bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation on the Combustion and Emission Characteristic of Diesel Engine with EGR
Authors: Yin Bi Feng , Xu Zhen Wei , He Jiang Guang , Xu Yi , Li Yong Qiang
Published: January 2011

Based on a diesel engine with common rail system, influence of EGR on combustion and emission characteristic were investigated. The test results show that EGR can cut down both cylinder pressure and the rate of pressure rise, which leads to the depression of instantaneous rate of heat release and combustion temperature and the extension of the whole combustion period.EGR make effective improvements on reducing NOx emissions in all the operating modes. In light load condition CO and HC emissions take a favorable turn with larger EGR rate, SOOT and fuel consumption are well maintained. In moderate and heavy load condition, the curve of HC ,CO emissions assume “hook-like”, which is get down first and then steep rise. SOOT is well maintained before the inflection point but get deteriorate after the point. As the working load rate of the engine become heavier, the rate of EGR whose inflection point located becomes smaller and the fuel consumption turn out to be worse.
Influence of Thickness and Substrate on the Transient Reflectivity of Copper Films
Authors: Ren Nai Fei , Wang Rong Xiao , Gu Jia Fang , Ren Jian Qing
Published: January 2011

Cu films were deposited on Si and K9 glass substrates by magnetron sputtering technique. The influences of varying thicknesses and substrates on the transient reflectivity of Cu films were studied by using femtosecond laser pump-probe technology. The results show that the transient reflectivity curve of Cu films in different thicknesses have the same trend except that when they reach the peak value and recover to the balance. When the laser power is 40 mW, the influence of Si and K9 substrates on the transient reflectivity curve of 20 nm Cu films is relatively small. But when the laser power is160 mW, the influence of Si and K9 substrates on the transient reflectivity curve of 20 nm Cu films have obvious difference, the former needs much less time to reach the thermal equilibrium than of the later. At the same time, the influence of different substrates on the transient reflectivity curve of 200 nm Cu is also small.
Optimization of Process Parameters for Vacuum Casting Micro-Gear
Authors: Dai Y.C. , Zhou Jian Zhong , Huang Shu , Guo J. , Xiao L.
Published: January 2011

A silicone mould fabrication technique based on vacuum casting was developed and its reproducibility was demonstrated. Orthogonal DOE method was adopted to analyze the effects of vacuum casting process parameters, and the process parameters that had an influence on the quality of the micro-mould cavities were identified and optimized. Micro-casting experiments were carried out using the optimized process parameters and the replicated micro-gears were obtained, these silicone copies were subjected to thorough analysis for dimensional accuracy against the master pattern. The results showed that the fabricated micro-mould was capable of producing functional micro-parts that were able to replicate micro-features, and micro-gears were successfully transferred from the silicone rubber moulds into PU resin pieces under vacuum conditions.
Fundamentals of Selective Laser Sintering of 316 Stainless Steel Powder
Authors: Bai Pei Kang , Li Yu Xin , Liu Bin
Published: January 2011

Selective laser sintering technology is used for manufacturing parts from 316 stainless steel powders. Experiments were carried out on a Nd:YAG laser machine (LMY400) with 400W. Powder is layered by a roller over the surface of a 100mm diameter build cylinder. Effects of processing parameter on the scan line width, the scan line height, the single layer structure and the multilayer structure are investigated. The results show laser power, scan speed and layer thickness have a great effect on the scan line width and line height. Furthermore, the stable and continuous vectors are formed with the increasing of the number of layers.
The Microstructure and Properties of LY12 Aluminum Alloy by Ultra-High Plastic Strain
Authors: Zhang Ling Feng , Luo Kai Yu , Lu J.Z. , Xiong Y. , Wang Y.Z.
Published: January 2011

The ultra-high plastic deformation behavior by laser shock processing on the LY12 aluminum alloy had been investigated. The morphology of the materials had been analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the grain refinement layer was formed in the thickness of about 100μm .The dislocation density of LY12 aluminum alloy should be large increased after laser shocking because the accumulation of dislocation was appeared on the grain boundary. With the laser energy density increased there formed subgrain structure and eventually generate ultra-fine grain. Hardness test results also show that the surface hardness obtains a big growth about 60% after laser shock processing. The results showed that the formation of ultra-high plastic strain can improve the surface hardness of LY12 aluminum alloy, and thus effectively improve the comprehensive mechanical properties.
A Study of Integration for Heterogeneous Network Positioning
Authors: Song Xiao Tian , Zhu Yi , Yan Shu , Chen Zu Jue
Published: January 2011

Nowadays, the trend for future development of the wireless communication is focused on heterogeneous network. With requirements such as E911, the positioning technology becomes widely concerned in heterogeneous network due to its added complexity compared with a simple homogeneous network. This paper discusses some typical scenarios for integration of heterogeneous network and focuses on direct mapping results to improve the final node integration accuracy; we also examine the feasibility and necessity of positioning integration based on the characteristics of heterogeneous network. This study provides for the integration of heterogeneous network positioning a theoretical framework.
Design for Multi-Parameter Wireless Sensor Network Monitoring System Based on Zigbee
Authors: Gui Fen , Liu Xing Qiao
Published: January 2011

The water monitoring environment has the characteristics of more measuring points, longer measuring time, more complex measuring situation and so on, in order to solve the problem of high cost and routing difficulty during monitoring, a new type of multi-parameter wireless monitoring system based on ZigBee is designed. This system realizes the multi-parameter collection, transmission and display, such as dissolved oxygen, pH and temperature. The fast and accurate transmission of the data between sensor node and coordinate is achieved through wireless sensor network. Then the system realized the real-time remote monitoring. Because of its simple structure, fast data transmission, easily function extended, and high self-organization and self-recovery ability, the system is suitable for many fields such as industry aquaculture, water environment, intelligent greenhouse and other domains.
Omnidirectional Vision Based Mobile Robot Hierarchical SLAM
Authors: Li Mao Hai , Sun Li Ning , Pan Ming Qiang
Published: January 2011

A hierarchical mobile robot simultaneous localization and mapping (SLAM) method that allows us to obtain accurate maps of large environments is proposed. The local map level is composed of a set of local metric feature maps that are guaranteed to be statistically independent. The global level is a topological graph whose arcs are labeled with the relative location between local maps. An estimation of these relative locations is maintained with local map alignment algorithm, and more accurate estimation is calculated through a global minimization procedure using the loop closure constraint. The local map is built with Rao-Blackwellised particle filter (RBPF). The particle filter is used to extend the path posterior by sampling new poses that integrate the current observation which drastically reduces the uncertainty about the robot pose. The landmark position estimation and update is also implemented through Kalman filter. Omnidirectional vision mounted on the robot tracks the 3D natural point landmarks, which are structured with matching Scale Invariant Feature Transform (SIFT) feature pairs. The matching for multi-dimension SIFT features is implemented with a KD-Tree. Experimental results on real robot in a medium size, real indoor environment show the practicality and efficiency of our proposed method.
Stress Relaxation in an AZ31 Magnesium Alloy
Authors: Lukáč Pavel , Trojanová Zuzanka
Published: January 2011

Stress relaxation tests have been used in order to determine parameters of a possible thermally activated process in AZ31 magnesium alloy. The samples were deformed at a constant initial strain rate of 6.7x10-5 s-1 at various temperatures between room temperature and 300 °C. Stress relaxation, i.e. a decrease in the stress with time, was measured at various stress levels and at various temperatures. An analysis of the stress relaxation curves enabled to estimate the internal stress as a function of the strain and the test temperature. It has been shown that the activation volume is a function of the effective stress independently of the deformation temperature.
Elastic-Plastic Stress Singularities of Plane V-Notches in Power-Hardening Materials
Authors: Niu Zhong Rong , Recho Naman , Yang Zhi Yong , Cheng Chang Zheng
Published: January 2011

Extensive studies have been carried out to deal with the stress singularity of V-notch problems in linear elasticity theory. In fact, the plastic deformation consequentially arises in the notch tip region because of the high stress concentration. The solution of linear elasticity is not adequate to explain the fracture failure of V-notch structures. Because of the difficulties of the nonlinear analysis and the singularity behavior, few results are given for the plastic stress singularities of general V-notch structures. In this paper, the plane V-notch structures in a power law hardening materials are considered. The Von Mises yield criterion and the plasticity total theory are adopted when the materials arise in plastic status. Similar to methods used in the elastic analysis, the plastic stress field near V-notch tips is assumed as an asymptotic expansion with respect to the radial coordinate originating from the notch tip. The governing equations of plastic behavior of plane V-notch are transformed to eigenvalue problems of nonlinear ordinary differential equations (ODEs) contained by the stress singularity order and the associated eigenfunctions. Consequently all of the stress singularities who are less than zero and the associated eigenvectors are accurately determined for the plane V-notches with arbitrary opening angle.
Complex Variable Green’s Functions for Crack-Microcracks Interactions
Authors: Chabaat M. , Ayas H.
Published: January 2011

In this study, interaction between a main crack and a surrounding layer of micro cracks is considered. A stress field distribution induced during these interactions is obtained using Muskhelshvili’s complex variables formalism which relies on the Green's functions. The effect of amplification and shielding on the resulting stress field is shown, herein, through a study of mode I Stress Intensity Factor (SIF). To quantify these effects, orientations as well as positions of microcracks with respect to the main crack is taken into consideration. Obtained results are compared and agreed with those of other researchers.
On Mathematical Modelling of the Diffusion Characteristics in the close Vicinity of Two Steels Welded Joint
Authors: Řeháčková Lenka , Kalousek Jaroslav , Dobrovská Jana
Published: January 2011

This paper deals with the quantitative evaluation of temperature and time effect on the concentration distribution of the substitutive elements in the vicinity of the welded joint. The calculations were performed for the weld of two different steels. The measurement of the concentration profiles of the elements in the weld was evaluated by the numerical optimalisation methods using the 2nd Fick’s law. The output of calculations defines quantitatively two terms: diffusion and penetration layers.
Design of Experiments in the Branch of Thermal Spraying
Authors: Rozum Ondrej , Zahálka František , Kašparová Michaela , Houdková Šárka
Published: January 2011

High quality methods of designing the experiments (DOE) seem to be a very useful exploratory tool at many points of material engineering. Designing the experiments is a natural way to find a systematic influences in the process. It is necessary to have a clear view on how the things are to have the processes under controll. Therefore the importance of DOE increases in management and industry all over the world. In this work, a general use in branch of thermal spraying is shown.
Pore Size Distribution in Foams
Authors: Matoušek Tomáš , Ponížil Petr , Galetka Marek
Published: January 2011

Physical properties of polymer foams depend on their macrostructure. In this paper, we study a range of polyuretane foams from the stereological point of view. Images of plane surfaces of studied samples were created by printing them on a sheet of paper and scanning these imprints. Consequent operations included reconstruction of pore section areas in the plane of printing and computation of pore volumes. The distribution of pore section was compared with data from computer tomography (CT) in order compare both methods.
Experimental Evaluation of Material Rollability in Profile Rolling
Authors: Lai Chi Ping , Chan Luen Chow , Lee Tai Chiu
Published: January 2011

This paper aims at presenting an experimental investigation to compare the rolling behaviors of selected materials under profile rolling process. Copper alloy (C37700), aluminum alloy (AA6063) and stainless steel (AISI304) in 6 mm diameter were selected as rolling specimens. The process parameters, i.e. spindle speed, forward speed, and fractorgraphic analysis were carried out to determine the deformation behaviours of selected materials. The outcomes of this investigation are valuable for engineers to design and fabricate high-quality precision components efficiently.
Structure of Rapidly Solidified Al-Fe-Cr-Ce Alloy
Authors: Michalcová Alena , Vojtech Dalibor , Novák Pavel , Procházka Ivan , Čížek Jakub , Drahokoupil Jan , Wienerová Kateřina , Saksl Karel , Rokicki Pawel , Spotz Zdeněk
Published: January 2011

An alloy containing Al – 3wt.% Cr – 3wt.% Fe – 0.8wt. % Ce, was prepared by melt spinning. Structure of obtained ribbons was observed by light, scanning and transmission electron microscopy. It was found out that the structure is very fine. Microhardness of cross sectioned ribbons was also measured. Defects in structure were determined by positron annihilation spectroscopy. The thermal stability of the alloy was observed by comparing rapidly solidified ribbons and ribbons annealed at 400°C and at 500°C for 100 h
Investigations on the Fatigue Behavior of Nanocrystalline Metals
Authors: Funk Matthias , Eberl Christoph
Published: January 2011

In this paper data on fatigue lifetime of nanocrystalline (nc) Ni samples is presented. The nc-Ni samples show high lifetimes and can resist large stress amplitudes. Furthermore a new method to determine the fatigue limit based on a Fourier analysis [7] is presented. First results of a load increase test suggest strong parallels to thermal and resistive measurements which can be used to determine the fatigue limit. Microstructural investigations on as received and failed samples show a strong increase in grain size induced by the cyclic loading. The processes behind this are not understood so far and will be investigated in the future.
Anomalous Transformation-Induced Deformation in Gum Metal
Authors: Morris Jr. John William , Chrzan D.C. , Kuramoto Shigeru
Published: January 2011

Tensile tests of single crystals of Gum Metal (Ti-36Nb-2Ta-3Zr-0.3O (wt %)) showed, anomalously, that (1) extensive, stress-induced (bcc)”(orthorhombic) transformation occurred in a crystal pulled in the <110> direction, but no transformation was observed in crystals pulled in the <100> or <111> directions and (2) little or no transformation occurred in tensile tests of severely worked rods, which are polycrystals with very strong <110> texture. Analysis of the energetics of the ” transformation offers straightforward explanations for these results. (1) An ” precipitate has very low elastic energy if it forms as a thin plate with a habit near {11√2}. A <110> tensile load significantly decreases the energy of this plate, promoting the transformation; loading along <100> or <111> is much less effective. (2) While cold-swaged rods of Gum Metal have a strong <110> axial texture, their perpendicular planes are severely distorted, increasing the elastic energy of ” and inhibiting the transformation.
Microstructure and Thermal Stability in CP Titanium Processed by Electroplastic Rolling
Authors: Gubicza Jenő , Khosravi E. , Stolyarov Vladimir V.
Published: January 2011

Ultrafine-grained (UFG) CP titanium (Grade-4) sample was processed by electroplastic rolling (EPR) at room temperature which was compared to a specimen processed by conventional cold rolling (CR). EPR was performed using pulsed unidirectional current with a current density of 95 A/mm2, pulse duration of 10-4 s and frequency of 1000 Hz. It was found that the sample processed by EPR has slightly higher dislocation density and smaller crystallite size than for the CR specimen resulting in a higher tensile strength for the former specimen. In the case of EPR sample, the relative fraction of  dislocations is lower than for CR specimen. During annealing the relative fraction of  dislocations decreased for both samples which can be explained by the fact that the  dislocations have larger Burgers-vector and consequently higher formation energy than the other two types.
The Impact of Manufacturing Technology on the Thermal and Electrical Properties of Ceramic Powders Intended for Spraying Using the APS Method
Authors: Moskal Grzegorz , Grabowski Andrzej
Published: January 2011

This article describes the microstructures, chemical and phase compositions, surface morphologies, and internal structures of three ZrO2 x 8Y2O3-type of powders obtained by different manufacturing methods. The first of the analyzed powders was a conventionally prepared form of the material obtained by the spraying method. The second powder was a spherically shaped form of the material obtained from the spray drying process. It displayed a distinctive surface morphology characterized by a rough structure with visible cavities. The particle sizes of these two powders were comparable. The third form of the powder was classified as “nano” and was obtained by a grinding and crushing method. The shapes of individual particles were generally polyhedral with smooth surfaces and no visible porosity. A study of the chemical composition of each form of the powder did not show significant differences, similar to the results obtained from the phase composition study. The results of thermal diffusivity and electrical impedance studies indicated that the electrical and thermal properties of the powders with spherical structures, i.e., sprayed and spray drying, were very similar. The thermal diffusivity and impedance properties of these two powders were greater than those of the ground powder with a finer grain size.
Effect of Elastic Mismatch and Anisotropy on Cracking of Brittle Films on Elastic Substrates
Authors: Kotoul Michal , Vyslouzil Tomas
Published: January 2011

The paper analyzes the depth and spacing of cracks in a tensile strained In0.25Ga0.75As epitaxial layer on a InP substrate using the minimum energy theorem. The elastic anisotropy of both the layer and the substrate is considered. The concept of weight function obtained numerically by means of detailed FEM is employed.
The Influence of Deposition Process on Structure of Platinum-Modifed Aluminide Coatings O Ni-Base Superalloy
Authors: Swadźba Lucjan , Nawrat Ginter , Mendala Boguslaw , Goral Marek
Published: January 2011

The modern jet engines used in commercial and military aircrafts are characterized by operating temperature in turbine section above 1000oC. The Ni-base superalloy turbine blades and vanes working in high temperature in very aggressive environment require using of protective coatings. The aluminide coatings are widely used to protect this engine parts. The pack cementation, out of pack and chemical vapour deposition (CVD) technologies are usually used to produce this type of coating. The aluminide coatings can be modified by platinum or other elements. The Pt-modified aluminide coatings are characterized by better oxidation and corrosion resistance in comparison with conventional aluminide coatings and can be used as a bond coat for Thermal Barrier Coatings deposited by EB-PVD technology. In present study the influence of deposition technology and their’s parameters on structure and chemical composition of Pt-aluminide coatings are presented. The base material for coatings was a Inconel 738 Ni-base superalloy. The first step of coatings production were Pt electroplating with different thickness of platinum layer. The second step of coating production was aluminising process. The aluminide coatings were produced by pack cementation and out of pack technologies. Additional the influence of heat treatment of base alloy with coatings was investigated. The structure of all deposited coatings was observed by scanning electron microscopy and the chemical and phase composition of coatings were investigated by EDS and XRD methods. The observed coatings were characterized by two types of structure: first based on NiAlPt phase obtained on thin Pt layer and the second with additional presence of PtAl2 phase on the thick Pt layer.
The Influence of Silicon Amount on Structure of Si Modified Aluminide Coating Deposited on Ti46Al7Nb Alloy by Slurry Method
Authors: Goral Marek , Moskal Grzegorz , Swadźba Lucjan , Hetmańczyk Marek
Published: January 2011

The alloys based on the intermetallic phases from Ti-Al system are materials which, on the grounds of their resistance characteristics, could be widely used in automotive and aerospace applications. The insufficient oxidation resistance of this alloys could be increased by the coating silicon modification. The technology used in this investigation was the immersion in water-based slurry containing metal powders. MHI high-Nb (14 wt %) alloy has been used as the research material for the coatings produced. The water-based slurries containing Al and Si powders have been prepared with 0-80 wt % Si content. The diffusion treatment has been done at 950oC in 4h in the Ar atmosphere. The investigation has showed that the thickness of the coatings ranged from 30 to 40 m. The structure of the Si-modified aluminide coatings is as follows: (a) outer zone consisting of TiAl3 phase and titanium silicides, (b) middle zone consisting of columnar titanium silicides in phase TiAl3 matrix (c) the inner zone consisting of TiAl2 phase. The XRD phase analysis has confirmed Ti5Si3 creation and, in case of the high silicon content (above 20 wt %), also other silicides: types Ti5Si4,TiSi2,TiSi
Structure of Al-AlN Composite Coatings Obtained by Arc-PVD Method
Authors: Mendala Boguslaw
Published: January 2011

In this paper the investigations concerning deposition of aluminium and aluminium nitride coatings by Arc-PVD method were presented. The tests were done on samples made of martensitic stainless steel EI962 (11H11N2W2MF) type. The aluminium base coatings are corrosion resistant in many environments and are anodic in comparison with most of steel. For this reason those coatings are expected to form a replacement for cadmium galvanic coatings. The main parameters of aluminium base coatings deposition by Arc-PVD processes were presented. Influence of Arc-PVD parameters on Al-AlN composite coatings structure was described. The models of Al-AlN composite coatings and Al/Al-AlN multilayer coatings as well as the scanning electron microscope microstructure and profile chemical composition by GDOS analysis of the coatings deposited on EI962 stainless steel were shown.
Comparative Studies of Fracture Surfaces of a Biomaterial with the Use of a Profilographometer and Confocal Microscope
Authors: Stach Sebastian
Published: January 2011

The aim of the paper is to present comparative studies of the parameters of the fracture surface topography of titanium alloy, obtained by means of two techniques. The research equipment consisted of a Taylor Hobson profilographometer, Talysurf, and a confocal microscope, LEXT OLS 3000 by Olympus. By means of a contact and non-contact method, files of coordinates of the investigated surfaces were obtained, based on which some chosen stereometric parameters were calculated. The tests carried out as part of the study confirmed the usefulness and the possibility of using a confocal microscope as a modern instrument for evaluating the topography of non-planar surfaces. In the case of statistical parameters representing the whole surface under examination, very high convergence of the stereometric structure parameters was obtained, described by means of profilographometry and confocal microscopy methods.
The Study of Microstructure and Properties of Al Diffusion Coating on Inconel 713LC
Authors: Hutařová Simona , Juliš Martin , Obrtlík Karel , Kianicová Marta , Podrábský Tomáš , Dvořáček Ondřej
Published: January 2011

Protective layers are used to improve high temperature performance of structural materials. However, the effect of coatings on mechanical and fatigue properties is not sufficiently known because it is a combination of many factors as high-temperature exposure time, thermal cycle and coating deposition technique. Interactions between the coating and the substrate under high-temperature conditions influence the life time of coated blades. This paper is focused on the study of microstructure and properties of aluminide protective layers deposited on cast polycrystalline nickel base superalloy Inconel713LC. The light microscopy with image analyses and scanning electron microscopy with energy dispersion spectroscopy were used. The surface treated specimens exposed at 800 °C in air and cylindrical specimens with protective layer cyclically loaded under strain control at 800 °C in air were studied. Experimental data on thickness, uniformity and chemical analysis of individual phases are obtained for as-coated specimens, for specimens exposed to 800 °C for 500 hours in air and for specimens fatigued to fracture at 800 °C in air.
Microstructure Oriented Modelling of Hierarchically Perfused Porous Media for Cerebral Blood Flow Evaluation
Authors: Tonar Zbyněk , Kochová Petra , Cimrman Robert , Witter Kirsti , Janáček Jiří , Rohan Vladimír
Published: January 2011

We used immunochemistry, light microscopy and stereological methods for quantitative description of the microvascular network in 13 tissue samples of the human brain. While the tortuosity of microvessels was comparable in all brain parts under study, the length density of microvessels was higher in subcortical grey matter (652.5±162.0 mm-2) and in the cortex (570.9±71.8 mm-2) than in the white matter (152.7±42.0 mm-2). The numerical density of microvessels was higher in subcortical grey matter (3782.0±1602.0 mm-3) and cerebral cortex (3160.0±638.4 mm-3) than in white matter (627.7±318.5 mm-3). We developed simulation software gensei which generates series of images representing three-dimensional models of microvessels with known length density, volume fraction, and surface density. The simulations are statistically similar to real microvessel networks and can be used for computer modelling of brain perfusion.
SEM Study of High-Chromium Martensitic Steel LCF Fracture
Authors: Eterashvili Tamaz , Kutelia Elguja , Dzigrashvili T. , Vardosanidze M.
Published: January 2011

Low cycle fatigue of high-chromium 13Х11Н2В2МФ stainless steel has been studied after cyclic tests at room temperature with the frequency of loading, 0.45Hz and amplitude, ± 1mm. The samples were v-notched with the dimensions x2x50, where =3mm. The peculiarities of fatigue crack propagation and influence of heat treatment, sizes of grains and laths, and disposition of microcrack and microstructure elements of the steel were studied. Next, the main effect on propagation direction is caused by the shape of grains and laths. It turned apparent that main microcrack is composed of individual micro-components with the lengths correlating with the dimensions of grains and martensitic laths. During growth crack propagation direction changes from lath to lath; however, general trend remains unchanged. The results of tests indicate that speed of fatigue failure rises when the frequency and amplitude of loading increases. The work includes x-ray characterization of the steel, statistical distribution curve for angles between the main direction of macrocrack propagation and micro-components, and explanation of micro- and macrocrack propagation alteration is given.
Non-Destructive Characterization of Micro-Sized Defects in the Solar Cell Structure
Authors: Macku Robert , Koktavý Pavel , Škarvada Pavel
Published: January 2011

This article discusses the issue of noise measurements application for the quality assessment of the solar cells themselves and production technology alike. The main focus of our research is the random n-level (in most case just two-level) impulse noise, usually referred to as microplasma noise. This noise was found to be in a direct consequence of local breakdowns in micro-sized regions and brings about a reduction of lifetime or a destruction of the pn junction. Non-destructive measurement methodology as presented here is suitable for testing of a large number of various semiconductor devices not only for solar cells. In this paper experimental measurement of noise signals in the frequency and time domain is presented. Furthermore the microplasma noise behaviour and defect geometry is discussed.
Electromagnetic and Acoustic Emission Signals Real-Time Measurement, Processing and Data Evaluation
Authors: Trčka Tomas , Tofel Pavel , Koktavý Pavel
Published: January 2011

This paper describes our new improved set-up for EME and AE signals measurement and includes some experimental results. This new measurement system is based on the PXI platform, which is one of the most extended modular platforms for measurement and automation systems. The complex program package in the LabVIEW graphical programming environment was developed for the continual multi-channel EME and AE signals measurement, real time processing and evaluation. It offers the possibility to observe the stressed materials response to applied mechanical load in real time.
Microcracks and Mechanical Behaviour of Corio-Epidermal Junction of Equine Hoof
Authors: Kochová Petra , Tonar Zbyněk , Witter Kirsti , Cimrman Robert , Mezerová Jana
Published: January 2011

The corio-epidermal junction (CEJ) of equine hoof is highly vascularized, tough, but flexible suspensory apparatus between the wall of the hoof and the third distal phalanx. The connection created by leaf-like lamellae has a key role in the solidity and health of the hoof. In this study we focus on mechanical behaviour of CEJ under tensile loading and on the origin and spatial spreading of cracks of CEJ produced by stress exceeding the ultimate strength of the junction. The results show visible relation between mechanical results and structural parameters: the probability of rupture origin is higher in the case of small values of Young’s moduli of elasticity in region with small deformations and small values of 2D length density in dermal region.
Microstructure Evolution and Phase Transformation in a Novel High-Alloyed TRIP Steel Observed during in-Situ Tensile and Cyclic Deformation
Authors: Weidner Anja , Biermann Horst
Published: January 2011

The tensile and cyclic deformation behaviour of a new metastable austenitic stainless cast steel were studied in-situ in a scanning electron microscope (SEM). The metastable steel was investigated in cast condition. The in-situ tests in the SEM show the evolution of the microstructure in dependence on the deformation degree for uniaxial deformation and the number of cycles during fatigue, respectively. The development of the microstructure (i.e. deformation bands) are correlated with the places, where the phase transformation of the metastable austenite into the hcp structure or the bcc ’- martensite (TRIP – effect; TRansformation Induced Plasticity) takes place by applying different SEM-techniques as electron backscatter diffraction (EBSD). In addition, calculations of local deformation fields developing during tensile and cyclic deformation using digital image correlation (DIC) are presented.
An Evaluation of Creep Mechanisms in Ultrafine-Grained Metals
Authors: Kvapilová Marie , Sklenička Václav , Dvořák Jiří , Král Petr
Published: January 2011

Our earlier published creep data are analyzed for ultrafine-grained pure aluminium and copper processed by equal-channel angular pressing (ECAP). The analysis demonstrates conclusively that creep occurs in the investigated materials after ECAP by the same mechanism as in conventional coarse-grained materials with intergranular dislocation glide and climb as the dominant rate-controlling flow process. Under creep conditions examined in this work diffusion creep is not important in pure aluminium and copper because the ultrafine grains are unstable at elevated and/or high temperature creep and the grains grow sufficiently to preclude any significant contribution from Nabarro-Herring or Coble creep.
A New Insight in the Plasticity of Ni3Al Intermetallic Compounds Using AFM Observations
Authors: Bonneville Joël , Coupeau Christophe , Charrier Dimitri
Published: January 2011

The positive temperature dependence of flow stress in Ni3Al is examined through fine slip trace analysis performed by atomic force microscopy. Slip traces, which result from dislocation movements, constitute outstanding markers for investigating the elementary dislocation mechanisms that control plasticity. The experiments were performed on two Ni3Al-base alloys, with Ta or Hf as additional elements. The results give evidence that the anomaly domain is accompanied by a drastic exhaustion of mobile dislocations and very short cross-slip distances on the cube cross-slip plane.
Fracture Mechanisms of Structural and Functional Multilayer Ceramic Structures
Authors: Bermejo Raúl , Šestáková Lucie , Grünbichler Hannes , Lube Tanja , Supancic Peter , Danzer Robert
Published: January 2011

The fracture of mechanically loaded ceramics is a consequence of material critical defects located either within the bulk or at the surface, resulting from the processing and/or machining and handling procedures. The size and type of these defects determine the mechanical strength of the specimens, yielding a statistically variable strength and brittle fracture which limits their use for load-bearing applications. In recent years the attempt to design bio-inspired multilayer ceramics has been proposed as an alternative choice for the design of structural components with improved fracture toughness (e.g. through energy release mechanisms such as crack branching or crack deflection) and mechanical reliability (i.e. flaw tolerant materials). This approach could be extended to complex multilayer engineering components such as piezoelectric actuators or LTCCs (consisting of an interdigitated layered structure of ceramic layers and thin metal electrodes) in order to enhance their performance functionality as well as ensuring mechanical reliability. In this work the fracture mechanisms in several structural and functional multilayer components are investigated in order to understand the role of the microstructure and layered architecture (e.g. metal-ceramic or ceramic-ceramic) on their mechanical behaviour. Design guidelines based on experiments and theoretical approaches are given aiming to enhance the reliability of multilayer components.
Enhanced Plasticity of WE54/SiC Composite Prepared by Powder Metallurgy
Authors: Száraz Zoltán , Trojanová Zuzanka
Published: January 2011

The deformation characteristics of the WE54 magnesium alloy reinforced by 13% of SiC particles have been investigated in tension at elevated temperatures. Composite material was prepared by powder metallurgy technique. The strain rate sensitivity parameter m has been estimated by the abrupt strain rate changes (SRC) method. SRC tests and tensile tests with constant strain rate ( ) were performed at temperatures from 350 to 500 °C. Increased ductility has been found at high strain rates. The corresponding m value was 0.3. The activation energy Q has been estimated. Microstructure evolution has been observed by the light microscope and scanning electron microscope.
Cyclic Plasticity and Cyclic Creep in Austenitic-Ferritic Duplex Steel
Authors: Polák Jaroslav , Petrenec Martin , Man Jiří , Kruml Tomáš
Published: January 2011

Smooth specimens made from austenitic-ferritic duplex steel were subjected to constant stress amplitude loading with positive mean stresses. Hysteresis loops were recorded during the fatigue life and plastic strain amplitude and cyclic creep rate were determined. Fatigue hardening/softening curves, cyclic creep curves and cyclic stress-strain curves for different positive mean stresses were evaluated. Typical dislocation structures developed in both phases of the duplex steel were identified using TEM, compared with the saturated plastic strain amplitude and correlated with the decrease of the cyclic creep rate during cycling and the slope of the cyclic stress-strain curve.
Microstructural Effect and Material Homogenization of Thermal-Hydroforming Magnesium Alloy Tubes
Authors: Wang Lin , Chan Luen Chow , Kong Ting Fai
Published: January 2011

The microstrctural evolution pre and post heat treatment is critical to achieve a successful product for metal forming process. This paper aims to investigate the microstructual effect of the magnesium alloy tubes undergone various heat treatment conditions to achieve material homogenization. The heat treatment conditions under various periods of time (1, 2, 6, 12 and 30 hours) at 400 °C were employed to investigate the microstructural effect on hydroforming magnesium tubes. The greatly reduced impurity embedded in grain boundaries and more uniform grain sizes do indicate the improvement of material strength and ductility. To validate the conclusion, corresponding tensile tests at the different temperatures (20 °C and 200 °C) were carried out. The increased engineering strain in two directions (hoop and longitudinal) implies that the microstructural evolution is unquestionably useful to enhance the ductility of the magnesium tubes. Subsequently, the tubes after optimal heat treatment condition at 400 °C for 6 hours were used to further carry out the thermal hydroforming process for validation. The defect-free hydroformed tubes were produced under the same working condition, which is unable to be achieved for tubes without the heat-treatment process.
Influence of Heat-Treatment on Mechanical Properties and Transformation Temperatures of Nitinol
Authors: Vojtěch Dalibor , Michalcová Alena
Published: January 2011

Nearly equi-atomic Ni-Ti alloys (nitinol) show shape memory behavior, superelasticity, high strength, excellent corrosion resistance and biocompatibility, making them of interest for various biomedical applications. In processing, they experience various heat treating steps. The present work illustrates influence of a short-time heat treatments (several minutes) at moderate temperatures (around 500°C) on transformation temperature Af and on mechanical properties.
Mechanical Evolution of Lime Mortars during the Carbonation Process
Authors: Arizzi Anna , Martínez Martínez Javier , Cultrone Giuseppe , Benavente David
Published: January 2011

Lime mortar is one of the most ancient and durable building materials. It is characterized by a slow carbonation during which Ca(OH)2 reacts with CO2 present in air and forms calcite, giving rise to a stronger and more compact material. This process takes place from the surface to the interior of the material and it is strongly affected by the reaction conditions. The aim of this study is to quantify the increase in strength and elasticity of different lime mortars according to their carbonation degree. For that, six types of mortars were elaborated, with different lime/aggregate proportions and aggregate mineralogy and grading. Mineralogical and textural studies were carried out to follow the carbonation process. Each mortar was tested in a uniaxial compression press after 15, 28, 60 days from the elaboration. In order to differentiate the mechanical behaviour of the external and internal parts of the mortars, two micro-samples (10×10×10 mm) were obtained from the first 10 mm and from the core of each prism. Results show that an increase in strength and especially in the elastic modulus is associated to the carbonation process, but it is different depending on the composition and compactness of the mortars.
Mechanical Characterisation of Ancient Egyptian Mortars
Authors: Sanchez Moral S. , Martínez Martínez Javier , Benavente David , Cuezva S. , Fernandez Cortes A.
Published: January 2011

Several samples of ancient mortars were studied in the context of the archaeological excavations at Djehuty (Luxor, Egypt). The studied mortars had two different applications: to render external walls and as structural elements (adobe walls, contact between stone blocks, etc). An understanding of the mechanical stability of these materials is necessary in order to guarantee correct preservation of the remains. However, their mechanical characterisation using standard tests would require large samples (over 50 mm in cubic/cylinder form), which archaeological excavations are unlikely to be able to provide. The aim of this research was to analyse the mechanical behaviour of different gypsum mortars by means of the uniaxial micro-compression test and relate this to their microstructure. The microstructure is described in terms of the mineralogical composition (XRD), texture (SEM) and pore structure (MIP). Results showed that the studied gypsum mortars presented a very low strength and elastic modulus (0.25-1.60 MPa and 97.56-260.97 MPa, respectively). These mechanical characteristics are closely related to the mortar microstructure, since they presented a highly porous texture (57.93-68.35%), a polymodal pore size distribution in the 0.1-10 m range, and low contact between crystals (very open texture). Micro-compression characterisation of ancient mortars and building rocks was compared to meso-compression results found in the literature and confirmed the effectiveness of the micro-compression test as a low-invasive technique for characterising materials from architectural heritage.
Wear Behavior of ZrO2-CNF and Si3N4-CNT Nanocomposites
Authors: Hvizdoš Pavol , Duszová Annamária , Puchý Viktor , Tapasztó Orsolya , Kun Peter , Dusza Ján , Balázsi Csaba
Published: January 2011

Tribological behavior of ZrO2 and Si3N4 based nanocomposites with addition of carbon nanofibres and nanotubes has been studied by the pin-on-disc technique. Friction coefficients were measured and recorded, wear rates were calculated in terms of material volume loss per load and sliding distance. The wear damage was studied using optical and electron microscopy and its mechanisms were identified. In monolithic materials the dominant wear mechanism was abrasion, in composites with CNF and with higher volume fraction of CNTs (5 and 10%) fiber pull-out and lubricating by the carbon phases occurred.
Damage Progression and Residual Strength Evaluation in Sandwich Panels Loaded at the Center
Authors: Oskouei Amir Refahi , Hajikhani Milad , Ahmadi Najaf Abadi Mehdi , Sharifi Amir , Heidari Mohammad
Published: January 2011

This paper addresses damage evaluation of loaded sandwich panels by using acoustic emission (AE) as a non-destructive method. The specimens were loaded monotonically out-of-plane in control of displacement and the tests were stopped at three different damage levels. Each loading level activates different failure mechanism that can influence on residual strength of material. After each quasi-static test, the damaged plate was cut by a diamond saw to obtain tensile specimens. After cutting, compression test carried out by using acoustic emission to monitor the process. Depend on loading level the damage value was variant as it caused different residual strength that was related to acoustic emission signals activities. There is a relation between AE signal energy and mechanical energy that can follow to evaluate the residual strength of panels in different loading level in sandwich panels. Results show that the using AE method having mechanical results can be effective in residual strength and progressive damage evolution.
Fatigue Properties and Design Criteria of a Gamma Titanium Aluminide Alloy
Authors: Beretta Stefano , Filippini Mauro , Patriarca Luca , Pasquero Giuseppe , Sabbadini Silvia
Published: January 2011

The fatigue properties of a Ti-48Al-2Cr-2Nb alloy obtained by electron beam melting (EBM) with a patented process has been examined by conducting high cycle fatigue tests performed at different loading ratios both at room temperature and at high temperatures, comparable to those experienced by the components during service. Some tests have been conducted in the superlong life regime well exceeding 10 million cycles, highlighting individual fatigue characteristics of the studied TiAl alloy.
Plasticity Induced Crack Closure under Plane Strain Conditions
Authors: Antunes Fernando , Branco R. , Rodrigues Dulce Maria Esteves
Published: January 2011

Plasticity Induced Crack Closure (PICC) is a main phenomenon affecting fatigue crack growth and must be included in the design of components. The objective of the present paper is to study the level of PICC under plane strain conditions. The numerical parameters were identified and optimized. The effects of load level and material model were studied.
Low Cycle Fatigue Behaviour of ODS Steels for Nuclear Application
Authors: Kuběna Ivo , Kruml Tomáš , Fournier Benjamin , Polák Jaroslav
Published: January 2011

This study deals with the low cycle fatigue (LCF) behaviour of two steels strengthened by oxide dispersion. The ODS Eurofer steel shows cyclic softening, slower than in the case of the same steel without oxide particles. The 14Cr ODS ferritic steel is cyclically stable, even a slight cyclic hardening is observed at 650 °C. The reasons for this different behaviour lie probably in the less resistant matrix with a lot of weak subgrain boundaries in ODS Eurofer, because no clear difference in the oxide particles distribution was found.
Geometrical Shielding Produced by Intergranular Crack-Tip Branching in Fe–V–P Alloy
Authors: Horníková Jana , Šandera Pavel , Pantělejev Libor , Pokluda Jaroslav
Published: January 2011

The geometrical shielding produced by intergranular crack-tip branching in the fracture toughness tests of the Fe–V–P alloy is quantitatively assessed particularly with respect to the contribution of crack splitting. This process was evaluated by an identification of secondary intergranular cracks visualized on metalographical samples perpendicular to the fracture surface. The analysis of mixed trans/intergranular fracture revealed no special influence of triple-point branching (splitting) on the total crack tip shielding in cases of such highly spatially tortuous crack fronts. Thus, the previously reported results taking only the effect of crack tip kinking and meandering into account were proved to be correct.