bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematical Model of Fan-Head Shear Rupture Mechanism
Authors: Tarasov Boris , Guzev Mikhail A.
Published: November 2013

Today frictional shear resistance along pre-existing ruptures (faults) is considered as the lower limit on rock shear strength for confined conditions. The paper proposes a mathematical model of recently identified shear rupture mechanism which can provide propagation of faults through the highly confined intact rock mass at shear stress levels significantly less than frictional strength of pre-existing faults. The model demonstrates that due to the self-unbalancing structure of the rupture head, representing the core of this mechanism, the failure process caused by the mechanism is always spontaneous and violent. It allows a novel point of view for understanding the nature of spontaneous failure processes including earthquakes.
Jet Theory in Microstructures
Authors: Kureš Miroslav
Published: November 2013

We present jet approach to microstructures, in particular to Cosserat continuum. We compare classical methods with the representation of Cosserat bodies by frame bundles. We demonstrate that nonholonomic, semiholonomic and holonomic bundles occur in such description.
Dynamic Recrystallization of the Alloy Fe-40at.%Al-Zr-B
Authors: Schindler Ivo , Kawulok Petr , Kawulok Rostislav , Rusz Stanislav
Published: November 2013

On the basis of the uniaxial compression tests realized in the temperature range from 800 °C to 1200 °C and at strain rates from 0.05 s-1 to 30 s-1 the value of the activation energy at hot forming of coarse-grained as-cast iron aluminide Fe40at.%Al-Zr-B was calculated as Q = 502 kJ·mol-1. With use of this material constant, relatively precise mathematical description of the maximum flow stress and the corresponding strain in dependence on the Zener-Hollomon parameter was possible. As was discovered by metallographical analysis, at high values of the Zener-Hollomon parameter slight decrease in flow stress occurs even without significant course of dynamic recrystallization.
Criterion for Crack Kinking out of the Interface of Two Orthotropic Layers Subjected to Thermal and Mechanical Loading
Authors: Damborský Petr , Ševeček Oldřich , Profant Tomáš , Kotoul Michal
Published: November 2013

The problem of crack path stability along the interface between two orthotropic elastically dissimilar materials under the presence of in-plane residual stresses is analyzed using the concept of Finite Fracture Mechanics and matched asymptotic procedure. An energy based fracture criterion is introduced for this problem and it is investigated whether and how is the criterion for the prediction of crack kinking from the interface affected by residual stresses. The complex stress intensity factor and the T-stress characterizing the stress state at the crack tip are calculated both for the thermal (residual stresses) and mechanical loading using the two-state integral. The matched asymptotic procedure together with FEM is used to derive the change of the potential energy induced by the crack growth by crack increment of finite length.
The Experimental Study and Numerical Estimation of Fracture Toughness of Heterogeneous Welded Joints
Authors: Moskvichev Egor
Published: November 2013

In this paper the mechanical heterogeneity of welded joints was studied. The experimental results show that the mechanical properties and fracture toughness vary significantly in zones of welded joint. To estimate the fracture parameter J-integral a numerical finite-element model based on the random variation of yield strength was proposed.
Application of Multi-Parameter Fracture Mechanics to Study of Crack Propagation Angle in Selected Mixed-Mode Geometry
Authors: Malíková Lucie Šestáková , Veselý Václav
Published: November 2013

The multi-parameter fracture mechanics becomes more and more significant, because it is shown that it can help to describe fracture processes occurring in cracked specimens more precisely than conventional linear elastic fracture mechanics. In this paper, the concept based on the Williams expansion derived for approximation of stress/displacement crack-tip fields is presented and applied on a mixed-mode configuration. Two fracture criteria for estimation of the initial crack propagation angle are introduced. A parametric study is performed in order to investigate the dependence of the crack propagation angle on the stress intensity factors ratio. Influence and importance of taking into account the so-called higher-order terms of the Williams expansion are discussed and some recommendations are stated.
Numerical Model of Plate from Hollow Core Panels with Contact – Target Pairs
Authors: Kršík Jakub , Křiváková Jarmila
Published: November 2013

The objective of this paper is the numerical modeling of elastically supported plate created from pre-stressed hollow core panels of Spiroll type by ANSYS program. Elasticity of supports is achieved by support beams, which are connected to plate by contact target pairs. Calculation is executed in time steps, which correspond to real loading steps. Evaluations of deformation in selected sections of the slab are presented, too.
A Numerical Estimation of Fatigue Crack Tip Plastic Zone Size and Shape under Mixed-Mode Loading Condition
Authors: Ondráček Jan , Materna Aleš , Oliva Vladislav
Published: November 2013

A 2D elastic-plastic FEM simulation of growing fatigue crack under combined mode I and II loading was performed. An inclined fatigue crack propagated in a sheet of an Al-alloy D16CT1. The effect of increasing mode-mixity on cyclic zone size, shape and the amount of dissipated energy was investigated.
Stochastic Fracture Simulations of Concrete Beams with Shallow Notches
Authors: Eliáš Jan , Vořechovský Miroslav
Published: November 2013

We present a numerical study on virtual concrete beams with shallow midspan notches loaded in three-point bending. We document how spatial randomness of material parameters allows a crack to initiate outside the shallow notch. The interacting effects of notch depth and fluctuation rate of material parameters are shown. We use a discrete meso-level model to simulate material behavior. An approach that introduces material spatial randomness into the discrete mechanical model for concrete fracture through an autocorrelated random field is briefly presented.
Contribution to the Life Prediction of Aluminium Alloys Parts under Isothermal Fatigue
Authors: Belkherchouche Adel , Boudiaf Achraf , Belouchrani Mohamed El Amine
Published: November 2013

Lifetime prediction, Isothermal fatigue, damage, cracking, aluminium alloys. Abstract. In this work, a tool for lifetime prediction of aluminium alloys parts employed under isothermal fatigue was developed. This tool is a computer code implemented in a "Visual-Fortran" environment and based on a coupled model of the elastoplastic damage accumulation presented by "Lemaitre and Chaboche" [. This model allows us to describe the damage evolution depending on the number of cycles until failure of the representative volume element (RVE). This failure results in the creation of a macro-crack, its propagation over loading cycles to reach a critical size which will cause the part breakdown. The crack growth phase cannot be neglected because it may contain a considerable number of cycles, this is why we have included in the developed model, this phase of crack growth after the initiation phase; it contains mainly the numerical integration of the "Paris" law.
Modeling of Fatigue Crack Initiation in Wire-Bonds Using a Novel Approach of Strain Gradient Theory
Authors: Lederer Martin , Khatibi Golta , Thuiner Dominik , Danninger Herbert
Published: November 2013

The fatigue life of wire-bonds was measured with use of a 20 kHz ultrasonic testing system. Thereafter, the experiments were interpreted by Finite Element Analysis. First, simulations were performed according to classical continuum mechanics. They predicted stress concentrations at the location where crack initiation was found experimentally. However, the stress concentrations showed the characteristics of stress singularities even for loading cases corresponding to the regime of very high cycle fatigue, i.e. fairly moderate loads. In subsequent simulations, the singularities of stress concentrations could be removed on the basis of a newly developed version of strain gradient elasticity, resulting in predictions that agreed well with experimental results.
Crack Growth Tendency of Surface Shear Cracks in Rolling Sliding Contact
Authors: Daves Werner , Yao Wei Ping , Scheriau Stephan
Published: November 2013

Surface cracks arising during rolling sliding contact of a wheel and a rail are investigated. A two-dimensional crack model is proposed which calculates the crack driving force using the configurational force concept. The numerical applicability of the configurational force concept for surface shear cracks under cyclic contact loading is discussed and compared to the J-integral concept. A single inclined crack in a rail loaded by an accelerated wheel is investigated. The material of the rail is described by a cyclic plastic kinematic hardening model. The evolution of the crack driving force during several cycles is investigated.
Geometry Transferability of Lemaitre's Continuum Damage Mechanics Model in the Plane Stress Specimens
Authors: Allahverdizadeh Nima , Manes Andrea , Giglio Marco , Gilioli Andrea
Published: November 2013

Different damage mechanics models have been proposed by researchers to calibrate the failure behavior of materials. Continuum damage mechanics (CDM) models are one of the main categories of damage models that can be exploited in numerical simulations. In this paper Lemaitres damage model, has been applied to finite element models of flat specimens. These models allow assessing the geometry transferability of the previously calibrated CDM model investigating in different geometry and loading conditions. Four different types of plane stress specimens have been designed to get different stress triaxialities which cover shear dominant and high triaxiality failure. Experimental tests were also done and the obtained data were critically compared with the results from numerical models. The tested material is Ti-6Al-4V titanium alloy which is a widely used material in aerospace industry because of its high strength and low density.
Influence of the Microstructure on the Fracture Behavior of Carbon Bonded Alumina
Authors: Soltysiak Stefan , Abendroth Martin , Kuna Meinhard , Dudczig Steffen
Published: November 2013

Carbon bonded alumina (Al2O3-C) in various compositions are developed for the production of open cell filters, which are used for melt metal filtration processes [. The Small Punch Test (SPT) is used to determine the mechanical properties of such materials. Previous investigations showed two different types of fracture behavior [2,, which can be distinguished by typical features of the load deflection curves of the SPT. This paper clarifies this behavior by examining the fracture surfaces using scanning electron microscopy (SEM).
Measurement of Residual Stresses around the Notch of Tensile Specimens of the High-Cr Tempered Martensitic Steel F82H-Mod
Authors: Ilchuk Nazar , Spätig Philippe , Davydov Vadim , van Petegem Steven
Published: November 2013

Residual elastic strains were measured by neutron diffraction using POLDI materials science diffractometer at PSI-Switzerland on pre-loaded notched flat tensile specimens made of the high-chromium tempered martensitic steel F82H-mod steel. To calculate the residual stresses using Hooke's equation, three perpendicular components of the residual strain field were determined. The measured residual strains and stresses were compared with those deduced from finite element simulation calculations. A very good agreement was found for the strains in the loading plane of the specimen while a somewhat larger discrepancy was observed for the out-of-plane residual strain, which was tentatively attributed to an uncertainty in the initial lattice spacing in that direction.
Microscopic Mechanism of Hydrogen Embrittlement in Fatigue and Fracture
Authors: Murakami Yukitaka , Yamabe Junichiro , Matsunaga Hisao
Published: November 2013

The microscope mechanism of hydrogen embrittlement (HE) is overviewed from the viewpoint of Mechanics-Microstructure-Environment Interactions. The plastic deformation (Mechanics) at crack tip for low strength steel is controlled by hydrogen concentration (Environment) to crack tip, eventually resulting in very strong time dependent phenomenon in static fracture and fatigue crack growth. Various typical phenomena in low strength steels which can be understood from the viewpoint of Mechanics-Environment Interactions will be presented. Fracture and fatigue of high strength steels (Microstructure) are strongly influenced by hydrogen. Especially, fatigue crack growth is remarkably accelerated by hydrogen-induced deformation twins. The HE phenomemon of the high-strength steels was applied to a newly inclusion rating method. Hydrogen trapped by nonmetalliec inclusions causes the elimination of fatigue limit at very high cycle fatigue. The values of threshold stress intensity factor KTH in hydrogen for small cracks are much smaller than those for long cracks measured by the standard WOL or CT specimens, which are eventually unconservative for the design of hydrogen components. This phenomenon is similar to the small crack problem in fatigue.
Grain Refinement and Deformation Behaviour of Medium Carbon Steel Processed by ECAP
Authors: Zrník Jozef , Dobatkin Sergey , Kraus Libor
Published: November 2013

The work presents the results on grains refinement of steel containing 0,45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experimental. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By application of thermomechanical (TM) controlled forging process, performing multistep open die forging, the refined ferrite-pearlite mixture was prepared. Final structure refinement of steel, having different initial structure, was then accomplished applying warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. Applying the highest shear stress (εef - 4) the mixed structure of subgrains and ultrafine grains was present within the ferrite phase. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting and breaking was found efficient. The coarse cementite lamellae spheroidization was more efficient in prior TM treated steel. The tensile deformation records confirmed strength increase and diversity in strain hardening behaviour.
Deformation Mechanisms in Ultrafine-Grained Zn at Different Strain Rates and Temperatures
Authors: Jenei Péter , Dirras Guy , Gubicza Jenő , Couque Hervé
Published: November 2013

The deformation mechanisms in ultrafine-grained hexagonal close packed Zn were investigated at different strain rates and temperatures. The influence of grain size on the deformation mechanisms was revealed by comparing the results obtained on ultrafine-grained and coarse-grained Zn. It was found that for coarse-grained Zn at room temperature and strain rates lower than 10-2 s-1 twinning contributed to plasticity besides dislocation activity. For strain rates higher than 103 s-1 the plasticity in coarse-grained Zn was controlled by dislocation drag. In ultrafine-grained Zn the relatively large dislocation density (~1014 m-2) and the small grain size (~250 nm) limit the dislocation velocity yielding the lack of dislocation drag effects up to 104 s-1. For ultrafine-grained Zn, twinning was not observed in the entire strain rate range due to its very small grain size. During room temperature compression at strain rates higher than 0.35 s-1 and in high temperature creep deformation of ultrafine-grained Zn besides prismatic and pyramidal  dislocations observed in the initial state, -type basal and pyramidal dislocations as well as other -type pyramidal dislocations were formed.
Preparing of Silver Nanoparticles by Selective Dissolving of Aluminium Matrix
Authors: Marek Ivo , Michalcová Alena , Harabišová Dominika , Vojtěch Dalibor
Published: November 2013

Metallic nanoparticles and nanocrystalline bulk materials are recently extremely popular. It is because of their properties and wide field of possible applications.In this work, silver nanoparticles were prepared by selective dissolving of the aluminium matrix from rapidly solidified (RS) AlAg30 (wt. %) alloy in the sodium hydroxide solution. This alloy was prepared by melt-spinning technique. The influence of production parameters such as sodium hydroxide concentration, dissolving temperature and using of ultrasound bath on the phase composition, morphology and size of the nanoparticles was studied.Phase compositions of the initial alloy and prepared nanoparticles were investigated by X-ray phase analysis. Furthermore, the nanoparticles were studied by means of transmission (TEM) electron microscope. Nanoparticle size was determined by image analysis of TEM micrographs and these results were also compared to the size of nanoparticles determined from diffraction patterns using Scherrer calculator.It was found that concentration of sodium hydroxide has significant effect on phase composition of the product and the dissolving temperature influences the particle size.
Recrystallization Temperature Influence upon Structural Changes of 90% Cold Rolled Ti-29Nb-9Ta-10Zr Biocompatible Alloy
Authors: Tabirca Cristina Mariana , Gloriant T. , Gordin Doina Margareta , Thibon Isabelle , Raducanu Doina , Cinca Ion , Nae Cătălin Iulică , Caprarescu Andreea , Cojocaru Vasile Danut
Published: November 2013

In recent years a significant increase in new Ti-based biocompatible alloys (such as TiTaZr or TiTa-Nb-Zr) development was reported. Titanium and its alloys have been widely used in medicine since the 1960s because of their known biocompatibility, superior mechanical properties, low density and remarkable chemical stability. The present study investigates the microstructures and the mechanical properties of a Ti-29Nb-9Ta-10Zr (wt.%) alloys in order to investigate structural changes occurred during recrystallization treatment of 90% cold rolled Ti-29Nb-9Ta-10Zr (wt.%) alloy. The investigated alloy was fabricated by vacuum arc induction melting in levitation, using a FIVES CELES MP 25 furnace, starting from elemental components. Structural changes occurred during recrystallization treatment were investigated using X-ray diffraction, using a Philip PW 3710 diffractometer, in Bragg-Brentano θ-2θ geometry, with negligible instrumental broadening. Data concerning alloys component phases, average coherent crystallite size and internal average micro-strain was obtained.
Computational Modeling of Porous Ceramics with Bioactive Layer
Authors: Marcián Petr , Valášek Jiří , Hrstka Miroslav , Majer Zdeněk , Ševeček Oldřich , Profant Tomáš , Dlouhy Ivo , Florian Zdeněk
Published: November 2013

The paper deals with a creation of computational model of a high porous ceramic material. This type of material has a large-scale industrial utilization. The computational model was created based on micro-CT data in the ANSYS 14.0 software using Finite Element Method. A creation of a porous ceramic struts model which respect a micro architecture is quite difficult (computer demanding and micro-CT data). The micro-CT slices are converted into a 3D model using image processing (used software STL Model Creator). The local first principle stress was analyzed because, ceramic is the brittle material. Furthermore, the influence of the thick layer around the individual struts was analyzed.
Local Mechanical Properties of Various Bone Cements
Authors: Hvizdoš Pavol , Jakubéczyová Dagmar , Hloch Sergej , Kľoc Ján , Balko Ján , Monka Peter
Published: November 2013

Various bone cements with different compositions were prepared in several model configurations which differed in volume (i.e. setting temperature profile) and mode of mixing (manual and vacuum bowl). Local mechanical properties (nanohardness, elasticity modulus) of all experimental states were measured by nanoindentation technique and compared. Role of the preparation route as well as influence of composition, particularly of presence of antibiotics, on the measured properties was investigated.
Atomistic Model Analysis of Local and Global Instabilities in Crystals at Finite Temperature
Authors: Umeno Yoshitaka , Nöhring Wolfram , Iskandarov Albert , Bitzek Erik
Published: November 2013

There have been a lot of studies dedicated to structural instability in solids. For local instability, theoretical (ideal) strength of crystals has been extensively studied with ab initio calculations. Global instability taking into account the collective motion of atoms involved in deformation has also been investigated. However, these studies have usually been done at 0 K and little has been understood about the effect of temperature. In this study, we demonstrate computational approaches to the effect of temperature on local and global instabilities. Ideal shear strength (ISS) of silicon at finite temperatures is calculated by molecular dynamics (MD) simulations with an empirical potential. ISS is obtained as a function of temperature. Our results imply that, unlike metals, the reduction in ISS by temperature cannot be estimated simply by taking into account thermal expansion of volume. In addition, global instability for dislocation nucleation in a Cu thin film model under tension is investigated. We first evaluated instability modes at 0 K with increasing strain, and then performed MD simulations at 50 K. After the nucleation of a partial dislocation, the second dislocation can be one to create a twin or one to create another partial dislocation. These different deformations can be understood as the competition of latent instability modes that have relatively small eigenvalues.
High-Density Ceramic Materials on the Basis of Silicon Carbide
Authors: Dallaeva Dinara Sultanovna , Kardashova Gulnara Darvinovna , Safaraliev Gadjimet Kerimovich , Tománek Pavel
Published: November 2013

This study describes the principles of synthesis and technological features of composition ceramics formation on the basis of silicon carbide and aluminum nitride by hot-pressing. The structural properties and composition of the ceramics were investigated by scanning electron microscope and the formation of the solid solution is confirmed. The elements distribution on the surface of failure pattern is shown. The results of the study are useful for optimization of manufacturing process of structural and functional high-density ceramics.
Estimation of Apparent Fracture Toughness of Alumina Based Ceramic Laminate
Authors: Máša Bohuslav , Náhlík Luboš , Hutař Pavel
Published: November 2013

The main aim of this contribution is the fracture behavior of layered ceramic composite with residual stresses. The influence of laminate composition on crack propagation (influence of material interfaces on crack shielding, effect of residual stresses, etc.) was investigated. The crack behavior was described by procedures based on linear elastic fracture mechanics (LEFM) and generalized LEFM. Computations were performed in 2D geometry under plain strain assumptions. For determination of the real crack front shape during the crack propagation the three dimensional FEM models were developed. Both (2D/3D) approaches were compared and differences were closely discussed. The influence of laminate composition with residual stresses on critical values for crack propagation through laminate interfaces was also determined. The results obtained can be used for a design of new layered composites with improved resistance against propagation of cracks.
Fatigue Response of Hybrid Ti/APC-2 Nanocomposite Laminates with Single-Edged Cracks
Authors: Jen Ming Hwa R. , Chang Che Kai , Lin Bo Cyuan
Published: November 2013

The aims of this study are to fabricate Ti/APC-2 hybrid composite laminates with and without (W/WO) nanoparticles and investigate the mechanical properties of laminates with single-edged cracks due to both tensile and cyclic tests. The mechanical properties such as ultimate tensile strength and longitudinal stiffness of original composite laminates W/WO nanoparticles were first obtained from the static tensile tests. However, the load-displacement diagrams were plotted for the crack laminates. The constant stress amplitude tension-tension cyclic tests were conducted to receive the S-N curves and fatigue data.
The ultimate strengths for both Ti/APC-2 composite laminates W/WO nanoparticles were very close at varied crack length. Ti/APC-2 cross-ply nanocomposite laminates had better fatigue resistance than that of laminates without nanoparticles. The longer the crack length is, the more their properties are reduced. Also, the values of fracture toughness of both hybrid cracked laminates W/WO nanoparticles were obtained by rule of mixtures and found acceptable. Finally, in predicting crack growth rate and residual life, instead of commonly used Paris Law for metals, the modified method was adopted for hybrid cracked laminates. The prediction is not satisfactorily acceptable, even if most results are in good agreement with empirical data.
Surface Relief Evolution in IN792-5A Nickel Superalloy under High Temperature Fatigue Straining with Hold Times
Authors: Šmíd Miroslav , Obrtlík Karel
Published: November 2013

The present paper is focused on scanning electron microscopy investigation of surface relief developed in cyclically strained specimens at high temperature. Symmetrical fatigue tests without hold times and with tensile or compressive hold times were used in strain control regime. The gauge length of specimens was analyzed after cyclic straining in a wide range of total strain amplitudes. Experimental temperature was 800 °C and selected hold time was 10 minutes.Surface relief is developed during the cyclic straining in localized plastic strain areas. Developed surface relief strongly depends on the type of fatigue test and a value of total strain amplitude. Well-developed surface persistent slip markings were observed after cyclic loading without hold times. Another group of observed slip markings with perpendicular orientation to stress axis exhibits irregular and wavy morphology. Similar markings were also observed on specimen surfaces after fatigue tests with tensile hold times as well as compressive hold times. Third group, named imperfect persistent slip markings, was observed after cyclic straining with tensile holds. In some suitably oriented grains, areas with high density of well-developed markings with irregular morphology were found.
Characteristics of Duplex Treated AISI 304 Stainless Steel
Authors: Joska Zdenek , Kadlec Jaromir , Hruby Vojtěch , Studeny Zbynek , Binar Tomas
Published: November 2013

The duplex treatment consisted of a plasma nitriding at 470 °C for 4 h and subsequent coating with TiN layer was applied on AISI 304L stainless steel. The article is concerned to a study of the chemical composition and mechanical properties of duplex system. GDOES method, laser confocal microscopy, nanohardness and indentation test were employed to characterize the chemical composition, depth profiles, surface morphology, hardness, adhesion. The results show that the duplex surface system possesses a desirable combination of properties especially hardness. Adhesion of PVD coating was increased on nitrided surface.
Influence of Localized Structural Defects on the PN Junction Properties
Authors: Škarvada Pavel , Tománek Pavel , Šicner Jiří
Published: November 2013

Local defects, as micro-fractures, precipitates and other material inhomogeneities in solar cell structure, evidently modify electrical and photoelectrical behavior of the latter. To improve the efficiency and lifetime of existing solar cells, it is important to localize these defects which influence the p-n properties, and assign them corresponding electrical characteristics. Although the electric breakdown can be evident in current-voltage plot, the localization of local defects in the sample, that generate this breakdown, is not so easy task. It has to be done by microscopic investigations and measurement of light emission from defects under electrical bias conditions. Thus to contribute to this end, the structure of defects is microscopically investigated and consequently, the defects can be removed by focused ion beam milling. The experimental results obtained from samples before and after milling are also discussed.
Particulate Composite Damage: Numerical Estimation of Micro-Crack Propagation Direction
Authors: Majer Zdeněk , Marcián Petr , Náhlík Luboš , Hutař Pavel , Knésl Zdeněk
Published: November 2013

In recent years, particle reinforced composites are widely used due their mechanical properties as construction materials, high-performance engineering materials or protective organic coatings. The paper was mainly focused on the estimating of the interactions of the micro-crack and the particles in the particulate polymer composites. A non-linear material behavior of the matrix was obtained from the experiment and it was used to investigation by means of the finite element method - using ANSYS software. A two-dimensional numerical model was developed and a micro-crack propagation direction was calculated based on the assumption of the linear elastic fracture mechanics. The results indicated that the presence of the interphase between particle and matrix can improve the fracture toughness of the polymer particle composites through debonding process. The paper can contribute to a better understanding of the behavior and failure of the composites with the polymer matrix reinforced by the rigid particles.
Study of the Influence of Structural Defects on Properties of Silicon Solar Cells
Authors: Šicner Jiří , Škarvada Pavel , Macků Robert , Koktavý Pavel
Published: November 2013

Solar cells of common sizes contains many of these defects and it is not easy to determine the influence of particular defects on the characteristics of the whole solar cell. Therefore, in our research we use samples of size of square centimeter at which we can disentangle the influence of the defect. We localize the defect by using a CCD camera, we measure the electrical, thermal and optical properties of the sample and then study it by means an electron microscope, we find the damaged structure and put it to focused ion beam. We expect the change in electrical, thermal and optical properties of the sample.
Investigation of the Mechanical Properties of Lead-Free Solder Materials
Authors: Otáhal Alexandr , Adamek Martin , Jansa Vojtech , Szendiuch Ivan
Published: November 2013

Reliability and life-time of electric/electronic products is still a highly actual and discussed topic. Every electric/electronic product is heterogeneous system which consists not only from components and constructional parts, but also from many interconnections. Basic segments of interconnection are solder joints, recently created by lead-free materials. The passing from well-proven lead solders to lead free compositions brought many new aspects in reliability and life-time of electronic systems. Some of the negative factors are their poor electro-mechanical properties, which are based on complicated microstructure of interlayer interface. This fact causes defects in solder joints and consequential failure of the function. This article is focused on an investigation of mechanical properties of lead-free solder joints. There are investigated various properties of common lead-free solder paste depending on various concentrations of O2 by reflow process and on various components size. Next, there are shown microstructures by micro sections for various concentrations of O2. Mechanical properties (mechanical strength) are tested by shear test equipment DAGE 2400.
Photo-Reflective Layer on Low Temperature Co-Fired Ceramic for Optical Applications
Authors: Klíma Martin , Holik Milan , Svatos Vojtech , Hubálek Jaromir , Szendiuch Ivan , Urban Frantisek
Published: November 2013

The article deals with photo-reflective layer on Low Temperature Co-fired Ceramic substrate deposition. Measurement of diffusion and specular reflectance and roughness of layer is included. Fabrication process and its optimization is also mentioned. For measurement of deposited layer optical properties, spectrometric method in spherical chamber was used. Further, profile of layers surface was measured by profilometer to acquire dependence between roughness and reflectivity. The main aim of work is to map the possibility of creation of photo-reflective layer on electrical, chemical and thermal resistant substrate in simple way.
Quantification of Liver Microcirculation Using X-Ray Microtomography of Vascular Corrosion Casts
Authors: Králíčková Anna , Eberlová Lada , Kalusová Kristýna , Gregor Tomáš , Kochová Petra , Liška Václav , Králíčková Milena , Tonar Zbyněk
Published: November 2013

We used corrosion casts and micro-CT for quantitative description of microvascular network in porcine liver. Using stereological methods, manual tracing of microvessels and analysis of orientation in 3D, we quantified the volume fraction, the surface density, the numerical density, the length density and the tortuosity of microvessels in series of images with 1.875 μm pixel resolution. Biodur E 20 resin was more suitable for preparing and quantifying microvascular tree corrosion casts when compared to Mercox II resin. Quantified data could be applicable for correlating 3D models with 2D liver histopathology, for enhancing the interpretation of routine medical CT and for providing data for computer models of tissue perfusion and angiogenesis.
Structural Transformation in Nanowires CuAu I with Superstructure of L10 of Tetragonal Symmetry at Uni-Axial Tension Deformation
Authors: Starostenkov Mikhail D. , Yashin Alexander , Sinica Nikita
Published: November 2013

This article deals with the research of the influence of the anisotropy of the alloys properties having non-cubic symmetry for example nanofibers CuAu I during deformation at low temperatures.
Experimental Studies of Excess Noise Sources in Concrete Based Materials as a Limiting Factor for Electromagnetic Emission Measurement
Authors: Macků Robert , Koktavý Pavel , Trčka Tomas , Holcman Vladimir
Published: November 2013

This paper deals with excess noise sources in dielectric materials. We focus especially on the concrete samples that are frequently tested to ensure information about the reliability and level of degradation. Nevertheless, the testing methods are limited mainly by the proper contact creation, signal detection and noise defined sensitivity. Our efforts are directed to the noise properties assessment. It turns out that the Johnson-Nyquist noise and the 1/f (flicker) noise are generated in the different regions with the different response to the internal or external electric field. In addition the noise analysis is affected by the internal polarization phenomena and the material residual humidity. This issue in connection with the sample geometrical properties and the dielectric noise measurement methodology take part in this paper.
Mechanical Induced Defects and Fractures in the Silicon Solar Cell Structure
Authors: Macků Robert , Koktavý Pavel , Šicner Jiří , Holcman Vladimir
Published: November 2013

Presented research is involved in excess electrical currents created when the silicon material contains cracks and fractures. We performed transport characteristics measurements and electrical noise measurement as well as sample visible and deep infra-red imaging. It turns out that mechanical induced defects are followed by specific electric characteristics. We observe crack-related local breakdowns and local overheating. It is also followed by the electrical current fluctuation in the 1/f form. All regions are thermally but also electrically stressed and the irreversible sample degradation originates. It could be pointed out that our detection methods are very sensitive and they could be also used for analyses of different materials.
Monitoring of the Damage in Stone Blocks by Means of Non-Destructive Methods
Authors: Kořenská Marta , Manychova Monika , Pazdera Lubos , Topolář Libor
Published: November 2013

This paper deals with the damage assessment in stone blocks dismantled from a historic bridge construction. Nonlinear ultrasonic spectroscopy and impact echo methods were used for evaluating the stone block integrity structure. Harmonic analysis of the sample response on well defined ultrasonic excitation was used in the case of nonlinear ultrasonic method application. The amplitude dependent spectral changes of the probing signals were measured in the damaged blocks. Measurement results showed that the analysis of amplitude dependent spectral changes is a promising method for the damage assessment in structures. The Impact-Echo method is a technique for detecting defects in material structure such as stone blocks. It is based on monitoring the propagation of elastic waves from a short-duration mechanical impact. The aim of this paper is to provide an overview of the technique and to discuss the important parameters involved in this type of testing. The impact echo method is used to generate low-frequency stress waves from 500 Hz to 50 kHz that propagate into the structure and are reflected by defects and external surfaces.
Structural Response of Metal Crystallite with BCC Lattice on Atomic Level under Nanoindentation
Authors: Kryzhevich Dmitrij Sergeevich , Korhuganov Aleksandr Vyacheslavovich , Zolnikov Konstantin Petrovich , Psakhye Sergei Grigorievich
Published: November 2013

Molecular dynamics investigation of metal crystallite with bcc lattice under nanoindentation was carried out. Potentials of interatomic interactions were calculated on the base of the approximation of the embedded atom method. The potentials chosen make it possible to describe with a high accuracy the elastic and surface properties of the simulated metal and energy parameters of defects, which is important for solution of the task posed in the work. For clarity and simpler indentation data interpretation, an extended cylindrical indenter was used in the investigation and loading was realized by its lateral surface. The simulated crystallite had a parallelepiped shape. The loaded plane of crystallite was modeled as a free surface while the positions of atoms in the opposite plane of crystallite were fixed along the indentation direction. Other planes of crystallite were simulated as free surfaces. The indenter velocity varied from 5 to 25 m/s in different calculations. The loading of the model crystallite was realized at 300 K. Influence of interfaces (free surfaces and grain boundaries) on peculiarities of plastic deformation nucleation and interactions of generated structural defects with interfaces in simulated crystallite under nanoindentation were investigated.
Microstructural Investigations of Nickel-Based Superalloys with Different Structure
Authors: Pytel Maciej , Nowotnik Andrzej , Szeliga Dariusz , Sieniawski Jan
Published: November 2013

This paper presents the results of analysis of superalloys microstructures with different structures: polycrystalline nickel-based superalloy René 80, Mar-M 200Hf directionally solidified with columnar grains and single crystal CMSX-4. Microstructure studies were performed using a scanning electron microscope Hitachi FE-SEM SU-70 and S-3400N equipped with a Thermo Scientific Noran System for analysis of chemical composition by X-ray dispersion. Metallographic microsections of the rods before and after heat treatment was performed, which were electrolytically etched using different reagents. The morphology of γ phase precipitates in the interdendritic areas and dendritic cores was analyzed. Single crystal rods of nickel superalloy CMSX-4 were cast by Bridgman technique in a vacuum furnace of ALD Vacuum Technologies. Rods were withdrawn with rate: 1mm/min and 5mm/min. EDS X-ray microanalysis showed significant differences in chemical composition between the cores dendrites and eutectic regions. Significant differences in the number of dendrites, the shape and length of the arms were observed. A lower speed rate causes that amount of eutectic is lower but value of primary dendrite arm spacing is higher, while a higher withdraw rate increases the amount of eutectic and decreases primary dendrite arm spacing.
The Effect of Radiation-Induced Structural Changes under Accelerated Irradiation on the Behavior of Water-Cooled Reactor Pressure Vessel Steels
Authors: Gurovich Boris A. , Kuleshova Evgenia A. , Maltsev Dmitry A. , Zabusov Oleg , Prikhodko Kirill , Frolov Alexey , Fedotova Svetlana V. , Erak Dmitry , Denis Zhurko , Saltykov Mikhail
Published: November 2013

In this paper the influence of fast neutron flux on the structural features and properties of VVER-1000 reactor pressure vessel steels was studied. It is shown that for high Ni steels the flux effect is due to hardening and non-hardening mechanisms of radiation embrittlement.
Damage and Fracture Behaviours in Aged Austenitic Materials during High-Temperature Slow Strain Rate Testing
Authors: Calmunger Mattias , Chai Guo Cai , Johansson Sten , Moverare Johan
Published: November 2013

Biomass power plants with high efficiency are desired as a renewable energy resource. High efficiency can be obtained by increasing temperature and pressure. An upgrade of the material performance to high temperature material is therefore required in order to meet the increased demands due to the higher temperature and the more corrosive environment. In this study, the materials high-temperature behaviours of AISI 304 and Alloy617 under slow deformation rate are evaluated using high-temperature long-term aged specimens subjected to slow strain rate tensile testing (SSRT) with strain rates down to 10-6/s at 700°C. Both materials show decreasing stress levels and elongation to fracture when tensile deformed using low strain rate and elevated temperature. At high-temperature and low strain rates cracking in grain boundaries due to larger precipitates formed during deformation is the most common fracture mechanism.
Structural and Fatigue Properties of Titanium-Steel Bimetallic Composite Obtained by Explosive Welding Technology
Authors: Karolczuk Aleksander , Kowalski Mateusz
Published: November 2013

Structure of bimetallic composite obtained during explosive welding process exhibits strong heterogeneity in the vicinity of interface. The interface usually has a wavy shape with characteristic increase of hardness and largely deformed grains. Recently obtained fatigue tests for titanium-steel bimetal specimens under fully reversed push-pull loading show ratcheting phenomenon. In order to investigate this phenomenon mechanical testing and structural observations of titanium-steel bimetal and titanium before cladding have been performed. Fatigue characteristics in the form of relation between strain amplitude and fatigue life for titanium (Grade 1), steel (S355J2+N) and bimetal will be presented.
Structural Modifications of the Aluminium Alloy in Conditions of Additional Shock Impulse Load
Authors: Hutsaylyuk Volodymyr , Czausow Mykola , Śnieżek Lucjan , Pylypenko Andrii , Ślęzak Tomasz , Berezin Valentin
Published: November 2013

This work has been done to research the physical nature of the mechanism of structural changes of the aluminum alloy 2024-T3 at the conditions of additional impulse load. There was revealed an anomaly growth in plasticity of the material after such type load realization at the room temperature. Based on fractographical research the impact of dynamic non-equilibrium processes on the structural changes of the material and its macro-mechanical properties was analyzed.
Comparison between Pile-Up Singularities and Stress Fields Induced by Thin Slip Bands. Application to the Prediction of Grain Boundary Microcrack Nucleation
Authors: Sauzay Maxime , Moussa Mohamed Ould
Published: November 2013

Slip localization is widely observed in metallic polycrystals after tensile deformation, cyclic deformation or pre-irradiation followed by tensile deformation. Such strong deformation localized in thin slip bands induces local stress concentrations in the quasi-elastic matrix around, at the intersections between slip bands (SBs) and grain boundaries (GBs) where microcrack initiation is often observed. Since the work of Stroh, such stress fields have been mostly modeled using the dislocation pile-up theory which leads to stress singularities similar to the LEFM ones. The Griffith criterion has then been widely applied, leading usually to strong underestimations of the macroscopic stress to GB crack initiation.
In fact, slip band thickness is finite: 20nm-1000nm depending on material, temperature and loading conditions. Then, many slip planes are plastically activated through the thickness, and not only one single atomic plane. To evaluate more realistic stress fields, numerous crystalline finite element (FE) computations have been carried out using microstructure inputs (slip band aspect ratio, crystal and GB orientation...).
A strong influence of slip band thickness close to the slip band corner has been highlighted, which is not accounted for by the pile-up theory. But far away, the thickness has a negligible effect and the predicted stress fields are close to the one predicted by the pile-up theory. Closed-form expressions are deduced from the numerous FE computation results allowing a straightforward prediction of GB stress fields. Slip band plasticity parameters, such as length and thickness, as well as crystal orientation, GB plane and remote stress are taken into account. The dependence with respect to the various parameters can be understood in the framework of matching expansions usually applied to cracks with V notches of finite thickness.
As the exponent of the GB stress close-field is only about one-half of the pile-up or LEFM crack one, the Griffith criterion may not be used for GB microcrack prediction in case of finite thickness. That is why finite crack fracture mechanics is used together with both energy and stress criteria. Taking into account SB finite thickness, t>0, leads to predicted remote stresses to GB microcrack initiation three to six times lower than the ones predicted using the to pile-up theory, in agreement with experimental data.
Elastic Properties of Porous Alumina, Zirconia and Composite Ceramics
Authors: Pabst Willi , Gregorová Eva , Uhlířová Tereza , Musilová Anna , Andelová Zuzana
Published: November 2013

Micromechanical calculations and elasticity standard relations are used to predict the elastic properties of porous alumina, zirconia and kaolin-based ceramics, as well as the high-temperature Young moduli of alumina-zirconia and alumina-mullite composites. The predictions are compared with experimental results obtained via impulse excitation. It is found that the Young moduli of highly porous (cellular) alumina ceramics can be predicted via the Gibson-Ashby power-law relation, whereas for partially sintered kaolin-based ceramics our exponential relation, albeit better than the Gibson-Ashby relation, does not give a satisfactory prediction. However, once the Young moduli are known, the shear and bulk moduli can be reliably predicted in both cases, based on rough information on the Poisson ratio. The temperature dependence of the Youngs moduli of two-phase composites can be quite precisely predicted as soon as the master curves of the constituent phases and the type of porosity (convex, concave, or saddle-point) are known.