Harry Kaytoo - Academia.edu (original) (raw)

Papers by Harry Kaytoo

Matériaux & Techniques, 1996

An optical method named In Situ Surface Observation Technique (ISSOT) is presen ted in this paper... more An optical method named In Situ Surface Observation Technique (ISSOT) is presen ted in this paper. This method is used to detect crack nucleation from a flaw (here a pit) at mesoscopic scale during a triangular push-pull cycling test under the control of charge amplitude in aqueous solution ofMgCl2 at 117°C. It can be found that the crack initiation time determined by using this technique represents 2 % of that estimated from a mechanical criterion. Moreover, the follow of the crack tip evolution by the ISSOT allows to measure average local crack growth rates. It has been shown that the variations of the latter were related to the effects of barriers such as grain boundaries, twin boundaries and grain boundaries triple junction.

Applied Surface Science, 2021

The research focuses on the development and characterization of innovative thin hybrid oxide coat... more The research focuses on the development and characterization of innovative thin hybrid oxide coatings obtained in subsequent processes of thermal (TO) and electrochemical (EO) oxidation. Four different surface modifications were investigated and the microstructure was determined, the mechanical, chemical and biological properties of the Ti-13Nb-13Zr alloy were assessed using scanning electron microscopy, X-ray dispersion analysis, glow discharge emission spectroscopy, Raman spectroscopy, nanoindentation and corrosion resistance measurements. The composite layers were evaluated for antimicrobial activity, cytotoxicity bioassays and wettability tests were performed. The conducted studies of two-stage oxidation (TO + EO) have shown that it is possible to obtain layers with a different structure-crystalline and nanotubular. The formation of a nanotube layer on the surface of the crystalline layer is dependent on the thickness of the crystalline layer. The produced double titanium oxide coatings show high surface roughness, high corrosion resistance, are hydrophilic, slightly antibacterial, and not cytotoxic, which has a huge impact on the process of connecting the tissue with the implant.

Coatings, 2020

The increasing demand for titanium and its alloys used for implants results in the need for innov... more The increasing demand for titanium and its alloys used for implants results in the need for innovative surface treatments that may both increase corrosion resistance and biocompatibility and demonstrate antibacterial protection at no cytotoxicity. The purpose of this research was to characterize the effect of two-stage anodization—performed for 30 min in phosphoric acid—in the presence of hydrofluoric acid in the second stage. Scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, glow discharge optical emission spectroscopy, nanoindentation and nano-scratch tests, potentiodynamic corrosion studies, and water contact angle measurements were performed to characterize microstructure, mechanical, chemical and physical properties. The biologic examinations were carried out to determine the cytotoxicity and antibacterial effects of oxide coatings. The research results demonstrate that two-stage oxidation affects...

Clinical and Experimental Dental Research, 2019

Objective: The accuracy of the information incorporated into brackets is a determining factor for... more Objective: The accuracy of the information incorporated into brackets is a determining factor for the efficacy of torque applied to teeth. The aim of this study was to compare the dimensions of a bracket's slots with the nominal values announced by the manufacturer. Materials and methods: A total of 730 maxillary right central brackets manufactured by seven companies (Dentsply Gac, American Orthodontics, Rocky Mountain Orthodontics, GC Orthodontics, 3M Unitek, and Dentaurum) were studied. The sample included 0.018 × 0.025 and 0.022 × 0.028 in., metal and ceramic, conventional and self-ligating brackets. Images were obtained with an Olympus BX51 optical microscope. Slot dimensions were measured at the base and at the face on both mesial and distal sides using ImageJ software. Data were analyzed using Wilcoxon, sign tests, two-and three-way ANOVA, and Tukey's tests. Intraclass correlation coefficient was employed to assess the intraobserver and interobserver variability. The threshold for statistical significance was p ≤ .05. Results: Statistical analysis showed that the slot dimensions of 90% to 97% of studied brackets were significantly different from nominal values. In general, slot size was oversized, with a face size larger than the base size. Comparison between mesial and distal sides showed that up to 45% of the brackets were significantly asymmetrical. The manufacturer had a significant effect for base and face widths (p = .0001) and for length (p = .003). Conclusion: This study shows that a large proportion of measured brackets displays dimensional inaccuracies when compared with stated values. Clinically, the slot oversize and the divergence of slot walls cause an increase of wire-slot play, inducing a loss of torque control. Practitioners cannot fully trust the precision of used appliances and should be aware that adjustments could be needed in the finishing stages of the treatment.

Advances in Materials Science, 2019

The investigations of high-temperature oxidation of zirconium alloys, applied for fuel pellets in... more The investigations of high-temperature oxidation of zirconium alloys, applied for fuel pellets in nuclear power plants, are usually limited to oxidation kinetics, phase transformations and microstructural characterization. The purpose of this research was to characterize the degradation phenomena occurring within oxide layer and at the interface oxide/metal, on internal and external Zircaloy-2 tube surfaces, below and over crystalline transformation temperature of zirconium oxides. The commercial tubes were oxidized at 1273 K and 1373 K in calm air for 30 min and then examined with a technique novel for such purpose, namely a high-resolution X-ray computer tomography. The light microscopy was used to examine the cross-surfaces. The obtained results show that the form and intensity of oxide damage is significant and it is in a complicated way related to oxidation temperature and on whether external or internal tube surface is studied. The found oxide layer damage forms include surfac...

Scientific Reports, 2019

Cell morphological analysis has long been used in cell biology and physiology for abnormality ide... more Cell morphological analysis has long been used in cell biology and physiology for abnormality identification, early cancer detection, and dynamic change analysis under specific environmental stresses. This work reports on the remote mapping of cell 3D morphology with an in-plane resolution limited by optics and an out-of-plane accuracy down to a tenth of the optical wavelength. For this, GHz coherent acoustic phonons and their resonance harmonics were tracked by means of an ultrafast opto-acoustic technique. After illustrating the measurement accuracy with cell-mimetic polymer films we map the 3D morphology of an entire osteosarcoma cell. The resulting image complies with the image obtained by standard atomic force microscopy, and both reveal very close roughness mean values. In addition, while scanning macrophages and monocytes, we demonstrate an enhanced contrast of thickness mapping by taking advantage of the detection of high-frequency resonance harmonics. Illustrations are give...

Catheterization and Cardiovascular Interventions, 2018

ObjectivesThe purpose of the study was to develop a standardized and global bench test protocol t... more ObjectivesThe purpose of the study was to develop a standardized and global bench test protocol to evaluate the biomechanical characteristics of the most currently used drug‐eluting coronary stents.BackgroundThe use of coronary stents has contributed to the reduction of cardiovascular mortality but can be associated with specific complications. Improving the biomechanical matching between the stents and the coronary anatomy may reduce these complications.MethodsWe assessed five commercially available drug‐eluting stents: the Absorb, Orsiro, Resolute Onyx, Synergy, and Xience Alpine stents. Following stent deployment at nominal pressure in ambient air, radial elastic recoil and foreshortening were measured. Flexibility (crimped and deployed stents) and longitudinal and radial resistances were evaluated using a mechanical tester.ResultsBiomechanical characteristics were significantly different for all tested devices (ANOVA, P < 0.01). The Synergy, Orsiro, and Xience Alpine stents p...

Advances in Materials Science, 2017

The presence of the oxide layers on Zr alloys may retard or enhance the hydrogen entry and materi... more The presence of the oxide layers on Zr alloys may retard or enhance the hydrogen entry and material degradation, depending on the layer features. This research has been aimed to determine the effects of pre-oxidation of the Zircaloy-2 alloy at a different temperature on hydrogen degradation. The specimens were oxidised in laboratory air at 350°C, 700°C, and 900°C. After, some samples were tensed at 10-5 strain rate and simultaneously charged with hydrogen under constant direct voltage in 1 N sulfuric acid at room temperature. Other specimens were charged without any tension, then annealed at 400°C for 4 h and finally tensed at above strain rate. The SEM examinations were performed on the cross-sections and fracture faces of specimens. The obtained results demonstrate the effects of the oxide layer on the cathodic current and hydrogen entry, mechanical properties and the appearance of hydrides and fracture behaviour.

Acta Materialia, 2016

A local approach coupling atomic force microscopy (AFM) observations and polycrystal finite eleme... more A local approach coupling atomic force microscopy (AFM) observations and polycrystal finite element calculations is proposed to provide data at the slip-band scale. From AFM measurements of slip bands emerging at the specimen surface during tensile loading, and from numerical results of strain fields at the grain scale, the method is able to determine at the local discrete scale the mean slip-band spacing and the number of dislocations emerging during the plastic strain. The methodology applied in the hydrogen embrittlement context highlights, quantitatively, at the grain scale an increased plastic strain localization with internal hydrogen.

Mechanics & Industry, 2015

This study deals with the in service durability of an alloy Al-Cu-Li 2050 friction stir welded. I... more This study deals with the in service durability of an alloy Al-Cu-Li 2050 friction stir welded. In an aeronautical context, this material could be submitted to mechanical stresses and a corrosive environment. Thus, the aim of this study is to characterize the intergranular stress corrosion cracking (IGSCC) behavior of the 2050 FSW weld nugget. First, a link has been established between several microstructural heterogeneities induced by the welding process and local strain variations, then between these heterogeneities and the initiation and propagation of IGSCC cracks.

Types 304L and 316L austenitic Stainless Steels (SS) are widely used in PWR environment. These pa... more Types 304L and 316L austenitic Stainless Steels (SS) are widely used in PWR environment. These past few years, a limited number of cases of intergranular stress corrosion cracking (IGSCC) have been detected in cold worked areas of non sensitized austenitic stainless steel components. A first study has been initiated at EDF to assess the conditions of the cracking. The main results include cold work thresholds of 240 HV0,1 for initiation cracking, and of 310 HV0,1 for crack propagation, and propose that a dynamic loading is necessary for SCC. The aim of the present paper is to provide a basis of a crack propagation model by investigating the effect of loading, material and cold-work. In order to try to approach a static loading, a trapezoidal cyclic loading is applied on high cold-worked (by rolling or by tensile loading) materials. It is shown that, for the most severe loading, the rolling cold-worked (RCW) materials undergo TGSCC whereas IGSCC is observed after tensile cold-working...

Advances in Materials Sciences, 2008

In order to highlight hydrogen effects on the plasticity, the slip morphology after straining (un... more In order to highlight hydrogen effects on the plasticity, the slip morphology after straining (under tension up to 4% of plastic strain in ambient air) of hydrogenated (at 135 wt.ppm) and non-hydrogenated 316L stainless steel polycrystals was compared. A statistical analysis of both slip band spacings (SBS) and slip band heights (SBH) was performed using atomic force microscopy. Tensile tests were performed at low strain rate, specimens being previously charged at controlled hydrogen concentration. The plastic strain field heterogeneity in polycrystals was taken into account thanks to numerical simulation of crystalline plasticity. On each grain, the calculated plastic shear was correlated with the distribution of SBS and the average number of emerging dislocations per slip band. In comparison with uncharged specimen and for an equivalent cumulated plastic strain, the hydrogenated specimen shows an increase of the slip band spacing (SBS) and of emerging dislocations. This result confirms a plastic localization induced by absorbed hydrogen.

Laminate composites made of glass fibre/epoxy resin filled with acrylic tri-bloc copolymers (Nano... more Laminate composites made of glass fibre/epoxy resin filled with acrylic tri-bloc copolymers (Nanostrength) have been successfully manufactured. Microstructure, thermomechanical properties and impact resistance have been investigated and compared with those of a glass fibre/epoxy resin system. Dynamic mechanical analysis (DMA) tests have been conducted to determine the effect of Nanostrength on storage, loss modulus and glass transition temperature. A drop weight tower was used to perform low-velocity impact tests on laminate composites. Addition of Nanostrength to the epoxy matrix led to an increase in both strength and impact resistance of the composite. Moreover, a moderate decrease of storage modulus and glass transition temperature was observed.

Advances in Materials Sciences, 2011

Intergranular corrosion sensitivity is studied for the friction stir weld nugget of aluminum allo... more Intergranular corrosion sensitivity is studied for the friction stir weld nugget of aluminum alloy 2050-T8. The weld nugget consists of fine equiaxed grains having average sizes from 4 to 20 µm, the grain size increases with decreasing of the distance from the weld surface. The weld nugget contains a particular microstructure called "onion rings" due to crystallographic orientations. The effect of the "onion rings" on stress corrosion cracks initiation is studied for stress corrosion cracking tests at a strain rate of 2.10-6 s-1. EBSD cartographies allow showing that the initiation site of the biggest cracks is located at boundaries between the texture bands. Corrosion and stress corrosion tests in 1.0 M NaCl are performed in order to show stress effect on intergranular corrosion. Pitting corrosion is observed during corrosion tests, whereas intergranular cracks appear during stress corrosion tests. The medium crack length is 20 µm and 168 cracks per mm 2 can be located. In these severe laboratory conditions, the order of magnitude of long crack growth rate is 5.10-8 m.s-1 .

Microscopy Microanalysis Microstructures, 1994

2014 Les films passifs qui se forment spontanément sur la surface des aciers inoxydables (Fe-Cr-N... more 2014 Les films passifs qui se forment spontanément sur la surface des aciers inoxydables (Fe-Cr-Ni) jouent un rôle primordial dans le phénomène d'endommagement par Corrosion Sous Contrainte et Fatigue Corrosion. L'apparition de la corrosion localisée et la propagation des fissures est étroitement liée à leur rupture. Cette rupture résulte des effets mécaniques et électrochimique liés à la déformation plastique du substrat par modification morphologique de l'interface film-métal. Il est donc nécessaire de connaître la rhéologie de ces films pour en prévoir la rupture. Les films passifs sont constitués d'un mélange d'oxydes et d'hydroxydes et leur épaisseur ne dépasse pas 10 nanomètres. Leurs caractéristiques mécaniques ne peuvent donc pas être atteintes par la métrologie classique. Une meilleur connaissance de la structure à l'échelle atomique et notamment du caractère cristallin ou amorphe devrait permettre de mieux appréhender la réponse de ces films à des sollicitations extérieures. Abstract. 2014 Passive films spontaneously formed on stainless steels surfaces play an essential role in Stress Corrosion Cracking and Fatigue Corrosion. Initiation of localized corrosion and propagation of cracks are linked to the rupture of these films. This rupture results on mechanical and electrochemical effects of the plastic strain of the substrate. To predict the damage of passive films, it is necessary to know their rheology. Passive films are made of a mixing up of oxides and hydroxides and their thickness doesn't exceed 10 nm. Their mechanical features cannot be determined by classical metrology. A better knowledge of atomic structure and more particularly of the crystalline or amorphous character permits to give information on the mechanical response of these passive films to external stress.

Corrosion Science, 2014

OLIVE-Effects of microstructure and local mechanical fields on intergranular stress corrosion cra... more OLIVE-Effects of microstructure and local mechanical fields on intergranular stress corrosion cracking of a friction stir welded aluminum-copper-lithium 2050 nugget-Effects of microstructure and local mechanical fields on intergranular stress corrosion cracking of a friction stir welded aluminum-copper

Journal of Computational Science and Technology, 2010

Many attempts were made in the past to investigate numerically the metal-hydrogen interactions at... more Many attempts were made in the past to investigate numerically the metal-hydrogen interactions at macro-scale but the actual microstructure was generally not introduced into the analyses. The objective of this work is to simulate, on an artificial polycrystal, the effect of the microstructure-induced stress-strain field heterogeneity on the internal hydrogen evolution. Finite element method is used to take into account explicitly the grain morphologies and their crystalline orientations into the description of the mechanical deformation. A one-way coupled crystal plasticity-transient hydrogen diffusion analysis is developed and applied to solve the boundary value problem. The analysis of the computed hydrogen content field shows that a segregation of hydrogen is observed mainly at the grain boundaries. It is also shown that grain size has a significant effect not only on the amount of hydrogen segregated at the grain boundaries but also on the relative size of concentration gradients.

Physical Review Letters, 2004

International Journal of Hydrogen Energy, 2011

Secondary Ion Mass Spectrometry (SIMS) analyses were carried out on type 304 austenitic stainless... more Secondary Ion Mass Spectrometry (SIMS) analyses were carried out on type 304 austenitic stainless steel. On annealed specimen exposed to hydrogen (10 MPa, 358 K), Element Depth Profiles SIMS mode was able to describe quantitatively the hydrogen profile content computed by the Fick's law. Based on SIMS analyses on the wake of a fatigue crack (propagation in hydrogen gas at 0.6 MPa and RT), it was possible to compute an apparent diffusivity and solubility in the crack tip region. The apparent solubility and diffusivity in the deformed regions were two times and five orders of magnitude higher than the ones on annealed material, respectively. High hydrogen content was found around the crack tip, where the plastic deformation was well developed (pronounced slip activity). The high apparent diffusivity is presumed to result from enhanced hydrogen transport induced by cyclic plastic activity at the crack tip.

Corrosion Science, 1998

The susceptibility to stress corrosion cracking (SCC) of the Al-Zn-Mg-Cu French 7010 alloy of dif... more The susceptibility to stress corrosion cracking (SCC) of the Al-Zn-Mg-Cu French 7010 alloy of different temper has been investigated by Slow Strain Rate Testing. The tests have been carried out at strain rate ranged between 10−5 and 10−7s−1, at corrosion potential and at cathodic polarisation, in NaCl and NaCl + As2O3 solution. The lowest susceptibility to SCC of overaged alloy has been explained by presence of large phase precipitates which increased the alloy resistance to pitting and intergranular corrosion, changed the conditions of crack initiation and trapped the absorbed hydrogen.