FEM Calculations Research Articles

New method for determining iron power losses in switched reluctance motors with laminated and composite magnetic cores

Power losses from motors and drives can decrease their efficiency. The development of devices with high efficiency is a necessity nowadays, with a view to reducing CO2 emissions. The application of new magnetic materials is one method for increasing the efficiency of motors, although prediction and calculation of the losses in the magnetic circuits of motors are also very important. To reduce the iron losses, iron powder composites are used here instead of Fe-Si laminated steel sheets, in a low-power switched reluctance motor (SRM), and a new method of determining the iron loss in the magnetic circuit is developed. Through the use of new materials in the motor, we can achieve a 19% decrease in the iron loss in comparison to a commercial motor. A comparison of the measurement results for our new method of iron loss prediction showed that the difference is approximately 20-26%, depending on the type of magnetic circuit used for the motor. The usage of soft magnetic composites rather than electrical steel sheets can decrease the loss in magnetic circuits. The results from our new method of determination of iron loss are in good agreement with results of measurements, meaning that it can be applied in a detailed analysis of SRMs. The application of soft magnetic composites in electromagnetic and electromechanical converters is a new method for lowering iron losses in new devices. The determination of such losses in SRMs is still challenging, and the proposed method broadens the state of the art in this area. The method developed here is based on motor current measurements, FEM calculations, and measurements of the magnetisation curves and iron loss for samples according to IEC standards. The results obtained in this work can be used by designers for the development of new kinds of SRMs.

Strength analysis due to thermal loading and tensile loading when metals are bonded by heat-curing adhesives

Heat-curing adhesives are widely used after being cured by heating to a temperature higher than room temperature. To evaluate the adhesive strength, therefore, it is necessary to consider both the thermal stress generated during heat curing and external loads such as tensile stress. Butt joint specimens are essential for evaluating tensile adhesive strength but also thermal strength. The interfacial strength can be discussed from the stress intensity factor (SIF) of a fictitious edge interfacial crack assumed at the interface end. This is because the SIF is controlled by the intensity of singular stress field (ISSF) at the crack-free interface end and a constant term associated with the thermal load. In this paper, a useful thermal SIF solution is proposed by superposing the SIF under tensile stress and the SIF under uniform interface stress associated with thermal loading. This general SIF expression provided under arbitrary material combination can be applied for predicting the tensile strength σc and critical temperature change ΔT without performing new FEM calculations. The usefulness of the expression is confirmed through the adhesive strength of Aluminum/Epoxy butt joint experimentally obtained. Once the critical SIF K1C can be obtained from the tensile strength σc and the temperature change ΔT, the adhesive strength can be expressed asK1C = constant of an assumed fictitious interface, and this can be used to predict critical σc for various temperature change ΔT and for various adhesive bondline thickness h.

Dislocation-based finite element method for homogenized limit domain characterization of structured metamaterials

PurposeHeterogeneous and micro-structured materials have been the object of multiscale and homogenization techniques aimed at recognizing the elastic properties of the equivalent continuum. The proposed investigation deals with the mechanical characterization of the heterogeneous material structured metamaterials through analyzing the ultimate strength using the limit analysis of the Representative Volume Element (RVE). To get the desired material strength, a novel finite element formulation based on the derivation of self-equilibrated solutions through the finite elements devoted to calculating the lower bound theorem has been implemented together with the limit analysis in Melàn’s formulation.Design/methodology/approachThe finite element formulation is based on discrete mapping of Volterra dislocations in the structure using isoparametric representation. Using standard finite element techniques, the linear operator V, which relates the self-equilibrated internal solicitation to displacement-like nodal parameters, has been built through finite element discretization of displacement and strain.FindingsThe proposed work presented an elastic homogenization of the mechanical properties of an elementary cell with a geometry known in the literature, the isotropic truss. The matrix of elastic constants was calculated by subjecting the RVE to numerical load tests, simulated with a commercial FEM calculation code. This step showed the dependence of the isotropy properties, verified with Zener theory, on the density of the RVE. The isotropy condition of the material is only achieved for certain section ratios between body-centered cubic (BCC) and face-centered cubic (FCC), neglecting flexural effects at the nodes. The density that satisfies Zener’s conditions represents the isotropic geomatics of the isotropic truss.Originality/valueFor the isotropic case, the VFEM procedure was used to evaluate the isotropy of the limit domain and was compared with the Mises–Schleicher limit domain. The evaluation of residual ductility and dissipation energy allowed a measurement parameter for the limit anisotropy to be defined. The novelty of the proposal consisted in the formulation of both the linearized and the nonlinear limit locus of the material; hence, it furnished the starting point for further limit analysis of the structures whose elementary volume has been described through the proposed approach.

Hydrogen penetration into the NiTi superelastic alloy investigated in-situ by synchrotron diffraction experiments

Microstructural changes induced by a hydrogen permeation into the NiTi superelastic alloy were investigated in-situ using the X-ray synchrotron diffraction. A new design of an electrochemical cell enabled to uncover time and position dependent processes under a flat alloy surface exposed to the cathodic hydrogen. The diffraction data supported by thermo-elastic FEM calculations helped to quantify an evolution of compressive stresses in the B2 austenitic phase hosting hydrogen atoms. The compressive stress state initiates a formation of martensitic phases starting from the exposed surface layer and advancing into the alloy volume with increasing time of hydrogen charging. We have performed the ab-initio DFT study in order to rationalize volumetric changes associated with variations in the B2 austenite and B19′ martensite lattice parameters. The numerical results also contributed to the identification of a new hydride phase with orthorhombic crystal structure and lattice parameters a = 0.8505 nm, b = 0.7366 nm and c = 0.4722 nm.

Elastoplastic Mechanical Properties and Kinematic Hardening Model of 35CrNi3MoVR.

The existing tensile-compression elastoplastic models are not suitable for varies of materials. An accurate constitutive model of the elastoplastic mechanical properties more suitable for 35CrNi3MoVR was produced by optimizing the existing fitting equations based on uniaxial tensile-compression tests, which are able to describe the elastoplastic stress-strain relation and Bauschinger effect varying with the maximum tensile plastic strain. A UMAT subroutine of the constitutive model in ABAQUS was proposed and conducted for FEM calculation. Hydraulic autofrettage tests were carried out under different pressures on thick-walled 35CrNi3MoVR tubes, and the results were compared with those of FEM calculations to further validate the accuracy of the fitting model. The results show that the constructed power function kinematic hardening model can effectively describe the elastoplastic mechanical properties of 35CrNi3MoVR and can be applied to the autofrettage calculation of this material. The comparison among the calculation results of different models proved that the model proposed in this research has better performance compared to other existing models. Taking the Mises stress at the inner surface of the thick-walled tubes as the evaluation criterion, the error of the power function kinematic hardening model reaches less than 3%, decreasing the error by at least 50%.

Development of Multi-Part Field-Shapers for Magnetic Pulse Welding Using Nanostructured Cu-Nb Composite

Magnetic pulse welding (MPW) employs a strong pulsed magnetic field to accelerate parts against each other, thus forming an impact joint. Single-turn tool coils and field-shapers (FSs) used in MPW operate under the most demanding conditions, such as magnetic fields of 40–50 T with periods lasting tens of microseconds. With the use of conventional copper and bronze coils, intense thermo-mechanical stresses lead to the rapid degradation of the working bore. This work aimed to improve the efficiency of field-shapers and focused on the development of two- and four-slit FSs with a nanocomposite Cu 18Nb brazed wire acting as an inner current-carrying layer. The measured ratios of the magnetic field to the discharge current were 56.3 and 50.6 T/MA for the two- and four-slit FSs, respectively. FEM calculations of the magnetic field generated showed variations of 6–9% and 3% for the two- and four-slit FSs, respectively. The ovality percentages following copper tube compression were 27% and 7% for the two- and four-slit FSs, respectively. The measured deviations in the weld-joining length were 11% and 1.4% in the two- and four-slit FSs, respectively. Compared to the previous experiments on an entirely steel inductor, the novel FS showed significantly better results in terms of its efficiency and the homogeneity of its magnetic field.

BEHAVIOR OF BIKE HANDLEBARS MADE OF BRAIDED CARBON FIBRE

The mechanical design of a bike handlebar made of carbon fibre is presented. Usually carbon fibre handlebars are constituted by unidirectional (UD) carbon fibre prepreg. That configuration usually leads to a light design of the piece but fragile. The proposed design allows the handlebar to withstand as high efforts as a steel bar could. On the contrary the carbon handlebar presents a weight much lower. This can be achieved thanks to the selected carbon braiding. Design, manufacturing on cheap PolyLactic Acid (PLA) 3D printed moulds, FEM calculation and testing of the developed carbon fibre handlebar are shown in this paper. Keywords: handlebar, carbon fibre, numerical simulation, test, braiding

Strength analysis and force distribution in a tensile metal joint

One of the methods of connecting several elements of mechanical structures to form an assembly is bolting. Unlike other types of connections, such as welding or riveting, this type of connection has the advantage of being disassembled, which is why bolted connections are quite common. At the same time, like other types of connections, it is an important structural element that requires additional attention in calculations. The most common calculation of a bolted connection is using analytical formulas. Every day, the requirements for accuracy, speed and versatility of approaches to the calculation of building structures are increasing. In addition, special attention should be paid to the calculation of nodes where structures abut each other, since depending on the operating conditions of the node, different distribution of the NDP is possible, which in turn affects the geometr2ic characteristics and operation of structures. In this regard, we compared the results of the distribution of stresses and forces in the bolt using the finite element method with the use of universal quadrilateral shell FEs, universal spatial eight-node isoparametric FEs, and the semi-analytical finite element method. The obtained results of solving the test case using universal quadrilateral shell FEs and universal spatial eight-node isoparametric FEs allow us to conclude that there is a slight difference in the stress distribution in the spatial formulation of the FEM and SFEM. In addition, based on the FEM and NEM calculations and, accordingly, the calculation according to the DBN, it can be concluded that when calculating according to the DBN standards, an analytical calculation can be used to determine the safety margin of a bolt for simple tasks.

Analysis of the Internal Structure of Brenna Sandstone Samples with Respect to the Differences in Measured Quasi-elastic Moduli

The Young’s modulus and Poisson’s ratio determined for the rocks under uniaxial or triaxial loading conditions represent necessary input parameters for solving many geotechnical tasks. However, these effective stiffness moduli, particularly the Poisson’s ratios, measured on different samples sometimes substantially differ, even for visually compact and macroscopically homogeneous rock. This has been observed for Brenna sandstone, especially under conditions of conventional triaxial extensions. The aim of this study was, thus, to reveal differences in rock structure that could cause such behavior. Several complementary methods were used to investigate the structure of this sandstone: X-ray computed tomography (CT), visual analysis using optical scanning and stereo-microscopy, and a new method combining water jet erosion with these visualization techniques. Analyses of this structure revealed mechanically more resistant compact thick and adjacent thin weak layers. In rock samples, these layers have different patterns and orientations. To demonstrate the influence of layer orientation on effective stiffness moduli measured under different loading conditions, FEM calculations were performed for idealized structural models. The outcomes of this numerical analysis are in qualitative agreement with the results of the loading experiments and the layered structure revealed in the samples. The ability of the proposed method using water erosion to analyze the rock structure in detail was verified. The method offers an interesting alternative to standard visual and X-ray CT techniques. The numerical calculations indicate the importance of latent layered defects in sedimentary rocks for fine measurements of stiffness moduli (especially the Poisson’s ratios) used as inputs for geotechnical applications.

STRENTH OF RC BEAM USING WASTE MATERIAL (plastic)& ADOPTING BUBBLE TECHNOLOGY

The utilization of these wastes(plastic) as an aggregate origin for concrete will help to clean the environment and help a cheaper and renewable aggregates source for construction industries. In the last few years the structure design process is based on superior the materials, their size and fabric, such that it resist under soundness of the structure. In modern Engineering, the formulator requires light weight, extra interpretation and few-cost structures. So, by Structural design in bubble method in use of plastic ball, the best possible structure beam to withstand the service load is achieved. Bubble technology is achieving the best with the so many resource while satisfying the structural beams. In bubble technology researchers used simple prismatic member as calculation of FEM is easy. In paper, they generally explain the simply supported structure domain with multiple point load & uniformely distributed load at whole beams. But in general the loads can be varied throughout the length (L/3, L/5, L/8 etc.). . In this project, M25 concrete mix is used to make beams. The trial mix is tested for compressive strength & split tensile strength. Flexure l test is done is done for 3 and 28 days of curing of the beams Which was actually a difficult problem to minimize the weight. In practical, load on the structure may be inclined, vertical and horizontal which again was a major to help this type of problems. However, after changing some line, all the above problems were solved and gave expected results.

Stress field and interaction forces between dislocations and precipitate distributions

AbstractA computational method is developed for calculation of the stress field and interaction forces between dislocations and precipitates of arbitrary shape and distribution. The internal stress generated by precipitates due to coherency strain is implemented within the discrete dislocation dynamics (DDD) framework. The s‐version finite element method (s‐FEM), which models a precipitate of arbitrary shape using a local mesh is used to calculate coherency stress fields. The method facilitates meshing precipitate volumes of arbitrary geometry, and multiple local meshes can be superimposed at various positions of the global mesh. Accuracy and convergence conditions of the method are established. For a single precipiate, the method is shown to be 3.5 times faster than a standard FEM calculation for the same accuracy, and the gain in speed increases with the number of precipitates. The CRSS of spherical precipitates is found to be higher than disk‐shaped precipitates of the same volume fraction.

Natural frequencies of bars with variable cross-sections

This paper presents the possibility of determining the natural frequency of flexural bars treated as Bernoulli-Euler beams using the Rayleigh method. It is assumed that the shape of the bar axis during vibration is the same as the shape of the deflection line of this bar under continuous load. By comparing the potential energy in the deflected position with the kinetic energy in the undeflected position, it is possible to determine the frequency and period of natural vibration as a function of Young's modulus and material density, as well as the parameters describing the geometric shape of the bar. Examples of solutions for truncated cone and truncated wedge-shaped bars are shown, as well as a solids of revolution with the generatrix described by linear and curvilinear (parabolic, exponential) forms. It applies to both solid and hollow bars, and different types of fixing the ends of the bar. The accuracy of the obtained results (compared with the literature and with the results of FEM calculations) is sufficient for practical applications. The authors also showed the possibility of extending the method to higher frequencies of vibration.

Piezoelectric actuation combined with ultrasound for enhancing drug delivery in gastric mucosa phantom in vitro

In recent years, treatments for gastrointestinal malignant tumors have attracted a lot of attention. However, due to size limitations and the working environment of gastrointestinal peristalsis, traditional treatment methods have poor efficacy. Herein, we proposed a novel drug release method of piezoelectric actuation combined with ultrasound in the endoscope biopsy channel. A bidirectional piezoelectric actuator was manufactured and inserted into the endoscope with an ultrasonic transducer, adjusting the distance between the transducer and the lesion. A gastric mucosa phantom was fabricated and a finite element (FE) model was established for ultrasound thermal calculation. For enhancing the drug release rate, a pulse-echo method was conducted using a Laboratory Virtual Instrument Engineering Workbench (LabVIEW) program for real-time monitoring and feedback. The results of FEM calculations show that the temperature in the phantom can reach the melting-phase transition temperature of the TSL (41 ± 1 °C). The drug release rate can increase from 2.2 × 10−4 mg min−1 to 39.2 × 10−4 mg min−1 with our actuator, the latter is nearly 18 times the former. Furthermore, the drug release rate can be increased to a maximum value of 45.8 × 10−4 mg min−1 by optimizing the driving parameter of our actuator. Therefore, our method has a bright application in targeted drug delivery of major gastrointestinal diseases in the future.

Development of a multi-way coupled discrete-finite element method simulation procedure for modelling soil-passive vibration tool interaction

Among the energy-saving tillage solutions, a promising technology is the application of passive vibration-based soil tillage tools. If the appropriate tillage parameters are applied, a tillage tool which involves vibration-based motion can reduce the draught force and energy requirements of the tillage process while enhancing its quality. The main focus of our research was on developing a coupled discrete-finite element procedure to investigate the interaction between passively vibrating tools and the soil. To validate this method, a soil bin measuring system was constructed to investigate the operation of a highly rigid structural steel (S235) tool along with a more flexible polymethyl methacrylate (PMMA) tool, with the soil bin at working depths of 18, 30, and 42 mm, tool velocities between 28 and 37 mm s−1, in sandy soil with 1 ± 0.1 % dry based moisture content. Soil bin measurements with the highly rigid S235 tool were simulated using the discrete element method (DEM) along with a coupled discrete-finite element (DEM-FEM) procedure, while the soil bin measurements applying the more flexible PMMA tool were simulated using the coupled DEM-FEM procedure. In the case of DEM calculations the hysteretic spring and linear cohesion contact models were applied, and in the case of FEM calculations the transient, linear elastic model was utilised with Rayleigh damping. During the parameter calibration process it was observed that the soil properties depend on depth, therefore a multi-layered soil model was created. After parameter calibration the simulated mean force and deformation values matched the measured values with less than 15 % difference. Furthermore the simulation results also supported the assumption that passively vibrating tillage tools loosen and mix the soil more effectively. Based on these results, it can be concluded that the coupled DEM-FEM procedure enabled the accurate modelling of passively vibrating tillage tools.

Toroidal Nanocrystalline Powder Core With Trapezoidal Cross Section

This paper introduces a toroidal nanocrystalline powder core with a trapezoidal cross section. The non-uniform magnetic flux distribution of toroidal cores with different cross sectional geometries is discussed, the inductance equations are derived, and the geometrical optimisation factor is given in order to retain the highest possible inductance value whilst minimising material usage. A 10-turn coil is wound on the core, with the measured inductance values showing a good match with both FEM and mathematical calculation. The near-field electromagnetic interference (EMI) radiation in close proximity to the inductor is investigated by both FEM and experimental validation, and the toroidal core with a trapezoidal cross section has shown reduced EMI. By adopting a trapezoidal cross section for the toroidal core, a 30 % reduction in material usage and lower EMI are achieved, albeit with a compromise of 14% in inductance.

Investigation on the sandwich aircraft lift surface structural layout with a prefabricated hexagonal cellular core strength characteristics

The possibility of using a new type of core structure for the aircraft lift surface, which is an alternative to the conventional structural layout, was reviewed. The study was carried out using the rudder of the ultralight aircraft "MC-15 Cri-Cri" as the example. A comprehensive comparative analysis of the prototype design with the proposed alternative option was made. The analysis of the studied structural layout variants strength characteristics was carried out using FEM calculations due to the complexity of the geometric shape of the proposed alternative. The prospects of using a prefabricated faceted core structure instead of the classical structural layout of the aircraft lift surface were revealed.

Component test of nickel-based alloys and their welded joints under long-term creep loading

The aim of the paper is to investigate experimentally the creep behavior of improved materials and welded joints at component scale under near-to-service operating conditions, which are promising for the application in highly efficient and flexible future power plants.It focusses on the creep behavior under multiaxial loading of similar and dissimilar welded joints of high temperature resistant nickel-based alloys (A740H, A617B and HR6W) in the temperature range between 650 °C and 750 °C by means of thick-walled-component tests. In this case, the temperature, the external axial load and the internal pressure remain constant during testing.Numerical simulations are used for the estimation of the component axial load in order to induce a meaningful damage evolution without causing a total component failure. The metallographic investigation on the welds A740H/A740H and A617B/A740H indicated no test-related damage. Small cracks in circumferential direction were found on the welds HR6W/HR6W and HR6W/A617B after having reaching 2% local creep strain. The damage mechanism could be classified as a typical creep damage with carbides formation in the grain boundaries and thus grain boundary separations occur, which ultimately lead to the crack formation.In general, the FEM calculation underestimates the axial creep strain on the investigated welds, especially the initial creep strain evolution is not accurately predicted. However, the long-term creep strain evolution could be well predicted by FEM. In this case, the material parameters for the creep law should be further optimized in order to minimize the underestimation.

Study of changes in the structure of zirconium alloy E125 after deformation by radial shear rolling

The rheological properties of the alloy E125 (Zr‑2.5 %Nb) were studied in the range of deformation rates 0.5–15 s‑1 and the temperature range 20–770 °C. A database for computer FEM modeling was created in the specified temperature and speed ranges. In the DEFORM‑3D software package, numerical simulation of a complex radial shear rolling process was carried out using the obtained database. The conditions conducive to the grinding of the alloy structure into an ultrafine‑grained state were determined. Based on the simulation results, a full‑scale experiment of rolling a bar made of alloy E125 on a radial shear rolling mill RSP‑14/40 in 7 passes from a diameter of 37 mm to 20 mm with a total compression in diameter of ε = 85 % was carried out. At the same time, according to the modeling, the total accumulated deformation in the most developed peripheral zone was 27,5 mm/mm. Due to the complex vortex flow of the metal, the distribution of accumulated deformation over the cross section was uneven with a gradient to the axial zone. This should also affect the change in the structure. The changes and the gradient of the structure were studied by the method of EBSD mapping of the sample section with a resolution of 2 mm. The microhardness gradient of the cross section was also investigated by the HV method. The axial and central zones of the sample were studied on the. The structure has a pronounced gradient from the formed equiaxed ultrafine‑grained (UMZ) structure on several outer millimeters of the peripheral section to an elongated rolling texture in the center of the rod. The work shows the possibility of processing with the formation of a gradient structure with enhanced properties for the E125 alloy, and also presents a database for FEM calculations.

Method for characterization of soil electrical resistivity based on Wenner measurements by means of Nelder–Mead algorithm and FEM calculations

Method for characterization of soil electrical resistivity based on Wenner measurements by means of Nelder–Mead algorithm and FEM calculations

A Bézier curve fit to melt pool geometry for modeling additive manufacturing microstructures

This work describes a Metropolis Monte Carlo model for modeling additively manufactured metallic microstructures which employs Bézier curves to formulate melt pool geometry induced by a moving laser heat source. With this formulation, a wide range of melt pool geometries can be modeled and their effects on microstructure morphologies can be evaluated. Melt pool geometries are fit with Bézier curves using melt pool dimensions of width, length, and depth obtained from FEM calculations of the thermal process. Assuming a steady state pool geometry, microstructures are simulated incrementally in the heat affected zone in much the same way an additively manufactured material part is built. The approach is computationally tractable as microstructure simulation is only required in the fusion and heat affected zones, thus requiring less computational resources than would be needed if the entire material/part domain was taken into account. Using the model, microstructures are simulated for LENS™ processed stainless steel. Demonstrations show the model can replicate microstructure morphologies seen in electron beam backscatter diffraction data.