română NICOLAE ŢĂRANU, DRAGOŞ BANU, GABRIEL OPRIŞAN, MIHAI BUDESCU, LILIANA BEJAN
Abstract
Fibre reinforced polymer (FRP) composites have been successfully implemented to strengthening of reinforced concrete (RC) slabs improving their structural response to various loading schemes. The most utilized techniques are based on prefabricated FRP composite strips bonded to the tension side with adhesives or by bonding quasi-unidirectional fabrics made of carbon or glass fibres impregnated with polymeric resins.
An extensive research program has been carried out at The Faculty of Civil Engineering and Building Services Iaşi, by testing a number of thin reinforced concrete (RC) slabs strengthened with CFRP strips in different solutions, to characterize the structural response, identify the failure modes and evaluate the structural efficiency of this composite strengthening solution. The structural response has been evaluated through testing a number RC slabs under bending from transverse loading. The difference in structural behaviour of unstrengthened and strengthened slabs has been revealed on both loading bearing capacity and stiffness. The validity of experimental results has been checked by numerical modelling using ABAQUS software package.
Keywords
thin RC slabs, strengthening, composite strips, bonding, failure modes, numerical modelling
ŞTEFANIA STOLERIU, ALEXANDRU CONSTANTINESCU, ECATERINA ANDRONESCU
Abstract
ZrO2 – Al2O3 composites were developed using the co-precipitation method starting from the corresponding chlorides (zirconia was fully stabilized by using 8% Y2O3 weight ratio).
relative density (over 99%) there were used oxide additives such as ZnO, CuO, MnO2 and TiO2 (2% weight ratio).
The sintering process of the compacted green bodies (obtained by uniaxial pressing) was carried out at temperatures between 1400° and 1600°C, with a maintaining time at highest temperature of 3 hours at the maximum temperature. For the heat treatment at 1500°C the soaking time was varied from 3 to 6 hours.
The microstructure and phase composition of the dense sintered ceramic composites were determined through the scanning electron microscopy (SEM) and X-ray diffraction (XRD). The compressive strength and Young’s modulus of sintered composites were measured, too. The results have indicated that the nature of the additive oxide and the sintering temperature are the key factors in controlling the mechanical behavior of studied ceramics composites.
Keywords
dense ceramic composite, high relative density, sintering additive
ŞTEFANIA STOLERIU, ALEXANDRU CONSTANTINESCU, ADRIAN VOLCEANOV
Abstract
The most common objective of the statistical analysis is to explain the influence of random variations and events. Perhaps the most important objective is to manage simultaneous and combined effects of several influencing factors, when those factors can not be easily controlled in the experimental frame.
Multivariate Analysis – MVA is based on the principle of multidimensional statistics, which involves observation and analysis of several statistical variables at a time. This analysis is used to study several dimensions simultaneously, taking into account the effects of all variables on the characteristics of interest [1-4].
By introducing ceramic properties of some dense composite ceramics, zirconia – alumina type, with oxide additives for densification as independent variables, it was obtained a quality model. The model proved that it is necessary a more rigorous control of these properties in order to improve the compressive strength [5-6].
The developed statistical models are consistent with existing assertions in this area - they are viable, but also offers new insights - of interest from the point of view of optimizing the composition and properties of specific ceramics.
Keywords
statistics, ZTA properties, prediction, dopants
ŞTEFANIA STOLERIU, ENIKÖ VOLCEANOV, ADRIAN VOLCEANOV
Abstract
The aim of present work was to obtain ceramic composites based on silicon carbide and vitreous silicon dioxide, under unconventional thermal treatment and sintering conditions.
Due to the low densification ability of silicon carbide, sintering additives were used to enhance the process. Thus, to the studied ceramic composites it was added in fixed proportion (10% wt.) a third component as sintering aid, namely: alumina, mullite and cubic zirconia.
Keywords
silicon carbide, unconventional sintering, composite, sintering aids
MIHAI EFTIMIE, ALEXANDRA POPESCU, VASILICA DIMA
Abstract
This paper presents experimental results made to obtain a composite material with glass matrix disperse reinforced with silicon carbide powder.
The glass matrix waste (E-type glass fibres) was grounded, with a specific surface area between 3500 - 4200 cm2/g, and the reinforcing material was the powder of SiC (F120 and F600) in a ratio of 10%, 20%, and 30%.
We determined the following physical and mechanical properties: density, porosity, thermal expansion. In order to characterize in terms of composition and microstructural we performed X-ray diffraction analysis and scanning electron microscopy measurements which showed the influence of the SiC powder particle size on the properties of the composite.
Keywords
Composite, glass matrix, SiC
AYKUT CANAKCI, TEMEL VAROL
Abstract
This paper was focused on the structural evolution and characterization of Al-15vol.% Al2O3 composite. Composite powders were characterized by X-ray diffraction and scanning electron microscopy, respectively. The relationship among the stages of mechanical alloying, relative density and microstructure of both pressed and sintered materials were also investigated. It was observed that mechanical alloying process reached the steady state after 5h of milling time and relatively equiaxed powders were synthesized within this time frame. The results showed that as the milling time increased, more homogeneous dispersion of Al2O3 particles was obtained in the Al alloy matrix.
Keywords
composites; mechanical alloying; sintering; porosity; hard materials
MYKOLA ZAICHENKO, SERHII LAKHTARYNA
Abstract
In order to optimize the grain size composition of Portland cement with the addition of silica fume and to activate the hardening process of composite cement the method for surface modification in high-voltage electric field is proposed. The electrical agglomeration setup to produce modified composite cement has been designed. An observation of a cross-section of a cement particle by scanning electron microscopy and an analysis of the element distribution on the surface of modified composite cement particles are shown. According to the test results, cement pastes based on the modified composite cement possess the 28-day compressive strength of up to 89.3MPa, a 37% increase over the reference.
Keywords
Portland-composite cements, silica fume, spherical cement, agglomeration
MUNIR TAŞDEMIR, SEZGIN ERSOY
Abstract
Thermoplastic resin-mineral filler composites have been widely used in molded products due to effective cost reduction. Generally, the addition of mineral fillers will have an embrittling effect on polymers although the rigidity of the polymers can be increased. Much effort has been devoted to improving the properties of polymers by the addition of inorganic fillers, such as SiO2, ZnO, CaCO3 and Mg(OH)2.
In this study, mechanical properties of the high density polyethylene (HDPE) composites filled with silicon dioxide (SiO2), zinc oxide (ZnO) magnesium hydroxide [Mg(OH)2] and calcium carbonate (CaCO3) were investigated. The structure and properties of the composites are characterized using a scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS). Furthermore, HDPE composites were subjected to examinations to obtain their tensile strengths, yield strengths, elasticity modulus, % elongation, Izod impact strength, hardness and melt flow index (MFI).
Keywords
silicon dioxide, zinc oxide, magnesium hydroxide, calcium carbonate