FEM Calculations Research Articles

Numerical simulation and testing of laser-MIG hybrid-welding angle-structure sheets.

Numerical simulation and experimental investigation of laser-MIG hybrid angle-welding low-carbon 1.5-mm-thin SPCC steel sheets are presented in this work. The transient simulation analysis provides an access to the thermal-fluid phenomena prediction by employing a hybrid three-dimensional heat source model. Special attention is paid to the melt dynamic behaviors within the triangular molten pool affected by the Marangoni convection. The simulation results show that the temperature and its gradient distribution are symmetrical with respect to the laser beam, which is validated well by the experimental study. The microstructure of the welded joints was analyzed by scanning electron microscopy and transmission electron microscopy. The results show that the cross-section microstructures of welded joint are mainly composed of the weld zone, narrow heat-affected zone, and substrate. The semielliptic-like molten pool shape is consistent with that of the simulated results. The finer microstructure in the weld bead results from the rapid cooling rate of laser welding confirmed by the FEM calculation. The columnar and equiaxed dendrites are formed in the peripheral and central region of the molten pool, which is beneficial for the improvement of the microhardness.

Interface horizontal shear strength requirement in Ultra-thin whitetopping (UTW) pavement.

Ultra-thin whitetopping (UTW) is a thin (5-10 cm) layer of concrete overlaying over an existing asphalt pavement. This concrete layer is bonded on the asphalt surface. Although UTW has been successful in strengthening asphalt pavement, in some cases, the composite pavement may debond at the interface under the concrete slab due to high shear stress. This paper aims to determine the interface shear strength required for UTW pavement systems using theoretical methods and calibrated numerical models (FEMs). The study analysed 432 pavement scenarios with different slab sizes, thicknesses, and material properties. The results show that higher shear stress occurs when the asphalt modulus is stiffer. The size of the slab, the modulus of the supporting layer, and the asphalt thickness have only a minor effect on the shear stress value. However, the thickness of the concrete slab significantly affects the maximum shear stress in the UTW, with an increase of up to 36.6% when reducing the slab thickness from 100mm to 50 mm. The FEM calculations can be used to determine the required interface horizontal shear strength for UTW.

Boundary Element Method for Tangential Contact of a Coated Elastic Half-Space

We present a formulation of the boundary element method (BEM) for simulating the tangential contact with an elastic half-space coated with an elastic layer with different elastic properties. We use the fast Fourier-transform-based formulation of BEM, while the fundamental solution is determined directly in the Fourier space. Numerical tests are validated by comparison with available asymptotic analytical solutions for a very thin and a very thick layer, as well as with FEM calculations for layers with finite thickness.

Predicting impact strength of perforated targets using artificial neural networks trained on FEM-generated datasets

The paper considers application of artificial neural networks (ANNs) for fast numerical evaluation of a residual impactor velocity for a family of perforated PMMA (Polymethylmethacrylate) targets. The ANN models were trained using sets of numerical results on impact of PMMA plates obtained via dynamic FEM coupled with incubation time fracture criterion. The developed approach makes it possible to evaluate the impact strength of a particular target configuration without complicated FEM calculations which require considerable computational resources. Moreover, it is shown that the ANN models are able to predict results for the configurations which cannot be processed using the developed FEM routine due to numerical instabilities and errors: the trained neural network uses information from successful computations to obtain results for the problematic cases. A simple static problem of a perforated plate deformation is discussed prior to the impact problem and preferable ANN architectures are presented for both problems. Some insight into the perforation pattern optimization using a genetic algorithm coupled with the ANN is also made and optimized perforation patterns which theoretically enhance the target impact strength are constructed.

A semi-analytical solution to the stress intensity factors of branched cracks

Crack branching is ubiquitous in engineering practice, and it often takes place when a crack is subjected to dynamic stress fields, or runs into heterogeneous regions. The mechanical analysis of branched cracks is of great significance in safety analysis and crack-path engineering. In this work we developed a theoretical method to calculate the stress intensity factors (SIFs) of branched cracks. By employing both Schwarz–Christoffel mapping and Muskhelishvili approach, we present an asymptotic approximation for the conformal mapping and SIFs of arbitrary branched cracks are then readily derived. We further demonstrate the convenience of this analytical approach to obtain the SIFs of forked crack as well as four-branched cracks. The theoretical solutions are validated by using finite-element simulations. It is shown that the semi-analytical approach agrees well with the FEM calculations on SIFs. The analytical methods supply a general way to solve the SIFs and therefore the energy release rate of branched cracks. It can then be adopted to understand crack splitting and crack network engineering.

Analysis of structural solutions of reinforced concrete tanks used in agricultural farms

The article presents the types of the most common underground or partially sunken tanks used on farms. The analyzed tanks were designed for the storage of zoonotic fertilizers. Solid or semi-liquid fertilizers should be stored in livestock premises in sealed tanks, protected from leakage into the ground. Basic static schemes of tanks and types of loads acting on tanks were considered. The durability and leak-tightness of the tanks were also addressed, and the insulation used to protect the walls and bottom plate of the tanks was discussed. A computational example presents the values of loads acting on the various elements of the tank at two computational schemes, and compares the results obtained by two computational methods, i.e., the separated plate method and the finite element method. The discrepancies in the obtained results were pointed out. Recommendations were formulated for the design of tanks in terms of meeting the tightness criterion. FEM calculations were made for two cases: with and without consideration of the soil stiffness.

Predictive Assessment of Maximum Contact Pressures in Metal-on-Polymer Hip Joint Implants by Analytical Method and FEM

In more than 90% of hip replacements, the acetabular cup is made of ultra-high molecular weight polyethylene (UHMWPE) and the femoral head is made of stainless steel, cobalt-chromium-molybdenum alloys, titanium or ceramic. The primary factor in evaluating soft-on-hard endoprostheses is the maximum contact pressure as the contact strength of UHMWPE. The level of these pressures is used as a criterion for the correct selection of the femoral head size and radial clearance in the connection during arthroplasty for a specific patient. According to the previously developed new analytical method is proposed for estimating maximum contact pressures in thermo-diffusion nitrided (TDN) titanium GRADE 2 – UHMWPE hip joint implant. The effects of implant femoral head diameter and radial clearance on maximum contact pressures are determined for the average load. Relationships between maximum contact pressures and the above-mentioned parameters are established. A comparison is made between maximum contact pressures estimated by the proposed analytical method and numerical analysis with ANSYS (2D and 3D). The maximum contact pressures calculated using the 2D model have been found to be the lower limit, and the pressures calculated using the 3D model in ANSYS are the upper limit for analytical calculations. Therefore, it should be expected that at thickness of cup ˜ 7…8 mm the contact stresses will not be significantly different than those obtained from the solution by the above method. The developed analytical method can be effectively used for research not only soft-on-hard endoprostheses (metal-on-polymer, ceramics-on-polymer), but also hard-on-hard endoprostheses (metal-on-metal, ceramics-on-ceramics). The results of analytical calculations were also related to the results of FEM calculations known in the literature and their convergence was established.

A Machine Learning Enabled Image‐data‐driven End‐to‐end Mechanical Field Predictor For Dual‐Phase Steel

AbstractThis contribution presents convolutional neural nets (CNN) based surrogate models for prediction of von Mises stress and equivalent plastic strain fields of commonly used Dual‐Phase (DP) steels in automotive applications. The models predict field quantities in an end‐to‐end manner, driven by segmented phase images from real experimental scanning electron micrographs as inputs and FEM calculations as outputs. Hereby, we train CNN models with the U‐net neural network structure based on around 900 elastoplastic FEM simulations of various DP steel microstructure samples under tensile test. The trained CNN models are validated and tested on 250 and 50 samples, respectively. Thereby CNN models are employed sequentially for different tasks , from the real micrographs to segmented phase maps, then from segmented phase maps to stress, strain field predictions, in an end‐to‐end manner. The field predictor model results show good agreement with the test data and convincing performance on unseen microstructural dataset. This work demonstrates the large potential of a Machine Learning model to make accumulatively use of the physics‐based simulation data of large number of boundary value problems with varying microstructure. It recaptures not only the physics, implied in each simulation training data obtained from the partial different governing equations of mechanics, but also the overarching correlation between the microstructure and the stress and strain field responses.

Modelling Manoeuvrability in the Context of Ship Collision Analysis Using Non-Linear FEM

Ship collisions are rare events that may have a significant impact on the safety of people, ships, and other marine structures, as well as on the environment. Because of this, they are extensively studied but events that just precede collision are often overlooked. To rationally assess collision risks and consequences, a ship’s trajectory, and consequently the velocity and collision angle, should be known. One way to achieve this is through accurate modelling of ship manoeuvrability in collision analysis using non-linear FEM (NFEM). The Abkowitz manoeuvring model is implemented in the LS-Dyna software code and is therefore coupled with FEM calculations. Hydrodynamic forces are calculated in each time step of the LS-Dyna calculation and added to the FE model continuously through calculation. The accuracy of the calculations depends on the choice of and values of hydrodynamic derivatives from the Abkowitz model. Abkowitz’s model derives hydrodynamic forces in the Taylor expansion series to provide hydrodynamic derivatives. The application of the procedure is sensitive on higher-order Taylor series members. This article reviews different sets of hydrodynamic derivatives available for the KVLCC2 ship. Each of them is incorporated into the LS-Dyna NFEM solver by a user-made Fortran subroutine, with standard Zigzag and turning manoeuvres simulated and results compared with the experimental tests. As a result, the optimal selection of hydrodynamic derivatives is determined, laying a foundation for assessing the risk of ship collision due to different ship manoeuvres prior to the collision itself.

Numerical Analysis of Cracking Processes in RC Beams without Transverse Reinforcement

The procedure of FEM calculations was presented in the paper. The numerical calculations concerned a simulation of crack distribution and propagation in concrete beams reinforced longitudinally without shear reinforcement. The analysis of the obtained FEM results showed different modes of failure in the beams when shear span-to-depth ratio was a/d = 2.5 and a/d = 1.8. In the analyzed beams, the ratio of longitudinal reinforcement and the mechanical properties of the steel bars were also changing parameters. The FEM results have showed that the shear failure of reinforced concrete beams without transverse reinforcement significantly depends on the ratio and yield strength of longitudinal steel bars. Furthermore, the results of numerical calculation for the beams of a/d = 2.5 were also juxtaposed with experiments performed by the author on two longitudinally reinforced concrete beams.

Seismic Response of Embedded Retaining Wall for Excavation Support

A comparative analysis of the solutions for the seismic impact on a flexible retaining wall designed to strengthen the construction excavation for a multi-storey building in Sofia has been performed. For this purpose, the following FEM calculation models of the interaction of the wall with the surrounding soil body were compiled: (1) a 1D beam-column-spring model of the wall, including spring support in its embedded length and pseudostatic seismic loading of the wall with active earth pressure, determined by the Mononobe-Okabe method; (2) a 2D model of the wall and soil body, with pseudostatic seismic loading in the form of inertial forces applied at the finite element nodes; (3) a time history FE analysis conducted with the accelerograms of two landmark earthquakes from the Balkan Peninsula - the 1976 Vrancea (Romania) earthquake and the 1986 Kalamata (Greece) earthquake. The pseudostatic seismic loading in analyzes (1) and (2) was determined on the basis of the reference pseudostatic acceleration of 2.3 m/s2, determined for the city of Sofia according to the seismic hazard map for Bulgaria. The accelerograms in analysis (3) were scaled to a maximum value of acceleration of PGA = 2.3 m/s2. The physical modelling of the soil body uses the HSM and HSsmall advanced constitutive laws, implemented in the Plaxis software.

Assessment of the Mechanical Properties of Selected PLA Filaments Used in the UAV Project.

The paper presents the evaluation of selected mechanical properties of PLA filaments used in the production of unmanned aerial vehicles (UAV). The manuscript covers a short description of the principles of pattern design and presents a shortened division of incremental manufacturing technologies. The authors present and argue the choice of material that can be used in the UAV drone design. This material has been subjected to experimental tests in order to assess selected mechanical properties that can be successfully adapted to CAD/CAM/CAE systems in order to conduct engineering analyses. The manuscript presents a discussion on the influence of the method of specimen production on selected mechanical properties, as well as the issue of errors made when measuring selected mechanical properties. In addition to the assessment of the mechanical properties of the selected filament, the manuscript indicates how to adapt the determined material constants to the FEM calculation model and presents the effectiveness of topological optimization in engineering design, which allows to reduce the weight of the drone frame by about at least 20% compared with the value originally assumed.

Study of the Blade Shape Impact on the Improvement of Fan Efficiency Based on State-of-the-Art Prototyping Methods

The article discusses the process of designing and testing as well as their results, carried out in order to increase the efficiency of axial fans, implemented as part of the European project INESI. Modifications of existing solutions based on rapid prototyping methods were presented. Scanning, FEM and CFD numerical calculations and 3D printing were used for that purpose. Rapid prototyping involved the use of a steel blade base and 3D-printed complex aerodynamic shapes that were bonded to create completely new blades. After their installation on the new rotor, enabling the angle of attack adjusting, a number of verifying tests of the fan were carried out. The solution was successfully tested and the results are discussed in the article.

Strategy for reducing the carriers transfer antagonistic effect between heterojunction and plasmonic effect and weakening photocorrosion of Cu2O for excellent photocatalytic bacteriostasis.

Heterogeneous catalysis composed of plasmonic metal and semiconductor has been utilized to tune local surface electron density in MOA (Molecular oxygen activation). However, there is a severe antagonistic effect between Schottky junction carriers and SPR (Surface Plasmon Resonance) induced hot carriers transfer routers when metal and semiconductor are both excited to dramatically reduce carriers separation efficiency. Hence, a highly effective photocatalytic antifoulant obtained by V-CN (carbon nitride with nitrogen vacancies) in-situ loading Cu2O and Ag nanoparticles (Cu2O/Ag/V-CN) was introduced to promote MOA to assist the metal ions sterilization. The DFT calculations (Density Functional Theory) and FEM calculations (Finite Element Method) intuitively proved the photocatalytic antifoulant belonged to a ternary Z-scheme heterojunction and could visibly weaken the antagonistic effect of hot carriers and Schottky carriers transport routes. The delocalized electron structure caused by V-CN and the effective electron mediator of Ag were the key to the formation of Z-scheme interfacial heterojunctions. These conclusions were also supported by experimental data, like more ∙O2- production capacity, efficient carriers separation, and higher carriers lifetime (27% higher than Cu2O and Cu2O/V-CN) as well as the weakened Cu2O photocorrosion tendency (Cu2O turning into CuO). Additionally, except for increasing nearly-three times adsorption energy of O2 for rapid activation, Cu2O/Ag/V-CN with abundant nitrogen vacancies can more significantly slow metal ions release (less about 97% to pure Cu2O and at least 22% higher than reported systems), which can observably save the amount of catalyst and heavy metals content. Therefore, Cu2O/Ag/V-CN has great potential for practical antifouling applications.

Development of FEM Calculation Methods to Analyse Subcooled Boiling Heat Transfer in Minichannels Based on Experimental Results

Even though two-phase heat transfer of refrigerants in minichannel heat sinks has been studied extensively, there is still a demand for improvements in overall thermal performance of miniature heat transfer exchangers. Experimental investigation and sophisticated heat transfer calculations with respect to heat transfer devices are still needed. In this work, a time-dependent experimental study of subcooled boiling was carried out for FC-72 flow in a heat sink, comprising of five asymmetrically heated minichannels. The heater surface temperature was continuously monitored by an infrared camera. The boiling heat transfer characteristics were investigated and the effect of the mass flow rate on the heat transfer coefficient was studied. In order to solve the heat transfer problem related to time-dependent flow boiling, two numerical methods, based on the FEM were applied, and based on the Trefftz functions (FEMT) and using the ADINA program. The results achieved with these two calculation methods were explored with an emphasis on the impact of the mass flow rate (range from 5 to 55 kg/h) on the resulting heat transfer coefficient. It was found that, with increasing mass flow, the heat transfer coefficient increased. Good agreement was found between the heat transfer coefficients, determined according to two numerical methods and the simple 1D calculation method.

Влияние жесткости угловых зон котлованов на перемещения подпорных стен в песчаных грунтах

Engineering calculations in the spatial formulation, as well as the results of field observations, show a significant decrease in lateral displacements of the foundation pit retaining walls in the area of the corner zones. At the same time, in design practice, a large number of decisions are made on the basis of calculations in a flat formulation. For pits with a depth of more than 10 m, the influence of corner zones can make a significant contribution to the reduction of movements and, as a result, internal forces in the retaining walls and restraint systems. The underestimation of the corner effect leads to an increase of the retaining structures construction cost.
 This article presents the results of FEM calculations studies of the monolithic reinforced concrete wall functioning in the corner zones of pit in sandy soils. As a result, it was revealed that the movement of the diaphragm wall in the area of the corner zones of the foundation pit is influenced by such factors as: the pit depth, the angle between retaining walls, and the stiffness of the retaining wall and struts. At the same time, the properties of the sand and the stiffness of the retaining wall and struts do not affect the distribution of displacements in the corner zones.

On the fatigue strength calculation of the welded shell structures from high-strength steels under low-cycle loading. Part 2: Development of the assessment methodology

The first part of this work substantiates the procedure for estimating the number of cycles before the appearance of a detectable fatigue crack in weld joints (stress concentrators) which are the usual places of crack occurrence in the absence of major technological defects. It is based on a physical model of the initial stage of fatigue failure, generalized data on the fatigue failure resistance of high-strength steels and their welded joints and FEM calculations. It is reduced to interpolation formulas summarizing the results of numerical modeling. This (second) part of the study presents information necessary to perform practical assessment of fatigue strength in the field of low-cycle loading, including the choice of reserve coefficients when calculating the resource of welded structures. The results of the assessments are compared with the data obtained during fatigue tests of welded joints of large thicknesses performed by multi-pass welding.

Performance of Lunar Regolith Shield under Meteoroid Impact: Uncertainties of a Numerical Prediction

The protection of the future lunar base from radiation, thermal stresses and impacts of meteoroids can be achieved by several options, generally consisting in a shielding system, made of either regolith or combined materials. In the present paper, the incidence of two sources of uncertainty on the FEM calculation of stress propagation through the covering regolith layer has been assessed. First, the investigation has pointed out, for a given impact and a given constitutive model, the uncertainty in the stress prediction related to the strain interval adopted for the soil stiffness measurement. Thereafter, calculation has been performed, for a given stiffness value, changing the assumed collision duration of one order of magnitude for equal impact momentum, that is, changing the maximum impact force too, correspondingly. The simulation has been performed based on physical and mechanical parameters of DNA-1A lunar simulant. The results provide indication of the relative importance of the calculation assumptions, which could address the design of a regolith shield.

3D FEM Analysis of the Subsoil-Building Interaction

This paper presents the process of advanced numerical analysis of interaction between a building and the subsoil. The analysis covered a wide range of work for both computing and research. As part of the research work, field and laboratory subsoil tests were carried out, as well as geodetic measurements of building settlement and measurements of natural vibrations of an object. The computational work included the analysis of a total of 47 FEM models. The subsoil was described using the Modified Cam-Clay model, with parameters determined using field CPT and SDMT tests, as well as triaxial and edometric laboratory tests. Parts with geodetic benchmarks were separated from the building model, and then multi-variant calculations were made on smaller, partial models with parameters obtained from various methods. Calibration of the main models was performed using 8 partial models for which calculations were carried out in 4–5 variants of parameters. This gave a total of 38 partial models. Then, calculations were carried out on the full model of the building with subsoil. At each stage, the results of vertical displacements were compared to the geodetic values. The measured settlement of the real building in the time from the construction of the underground story to its use for the period of 1 year, was from 2.3 mm to 7.8 mm. The settlement from FEM calculations of small calibration models for the same benchmarks was from 2.0 mm to 9.8 mm with parameters derived from CPT tests and from 1.8 to 7.3 mm for parameters derived from SDMT. For the full building model, settlement from FEM calculations ranged from 2.2 to 8.8 for the variant with a simplified subsoil model, and from 3.7 to 10.5 for the model taking into account the inhomogeneity of the subsoil. As a result, it was found that the displacements from the numerical analysis were convergent with the geodetic values. Detailed numerical analyses also allowed to detect the deviations of the segments from the vertical and to indicate potential damage to the structure. It was also indicated how the work of the subsoil influences the stress distribution in selected structural elements. Behaviour of the subsoil has an impact on the behaviour of the building and its deformations, as well as on the distribution of stresses in the structural elements, and, as a result, on the change in the distribution of internal forces in the structure.

Investigations of a compliant manipulator implementing micro-scale 2D displacements

The paper summarises the results of investigations of a 2D compliant manipulator implementing two independent orthogonal linear displacements. The device is comprised of a steel element with monolithic design, its motion induced by two independent screw-drive actuators. Underpinning the monolithic system design is the classical planar lever mechanism model. Macro-scale motions of the drives are reduced by two variators (variable displacement transmission units) effecting seamless control of displacement limitation via the settings of two additional independent screw-drive actuators. The resultant of thus reduced independent displacements is obtained at one vertex of the square platform where an end-effector or gripper may be mounted. A transformation matrix is formulated containing kinematic and coupling ratios. FEM calculations were performed to estimate the stress levels in flexure hinges in the neighbourhood of the motion stages. The manipulator workspace where elastic stresses will arise in flexure hinges has been determined. Tests conducted with the use of a microscope have validated the predicted motion properties of the monolithic system.