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EN
Quasi-static uniaxial compressive tests of open-cell copper (Cu) foams (OCCF) were carried out on an in-situ bi-direction tension/compress testing machine (IBTC 2000). The effects of strain rate, porosity and pore size on the energy absorption of open-cell copper foams were investigated to reveal the energy absorption mechanism. The results show that three performance parameters of open-cell copper foams (OCCF), involving compressive strength, Young modulus and yield stress, increase simultaneously with an increase of strain rate and reduce with increasing porosity and pore size. Furthermore, the energy absorption capacity of OCCF increases with an increase of porosity and pore size. However, energy absorption efficiency increases with increasing porosity and decreasing pore size. The finite element simulation results show that the two-dimensional stochastic model can predict the energy absorption performance of the foam during the compressive process. The large permanent plastic deformation at the weak edge hole is the main factor that affects the energy absorption.
EN
This work aims at increasing the performance prediction for acoustic propagation systems that will operate in the presence of the inevitable parameters uncertainty. In the present contribution, the finite element method is applied to solve an acoustic problem described by the Helmholz equation when the geometric and material properties present uncertainty. The influence of the uncertainty of physical parameters on the pressure field is discussed. The results using the polynomial chaos expansion method are compared with Monte Carlo simulations. It is show that uncertainty levels in the input data could result in large variability in the calculated pressure field in the domain.
EN
Series of experiments and a detailed computational analysis has been performed to investigate the high strain rate behaviour of homostacked Al 6063-T6 and IS 1570 alloys. Split Hopkinson pressure bar technique was utilized to study the effect of high rate loading on the stress strain relationship of single, double, tri and quad layered/stacked specimens. Three different specimen aspect ratios 1, 0.75 and 0.5 were also evaluated for different strain rates. A 2 mm thick pulse shaper was employed in achieving dynamic stress equilibrium, a near constant strain rate and a high rise time as per requirements. After analyzing the results from the experiments it was observed that single and halved specimens showed a close match in both the elastic and plastic regions for aluminium alloy as well as for steel. In the case of Al 6063-T6, a nearly bi-linear nature of the constitutive curve was observed for single and halved specimens, which transformed into near tri-linear nature for tri and quad stacked specimens. The dynamic numerical analysis showed a good agreement between the numerical and experimental results for a single and halved specimen in the case of Al alloy. For steel, a close correlation was observed for all the four cases.
EN
This research work is devoted to the theoretical study of the pipe calibration on a mandrel. The aim of the study is to improve the precision of the calibrated pipes. As the paper shows, it is advisable to apply different methods of research depending on the purpose of the study of metal forming processes: mathematical, computer or physical simulation. Analytical review of existing mathematical models of the pipes calibration on a mandrel showed that the set of assumptions adopted in the mathematical modeling does not allow assessing the precision of the pipes during calibration. Therefore, finite-element method simulation package was used for this research. Research method and pipes precision index were developed on the basis of the computer simulation using Deform-3D package. The investigations have allowed us to get the dependence of the pipe precision on technological factors and to identify the root cause of reduced efficiency calibration – extrafocal deformation.
EN
The study proposed the model of "guide mark" defects formation on the internal surface of pipes, produced on PRM mills of PRP–140. The research of pipe forming at plug rolling mill with stub mandrel has been carried out; regularities of the dimens ionless parameters characterizing the deformation of the gap release, depending on the reduction ratio, were determined. The model of "guide mark" defect formation on the internal surface of the pipe has been proposed. This allows for lesser wall thickness variation o f rough tubes. It has been shown that, when using dioctahedral pass designs in comparison with hexagonal pass designs the proportion of displaced volume along the pipe axis is greater but the value is lower; thereby, the risk of "guide mark" defect forming is red uced.
EN
Due to its attractive mechanical properties, aluminum 2024 is widely used in aircraft manufacturing industries, especially as fiber metal laminates, such as GLARE. In the present work, a series of experiments for different stress triaxialities are used to study the ductile damage of Al 2024 considering continuum damage mechanics (CDM). Stress triaxiality is produced using notched specimens. The main objective of the present study is to predict the local equivalent plastic strain to fracture and introducing a relation which describes the effect of stress triaxiality factor (TF) on it in the medium range of stress triaxiality. Hence, a nonlinear damage model is utilized for Al 2024 and its parameters are determined by an experimental/numerical/optimization procedure using tensile test on plain specimens. The experiments showed that for large notch specimens (Al-NL) and medium notch samples (Al-NM) fracture started from the center of the notch root of the specimens, whereas for small notched specimens (Al-NS) the failure initiated from the notch root surface. Finite element simulations are performed using the presented nonlinear damage model and are compared with the experimental data. Results show that the proposed damage model can predict the damage evolution for different stress triaxialities.
EN
Trephination is one of the basic operations of keratoplasty, and the biomechanical mechanism of the operation can be revealed based on three-dimensional modeling and simulation of trephine cutting cornea. Methods: Based on the analysis of the physical and biomechanical characteristics of corneal trephination, a three-dimensional numerical model of corneal trephination is built, where the cornea can be simplified to two layers structure including stroma and epithelium, and the trephine cuts the cornea under the vertical motion load and the rotational motion load. A three-dimensional failure criterion of corneal material is proposed based on the yield strength theory. On this basis, trephination simulation is carried out, and the units of corneal material are removed from the model when they meet the defined failure criterion. Results: Under the given parameters including the velocity, the angle and the angular velocity, the trephine force curves, include the linear cutting force and the rotary cutting force are obtained, and show the change of the forces with displacement during the process of trephination simulation. The maps of the equivalent stress show the destruction and deformation of the cornea. Then, the experiment of robotic trephination is carried out under the same parameters and the effectiveness of the simulation is evaluated. Conclusions: Based on mechanics theory and finite element method, the process of trephine cutting cornea has been reproduced, and the interaction mechanism is revealed, which lays the foundation for the development of real-time simulation and virtual system of the corneal surgery.
EN
In this study we focus on finite element simulation of gas tungsten arc welding (GTAW) of AA2219 aluminum alloy and the behavioral of the microstructure before and after weld. The simulations were performed using commercial COMSOL Multiphysics software. The thermal history of the weld region was studied by initially developed mathematical model. A sweep type meshing was used and transient analysis was performed for one welding cycle. The highest temperature noted was 3568 °C during welding. The welding operation was performed on 200×100×25 mm plates. Through metallurgical characterization, it was observed that a fair copper rich cellular (CRC) network existed in the weld region. A small amount of intermetallic compounds like Al2Cu is observed through the XRD pattern.
EN
This paper presents the review concerning mechanical properties of bone and the miniature specimen test techniques. For developing a realistic understanding of how factors such as moisture content, mineralization, age, species, location, gender, rate of deformation etc. affect the mechanical properties of bone, it is critical to understand the role of these factors. A general survey on existing research work is presented on this aspect. The essential features of miniature specimen test techniques are described, along with the application of small punch test method to evaluate the mechanical behavior of materials. The procedure for the determination of tensile and fracture properties, such as: yield strength, ultimate strength, ductility, fracture toughness etc. using small punch test technique have been described. The empirical equations proposed by various investigators for the prediction of tensile and fracture properties are presented and discussed. In some cases, the predictions of material properties have been essentially made through the finite element simulation. The finite element simulation of miniature specimen test technique is also covered in this review. The use of inverse finite element procedure for the prediction of uniaxial tensile constitutive behaviour of materials is also presented.
10
Content available remote Modelling of textile composite reinforcements on the micro-scale
EN
Numerical simulation tools are increasingly used for developing novel composites and composite reinforcements. The aim of this paper is the application of digital elements for the simulation of the mechanical behaviour of textile reinforcement structures by means of a finite element analysis. The beneficial computational cost of these elements makes them applicable for the use in large models with a solution on near micro-scale. The representation of multifilament yarn models by a large number of element-chains is highly suitable for the analysis of structural and geometrical effects. In this paper, a unit cell generating method for technical reinforcement textiles, using digital elements for the discretization, is introduced.
EN
In the present paper the drawing processes of thin wire of biocompatible magnesium alloys in heated die was investigated. Due to the hexagonal close packet structure magnesium alloys have low plasticity. In order to design the technological parameters the FEM model of wire drawing process in heated die and models of yield stress and ductility were developed. The relationship between technological parameters of drawing and fracture parameters was obtained based on developed models. The maps of possible elongation for MgCa0.8 and Ax30 magnesium alloys were developed using simulations. The draft schedule for final wire diameter 0.1 mm was design assisted with FEM model in experimental part of work. Based on this draft plan the drawing process from initial diameter 1.0 mm to final diameter 0.1 mm in heated die was performed in designed by author’s device.
PL
Specjalne stopy magnezu (MgCa08, Ax30), wykazujące wysoki poziom biokompatybilności ze środowiskiem organizmu człowieka, stały sie alternatywnym materiałem do zastosowania na implanty medyczne. Jednym z ich zastosowań mogą być nici chirurgiczne, służące do spajania tkanki miękkiej. Nici takie powinny mieć średnice rzędu 0.1 mm. W związku z niską technologiczną plastycznością tych stopów zaproponowano, aby proces ciągnienia prowadzić w podgrzewanych ciągadłach. W pracy analizowano proces ciągnienia w podgrzewanych ciągadłach cienkich drutów z biokompatybilnych stopów magnezu. W celu wyznaczenia technologicznych parametrów procesu ciągnienia użyto modelu MES, który rozbudowano o rozwiązanie cieplne w ciągadle, funkcje naprężenia uplastyczniającego oraz model utraty spójności analizowanych stopów. W oparciu o opracowany model wyznaczono zależności pomiędzy technologicznymi parametrami procesu ciągnienia i kryterium utraty spójności. W oparciu o symulacje numeryczne zbudowano mapy dopuszczalnych odkształceń dla stopów magnezu MgCa0.8 oraz Ax30.Wczesci eksperymentalnej pracy w oparciu o symulacje numeryczne wyznaczono schemat odkształceń do uzyskania drutu o średnicy 0.1 mm. W oparciu o wyznaczony schemat przeprowadzono proces ciągnienia w podgrzewanych ciągadłach ze średnicy początkowej 1.0 mm do średnicy końcowej 0.1 mm w urządzeniu skonstruowanym przez autorów.
12
EN
A model of burr formation on the edge of the workpiece in the course of machining is presented. The material being machined, the cutting tool and the machining parameters were modelled. Material properties and type of its deformations have been modelled with the use of a constitutive Johnson - Cook model. Material damage initiation criteria and associated damage evolution have been modelled with the use of the ductile damage and the Johnson- Cook damage initiation criterion. Simulations of the machining process for different depths of cut were carried out. The real burr formation presented by Hashimura was compared with the modelled one. The influence of the cutting parameters on the form and size of burr has been analysed. Calculations have been realised utilising finite element method with the use of nonlinear analysis in ABAQUS/Explicit environment. Based on simulation results, the assessment of the form and size of burr has been made. Burr height was used to evaluate its size, which was derived according to ISO 13715 standard. The goal was to obtain a model that reliably reflects the behaviour of material during machining, with particular emphasis on supporting the creation of cutting phenomenon of burr formation. The results of simulation and computational analysis confirmed that the model reflects the real behaviour of the material.
13
EN
This paper presents a finite element simulation of an oncology knee-joint endoprosthesis in a various degrees of flexion. The simulation has been made in accordance with an ISO 14243 [1-3]. A model of the knee implant (produces by ProSpon, s.r.o. [4]) consists of following parts: femoral stem, femoral replacement, femoral component, PE bushings, and tibial plateau. Results for four positions of flexion (1.53deg, 8.13deg, 15.31deg and 26.33deg) gave better understanding of strain and stress distribution along the endopros-thesis and pointed out also the most crucial areas requiring the attention. These foundlings are useful for individual design of the knee-joint prosthesis and for further development.
14
Content available remote Modeling of articular cartilage replacement materials
EN
The development of replacement material for human articular cartilage exhibiting similar mechanical properties as the native tissue is a problem of high actuality in biomeclicine. In the present work a new condensed collagen material is investigated. The study aims at developing a mechanical model especially adapted to this particular collagen material. For this purpose, a viscoelastic-diffusion (VED) model is proposed, accounting for two different diffusion evolutions assumed. Moreover, the need for a gradient material description is discussed in order to cover fabrication influences leading to a variable Young's modulus for the material. On this background, a phe-nornenological law is presented to predict deformation-dependent diffusion behavior and internal reaction forces. Furthermore, the present approach allows a practible identification of diffusion parameters. The theoretical model is implemented into a finite element code and parameters are identified by tension tests. The simulation results are validated experimentally.
15
Content available Finite element analysis of lower limb
EN
This paper presents a finite element simulation of a human lower limb in a full extension after a knee joint arthroplasty. Aside a total knee endoprosthesis Medin Modulár (size 76, right knee) provided by Medin Orthopedics, a.s., Czech Republic, two long bones, femur and tibia were used. As for a load, more than 30 most important muscles of the lower limb and 8 knee ligaments were disigned. Compared with our former results, this model gives reduced stress and contact pressures values which were given by more realistic ankle and hip joint definition. Their distributions correspond our former findings.
EN
The plywood is considered as a layered cross-ply unidirectional fibre reinforced composite. The experimental Compact Tension (CT) tests carried out in different directions of plywood fibre orientation show that the characteristics of damages are fibre bundle rupture, matrix cracking along the fibres, and delamination at the ply interlayers of glue. The plywood CT specimens are modelled by continuum shell and cohesive finite elements with damage evolution in material models. The Finite Element (FE) model simulates the experimental behaviour of plywood samples very well and allows deep investigation of the different types of damage development and interaction. The FE model of plywood is useful for its lay-up optimization and for development of very efficient in large-scale simulations computational models of plywood.
17
EN
In this paper, the additional iron loss due to the stator teeth punching is evaluated for a high speed permanent magnets machine. First, thanks to an original Grid structure, the B(H) curve and losses of the stator teeth are characterized from 50 Hz to 800 Hz and up to 1.7T. The results highlight the simultaneous influence of frequency and punching. The B(H) is particularly affected especially near the saturation knee but the degradation is quite independent of frequency. The punching effect on magnetic losses is also important. It decreases slowly with frequency and reaches a constant limit at 500Hz. Secondly, these results are considered into an iron loss estimation method which associates a finite element simulation using Flux? software and the Loss Surface dynamic hysteresis model. Applied to the studied machine, this method shows that the teeth punching generates 15 to 30 % of additional iron loss in the stator. Experimental tests of the machine validate this approach, the total iron loss being predicted with better than 20%.
PL
W artykule zbadano dodatkowe straty spowodowane procesem tłoczenia kształtu stojana stosowanego wysokoobrotowych maszynach elektrycznych o magnesach trwałych. Najpierw zbadano oryginalną strukturę ziarnistą, krzywą magnesowania i straty w paśmie częstotliwości 50 – 800 Hz przy indukcji do 1.7 T. Oceniono wpływ częstotliwości i naprężeń wynikających w procesu tłoczenia. Krzywa magnesowania znacznie zmienia się w pobliżu kolana nasycenia i efekt ten jest prawie niezależny od częstotliwości. Proces tłoczenia znacząco wpływa na straty. Maleją one z częstotliwością i osiągają stała wartość przy częstotliwości około 500 Hz. Następnie rezultaty badań przeanalizowano teoretycznie wykorzystując symulację zaimplementowaną w programie FluxTM i dynamicznym modelu histerezy. Wyniki analizy wykazały że proces tłoczenia powoduje 15 – 30% dodatkowe straty w stojanie. Eksperyment potwierdził wyniki analizy.
EN
The nature of percolation in continuum media inhomogeneous media is a current topic of debate. In this work, Monte Carlo and finite element simulations of the effective complex permittivity, e- e -ye, of two phase random composite media are analyzed using the two exponent phenomenological percolation equation (TEPPE) due to McLachlan. The continuum-percolation system consists of two-dimensional equilibrium distributions of randomly distributed monodisperse circular and partially penetrable disks (or parallel, infinitely long, identical, partially penetrable circular cylinders) throughout a host matrix. The study is performed on a set of calculations, covering wide ranges of various parameters including the intrinsic constituent permittivity, the surface fraction, and the degree of impenetrability. In our analysis, we first determine the parameters that characterize the critical behavior at the percolation threshold. Our data suggest that the phenomenological TEPPE does not fit the simulation data well over the entire range of surface fraction, and whatever the degree of impenetrability considered. This is attributed, in part, to the fact that the effective medium approximation (restricted to dipolar interactions only) ignores the local field fluctuations explicitly. Moreover, the mixtures exhibit clustering in equilibrium which is not conceptually incorporated in the TEPPE, i.e. the inclusions form cluster with a percolating spongelike topology accompanied by strongly dependent shape of the radial distribution function on the degree of impenetrability. It is argued that further efforts are still needed to fully grasp the numerically (and experimentally) observed features of the effective properties of dielectric heterostructures.
EN
This work is currently under development within the framework of an American-European project (Digimat Project) whose principal purpose is to model recrystallization in metals using a multiscale approach. The modelling effort is centered around a digital material framework. This framework is based on a digital representation of the material structure, where data coming from different scales can be stored or probed. The digital representation can be converted into finite element meshes, which are then used to model plastic deformation and subsequent recrystallization. The local behaviour of individual microstructure components is computed through models operating at different scales. In particular, grain constitutive models are derived from crystal plasticity concepts, with appropriate hardening/recovery laws which are linked to lower scale approaches at the dislocation level. Grain boundary motion is similarly described by connecting the continuum mechanical and thermal fields to simulations at the atomistic/dislocations levels. A detailed confrontation of the multiscale approach with experiment will be done at the ESRF synchrotron facility in Grenoble (France). In this paper, the needed development of numerical tools is presented together with the first finite element simulations. The development of the DIGIMAT software, dedicated to the concept of digital material, is first detailed. The construction of the virtual material consists in building a multi-level Voronoi tesselation. A polycrystalline microstructure made of grains and sub-grains can be obtained in a random or deterministic way. The software is at a stage of its development where it is possible to cut the microstructure along given planes, to approximate the grain shapes by a set of fitting ellipsoids, to roughly optimize the digital microstructure, and to generate a coarse mesh of the microstructure at each level of the microstructure (level 1 = external shape, level 2 =grains, level 3 = sub-grains). A second part of the work concerns the first finite elements simulations of a uniaxial compression test under large strain. The initial mesh is fine and anisotropic, taking into account the presence of interfaces between grains and sub-grains. A level-set approach is used to follow the grain boundaries during the deformation. In fact, with this method, the interface is modelled by the zero level-set of a time dependant level-set function which moves according to the mesh velocity field. The most complex test case carried out to date is a multi-domains Stokes problem, deforming at 85\% a cubic Volume Element made of 250 grains. Boundary conditions use a constant velocity in the compression direction, and free motion in the plane perpendicular to that direction. The constitutive law is a viscoplastic power law with a rate sensitivity of 0.2, and a variable hardness from one grain to another. The constitutive law will soon be replaced by a crystallographic formulation. Automatic isotropic and anisotropic remeshing, and parallel computation were successfully implemented, both features being crucial with respect to the Digimat project objectives (large strain to induce recrystallization, and large number of elements for a good representation of the microstructure). Finally, the bases of our first recrystallization simulations will be explained, including the description of nucleation and grain growth.
PL
Praca jest realizowana w ramach Amerykańsko-Europeskiego projektu (Digimat Project). W artykule opisano rozwój numerycznych narzędzi przeznaczonych do cyfrowej reprezentacji struktur metalicznych oraz do generowania powiązanych siatek anizotropowych dla modelowania metodą elemen­tów skończonych dużych odkształceń polikrystalicznych mikrostruktur. Metoda ustalonych poziomów stosowana do opisu mikrostruktury stanowi wspólną bazę dla wszystkich analizowanych rozwiązań.
EN
Finite element simulations of structures and structural details require suitable material models. Today there is still a lack of such constitutive material models in timber engineering. Therefore, a perennial research project at the Institute for Mechanics of Materials and Structures at the Vienna University of Technology was performed. In this paper the testing equipment, the experiments, the developed material model and its implemetation in finite element software will be explained. One focus of the mentioned project is the acquisition of the mechanical behaviour of biaxially, obligue to fibre direction loaded spruce wood. This enables a better simulation of multiaxial stress states in real timber structures. The applicability of the implemented constitutive model will be demonstrated by means of a nonlinear finite element analysis of a bone-shaped test specimen.
PL
Analiza konstrukcji i elementów konstrukcyjnych metodą elementów skończonych wymaga użycia odpowiednich modeli materiałowych. W chwili obecnej wciąż brak jest tego typu modeli przydatnych do konstrukcji drewnianych. W Institute for Mechanics of Materials and Structures, Vienna University of Technology prowadzono długookresowy projekt badawczy dotyczący budowy modeli materiałowych. Istotnym punktem wspomnianego projektu było pozyskanie danych o właściwościach mechanicznych drewna świerkowego obciążonego dwuosiowo w kierunku skośnym w stosunku do włókien. Umożliwiło to lepszą symulację stanu naprężeń wieloosiowych w rzeczywistych konstrukcjach drewnianych. W pracy opisano urządzenia pomiarowe, eksperymenty, zaproponowany model materiału i jego implementację w oprogramowaniu metody elementów skończonych. Użyteczność modelu została wykazana przy użyciu nieliniowej analizy elementów skończonych testowej próbki o kształcie kości.
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