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In this paper we propose a new Finite Element Modeling (FEM) strategy to simulate fretting wear profiles, taking account of the presence of a third body layer evolving over time. To validate this approach, the simulations were compared to experimental results on a gross slip Ti-6Al-4V cylinder/plane interface. A simple experimental procedure based on adequate superimposition of worn surface profiles allowed the estimation of individual cylinder and plane friction energy wear rates and quantification of the thickness of the third body embedded within the interface. A third body conversion factor, expressing the proportion of worn thickness transferred to the third body layer at a given position in the fretted interface was developed. The various quantitative variables were introduced in a coupled Matlab-Python-Abaqus algorithm where the worn thickness of counterfaces was simulated using a friction energy wear approach while the third body layer was progressively established by loading a “bell” thickness profile. The constant ( γ ) and parabolic distribution ( γ x ) of third body conversion factors were examined. Quantitative comparison with experimental results confirmed the interest of this new numerical strategy. Maximum wear depth, which was underestimated by nearly −80% using the wear model without taking account of the third body, was perfectly predicted, with error less than 10%, using the γ x third body model. Comparison with longer tests, up to 30,000 fretting cycles, confirmed the stability of the approach which, in addition to providing very good prediction of fretting scar profiles allows more conservative prediction of fretting crack risk. [ABSTRACT FROM AUTHOR]

When high speed machining polycrystalline metal, severe plastic deformation usually undergoes in the machined surface layer, accompanied by the microstructural variation of the crystallographic orientation. In the present paper, the machined surface plastic deformation and microstructural texture evolution during high speed machining of titanium alloy Ti-6Al-4V were investigated using finite element method (FEM) simulation. Firstly, a two dimensional FEM model was established, and was validated in terms of cutting forces and chip shape characteristics with experimental results of orthogonal machining. The plastic deformation on the machined surface was analyzed on the basis of finite element simulation. Results revealed that the plastic shear strain was much larger than the other strains in different directions. In addition, the variation of plastic shear strain and strain rate versus cutting time was obtained. When the feed rate was constant, the strain decreased and the maximum strain rate increased as cutting speed increased. Finally, the machined surface texture was simulated and analyzed using the Viscoplastic Self-consistent (VPSC) program based on the variation of plastic shear strain and strain rate, combined with polycrystalline plasticity theory. The machined surface texture evolution during machining was expressed by pole figures and orientation distribution function (ODF) diagrams. And the cylinder texture was identified from the pole figures. Four typical shear textures, including Y, C 1 , C 2 , and B fiber textures, were obtained from the ODF diagrams. Meanwhile, the orientation density of texture decreased with the increasing of cutting speed. [ABSTRACT FROM AUTHOR]

This paper describes the implementation and assessment of the predictive performance of a two dimensional mixed-mode fracture smeared crack model (MMFSCM) in a finite element method (FEM) based software. The referred constitutive model is based on the integration of the aggregate interlock and fibre pullout resisting mechanisms to simulate the behaviour of Fibre Reinforced Concrete (FRC) in both fracture mode I and II. The models used to simulate the contribution of each resisting mechanism predict the normal and shear stresses at the crack level based on the crack opening and sliding displacements. For this purpose, two aggregate interlock models and three fibre pullout models are used. The appraisal of this approach is conducted by simulating two numerical case studies consisting of a three-point notched beam bending test (3PNBBT) for assessing the structural behaviour in mode I, and shear panel tests to appraise the predictive performance of the model in mode II. In addition, modifications to the original formulation of the fibre pullout models are proposed, and a multi-linear branch model is also developed and implemented in order to facilitate the use of inverse analysis tools for defining the mode I behaviour. The numerical simulations have predicted with good accuracy the experimental responses, both in mode I and mode II, capturing not only the peak loads but also the evolution trend of the post-peak responses of the analysed scenarios. The modifications proposed to the fibre pullout models enhanced the overall predictive performance of the MMFSCM. The multi-linear branch model exhibited excellent performance, capturing the experimental response with very good accuracy in all 3PNBBT simulations. • Two-dimensional integrated mixed-mode smeared crack model for simulating FRC. • Aggregate interlock and fibre pullout models used to simulate the fracture process of FRC. • Implementation of the proposed constitutive model in a FEM based software. • Improvements were implemented in the fibre pullout models for increasing their predictive performance. • The good predictive performance of the MMFSCM is demonstrated by using experimental data. [ABSTRACT FROM AUTHOR]

Power cables are one of the key components of fast-growing HVDC transmission systems. The long-term reliability of HVDC cables is closely related to the occurrence of partial discharges (PDs) in their insulation systems. The article analyzes the conditions for the formation of PD pulses in gaseous voids located in the XLPE insulation of an HVDC cable. For this purpose, the MATLAB® procedure and the coupled electro-thermal simulation model implemented in COMSOL Multiphysics® software were used. The FEM model was used to study the effect of the applied voltage, the temperature field (created in the insulation of the loaded cable) and the location of the gaseous void (on cable radius) in the distribution and values of the electric field in the cable insulation. The model takes into account the influence of temperature and the electric field on the conductivity of the insulating material and relates the value of the PD inception field to the temperature/pressure of the gas inside the void. In the numerical simulation procedure, the time sequences of PDs arising in the gaseous defects of the HVDC cable insulation were analyzed, by observing changes caused by the increase in the temperature of the cable core. The model was used for a study of conditions for PD formation in models of three HVDC cables, for DC voltages from 150 kV to 500 kV. The critical dimensions of gaseous voids were also estimated for each of the analyzed cables, i.e., the dimension which, if exceeded, makes a void a source of PD. [ABSTRACT FROM AUTHOR]

The article analyzes the microstructure evolution of Co-Cr-Mo alloy during isothermal forging. The process of isothermal forging can be a technological solution to produce a semi-finished product for subsequent deformation processing and obtain a high-quality microstructure that excludes casting defects. Based on analysis of microstructure and phase composition and calculations, the required modes of ingot homogenization are determined. Finite element method simulation of the forging has shown that temperature and deformation conditions make deformation in the single-phase γ-region possible. However, at lower temperatures, σ-phase particles may precipitate at the last steps of deformation. After isothermal forging and water quenching, a mixture of recrystallized and polygonized structures with an average grain size of 5–10 μm and precipitation of ultra-fine dispersed particles of σ-phase (~0.13 μm) at grain boundaries are formed. Isothermal forging in the temperature range of 1100–1200 °C and at low strain rates of up to 1 s−1 allows obtaining a microstructure without pores, cracks, and large inclusions. Thus, it makes it possible to use the forging billet for further deformation by different metal forming methods. [ABSTRACT FROM AUTHOR]

This theoretical study analyzes the possibility to use the classical Mott's hypothesis to model the natural fragmentation of cylindrical structures with two or more metal cylinders arranged coaxially. A critical analysis on the validity of the used hypothesis was conducted based on empirical relations and numerical simulations. The established algorithm allows the determination of a fragment mass scale parameter for each individual cylinder, which is why the cumulative distribution of fragments for the entire structure may be calculated. The results obtained for the structures with two and three cylinders, with equal masses or equal wall thicknesses, can be approximated using a modified Mott's distribution formula in which the number of cylinders is used as an additional parameter. [ABSTRACT FROM AUTHOR]

The first-step drawing process of the platinum-clad nickel composite bar was numerically simulated using DEFORM 3D finite element analysis software. The Taguchi method was used to study the effect of the first-step drawing parameters (the semi-angle of die α, the friction coefficient between the platinum tube and die μ1, the friction coefficient between the platinum tube and nickel rod μ2 and the outer diameter of the original platinum tube D) on the effective stress of platinum-clad nickel bar. Then, the optimal combination of parameters (D = 7.55 mm, μ1 = 0.2, μ2 = 0.3, α = 3°) was obtained. Furthermore, the results of the deformation behavior, cladding behavior, stress effectiveness and the distribution of the damage of the composite bar using optimization schemes were compared and analyzed with Numerical Simulations 8, which showed the worst result. Meanwhile, the experimental results were in general agreement with the simulation results of optimal combination of parameters, indicating that our simulation results are plausible. This has certain guidance significance to improve the quality of platinum-clad nickel composite wires in actual production. [ABSTRACT FROM AUTHOR]

The micro-milling process of brittle materials involves macro-scale tool and nano-scale cracks. This multi-scale coupling problem makes it difficult to accurately predict the milling morphology using conventional methods. In this paper, a novel method is proposed to predict the milled surface quality of brittle materials by the combined method of analytical model and finite element method (FEM) simulation. In the proposed method, the chip thickness model for inclined ball end mills was established. Thus, the multi-scale coupling milling process of fused silica was discretized into several nano-scale local cutting processes to accurately calculate the crack. The chip thickness, as the dominant factor to influence cracks of brittle materials, not only can be used to solve the multi-scale coupling problem, but can predict the crack distribution on the milling groves. In this paper, an instantaneous chip thickness model for inclined ball end mills was established. Then, the chip thickness and cutting force under different tool inclination angles were analyzed. Next, the chip thickness of serial characteristic positions were used as the cutting depth, and the nano-scale local simulations was carried out at several characteristic positions on the cross section of the milled grooves. At last, the milling experiments were carried out under different inclination angles and feed rates to verify the effectiveness of the proposed method. Besides, the collapse phenomenon on the upper surface and side surface was observed and discussed. [ABSTRACT FROM AUTHOR]

This paper analyses three components of total cutting force and chip shape changes when finish turning 17-4 PH (precipitation hardening) stainless steel. A Finite Element Method (FEM) simulation of cutting forces was also performed using the Johnson–Cook constitutive model. The results were compared with those obtained from experimental studies. Variable feeds of 0.05–0.4 mm/rev and depth of cut of 0.2–1.2 mm with a cutting speed of 220 m/min were used. The studies were carried out under dry and wet cooling conditions and with the use of minimum quantity lubrication (MQL). This research was realized based on the Parameter Space Investigation (PSI) method. Statistical analysis of the obtained results was carried out using Statistica-13 software. It was found that the cutting force Fc and feed force Ff depend on the depth of cut and feed, and the passive force Fp depends mainly on the feed. Compared to dry cutting conditions, a reduction of 43% and 39% of the cutting force Fc was achieved for wet machining and MQL machining, respectively. Regardless of the cooling conditions, a favorable chip shape was registered for ap = 1–1.1 mm and f = 0.25–0.3 mm/rev. Compared to the experimental studies, the FEM simulation showed differences of ~13% for the cutting force Fc and of ~36% for the feed force Ff. [ABSTRACT FROM AUTHOR]

In this paper we outline a certain way of understanding of macroscopically uncontrollable emergence of the so called Mannesmann effect by means of its induced controllable quantum-mechanical background. In other words, we factually present a modus operandi of how to avoid macroscopic models of specific atomic-level cavity origin based consequently on a classical fracture mechanics theory. Under such circumstances, the target solution of the controllable microscopic model cannot be determined, since it can obviously arise only as a macroscopic state of the structurally disturbed rolled metal semi-product during the Mannesmann process. We obtain this irrelevance of the target solution, using a very special kind of control of the famous Schrödinger equation employed as a fundamental model equation here. We show contextually that such control follows from some very elementary aspects of the group theory conditioning a physical meaning of the Schrödinger equation written in a controllable form. We specially emerge primary cyclic groups of symmetry of special solutions to the Schrödinger equation. Their imaginary part is given by a control satisfying the Klein-Gordon equation which can be driven (through a specific avoidance of the cyclic group Z4) into a connection with the characteristic series of primary cyclic groups and/or torsion groups respectively. We obtain a physically controllable special results representing a strange correspondence between a certain LET (Linear Energy Transfer) and "quantum-like" tunnelling interpreted for some "everyday" objects, particularly for the considered Mannesmann piercing process with a torsion known from metallurgy. The process violations are shown and further reflected via a standard finite element method (FEM) simulation. [ABSTRACT FROM AUTHOR]

Defects generated during the casting process of steel can be reduced by forming processes such as hot rolling. During these processes the effective strain, the temperature, the stress state and the alternation of the forming direction all influence the defect evolution. Analytical or numerical models are available in the literature to predict the defect evolution. However, experiments have to be carried out to identify the parameters of these models. Thus, the quality of the identification depends on the representativeness of the experiments with respect to the industrial forming process. This paper proposes a methodology to design reduced scale experiments with an improved level of representativeness. This methodology consists first in the identification of the thermomechanical parameters driving the defect evolution and the quantification of these parameters in the industrial process by FEM simulation. These last results are then utilised as criteria for the representative experiment design. In this work the methodology is applied to the rolling of bars. The representative experiment consists of successive forming operations of a cylindrical sample between shaped anvils reproducing the roll shape at a 1:10 scale. A validation is finally achieved by reproducing qualitative results concerning the evolution of voids in the vicinity of hard inclusions. [ABSTRACT FROM AUTHOR]

The chip is the core component of the integrated circuit. Degradation and failure of chip solder joints can directly lead to function loss of the integrated circuit. In order to establish the degradation model of chip solder joints under coupled stress, this paper takes quad flat package (QFP) chip solder joints as the study object. First, solder joint degradation data and failure samples were obtained through fatigue tests under coupled stress. Three types of micro failure modes of solder joints were obtained by scanning electron microscope (SEM) analysis and finite element model (FEM) simulation results. Second, the characterization of degradation data was obtained by the principal component of Mahalanobis distance (PCMD) algorithm. It is found that solder joint degradation is divided into three stages: strain accumulation stage, crack propagation stage, and failure stage. Later, Coffin–Manson model and Paris model were modified based on the PCMD health index and strain simulation. The function relationship between strain accumulation time, crack propagation time, and strain was determined, respectively. Solder joint degradation models at different degradation stage were established. Finally, through strain simulation, the models can predict the strain accumulation time and failure time effectively under each failure mode, and their prediction accuracy is above 85%. [ABSTRACT FROM AUTHOR]

Flip anchors are a kind of ground anchor that rotate and open in the ground to attain pull-out resistance without the use of grout. Compared to ordinary grouted ground anchors, flip anchors can be driven into the existing ground quickly and are suitable for the emergency reinforcement of slopes. However, little research has been done on the slope reinforcement effect of flip anchors. In this paper, experiments on a model slope reinforced by plate anchors or flip anchors were conducted. During the experiments, vertical loading with a rigid loading plate was applied to the shoulder of the model slope to investigate its stability. Experiments were firstly conducted with and without model plate anchors under a plane strain condition. Then, experiments were conducted using actual flip anchors under a three-dimensional condition. In these experiments, the depth of the anchor plates, h , and the installation state of the anchor heads of the flip anchors (open or closed anchor head condition) were varied. After the experiments, corresponding numerical simulations (FEM) were conducted, and a subloading t ij model was applied to describe the soil behaviour. The numerical method used in this research successfully reproduced the reinforcing effect of the flip anchors. According to the test and calculated results, compared with the cases without reinforcement and with plate anchors, the effectiveness of the flip anchors for slope stability was verified. Moreover, the flip anchors installed under the closed anchor head condition required a larger displacement to produce a reinforcing effect than the anchors installed under the open anchor head condition. [ABSTRACT FROM AUTHOR]

This paper studies thickness and hardness of workpiece hardened surface layer, case of C45 steel orthogonal cutting, as function of cutting regime parameters and geometry of cutting tool. Simulations of orthogonal cutting using DEFORM 2D™ software are performed for different values of cutting speed, cutting depth, rake angle of the cutting tool and tool point radius, in order to determine the hardened workpiece surface layer thickness. Next, an experimental plan is set to validate simulations by means of cutting forces and hardness measurements. Taylor type new mathematical models of workpiece surface layer for stress, thickness, cutting forces and hardness are determined. [ABSTRACT FROM AUTHOR]

Wind load of high voltage overhead transmission line con ductors in field measurements, time domain simulations and standard. The loading of overhead lines comprises of natural actions mainly. Wind loading signifies an important load case in the design of overhead transmission line structures. Conductors spanning often several hundreds of meters contribute significantly to the overall loading of suspension towers. Those towers are often designed as a mass product to support the dead and wind load of the conductors between two dead end towers. Estimating the reaction of the conductors to strong winds, both geometric nonlinearities because of the large deformations as well as aerodynamic nonlinearities need to be considered. Particularly for design procedures, those effects should be simplified. This paper presents a thorough investigation comprising field measurements along an existing overhead line, simulations with FEM combined with wind tunnel tests and generated wind fields. It is the aim of the study to validate the actual design procedure regarding loading of wind acting on conductors. Most important herein in order to describe the extreme response are assumptions on turbulence distribution and dynamic behavior of wide spanning overhead line conductors. According to usual design procedure, by means of so called span reduction factors, relevant parameters such as span length and wind turbulence can be considered. [ABSTRACT FROM AUTHOR]

FEM simulation is known for its ability to simulate various cutting conditions in machining process and hence significantly reduce the number experimental trial to achieve the actual optimum cutting condition. This paper presents the capability of dynamic and non-dynamic cutting tool options that are available in the Third Wave AdvantEdge FEM software. The dynamic option was utilised for identifying the turning parameters for dimple structure fabrication and analysis of machining response such as cutting force and cutting temperature generated. The selected ranges of frequency which can be set in the dynamic assisted tooling for turning (DATT) along with other cutting parameters were simulated using dynamic cutting tool option resulted in stable wave shape that suitable for dimple fabrication. Furthermore, the simulation result also shows that cutting temperature and cutting force generated are smaller with a dynamic cutting tool than the non-dynamic cutting tool option. The dynamic cutting tool option in the Third Wave AdvantEdge was found to be very helpful and effective in determining a suitable range of cutting conditions and therefore, reducing the number of experiments for producing a dimple structure using the turning process. [ABSTRACT FROM AUTHOR]

This work presents description and comparison of internal and state variable models of flow stress in varying processing conditions. Three models were analyzed. The first one is based on dislocation theory and describing the mechanical behavior of f.c.c. polycrystalline structures. The second and third models are standard and modified Sellars' flow stress models. Models were adapted for two commercial codes based on finite element method: QForm7 and Forge 2005. The compression test of 45 grade steel with instant changes of strain rate was simulated. Calculated compression force and flow stress were compared with the experimental data from plastometric tests. The forging process was simulated by QForm7. Results obtained by both internal and modified Sellars' models confirm their high accuracy for analysis and prediction of the flow stress under the varying deformation conditions. [ABSTRACT FROM AUTHOR]

A simple method for evaluating the mechanical behavior of coated systems is the scratch test, which allows the analysis of the adhesion strength and the failure modes generated during contact. In this test should be considered parameters and properties as indenter geometry, loading rate, sliding rate and the system properties as hardness, fracture toughness, microstructure, surface roughness, coating thickness, residual stresses, among others. This paper analyzed via finite element, the longitudinal stresses (Sxx) obtained during the computational simulation of scratch test, where was considered the effect of coating thickness, which was considered as 2 μm and 4 μm, and the surface and interface roughness Ra 0,16 μm and 0,35 μm. The results suggest that thicker coatings, favoring the load carrying capacity, also demonstrated the importance of roughness of the system in the computer simulation. The increased roughness in the system increases the possibility of cracking of the coating. [ABSTRACT FROM AUTHOR]

Biofilms are ubiquitous at interfaces of natural and technical origin. Depending on type and application, biofilm formation is desired or has to be prevented. Therefore, reliable detection of initial biofilm growth is essential in many areas. One method of biofilm monitoring is the electrochemical impedance spectroscopy. Among other factors, this method is heavily dependent on the electrode geometry. In order to achieve a high measurement sensitivity, the electrode size must be chosen according to the biofilm that is to be measured. This paper presents an approach for simulating and modeling the optimal electrode geometry for a specific biofilm. First, a geometric model of a biofilm with up to 6000 individual bacteria is generated. The simulated impedances are used to calculate which electrode geometry maximizes sensitivity depending on the biofilm height. In the chosen example of an E. coli biofilm in a nutrient solution, the optimum size of an interdigital electrode (bar gap equals width) was 2.5 µm for a biofilm height of up to 2 µm. The used algorithms and models can be simply adapted for other biofilms. In this way, the most sensitive electrode geometry for a specific biofilm measurement can be determined with minimal effort.

Flip anchors are a kind of ground anchor that rotate and open in the ground to attain pull-out resistance without the use of grout. Compared to ordinary grouted ground anchors, flip anchors can be driven into the existing ground quickly and are suitable for the emergency reinforcement of slopes. However, little research has been done on the slope reinforcement effect of flip anchors. In this paper, experiments on a model slope reinforced by plate anchors or flip anchors were conducted. During the experiments, vertical loading with a rigid loading plate was applied to the shoulder of the model slope to investigate its stability. Experiments were firstly conducted with and without model plate anchors under a plane strain condition. Then, experiments were conducted using actual flip anchors under a three-dimensional condition. In these experiments, the depth of the anchor plates, h, and the installation state of the anchor heads of the flip anchors (open or closed anchor head condition) were varied. After the experiments, corresponding numerical simulations (FEM) were conducted, and a subloading tij model was applied to describe the soil behaviour. The numerical method used in this research successfully reproduced the reinforcing effect of the flip anchors. According to the test and calculated results, compared with the cases without reinforcement and with plate anchors, the effectiveness of the flip anchors for slope stability was verified. Moreover, the flip anchors installed under the closed anchor head condition required a larger displacement to produce a reinforcing effect than the anchors installed under the open anchor head condition.

The objective of this research is to define an optimized strategy for wire arc additive manufacturing (WAAM) process with a numerical tool. In this paper, a three-dimensional scaled steel plate model (120 mm × 24 mm × 6 mm) is built for numerical simulations to replace the expensive physical WAAM experiments. A series of thermo-metallo-mechanical analyses is conducted by using ABAQUS CAE user subroutines in which, thermal, metallurgical and mechanical models for gas metal arc welding (GMAW) process are implemented. Groups of variables in WAAM process namely wire melting current, voltage and torch moving speeds, as well as interval layer cooling coefficients, are chosen as input parameters of the artificial neural network (ANN). The two targeted values are hardness and ultimate strength of the steel plate model, which are obtained by fully coupled thermo-metallo-mechanical simulations or by quick results from commercial software JmatPro, and by real measurements on the test samples of WAAM experimental plates. In this primary study, Taguchi algorithm is used for data preparations of the numerical experiments. The tests are fulfilled with Neural Networks (NN) tool in MATLAB. A typical three-layer feedforward network is used for general works. The developed models show good prediction capability for hardness and ultimate strength. The ANN algorithm presents high potential in bidirectional modeling to develop the WAAM strategy tool. It is possible to realize the inverse modeling from properties obtained by fractions of phase volume to WAAM processing parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent studies, some structures with alternating positive and negative Poisson's ratio have been proposed, which provides a new direction for structural design. The novelty of this paper is that the proposed structure can not only have different Poisson's ratio signs under tension and compression, but also adjust the Poisson ratio under tension or compression separately. The Poisson's ratio of the proposed cell structure under tension and compression is studied by FEM simulation and experiments. The results show that the Poisson's ratio under tension and compression has the opposite sign, and the value of the Poisson's ratio under tension or compression can be changed separately by adjusting the geometric parameters. The unique deformation law of the proposed structure does not depend on the material properties. 2D and 3D cellular structures composed of 2D unit cell arrays maintain these unique features. The proposed structure makes use of the self-contact effect, which provides a fresh perspective for the adjustability of the structural Poisson's ratio and structural design. • A novel cellular structure that can switch the sign of Poisson's ratio with loading state was proposed. • Poisson's ratio of designed 2D unit structure in either tension or compression can be adjusted independently. • The unique deformation law of the proposed structure is independent of the material properties. • 2D and 3D cellular structures composed of 2D unit cell arrays maintain these unique features. [ABSTRACT FROM AUTHOR]

In this study, the possibility of using modern AM technologies to produce designed heels for personalized orthopedic footwear with a medium heel was explored. Seven variants of heels were produced using three 3D printing methods and polymeric materials with different natures: PA12 heels made using the SLS method, photopolymer heels made using the SLA method, and PLA, TPC, ABS, PETG, and PA (NYLON) heels made using the FDM method. A theoretical simulation with forces of 1000 N, 2000 N, and 3000 N was performed in order to evaluate possible human weight loads and possible pressure during orthopedic shoe production. The compression test of the 3D-printed prototypes of the designed heels showed that it is possible to replace the traditional wooden heels of hand-made personalized orthopedic footwear with good-quality PA12 and photopolymer heels made using the SLS and SLA methods, but also with PLA, ABS, and PA (NYLON) heels printed using a cheaper FDM 3D printing method. All of the heels made using these variants withstood loads of more than 15,000 N without damage. It was determined that TPC is not suitable for a product of this design and purpose. Due to its greater brittleness, the possibility of using PETG for orthopedic shoe heels must be verified by additional experiments. [ABSTRACT FROM AUTHOR]

Pressure bulge testing is one of the standard techniques for characterizing the mechanical properties of thin films, whereas it is far less often used to characterize the mechanical properties of 2D materials. In the present work, the effectiveness of bulge testing on determining the mechanical properties of 2D materials is systematically investigated using numerical analysis. After assuming 2D materials as continuum thin films, we start by simulating the relationship between the pressure difference across the suspended film and the film deflection, and then fit the results with analytical models to extract the elastic modulus of the film. It should be noted that the clamped, pre-stretched film widely assumed in the existing analytical model is not appropriate for atomically thin materials; instead, freestanding 2D materials are actually slack in bulge testing due to the delamination of their adhesive boundary condition. Therefore, the initially unstressed flat films, pre-stretched films and slack films are investigated in the present work, and the Poisson's ratio effect is considered to investigate the effectiveness of bulge testing for most 2D materials. It is found that bulge testing can be an effective approach to characterize the mechanical properties of 2D materials. [ABSTRACT FROM AUTHOR]

The CVD diamond micro-grinding tool highly promising for micro-scale high accuracy machining. To improve the lubrication and chip removal performance in the grinding zone, a kind of micro-structured CVD diamond micro-grinding tool. Firstly, the commercial FEM software was adopted to analyze the effects of micro-structure parameters on the deformation and stress distribution of the micro-grinding tool. And then, the coolant flow fields in the grinding zone included the macro flow field, micro flow field and chip evacuation were simulated. The effects of micro-structure parameters and grinding parameters on the flow field performance and the transport capacity of chips were obtained, which provides a basis for the surface micro-structure design and optimization of the CVD diamond micro-grinding tools. [ABSTRACT FROM AUTHOR]

Aluminum alloys are one of the most common structural materials. To improve the mechanical properties, an alloy of the Al–Zn–Mg–Ca–Fe system was proposed. In this alloy, when Fe and Ca are added, compact particles of the Al10CaFe2 compound are formed, which significantly reduces the negative effect of Fe on the mechanical properties. Because of the high solidification rate (about 600 K/s) during cylindrical ingot (~33 mm) production, the electromagnetic casting method (ECM) makes it possible to obtain a highly dispersed structure in the cast state. The size of the dendritic cell is ~7 μm, while the entire amount of Fe is bound into eutectic inclusions of the Al10CaFe2 phase with an average size of less than 3 μm. In this study, the effect of radial shear rolling (RSR) on the formation of the structure and hardening of the Al–8%Zn–3.3%Mg–0.8%Ca–1.1%Fe alloy obtained by EMC was studied. Computer simulation of the RSR process made it possible to analyze the temperature and stress–strain state of the alloy and to select the optimal rolling modes. It was shown that the flow features during RSR and the severe shear strains near the surface of the rod (10 mm) provided a refining and decrease in the size of the initial Fe-containing particles. [ABSTRACT FROM AUTHOR]

This work aims to characterize printing structures with various infill densities composed of a thermoplastic material containing magnetic particles composed of mainly Iron(III) oxides with regard to their possible processing with the additive technology of Fused Filament Fabrication. A polyethylene terephthalate glycol (PET-G) structural thermoplastic with the addition of Iron(III)) oxides has been selected, and correct processing temperatures have been determined using thermal analysis. The paramagnetic properties of printed products consisting of different filling densities have been tested. Relative permeability has been identified to be strongly dependent on the printed internal structures of tested products. The samples composed of the densest structure have shown relative permeability higher by 18% with respect to the sample printed with the least dense structure. Finite Element Modelling (FEM) simulations have been applied to determine magnetic field distributions and, moreover, to calculate the holding forces of all printed samples. The performed simulations confirmed that produced composites might be utilized as magnetic switches and sensors or as more advanced components for homogenizing electric motors' magnetic fields. Moreover, magnetic properties might be tuned according to the specific needs printing structure with the suitable density. [ABSTRACT FROM AUTHOR]

This paper deals with the dynamic response of pump-turbine impellers. A pump-turbine impeller is a complex structure attached to a rotor and rotating inside a casing full of water with very small clearances between the rotating and the stationary parts. The dynamic response of this type of structures is very complex and it is very much affected by the connection to the rotor as well as by the added mass and boundary conditions. As a consequence its calculation presents several uncertainties. First, the dynamic response of pump-turbine impellers is introduced. Second an experimental investigation in a real impeller attached to the rotor and inside the machine was carried out. For this investigation, the impeller of an existing pump-turbine unit with an installed power of 110 MW and a diameter of 2.87 m was studied. For a better analysis of the experimental results a numerical model using FEM was also built-up. Frequencies and mode-shapes were identified numerically and experimentally and the characteristics of the structural response analyzed. To determine the influence of the rotor and supporting structures on the impeller response the results were compared with the ones obtained with the same impeller but suspended (non-connected to the rotor). Experimental and numerical simulation were also used for this case. The changes in the dynamic response due to the rotor connection were determined. Finally the results obtained are compared with the results from other pump-turbine impellers of different designs and general conclusions about the dynamics of this type of structures are given. [ABSTRACT FROM AUTHOR]

The paper presents a measurement of temperature in a steelmaking furnace with an oxygen refining process, specifically in a tandem furnace. Knowledge of the temperature is important for optimizing the manufacturing process and extending of the life cycle of the inner furnace lining. Conditions in the furnace are very demanding; the temperature may temporarily exceed 2000 °C and exhibits changes of 60 °C s −1 . The atmosphere in the furnace is mainly oxidizing and its chemical composition is very variable. In the atmosphere there are also present liquid and solid compounds which act chemically and abrasively on the lining and on the sensor. These conditions make it impossible to use a suction pyrometer, contactless optical or acoustic measurement methods. It was decided to use a thermocouple in a protective tube. The sensor was inserted into the furnace through a steel bushing with water cooling. For the first measurement the type B thermocouple in Al 2 O 3 protective tube inside an outer shielding tube made from SiC was used. The second sensor used the type C thermocouple in a special thick-walled protective tube made from sintered SiC. The sensor does not measure the temperature of the gas itself, since it is affected by radiation of the surrounding areas. Conditions for heat transport from the furnace to the sensor are variable and difficult to determine; therefore, the accurate identification of the atmosphere temperature is not possible. Limit values of the temperature interval of the atmosphere were determined, for hypothetical cases of athermanous and ideally diathermic atmospheres. [ABSTRACT FROM AUTHOR]

This paper shows the mathematical model used to calculate the pressure variation on the contact surface between shoe and drum. The braking system is one of the most important systems of a vehicle's active safety. Hence, it turns to be extremely important to adopting effective solutions from both of the braking performances and reliability/maintainability points of view. The friction between the brake shoe and drum occurs along a circular arc of contact surface. Using a specialized FEM (Finite Element Method) program, I have modeled the drum-and-shoe brake of the vehicle and I have simulated its working modes as close to the real life as possible. The FEM spotted thermal accumulation points as well as the intensity of the heat transfer process for the drum, friction lining and shoe. [ABSTRACT FROM AUTHOR]

The Tapered Double Cantilever Beam (TDCB) is the common specimen to study self-healing thermosetting polymers. While this geometry allows characterising the mode I fracture toughness without taking into account the crack length, the experiments show an important dispersion and unstable behaviour that must be taken into account to obtain accurate results. In this paper, finite element simulations have been used to understand the experimental behaviour. Static simulations with a stationary crack give the local stresses and the stress intensity factors at the crack tip when the TDCB is under load. In addition, the eXtended Finite Element Method (XFEM) has been used to make quasi-static crack propagation simulations. The results indicate that the crack tip has a curved profile during the propagation, advancing more at the edges than at the centre. The crack propagation begins when the applied load reaches a critical value. The unstable crack propagation noted in the experiments can be reproduced by introducing an unstable behaviour in the simulations. Finally, the sensitivity of the critical load has been studied as a function of the friction between pin and hole, tolerance of geometrical dimensions, and cracks out of the symmetric plane. The results can partially explain the dispersion of the experimental data. [ABSTRACT FROM AUTHOR]

The paper presents numerical simulations of punching shear in a reinforced concrete slab-column configuration formerly tested in the laboratory. A brief description of the test program at the University of Waterloo is reported. For the simulation, a symmetric quarter of the test configuration is employed. Full three-dimensional finite element discretized geometry is considered together with elastic–plastic reinforcement embedded as truss elements in concrete. Two regularized numerical models of concrete, formulated within elastic–plastic-damage theories, are applied. The first one, called gradient damage, is refined by an additional averaging equation where gradient enhancement involves an internal length scale. In the second one, called rate-dependent damaged plasticity model, a viscoplastic strain rate is introduced. The results for the first model implemented in FEAP and the second model from ABAQUS are discussed in detail. Different issues of numerical simulation to properly predict punching shear behaviour in the slab-column configuration are presented. [ABSTRACT FROM AUTHOR]

This paper addresses the localization of Partial Discharge through a 3D Finite Element Method analysis of acoustic wave propagation inside a 3-phase 35kV transformer with the help of COMSOL Multiphysics software. Due to the complexity inside transformers, acoustic waves generated by PDs cannot simply be detected with typical acoustic sensors, especially when PDs happen inside inner windings. These waves are distorted and attenuated along with their propagation. The type, number, and position of sensors are essential factors in PD localization inside a transformer. A new installation arrangement of fiber-optic acoustic sensors inside the transformers is proposed with this information. This array of acoustic sensors has significant effects on PD localization accuracy and has immunity from on-site noise and interference; more importantly, they can be installed after transformer manufacturing. They are reachable if needed to be repaired or replaced. Several numerical studies have been carried out considering different PD source positions, and the Levenberge-Marquardt algorithm is employed for solving localization equations.

The in-situ TiB2/7050Al composite is a new kind of Al-based metal matrix composite (MMC) with super properties, such as low density, improved strength, and wear resistance. This paper, for a deep insight into its cutting performance, involves a study of the chip formation process and finite element simulation during orthogonal cutting in-situ TiB2/7050Al MMC. With chips, material properties, cutting forces, and tool geometry parameters, the Johnson–Cook (J–C) constitutive equation of in-situ TiB2/7050Al composite was established. Then, the cutting simulation model was established by applying the Abaqus–Explicit method, and the serrated chip, shear plane, strain rate, and temperature were analyzed. The experimental and simulation results showed that the obtained material’s constitutive equation was of high reliability, and the saw-tooth chips occurred commonly under either low or high cutting speed and small or large feed rate. From result analysis, it was found that the mechanisms of chip formation included plastic deformation, adiabatic shear, shearing slip, and crack extension. In addition, it was found that the existence of small, hard particles reduced the ductility of the MMC and resulted in segmental chips. [ABSTRACT FROM AUTHOR]

• Prediction of leakage current of a 20 kV polymeric insulator in the presence of real conditions of asymmetric non-uniform fan-shaped contamination by considering effective parameters associated with each shed such as electrical conductivity, segmental angle and thickness of contamination layer. • Proposing a hybrid finite element method (FEM) combined with the method of moment (MOM) to calculate leakage current with lower error values than the FEM simulation method compared to the actual values obtained from experimental test. • Perform experimental tests to validate the data obtained for training using neural network. • Reduce the error of insulator leakage current prediction values by multiplying the trained data. The accumulation of environmental pollution in symmetrical and asymmetrical categories conditions can lead to the aging of polymeric insulators through leakage current enhancement. In this paper, real asymmetric contamination, namely fan-shaped, is investigated accurately. However, the main approaches are that the real configuration of fan-shaped pollution is not normally uniform, and asymmetrically non-uniform fan-shaped pollution is detected. In particular, the segment angle, thickness, and electrical conductivity of the contamination layer are three major effective parameters in the insulation analysis of a fan-shaped polluted insulator. Finite element method (FEM) simulation and the proposed hybrid FEM combined with the method of moment (MOM) of a 20 kV polymeric insulator under asymmetric non-uniform fan-shaped contamination through leakage current calculations illustrate that variation in non-uniformity of related parameters of contamination layer are so crucial in the insulation situation of insulator. Also, leakage current is predicted using an artificial neural network (ANN) in processing obtained data from proposed methods, by applying effective parameters of non-uniform fan-shaped contamination. Experimental tests have been performed to validate the results and evaluate the leakage current of the fan-shaped polluted insulator. The results of the predicted values show that the difference is less than 5% compared to the actual values. [ABSTRACT FROM AUTHOR]

This work aims to develop a light symmetrical structure that can be realized through rapid prototyping techniques. The structure must meet some restrictions imposed by possible practical applications. It must withstand a moderate load, be able to adapt to a specific external shape, be relatively light, allow the execution of some changes according to user requirements, allow execution with the help of owned equipment, and allow relatively fast production (its structure and form). The major application for which the structure is designed is that of an exoskeleton for medical rehabilitation, realized by the authors. The creation of such an exoskeleton is followed by a series of research regarding different aspects of acceptability, reliability, ease of use, and the shortcomings that such a structure can cause. In this study, the authors focused on the mechanical part of the exoskeleton realization, which would fulfill some imposed kinematic and constructive conditions. [ABSTRACT FROM AUTHOR]

Controlling the electric field distribution in HVDC cable accessories requires a tight knowledge of the properties, particularly the electrical conductivity of the insulating materials constituting the system. [ABSTRACT FROM AUTHOR]

Finned tube air heat-exchangers are built by joining the tubes to the fins by various techniques. A technique mostly used for large heat-exchangers consists of fitting the tubes into the holes of the fins by expanding the tubes using a mechanical process. The expansion is achieved by inserting an ogive of a larger diameter into the tube. The intimate contact of tubes and fins due to the press fitting ensures the proper thermal connection. This work tries to describe an experimental-numerical procedure useful to study and predict the mechanical process and the process parameters. The procedure, based on material properties obtained from tensile tests and the use of the inverse method to identify the material parameters, is based on bi-dimensional finite element (FE) models used to simulate the expansion process. The FE model is then used for process optimisation regarding such parameters as the ogive shape and ogive sizes, friction coefficient and speed of insertion of the ogive into the tube. Indeed, size and shape uncertainties strongly influence the process parameters and the process quality, as well as the heat-exchanger efficiency. The use of numerical models was proven highly effective in predicting and optimising the process by quickly analysing the influencing factors and optimising the production. [ABSTRACT FROM AUTHOR]