2025-11-28 14:24:20
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Study on mechanism of crack propagation of sapphire single crystals of four different orientations under impact load and static load
摘要： Sapphire has a wide range of applications due to its excellent physical properties. Sapphire is a typical anisotropic material, whose parts are usually employed in the complex conditions, including static and dynamic load. The mechanism of crack propagation under different loading conditions has important significance for successful application of sapphire. In this study, impact and static load tests have been performed on the A-plane, C-plane, M-plane and R-plane of sapphire by the high frequency cyclic impact test device, respectively. The force signals applied to sapphire have been obtained under different test conditions. The crack propagation has been analyzed based on the fracture morphology of specimen. It is found that sapphire will quickly crack and break under impact load, and then enter the fatigue stage. In the static load indentation tests, the force applied to sapphire seems to increase linearly with the linear increase of load, but this relationship is not yet linear in the unloading procedure. The crack propagation is affected by the crystal orientation, which leads to different characteristics of the surface morphology of the different crystal orientations sapphire after fracture. So four different models of crack system are proposed for A-plane, C-plane, M-plane and R-plane respectively. In addition, the three-dimensional morphology of sapphire is observed by a white-light interferometer. It seems that the Hertzian cone crack occurs only on the R-plane sapphire after impact load, but it cannot be sure whether the cone crack occurs when impacting A-, C-, and M-planes sapphire.
关键词： Impact load,Static load,Sapphire,Crystal orientations,Crack propagation,Crack system
更新于2025-09-23 15:23:52
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A study of methods to enhance infrared emissivity of Molybdenum surfaces
摘要： Single crystal Molybdenum is one of the most promising materials for the First Mirror (FM) of ITER optical diagnostics due to its high resistance to erosion under neutral atom bombardment. Other advantages are: low CTE, high thermal conductivity, and advantageous mechanical properties at elevated temperatures. The FMs are normally located in the front-end of ITER port plugs, being subject to volumetric heat loads up to ～1 W/cm3 and higher. Active cooling of Mo mirrors by water or gas flow has limited applicability due to remote handling, integration and risk requirements. An athermal design with radiative cooling was developed for the H-alpha FM unit (FMU) with an all-Mo/TZM structure comprising a TZM housing, two Mo mirrors and the TZM cleaning electrodes. The main idea is to minimize mirror angular displacements and to keep the alignment at temperatures up to ～350 °C. That requires a balance between thermal contact and radiative heat sinks. The most uniform temperature profile is obtained by weak thermal contact between FMU and support structure, but that leads to the highest FM temperature, since the normal as-milled Mo surface has a very low effective emissivity (ε < 0.1 at 200…400 °C). Well-known tools for surface blackening are: enhanced roughness, oxidation, V-grooving, and coatings, which should be analyzed for outgassing rate, thermal radiation and long-term stability in Hydrogen environment. In this study, a number of techniques to enhance Mo surface effective emissivity were tested: V-grooving, detonation spray coating, drilling and surface electro-erosion. Spectral emissivity of the test samples was measured by Bruker Vertex-70 infrared Fourier spectrometer and the effective values were derived for subsequent thermal analyses. Alumina coatings were found to be the most effective tool with ε ≈ 0.8…0.9. However, V-grooving and drilling also provide acceptable results (εeff ≈ 0.25…0.3) and do not require qualification for applicability to ITER. The trade-off between different techniques is discussed in detail.
关键词： Emissivity,ITER,Heat load,Molybdenum,Mirror
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE Power & Energy Society General Meeting (PESGM) - Portland, OR, USA (2018.8.5-2018.8.10)] 2018 IEEE Power & Energy Society General Meeting (PESGM) - An Innovative Methodology for Load and Generation Modelling in a Reliability Assessment with PV and Smart Meter Readings
摘要： With a paradigm shift from centralized to decentralized integration of distributed generation, particularly the photovoltaic (PV) systems made significant impacts on the reliability of power systems. The intermittency of PV and the stochastic nature of load results in a complex interaction of PV and load profiles, in a reliability assessment. In order to reduce the complexities of intermittent power generation interaction with smart meter customer consumptions, this paper presents an innovative methodology for the modeling of intermittent PV generation and smart meter readings in a reliability assessment in a power system. A case study was performed incorporating different scenarios of PV integrations with real-world smart meter load data, and climate projections weather in a UK environment. The results validate robustness of the proposed modeling framework for the reliability assessment in a power system with an accuracy of more than 99.5% and 97.5%, compared with actual generation and load profiles respectively.
关键词： PV modelling,Reliability assessment,Load modelling,Expected energy not supplied
更新于2025-09-23 15:23:52
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Optimal load dispatch of community microgrid with deep learning based solar power and load forecasting
摘要： A deep recurrent neural network with long short-term memory units (DRNN-LSTM) model is developed to forecast aggregated power load and the photovoltaic (PV) power output in community microgrid. Meanwhile, an optimal load dispatch model for grid-connected community microgrid which includes residential power load, PV arrays, electric vehicles (EVs), and energy storage system (ESS), is established under three different scheduling scenarios. To promote the supply-demand balance, the uncertainties of both residential power load and PV power output are considered in the model by integrating the forecasting results. Two real-world data sets are used to test the proposed forecasting model, and the results show that the DRNN-LSTM model performs better than multi-layer perception (MLP) network and support vector machine (SVM). Finally, particle swarm optimization (PSO) algorithm is used to optimize the load dispatch of grid-connected community microgrid. The results show that EES and the coordinated charging mode of EVs can promote peak load shifting and reduce 8.97% of the daily costs. This study contributes to the optimal load dispatch of community microgrid with load and renewable energy forecasting. The optimal load dispatch of community microgrid with deep learning based solar power and load forecasting achieves total costs reduction and system reliability improvement.
关键词： community microgrid,load forecasting,deep learning,Optimal load dispatch,solar power
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe) - Sarajevo, Bosnia and Herzegovina (2018.10.21-2018.10.25)] 2018 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe) - Peak Shaving of a Grid connected-Photovoltaic Battery System at Helmholtz Institute Ulm (HIU)
摘要： High demand of photovoltaic (PV) energy presents a challenge to operation and control of a power system. A Battery Energy Storage System (BESS) is an effective way to shave the peaks and to smooth the load during energy production changes with dynamic power demand. This paper introduces a novel peak shaving method with a PV-battery storage system. The method is tested on a system in Ulm, Germany. The PV-battery system has 31 kWp from a PV array, which is connected to a 76 kWh Li-Ion battery with a peak power of 60 kW. The system has been in operation since May 2015. The threshold on load and State of Charge (SOC) of the battery is applied in the peak shaving method. The average of SOC and actual state of energy of the battery are used for the determination of the change in the threshold value on load.
关键词： Load,Peak shaving,target power,Control system
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Power Electronics and Application Conference and Exposition (PEAC) - Shenzhen, China (2018.11.4-2018.11.7)] 2018 IEEE International Power Electronics and Application Conference and Exposition (PEAC) - A 25kW SiC Universal Power Converter Building Block for G2V, V2G, and V2L Applications
摘要： This paper presents a universal power converter building block (PCBB) with isolation transformer which can perform various functionalities such as charging (G2V), vehicle to grid (V2G) regenerative capability, and vehicle to load (V2L) feature. This converter can output different types of voltage, such as AC or DC, high voltage or low voltage, single-phase or three-phase. With different combinations of modularized PCBB, various voltage and power rating can also be achieved. The control algorithms for each operation mode are explained, including G2V, V2G, and V2L. Simulation results are accompanied to validate its capability. To achieve high power density, SiC MOSFET power module with high frequency switching is adopted along with the isolation transformer of nanocrystalline core. Overall, this paper extends a promising circuit topology of multiple practical and essential features for vehicle electrification.
关键词： Vehicle to Grid (V2G),Dual Active Bridge,Vehicle to Load (V2L),Solid State Transformer,Bidirectional DC/DC,On-board Charger,Electric Vehicle
更新于2025-09-23 15:22:29
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Size-Dependent Buckling and Vibrations of Piezoelectric Nanobeam with Finite Element Method
摘要： In the present paper, a finite element method is used to study the vibrations and buckling of a piezoelectric nanobeam. The beam theory used here is Bernoulli–Euler model. In order to achieve the goal, first, the governing equations of the piezoelectric nanobeam were obtained via the Hamilton principle, based on the higher-order theory such as modified couple stress. The shape functions were embedded in these equations, and the matrix form of the equations was obtained. In other words, the governing equations were discretized by the finite element method. By calculating the matrix form of equations, mass matrices, mechanical stiffness and electrical stiffness of the beam were obtained. It should be noted that when calculating stiffness matrices, first, the definition of a new element must be added to the effects of the electric field in the elements of the beam, and the effects of the gradient of strain should be added in the form of non-classical matrix to the stiffness matrix. With the aid of these critical load matrices, the buckling force and voltage and the natural frequency of the piezoelectric nanobeam have been calculated. Numerical results show that this method can involve the size effects.
关键词： Size effect,Piezoelectric,Buckling voltage,Couple stress theory,Free vibration,Buckling load
更新于2025-09-23 15:22:29
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Performance-Aware Energy Saving for Data Center Networks
摘要： Today’s data center networks (DCNs) tend to have tens to hundreds of thousands of servers to provide massive and sophisticated services. The architectural design of DCNs usually over-provisioned for peaks workloads and fault-tolerance. Statistically, DCNs remain highly under-utilized with typical utilization of around 30%. Network over-provisioning and under-utilization can be exploited for energy-saving. Most research efforts on data center network energy saving focus on how to save maximum energy with little or no consideration to the performance of the residual network. Thus, the DCN performance degraded and the network left vulnerable to sudden traffic surges. In this paper, we have studied energy-saving problem in DCNs while preserving network performance. The problem was formulated as MILP that is solvable by CPLEX to minimize the energy consumed by DCN, meanwhile, safety threshold constraints for links utilization are met. To overcome CPLEX high computational time, a heuristic algorithm to provide practical and efficient solution for the MILP is introduced. The heuristic algorithm uses switches grouping and links consolidation to switch the traffic to a small number of network devices and turn-off unused switches and links. Valiant load-balancing is used to distribute the loads over active links. Simulation experiments using synthetic and real packet traces were conducted to validate the heuristic in terms of energy consumption and network performance. The results show that the heuristic can save up to 45% of the network energy and improves the average imbalance-scores for links and switches by more than 50% with minimal effect on network performance.
关键词： Load Balancing,Energy Saving,Data Center Networks
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE Industry Applications Society Annual Meeting (IAS) - Portland, OR, USA (2018.9.23-2018.9.27)] 2018 IEEE Industry Applications Society Annual Meeting (IAS) - An Approach For Net-Load Management To Reduce Intermittency And Smooth The Power Output On Distribution Feeders With High PV Penetration
摘要： This paper presents a novel ramp rate control and active power smoothing methodology for net-load profiles in large power distribution networks where high Photo Voltaic (PV) penetration levels exist. The novelty is to break large systems into virtual local net-load locations where energy storage systems (ESSs) technologies are installed to mitigate severity of the anticipated shape of system net-loads. The proposed methodology uses Fast Fourier signal Transformation (FFT) to generate reference curves that adequately fit ESS active and reactive power capabilities. Then, a least square minimization (LSM) technique is applied taking both ancillary applications into consideration as well as maintaining State of Charge (SoC) within limits for ESS to function efficiently throughout the day. The methodology is applied on a sample aggregated US power distribution system and a 8000 nodes US power grid using CYMEDist simulation platform. Results show significant level of net-load ramp rate reduction as well as smoothing of fast fluctuations due to both PV intermittency and load changes.
关键词： PV Power Generation,Active Power Management,Net-load Smoothing,Ramp Rate Control
更新于2025-09-23 15:22:29