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Davood Niknezhad Nordine Leklou Ouali Amiri 《Journal of Adhesion Science and Technology》2013,27(23):2535-2566
Explosive spalling of cementitious composites when it is heated from surface is considered to be the most dangerous effect of damage of concrete structures subjected to fire attack, especially when it occurs in restricted areas such as underground tunnels. The main objective of the study presented in this paper is to investigate the influence of high temperature on mechanical behavior, pore size distribution and transport properties of self-compacting concrete reinforced with polypropylene fibers (PPF). The experiment investigation was carried out using two mixtures with a constant water-to-binder ratio (w/b) of 0.37. Two SCCs mixtures were manufactured using an industrial cements according to European standard EN 197 1: CEM I 52.5?N (Portland cement), the difference between the mixtures is the presence of PPF. The amount of fibers used was fixed in 2?kg/m3, as recommends Eurocode 2 for high performance concrete to avoid explosive spalling. The specimens were subjected to various heating-cooling cycles from the room temperature 20?°C to 200?°C, 300?°C, 400?°C and 500?°C. The chloride resistance of the two SCC produced with the different mixtures in damaged and undamaged state are measured using a chloride migration test accelerated by an external applied electrical field. Intrinsic permeability is measured using the nitrogen gas. Klinkenberg approach is used for the determination of the intrinsic permeability. Torrent permeability measurement method was applied in this article, and a correlation was obtained between measure of intrinsic permeability and the Torrent permeability measurement. Finally, a relationship between thermal damage indicators and the increase in permeability and migration coefficients is also obtained. 相似文献
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Process selection for repair of mechanical components due to wear and corrosion, e.g. damage of aluminum casting housings of fuel injection systems, is based on cost and response time factors, provided that the mechanical performance is maintained within acceptable limits. One of the promising and emerging repair technologies is Cold Gas-Dynamic Spray (CGDS) coating, where a high-pressure gas propels fine powder particles to very high velocities to produce surface coating. It is essential to identify the optimum process conditions and powder composition to produce repaired surfaces with tribological properties close to those of the originally manufactured part (without coating). The objective of this work is to compare the dynamic friction and fretting wear properties of the repaired surfaces using various types of coating composition and spraying techniques. Eight types of CGDS coatings, applied to AMS 4260 aluminum specimens, were fretted against 440C stainless steel specimens at low and high nominal loads to assess their fretting wear resistance, dynamic friction properties and damping capacity. The optimum coating composition and process conditions were identified. In comparison to the uncoated specimen, this optimum coating offered tribological characteristics close to the uncoated material and even better dynamic friction properties. 相似文献
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Shankar Krishnan J. K. Richard Weber Robert A. Schiffman Paul C. Nordine Robert A. Reed 《Journal of the American Ceramic Society》1991,74(4):881-883
The real part, n , of the refractive index of pendant drops of laser-heated liquid Al2 O3 was measured by laser ellipsometry at 0.6328 μm. At temperatures from 2327 to 2600 K, n for the liquid was 1.744 ± 0.016. No significant differences were observed in the results obtained on ruby specimens and in oxygen or argon atmosphres. 相似文献
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Meriem Meziani Ouali Amiri Nordine Leklou Nasser Chelouah 《Journal of Adhesion Science and Technology》2019,33(3):286-300
The aim of this research is to determine the effects of replacing cement with tuffs on the transport properties and service life of cement-based materials. Specimens were prepared replacing 5% and 15% by weight of cement with both white and brown tuffs. Additional specimens were prepared replacing cement with 5% and 15% limestone filler and granodiorite to compare the effects of these types of materials. For these four types of specimen as well as a control mortar with no cement replacement transport properties (gas permeability and chloride ingress) were measured as well as porosity and pore diameter. The transport properties were compared the changes in these porosity and pore diameter. Based on the results, white tuff significantly improves the transport properties of the mortars due to its pozzolanic reaction and that white tuff may be an economically and functionally viable replacement for cement where concrete durability is important. Pore diameter and porosity did not correlate well with transport properties. 相似文献
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Shankar Krishnan J. Richard K. Weber Stuart Ansell April D. Hixson Paul C. Nordine 《Journal of the American Ceramic Society》2000,83(11):2777-2780
We report the first measurements of the structure factor, S ( Q ), and the pair distribution function, G ( r ), of Al6 Si2 O13 (3:2 mullite) in the normal and supercooled liquid states in the temperature range 1776–2203 K. Measurements are obtained by synchrotron X-ray scattering on levitated, laser-heated liquid specimens. The S ( Q ) shows a prepeak at 2.0 Å−1 followed by a main peak at 4.5 Å−1 and a weak feature at 8 Å−1 . The G ( r ) shows a strong (Si,Al)–O correlation at 1.80 Å at high temperature that moves to 1.72 Å as the liquid is supercooled. The second and third nearest neighbor peaks at 3.0 and 4.25 Å sharpen with supercooling. The short-range structure of the high-temperature liquid is similar to the corresponding glasses produced by rapid quenching. Supercooling causes an increase in the concentration of tetrahedral Si4+ ions, which is manifested by the large shift in the first peak to lower ionic distance, r , values in G ( r ). The increase in tetrahedrally coordinated Si4+ ions is offset by an increase in octahedral Al3+ ions. The clustering of the SiO4 4− tetrahedral units results in increased viscosity of the liquid at temperatures below the melting point, which is consistent with Al6 Si2 O13 being a fragile liquid. 相似文献
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A fully automated Mueller-matrix ellipsometer with a division-of-amplitude photopolarimeter as the polarization-state detector is described. This device achieves Mueller-matrix ellipsometry by measuring the Stokes parameters of reflected light as a function of the fast axis C of a quarter-wave retarder, which, in combination with a fixed linear polarizer, determines the polarization state of incident light. The reflected Stokes parameters were Fourier analyzed to give the 16 elements of the Mueller matrix. We investigated depolarization of polarized light on reflection from rough, heterogeneous, and anisotropic surfaces by obtaining measurements on rolled aluminum and plant leaves. The results demonstrate (1) a variation of degree of polarization of reflected light with the input polarization state, (2) the precision with which the measured matrices describe the depolarization results, (3) effects of surface anisotropy (rolling direction) on depolarization and cross polarization by reflection from aluminum surfaces, and (4) large values and differences in the depolarization effects from conifer and deciduous leaves. Depolarization of light reflected by the aluminum surfaces was most sensitive to the angle between the plane of incidence and the rolling direction when the incident Stokes parameters S(1), S(2), and S(3) were equal. 相似文献
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Jean-Emmanuel Aubert Gilles Escadeillas Nordine Leklou 《Construction and Building Materials》2009,23(12):3583-3585
This paper aims to open a discussion on the relevance of the laboratory studies on heat-induced internal sulphate attack. The results presented here show that specimens of mortars conserved in frequently renewed deionised water expand after 3 years and a half. The same specimens conserved in water that is not renewed still do not expand after more than 5 years of conservation. So, it seems that the appearance of the phenomenon is linked to the experimental conditions of the test. Moreover, the period before the beginning of the expansion is very long. These results raise two important questions: may the laboratory studies be used for the prediction of the field DEF behaviour and, if so, what minimal duration should formulation qualification tests have to ensure the durability of the constructions faced with this pathology? 相似文献
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S. Krishnan CD. Anderson J. K. R. Weber P. C. Nordine W. H. Hofmeister R. J. Bayuzick 《Metallurgical and Materials Transactions A》1993,24(1):67-72
The spectral emissivities, refractive indices, and extinction coefficients of liquid titanium-aluminum alloys were measuredvs temperature by He-Ne laser ellipsometry at 632.8 nm. Results were obtained on overheated liquids and on liquids undercooled
by as much as 350 K. The experiments were conducted under containerless conditions using electromagnetic levitation and heating
supplemented by CO2 laser beam heating. The undercooled melts exhibited spectral emissivities that were nearly independent of temperature, and
emissivities varied slightly with temperature for the stable liquids. The spectral emissivities showed a maximum at near-equiatomic
compositions and a minimum at a composition near pure liquid aluminum. The temperature coefficients of emissivity were negative
for near-equiatomic compositions and positive for aluminum-rich alloys. The emissivity was determined to be independent of
temperature at a composition of approximately 75 at. pct Al. This was termed the “X-point composition,” because it is the
composition at which, for a wavelength of 632.8 nm, the spectral emissivityvs composition isotherms cross. Significant errors in noncontact temperature measurements would result if the spectral emissivities
were estimated from a linear interpolation between the pure elements.
Formerly with the Department of Materials Science and Engineering, Vanderbilt University 相似文献
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Paul C. Nordine Robert M. Atkins Atilla M.öner 《Metallurgical and Materials Transactions A》1983,14(1):53-60
The reaction of gadolinium with fluorine was studied in a low pressure, transonic flow reactor. Atomic fluorine reactant was
generated by microwave discharge dissociation of F2 in argon. Kinetic measurements included the rate of change of the electrical resistance of isothermal gadolinium filaments
due to reaction with atomic and molecular fluorine and the intensity of chemiluminescence from the vapor phase Gd/F2 reactionvs time, temperature, and F2 partial pressure. The surfaces of reacted Gd specimens were examined by scanning electron microscopy, polished specimen cross
sections were viewed under the optical microscope, and the Gd/F2 chemiluminescent emission spectrum was obtained. A nonpassivating, metal rich, high melting and involatile fluoride, GdFx, forms on the metal at temperatures above 1180 K. An orthorhombic, passivating GdF3 forms at lower temperatures. The surface Gd activity remains high at the GdFx/fluorine interface, and F-atom reaction is first order with a reaction probability approximately 0.28. Rapid reaction atT < 1180 K is followed by an abrupt transition to passivated behavior. This change in reactivity is attributed to a phase transition
from GdFx to orthorhombic GdF3 that occurs as the oxygen impurity concentration of the reacting metal decreases from its value near the original specimen
surface to that of the bulk material. 相似文献