bluuebunny/crossref_metadata_2025 huggingface dataset:
Double Windows in Heritage Listed Buildings
Authors: Kolář Radim , Sobotka Jindřich
Published: December 2016

Heritage listed buildings, or their parts, are subject to the decisions of state authorities in the field of heritage preservation. When windows are reconstructed, the requirements concerning the new design are most often based on the original appearance of the windows. In the case of double windows - the traditional style with space and reveal in between - the outer window is installed with insulated glazing while the inner window has a simple glazing, in order to meet the conditions of thermal related technical standards. For this reason, the contact between the window frame and the reveal must be tight with very low air permeability. The article presents the measurements of surface temperatures of both of the window parts and explores the issue of thermal humidity condition in the area between the windows.
Effect of the Moisture in the Heat Storage Capacity of Building Structures
Authors: Szodrai Ferenc , Lakatos Ákos
Published: December 2016

Buildings in Europe, account for about 20–40% of total final energy consumption. Therefore reduction of energy demand is crucial. It has become one of the most important issues to achieve energy saving at installations and refurbishments of buildings. Humidity in the wall structure of buildings produced by precipitate and other circumstances could modify the building’s heat capacity, the heat transfer coefficient furthermore density and/or other factors. In this study, wall structures of buildings with nearly zero net energy consumption were examined that were built from different materials with different moisture load. By applying different experiments and calculations we presented the changes of the stored heat energy of different wall structures in relation to the duration of the wetting time. The external wall of the building is the interface between the interior of the building and the outdoor environment. From the perspective of sorption and heat capacity, knowledge of the behavior of structures in relation to their moisture content, can help us to select the perfect type of wall. We have found three major traits peculiar to the change in the stored heat of different building structures in relation to the moisture load.
Comparison of Meteorological Climate Data Sets from Greater Žilina and their Influence on Temperatures within the Experimental Wall
Authors: Staffenova Daniela , Ponechal Radoslav
Published: December 2016

The experimental wall fragment (consisting of five different sections) was completed in 2010. Temperatures inside the sections had been recorded since. The laboratory centre of our department is also equipped with the own detached experimental weather station. In this paper, the outdoor boundary conditions obtained from the experimental weather station are compared to the automated weather station Dolny Hricov and to the phenological weather station in Zilina (with registering period of three times a day), both maintained by Slovak Hydrometeorological Institute (SHMU). For the comparison, there were selected 14 days from the years 2014-2016, to find some extremes. Differences between the data sets obtained from the stations were computed to each other and analysed in terms of boundary conditions for the HAM computer simulations. Differences between the temperatures under finish of the experimental wall fragment were found out by use of ESP-r software.
Calibration Method of Cool Box Used for Measuring of Thermal Conductivity Coefficient
Authors: Kurečka Petr , Teslík Jiří
Published: December 2016

One of the methods used for determining of the thermal conductivity coefficient value of building materials is the Calibrated and Guarded Hot Box method. This method is based on the principle of measuring the heat flux density that passes through the test specimen at a temperature difference between warm and cool parts of the measuring box. For measuring of thermal conductivity coefficient is at the Faculty of Civil Engineering of VŠB-TUO used the Cool Box. Measuring in Cool Box uses the same principle of measuring as Calibrated and Guarded Hot Box. For creating temperature difference during the measurements at the Cool Box is not used heat, but cold. Measurement of the thermal conductivity coefficient by a Cool Box is very complex in terms of measurement accuracy. That the resulting values as accurate as possible, it is necessary to calibrate itself refrigerated cabinets and all sensors that are used for measurements. This paper describes the principles of calibration of Cool Box and other components, which are used for measuring the thermal conductivity coefficient of selected natural building materials. Determination of the thermal insulation properties of selected materials is part of a long-term research focused on conventional and unconventional natural building materials.
Impact of Inlet Boundary Conditions on the Fluid Distribution of Supply Duct
Authors: Czetany Laszlo , Lang Peter
Published: December 2016

Ventilation is important to maintain the indoor air quality and other comfort parameters in the occupied zone. The design of ventilation systems is based on one dimensional approach. When the air distribution is modelled in the ventilated space usually CFD simulation is performed and simplified boundary conditions are defined at the locations where the supply air enters the room. However, in some cases it is difficult to predict the duct flow by 1D methods. The flow in the duct system determines the outflow at the air terminal devices. The interaction between the multiple system elements is important, since many different combinations are possible, for instance multiple bends can create a special flow field which also influences the distribution performance of the duct. It is very important to determine this impact, because the room airflow depends on it. In this study the impact of the inlet boundary conditions on the fluid distribution performance of a special supply duct –which is designed to provide uniform distribution– is investigated with CFD. Three different inlet boundary conditions are defined: constant inlet velocity and turbulence parameters estimated from intensity and hydraulic diameter, diffuser after fully developed turbulent pipe flow, diffuser with one bend and a Venturi-tube upstream. In each case, the simulations are performed with the realizable k-epsilon model. The reliability of the results is estimated with the grid convergence index.
Energy Saving Potential of Personalized Ventilation Applied in an Open Space Office under Winter Conditions
Authors: Krajčík Michal , Kudiváni Lucia , Mahdavi Ardeshir
Published: December 2016

Mixing and displacement air distribution are the main ventilation principles applied in both residential and non-residential buildings. Recently, personalized ventilation when the fresh air is delivered directly to the occupants at a high ventilation effectiveness has become an alternative. Despite of this fact, little research has been carried out to quantify the energy saving potential of personalized ventilation. This study aimed to quantify the effect of ventilation effectiveness and control strategy on the energy performance and thermal comfort for an open plan office equipped by different types of ventilation systems, including mixing ventilation with constant air volume, demand control ventilation and personalized ventilation. A model was created in a program for dynamic energy simulations TRNSYS, representing one floor of a typical office building divided into four zones with different orientations and a core. Space heating and cooling were provided by ceiling fancoil units recirculating the room air, thus the tasks of ventilation and air conditioning were provided by two separate systems. The potential of personalized ventilation to save energy for fans and for the heating coil of the ventilation system presented about 70% compared to constant air volume mixing ventilation, however, the overall saving was only 20% when also the energy demand for space heating was considered. The energy benefit of demand control ventilation and personalized ventilation depends on the energy need for space heating and cooling, system configuration and operation, and occupancy.
Experiment Based Analysis of Complex Posterior Waterproofing Systems
Authors: Dudás Annamária , Horn Valéria V. , Vinczlér Gergő
Published: December 2016

In connection with the problems of aging European building stock, the opportunity of posterior waterproofing methods emerges as a relevant solution. There are different technologies which are suitable against rising damp in walls, but the chemical injection system through injection boreholes is the most commonly used method due to its extensive usability and fast implementation. The aim of the experimental research was to measure the efficiency of the chemical injection method by the penetration of the injection agents. There were built several specimens of small size solid bricks and some further ones of coarse limestones. The three months long research allowed to determine the moisture content of the specimens before and after the injection process. The received results were mass-based and moisture content data was measured by Protimeter. Surface coating and renovation plaster give additional moisture protection and along with the chemical injection provide a complete posterior waterproofing system. The elements of posterior waterproofing cause changes in the vapour diffusion of renovated structures. However, diffusion-open orders of layers can solve the problem of evaporation, as environmental friendly reconstruction solutions. Based on the measured results of rising damp and known characteristics of cement-based waterproofing and renovation plasters, thermal simulations and hygrothermal analysis and thus building physical conclusions have been performed.
Analysis of Unreinforced Ceramic Wall Panels in the Mounting State
Authors: Karlík Štěpán , Lavický Miloš , Pěnčík Jan
Published: December 2016

Properties of building materials used for the construction of surrounding structures significantly contribute to creating a healthy and comfortable microclimate inside the rooms. Ceramics belong among materials which exhibit very suitable properties for the formation of the healthy environment. It is also one of the reasons that the fired clay structures remain popular among builders and that recovery of ceramic prefabrication can be seen in the Czech Republic. The important step towards rediscovering the benefits of the prefabricated ceramic elements is forthcoming production of unreinforced ceramic wall panels made of fired clay masonry units with tongue and groove, connected in the bed joints by two-component adhesives. Conventional analytical model for vertical loads is used in the operating state. However, in the transport and mounting state it is a structure stressed by bending in its own plane. This paper is focused on the issue of load-bearing capacity of structures with masonry units cross-sections that are not filled in head joints and therefore are unable to transfer either tensile or compressive stresses. On the segment of the wall panel is performed numerical model analysis using the finite element method in the computing program ANSYS and comparison of this analysis results with the results of the experimental tests.
Design and Numerical Modelling of Prefabricated Roller Blind Lintels
Authors: Lavický Miloš , Pěnčík Jan , Karlík Štěpán
Published: December 2016

The prefabricated roller blind lintels have become common solution, particularly for the single-leaf masonry structures without external thermal insulation system. These lintels, representing simple system solution, are designed to interrupt thermal bridges in a place of above the window lintel and simultaneously to provide sufficient reliability of load transfer. The actual outdoor blinds contribute to increase the thermal stability in the room in summer and winter season. They prevent overheating of the room in the summer months and reduce heat transmission through a window in the winter. This paper is focused on the design and numerical modelling of the prefabricated roller blind carrier lintels solutions. Methods of elimination of the thermal bridge are demonstrated on the example of a real produced prefabricated lintel. At the same time this paper deals with its structural analysis. Analyses were carried out using the method of numerical modelling, using finite element method and computing software ANSYS.
Rule Based Building Construction Generation: An Approach Based on Formal Language Methods
Authors: Sustr Christian , Pont Ulrich , Mahdavi Ardeshir
Published: December 2016

The composition of efficient and appropriate building constructions is a key agenda in the building delivery process. While this process is regularly considered to be of highest importance for the final quality of a building, many involved stakeholders regard it as a cumbersome and repetitive routine. Therefore, approaches to facilitate this process should be investigated. Toward this end, we address the layer-wise building component composition via formal language methods. These are regularly used in computer science to formalize real-world processes into a language that can be processed by a computer. Regarding building component generation, relationships and interdependencies between different layers need to be considered. While these are easy to understand for a skilled human planner with pertinent domain knowledge, the exact formulation of building composition rules is far from trivial. Thus, automated building part generation requires collection and formalization of the required knowledge regarding building component composition, so that it can be readily transformed into a processual form. After collection, definition and structuring of such rules, the overall process of component generation can be expressed in Pseudo-Code. This offers three major advantages: i. Pseudo-code is vendor and platform neutral and is a widely used concept in computer science; ii. Potential mistakes and issues can be easily identified, iii. Flexibility, extensibility and editing ease is ensured. In this contribution we illustrate a general approach, define certain rules and thresholds, and introduce a formalized method for building part generation. Furthermore, we demonstrate the concept via a limited number of constructions and discuss potential application scenarios.
Environmental Assessment of Buildings Constructed by Modern Methods of Construction
Authors: Mackova Daniela , Spisakova Marcela , Kozlovská Mária , Svajlenka Jozef
Published: December 2016

Currently, we are witnessing the significant impact of industrial activity on the environment. A recent study shows that construction is the third largest industry sector in terms of environmental pollution. One option to reduce these negative effects is environmental assessment of buildings, as well as the used building materials. One of the most comprehensive environmental assessment methods is LCA (Life Cycle Assessment), which includes the assessment of impacts within mode ”Cradle-to-gate” which is focused on assessment of a partial product life cycle from resource extraction (cradle) to the factory gate (i.e., before it is transported to the consumer). The aim of this paper is a comparison of the environmental impact of selected material variants applied within modern methods of construction. The comparison will be processed through the results of the case study containing three material variants of family houses construction in term of three selected parameters - embodied energy, global warming potential and acidification potential.
Testing of Fire Retardants
Authors: Fanfarová Adelaida , Makovická Osvaldová Linda , Gašpercová Stanislava
Published: December 2016

The authors deal with the importance and significance of fire retardants for fire protection in practice. The main aim of this paper is to inform the readers about the possibilities of wood modifications by fire retardants. The authors present the experiment of testing wood specimens applying the experimental scientific method of test for limited flame spread on the test bench under laboratory conditions. The results of the experiment represent fire-technical characteristics that describe the wood behavior during the process of combustion. Different types of fire retardants are evaluated according to the selected evaluation criterion - the weight loss of test specimens. The conclusion summarizes the results of the experiment and recommendations for fire retardant modification in practice.
Finite Element Analysis of Composite Ceramic-Concrete Slab Constructions Exposed to Fire
Authors: Nagy Balázs , Tóth Elek
Published: December 2016

In this research, conjugated thermal and fluid dynamics simulations are presented on a modern hollow clay slab blocks filled pre-stressed reinforced concrete beam slab construction. The simulation parameters were set from Eurocode standards and calibrated using data from standardized fire tests of the same slab construction. We evaluated the temperature distributions of the slabs under transient conditions against standard fire load. Knowing the temperature distribution against time at certain points of the structure, the loss of load bearing capacity of the structure is definable at elevated temperatures. The results demonstrated that we could pre-establish the thermal behavior of complex composite structures exposed to fire using thermal and CFD simulation tools. Our results and method of fire resistance tests can contribute to fire safety planning of buildings.
Study on Surface Treatments of Modified Wood Plastic Composite (WPC) to Improve Adhesion
Authors: Nečasová Barbora , Liška Pavel , Kelar Jakub
Published: December 2016

The presented case study is focused on the complications that affect the adhesion properties of wood plastic composites. In an effort to improve the physical properties of the WPC and the adhesive bonding between the selected material and adhesive systems intended for façade bonding, several surface pretreatments were performed. The surface modification consisted of mechanical roughening or physical treatment with diffuse coplanar surface barrier discharge. The shear strength of the adhesive bond was tested following ČSN EN 1465 and the maximum shear stress was calculated for each treatment method. Although, the increase in bond strength due to these treatments was measured only for one tested adhesive system where the strength was increased by 100% with respect to the control, the diffuse plasma treatment improved the adhesive bondability and a change in failure mode was observed in all tested cases.
Interaction of Dislocations at Interfaces in Multilayered Materials
Authors: Koguchi Hideo , Tanaka Yusuke
Published: December 2016

The authors construct a bridge between a microscale view and a nanoscale one in continuum mechanics. When the size of structure reduces to nanolevel, the ratio of surface to volume increases. Then, the surface stresses, which like to surface tension in fluid, influence on bulk stresses. In the present paper, the authors analyze a problem that anisotropic nanothin layers are deposited on a half substrate. Interface stresses and interface elasticity are taken into account for the boundary condition for each layer. Furthermore, misfit dislocation networks which generate from a mismatch of lattice parameters in crystals composing multilayers exist at each interface. A complicated interaction between misfit dislocation networks located at different interfaces will be demonstrated, and the results in the theory will be compared with those in a molecular dynamic method using a generalized embedded atomic potential.
Study of Influence of Residual Stresses on Crack Propagation in Particulate Ceramic Composites
Authors: Majer Zdeněk , Náhlík Luboš , Štegnerová Kateřina , Hutař Pavel , Bermejo Raúl
Published: December 2016

The aim of the present work is to analyze the influence of residual stresses in the particulate ceramic composite on the crack propagation. The crack propagation direction was estimated using Sih’s criterion based on the strain energy density factor. A two-dimensional finite element model was developed for determination of crack path. The residual stresses resulting from the mismatch of coefficients of thermal expansion during the fabrication process of the composite were implemented to the computational model. The effect of the particles shape on the crack propagation was investigated. Conclusions of this paper can contribute to a better understanding of the propagation of micro-cracks in particulate composites in the field of residual stresses.
Behavior of Lode Dependent Plasticity at Plane Strain Condition and its Implication to Ductile Fracture
Authors: Šebek František , Petruška Jindrich , Kubík Petr
Published: December 2016

Variety of metals are complex materials exhibiting various behavior under different loading. Many metallic materials exhibit Tresca-like behavior rather than von Mises. It means different behavior in tension under plane strain and uniaxial stress conditions. This might be described by Lode dependent plasticity which should result in better prediction in force or torque responses of material tests. Good agreement between computation and experiment is also very important when calibrating the ductile fracture criteria. Several tests under plane strain and uniaxial stress states were carried out on aluminum alloy 2024-T351 where the Lode dependency was significant. The Lode dependent plasticity was implemented along with von Mises and Tresca-like yield criteria, which resulted in improvement of force–displacement responses of plane strain tests simulations. But it also caused significant change in the stress state of tensile flat and grooved plates which wrongly approached uniaxial tension condition. This inconvenience prevents plane strain experiments from using for calibration of ductile fracture criteria under these circumstances.
Fretting High-Cycle Fatigue Assessment through a Multiaxial Critical Plane-Based Criterion in Conjunction with the Taylor’s Point Method
Authors: Ronchei Camilla , Carpinteri Andrea , Fortese Giovanni , Scorza Daniela , Vantadori Sabrina
Published: December 2016

The critical plane-based multiaxial criterion originally proposed by the authors for plain fatigue is here applied to estimate the crack initiation life of fretting high-cycle fatigued structural components. Although fretting fatigue can be regarded as a case of multiaxial fatigue, the common multiaxial fatigue criteria have to be modified to account for the severe stress gradients in the contact zone. Therefore, the above criterion is used in conjunction with the Taylor’s point method to numerically estimate the fatigue life of Ti-6Al-4V and Al-4Cu specimens under cylindrical contacts.
Hydrogen-Induced Ductility Loss of Austenitic Stainless Steels for Slow Strain Rate Tensile Testing in High-Pressure Hydrogen Gas
Authors: Matsuoka Saburo , Yamabe Junichiro , Matsunaga Hisao
Published: December 2016

For slow strain rate tensile (SSRT) test in hydrogen gas, the degradation in relative reduction in area (RRA) of 300-series austenitic stainless steels is mainly attributed to hydrogen-assisted surface crack growth (HASCG) accompanied by quasi-cleavages. To establish novel criteria for authorizing various austenitic stainless steels for use in high-pressure gaseous hydrogen, a mechanism of the HASCG should be elucidated. At first, this study performed SSRT tests on six types of austenitic stainless steels, Types 304, 316, 316L, 306(hi-Ni), 304N2 and 304(N), in high-pressure hydrogen gas and showed that the RRAs were successfully quantified in terms of a newly-proposed nickel-equivalent equation. Then, to elucidate the microscopic mechanism of the HASCG, elasto-plastic fracture toughness (JIC), fatigue crack growth (FCG) and fatigue life tests on Types 304, 316 and 316L were carried out in high-pressure hydrogen gas. The results demonstrated that the SSRT surface crack grew via the same mechanism as for the JIC and fatigue cracks, i.e., these cracks successively grow with a sharp shape under the loading process, due to local slip deformations near the crack tip by hydrogen. Detailed observations of SSRT surface cracks on Types 304 and 316L were also performed, exhibiting that the onset of the HASCG occurred at the true strain of 0.1 or larger in high-pressure hydrogen gas.
Intrinsic Behaviour of Mode II and Mode III Long Fatigue Cracks in Zirconium and the Ti-6Al-4V Alloy
Authors: Vojtek Tomáš , Pokluda Jaroslav , Hohenwarter Anton , Pippan Richard
Published: December 2016

This work is focused on experimental study of micromechanisms of mode II and mode III fatigue cracks in metallic materials in the near-threshold regime. The resistance to fatigue crack growth can be divided to an intrinsic component (ahead of the crack tip) and an extrinsic component (shielding, closure), which is significantly higher than the intrinsic one. Fracture surfaces from the Ti6Al4V alloy and pure zirconium were observed in three dimensions. Experiments were conducted using a special device for simultaneous crack loading in modes II and III. Additionally, pure mode II and pure mode III experiments were done using CTS and torsion specimens, respectively. At the beginning of all experiments, crack closure was eliminated due to precracks generated under cyclic compressive loading. A common mechanism of local mode II advances was observed in both modes II and III. The results were similar to those of pure titanium. The hcp metals exhibit a transition behaviour between materials with coplanar shear-mode crack propagation and materials with a high tendency to deflect to the opening mode I.
Deformation and Fracture of Metallic Nanowires
Authors: Aish Mohamed Mahmud , Starostenkov Mikhail D.
Published: December 2016

A many-body interatomic potential for metallic nanowires within the second-moment approximation of the tight-binding model (the Cleri-Rosato potential) was employed to carry out three dimensional molecular dynamics simulations. Molecular dynamics simulation results for metallic nanowires at various temperature are presented. The stress–time and stress length curves for nanowires are simulated. The breaking and yield stress of nanowires are dependent on the Volume and temperature. The necking, Plastic deformation, slipping domain, twins, clusters, microspores and break-up phenomena of nanowire are demonstrated. Stress decreases with increasing nanowire volume and temperature. The final breaking position occurs at the central part of the nanowire when it is short, as the nanowire length increases the breaking position gradually shifts to the ends.
Micromechanism of Thermally Induced Breaking of One-Dimensional Nanocrystals
Authors: Kotrechko Sergiy , Stetsenko Nataliya , Kolyvoshko Eugene
Published: December 2016

Thermo-fluctuation model of failure of one-dimensional nanocrystals is offered for wide range of change in temperature, time and applied loading. Unlike the classic models, which are based on the theory of reaction rates, in present model the failure initiation is related to the instability of atomic interaction. It enables to account for the effect of both temperature and applied loading on the lifetime of crystal within a framework of the unified approach. The model proposed was employed to predict the temperature dependence of both strength and lifetime of carbyne nanoconductor (CNC). Obtained temperature dependences agree well with the MD-simulation findings. Within the framework of the above model, CNC lifetime was estimated. It is exhibited that for temperatures not higher than 600K, CNC have a long-lasting lifetime, so, they can be used in nanodevices.
Fatigue Crack Surface Topography after Plasma Nitriding Process
Authors: Studeny Zbynek , Pokorný Zdeněk , Dobrocký David
Published: December 2016

Fatigue characteristics of steel 41CrAlMo7-10 and topography analysis testing methodology of fish eye were studied. Both sets of samples were heat-treated at the same conditions and subsequently were plasma nitrided. The mixture ratio of these main gases, forming the atmosphere during the plasma nitriding was inverted for both sets of samples. Process parameters such as the duration, the applied voltage and the pulse length were identical for all samples. Following test after heat treatment and surface layer formation by plasma nitriding process for both sets of samples was the rotating bending fatigue testing in the machine R.R.Moore L2568 of Instron Co. The fatigue tests were carried out in accordance with the CSN 42 0363 Fatigue Testing of Metals, Methodology of Testing. Then, tests were evaluated numerically and graphically using Wöhler`s (S-N) curve in a semi-logarithmic form. The testing was stopped after reach the fracture of tested sample or after 107 cycles. The surface topography of fatigue cracks were evaluated on Talysurf CCI. The topography analysis was mainly focused on the initial part of fatigue crack called the fish-eye. The topography analysis was performed only on one selected sample of each series.
Toughening Behavior in Alloy 617 with Long Term Ageing
Authors: Chai Guo Cai , Calmunger Mattias , Johansson Sten , Moverare Johan
Published: December 2016

The influence of ageing at temperature 700°C for up to 20 000 hours on the deformation, damage and fracture behavior of Alloy 617 has been investigated by two toughness tests. Dense nano γ` phase and carbides are the main precipitates. However, the long-term aged material still shows high toughness. The mechanism has been studied using electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). The results show that dense nano/micro-twins have been formed in the adjacent of the fracture front during the impact toughness or CTOD testing. Increase of ageing time reduces the number of nano/micro-twins, but they can be observed in all aged materials in spite of different strain rates. This indicates that besides dislocation slip, twinning is another deformation mechanism in long term aged material during the toughness tests. Formation of nano/micro-twins may be one of contributions to high toughness in the aged material, which is termed as twin induced toughening.
Stress Intensity Factors for Rough Cracks Loaded in Mode II
Authors: Žák Stanislav , Horníková Jana , Šandera Pavel
Published: December 2016

Most fracture mechanical models do not take the materials microstructure into account and use averaged material properties although the real crack flanks and fronts exhibit microstructurally induced tortuous shapes. These influences the stress-strain field at the crack front as well as the related stress intensity factors. This phenomenon was investigated by some authors only for remote mode I loading and was named geometrically induced shielding. This study is focused on the analysis of the stress intensity factors for rough cracks loaded in the shear mode II by modelling the Compact-Tension-Shear (CTS) specimen containing cracks of various roughness. The study revealed that, in accordance with our previous study, already small changes in the crack roughness have a rather high influence on the local field of stress intensity factors. The local stress intensity factor KII decreases with increasing roughness and, for its higher levels, it converges to a constant value that is significantly lower than that of the remote mode II loading associated with the planar crack of the same length.
{332}<113> Twinning Deformation in a Cold-Rolled Biocompatible Ti-Nb-Zr-Fe Alloy
Authors: Cojocaru Vasile Danut , Cinca Ion , Serban Nicolae , Gordin Doina Margareta , Angelescu Mariana Lucia , Cojocaru Elisabeta Mirela , Raducanu Doina
Published: December 2016

In the present days titanium and titanium alloys are extensively studied and used as biomaterials due to their biological, mechanical and physical properties. During last year’s special attention was paid to β-Titanium alloys due to their low elastic modulus. The present study investigates the twinning deformation features occurred during multi-pass cold-rolling processing of a biocompatible Ti-Nb-Zr-Fe alloy. Twinning deformation features were investigated using EBDS analysis by means of Inverse Pole Figures (IPF’s), Pole Figures (IP’s) and computed Schmid factor (SF’s) for the possible {332}<113> twinning variants.
Ni-Ti Self-Expanding Vascular Stent Configuration and Biomedical Interaction with Artery: Finite Element Analysis
Authors: Shayanfard Pejman , Šandera Pavel , Horníková Jana , Petruška Jindrich , Sittner Petr , Pokluda Jaroslav
Published: December 2016

In spite of the fact that the US Food and Drug Administration (FDA) has approved Intracoil and s.m.a.r.t Nitinol stents for superficial femoral artery (SFA), some alternative designs of Nitinol stents are being implanted today, representing the off-label use of the devices. Among the currently stents used for the SFA, s.m.a.r.t and Intracoil stents show the most desirable long-term results but it is not understood why. In the present work, delivery of the s.m.a.r.t and Intracoil Nitinol stents and their release inside a stenotic point of the artery was simulated by FE implemented SMA model using a creative manual controlled method. The influence of the stent design on the stent–vessel interactions and stress state within the stent material after completion of the deployment was revealed. It was found that the Intracoil stent shall be more successful in eliminating the stenosis and less prone to fatigue failure, even though it had less thickness and less mean coil diameter.
Durability of Amorphous and Crystalline BMAS Thermal Barrier Coatings Produced by Plasma Spraying
Authors: Čelko Ladislav , Jech David , Dvořák Karel , Šulák Ivo , Klakurková Lenka , Obrtlík Karel
Published: December 2016

Barium-Magnesium-Aluminium-Silicate (BMAS) powder was produced from a mixture of initial compounds BaO–MgO–Al2O3–SiO2 by means of solid state synthesis at the temperature of 1200 °C for 3 hours in a laboratory furnace. Synthetized powder was crushed into the fraction of 15-45 μm in a planetary ball mill. Thermal barrier coating system consisting of CoNiCrAlY (bond coat) and BMAS (top coat) was sprayed by atmospheric plasma spray technique onto the polycrystalline nickel-based superalloy substrate. During plasma spraying process, the BMAS underwent phase transformation and the amorphous phase within the top coat was produced. Therefore, after the spraying, several samples were crystallized via annealing in a furnace (4 hours at 1200 °C or 24 hours at 1000 °C) or by subjecting them to several passes of plasma jet. Both samples with an amorphous phase and fully-crystallized samples were subjected to the fire in a burner-rig test (propane-oxygen flame, single 3 + 3 minute cycle), where the top coat reached the temperature of 1150 °C. Top coat failure occurred during the cooling period due to the transformation of the amorphous phase into the crystalline one and/or due to the difference in thermal conductivity and expansion between the top coat and the bond coat.
Nanostructural Investigation of Case Hardened Steels for Speed Gears Applications by Small-Angle Neutron Scattering (SANS)
Authors: Rogante M. , Havránek Vladimír , Mikula Pavol , Ryukhtin Vasyl
Published: December 2016

17NiCrMo7, 19MnCr5 and 27MnCr5 low-alloy case-hardening steels samples have been investigated by SANS (Small-Angle Neutron Scattering), to achieve data on bulk nanoscale structure characterisation and complementary analytical and crystallographic information. The reported results are related in particular to the size distribution of nanosized pores which can help to comprehend the structural basis for the physico-chemical properties and thus to improve quality and durability of the considered materials. A complementary PIXE investigation has been also carried out, with the aim of a non-destructive assessment of the elemental composition of the considered samples.
Influence of the Loading Path on the Deformation Mechanisms of Magnesium Alloys
Authors: Máthis Kristián , Čapek Jan , Clausen Bjørn , Panzner Tobias
Published: December 2016

The evolution of deformation mechanisms in randomly textured magnesium alloy during uniaxial and biaxial mechanical tests has been monitored using concurrent application of acoustic emission and neutron diffraction methods. The influence of the loading path on both twinning and dislocation slip is discussed in detail. It is shown that both the twinning and non-basal slip are sensitive to the loading direction.
Influence of Carbon Admixtures to the Electrical Conductivity of Slag Mortars
Authors: Kusák Ivo , Lunak Miroslav , Mikova Maria , Rovnaník Pavel
Published: December 2016

Applied research tries to offer new materials from the slag mortars. Basic research tries to explore these engineered materials from the perspective of all the possible test methods. Modern vector analyzer R&S ZNC with a coaxial probe DAK-12 from Speag company was used to determine permittivity and dielectric loss factor of the beams and interesting spectrums of electric resistance were measured for samples with varying content of carbon powder. Carbon contributes from the viewpoint of electrical properties, for example it improved antistatic properties of the floor. In addition to the vector analyzer – the simpler measuring unit was also used. In a frequency range of 40 Hz to 1 MHz values of electrical resistance and permittivity values of the beams with different content of graphite powder, labeled Cond 896 were determined. The higher content of graphite powder increases the electrical conductivity; building materials based on cement are becoming more measurable using electromagnetic measuring methods. The most striking change in the relative conductivity was observed at excitation frequency of the external electric field of 1 kHz. At high frequencies of electrical excitation field from 10 MHz to 3 GHz values of the real part of permittivity were determined by vector analyzer. These measurements are among the building materials used rarely and they open new possibilities of diagnostics.
Damage Progression and Fragmentation in Atomistic, Single Crystal Copper at High Strain Rates
Authors: Huddleston Bradley D. , Dickel Doyl E. , Horstemeyer Mark F. , Williams Neil , Danielson Kent , Hammi Youssef
Published: December 2016

We show a correlation between nanoscale damage and fragmentation length scale through atomistic simulations. We simulated homogeneously expanding perfect, single crystal copper at rates ranging from 1E+08 to 3E+10 s-1 and temperatures from 200 to 1000 K. Damage was quantified in terms of void number density, average void volume, and void volume fraction. We quantified fragmentation size in terms of a length scale parameter, the solid volume per void surface area. A-1⁄2 power law relationship between the fragment length scale and strain rate was observed following the predictions of Mott. The fragmentation length scale and the maximum void number density are strongly correlated for this damage mechanism. We can scale up the relationships between damage and fragmentation observed in the molecular dynamics simulations to motivate a continuum scale fragmentation model.
Effect of the Load Eccentricity on Fracture Behaviour of Cementitious Materials Subjected to the Modified Compact Tension Test
Authors: Seitl Stanislav , Ríos José D. , Cifuentes Héctor , Veselý Václav
Published: December 2016

Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or possibly other relevant fracture models. Our contribution is focused on a set of experimental tests which are used to study the fracture behaviour on notched dog-bone-shaped specimens made of cementitious materials. These specimens are subjected to modified compact tension (ModCT) test under a specific range of eccentricity of the tensile load. This type of test generates a stress state in the specimen ligament which combines a direct tension with a defined level of bending due to eccentricity of the tensile load. Several values of relative notch length are also considered. While the crack propagates, a variety of stress states, resulting in variations in the crack-tip stress and deformation constraint, appears in the ligament zone because of the changes in the eccentricity of the applied load, which influences the fracture behaviour of the investigated specimens. The K-calibration, T-stress, CMOD and COD curves for ModCT specimens are introduced and variations of these curves with varying load eccentricity are discussed.
The Influence of Plasma Nitriding Process on Mechanical Properties of 14NiCr14 Steel
Authors: Dobrocký David , Manas Pavel , Pokorný Zdeněk , Studeny Zbynek
Published: December 2016

The article deals with an alteration of mechanical properties of plasma nitrided steel. Experimental work was focused on evaluation of influence of plasma nitriding process on the notch toughness of steel. Experiments were realized on V-notch samples of size 10x10x55 mm (according to ISO 148-1 standard) from 14NiCr14 steel. The 14NiCr14 steel was heat treated prior plasma nitriding. The heat treatment consisted of hardening at 850 °C and tempering on elimination of internal stress at 200 °C. Heat treated experimental samples were plasma nitrided at 450 °C, 500 °C and 550 °C. The notch toughness tests of steel were carried out using the instrumental Charpy hammer at test temperatures-40 °C, +21 °C and +70 °C. The notch toughness of plasma nitrided samples achieved nearly identical values as heat treated samples thus plasma nitriding did not reduce the values of notch toughness. The increase in temperature of the plasma nitriding process even led to achievement of higher values of notch toughness compared with heat treatment specimens namely at all test temperatures.
Dynamics of Bicomponent Nanoparticle Formation under Metal Wire Explosion
Authors: Zolnikov Konstantin Petrovich , Kryzhevich Dmitrij Sergeevich , Korchuganov Aleksandr Vyacheslavovich , Psakhie Sergey Grigorievich
Published: December 2016

A molecular dynamics simulation of bi-component nanoparticle formation under synchronous electric explosion of Cu and Ni wires was carried out. The approximation of the embedded atom method for a description of the interatomic interactions was used. The simulated nanowires had a cylindrical shape. Periodic boundary conditions were used along the cylinder axis, while in the other directions a free surface was simulated. Heating of the nanowires was performed by scaling of the atomic velocities following a linear law while maintaining a Maxwell distribution. It was shown that as a result of the synchronous electrical dispersion of metal wires the bi-component nanoparticles having a block structure may be formed. The basic mechanism of particle synthesis was the agglomeration of smaller clusters, and the minor one was the deposition of atoms from the gas phase on the particle surfaces. It was found that the distribution of chemical elements was non-uniform over the cross section of the synthesized particles. The concentration of Cu atoms in the subsurface region was higher than in the particle volume. It was noted that the method of molecular dynamics can effectively be used to select the optimal technological mode of producing nanoparticles with a block structure using electric explosion of metal wires.
Low Temperature Strain Rate Sensitivity of Titanium Alloys
Authors: Vigié Héloise , de Paula Thalita , Surand Martin , Viguier Bernard
Published: December 2016

Titanium alloys are widely used in many industrial applications such as in aeronautics due to their combination of good mechanical properties, excellent corrosion resistance and low density. The mechanical behaviour of titanium alloys is known to exhibit a peculiar dependence on both deformation temperature and strain rate. Titanium alloys show significant room temperature creep and they are very sensitive to dwell fatigue and sustained load cracking. This behaviour is related to the viscosity of plastic deformation in titanium alloys, which can be represented by a strain rate sensitivity (SRS) parameter. The present study aims to compare the tensile behavior of two different titanium alloys, Ti-6Al-4V and β21S, which exhibit dissimilar microstructures. Results of tensile tests, performed under constant strain rate and including strain rate changes, are reported in terms of flow stress, ductility and SRS over a wide range of temperatures.
Creep Processes in MAR-M247 Nickel-Base Superalloy
Authors: Kvapilová Marie , Kuchařová Květa , Hrbáček Karel , Sklenička Václav
Published: December 2016

Creep processes in MAR-M247 Nickel - Base Superalloy were studied at elevated temperatures. The stress exponents of creep rate n and time to fracture m indicate power-low (dislocation) creep regime and suggest the same controlling mechanism for the creep deformation and fracture. The variation of values of parameter n within the interval of applied stress may indicate changes in the rate-controlling creep deformation mechanism. The possibility of using of Monkman-Grant relationship for creep life prediction was demonstrated.
Influence of the Microstructure on the Fatigue Cracks Growth in the Joint Zirconium-Steel Made by Explosive Welding
Authors: Prażmowski M. , Rozumek Dariusz , Paul Henryk
Published: December 2016

This paper assesses the effect of various values of detonation velocity on the quality of the bond zone. The results of structural, static and fatigue studies were presented for bonds in the initial state. Depending on the applied technological settings of welding, most cases displayed a wavy bond with highly diversified parameters of the wave. High detonation velocities favoured the formation of waves with great height and length and clearly affect the increase in the volume of hard and brittle regions of melt in the bond zone. Increased volume of the melted regions in the bond zone results in the decrease of fatigue resistance and strength properties of the clads.
Joining Low Temperature Co-Fired Ceramics, Al2O3 and SiC Substrates for Higher Operating Temperature Applications
Authors: Somer Jakub , Klíma Martin , Machac Petr , Szendiuch Ivan
Published: December 2016

The article deals with forming solid joints of Low Temperature Co-fired Ceramic with Alumina or Silicon Carbide chips. The aim of this study is to find material of standard thick film layer process, which would be useful for electronic chip packages designed for higher operating temperatures (from 150 up to 800 °C). Heraeus Hera Lock 2000 Low Temperature Co-fired Ceramics (LTCC) was chosen, because of its nearly zero shrinkage during firing. Also other LTCC types were used to comparison of results. Conductive and isolating thick film pastes are used for joining. Temperature cycling of samples was applied. Strength of cycled samples was investigated by mechanical shear tests. The structure of microsection of joints was analyzed using optical and scanning electron microscope. The results show that thick film pastes are usable for joining above mentioned materials in specific temperature range.