Abstract: Because of the various industrial and scientific interests, a proliferation of roughness parameters, possibly running into hundreds, has been developed to describe the different kinds of surface morphology with regard to specific functions, properties or applications. In spite of this of roughness parameters, there is still no complete comprehensive account for the relevance of all these parameters. Hence, the selection of a roughness parameter for describing and/or modelling a surface morphology is very often subjective. Thanks to a methodology based on the Computer-Based Bootstrap Method (CBBM), the experimental results of this study exhibit the major influence of the order parameter as far as the relationships between the surface morphology of Ti6Al4V substrates and the in vitro cell adhesion of human osteoblasts are concerned. The lower is the value of this roughness parameter that characterises the surface texture, the better is the cell adhesion. Moreover, the cell adhesion seems to be rather affected by the surface morphology than by the surface chemistry in the experimental conditions of our work.

Abstract: Composite coatings constitute a new class of materials, which are mostly used in mechanical and tribological applications as well as because of anti-corrosion properties. Laser surface alloying of 35NCD16 bainitic steel and iron substrates with silicon powder was studied. It is principally the nature of substrate, which determines the thickness of heat affected zone (HAZ) and melted zone (MZ). The MZ was found to be homogeneous in composition and concentration in alloying elements and mainly constituted of rapid solidified structure. Depending on carbon and Si contents, residual stresses and phase transformations, the superficial zone could be cracked. The cracking phenomenon is observed in the MZ of iron substrate whenever the Si deposit thickness and when more than 20 mum of Si powder is alloyed with steel substrate. Hardness and cracking depend on residual stress level. The result is a superficial hardness increase up to a maximum and then a decrease with apparition and generalization of cracks associated to reduction of stress level.

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Abstract: Topography is a surface characteristic which is as important as the chemical composition with regard to its functional properties. Topography can be mainly described by three kinds of roughness parameters: amplitude, frequency and hybrid parameters. The present study aims to perform a multiscale morphological analysis of 316L austenitic stainless steel ground surfaces with 11 different paper grades. It is shown that the values of the most commonly used roughness parameters R-a (average arithmetic roughness) and R-t (peak to valley) depend on the observation scale with values distributed into three characteristic stages. At small observation scales, less than,5 mm, the abraded surfaces are not characterised by any particular scaling law. At large observation scales, more than similar to 60 mu m, the evolution of the roughness parameters indicates that the abrasion mechanism follows an homothetic scaling law for the different paper grades. These two extreme stages are separated by a transition stage that can be characterised by an index, which exhibits an increasing linear evolution with the size of the abrasive grains.

Abstract: This paper proposes a new multi-scale measurement approach performed to compare the surface roughness and the visual aspect of polished surfaces. In this investigation, five specimens of glass moulds presenting different visual aspects are considered. All roughness profiles assessed by tactile profilometry were rectified by a first degree polynomial fitting, and current roughness parameters were calculated with respect to the evaluation length among which they are estimated. A variance analysis was then performed to discriminate each roughness parameter and each evaluation length with regard to a correlation with the visual aspect. Although the average roughness amplitude is about 100 run, the results show that the optimal correlation with the visual aspect is obtained for a 400 mu m evaluation length. Moreover, the multi-scale method allows to confirm results already found in the bibliography about the high wavelengths origin of "orange peel" aspect. This application allowed us to conclude on the advantages and the limits of the implemented method. (C) 2006 Elsevier B.V. All rights reserved.

Abstract: The method of moments is a popular technique for estimating the parameters of a generalized lambda distribution (GLD), but published results suggest that the percentile method gives superior results. However, the percentile method cannot be implemented in an automatic fashion, and automatic methods, like the starship method, can lead to prohibitive execution time with large sample sizes. A new estimation method is proposed that is automatic (it does not require the use of special tables or graphs), and it reduces the computational time. Based partly on the usual percentile method, this new method also requires choosing which quantile u to use when fitting a GLD to data. The choice for u is studied and it is found that the best choice depends on the final goal of the modeling process. The sampling distribution of the new estimator is studied and compared to the sampling distribution of estimators that have been proposed. Naturally, all estimators are biased and here it is found that the bias becomes negligible with sample sizes n >= 2 x 10(3). The .025 and .975 quantiles of the sampling distribution are investigated, and the difference between these quantiles is found to decrease proportionally to 1/root n.. The same results hold for the moment and percentile estimates. Finally, the influence of the sample size is studied when a normal distribution is modeled by a GLD. Both bounded and unbounded GLDs are used and the bounded GLD turns out to be the most accurate. Indeed it is shown that, up to n = 10(6), bounded GLD modeling cannot be rejected by usual goodness-of-fit tests. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: A numerical technique was proposed to plot the Abbott curve and to compute its associated parameters defined by the DIN 4776 and ISO 13565 norms. These parameters were then extended and applied to non-sigmoid Abbott curves. By studying the discretisation errors, we show that a minimum of 200 intercepts, with parabolic interpolations between discretised data profiles, have to be taken into consideration to calculate the parameters as accurately as possible. Experimental profiles were eroded by means of a numerical wear model, and it was shown that the Abbott parameters correlate well with the wear model parameters. Our numerical estimations of Abbott parameters were performed for electro-eroded, tool machined, polished, worn and sandblasted surfaces. Manual measures were compared with our algorithmic method and it was shown that the difference is lower than 1% for Mr1 and Mr2 Abbott parameters, but the numerical technique leads to a lower dispersion. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract: The extensive use of appropriate coatings to improve wear resistance, friction coefficient, electrical properties, corrosion resistance and biomedical application has stimulated a growing interest in their mechanical properties and especially hardness testing that is routinely used for coating evaluation. In this study Jonsson and Hogmark model is applied for the porous hydroxyapatite produced by plasma spraying on Ti6A14V substrate. Firstly, the effect of indentation load on hardness values of coating and substrate are studied. The modified Jonsson and Hogmark model is used to explain the composite hardness behavior and the effect of coating porosity.

Abstract: The MEMS structure integrity, their dynamic properties as well as their electrostatic characteristics, strongly depend on the achieved surfaces roughness produced by the micromachining process. It is therefore, not surprising that numerous works are devoted to propose relations between roughness and physical or mechanical properties in this field. Yet the issue is full of complexities since roughness parameters depend on the method used for their evaluation. This article introduces a new approach of the roughness characterization, based on the scaling analysis. Experimental results obtained on micro machined surfaces show that the range roughness amplitude depends on the scan length and that roughness amplitude follows three stages. The stage I is due to a smoothing effect of the surface induced by the tip radius of the protilometer, stage II presents a piecewise power-law roughness distribution until a critical length that characterises the fractal behaviour of the surface, and stage III is characterised by extreme values statistics. The fractal parameter, the extreme values estimators and the crossover between stages II and III are shown to be related to the micromachining process. As a result, an original probabilistic model based on the Generalized Lambda Distribution (GLD) is proposed to estimate the multi-scale roughness in the stage III. Finally, thanks to a Bootstrap protocol coupled with a Monte-Carlo simulation, the maximal roughness amplitude probability density function is estimated at a scale higher than the scanning length. (C) 2006 Elsevier B.V. All rights reserved.

Abstract: When calculating independently the false alarm rate of the eight usual runs rules used in SPC control chart, it appears that the proposed rule designed to detect mixture patterns corresponds to a Type-I error strongly lower than the seven other rules. This discrepancy is underlined and the mixture rule is showed to be useless both for in-control and out-of-control processes. Thus a modi. cation of the mixture detection rule is proposed and the impact of this new mixture rule is then illustrated and discussed using Monte Carlo calculations.

Abstract: Usually, corrosion and mechanical resistance of dental prosthesis are affected by the surface roughness of the implant materials. This study aimed at evaluating the ability of a new polishing process: Ecoclean. For different dental-alloys, polishing was performed by varying testing conditions. A computer-based bootstrap method developed in our laboratory is then used to calculate more than one hundred roughness parameters from results recording on these samples by tactile profilometer and to correlate the roughness parameters with experimental conditions. The results were compared with mechanical polished samples one. This method allows us to determine the appropriate experimental conditions to obtain a given set of roughness parameters.

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Abstract: The influence of the morphological texture (flat and structured) of a polyester based paint coating on the low wear damage is characterised by means of roughness and gloss measurements. Using statistical methods, the aim of the investigation is to determine, among about 60 surface roughness parameters, the most relevant of them with regard to the morphological texture and the wear behaviour of polymer coatings. The level of relevance of each roughness is quantitatively assessed through the calculation of a statistical index of performance determined by combining the two-way analysis of variance (ANOVA) and the computer based Bootstrap method (CBBM). For the experimental conditions related to the present investigation, the fractal dimension and a roughness parameter directly related to the number of inflexion points of the profiles are shown to be the most relevant parameters for discriminating the different morphological textures of studied coatings and for characterising the low wear damage, respectively. Even if the gloss reduction related to the low wear damage is more visually perceptible at a macroscopic scale for the flat products than for the structured ones, the magnitude of this damage is shown to be however very similar at a microscopic scale whatever the morphological texture of the paint coatings. (C) 2006 Elsevier B.V. All rights reserved.

Abstract: A surface morphology can be described by numerous roughness parameters. Making the most of the power of modem computers, the relative relevance of a hundred surface roughness parameters is assessed in this investigation with regard to the relationships between the morphological texture, the low wear damage and the gloss of polymer coatings. The relevance of each roughness parameter is quantitatively determined by statistical indexes of performance defined and calculated by combining the two-way ANalysis Of VAriance (ANOVA) and the Computer Based Bootstrap Method (CBBM). The fractal dimension is shown to be the most relevant parameter for characterising the different morphological textures of studied coatings and the average curvature radius of peaks for characterising the effect of wear. A linear relationship is found between the reduction of gloss and the reduction of the average curvature radius of peaks due to wear. Besides, it is also shown that angles of 85 degrees and 20 degrees are the most relevant for characterising, respectively, the effects of the morphological texture of polymer coatings and wear on the gloss measurements. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: This study aims to contribute to the definition of a methodology, which can help to select a relevant roughness parameter with a view to describing the topography of orthopaedic bearing surfaces. In this investigation, the surface topography of a retrieved titanium alloy (TA6V) femoral head was characterized using visual inspection, optical microscopy and three-dimensional contacting profilometry. A numerical analysis of roughness measurements was then undertaken to assess in a first step the values of different roughness parameters of interest found in papers dealing with the topography of orthopaedic bearing surfaces. In a second step, the Analysis of Variance (ANOVA) and the Computer-Based Bootstrap Method were combined to determine statistically, and without preconceived opinion, which of those parameters is the most relevant to describe the different investigated worn regions of the studied femoral head. (c) 2006 Elsevier Ltd. All rights reserved.

Abstract: The relevance of small-punch tests and indentation (hardness) tests are compared with regard to the determination of a constitutive law in the case of non active ferrite-bainite steel taken from a French power plant. Firstly, small-punch tests were performed on material samples and the load deflection curves were compared with finite element calculations using the FORGE2 Standard code. As a result the strength coefficient and the strain hardening exponent of Hollomon's constitutive law were determined by an inverse method (Simplex method). Besides, it was shown that a three-parameter constitutive law such as Ludwik Hollomon's leads to an indetermination since its parameters are correlated with each other. Secondly indentation tests were performed with a ball indenter and the parameters of the constitutive law were determined from the analysis of the load-indentation depth curves. Both methods give results in good agreement with the true stress-true strain curve obtained by classical tensile testing, thus proving their applicability to nuclear materials. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: This paper introduces an analyse of the fractal dimension by Richardson's method. Two different ways to calculate the fractal dimension are presented with their related calculation errors and applied the Von Koch curves. A Monte-Carlo simulation of the evolution of the grains' boundaries when heating shows that the interfaces lose their fractal characteristics as reported in experimental work. This result is interpreted by dissipation of the energy during the evolution of the grain boundary. (c) 2006 Springer Science + Business Media, Inc.

Abstract: In statistical process control (SPC) methodology, quantitative standard control charts are often based on the assumption that the observations are normally distributed. In practice, normality can fail and consequently the determination of assignable causes may result in error. After pointing out the limitations of hypothesis testing methodology commonly used for discriminating between Gaussian and non-Gaussian populations, a very flexible family of statistical distributions is presented in this paper and proposed to be introduced in SPC methodology: the generalized lambda distributions (GLD). It is shown that the control limits usually considered in SPC are accurately predicted when modelling usual statistical laws by means of these distributions. Besides, simulation results reveal that an acceptable accuracy is obtained even for a rather reduced number of initial observations (approximately a hundred). Finally, a specific user-friendly software have been used to process, using the SPC Western Electric rules, experimental data originating from an industrial production fine. This example and the fact that it enables us to avoid choosing an a priori statistical law emphasize the relevance of using the GLD in SPC. (C) 2006 Elsevier Ltd. All rights reserved.

Abstract: Dealing with fatigue lifetime prediction, this paper aims to report on a new statistical method combining the Lambda Distributions and the Bootstrap technique. This method is first applied for determining the Probability Density Function (PDF) of the C and n coefficients in the Paris relationship of a fatigue crack propagation curve. Then, introducing the initial crack's length distribution, the fatigue lifetime prediction is obtained and discussed considering various standard deviations of the initial crack's length. It is shown that the scattering of the initial crack's length needs to be taken into account in predicting lifetime, and that the stochastic nature of the crack's propagation is not self-sufficient to explain completely the experimental asymmetry of the PDF lifetime. This paper shows that the Lambda Distributions are a powerful toot for modelling the PDF lifetime, compared with traditional Gaussian or lognormal PDF. (c) 2005 Elsevier Ltd. All rights reserved.

Abstract: In this paper, we propose to create a fractal function defined by an infinite series to model worn surfaces obtained by a grinding process. In this series, each elementary term characterizes a wear process at a given scale. This series is only defined by two parameters: an amplitude parameter and the fractal dimension. This model is tested on worn profiles obtained by using different grinding paper grades and roughness is assessed by tactile profilometry. Then an inverse method is developed to obtain simulated profiles that present the same morphology as the experimental ones. The results from this study prove that our method allows simulation of profiles with elementary functions that characterize the wear process. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: The degradation of the femoral head roughness caused by scratching is known to increase the wear rate of the polyethylene counterface of the Chamley total hip prostheses and therefore to have an impact on osteolysis. The knowledge of the scratching mechanism is hence of paramount importance to improve the long-term clinical performance of these prostheses. The aim of this study is to identify the mechanism of scratch generation of a retrieved titanium (TA6V) femoral head through an accurate characterisation, of its surface topography. The surface topography features have been assessed both qualitatively and quantitatively by respectively using an optical microscope and a three dimensional contacting profilometer. Based on the scanning of about 80 areas spread over the entire surface of the retrieved femoral head, hypotheses on the mechanism of scratch generation have been formulated after analysing the observed topographical patterns, the arithmetic mean roughness and the amplitude density function (ADF). The formulated hypotheses have finally been verified comparing the ADF and the bearing area curves of profiles related to the most severely scratched areas with those of simulated worn profiles. This study highlights the major influence of foreign third bodies on the scratching of metallic femoral heads of the Chamley type prostheses. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: In a high number of diffusive systems, measures are processed to calculate material parameters such as diffusion coefficients, or to verify the accuracy of mathematical models. However, the precision of the parameter determination or of the model relevance depends on the location of the measure itself. The aim of this paper is first to analyse, for a mono-dimensional system, the precision of the measure in relation with its location by an inverse problem algorithm and secondly to examine the physical meaning of the results. Statistical mechanic considerations show that, passing over a time-distance criterion, measurement becomes uncertain whatever the initial conditions. The criterion proves that this chaotic mode is related to the production of antientropy at a mesoscopique scale that is in violation to quantum theory about measurement. (C) 2003 Elsevier Ltd. All rights reserved.

Abstract: The aim of this paper is to analyze the physical meaning of the numerical instabilities of the parabolic partial differential equations when solved by finite differences. Even though the explicit scheme used to solve the equations is physically well posed, mathematical instabilities can occur as a consequence of the iteration errors if the discretisation space and the discretisation time satisfy the stability criterion. To analyze the physical meaning of these instabilities, the system is divided in sub-systems on which a Brownian motion takes place. The Brownian motion has on average some mathematical properties that can be analytically solved using a simple diffusion equation. Thanks to this mesoscopic discretisation, we could prove that for each half sub-cell the equality stability criterion corresponds to an inversion of the particle flux and a decrease in the cell entropy in keeping with time as criterion increases. As a consequence, all stability criteria defined in literature can be used to define a physical continuous 'time-length' frontier on which mesoscopic and microscopic models join.

Abstract: This article presents a new method for the study of the evolution of dynamic systems based on the notion of quantity of information. The system is divided into elementary cells and the quantity of information is studied with respect to the cell size. We have introduced an analogy between quantity of information and entropy, and defined the intrinsic entropy as the entropy of the whole system independent of the size of the cells. It is shown that the intrinsic entropy follows a Gaussian probability density function (PDF) and thereafter, the time needed by the system to reach equilibrium is a random variable. For a finite system, statistical analyses show that this entropy converges to a state of equilibrium and an algorithmic method is proposed to quantify the time needed to reach equilibrium for a given confidence interval level. A Monte-Carlo simulation of diffusion of A* atoms in A is then provided to illustrate the proposed simulation. It follows that the time to reach equilibrium for a constant error probability, t(e), depends on the number, n, of elementary cells as: t(e) proportional to n(2.22+/-0.06). For an infinite system size (n infinite), the intrinsic entropy obtained by statistical modelling is a pertinent characteristic number of the system at the equilibrium. (C) 2003 Elsevier Ltd. All rights reserved.

Abstract: Purpose of the study The objective of this work was to identify the mechanisms leading to deterioration of the polyethylene acetabular surface in total hip prostheses. Material and methods We conducted an in vivo analysis of damage caused to articulating surfaces of metal-on-polyethylene total hip prostheses. This analysis was performed on three of the 45 explants of Harris-Galante prostheses available to use from our series of 1480 implantations performed between 1985 and 1996. These three pieces were selected because large-sized fibers of metallic debris were identified on the polyethylene surface and because the explants had been performed for reasons other than loosening in aseptic patients. Macroscopic examination was combined with scan electron microscopy to analyze morphological changes. Results We found that identical damage could be observed on the polyethylene explants despite the different sizes of the metallic heads and different metal-on-polyethylene combinations. Our analysis confirmed the deleterious effect of metallic foreign bodies trapped in contact with the articulate surfaces. These foreign bodies resulted in one case from rupture of a multifilament wire used for the trochanteric fixation and in two cases from the surfacing of the non-cemented Harris-Galante cups. The microscopic analysis demonstrated several successive localizations of the foreign bodies on the polyethylene surface before becoming deeply encrusted in the polyethylene where they deteriorated the femoral head surface (rough) and wore the polyethylene surface (abrasion). When the fibers came from the surfacing of the Harris-Galante cups, the metallic debris remained unrecognized during the revision procedure and were only identified later during the systematic examination of prosthetic explants. Discussion and conclusion These findings emphasize the importance of quality surface treatments for non-cemented prostheses and argue in favor of particular precautions during operative manipulation of these components. A systematic analysis of the prosthetic explants is advisable, particularly for components explanted because of wear or unexplained osteolysis. Use of multifilament trochanteric wires should be avoided because rupture raises the risk of intra-articulate migration of metallic debris. If the prosthesis involves a polyethylene acetabular surface, ceramic heads should be preferred to improve resistance to abrasion, particularly to limit the deleterious effect of a third body.

Abstract: This paper comments upon some statistical aspects of the slit island method which is widely used to calculate the fractal dimension of fractured surfaces or of materials' features like grain geometry. If a noise is introduced when measuring areas and perimeters of the islands (experimental errors), it is shown that errors are made in the calculation of the fractal dimension and more than a false analytical relation between a physical process parameter and the fractal dimension can be found. Moreover, positive or negative correlation with the same physical process parameter can be obtained whether the regression is performed by plotting the variation of the noisy area versus the noisy perimeter of the considered islands or vice versa. Monte-Carlo simulations confirm the analytical relations obtained under statistical considerations. (C) 2003 Elsevier Ltd. All rights reserved.

Abstract: The aim of this paper is to present how to make the most of the recent and powerful statistical computer-based bootstrap method (CBBM) in roughness studies. This work shows that this statistical method can help to determine quantitatively, and without preconception, the most relevant roughness parameter that characterises the surface morphology of a manufactured product as far as a correlation with a particular function, property or application is concerned. The efficiency of this statistical method is illustrated in this paper describing the relationships between the brightness level and the surface roughness of cold-rolled low carbon steel strips; the relevance of 100 or so roughness parameters was studied via a computer software we have been upgrading for a few years. (C) 2003 Elsevier Science B.V All rights reserved.

Abstract: Because of the various industrial and scientific interests, a proliferation of roughness parameters, possibly running into hundreds, has been developed to describe the different kinds of surface morphology with regard to specific functions, properties or applications. In spite of this of roughness parameters, there is still no complete comprehensive account for the relevance of all these parameters. Hence, the selection of a roughness parameter for describing and/or modelling a surface morphology is very often subjective. Thanks to a methodology based on the Computer-Based Bootstrap Method (CBBM), the experimental results of this study exhibit the major influence of the order parameter as far as the relationships between the surface morphology of Ti6Al4V substrates and the in vitro cell adhesion of human osteoblasts are concerned. The lower is the value of this roughness parameter that characterises the surface texture, the better is the cell adhesion. Moreover, the cell adhesion seems to be rather affected by the surface morphology than by the surface chemistry in the experimental conditions of our work.

Abstract: Depth of pits that propagate during a pitting corrosion process is an important characteristic of the damage of steels; the greater the depth, the more dramatic the damage. For evident reasons of safety and reliability of industrial installations, statistical procedures must be constructed to assess the maximum pit depth to perform proper maintenance from limited inspection data. This paper outlines a hew methodology to predict accurately the pit depth extreme value. related to a localized corrosion process independently Of the nature of the unknown parent distribution of the experimental data. Based on computer calculations and simulations, this methodology combines the Generalized Lambda Distribution (GLD) and the Bootstrap statistical methods. The GLD method was used in this study to determine a. modeled distribution that fits the experimental frequency distribution of pit depths produced on a ferritic stainless steel sample during an,accelerated corrosion test. This modeled distribution was used to generate, thanks to the Computer-Based Bootstrap Method (CBBM), simulated distributions of corrosion pit depths equivalent to the experimental one, An estimation of the mean with a 90% confidence interval of the maximum pit depth can be finally deduced not only for these simulated samples of equivalent surface size than the experimental one but also for a large scale installation.

Abstract: Composite coatings constitute a new class of materials, which are mostly used in mechanical and tribological applications as well as because of anti-corrosion properties. Laser surface alloying of 35NCD16 bainitic steel and iron substrates with silicon powder was studied. It is principally the nature of substrate, which determines the thickness of heat affected zone (HAZ) and melted zone (MZ). The MZ was found to be homogeneous in composition and concentration in alloying elements and mainly constituted of rapid solidified structure. Depending on carbon and Si contents, residual stresses and phase transformations, the superficial zone could be cracked. The cracking phenomenon is observed in the MZ of iron substrate whenever the Si deposit thickness and when more than 20 mum of Si powder is alloyed with steel substrate. Hardness and cracking depend on residual stress level. The result is a superficial hardness increase up to a maximum and then a decrease with apparition and generalization of cracks associated to reduction of stress level.

Abstract: This paper outlines a new compression algebra formalism for analysing the relations between entropy, negentropy and data reduction, where reduction is described as a dimension (D) of a subspace in the initial system. First used to analyse a random system with different states, this formalism showed that there exists an isomorphism between the system entropy and its dimension (D) that becomes a random value. Applied to a physical system, we show that D well characterises the diffusion rate law of coarsening processes and particularly the different stages of diffusion with respect to time, i.e. a linear relation in liquid-solid phase, a power law in solid-solid diffusion and a constant value at equilibrium. A relation between D and the fractal dimension is shown on a grain with self-similar fractal structure submitted to a diffusion process. D could be an efficient parameter to quantify the influence of a variable in the dynamics of a physical system and it is particularly helpful in the research of invariant parameters. (C) 2003 Elsevier Science Ltd. All rights reserved.

Abstract: Hardness measurements of paint coating deposited on galvanised steels used for domestic appliance housing were performed by different techniques depending on the applied load: Vickers ultra-microhardness (0.4-100 mN), Vickers microhardness (0.05-20 N) and Vickers macrohardness (50-1200 N). The Jonsson and Hogmark model based on the area law of mixture used to characterise the composite (substrate+film) response hardness is not consistent with the experimental results. The authors propose modifications, taking into consideration the very strong plastic deformation of the film under the applied load. These modifications are verified by metallographic observations of the deformed coating near the indentation print and introduced in two other models. The hardness variation with the indentation depth is studied and therefore a guideline is proposed to improve the mar resistance of organic coatings. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: The aim of this paper is to present how to make the most of the recent and powerful statistical computer-based bootstrap method (CBBM) in roughness studies. This work shows that this statistical method can help to determine quantitatively, and without preconception, the most relevant roughness parameter that characterises the surface morphology of a manufactured product as far as a correlation with a particular function, property or application is concerned. The efficiency of this statistical method is illustrated in this paper describing the relationships between the brightness level and the surface roughness of cold-rolled low carbon steel strips; the relevance of 100 or so roughness parameters was studied via a computer software we have been upgrading for a few years. (C) 2003 Elsevier Science B.V All rights reserved.

Abstract: Describing and modelling a machined surface require the selection of relevant roughness parameters. However, this selection is difficult since a machined surface morphology can be described by a large number of roughness parameters. This investigation focuses on the roughness of metallic surfaces taking for two applications: a) the description of machined surface morphologies produced by grinding b) the relationships between machined surface morphologies (grinding or cold-rolling) and their brightness level when irradiated by the white light beam of an optical glossmeter used for industrial surface quality control. For each application, the aim is to determine, from an objective quantitative point of view, the relevance of one hundred or so surface roughness parameters. To reach this objective, a specific software program has been developed to determine a ranking of relevance thanks to the calculation of a computed statistical index of performance. The statistical results of this study show that the fractal dimension estimated by an original method is the most relevant roughness parameter to describe the surface morphology after grinding or rolling. Because of this relevance, this roughness parameter has also to be taken into consideration in models showing the interactions between machined surfaces and an optical wave. The methodology presented in this study can be a useful tool in the quality control phase to keep under control the fabrication process parameters of manufactured objects in industrial environments. (C) 2003 Kluwer Academic Publishers.

Abstract: A new method to calculate the fractal dimension called Slit island average normalised autocorrelation method is proposed and validated on deterministic and stochastic fractal curves. This method well estimates the fractal dimension and does not require self affinity or self similarity of the surface or the interface. Then fractal grains are constructed by an iteration function system (IFS) method and a simulation of grain growth is carried out by the Monte Carlo method. It is shown that the fractal dimension of the grain boundaries decreases with the annealing time and follows a sigmoidal equation that converges to unity. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: Surface roughness has been shown to be an influencing parameter for cell response. In this experience we attempted to compare the effect of roughness organization of Ti6Al4V or pure titanium substrates on human osteoblast (hOB) response (proliferation, adhesion). Surface roughness was extensively analyzed at scales above the cell size (macro-roughness) or below the cell size (micro-roughness) by calculation of relevant classic amplitude parameters (Ra, Rt) and original frequency parameters (Order, Delta). We developed a new process to prepare isotropic surfaces (electro-erosion), which were compared to isotropic surfaces obtained by polishing and anisotropic surfaces obtained by machine-tooling. The hOB response on electro-eroded (EE) Ti6Al4V surfaces or pure titanium (Ti) surfaces was largely increased when compared to polished or machine-tooled surfaces after 21 days of culture. Moreover, the polygonal morphology of hOB on these EE surfaces was very close to the aspects of hOB in vivo on human bone trabeculae. By a complete description of the surface topography of EE surfaces, we concluded that when the topography was considered below the call scale, hOB appreciated their isotropic smooth aspect, although when the topography was considered above the cell scale they appreciated their rough isotropic 'landscape' formed by many 'bowl-like nests' favouring cell adhesion and growth. Electro-erosion is a promising method for preparation of bone implant surfaces, as it could easily be applied to preparation of most biomaterials with complex geometries. (C) 2002 Elsevier Science Ltd. All rights reserved.

Abstract: A new method of characterisation of the diffusion is proposed by analysing the results obtained by data compression. By analysing the results of the diffusion process using a Monte Carlo method, it is shown that the ratio of compression could be a good parameter to quantify the rate of the dynamic process and the time to reach the equilibrium. If an accurate method of data compression is used, then some power laws can be found to characterise the diffusion time with both the size of the system and the increase in entropy. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We present a new parameter to quantify the order of a surface. This parameter is scale-independent and can be used to compare the organization of a surface at different scales of range and amplitude. To test the accuracy of this roughness parameter versus a hundred existing ones, we created an original statistical bootstrap method. In order to assess the physical relevance of this new parameter, we elaborated a great number of surfaces with various roughness amplitudes on titanium and titanium-based alloys using different physical processes. Then we studied the influence of the roughness amplitude on in vitro adhesion and proliferation of human osteoblasts. It was then shown that our new parameter best discriminates among the cell adhesion phenomena than other parameters (average roughness (Ra...)): cells adhere better on isotropic surfaces with a low order, provided this order is quantified on a scale that is more important than that of the cells. Additionally, on these low ordered metallic surfaces, the shape of the cells presents the same morphological aspect as that we can see on the human bone trabeculae. The method used to prepare these isotropic surfaces (electroerosion) could be undoubtedly and easily applied to prepare most biomaterials with complex geometries and to improve bone implant integration. Moreover, the new order parameter we developed may be particularly useful for the fundamental understanding of the mechanism of bone cell installation on a relief and of the formation of bone cell-material interface. (C) 2002 Published by Elsevier Science B.V.

Abstract: Various surface treatments have been developed to increase the clinical performance of titanium-based implants. Many in vitro tests have been carried out on substrates with varied surface topography for a complete understanding of osteoblasts. In previous research, we made the observation that surface roughness must be taken into account, not only in terms of amplitude but also in terms of organization. In this study, we tested the adhesion and proliferation of human primary osteoblasts on grooved titanium surfaces with various amplitudes and organizations of topography. The roughness was described at a scale above (macro-roughness) or below (micro-roughness) the cell size. We observed better orientation and proliferation of human osteoblasts on surfaces with a micro-roughness characterized by a lower Order (parameter describing the organization of topography) and by a higher Ra and Rz (parameters describing the amplitude of topography). It appears that cultured human osteoblasts prefer surfaces with relatively high micro-roughness amplitude and with a low level of repeatability. (C) 2002 Wiley Periodicals, Inc.

Abstract: Drastic aseptic conditions are necessary in implantological treatments. A good sterilizing procedure of the specific instrumentation, like drills, is based on an efficient cleaning. Because of their design, the cleaning of drills is a real challenge. The aim of this investigation is to evaluate two different cleaning procedures usually used by implantologists. One is based on a manual cleaning, the other on an ultra-sonic cleaning. The instrument observed by scan-electron-microscope, is a I.T.I. system drill. The results show the superiority of the ultra-sonic cleaning. The manual cleaning is especially ineffective on the inside and the cutting part of the drill. Even if ultra-sonic cleaning is definitely a better procedure, it has to be improved. A extensive study should be conducted to optimize the cleaning parameters, if not, single-use drill should be definitely preferred by implantologists.

Abstract: This paper presents a new method of calculating the fractal dimension of surfaces as well as a correction method which improved the results. To test its efficiency, the algorithms have been applied to stochastic surfaces of mathematical functions with known fractal dimensions and compared with the oscillation and the structure method. Better results have been found. This method, called ANAM, has been used to characterize the roughness of orthopaedic metallic substrates (Ti6A14V alloy) in relation with human osteoblast adhesion. It has then been shown that the fractal dimension parameters correlated statistically with proliferation of cells, corresponding to a lower adhesion on less organized surfaces. The significant correlation observed between fractal dimension parameters and cell adhesion therefore adds a new concept to substratum roughness influence on cell behaviour. (C) 2001 Elsevier Science Ltd. All rights reserved.

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Abstract: This study deals with the mechanical behavior of galvanized, interstitial free (IF) steel in air and sodium chloride water. Tensile tests conducted in air at different strain rates lead in general to a ductile behavior. It can become brittle when tested in a NaCl solution at particular strain rate values. Fractographic analysis shows a brittle fracture similar to hydrogen embrittlement (AE). A detailed analysis taking into account both the individual mechanical strength of the phases on the coating as well as the electrochemical reaction between Zn and water allow the explanation of this embrittlement. Hydrogen can be produced and can penetrate the cracks formed inside the intermetallic phases of the coating during loading, thus, reaching the steel substrate. The HE of the IF steel, assisted by zinc dissolution and galvanized coating low toughness, appears to be the cause of the loss of ductility observed in the presence of specific environmental conditions, strain rates and morphologies of the coating. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: We quantitatively evaluated the adhesion of human osteoblasts on orthopedic metallic substrates (Ti6Al4V alloy) with various surface roughnesses at several times after inoculation and studied its correlation with qualitative changes in the expression of adhesion proteins and with parameters extensively describing the surface topographies. Cells were orientated in a parallel order on polished surfaces. This orientation was not affected by residual grooves after polishing. On sandblasted surfaces the cells never attained confluence and had a stellate shape, and the cell layer had no particular organization. Extracellular matrix (fibronectin, type I collagen, osteopontin) and cytoskeletal protein (actin, vinculin) orientation reflected the cell layer organization. In our experiment human osteoblasts expressed alpha 3 beta 1 integrin but not alpha 2 beta 1 integrin. In addition to currently analyzed roughness magnitude parameters, we calculated roughness organization parameters (fractal dimension parameters) of the substrates. We observed lower adhesion and proliferation on less organized surfaces (i.e., sand-blasted ones). The significant statistical correlation observed between fractal dimension parameters (describing surface roughness organization) and cell parameters adds a new concept to the studies of substratum roughness influence on cell behavior. An attempt at modelization of the cell-surface interaction was made that includes the influence of fractal dimensions parameters. (C) 2000 John Wiley & Sons, Inc.

Abstract: Excessive wear of polyethylene in total replacement hip prostheses elicits deleterious biologic reactions and may be thus a limiting factor that compromises the long-term performance of these devices. This study is based on the report of two clinical failures of total hip prostheses with metallic femoral heads and polyethylene acetabular cups. The investigations reveal that foreign bodies (titanium fibermesh pieces) can migrate into the joint space of total hip prostheses and participate in abrasive third-body wear of the polyethylene cups. This excessive wear of polyethylene enhanced by the modification of the metallic counterface roughness is likely to induce the early loosening of the devices. (C) 2000 Kluwer Academic Publishers.

Abstract: The effect of cathodically charged hydrogen in austenitic stainless steels with or without nitrogen addition was studied by microhardness experiments carried out on single crystals. With our experimental conditions, it can be demonstrated that hydrogen penetration depth is near 25 mu m and induced a higher apparent hardness, In fact, the hardness improvement is mainly a consequence of the residual stresses induced by hydrogen diffusion. By studying the variation of hardness with the reciprocal length of the indentation print obtained with load varying between 0.5 and 200 N, it was observed that the slope (VHN vs 1/d) only depends on the aging time.

Abstract: The fractal aspect of different kinds of music was analyzed in keeping with the time domain. The fractal dimension of a great number of different musics (180 scores) is calculated by the Variation method. By using an analysis of variance, it is shown that fractal dimension helps discriminate different categories of music. Then, we used an original statistical technique based on the Bootstrap assumption to find a time window in which fractal dimension reaches a high power of music discrimination. The best discrimination is obtained between 1/44100 and 16/44100 Hertz. We admit that to distinguish some different aspects of music well, the high information quantity is obtained in the high frequency domain. By calculating fractal dimension with the ANAM method, it was statistically proven that fractal dimension could distinguish different kinds of music very well: musics could be classified by their fractal dimensions. (C) 2000 Elsevier Science Ltd. All rights reserved.

Abstract: Proliferation and adhesion of mouse (MC3T3-E1) osteoblastic cells and primary human osteoblastic cells were carried out on Ti6Al4V titanium alloy samples with varied surface roughnesses. Mechanically or manually polished surfaces were prepared to produce respectively non-oriented or oriented residual polishing grooves. Sand-blasted surfaces were prepared using 500 mu m or 3 mm alumina particles. Surface roughness parameters showed a negative correlation in comparison to proliferation and adhesion parameters. X-ray microprobe chemical surface microanalysis showed complete disturbance of the surface element composition of the Ti6Al4V alloy following sand-blasting treatment. An AlOx-enriched layer was observed on sample surfaces. This may lead to the suspicion that the concomittant effect of surface roughness amplitude and AlOx surface concentration has an effect on osteoblastic cell proliferation and adhesion. These findings show the significance of chemical surface analysis after any surface treatment of titanium-based implants before any biological use. (C) 2000 Elsevier Science Ltd. All rights reserved.

Abstract: A surface morphology can be described by numerous surface parameters (arithmetic average roughness R-a, root-mean square roughness R-q, number of peaks per inch CTE_PC, correlation length L-ac, fractal dimension Delta...). The main purpose of this study is to describe the relationships between surface morphology induced by a cold-rolling process and the brightness level of low carbon steel strips. Coupling the Bootstrap theory with the conventional theory of linear correlation analysis, it is shown that : a) the commonly used amplitude and frequency parameters (R-a, R-q, CTE_PC, L-ac) are not the most relevant ones to describe the surface morphology of cold-rolled strips of low carbon steel with regard to their brightness level, b) fractal dimension estimated by the ANAM (Average Normalised Autocorrelation Method) is the most relevant parameter, c) the brightness level of a cold-rolled low carbon steel strip increases linearly with the fractal dimension of its surface. A critical discussion on the relevance of surface parameters with regard to the existing models is proposed taking into consideration our experimental results.

Abstract: Excessive wear of polyethylene in total replacement hip prostheses elicits deleterious biologic reactions and may be thus a limiting factor that compromises the long-term performance of these devices. This study is based on the report of two clinical failures of total hip prostheses with metallic femoral heads and polyethylene acetabular cups. The investigations reveal that foreign bodies (titanium fibermesh pieces) can migrate into the joint space of total hip prostheses and participate in abrasive third-body wear of the polyethylene cups. This excessive wear of polyethylene enhanced by the modification of the metallic counterface roughness is likely to induce the early loosening of the devices. (C) 2000 Kluwer Academic Publishers.

Abstract: This paper presents a original statistical method based on a resampling technics called the Bootstrap to determine the different stages on the Fatigue Crack Growth Rates (FCGR). This method, gives some confidence intervals on the FCGR coefficients and a set of possible values describing a PDF. We proposed to analyse by a Bootstrap technique the effect of the stress ratio on the low fatigue crack growth rates for A508-2 forged steel tested in room temperature at the frequency of 160 Hz.

Abstract: The purpose of the present work was to investigate the mechanical behavior of metaphosphate glass coatings of the Na2O-CaO-P2O5 system on steel substrates. These coatings may be used as thermal barriers or to give anti-corrosion protection. Coacervates of glasses under consideration were obtained by a coacervation process, from Graham's salt and deposited on aluminized steel substrate. Chemical composition of coacervate phases was improved by the choice of cations and addition of a filler to reduce the residual stresses in glass metal joints due to the thermal expansion coefficient mismatch. The chemical and mechanical properties of both the coating and the interface were studied by energy dispersive spectrometry (EDS) and hardness measurements. It was shown that an alumina layer is formed by the reaction between the phosphates compounds during curing. This layer acts as a barrier for the iron diffusion. The fracture toughness of the glass coating was investigated by Vickers indentations. Inasmuch the cracks are of the Palmqvist form, the Evans and Charles formula holds for calculating K-IC. A value near 0.85 MPa m(1/2) was found for all the glasses investigated. Residual stress distribution was calculated. The glass coating was in compression and residual stresses were reduced by the interlayer formation. A good adhesion was found since cracks produced by indentation near the glass steel interface propagated in the coating rather than along the interface. (C) 1999 Kluwer Academic Publishers.

Abstract: The statistical dispersion in Vickers hardness measurements is discussed in order to check the reliability of hardness measurements. Several indentations were made under the same nominal conditions on a hardness standard. This was repeated for different loads. The distribution of diagonal lengths of: indentation prints is found to be of Gaussian type. From the distribution function of the indentation lengths, the probability density function of the hardness is derived For the general case of several indentation measurements. The mean value and variance of hardness are compared with results based on Gaussian statistics. From this comparison. it follows that statistical analysis relying upon Gaussian distributions can be carried out within a given confidence level which depends on the number of indentations. A method is presented to calculate the number of indentations needed to achieve a certain level of accuracy. (C) 1999 Elsevier Science S.A. All rights reserved.

Abstract: Zinc coating is formed by heterogeneous assembly of phases in which mechanical properties greatly differ. In the galvanizing process the great difference between the linear thermal expansion of the iron substrate and the Zn has proven to be the source of important residual stresses. The primary objective of this paper is to determine the residual stresses which promote crack formation and deterioration of corrosion resistance. Because direct determination by x-ray diffraction has been difficult, three other methods are proposed. The first one led us to calculate an average stress by measuring the variation of crack length with applied load resulting from a Vickers small indentation. The second is an application of the Timoshenko's bimetallic strip method based on the difference in thermal expansion coefficients. The third is deduced from the variation of the curvature of one-face galvanized specimens. These results are compared and the homogeneous value of residual stresses are shown.

Abstract: Dealing with fatigue crack propagation, this paper aims to report on a statistical method to determine the coefficients C and n of the Paris relationship and the range along which the equation holds. The Probability Density Function (PDF) of those coefficients was calculated using a bootstrap technique. Then a 3-segment piece-wise linear regression FCGR was used to modelize the whole fatigue crack growth data. The statistical results are finally applied on a classical fracture mechanic problem to obtain the PDF lifetime prevision. The PDF lifetime obeys a Gaussian or lognormal PDF which depends on the variance of the initial crack's length. (C) 1999 Elsevier Science Ltd. All rights reserved.

Abstract: Zinc coating is formed by heterogeneous assembly of phases in which mechanical properties greatly differ. In the galvanizing process the great difference between the linear thermal expansion of the iron substrate and the Zn has proven to be the source of important residual stresses. The primary objective of this paper is to determine the residual stresses which promote crack formation and deterioration of corrosion resistance. Because direct determination by x-ray diffraction has been difficult, three other methods are proposed. The first one led us to calculate an average stress by measuring the variation of crack length with applied load resulting from a Vickers small indentation. The second is an application of the Timoshenko's bimetallic strip method based on the difference in thermal expansion coefficients. The third is deduced from the variation of the curvature of one-face galvanized specimens. These results are compared and the homogeneous value of residual stresses are shown.

Abstract: The relation between quantities resulting from fracture energetics and those describing the geometrical structure of a surface is of fundamental importance in investigating the physical nature of a fracture. Since the Mandelbrot's works, fractal geometry has been extensively applied to characterize the roughness of fracture surfaces and to correlate it with mechanical properties. We will first make a survey of several experimental methods to determine the fractal dimension, D-f, according to the roughness of fracture surfaces. Then we will discuss the experimental results reported in the bibliography and the relations inferred to correlate the fractal dimension of fracture surfaces with mechanical properties, These results show that a general conclusion cannot easily be drawn. Some works report a positive variation of fracture toughness along with D-f and others a negative one. To other researchers, there is no correlation and the fractal dimension of the fracture surface is a universal constant. The discrepancy between these results is related to the methods used to calculate the fractal dimension. Theoretical and experimental problems exist and have to be solved before correlating the fractal dimension to mechanical behaviour. (C) 1998 Elsevier Science Ltd. All rights reserved.

Abstract: In this study we investigated the relationship between the coefficients of the Norton law for low-stress high-temperature deformation results of different materials reported in the literature. These coefficients are interrelated and it is shown that this relation can be theoretically deduced from the assumption of a variation of the activation area with the inverse of the effective stress (i.e, a variation of the activation energy with the logarithm of the stress). As a consequence, all the straight lines In(strain-rate)-In (stress) intersected at the same point, named the pivot point. This pivot point is characteristic of each material. Such a correlation can be found in the field of the mechanics of materials when a power-law relation holds. (C) 1998 Kluwer Academic Publishers.

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Abstract: Among the formulas used to represent the cracking speed with respect to the stress amplitude, the Paris formula: da/dN = C Delta K-m is certainly the most widespread, Even though many studies have tried to find a relationship between the coefficients m and C of this equation, controversies still exist. We show that this relation exists but does not have the general character given to it in the literature, and that it depends on the material, We then study the influence of various factors: temperature, heat treatments and the load factor, before trying to make a physical interpretation and to show the practical interest of this approach.

Abstract: In this study we investigated the relationship between the coefficients of the Norton law for low-stress high-temperature deformation results of different materials reported in the literature. These coefficients are interrelated and it is shown that this relation can be theoretically deduced from the assumption of a variation of the activation area with the inverse of the effective stress (i.e, a variation of the activation energy with the logarithm of the stress). As a consequence, all the straight lines In(strain-rate)-In (stress) intersected at the same point, named the pivot point. This pivot point is characteristic of each material. Such a correlation can be found in the field of the mechanics of materials when a power-law relation holds. (C) 1998 Kluwer Academic Publishers.

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Abstract: The in vitro tests on cell viability reveal a favorable position for steel and hydroxyapatite (HA)? However, the roughness induces a negative effect on cell proliferation. Sandblasting of the stainless steel considerably decreased cell number compared with the polished substrate. HA showed a better percentage of proliferation in spite of the surface effect compared with controls. For in vivo biocompatibility, intramuscular implants revealed localized inflammatory reactions for the HA treated stainless steel but nor for the untreated alloy.

Abstract: An in vitro study has been carried out in different cell systems to determine the biological response of TiNb30 alloy before and after a surface treatment with hydroxyapatite (HA) and tricalcium phosphate (TCP) by the sol-gel method. TiNb30 pure Ti induce favorable cell viability with respect to pure Ni showing a high cytotoxic effect. After surface treatment with HA or HA-TCP mixtures, no difference in cell proliferation can be observed between amorphous and cristalline forms. However, HA decreases (75 +/- 15%) and HA-TCP mixtures increase (133 +/- 11%) significantly cell proliferation compared with controls.

Abstract: The extensive use of appropriate coatings to improve wear resistance, friction coefficient, electrical properties and protection from corrosion has stimulated a growing interest in their mechanical properties, and especially hardness measurements. The objects of this study are to compare the predictions obtained using different models and to understand why it is often reported that the Jonsson and Hogmark model does not hold for indentation prints less than the coating thickness. Methods were reviewed for calculating the composite hardness, and it was found that the simplifications made by the authors are not always valid. By taking in account all the terms of the equations of Jonsson and Hogmark, it was found that the relation between the hardness and the reciprocal length of the indentation print is not linear and depends on the ratio between the film thickness and the indentation print, as well as the variation of the hardness of the substrate and the film with the applied load. Comparison of the Burnett and Rickerby experimental data with the modified model led to very good agreement.

Abstract: The paper aims to evaluate the fractal dimension of one-variable function graphs based on the topological space L(alpha). A good convergence of calculated fractal dimensions can be found by using curves whose fractal dimensions are known. The results obtained by ANA or ''conventional methods'' are improved by an estimation of discretization errors. An algorithm has been derived from the algebraic relations and converges rapidly. This algorithm could also be used to evaluate the fractal dimension of measured profiles and to screen multifractals.

Abstract: The purpose of this investigation was to study the load dependence of the microhardness, typically in the range 5-500 gf. This well known phenomena is called the indentation size effect (ISE) and was investigated for two sets of specimens: titanium and aluminium alloys. Variation of the hardness with applied load was first compared with various existing models and the surface profile, near the indent, was measured by confocal microscopy. The formation of pile-ups near the indentation print led to the correction of the indent diagonal which is found to fit well with our experimental data as well as with other results in the literature. For the materials investigated, the ISE effect is an artefact, i.e. the variation of hardness with the applied load is only a consequence of the variation of the contact surface between the specimen and the indenter.

Abstract: Dental impressions can increase the transmission of microorganisms and infections. The purpose of this study was to assess the influence of three disinfectant solutions on the dimensional accuracy of seven elastomeric impression materials. Impressions of a test block were either left untreated (controls) or treated by immersion in a disinfectant solution, Measurements were taken on die stone replicas of the impressions. Comparisons mere made between (1) the measurements for the variations in the nontreated impressions and those for the treated impressions and (2) measurements for the treated impressions and the test block. Results indicated that the aminoamphoteric agent or glutaraldehyde derivative-based solutions created little change in relation to the initial dimensional accuracy of the impression products. However, the sodium hypochlorite solution often leads to expansion by comparison with controls. By comparison to the test block, this expansion then makes it possible in most cases to obtain better dimensional accuracy than initially. Within the limits of this study this expansion could lead to an improvement in clinical fixed prosthodontic procedures.

Abstract: A new method is proposed in order to improve the surface properties of titanium alloys used in biomedical applications. This paper considers the surface modification that appears after the reaction between metaphosphate glasses and titanium alloys (TA6V). The structural characterization of this material has been realized by several spectroscopic methods of investigation such as scanning electron microscopy, energy-dispersive X-ray analysis and wavelength-dispersive spectroscopy. Measurements of Vickers microhardness exhibit a correlation between the phosphorus profile and the evolution of hardness of the modified titanium alloy surface. The relative increase in the Vickers microhardness is about 65%. By application of the composite model, the absolute hardness of the coating was found to be HV0 = 550.

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Abstract: A critical assessment has been performed by compiling experimental data concerning the temperature dependence of stage II fatigue crack growth. For aluminium alloys, high strength steels, austenitic stainless steels and superalloys, the power coefficient, m, for the Paris relationship is temperature dependent, and all ln(da/dN) vs ln(DELTAK) curves cross at one point, designated as the pivot point (PP), which is a material-dependent parameter. The assumption is made that PP corresponds to a transition point for the fatigue crack growth mechanism.

Abstract: Corrosion resistance of a galvanized steel depends on the adhesion and mechanical characteristics of intermetallic components of the protective layer formed. To understand better the deterioration process of this layer, we measure the toughness of the delta phase, the most fragile of the constituents, using the Vickers hardness test. After a first bibliographic part, we study the geometry of cracks and apparent toughness with respect to experimental galvanizing conditions. We also show the residual stresses in traction that are partly responsible for the fragility of the delta phase.

Abstract: The effect of load ratio on the stage II fatigue crack growth rate was analysed in relation to the empirical equation m = a+b In C between the coefficients of the Paris law. From experimental data found in the literature, a relationship, dependent on the material, was developed to take into account the influence of load ratio on the coefficients a and b. It was shown that this relationship is related to the transition between ductile striation and cyclic cleavage or other additional modes of propagation.

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Abstract: Corrosion on orthopaedic implants has been studied. Twelve intramedullary nails and twelve osteosynthesis plates were implanted up to eight and thirteen years, respectively. Analysis of biological fluids from all patients was carried out and revealed high concentrations of nickel and chromium that correlated to the implantation time. All implants were corroded by both crevice and intergranular corrosion. Intergranular corrosion is related to mechanical and heating treatments. Crevice-like corrosion is probably enhanced by sulphur present in amino-acids. Electronic probe analysis shows the reaction study between both sulphur and nickel and sulphur and chromium. These results are compared to the metal distribution in body fluids. After a certain incubation time the corrosion accelerates as is characteristic for crevice-like corrosion processes. Studies of the distribution rate of two Ni-Fe-Cr dental alloys in a cell culture system give similar results: metal-ion release increases with the exposure time.

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