Search

The present research investigates optimizing the impact resistance of functionally graded sandwich structures using experimental and numerical approaches. The low-velocity impact (LVI) responses of functionally graded sandwich composite (FGSC) with different configurations with skin material jute/rubber/jute (JRJ) and core material having epoxy and sea sand by volume fraction of sea sand at 0%, 10%, 20%, and 30%. Sandwich structures were impacted with LVI (5.89, 10.92, and 15.18 m/s), with the impactor dropped from heights of 0.5, 1, and 1.5 m with precompressed spring loads. FGSC samples are considered a deformable body, and the impactor is modeled as a rigid body using commercially accessible dynamic explicit software. The burnout test and weight method were used to test the core's gradience; both methods' results substantially matched, and the variance in gradation could be observed. The proposed sandwich structure characteristics are examined by energy absorption, peak force, energy loss percentage, and coefficient of restitution. Results showed that SC30S provides greater energy absorption and superior damage resistance when tested on LVI. To evaluate the accuracy of experimental findings in predicting the indentation behavior of the sandwich structure, the finite element analysis was used to compare with the experimental results. According to the examination of these proposed FGSC overall performance, they could potentially be employed as sacrificial materials for LVI applications like claddings to shield major structural components. The systematic approach used in this work serves as a standard for choosing and using FGSC effectively for LVI applications. Highlights • Low-velocity impact behavior of sandwich structures was investigated. • Combining flexible skin and epoxy core enhances energy absorption. • Based on impact energy levels, impact damage areas were determined. • Examined sandwich structure advantages in structural and aerospace uses. • In terms of time and cost, the numerical analysis method would be useful. [ABSTRACT FROM AUTHOR]

In this research, the flexural behavior of lightweight biodegradable sandwich panel consisting of the outer green composite facesheets with polylactic acid (PLA) matrix and natural kenaf and cotton fibers, with five various stacking types of standard cardboard egg boxes cores under three‐point bending loads as an environmentally friendly alternative to conventional synthetic sandwich structures is investigated. The stiffness of this structure in bending is also studied using finite element simulations. The thickest specimen absorbed the most energy during flexural testing, however, the specimens containing two egg boxes inside each other were found to have a higher strength and stiffness. Using finite element method simulations to investigate the influence of composite facesheet thickness on flexural loads, it was found that the amount of the load carried by each sandwich specimen with doubled thickness was increased at least by about 50%. By changing the core's material from cardboard egg box to bamboo/PLA or kenaf‐cotton/PLA egg boxes, stiffness and strength and also the energy absorption were significantly increased. Therefore, it is possible to fabricate composite sandwich structures which are light and biodegradable for green environment and has the potential to replace many plastic products and structures that are used in food packaging and medium loads structures applications. [ABSTRACT FROM AUTHOR]

This paper presents the structural behavior of precast concrete sandwich panels (PCSPs) containing recycled tyre crumb rubber core under uni‐axial compression and compared with that containing commonly used expanded polystyrene (EPS) foam. A total of six panels were cast and tested. Two for each category of precast concrete panels that is, solid concrete panel, crumb rubber sandwich panel and foam sandwich panel. Results showed that the ultimate axial load of crumb rubber sandwich panel was found to be 91% of solid concrete panel and also exhibited higher structural response in comparison to foam sandwich panel. It was observed that all panels failed in a similar manner by crushing of concrete at ultimate load. Moreover, a finite element model was developed in ABAQUS using in‐built model of concrete plasticity damage to simulate the ultimate axial capacity of recycled tyre crumb rubber concrete sandwich panel and its failure in uniaxial compression. Analysis showed that the finite element modeling slightly overestimated the experimental results. Furthermore, the experimental test results showed that the recycled tyre crumb rubber can be utilized as an alternate core material in PCSPs without substantially compromising the ultimate strength or any change in structural response. [ABSTRACT FROM AUTHOR]

This paper presents a reluctance-based model considering the frequency-dependent loss nature of the windings for the analysis of three-phase five-leg transformers under grid voltages with direct current (DC) bias. This is very important especially for proper determination of their harmonic current distortion and maximum loading capability (MLC) under DC-biased grid voltage conditions. To figure out the developed model's validity under sinusoidal and DC-biased grid voltage cases, it is comparatively analyzed with the model based on 2D finite element method (FEM). Thus, for the considered transformer type operated under DC bias, the excitation current's harmonic pollution, losses, and reactive power demand parameters are analyzed by using the developed model. Additionally, by regarding these performance parameters, the DC susceptibilities of the considered-type transformer and the single-phase shell-type transformer are comparatively evaluated. Finally, for the studied grid voltage conditions, the effects of two important design considerations as (i) magnetic core material selection and (ii) legs' cross-sectional area sizing on the MLC are investigated. It is concluded from these investigations that under saturation conditions, the transformers, which have the core material with higher permeability or lower reluctance, draw higher excitation current, and have lower MLC ratio when compared to ones having the core material with lower permeability or higher reluctance. However, for unsaturated transformers, which work under DC bias, the case is the opposite to that in saturation conditions. On the other hand, under DC bias conditions, the effect of cross-sectional area sizing on the MLC ratio is much more for the transformer with high permeable magnetic core material with regards to ones with low permeable magnetic core material. [ABSTRACT FROM AUTHOR]

This paper proposes an automatic design method of typical parameters such as number of phases, number of poles, stack thickness, stator outer diameter, rotor outer diameter, and number of turns of a switched reluctance motor from the requirement of the N‐T characteristic. In particular, a specific parameter related to the magnetic saturation is defined in order to arbitrarily determine how much to use the magnetic properties of the iron core material. In the proposed method, the typical motor parameters in order to realize a miniaturized volume which satisfies an input N‐T characteristic are obtained by setting the parameter related to magnetic saturation, maximum electrical frequency, maximum current density, maximum copper loss, conductor slot fill factor, magnetic properties of material, and input voltage. The designed motor is analyzed using the Finite Element Method (FEM) in order to validate the proposed method. [ABSTRACT FROM AUTHOR]

The magnetically coupled three‐phase dual‐active‐bridge (DAB3) DC‐DC converter is highly suitable for high‐power applications. Although the converter has many advantages, the structure, working mode and electromagnetic effect of its key magnetic component—high‐power medium‐frequency three‐phase transformer (MFT3) is more complex, and the capacity, frequency, loss, temperature rise and leakage inductance restrict each other, forming a complex and systematic design problem. This paper focuses on the overall design method and performance of high‐power MFT3. Based on the analysis of steady‐state voltage and current waveforms of DAB3 converter, the expression of harmonic current is derived by using fundamental wave analysis, and the analytical calculation method of copper loss is proposed. According to the piecewise linear flux density waveform excited by six‐step voltage wave, the modified IGSE method is proposed to calculate the core loss. For MFT3 with three‐phase five column core topology, a lumped parameter thermal network model with 14 temperature nodes is established to obtain the temperature rise. The influence of winding arrangement on leakage inductance is analyzed, and the analytical expression of leakage inductance is presented. On this basis, the design method of high‐power MFT3 is proposed based on the free parameter scanning method. A 5 kHz, 15 kW MFT3 model with the nanocrystalline core material is made, and the leakage inductance, core loss, copper loss and temperature rise are extracted by finite element method (FEM) and experiment. The effectiveness of the proposed method is verified by comparing the design results with the FEM simulation and experimental results. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Auxeticity of materials improves several of their mechanical properties, especially shear, impact, and bending resistance. It also improves ability of materials to absorb impact energy as well as the overall stiffness of structures. In this research, authors examine synclastic panels made from novel wood‐based composites. The aim is to determine the force–displacement characteristics during uniaxial compression and obtain the stiffness of the panels. These data allow one to predict the behavior of a panel during two‐axial bending with different support scenarios. Finite element method (FEM) analysis is performed, with the use of model material, to determine the impact of varied facings thickness as well as different types of materials and core structures, on the stiffness of synclastic panels. It is demonstrated that proposed multilayer composites allow forming (technologically difficult) spherical shapes, without additional heat and pressure treatment. The type of an outer layer material strictly determines the usability and ease of two‐axial bending process. Presented composites are interesting materials, that can be adopted into the wood industry as a replacement for traditional materials, e.g., bent plywood. [ABSTRACT FROM AUTHOR]

In LLC resonant converters, litz-wire high-frequency gapped transformer (HFGT) is one of the most critical components, responsible for efficient operation. However, it is also a major contributor to overall weight and volume. Therefore, designers perform multi-objective optimisation for minimising its losses and size, which is itself complex and cumbersome. This usually requires many iterations because the losses vary non-linearly with the decrease in size. The selection of initial-setup parameter (ISP) values, plays a vital role in overall performance improvement of the optimisation. The closer the ISPs to optimal values, the smaller are the iterations required for convergence. Therefore, this study proposes an optimal peak flux density model (OPFDM), considering the voltage excitation waveform, duty cycle, core material parameters, and the response of litzwire to high-frequency. The aim is to obtain an optimised HFGT design through a non-iterative approach by directly estimating optimal values of ISPs through OPFDM. The designed HFGT results in minimised losses and size, while keeping the thermal constraints within limits. Moreover, the impact of frequency and duty cycle on OPFDM is also presented. The proposed model is implemented to design HFGT for 380 VDC/12 VDC LLC converter. Comparison-based analytical, finite-elements method and experimental results validate the model. [ABSTRACT FROM AUTHOR]

This study investigates an advanced finite-element (FE) technique for the evaluation of rotational iron losses based on a time-domain computation, where the bulk conductivity of the core materials is considered. The iron-loss characteristics are discussed for a radial flux permanent magnet synchronous machine (PMSM) for a wind generation application, with closed slots and outer rotor topology. The following factors are taken into account: (i) a real-time rotational iron-loss computation; (ii) the bulk conductivity of the steel laminations; and (iii) the influence of the controller harmonics on the system during transient conditions. The magnetic induction vector locus of each iron component is also discussed, where the magnetic induction is numerically modelled [three-dimensional (3D) finite element analysis (FEA)], computed using multiple magnetic antennae and is also experimentally verified. This comparative study shows a torque–frequency-loss computation that is presented from low to high frequencies (50–800) Hz. The FE model of the total iron losses for the PMSM using both pure sinusoidal and proportional–integral pulse-width modulation currents is studied and experimentally verified on a surface-mounted PMSM. The proposed method of iron losses prediction significantly reduced the rate of error between 3D FEA and experimental data to 1.7%. [ABSTRACT FROM AUTHOR]