bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Aspects of Gravitational Ventilation in the Heating Season
Authors: Kalmár Ferenc
Published: December 2016

Natural ventilation is currently widely used in existing buildings in order to assure the fresh air needed by occupants. The low investment and operational costs are the most important advantages of this type of ventilation. However, the dependency on the meteorological parameters has to be considered as disadvantage of the natural ventilation. In case of buoyancy-driven ventilation, the variation of the outdoor temperature results in the variation of the infiltrated air flow, CO2 concentration in the indoor air and energy demand of the ventilation. The air inlet and outlet orifices have to be properly chosen in order to meet the indoor air quality and energy requirements at the same time. In this paper the CO2 concentration and energy aspects of gravitational ventilation are discussed in case of a typical block of flats.
Analysis of Energy Sources on Energy Indicators Performance
Authors: Pitonak Anton , Lopusniak Martin
Published: December 2016

In the members states of the European Union, portion of buildings in the total consumption of energy represents 40%, and their portion in CO2 emissions fluctuates around 35%. The European Union is trying to protect the environment by reducing energy demand and releasing CO2 emissions into the air. Energy performance is the quantity of energy, which is necessary for heating and domestic hot water production, for cooling and ventilation and for lighting. Based on results of energy performance, individual buildings are classified into energy classes A to G. A global indicator (primary energy) is the decisive factor for final evaluation of the building. The new building must meet minimum requirements for energy performance, i.e. it must be classified to energy class A1 since 2016, and to energy class A0 since 2020. The paper analyses effect of the use of different resources of heat in a family house designed according to requirements valid since 2020, and its subsequent classification into an energy class.
Glazing with Low-Emissivity Layers and its Performance Simulation
Authors: Rabenseifer Roman
Published: December 2016

The contribution deals with the importance of low-emissivity glazing layers in improving the energy balance of building interiors. It describes the effects of changes in surface emissivity of glass, depending on the position of low-emissivity layer. It also discusses principles, advantages and disadvantages of the most common glazing combinations with regard to interior visual and thermal comfort and also slightly misleading interpretations caused by complexity of the matter. The discussion (and comparison) is based on methods and tools used in computer-aided building performance modelling and simulation and on recent information from glass industry.
Incidence of Microorganisms on Insulated Facades in the Selected Location (Ostrava-Poruba)
Authors: Kubečková Magdaléna , Kubečková Darja , Kučeriková Veronika
Published: December 2016

Incidence of microorganisms on thermal-insulated facades in the selected location (Ostrava-Poruba). Incidence of microorganisms on facades is more and more common. It benefits mostly from façade´s thermal insulation. This problem is not only esthetical. Incidence of microscopic fungi increased due to environmental changes. Every person is breathing spores (reproductive particles of mould) unknowingly. There is evidence that spores are closely related to respiratory illnesses. Objects that are vulnerable to microorganisms should be managed in a way, where there is no risk of harm to us or people around us.
Analysis of Thermal Comfort in Flat in New High Residential Building
Authors: Budiaková Mária
Published: December 2016

This paper focuses on the analysis of thermal comfort in a flat in the new high residential building. Providing the optimal parameters of thermal comfort in each room of the flat is the basic prerequisite for the satisfaction with housing. Incorrect position and size of heating elements, incorrect positioning of the furniture and incorrect use of residential interiors may significantly disturb the thermal comfort. Residential areas in the new residential buildings are much more intensively used as in the other types of buildings. Surface of new flats is the most optimized. Experimental measurements were carried out in the winter season in 2016 in the residential rooms of the large flat in the new high residential building. Device Testo 480 with temperature and humidity sensor, globe thermometer and turbulence sensor was used for the measurements. Obtained values of air temperature, air relative humidity, air velocity, globe temperature and indexes PMV, PPD are presented in the graphs. Heating system of the flat and the possibility of its regulation, positioning and size of the heating elements in the individual rooms, positioning of the furniture and the utilization of rooms were evaluated on the basis of parameters of thermal comfort. In the conclusion of the paper, there are principles on the architectural design of the residential interiors and their heating in the new residential buildings.
Recommendations for Automatic Opening Vents (AOV) in an Office Building in Terms of Thermal Instability in Relation to Natural Ventilation and Cooling
Authors: Sedlák Pavol , Stuart Jay , Búryová Dominika
Published: December 2016

One of the optimal and most economic ways of completing a thermal assessment of a building is with a precise dynamic thermal simulation, where a building envelope and its systems are simulated and evaluated in a virtual climate using real meteorological data. The simulation parameters can be exported to a Building Management System for a particular building, as simulation problems of natural ventilation reflects the real behaviour of a building. Instability of dynamic thermal simulation is a typical issue for certain conditions, as window operations can cause excessive interior temperature fluctuations and even trigger the heating system if the common ON/OFF or simple linear operation function is used. To solve the problem, reduction of the simulation time-step is usually used, though the principle of the air flow is not handled. Additionally this solution multiplies the simulation complexity, though the instability of the model is significantly reduced. The case model clearly showed a negative contribution of AOVs operated by linear function related to temperature or CO2 at initial simulations, by increasing the energy consumption of the building.
Monitoring of a Prototypical Free-Running Building: A Case Study in a Hot-and-Humid Climate
Authors: Eikemeier Sören , Schuss Matthias , Pont Ulrich , Mahdavi Ardeshir , Wimmer Robert
Published: December 2016

The provision of comfortable indoor conditions is widely considered as one of the key tasks of architecture. Hereby, different climatic regions require different concepts for the operation of buildings. Achieving thermal comfort in buildings in hot and humid regions without Air-Conditioning can be considered as a challenging task. In this context we present a monitoring study of the indoor conditions in a new prototype building, called the Zero Carbon Resort Demonstration Cottage. This building was designed according to passive cooling principles with the intent to reach a high degree of sustainability and to have little environmental impact. To explore the viability of this concept, we deployed a comprehensive monitoring of the outdoor conditions via a weather station and of the indoor conditions via air temperature and relative humidity sensors. Moreover, short-term monitoring of thermal comfort was conducted. In a first analysis step we compared the results of the indoor monitoring with the corresponding outdoor measurements. In a second step we conducted a standardized thermal comfort study. Thereby we considered the special circumstances of the thermal comfort in naturally ventilated buildings. Results suggest that acceptable indoor conditions can be maintained, if passive cooling methods are applied properly.
Effect of Ventilation in Protected Escape Ways upon the Thermal Properties of these Spaces
Authors: Rusinová Marie , Sedláková Markéta , Kalousek Miloš
Published: December 2016

Protected escape routes enable the rescuing of persons to the outside of a building on fire. They are characterized, in particular, by strict requirements relating to the aeration of such spaces. However, the fulfilling of these limits may impact the monitored thermal characteristics of the respective internal areas. The outlined dilemma will be illustrated by way of an example of a protected escape route aerated by positive-pressure ventilation.
Economic Analysis of Energy Saving Measures in Current Prefabricated Panel Buildings
Authors: Pašek Jan , Tvrzníková Diana
Published: December 2016

The paper focuses on analysis and assessment of economic effectivity of measures taken in order to lower energy demands of prefabricated panel residential buildings. For this purpose, a group of buildings with previously made modifications with potential to lower the energy and heating consumption were selected. Next, the development of their energy consumption and their costs was monitored. The assessment of achieved figures was made with regards to amount of costs which were paid for these measures and also with regards to their service life, amount of gained subsidy and decrease of consumed energies and operational costs of the buildings after the measures were taken. It was found that there had been a significant difference in investment returns for constituent technical measures. For some of them, it is not even realistic to expect reaching the return of investments during their service life period.
Impact of External Shading on Light Comfort and Energy Efficiency in Apartment Buildings
Authors: Iringová Agnes
Published: December 2016

The paper is focused on an example of volume solution of a superstructure designed within allowable legislative limits and its impact on light comfort in shaded flats. It deals with issues such as : optimizing allowable amount of external shade in relation to sustainable hygienic quality of residential environment, an impact of superstructure ́s shade on insolation time in affected flats and consequently on passive solar gain intensity of apartment buildings, as well as evaluation of energy efficiency of infill walls in compensating of their heat loss in heating period, depending on the amount of external shading, their orientation, and thermo-insulation quality in all model scenarios - current, legislatively allowable, and optimized. It solves compatibility of optimized shading in terms of hygienic quality in relation to the increased efficiency of solar gains utilization to cover heat loss by heat-exchange shell in contemporary and prospective low-energy buildings.
A Comparative Assessment of Diffuse Fraction Models
Authors: Vazifeh Ehsan , Schuss Matthias , Mahdavi Ardeshir
Published: December 2016

Many building performance applications (energy use, solar gains, thermal comfort, renewable energy systems, daylight, etc.) require information about both direct and diffuse components of the incident solar radiation. However, most meteorological stations only monitor global horizontal irradiance. Consequently, multiple methods have been proposed in the past to derive from measured global horizontal irradiance data the diffuse fraction. Thereby, additional data regarding other parameters such as clearness index, solar altitude, air mass, and turbidity are used. Given the importance of this procedure for the down the line tools, its reliability represents a critical issue. To address this point, we pursued an empirical approach. A number of existing methods for the computation of the diffuse fraction were selected. Actual measurements of global and diffuse irradiance were obtained for seven locations in USA and one location in Austria. The measured global irradiance data for these locations were fed to the aforementioned diffuse fraction models. The calculation results were then compared with the corresponding empirical data. The comparative assessment yielded a number of findings. The relative performance ("ranking") of the models was found to be more or less consistent across the different locations. However, none of the models can be said to be performing wholly satisfactory. For instance, the best performing model displayed only in 45 to 65 percentage of the cases relative errors less than 20%. In case of the worst performing model, the percentage of the cases for which relative errors were less than 20% was even smaller, namely 30% to 60%.
The Impact of Decisions Made in Various Architectural Design Stages on Life Cycle Assessment Results
Authors: Kiss Benedek , Szalay Zsuzsa
Published: December 2016

Life Cycle Assessment (LCA) is an advantageous tool for the analysis of the overall environmental effects of a building. Most of the decisions that influence the final result of an LCA are made during the design process of the building. Therefore, LCA in early design stages is crucial, because the changes in this period of design are cheaper and more effective. However, there are many other aspects that influence the design of a building. During the design process a high number of variables have to be defined, and in each design stage a specific number of variables have to be fixed depending on various engineering considerations. In this paper we investigate the effect of decisions made in each design stage on LCA results. Within this paper the available possibilities are compared with the variant that was actually selected in each stage, and it is evaluated how environmental indicators evolve during the whole design process. The approach is demonstrated on a case study of a realized single family house.
Environmental Simulations and their Role in the Research of Human Responses to Environmental Stimuli
Authors: Kotradyová Veronika , Salcer Igor , Vavrinský Erik
Published: December 2016

The paper is aimed at the problematics of environmental simulations as one of the efficient methods of behavioural research for exploring the reactions of respondents to certain environmental settings. It explores the contemporary situation of the development of simulation at different levels within the environment, serving as visualizations of designed spaces, for games and simulation /testing of subjective and objective responses to different environmental stimuli. In our long-term research at the BCDlab, we are focused on body conscious design, which means exploring relationships: body/nervous system and the environment with an aim to design human friendly solutions through spatial design. To gain our own experiences with environmental simulations and their impact, in 2015, the Faculty of Architecture BCDlab, developed an interactive application, BCD-APP, which works as a web interface and also in virtual reality. The paper presents the process of setting research methods and results of the first pilot tests of the app as a research tool, with a small controlled group of respondents. They were confronted with pre-selected settings of materials, colours and surface finishing, and with the setting of their own choice, the subjective and objective physiological reactions (brain waves and respiration) were measured by EEG sensors and evaluated in a Labchart environment.
Research on Slaked Lime as Ecological Moisture Retardant on Sheep Wool and Straw
Authors: Mitterböck Michael , Korjenic Azra
Published: December 2016

This paper is about an experiment which should prove that slaked lime is suitable as an ecological moisture retardant. Therefore, the performance of straw, sheep wool, hemp and directed hemp covered with slaked lime was monitored over a long period. The other half of the probes were uncovered to serve as reference data. The main focus of this experiment is to determine the moment when the probes start to mold as extreme humidity in reality only lasts for a short time. During the experiment the used material is continuously exposed to moisture whereas under non-experimental conditions exposure to moisture would last for a much shorter period of time (cooking, cleaning, etc.) This paper only covers the performance of straw and sheep wool covered with lime. Also the spreading of mold will not take place.
Influence of Impurities on Grain Boundaries Cohesion in B2-TiMe
Authors: Kulkova Svetlana , Bakulin Alexander , Kulkov Sergey
Published: December 2016

The effect of interstitial and substitutional impurities on grain boundary (GB) cohesion in the series of B2-TiMe alloys is studied from first principles using pseudopotential approach. It is shown that the TiMe Σ5(310) symmetrical tilt GB cohesion is reduced by the segregation of hydrogen while it is increased due to boron or carbon segregation. We analyze also the combined and accumulation effect of interstitial B (C) and H impurities on the change of the Griffith work.
Interpretation of Plasticity Effects Using the CJP Crack Tip Field Model
Authors: James M. Neil , Christopher Colin J. , Díaz Garrido Francisco Alberto , Vasco-Olmo Jose M. , Kakiuchi Toshifumi , Patterson Eann A.
Published: December 2016

This paper will outline the development of a model of crack tip fields that represents an innovation in incorporate the influences on crack tip displacement and stress fields of the zone of local plasticity that envelops a growing fatigue crack. The model uses assumed distributions of elastic stresses induced at the elastic-plastic boundary via wake contact and compatibility requirements, and defines a set of modified elastic stress intensity factors to characterise the crack stress or displacement tip field. In particular, recent work will be presented that compares the interpretation of plasticity-induced shielding obtained from trends observed in KR and KF with values of so-called ‘crack closure’ obtained via traditional strain gauge determination.
Continuum Model of the Layered Medium with Slippage and Nonlinear Conditions at the Interlayer Boundaries
Authors: Nikitin Ilya S. , Burago Nikolay G. , Nikitin Alexander D.
Published: December 2016

The equations for layered medium with slippage are obtained using the asymptotic method of homogenization. The terms of second order respectively the small parameter of layer thickness are taken into account. The linear slip condition defines the dependence between the tangential jumps of displacements at the contact boundary and the shear stresses. Such generalized models are needed in the study of static and dynamic deformations of layered rock media. Also these models may be useful for description of composite materials with additional soft sublayers between more rigid layers.
The Life Duration for Compressor Disc under Torsional Vibrations of the Blades
Authors: Nikitin Ilya S. , Burago Nikolay G. , Nikitin Alexander D. , Yushkovskiy Pavel A.
Published: December 2016

The purpose of the research is calculating the stress-strain state of the elastic compressor disks of gas turbine engine due to vibrations of blades. The thickness of the disks is variable along the radius. The solution presented by power and Fourier series and the Fourier coefficients are found from the boundary value problems for systems of ordinary differential equations along the radial coordinate. The obtained results are used to estimate the durability of the disks in very-high-cycle fatigue mode.
Fan-Hinged Shear as a Unique Mechanism of Dynamic Shear Ruptures
Authors: Tarasov Boris , Guzev Mikhail , Sadovskiy Vladimir , Losev Alexander
Published: December 2016

Recently a new fan-hinged shear rupture mechanism has been identified as a unique mechanism of dynamic shear ruptures. In the fan-mechanism, the shear rupture propagation is driven by a fan-shaped rupture head consisting of an echelon of intercrack (domino-like) blocks formed due to the consecutive creation of small tensile cracks in the rupture tip. The fan-structure propagates through the intact material as a wave and has a number of extraordinary features, one of which is extremely low shear resistance of the rupture head (below the frictional strength). Here we present a mathematical model elucidating the principles of this new mechanism. The model will support comprehensive studies of unique features of the discovered phenomenon.
Multi-Parameter Based Stress Distribution in Vicinity of Sharp Material Inclusion Tip
Authors: Krepl Ondřej , Klusák Jan
Published: December 2016

General Singular Stress Concentrators (GSSCs) which exhibit singular stress concentration are often responsible for crack initiation and thus failure of the component. The GSSC of the type of bonded bi-material junction occurs in a variety of technical applications including but not limited to sharp material inclusions, silicate based composites and electronic components. The GSSC cannot be assessed by means of standard fracture mechanics. Approaches of generalized fracture mechanics require precise description of stress distribution near the stress concentration points. In order to determine the stress field accurately, the paper incorporates the multi-parameter based description.
Temperature and Stress Dependence of Mobility of Screw Dislocation in BCC Iron
Authors: Mori Hideki
Published: December 2016

The Peierls stress and barrier of a screw dislocation in body-centered cubic iron at finite temperature is investigated by using the free energy gradient method. The Peierls barrier is shown to decrease from 12 to 5 meV per unit length of the Burgers vector with increasing temperature from 0 to 400 K. The entropy term of the Peierls barrier is estimated to be 0.2kB. The Peierls stress also decreases from 900 to 400 MPa with increasing temperature from 0 to 300 K. The change in the Peierls stress due to the entropic effect is larger than that of the Peierls barrier because of thermal softening.
Analysis of Micro-Cracks Using Modified Couple-Stress Elasticity under Anti-Plane Deformation
Authors: Vafa Jalil P. , Fariborz Shahriar J.
Published: December 2016

Based on the modified couple stress theory the solution to a screw dislocation is obtained, in an isotropic elastic plane, via Fourier integral transform method. The asymptotic analysis of displacement field at the tip of a stationary crack reveals that stress field is not singular. A crack under anti-plane deformation is modeled by the distribution of screw dislocations. The ensuing integral equations are solved numerically to determine the density of dislocation on a crack surface. The dislocation solution is used to study the interaction between two parallel non-collinear micro-cracks.
Prediction of the Traction Separation Law of Ceramics Using Iterative Finite Element Modelling
Authors: Kozák Vladislav , Chlup Zdeněk , Padělek Petr , Dlouhý Ivo
Published: December 2016

Specific silicon nitride ceramics, the influence of the grain size and orientation on the bridging mechanisms was found. In ceramic matrix composites, crack-bridging mechanisms can provide substantial toughness enhancement coupled with the same and/or increased strength. The prediction of the crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated. From a number of damage concepts the cohesive models seem to be especially attractive for the practical applications. Within the standard finite element package Abaqus a new finite element has been developed; it is written via the UEL (user’s element) procedure. Its shape can be modified according to the experimental data for the set of ceramics and composites. The element seems to be very stable from the numerical point a view. The shape of the traction separation law for four experimental materials is estimated via the iterative procedure based on the FEM modeling and experimentally determined displacement in indentation experiments, J–R curve is predicted and stability of the bridging law is tested.
Influence of Particle Attributes on Residual Stresses in Particulate Ceramic Composites
Authors: Štegnerová Kateřina , Náhlík Luboš , Bermejo Raúl , Hutař Pavel
Published: December 2016

The contribution deals with the issue of residual stresses in particulate ceramic composites used in microelectronics. Residual stresses are developed in the composite due to cooling during manufacturing process. Different coefficients of thermal expansions of particles and matrix cause important residual stresses in the composite influencing their mechanical behaviour. The main aim of the paper is to determine influence of particle properties on magnitude and distribution of residual stresses in the composite matrix. Three dimensional numerical model was developed and finite element method (FEM) was used for numerical simulations. Results obtained contribute to a better understanding of residual stresses distribution and fracture processes in the studied type of composite.
Model of the Damaged Medium for the Assessment of Resource Characteristics of Structural Alloys for Degradation Mechanisms that Combine Fatigue and Creep of Material
Authors: Volkov Ivan , Vorobtsov Igor , Igumnov Leonid A. , Ipatov Aleksandr
Published: December 2016

A mathematical model of damage accumulation processes in structural steels is developed. This model considers degradation mechanisms that combine fatigue and creep of the material. The processes of viscoplastic deformation and damage accumulation in 08Х18Н10Т and 12Х18Н9 structural steels are numerically studied. The numerical results are compared with the data from full-scale experiments. The reliability of chosen defining equations describing combined effect of fatigue and creep mechanisms is confirmed.
Complete Williams Asymptotic Expansion near the Crack Tips of Collinear Cracks of Equal Lengths in an Infinite Plane
Authors: Stepanova Larisa , Roslyakov Pavel , Gerasimova Tatjana
Published: December 2016

The present study is aimed at analytical determination of coefficients in crack tip expansion for two collinear finite cracks of equal lengths in an infinite plane medium. The study is based on the solutions of the complex variable theory in plane elasticity theory. The analytical dependence of the coefficients on the geometrical parameters and the applied loads for two finite cracks in an infinite plane medium is given. It is shown that the effect of the higher order terms of the Williams series expansion becomes more considerable at large distances from the crack tips. The knowledge of more terms of the stress asymptotic expansions allows us to approximate the stress field near the crack tips with high accuracy.
Cracks Loaded by Rolling Contact - Influence of Plasticity around the Crack
Authors: Daves Werner , Kráčalík Michal
Published: December 2016

For the description of cracks in rolling/sliding contacts many overlapping interactions has to be regarded and most of them are non-linear phenomena. This paper emphasis the aspect of plasticity around cyclically loaded shear cracks which is omitted very often in the common literature. It is shown that this plasticity can be calculated and regarded in computed crack driving forces; however, the problem is not solved after doing this. It is a first estimate only to regard the crack driving force calculated in the finite elements surrounding the crack tip as a relevant measure.
Mechanical Behavior of 3D Printed Stochastic Lattice Structures
Authors: Maliaris Georgios , Sarafis Elias
Published: December 2016

Stochastic lattice structures are modeled using a generative algorithm. In particular, the voronoi tessellation technique is applied for modeling cellular solids with irregular cell geometry and variable strut sections. The ligaments are formed considering the volume and shape characteristics of the voronoi cells. This way, the strut cross section variability is linked to the adjacent cell topology. The developed geometry is used for 3D printing the structures through a high accuracy SLA 3D printer. The mechanical properties of the photosensitive resin were determined by conducting tension experiments on appropriate 3D printed specimens. The printed stochastic structures were subjected to compressive loads in order to investigate their mechanical response. A finite element model of the compressive tests using the generated geometry, is also developed. The calculated results provide a good correlation with the experimental ones and also provide precious insight for the characterization of the mechanical behavior of the tested structures.
On the Influence of Internal Void Size on the Fracture Stress of Constrained Solder Joints
Authors: Lederer Martin , Khatibi Golta , Magnien Julien
Published: December 2016

The fracture strengths of thin solder joints were investigated experimentally and with Finite Element Analysis. Due to a constraining effect, thin solder joints can carry loads which are much higher than the ultimate tensile strength of bulk solder material. On the other hand, thin solder joints show a tendency of being brittle. In fact, the tensile properties show a dependence on the quality of the intermetallic compound at the interface to the base material. Consequently, the size of microscopic defects in the intermetallic compound has a dominant influence on the fracture stress. This behavior could nicely be explained with Finite Element simulations based on strain gradient elasticity.
Prediction of Elastic Constants of Carbon Fabric/Polyurethane Composites
Authors: Hwang Shun Fa , Liu Hsuan Ting
Published: December 2016

The purpose of this work is to study a new composite material consisting of polyurethane (PU) resin and carbon fiber fabric. This PU resin is superior in impact, viscosity, low curing temperature, and short curing time. If this resin is combined with fiber fabric by vacuum assisted resin transfer method, the fabrication time will be short. Since it is a braided composite, it’s important to have a model to predict the elastic constants for different braid angels. To predict the elastic constants including Young’s modulus, shear modulus, and Poisson’s ratio, a finite element model is established. In this model a braided layer is treated as two uni-directional layers. Then, the elastic constants of this composite with different braid angels are estimated. After that, the composites with different braid angels are fabricated and tested to obtain the elastic constants, and the comparison with the finite element results is made. The results indicate that the agreement is very good for the Young’s modulus. For the Poisson’s ratio, the difference between the prediction and the measurement is reasonable. From the comparison, it can be concluded that the finite element model is good. Then, this model is used to predict all in-plane elastic constants for arbitrary braid angles.
Crack Growth Studies in a Welded Ni-Base Superalloy
Authors: Iyer Anand Harihara Subramonia , Stiller Krystyna , Hörnqvist Colliander Magnus
Published: December 2016

It is well known that the introduction of sustained tensile loads during high-temperature fatigue (dwell-fatigue) significantly increases the crack propagation rates in many superalloys. One such superalloy is the Ni-Fe based Alloy 718, which is a high-strength corrosion resistant alloy used in gas turbines and jet engines. As the problem is typically more pronounced in fine-grained materials, the main body of existing literature is devoted to the characterization of sheets or forgings of Alloy 718. However, as welded components are being used in increasingly demanding applications, there is a need to understand the behavior. The present study is focused on the interaction of the propagating crack with the complex microstructure in Alloy 718 weld metal during cyclic and dwell-fatigue loading at 550 °C and 650 °C.
The Influence of Microstructure Heterogeneities on the Very High Cycle Fatigue Behavior of Duplex Stainless Steel
Authors: Krupp Ulrich , Söker Marcus , Waurischk Tina , Giertler Alexander , Dönges Benjamin , Christ Hans-Jürgen
Published: December 2016

As being used for structural applications, where a high corrosion resistance is required, the fatigue behavior of duplex stainless steels (DSS) is governed by the partition of cyclic plasticity to the two phases, ferrite and austenite, respectively. Under very high cycle fatigue (VHCF) loading conditions, the heterogeneous distribution of crystallographic misorientations between neighboring grains and phases yields to a pronounced scatter in fatigue life, ranging from 1 million to 1 billion cycles for nearly the same stress amplitude. In addition, the relevant damage mechanisms depend strongly on the atmosphere. Stress corrosion cracking in NaCl-containing atmosphere causes a pronounced decrease in the VHCF life. By means of ultrasonic fatigue testing at 20kHz in combination with high resolution scanning electron microscopy, electron back-scattered diffraction (EBSD), focused ion beam milling (FIB) and synchrotron tomography, the microstructure heterogeneities were quantified and correlated with local fatigue damage. It has been shown that the fatigue process is rather complex, involving redistribution of residual stresses and three-dimensional barrier effects of the various interfaces. The application of a 2D/3D finite element model allows a qualitative prediction of the fatigue-damage process in DSS that is controlled by stochastic local microstructure arrangements.
Crack Initiation in Austenitic Stainless Steel Sanicro 25 Subjected to Thermomechanical Fatigue
Authors: Petráš Roman , Škorík Viktor , Polák Jaroslav
Published: December 2016

Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the specimens. Mechanical response was recorded and fatigue lives were obtained. Scanning electron microscopy combined with FIB technique was used to study the mechanism of crack initiation in in-phase and in out-of-phase thermomechanical cycling. Different mechanisms of the crack initiation were found in these two types of loading. During in-phase loading fatigue cracks start in grain boundaries by cracking of the oxide. Cracks grew preferentially along grain boundaries which resulted in rapid crack initiation and low fatigue life. In out-of-phase loading multiple cracks perpendicular to the stress axis developed only after sufficiently thick oxide layer was formed and cracked in low temperature loading half-cycle. The cracks in oxide allowed localized repeated oxidation and finally also cracking. The cracks grow transgranularly and result in longer fatigue life.
Method of Threshold Stress Determination for a Local Approach to Cleavage Fracture
Authors: Kotrechko Sergiy , Gryshchenko V. , Kozák Vladislav , Dlouhý Ivo
Published: December 2016

The contribution is focused on a new methodology description for determination of threshold stress, as the third parameter in Beremin local approach to cleavage fracture that is using three-parameter Weibull statistics. Nature of the methodology lies in tensile testing of rounded notched specimens at liquid nitrogen temperature and corresponding calculations. Reactor pressure vessel steel was chosen as an example for the illustration.
Numerical Determination of Fatigue Threshold from CTOD
Authors: Camas Daniel , Loureiro Pedro , Prates Pedro , Antunes Fernando
Published: December 2016

The experimental procedure to obtain valid and comparable values of ΔKth is laborious and time consuming. The objective of this work is to determine ΔKth using a numerical approach. The CTOD is plotted versus load, and the fatigue threshold corresponds to the onset of plastic deformation. A parametric study was developed in order to understand the effect of material parameters on ΔKth.
Crystal Plasticity Simulations of Haynes 230, an Analysis of Single Crystal and Polycrystalline Experiments
Authors: Luccarelli Pietro Giovanni , Foletti Stefano , Pataky Garrett , Sehitoglu Huseyin
Published: December 2016

The behavior of a Ni-based superalloy, Haynes 230, was investigated at macro and micro scale level by means of a Crystal Plasticity (CP) model implemented in an open source Finite Element code, Warp3D. Single Crystal and polycrystalline specimens have been experimentally characterized with Digital Image Correlation (DIC) to identify the local strain field evolution. The results of single crystal’s tensile tests were used to obtain an estimation of the constitutive model parameters. Then a polycrystalline model, reproducing a tensile test with loading/unloading steps, was created starting from the microstructural data obtained with EBSD (electron back-scatter diffraction), which allowed the identification of grains geometry and orientations. The polycrystalline simulations were used to verify the prediction of the CP model over the experiment. The results of this study show that the comparison between experiments and numerical analysis is in good agreement on both global and local scale levels.
Development of Bond-Order Potentials for BCC Transition Metals
Authors: Vitek Vaclav , Lin Yi Shen , Mrovec Matous
Published: December 2016

In this paper we present bond-order potentials (BOPs) based on the tight-binding method. The potentials have been developed for bcc non-magnetic metals of group V.B (V, Nb, Ta) and group VI.B (Cr, Mo, W) as well as for the ferromagnetic bcc iron. The testing of the transferability of BOPs involves energies of alternate structures, formation energies of vacancies and self-interstitials, transformation paths between different structures and phonon dispersion relations. An example of the application of these potentials is modeling of the structure and glide of 1⁄2<111> screw dislocations under the effect of applied shear and tensile/compressive stresses.
Surface Roughness Effects on the Fatigue Behavior of As-Machined Inconel718
Authors: Javadi Hamid , Jomaa Walid , Texier Damien , Brochu Myriam , Bocher Philippe
Published: December 2016

Surface finish of machined components plays a key role in their life performance. The aim of this research is to investigate the effect of different roughness parameters on high cycle fatigue behavior of Inconel718. Rotating bending fatigue tests have been performed on Inconel718 specimens with various surface roughnesses produced by turning. Height and amplitude distribution roughness parameters were investigated. Statistical analyses show that a valley material component (Mr2), as one of the amplitude distribution parameters, is the most relevant parameter for the high cycle fatigue life of machined specimens. Observations conducted at the surface of broken specimens gage length, have shown the impact of surface roughness and residual stresses on the crack propagation mode. When the roughness increases, valleys were shown to be deeper and larger, leading to a higher Mr2 value and an increase of stress concentration.
Correlation of Fatigue Limit and Crack Growth Threshold Value to the Nanobainitic Microstructure
Authors: Müller Inga , Rementeria Rosalia , Caballero Francisca G. , Kuntz Matthias , Kerscher Eberhard
Published: December 2016

The recently developed nanobainitic steels show high ultimate tensile strength (UTS) as well as high ductility. Although this combination seems to be desirable for fatigue design, fatigue limit of nanostructured bainite is often disappointingly low. To improve fatigue properties we tried to earn a fundamental understanding of the microstructural parameters governing fatigue behavior.Therefore our hypothesis to improve the fatigue behavior was not necessarily avoiding the initiation of a fatigue crack – which could lead to failure of the material – but to improve the ability of the present microstructure to slow down or stop growing cracks. Thus, the key to understand the fatigue behavior of nanostructured bainite is to understand the role of the microstructural features which could act as barriers for growing cracks.We tried to correlate our results of fatigue tests and analysis of fracture surfaces to the size of microstructural features like bainitic ferrite plates, crystallographic bainite blocks and packets or prior austenite grains, as well as cracks induced at nonmetallic inclusions. Thereby we found that the crystallographic bainite block size governs fatigue behavior. Additionally, threshold values were determined from crack growth experiments and related to the characteristic microstructural features.
Characterization of TiNb Films on Ti Alloys for Hard Tissue Replacement
Authors: Starý Vladimír , Cvrček Ladislav , Daniš Stanislav , Krčil Jan , Málek Jaroslav , Tolde Zdeněk
Published: December 2016

We present here a study of coatings prepared from β-Ti binary alloy Ti-39wt%Nb, a promising metallic material. TiNb is a highly corrosion-resistant and non-toxic material that is potentially applicable as a biomaterial. TiNb coatings can be prepared on substrates of widely-used materials, and promise not only improved properties but also a less high price of potential TiNb implants. A TiNb film can also be used as a barrier for limiting the potential diffusion of some allergens and toxic elements from the substrate to the surface, which can be influenced by layer properties. We deposited thin layers of TiNb by magnetron sputtering, which provides excellent layer properties in applications. These layers were prepared on substrates made from Ti, Ti alloys (Ti39Nb and Ti6Al4V) and stainless steel AISI316. The aim of our work was to characterize the structure and the mechanical properties of the layers, in dependence on the type of substrate, for application as coatings for medical implants.
Different Ab Initio Approaches for Doping Descriptions: Tetragonal Deformation of Ni-Mn-Ga Alloys
Authors: Zelený Martin , Dlouhý Ivo
Published: December 2016

The influence of Co and Cu doping on Ni-Mn-Ga alloy is investigated using the different ab initio methods for description of chemical disorder. The exact muffin-tin orbital method in combination with the coherent-potential approximation provides almost identical profiles of total energies along the tetragonal deformation path compared to the supercell approach used within the projector-augmented wave method. On the other hand, the simple virtual crystal approximation exhibits different results and thus it is not able to describe doping in Ni-Mn-Ga alloy properly.
First Principles Study of Water-Based Self-Assembled Nanobearing Effect in CrN/TiN Multilayer Coatings
Authors: Holec David , Paulitsch Jörg , Mayrhofer Paul H.
Published: December 2016

Recently, we have reported on low friction CrN/TiN coatings deposited using a hybrid sputtering technique. These multilayers exhibit friction coefficients μ below 0.1 when tested in atmosphere with a relative humidity ≈ 25 %, but μ ranges between 0.6–0.8 upon decreasing the humidity below 5 %. Here we use first principle calculations to study O and H adatom energetics on TiN and CrN (001) surfaces. The diffusional barrier of H on TiN(001) is about half of the value on CrN(001) surface, while both elements are stronger bonded on CrN. Based on these results we propose a mechanism for a water-based self-assembled nanobearing.
Anodizing of Zinc-Titanium Alloy in NaOH and KOH Baths
Authors: Remešová Michaela , Klakurková Lenka , Čelko Ladislav , Sládková Lucia , Jech David , Kaiser Jozef
Published: December 2016

Electrochemical process of conversion coatings formation on Zn-Ti alloy surface during one-step anodizing process was studied in NaOH and KOH electrolytes over the range of voltages (4-50 V) and constant time in order to investigate parameters for the origin of anodic zinc coating. Stainless steel was used as a counter electrode and electrolyte during the anodizing process was agitated by compressed air. Coatings microstructures and morphology were characterized by means of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Surface topography was investigated prior and after the anodizing using non-contact optical 3D profilometer. It was found that high voltage (50 V) and low concentrations of electrolyte (0.04 and 0.1 mol/L NaOH) led to origin of white coloured oxide coatings, while lower voltage (4 and 6 V) and higher concentrations of electrolyte promote the origin of black coloured oxide coatings. Concentration of electrolyte and voltage influenced the thickness of conversion coatings and its surface morphology. Moreover, the surface morphology of the coatings was also influenced by the heterogeneity of substrate alloy.
Absorption and Diffusion of Oxygen in Ti-Al Bulk Alloys
Authors: Bakulin Alexander , Latyshev Alexander , Kulkova Svetlana
Published: December 2016

The oxygen absorption and diffusion properties are studied in γ-TiAl and TiAl3 alloys within density functional theory using projector augmented wave method in the plane-wave basis. It is shown that the octahedral site inside the Ti-rich octahedron is preferable for oxygen in case of γ-TiAl alloy whereas the Al-rich octahedron is more favorable environment for oxygen in TiAl3. It is shown that the energy barriers for oxygen jumps between different sites in bulk alloys depend significantly on the local environments of oxygen and increase for its jump from Ti-rich sites. The trajectories with minimum energy barriers are determined for both Ti-Al alloys. It is shown that the increase of Al content in alloy leads to the decrease of barriers for oxygen jumps.
W-B-C Nanostructured Layers - Microstructure and Mechanical Properties
Authors: Buršík Jiří , Kuběna Ivo , Buršíková Vilma , Souček Pavel , Zábranský Lukáš , Mirzaei Saeed , Vašina Petr
Published: December 2016

Several W-B-C layers were prepared by magnetron sputtering. The microstructure of thin layers was observed by means of scanning and transmission electron microscopy on cross sections prepared using a focused ion beam. Both undisturbed layers and the volume under indentation prints were inspected. The W-B-C layers are fine nanostructured materials about 2 μm thick and indents with loads up to 1 N do not cause any visible defects (cracks, delamination etc). The results were correlated with mechanical properties characterized by means of nanoindentation experiments in both the static and the dynamic loading regime using a Berkovich indenter. Elastic modulus, indentation hardness and fracture resistance of prepared nanostructured coatings were evaluated and discussed.
On the Preparation of Advanced Materials via Pulsed Electric Current Sintering Procedures
Authors: Díaz de la Torre Sebastián , Čelko Ladislav , Casas Luna Mariano , Montúfar Edgar Benjamin
Published: December 2016

A general overview on the processing of a series of advanced engineering materials, synthesized via pulsed-electric-current-sintering related techniques, and the similarities in between those techniques are introduced in this work. This paper is focused on two major techniques; namely, the Spark Plasma Extrusion (SPE) and Current Assisted Infiltration Sintering (CAIS), which in turn are derived from the Spark Plasma Sintering (SPS) technique, all widely used by this research group. Not only the geometry but also the microstructure of thus prepared specimens might vary depending on the selected technique. The resulting specimens can be under the forms of discs (flat or thick coin-like), rivets (enlarged cylindrical bars)-like and/or disclosing interpenetrated periodic networks with regular or irregular (either coin or rivet/screw)-like specimens, respectively. As for the CAIS technique, either 3D printed ceramic frameworks or naturally synthesized porous substrates (such as bone-like structures), can be infiltrated with virtually any metal or alloy. Among the series of produced materials we can include, for example: biomaterials such as: Ti-and Mg-hydroxyapatite, pure hydroxyapatite HA, composites, e.g., Al5083-CNT ́s, just to name a few. The expanding possibilities of SPS, SPE and CAIS techniques are briefly indicated here.