Browsing by Author "Ackermann, Michal"

Now showing 1 - 13 of 13
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    Analysis of contact pressure on the unicondylar knee replacement
    (Technical University of Liberec Studentska, 2009-01-01) Ackermann, Michal; Čapek, Lukáš
    The paper deals with contact pressure analysis on two constructional types of modern type of knee prothesis - the unicondylar knee replacement. Contact pressure is analysed in two ways, the first is experimental using pressure sensitive Pressurex® films, and the second approach is numerical analysis made in FEM software package ANSYS Multiphysics 10. Results from both approaches are confronted and at the end there's judged what type of partial knee prothesis is more suitable for use.
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    CERAMIC 3D PRINTING: COMPARISON OF SLA AND DLP TECHNOLOGIES
    (MM SCIENCE, PRIPOCNI 1519-10A, PRAGUE 10, 10100, CZECH REPUBLIC, 2020-06-01) Truxová, Veronika; Šafka, Jiří; Seidl, Martin; Kovalenko, Iaroslav; Voleský, Lukáš; Ackermann, Michal
    Complex ceramic parts tend to be difficult or even impossible to produce by conventional methods. Therefore, the 3D printing technologies have started to spread widely in the area of ceramic parts production. The aim of this paper is to compare the efficiency of Stereolithography and Digital Light Processing technologies in 3D printing of ceramic parts. Firstly, indicative chemical analysis was performed on a chosen ceramic suspension. Secondly, sample parts of different shapes were designed and printed using both technologies. Next, printed samples were analyzed using thermogravimetric and optical analyses. Finally, printed parts were debound and sintered, and final ceramic parts were consequently reanalyzed. Both technologies show the best results in the printing of thin-walled and hollow models. The DLP was significantly faster, especially when the printing platform was close to full occupancy.
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    Fatigue Properties of Shape Memory Alloys with Regard to Their Use in Medicine
    (Technická Univerzita v Liberci, 2015-01-01) Ackermann, Michal
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    Influence of different coupling agent type on processibility and applicability of polymer composites
    (Trans Tech Publications Ltd, 2016-01-01) Seidl, Martin; Habr, Jiří; Běhálek, Luboš; Šafka, Jiří; Ackermann, Michal; Bobek, Jiří
    The contribution deals with the processibility and applicability of polymer composite systems based on polypropylene matrix. The composites were filled with vegetable fibres (particularly the cotton fibres, coir fibres, hemp fibres and jute fibres) and the interface between the polymeric matrix and the natural fibres was modified using two types of coupling agents (the organosilane coupling agent and maleic anhydride grafted polypropylene). For evaluation of the final impact of all three phases presence on the processibility of the polymer composite the melt flow behaviour was analyzed (MFI analysis according to ISO 1133) for the filler concentration of 10, 20 and 30 wt. %. This study involves also the natural fibre surface profile analyses (based on SEM observation) and the applicability of created composite materials was determined using the heat deflection temperature (HDT analysis according to ISO 75). © 2016 Trans Tech Publications, Switzerland.
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    Modelling of materials with shape memory effect with using finite element method
    (Brno Univ. of Technology, 2011-01-01) Ackermann, Michal; Čapek, Lukáš
    Materials with shape memory effect exceed conventional materials especially in high reversible deformations (pseudoelasticity) and a possibility of permanent deformation disappearance after applying a heat on them (shape memory effect). The purpose of this article is to define a procedure to acquire characteristic mechanical constants of these materials in order to use Auricchio's material model in FEM software MSC.Marc. A sample in the form of a wire made of the binary NiTi alloy was subjected to tensile test. From the gained stress-strain function the needed values were evaluated. Because of the mechanical properties are strongly temperature-dependent, the tensile tests were performed under various temperatures: 19 °C, 37 °C, 60 °C and 80 °C. Dislocation of a hyperelastic plateau up to higher stresses with increasing temperature is clearly visible. Variation of Young's modulus of both phases (austenite, martensite) which the material is passing through during loading and unloading of the sample is also obvious. The conditions of tensile test were simulated in MSC.Marc and gained graph was compared with experimental data. These results will be used for creating a finite element model of endovascular stent. Another advantage of NiTiNOL is, among the other ones, its excellent biocompatibily. © Tomáš Návrat, Vladimír Fuis, Lubomír Houfek and Miloš Vlk, 2011.
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    Numerical durability evaluation of Nitinol stent
    (Technická Univerzita v Liberci, 2012-01-01) Ackermann, Michal; Čapek, Lukáš
    Shape memory alloys, such as binary NiTi alloy, have gained the attention of researchers, thanks to their remarkable properties. In comparison with other usually used materials, they exhibit large reversible strains (pseudoelasticity) and especially a heat-induced regaining of their original shape even in the case of significantly large deformations (shape memory effect) (Yahia 2000; Lagoudas 2008). Even though many articles have been written on account of these materials (Duerig et al. 1999; Kleinstreuer et al. 2008; Nayan et al. 2009), only a few deal with their fatigue properties. The need to know and understand the behaviour of the material under cyclic loading came from a project which deals with coronary Nitinol stent grafts. Stents (Figure 1), which form a skeleton of an implant, are made up of NiTi wires. After an implantation of a stent graft into a blood vessel, it is subjected to cyclic change of its diameter due to the alternation between the systolic and diastolic blood pressure. The aim of this study was to carry out fatigue analysis of a Nitinol stent, subjected to a cyclic crush test, and to reveal critical areas of its construction. In previous work, the dependency of stress amplitude versus number of cycles until the failure of a specimen was evaluated experimentally. This dependency is called Wo¨hler’s or the S –N curve, and is one of the basic indicators that define the fatigue properties of a material. Thanks to our knowledge of the S –N curve of NiTi alloy, we were able to predict the life of a Nitinol stent with the support of data gained from a crush test of a stent performed using the finite element method (FEM) in MSC Marc software.
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    Optimalizace unikondylární náhrady kolenního kloubu s ohledem na kontaktní tlaky
    (Technická Univerzita v Liberci, 2009-01-01) Ackermann, Michal; Čapek, Lukáš
    This final year project deals with contact pressure analysis on two constructional types of modern type of knee prosthesis-the unicompartmental knee replacement. In the first part of the project the contact pressure distribution on replacements is analyzed in two ways. The first method is experimental with using pressure sensitive Pressurex\regm{} films. Second approach is numerical analysis with the support of finite element method (FEM) made in ANSYS Multiphysics 10.0 software package. Results from both approaches are confronted at the end of first part and as conclusion there's considered which tested type of partial knee replacement is more suitable for use. In second part the better of two replacements is put through an optimization process which goal is to reduce contact pressure and therefore take its full advantages.
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    Selective laser melting technology and individual ti-6al-4v implants
    (MM publishing Ltd., 2019-06-01) Ackermann, Michal; Šafka, Jiří; Čapek, Lukáš; Bobek, Jiří; Mendřický, Jaromír
    This paper deals with the use of additive manufacturing from Ti-6Al-4V metal powder in the field of individual implants. Additive technologies such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM) enable the manufacturers to design the implants precisely with respect to actual anatomy of each patient. In this paper, two major properties of the printed parts are studied. In the first part, monotonic mechanical properties of the material in as-built and heat treated condition are evaluated. In the second part of the work, shape accuracy is evaluated on the model of individual cranial implant. For this study, the cranial implant was once built as a fully dense part and once using lightweight structure. Both parts were submitted to optical 3D scanning to evaluate the nominal deflections from CAD model. Uniaxial tests show full usability of additively manufactured Ti-6Al-4V parts. Basic material constants are comparable to those evaluated on conventional bulk material. Apart from shortening the build time, lightweight structures also significantly reduce deflections of the model.
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    Selective laser melting technology and manufacturing of accurate thin structures
    (Trans Tech Publications Ltd, 2016-01-01) Ackermann, Michal; Šafka, Jiří; Voleský, Lukáš
    This paper deals with finding the building parameters for manufacturing of fine structures with regard to their size precision and structural consistency. Practical use of these structures can be found in areas such as microelectronics, fine mechanics and automotive. Very fine structures with thickness lower than 0.3 mm are very hard to be manufactured due to the limitations of Selective Laser Melting (SLM) technology. These limitations lie in building parameters including mean size and shape of the powder particles, diameter of laser spot and scanning speed. Practical part of the work consists of printing the testing matrices from AlSi12 material with different building parameters for each element. Final products are then evaluated using scanning electron microscope in order to verify final size and structural properties of the specimens. Thanks to these tests, it was possible to find actual border of the technology for given type of powder. Structure with minimal thickness and sufficient strength was found to be 0.21 mm. Moreover, the method for finding parameters for manufacturing of fine structures is applicable for other types of materials. © 2016 Trans Tech Publications, Switzerland.
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    Thermo-physical properties investigation in relation to deposition orientation for SLM deposited H13 steel
    (ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020-01-01) Dzugan, J.; Halmesova, K.; Ackermann, Michal; Koukoliková, M.; Trojanová, Z.
    Components produced by additive manufacturing (AM) exhibit a heterogeneous microstructure, hence results in anisotropic mechanical properties. There are very limited studies available on thermo-physical properties variation in relation to the deposition orientation. Variation in these properties may result in an uneven stress distribution. In this work, thermo-physical properties of H13 tool steel fabricated by selective laser melting (SLM) process were experimentally investigated. The effect of three deposition directions (vertical, horizontal and 45 degrees to base plane of build platform) on thermal expansion, thermal diffusivity, specific heat, thermal conductivity and simplified CCT diagram was studied. Additionally, mechanical properties and metallographic studies of the microstructure were carried out together with the porosity evaluation measurements across the specimens.
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    Únavové vlastnosti slitin s tvarovou pamětí s ohledem na jejich využití v medicíně
    (Technická Univerzita v Liberci, 2015-01-01) Ackermann, Michal
    This work deals with characterization of Nickel-Titanium shape memory alloy which is used for production of cardiovascular stents. Material tests such as Differential Scanning Calorimetry and tensile tests carried out under different values of temperature allowed for precise description of material's pseudoelastic effect. Moreover, fatigue tests of the alloy were done under two different values of temperature and its corresponding S-N curves were constructed. On the basis of experimental data, full range of loads which are imposed on stent during its life are studied using finite element method. In this part, loading a stent into catheter and its subsequent deployment in blood vessel was simulated. Following simulation of pressure pulse offered data about cyclic loading to which the stent is exposed when implanted into an artery. Thanks to previous simulation and known S-N curve of the material, durability analysis of the stent was done with use of nominal stress approach. In last part of the work, a device dedicated to cyclic testing of the whole stent-graft structure is constructed. Concept of the machine, together with corresponding calculations are shown. Outcome of this work is a fully operational machine at which eight stent-grafts can be tested at the same time. Pressure characteristics which acts inside mock arteries was experimentally verified to be similar to conditions in human body.
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    Use of composite materials for FDM 3D print technology
    (Trans Tech Publications Ltd, 2016-01-01) Šafka, Jiří; Ackermann, Michal; Bobek, Jiří; Seidl, Martin; Habr, Jiří; Běhálek, Luboš
    This article deals with specific polymer composites modified for the Fused Deposition Modeling (FDM) which is a 3D print technology. These two phase systems involve thermoplastic matrix filled with natural fibres. The crucial demand of this progressive technology is put on the accuracy of the semi-product formed into the filament shape. To reach the smooth production of 3D prototypes the filament should have a constant diameter. In the article, individual steps of the polymer composite pelletization and following pre-processing and processing activities are described. Among these steps the extrusion of the filaments belongs and subsequent print test on “RepRap” device accompanied by optimization of building parameters. Tensile specimens were chosen for print with regard to maps mechanical properties of this newly developed material which was the final stage of this work. Tensile test curves were then compared with those graphs which can be found for the material produced by conventional technologies such as injection moulding. © 2016 Trans Tech Publications, Switzerland.