bluuebunny/crossref_metadata_2025 huggingface dataset:
Micro- and Macro-Scale Thermomechanical Modelling of Bulk Deformation in Early-Age Cement-Based Materials
Authors: Vala Jiří , Šťastník Stanislav , Kozák Vladislav
Published: January 2011

Final user properties of concrete and other silicate composite structures are conditioned by their early-age history. Bulk deformation in early-age cement-based material system, not subjected to external forces, but generating significant stresses and temperature and humidity redistributions, is associated with the internal volume reduction of cement/water mixture during the hydration process. The proposed experimentally supported computational model starts at the micro-scale balance of mass, momentum and energy to and comes to the macroscopic mixture analysis with (at most) 20 primary variable fields, taking into account full coupling between mechanic strains and stresses, thermal and moisture transfer and chemical phenomena, including phase changes. The evolution of all variables is driven by kinetics of cement hydration, characterized by hydration degree as a function of chemical affinity.
Numerical Modeling of Macroscopic Behavior of Particulate Composite with Crosslinked Polymer Matrix
Authors: Náhlík Luboš , Máša Bohuslav , Hutař Pavel
Published: January 2011

Particulate composites with crosslinked polymer matrix and solid fillers are one of important classes of materials such as construction materials, high-performance engineering materials, sealants, protective organic coatings, dental materials, or solid explosives. The main focus of a present paper is an estimation of the macroscopic Young’s modulus and stress-strain behavior of a particulate composite with polymer matrix. The particulate composite with a crosslinked polymer matrix in a rubbery state filled by an alumina-based mineral filler is investigated by means of the finite element method. A hyperelastic material behavior of the matrix was modeled by the Mooney-Rivlin material model. Numerical models on the base of unit cell were developed. The numerical results obtained were compared with experimental stress-strain curve and value of initial Young’s modulus. The paper can contribute to a better understanding of the behavior and failure of particulate composites with a crosslinked polymer matrix.
The Simulation and Modelling of the Crack Path of Biomaterials
Authors: Stach Sebastian
Published: January 2011

Analysis of issues related to the cracking process of materials requires a quantitative description of the problem which frequently, due to its complexity, is difficult or impossible to solve. In a number of cases, the deficiencies of a quantitative description made using classical methods are compensated for by such unconventional tools as percolation, which requires creating an appropriate model. The aim of the study was to use a three-dimensional minimal spanning tree (3DMST) to create a model of the crack path, based on an example of a metallic biomaterial. For this purpose, a stereometric file, obtained as a result of measuring its fracture surface, was applied.
First-Principles Modeling of Tungsten-Based Alloys for Fusion Power Plant Applications
Authors: Nguyen Manh Duc , Muzyk M. , Kurzydlowski Krzysztof J. , Baluc Nadine L. , Rieth Michael , Dudarev Sergei L.
Published: January 2011

We describe a comprehensive ab initio investigation of phase stability and mechanical properties of W-Ta and W-V alloys, which are candidate materials for fusion power plant applications. The ab initio density functional calculations compare enthalpies of mixing for alternative ordered atomic structures of the alloys, corresponding to the same chemical composition. Combining the ab initio data with large-scale lattice Monte-Carlo simulations, we predict several low-energy intermetallic compounds that are expected to dominate alloy microstructures, and hence the low-temperature phase diagrams, for both alloys. Using the predicted ground-state atomic alloy configurations, we investigate the short-range order, point defect (vacancy and self-interstitial atoms) energies, and thermodynamic and mechanical properties of W alloys as functions of their chemical composition. In particular, we evaluate the anisotropic Young modulus for W-Ta and W-V alloys from ab initio elastic constant calculations, with the objective of comparing the predicted values with experimental micro-cantilever measurements. Also, using the calculated Poisson ratios for binary W alloys, which combine tungsten with more than 40 different alloying elements, we investigate if alloying improves the ductility of tungsten-based materials.
Fatigue Fracture Model for Weak Fiber/Matrix Interface Composite within Three Point Bending Test
Authors: Khvostunkov Kirill A. , Shpenev Alexey G.
Published: January 2011

The model of fiber/matrix interface degradation due to abrasive wear of fiber/matrix contact surfaces is presented. This model explains weak interface composites low cycle fatigue effect and cycle to cycle creep rate increase. The authors consider the results of experiments series carried out at the Institute of Solid State Physics located at Chernogolovka town. During this experiments series some weak interface nickel-oxide composite samples were subjected to a cyclic load in the course of a three point bending test and the samples central point set displacement rate was registered. Then there was created a fiber-matrix interface cyclic degradation model. The authors compared their theoretical assumptions to experimental data (for reference kindly see the below calculations) and evaluated low cycle fatigue influence on composite fracture.
Short Term Creep Small Punch Testing of P91 and P92 Steels, Observations and Correlations with the Numerical Results
Authors: Dymáček Petr
Published: January 2011

The contribution is presenting experimental results of conventional creep and small punch testing performed on miniaturized discs prepared from P91 and P92 steels. Some of the test cases were also numerically modeled by Finite Element Method (FEM) with help of Norton's constitutive model and the results were compared with the experiment. Presented work complements the existing empirical investigations on small punch and conventional creep tests relations.
The [100] Compressive Strength of Perfect Cubic Crystals under Superimposed Biaxial Stresses
Authors: Řehák Petr , Černý Miroslav , Pokluda Jaroslav
Published: January 2011

Stress-strain responses of five fcc crystals subjected to triaxial loading are investigated by means of pseudopotential density functional method. Particularly, the influence of superimposed transverse biaxial stresses on the maximum uniaxial stresses is evaluated for both tensile and compressive regions. The obtained results revealed that the compressive strengths (maximum compressive stresses) of all studied metals are more sensitive to the superimposed stresses than their tensile strengths. The compressive strengths were found to be increasing linear functions of the compressive transverse stresses.
Control of Domain States in Individual PbTiO3 Nanoparticles by Prescribed Strains
Authors: Hong L. , Soh A.K.
Published: January 2011

A three dimensional phase field model has been devised to account for the manipulation of domain states in individual ferroelectric (PbTiO3) nanoparticles. Vortex structures and dipole flux domain patterns were obtained by applying tensile and compressive strains, respectively. The direction of the two domain configurations was found to correlate with the plane on which the strains were applied, mainly due to dipole-strain coupling and depression of depolarizing field.
Experimental Evaluation of the Cyclic Slip Irreversibility Factor
Authors: Weidner Anja , Sauzay Maxime , Skrotzki Werner
Published: January 2011

Cyclic slip irreversibility is one of the most important features of fatigue processes in ductile metals because it induces surface relief evolutions during cycling which are mainly responsible for crack initiation. The reversible and irreversible parts of the slip within persistent slip bands (PSBs) in polycrystalline nickel are measured directly after half-cycle deformation and one full cycle on specimen surfaces once more well-polished after 60% of fatigue life using atomic force microscopy (AFM) and different techniques of scanning electron microscopy as electron channelling contrast imaging and electron backscattered diffraction. Using AFM measures on the same slip steps after half-cycle and full cycle, the cyclic slip irreversibility factor is directly evaluated and discussed with respect to the literature.
Advanced Local Quality Assessment of Monocrystalline Silicon Solar Cell Efficiency
Authors: Škarvada Pavel , Grmela Lubomír , Tománek Pavel
Published: January 2011

Solar cells, or photovoltaic cells, are used to convert sunlight into electrical power. The defects or imperfections in silicon solar cells lower the light-current conversion and consequently also an efficiency of the device. These defects in the semiconductor structure are normally detected by electric measurements. The thermal dependency of breakdown voltage is positive and the defects can be revealed by surface inhomogenity. To ensure a higher quality of the solar cells, advanced local quality assessment is provided and experimental results of solar cell defect measurement in microscale region are presented. Using Near-field optical beam induced current and voltage method, both current and voltage in defect area were detected and individual defects were localized with higher spatial resolution. This measurement also verifies that in reverse biased electroluminescence spots the quantum efficiency is lower and so these spots affect overall quality of the cell.
Influence of Case Hardening on Fatigue Resistance of Models of Hollow Shafts with Production Surface Defects
Authors: Čipera M. , Černý Ivo , Pospíchal V. , Mikulová Dagmar , Fürbacher Ivan
Published: January 2011

This work analyses an influence of case hardening on fatigue resistance of models of hollow shafts which have a variable diameter ranging from 40 mm to 67 mm, wall thickness of 7 mm and production surface defects on an inner surface layer of the hollow shafts. Case hardened (on both sides) and non case hardened shafts were tested. Both types of shafts were made out of 16MnCrS5 (DIN) steel by cold reduction rolling and were subjected to a flat bending. Tests indicated that the fatigue resistance of the case hardened shafts was significantly higher. The main reason for the lower resistance of the non case hardened shafts was initiation of magistral cracks from the defects on inner surfaces. In case of the case hardened shafts the magistral cracks initiated from the notch on outer surfaces where macroscopic stress was maximal. Different mechanisms of the cracking are discussed from the point of view of compressive residual stresses in the case hardened layer.
Role of Impurities and PSBs on Microcracking of Polycrystalline Copper at Very High Numbers of Cycles
Authors: Stanzl-Tschegg Stefanie , Eichinger Karl , Weidner Anja , Tschegg Elmar , Bernardi Johannes , Schönbauer Bernd
Published: January 2011

Fatigue cracks in polycrystalline copper may originate from PSBs or grain boundaries. They usually form at the specimen surfaces, but also internal small stage I (shear) cracks have been observed with the ECC/SEM technique. They are formed together with a strongly elongated dislocation cell structure, which is reflecting in many cases localized deformation in “slip lamellae” with eventual ladder-like features, being typical of PSBs. Both, PSBs and small non-propagating cracks are initiated at cyclic stress/plastic strain amplitudes below the conventionally reported PSB threshold values, if the number of cycles exceeds a minimum, e.g. approximately 5x108 in the VHCF range. The internal small cracks are formed not only in polycrystalline electrolytic copper of 99.98% purity but also in high purity (99.999%) material.
Fracture Process Characterization by Acoustic Emission Signal Components
Authors: Antonaci Paola , Masera Davide
Published: January 2011

The aim of this work is to develop a procedure to follow the evolution of micro and macro-crack in unreinforced and reinforced masonry walls by means of Acoustic Emission signal analysis. In particular the main goal of this experimental work want to be the definition of a characteristic signal parameter able to represents the evolution of the fracture dimension in the masonry walls during the fracture process. To this end laboratory tests were carried out at the Non-Destructive Testing Laboratory of the Politecnico di Torino.
Statistical Properties of Deformed Single-Crystal Surface under Real-Time Video Monitoring and Processing in the Desktop Grid Distributed Computing Environment
Authors: Gatsenko Oleksandr , Baskova Oleksandra , Lodygensky Oleg , Fedak Gilles , Gordienko Yuri
Published: January 2011

Many crucial processes of damage initiation and propagation take place dynamically in the wide observable time domain from 10-3 seconds to 103 seconds and on the many scales from 10 6 m (solitary defects places) to 10-2 m (correlated linked network of defects). The new multiscale image and video processing method is used to observe and characterize the dynamic behavior of metals under mechanical deformation, record its surface evolution, and process the observed surface statistical parameters. The calculations include many parameters of physical process and video processing parameters (size distribution, anisotropy, localization, scaling parameters, etc.). The typical multiscale analysis of the dynamic video sequence (with 103-106 frames) of deformed metal surface (depicting it time evolution) takes approximately several weeks on a single modern processor. That is why the more powerful computational resources are in extreme need. The free high-performance grid-enabled version of the video processing software is designed and tested in our Desktop Grid (DG) distributed computing infrastructure (DCI).
PN Junction Defects Detection in Solar Cells Using Noise Diagnostics
Authors: Paračka Petr , Koktavý Pavel , Macku Robert
Published: January 2011

PN junction is one of the most important parts of solar cells. Its quality affects lifetime and efficiency of solar cells. Local defects which appear in PN junctions during the manufacture process are very important from this point of view. These are caused by localized areas with high donor or acceptor doping agents, impurities, dislocations or other mechanisms which effect in lower breakdown voltage of PN junction in reverse bias. Several base methods can be used for solar cells nondestructive diagnostics. Measuring methods of low-band noise current effective value with reverse bias junction were used in this paper. This method allows detection of local defects and volume degradation in PN junctions of solar cells and it can be used for detection of microplasma noise. This noise is an impulse noise and it is caused by local avalanche breakdowns in small area of the junction. It can be recognized by two or more level random square current pulses with constant height, random appearance time and random pulse length. Information about these effects can be used in noise diagnostics of structural defects of PN junctions and then it can be used for quality and lifetime estimation of samples with these parameters.
Influence of Severe Plastic Deformation on Microstructure and Thermal Properties of Cu
Authors: Rodak Kinga , Moskal Grzegorz
Published: January 2011

The evaluation of microstructure and the thermal diffusivity of copper subjected to severe plastic deformation using multi-axial compression was investigated. The investigations were performed on copper (M1E grade) processed to effective strain at range f =1-14.9. The multi- axial compression resulted in an refining structure. The evolution of dislocation structure, misorientation distribution, crystalline size were observed by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipment with electron back scattered diffraction (EBSD) facility. The thermal diffusivity measurements were performed by using the LFA427 apparatus based on the laser-flash method. Subgrain and grain size for f =3.7 reaches about 250 nm and 550 nm respectively. The local recrystallization occur in analyzed microarea especially at f =7.5 and delay the reduction of sub(grain) size. In consequence no more large changes in structure occur during further processing up to the largest strain. The microstructural phenomena have an influence on the thermal parameters. The value of this parameters insignificantly decreased with increasing of accumulated strain.
Shrinkage Pores and Fatigue Behavior of Cast Al-Si Alloys
Authors: Konečná Radomila , Fintová S. , Nicoletto Gianni
Published: January 2011

The fatigue strength of cast Al-Si alloys is strongly sensitive to the presence of casting defects. Extensive rotating bending fatigue testing of cast AlSi7Mg alloy at room temperature and 50 Hz is reported showing that shrinkage pores are the critical casting defect. The porosity of selected fatigue specimens extracted from castings is characterized with metallography using different pore sizing criteria. Data are fitted to EVS distributions and used for critical size prediction. Fatigue fracture surfaces are inspected in the SEM and the critical pores originating the fatigue cracks identified and measured according to criteria used in the metallographic inspection.
Mechanical Behaviour and Microstructure Evolution of Eurofer97 during Low-Cycle Fatigue at Room Temperature and 550°C
Authors: Giordana M.F. , Alvarez-Armas I. , Sauzay Maxime , Armas A.F.
Published: January 2011

The cyclic behaviour of the steel EUROFER 97 during isothermal plastic strain-controlled tests was investigated at room temperature and at 550°C. Under these test conditions, the steel shows, after the first few cycles, a cyclic softening following a power-law function that continues up to failure. The rate of softening increases with temperature, being very pronounced at temperatures above 500°C. The evolution of the flow stress during cycling was studied by analyzing the so-called “back” and “friction” stresses obtained from the hysteresis loops measured along the entire test. From the analysis of the hysteresis loops and corroborated by electron microscopy observations, it can be concluded that the strong cyclic softening observed on these samples with a "tempered martensite" structure is produced by the softening exhibited by both stresses. However, the importance of each of these stresses on the softening depends on the applied strain amplitude and temperature. It was observed that, at low temperatures and applied strains, the friction stress shows the strongest influence on the cyclic softening. On the contrary, at higher temperatures and applied strains the back stress reveals the most important changes occurring in the interior of the material.
Cyclic Deformation Behavior of Austenitic Steels in the Temperature Range -60°C ≤T ≤550°C
Authors: Smaga M. , Hahnenberger F. , Sorich A. , Eifler Dietmar
Published: January 2011

In this investigation specimens of the austenitic steels AISI 304, AISI 321 and AISI 348 were investigated in fatigue tests in the temperature range -60°C ≤ T ≤ 550°C. A detailed microstructure-based characterization of the cyclic deformation behavior of austenitic steels was performed by means of stress-strain hysteresis, electrical resistance and magnetic measurements. Up to ambient temperature the occurring deformation induced martensite formation was measured in-situ with a ferritescope during cyclic loading. The temperature range for dynamic strain aging was reliably identified by means of a temperature increase fatigue test with one single specimen.
Microstructure and Hemming Properties of AA6016 Aluminum Alloy Sheets
Authors: Davidkov Aleksandar , Petrov Roumen H. , Bliznuk Vitaliy , Ratchev Petar , De Smet Peter , Schepers Bruno , Kestens Leo A.I.
Published: January 2011

The use of Al-Mg-Si-(Cu) heat treatable 6xxx alloys is steadily increasing in the automotive industry. The possibility of weight reduction of the cars in combination with the good formability and high in-service dent resistance of these alloys, make them a favorable material for body panel applications. One of the most common, environment-friendly and easy to perform processes used to join aluminum sheets, is the hemming joining operation. This operation heavily relies on the bendability of the sheets, because they are bent to an angle of 180° over of a radius equal to their thickness. Tearing or cracking of the outer bent surface are often very common. In this study we attempt to understand the relations between the microstructural features of the sheets and their hemming behavior. The hemming experiments are performed in laboratory conditions and the results are discussed together with the data obtained from crystallographic, microstructural and textural investigations. Relations between the hemming appearance, chemical composition, natural aging time and dispersoid’s density are found and discussed.
Long-Term Thermal Degradation of Mn-V Steel (W. Nr. 1.1133)
Authors: Svobodová Marie , Horvath Ladislav , Douda Jindřich , Shejbal Jaromír , Svobodová Eva
Published: January 2011

This paper summarizes the achieved results of microstructure analysis and mechanical testing of long-term degradation of Mn-V steel (W. Nr. 1.1133, ČSN 41 3123) frequently used in small and middle boiler pressure systems operating under creep conditions. In these systems, non-exchangeable components often limit a safety of their service operation. Therefore in view of the monitoring, non-destructive methods like replica technique, hardness testing and defectoscopy, and probabilistic approach to residual life assessment seems to be the only way how to quantitatively determine a residual life of the boiler pressure system. Achieved results of as-exposed and as-secondary aged Mn-V steel confirmed that besides NDT controlling of sheet welds due to possible cracks, the replica technique (on available component surface) accompanied by hardness measurement on each segment of weldment should be sufficient for residual life assessment of thick-walled components of boiler pressure system operating under creep conditions. Additionally as a very rough estimate, a value of limit hardness of steel for safety operation is estimated at about 150 HV.
Influence of Twins on Short Fatigue Cracks in Type 316L Stainless Steel
Authors: Al Shahrani S. , Marrow T. James
Published: January 2011

The nature of arrested cracks in run-out fatigue tests of a type 316L austenitic stainless steel with electropolished surfaces has been investigated. The fatigue limit was determined in rotating-bending by means of the staircase method to be 302 ± 5 MPa. Arrested crack nuclei were shown to arrest at coherent deformation twins, developed by fatigue.
Mechanisms of the 2024-T351 Al-Alloy Fatigue Cracking in Bifurcation Area after Laser Shocks Hardening Procedure
Authors: Shanyavskiy Andrey
Published: January 2011

The fatigued specimens have attested the surface hardening of the 2024-T351 aluminum alloy based on the laser shock peening (LSP). Tests were carried out with simple regular specimens bending. It was shown that each crack started from or near to the specimen-hardened surface of the thickness 4mm. The hardened surface layer influenced material fatigue cracking on the Stage I of crack growth as well as on the Stage II where fatigue striations formation mechanism takes place. Parameters of S-N curves were analyzed for tested specimens and bimodal distribution of the fatigue durability (BDFD) was revealed. The left branch of the BDFD attested fatigue behavior of not hardened material. The right branch of S-N curves attested the material behavior after surface-hardening procedure by the LSP technology. The paper discussed mechanisms of material fracture in the bifurcation area for the stresses interval ranged from 270-295 MPa where transition from the left to the right branch of the discovered BDFD takes place. The subsurface crack origination occurs for the right branch of BDFD because of twisting of material volume under combination of material compression in a local area of crack origination with gases diffusion in the volume of crack origin.
An Enhanced Local Approach Model for the Assessment of Brittle Fracture Based on Micromechanical Investigations
Authors: Hardenacke Volker , Hohe Jörg , Friedmann Valérie , Siegele Dieter
Published: January 2011

The objective of the present study is the development of a micromechanically based probabilistic model for the assessment of the cleavage fracture probability of ferritic steels. Brittle fracture of ferritic steels is a probabilistic process, triggered by the failure of randomly distributed brittle particles. These particles fracture due to plastic deformation of the surrounding matrix, resulting in the nucleation of micro-cracks. Once nucleated, the local stress state controls the possible instability of the defects. In this context, the local stress-triaxiality is assumed to govern the blunting of freshly nucleated micro-defects. The local approach models available in literature account for the above-mentioned correlations only in a simplified manner. Based on Representative Volume Elements (RVE) of the microstructure, accounting for the grain-structure as well as for the brittle particles, the cleavage initiation process was modelled in order to investigate the relevant parameters and their interactions. The RVE’s were loaded according to the local mechanical field quantities determined numerically for a variety of specimen types at the cleavage-origins. Thus, the behaviour of the particles against the micromechanical conditions could be specified, resulting in a better understanding of the processes at cleavage fracture initiation. Based on the results, an enhanced probabilistic cleavage model is proposed.
Probabilistic Simulation for Combined Cyclic Fatigue in Composites
Authors: Chamis Christos C.
Published: January 2011

The combined cyclic fatigue is computationally simulated by a judicious combination of three independent computational modules: composite mechanics, a multi-factor equation module (MFIM) and probabilistic algorithm (FPI). The inputs to each module are constituent material properties, processing variables, loading and environmental conditions and probabilistic variables. The composite fatigue is simulated by considering an inplane loaded-component in a structure which is subjected to fatigue because of cyclic loading. Typical results show that the low probability fatigue cycle is about 50 percent of the corresponding static value.
In-Situ Observation and Modelling of Intergranular Cracking in Polycrystalline Alumina
Authors: Marrow T. James , Gonzalez David , Aswad Mohsin , Da Fonseca Joao Quinta , Withers Philip J.
Published: January 2011

A 3D model for intergranular thermal stresses in coarse polycrystalline alumina has been derived using Diffraction Contrast Tomography. Larger tensile thermal strains develop when the (0001) pole of adjacent grains lies closer to the grain boundary normal. This agrees with observations of cracked boundaries, obtained through digital image correlation of in-situ observations in fine alumina.
Stabilizing Effect of (100) Compound Twinning in NiTi Martensite
Authors: Šesták P. , Černý Miroslav , Pokluda Jaroslav
Published: January 2011

According to experimental findings, the martensite structure of NiTi is monoclinic (B19'). However, previous first principles calculations have shown that, after a full optimization of the lattice, the ideal martensite structure relaxed into orthorhombic B33 structure. Present calculations reveal that a presence of twins in a real martensite can stabilize the B19' structure.
Peierls Stresses Estimated from CRSS Vs. Temperature Curve and their Relation to the Crystal Structure
Authors: Kamimura Yasushi , Edagawa Keiichi , Takeuchi Shin
Published: January 2011

Peierls stresses P of a variety of pure crystals, bcc metals, NaCl type crystals, elemental and compound tetrahedrally coordinated crystals, intermetallic compounds and ceramic crystals, have been estimated from the critical resolved shear stress (c) vs. temperature curves. For high P crystals where CRSS data are available only at high temperatures, P has been estimated from the critical temperature T0 at which steep temperature dependence of c vanishes: T0 is related to the kink-pair formation energy which is a function of P, material parameters and dislocation character controlling the deformation. The estimated p/G values are semi-log plotted against h/b value, where G is the shear modulus, h the slip plane spacing and b the Burgers vector. Two facts should be noted. First, P/G values for a group of crystals with the same crystal structure are within a range of a factor of 10. Second, most of the data points lie in between the classical Peierls-Nabarro relation and the Huntington’s modified relation. These facts indicates that Peierls stress is primarily determined by the crystal structure.
Concrete-Polymer Composites – The Past, Present and Future
Authors: Ohama Yoshihiko
Published: January 2011

The present paper deals with the principles of process technology for concrete-polymer composites, the research and development history of the concrete-polymer composites, the recent trends in the research and development of the concrete-polymer composites and the present status of major standardization work for the concrete-polymer composites, on the basis of comprehensive literature survey. The future trends in the research and development of the concrete-polymer composites are predicted, and sustainable concrete-polymer composites are proposed for the 21st century.
Chemical Shrinkage of Pastes Made with Shrinkage Reducing Admixtures
Authors: Ribeiro António Bettencourt , Medina Vasco , Gomes Augusto , Gonçalves Arlindo
Published: January 2011

Shrinkage Reducing Admixtures (SRA) are being used more often in concrete structures in order to better control shrinkage cracks. High-performance concrete, nowadays with large application, has more proneness to crack at very early age due to the lower W/C. In this type of concrete, autogenous shrinkage is usually more important than drying shrinkage. Autogenous shrinkage is due to the volume decrease inherent to binder hydration reactions. The rate of these reactions is influenced not only by the type of binder but also by the presence of chemical admixtures. It is recognized that SRA delay the hydration, being a secondary effect of this type of admixtures. In this work changes on the degree of hydration of cement pastes with SRA and different binders are presented, using the chemical shrinkage test.
Development of an Ultra-Lightweight Thin Film Polymer Modified Concrete Material
Authors: Kruger Deon , van der Westhuizen Michael
Published: January 2011

Certain construction situations call for the use of ultra-lightweight concrete materials. The properties of such materials allow for the utilisation of concrete in weight critical applications, for example precast elements, roofing panels, flooring and cladding of structures. The weight saving benefits of lightweight concrete are evident, yet a trade-off in the strength and durability characteristics of the concrete are made. This paper sets out to develop an ultra-lightweight thin filmed polymer modified concrete material for such applications. This material may incorporate specialised aggregates and admixtures to meet performance requirements but the effects of these on the performance of the lightweight concrete are to be carefully evaluated. This paper presents some of the results obtained by means of laboratory testing as well in-situ testing. As part of the in-situ testing, the paper also reports on the practical evaluation of the ultra-lightweight material characteristics performed through the construction of a light weight concrete racing canoe. This allowed for the evaluation of the material performance characteristics and the establishment of acceptable work and application methods when constructing with this material.
Seven Well Known Fundamental Flaws against Innovations in Construction Chemistry
Authors: Seidler Peter
Published: January 2011

Construction chemistry is underdeveloped compared to other chemical branches. Innovation is realized by new products, improved pro¬cesses or / and more efficient organization. Innovation becomes evident when a noticeable progress is achieved by implementing changes. There are seven fundamental hindrances or flaws possible which are briefly considered. The state-of-the-art must be known. Innovation is measured in comparison to this state-of-the-art. If this level is not yet attained, progress is easily realized by introducing the actual knowledge. The realization is measured according to qualitative or preferably quantitative bench¬marks. Unfortunately, this is not currently done in the field of construction chemistry. Before benchmarking starts, communication based on truth and trust must be effective. The available scientific me¬tho¬dology must be known. Benchmarking will possibly show deficiencies in education and training. This will stress the need for adequate trans¬parency to improve efficiency. Hope¬ful¬ly, a self-regulating process improving pro-ducts and processes will be created in this way.
Polymer-Modified Mortars for Corrosion Protection at Offshore Wind Energy Converters
Authors: Lohaus Ludger , Weicken Hannes
Published: January 2011

The importance of renewable energy for our world’s energy supply is steadily increasing. Starting last year, offshore wind parks are being developed along the German coastline following the success achieved in the onshore wind energy. The first German offshore wind energy park is be erected on the Alpha Ventus test field near the isle of Borkum, where the depth of the sea amounts to 30 meters. Due to the hazardous conditions associated with the sea water, many challenges regarding corrosion control have to be met. With the combined effects of sea water, varying moisture conditions and impact damages caused by ice and flotsam, the conventional methods of corrosion protection with mean thicknesses of 1000 μm will not suffice to protect the steel for an operating life expectancy of 25 years. As a result, the thickness of the various construction elements need to be increased beforehand leading to an excessive usage of steel. For the new corrosion protection system presented in this paper, a layer made of high performance mortar with a thickness of about ten millimeters will be sufficient to protect the steel. To unfold its protecting effect, the mortar needs to comply with stringent requirements such as exhibiting high resistance to chloride ingress, frost and abrasion.
Optimization of Polymer-Cement Coating Composition Using Material Model
Authors: Czarnecki Lech , Sokołowska Joanna Julia
Published: January 2011

The paper focuses on optimizing the elastic polymer-cement protection coating composition using material model. The material model consists of mathematical relations between composition and technical features demanded for protection, which are: flexibility, waterproofness and vapor permeability. The optimization that enabled obtaining the desirable values of features was proceeded by using statistical experimental design. Taking data from tests and choosing material variables, a material model based on quadratic functions was determined and in consequence three top rank compositions – each for a given feature – have been formulated. Evaluation of compositions was done using the desirability function approach. The individual desirability functions for the particular feature and the combined overall desirability function were treated as additional properties of the coating. Also, after defining the relation between desirability and composition, the overall desirability was enclosed in the material model as its generalization. High values of overall desirability confirmed the usefulness of compositions. The investigation proved that material models based on statistical methods are efficient tools for designing polymer-cement protective coatings.
Microstructural Analysis of Paste and Interfacial Transition Zone in Cement Mortars Modified with Water-Soluble Polymers
Authors: Knapen Elke , Van Gemert Dionys
Published: January 2011

The presence of water-soluble polymers affects the microstructure of polymermodified cement mortar. Such effects are studied by means of SEM investigation. Polyvinyl alcohol-acetate (PVAA), Methylcellulose (MC) and Hydroxyethylcellulose (HEC) are applied in a 1 % polymer-cement ratio. The polymers provide an improved dispersion of the cement particles in the mixing water. The tendency of certain water-soluble polymers to retard the flocculation of the cement particles minimizes the formation of a water-rich layer around the aggregate surfaces. They also provide a more uniform distribution of unhydrated cement particles in the matrix, without significant depletion near aggregate surfaces. Both effects enable to reduce the interfacial transition zone (ITZ). The polymers also provide a more cohesive microstructure, with a reduced amount of microcracks.
The Effect of Latex and Chitosan Biopolymer on Concrete Properties and Performance
Authors: Bezerra Ulisses Targino , Ferreira Rui Miguel , Castro-Gomes João Paulo
Published: January 2011

this paper presents the results of a study in which the combination of two polymeric additives in concrete with the intention of improving its mechanical and durability performance is analysed. The additives are a synthetic latex and a biopolymer – chitosan. An evaluation of the mechanical properties as well as the phases formed based on scanning electron microscopy (SEM) and X-ray diffraction (XRD) was performed. The concretes were prepared with each of the polymers separately, and the results were ordinary. However, when combined, the results show an interesting interaction improving the mechanical strengths of the concrete. Several concrete samples were prepared with 0 – 4 % of each polymer with 1 % increments. The mechanical properties were shown to be sensitive to the incorporation of polymers. The desired effect of the interaction between the biopolymer and the latex was observed, because the strengths increased when both additives were present, namely for the combination of 2 % of each polymer. SEM images revealed a heterogeneous distribution in the polymer cementitious matrix, mainly with regards to latex. The presence of well defined polymer fibers on a fracture surface of composites prepared with biopolymer (4 %) was observed, indicating that the fibre pullout and not fracture was the cause of failure, resulting from the poor adherence of the fibers in matrix. Composites prepared with both polymers revealed abundant formation of C-S-H and the absence of ettringite, explaining the improvement of mechanical properties. The presence of reticulated structures of C-S-H dispersed in the microstructure and involving the calcium hydroxide corroborates the results of mechanical properties, mainly for the percentages of 3 % of biopolymer and 1 % of latex.
Effect of Types and Contents of Polymer Resin on Spalling Prevention of High-Strength Concrete Subjected to Fire
Authors: Han Cheon Goo , Han Min Cheol , Pei Chan Chun , Yang Seong Hwan
Published: January 2011

In this study, the fundamental and spalling properties of high-strength concrete were examined, especially when various types and varying content of polymer resin were added. Two types of polymers were used in this study: ethylene vinyl acetate copolymer (EVA-P) and polyvinyl acetate copolymer (PVA-P) as powders and polyvinyl acetate copolymer (PVA-F) and polypropylene copolymer (PP-F) as fibers. Test results showed that the addition of EVA-P and PVA-F to concrete slightly decreased flowability, whereas the addition of PP-F and PVA-P enhanced the viscosity, leading to a remarkable reduction in flowability. The air content of concrete containing EVA-P, PVA-F, and PP-F showed no significant variation. The addition of PVA-P to concrete also caused a slight reduction in compressive strength, whereas the other additives had insignificant effects. After a fire test, the control concrete and concretes with EVA-P, PVA-P, and PVA-F exhibited severe explosive spalling regardless of the dosages. This was because the polymer does not provide sufficient void networks, which is important for vapor evacuation, which enables the release of steam pressure inside the concrete. However, when more than 0.10% of PP-F was added, spalling was effectively prevented. For the residual compressive strength, higher polymer dosage in the concrete produced better results regardless of the polymer type. The powder-type polymers did not contribute to preventing spalling in concrete subjected to fire. This is due to their geometric shape and high melting point. It is concluded that a high aspect ratio and low melting point is critical during polymer selection to prevent spalling in high-strength concrete.
Influence of Environmental Temperatures on the Performance of Polymeric Stabilising Agent in Fresh Cementitious Materials
Authors: Schmidt Wolfram , Brouwers Henricus Jozef Hubertus , Kuehne Hans Carsten , Meng Birgit
Published: January 2011

Stabilising admixtures are commonly used additives in repair mortars and grouts. Beyond this, such type of admixture is increasingly used in concrete and other cementitious materials. In particular when fresh mortar or concrete properties have to be adjusted reliably, stabilising agents can be beneficially used to improve workability and robustness of the mixture. The mode of operation of these admixtures varies, rather affecting either the liquid phase or the solid particles in the dispersion, both causing strong interactions with the mortar or concrete system, and significant changes in their rheological behaviour. Furthermore, these are strongly affected by the environmental temperature during the casting process. In the paper the effect of temperature on the performance of stabilising agents in cementitious systems is presented and how performance changes affect fresh and hardening mortar or concrete properties. Particular attention is placed on interactions between stabilising agents and superplasticizers. Results are discussed with special focus on self-compacting concrete.
Local Structural Analysis of Al2O3, Cr:Al2O3 and V:Al2O3 Using Powder XRD
Authors: Thirumalaisamy T.K. , Lakshmi Sri K.J , Saravanan R.
Published: January 2011

The electron density distribution and the local structure of aluminum oxide (Al2O3), chromium doped aluminum oxide (Cr:Al2O3) and vanadium doped aluminum oxide (V:Al2O3) have been studied. Powder X-ray data set of Al2O3 , Cr:Al2O3 and V:Al2O3 is analyzed in terms of cell parameters, thermal vibration parameters, 1D, 2D and 3 Dimensional electron density distributions. The bonding between the atoms using the maximum entropy method (MEM) and bond length distribution using pair distribution function (PDF) has been analyzed. The particle size of Al2O3 , Cr:Al2O3 and V:Al2O3 is also analyzed using XRD and SEM.
Studies on the Removal of Malachite Green Dyes by Adsorption onto Activated Carbons – A Comparative Study
Authors: Xavier A. , Usha D. , Gandhi Rajan J. , Malarvizhi M.
Published: January 2011

Malachite Green is an organic compound that is used as a dyestuff for the materials like silk, leather and paper. As a part of removal of malachite green dye from textile and leather industrial wastes, using activated carbon as adsorbents namely, commercial activated carbon (CAC), rose apple carbon (RAC), coconut shell carbon (CSC) and saw dust carbon (SDC). The percentage of malachite green adsorbed increases with decrease in initial concentration and particle size of adsorbent and increased with increase in contact time, temperature and dose of adsorbent. The pH is highly sensitive for dye adsorption process. The adsorption process followed first order kinetics and the adsorption data with Freundlich and Langmuir isotherm models. The first order kinetic equations like Natarajan Khalaf, Lagergren, Bhattacharya and Venkobhachar and intra particle diffusion were found to be applicable. A comparative account of the adsorption capacity of various carbons has been made. These activated carbons are alternative to commercial AC for the removal dyes in General and MG is particular. These results are reported highly efficient and effective and low cost adsorbent for the MG. The thermodynamics parameters are also studied and it obeys spontaneous process. The results are confirmed by before and after adsorption process with the help of the following instrumental techniques viz., FT-IR, UV-Visible Spectrophotometer and SEM photos.
Elaboration of Titanium-Nickel Alloy with Special Properties through Mechanical Milling
Authors: Gligor Ionuţ , Cândea Viorel , Arghir George , Popa Catalin
Published: January 2011

Shape memory Titanium-Nickel alloys, also known as Nitinol, are amongst the most utilized materials with special properties in the medical field. Together with the properties of shape memory and superelasticity, these alloys have a very good biocompatibility. In this study, the equiatomic Ti-Ni alloy was obtained in the form of alloyed powder, starting from elemental high purity powders, through mechanical alloying. Specimens for testing the mechanical characteristics of the material, as well as smaller samples for biocompatibility tests were manufactured. The latter ones were prepared for implantation on live tissue, on Wistar rats and Guinea pigs. The structure of samples was studied by microscopy and X-Ray diffraction analysis. All the results have demonstrated the presence of the TiNi intermetallic compound as the quantitative dominant phase. After applying an adequate thermo-mechanical treatment, the tested samples displayed measurable shape memory effect and superelasticity. The in vivo biocompatibility tests, done according to international standards, demonstrated the material’s bio-inertness in relation with living tissue. The obtained results have shown the possibility to elaborate Ti-Ni biocompatible alloys by mechanical milling and sintering.
FeNi-TiC Composite Powders Obtained by Electrolytic Co-Deposition
Authors: Jumate Nicolaie , Vida-Simiti Ioan , Nemeş Dorel , Thalmaier György , Sechel Niculina , Moldovan Valentin
Published: January 2011

The paper presents a preliminary study on the obtaining of a composite powder by an electrolytic method. The composite powder particles are composed of iron nickel alloy that represents the matrix of the composite, and titanium carbide as the reinforcement. The matrix was obtained by electrolytic co-deposition from pure iron and nickel, in form of consumable electrodes. The titanium carbide powder is in suspension in the electrolyte. By the migration of metallic ions towards the cathode, the iron- nickel alloy is formed and, by simultaneously driving the carbide particles found in the electrolyte onto the cathode, the composite powder is obtained. The resulted composite powders were characterized by optical and electron microscopy. The influence of obtaining conditions over the morphology and structure of composite powders is emphased.
Zinc Ferrite Powder Synthesized by High Energy Reactive Ball Milling
Authors: Marinca Traian Florin , Chicinaş Ionel , Prică Virgiliu Călin , Popa Florin , Neamţu Bogdan Viorel
Published: January 2011

The nanocrystalline zinc ferrite (ZnFe2O4) powder was synthesized by high energy reactive ball milling (RM) in a planetary mill. As starting materials a mixture of commercial zinc oxide (ZnO) powder and iron oxide (Fe2O3) powder was used. The starting mixture was milled for different periods of time, up to 30 h. The milled powders were annealed for 4 h at 350 oC in order to eliminate the internal stress and to finish the solid state reaction of ferrite formation. Zinc ferrite formation was investigated by X-ray diffraction. The obtained powder has a mean crystallite size of 12 nm after 20 h of milling. Using scanning electron microscopy (SEM) the particle morphology was studied. Particles size range of the powders was also determined using a laser particle size analyser.