In this work, the influence of martensite volume fraction, load and attack angle on hardness, friction and wear of ferrite and martensite phases of a dual-phase microstructure is investigated through nanoindentation and scratch tests with conical tips. Friction coefficient increases with the attack angle and is always higher for ferrite than for martensite. For martensite phase, friction coefficient increases and wear resistance decreases as martensite volume fraction increases. As the attack angle increases, wear mechanism changes from ploughing to cutting for martensite. Experimental results correlate to the Axén & al. approach based on the Equal Pressure model.

Galling resistance of different stainless steels was investigated using the ASTM G98 standard. Galling resistance is often only addressed via galling threshold but an increasing number of studies nowadays focus on galling severity. During these studies, three galling categories have recently been identified in stainless steel, based on surface topography evolution, SEM observation, and local chemical analyses. These three categories of galling, namely tolerant, moderate galling, and severe galling have been depicted but still poorly understood. The objective of this work is to determine the relationships between the microstructure, its evolution, and the galling response of the different materials. The authors aim to clarify these relationships and propose an explanation of the consequences of galling on the microstructure of the galled samples. A correlation between the galling severity and the subsurface plastic behaviors is proposed. In particular, the mobility of dislocations in close surface is investigated as a plausible parameter determining galling severity.

This paper investigates the characterization and numerical modeling of the elastic behavior of the human humerus bone using a recently developed micromechanical approach coupled to nanoindentation measurements. At first, standard three-point bending experiments were conducted under low static loading, using several humerus diaphysis in order to identify the apparent elastic modulus of the bone in static regime. Then, a drop tower impact experiment was used on the same set of humerus diaphysis specimens, in order to assess the elastic modulus in dynamic regime. These measurements will be used as reference bases for comparison purpose. The originality of this work, lies in the coupling between a two-phase micromechanical approach based on Mori-Tanaka homogenization scheme for cylindrical voids and nanoindentation measurements of the elastic modulus of the bone matrix phase. This model has been implemented using a user defined material subroutine VMAT in ABAQUS© Explicit code. The bone mechanical response prediction using the proposed methodology was validated against previous standard experimental data. Finally, it was shown that the numerical predictions are consistent with the physical measurements obtained on human humerus via the good estimation of the ultimate impact load.

This paper focuses on the galling mechanisms occurring in stainless steels and aims to provide a better comprehension of the effects of microstructure on galling resistance. Five stainless steels are studied in this paper, namely Nitronic60, AISI660, 316L, 316LN (austenitic stainless steels) and Uranus45 N (duplex austenite-ferrite). Both surface topography and in-depth microstructure are characterized in order to determine the consequences of galling apparition. Experimental investigations at macroscopic and microscopic scales show that galling can occur following several mechanisms. Galling leads to either adhesive wear spots randomly distributed on the surface (tolerant galling), adhesive wear initiated on the periphery of the pin (moderate galling) or abrasive wear and smearing (severe galling). Depending on these categories, the galling threshold and severity are highly variable. Studying these specific mechanisms can help us predict and eventually increase galling resistance for a given material couple. Thus, several microstructural investigations have been performed in order to discuss about the possible origins of these galling categories.

Galling mechanisms have been investigated in several stainless steels following ASTM G98 test method. Galled samples have been studied by both surface and in depth analysis. This characterization leads to the determination of new galling categories.

Polymer coatings exhibiting photodynamic bacterial inactivation properties have been successfully engineered. Such coatings were obtained by photoinduced crosslinking of a PEG-diacrylate monomer associated with the eosin Y dye which was used as both a radical photoinitiator and an antibacterial agent. A dual curing process was followed by combining compatible and solvent-free polymerization mechanisms, i.e. Aza-Michael reaction and free-radical polymerization in the presence of amines. The kinetics evolution of the photopolymerization process was followed using in situ Fourier transform infrared spectroscopy, allowing for the elucidation of the underlying mechanistic pathways. The influence of eosin Y and amines on the thermal and mechanical properties of the films was evidenced and discussed in terms of crosslinking chemistry. The antibacterial properties of the coatings against two different strains (Escherichia coli and Staphylococcus aureus) were evaluated on short and long terms, revealing that eosin confers both photodynamic inactivation and antimicrobial properties to the films. These coatings are therefore particularly promising for disposable medical devices.

Synthesis of antibacterial coatings derived from epoxidized soybean oil and curcumin for the efficient inhibition of bacteria proliferation.

This article assessed the roughness induced by ultrasonic shot peening. Surface properties of AISI 316L steel specimens were modified through the variation of ultrasonic shot-peening parameters (shot material, shot diameter, sonotrode amplitude vibration and coverage). Each surface was characterized using fifty surface roughness parameters and two types of robust Gaussian filter (low pass and high pass) associated with twenty one cut-off lengths. For each type of processing parameter, the most relevant roughness parameter and its corresponding length scale and filter were found. A linear relationship was identified between the four ultrasonic shot-peening parameters and the mean density of furrows with a coefficient of determination equal to 0.97.

Quantification of the mechanical properties of cortical bone through life span models is an invaluable source of data for bone modeling and numerical simulations. This data allows the validation of different theories of bone remodeling and corroborates the interactions between different microstructural components. However, human life span models are difficult to obtain due to ethical and manipulation samples issues. In this study, the Wistar rat life span model was used to quantify the evolution of the mechanical properties with ageing. The life span covers from growth until senescence with samples of 1, 4, 9, 12, 18 and 24 months old. The surfaces of the samples were ground and polished in order to expose all their microstructural features. The experimental data was obtained from nanoindentation tests by using a specific indentation protocol allowing the quantification of several mechanical properties from a single test [1,2]. The mechanical properties include elasticity, viscoelasticity, plasticity and viscoplasticity. From the experimental data, predictive models were computed to estimate the values of the mechanical properties at different ages. Two types of predictive equations for fitting the experimental data are proposed in this work. The first type is based on a growth model inspired in the Gompertz curve [3]. That growth model describes the evolution of the results as a function of the age. It is composed of and exponential function integrated by an asymptotic parameter, the growth rate and an adjusted factor. The second type of equations was calculated using multivariable linear regression. For that purpose, previous physical-chemical properties measured in a similar set of bone samples [4] were correlated to the mechanical properties. Then, the best-correlated parameters were used to perform multivariable linear regressions. Results show that both predictions equations are useful to describe the mechanical behavior of bone. However, supported on the determination coefficient, the equations computed from physical-chemical properties using multivariable linear regressions are more accurate that those obtained from Gompertz model. S. Jaramillo-Isaza, P.-E. Mazeran, K. El-Kirat and M.-C. Ho Ba Tho

A novel method is developed to improve the accuracy in determining the mechanical properties from nanoindentation curves. The key point of this method is the simultaneous statistical treatment of several loading curves to correct the zero point error and identify the material properties considering size effects. The method is applied to four sandblasted aluminum-based specimens with different surface roughness. A linear relationship is obtained between the standard deviation of the initial contact error and the roughness which highlights the effect of the surface roughness on the reproducibility of the indentation curves. Moreover, the smaller standard deviation of the hardness given by the method confirms the importance of considering the initial contact error for an accurate determination of the material properties.

"Effects of bone density in the time-dependent mechanical properties of human cortical bone by nanoindentation." Computer Methods in Biomechanics and Biomedical Engineering, 17(sup1), pp. 34–35Keywords:: cortical bonedensitynanoindentationtime dependent AcknowledgementsThis project is co-financed by the European Union engaged in Picardie with the European Regional Development Fund and CNRS (grant Collegium UTC CNRS INSIS).

In this paper, precision hard turning is proposed for the finishing of the AISI 52100 bearing components to improve rolling contact fatigue life. This finishing process induces a homogenous microstructure at surface and subsurface layers. Fatigue life tests performed on a twin-disk machine show that rolling contact fatigue life increases as Ra value decreases. The bearing components reached 0.32 million cycles for Ra=0.25μm and 5.2 million cycles for Ra=0.11μm. In comparison, the bearing components achieved 1.2 million cycles with grinding (Ra=0.2μm) and 3.2 million cycles with grinding followed by honing (Ra=0.05μm) respectively.

Nanoindentation is a widely used method for determining mechanical properties, such as hardness, and elastic modulus.Nevertheless, in the case of viscous materials, the time dependent response of the material generates a bulge on the unloading curve that leads to incorrect values of the contact stiffness and thus of the mechanical properties.This paper presents methods developed on two viscoplastic materials (indium and indium-tin eutectic) to measure the elastic modulus and the creep exponent.To fix the bulge problem, we propose to realise cyclic indentations in order to obtain unloading and reloading curves.Results show that the lower parts of these two curves are similar because creep behaviour becomes negligible.Thus, the values of the modulus calculated from the initial slope of the reloading curve are constant and in good agreement with the values obtained from standard tensile tests.Furthermore, a method has been developed to measure the creep exponent.It consists of measuring the contact pressure as a function of the strain rate during hold load plateaux.Experiments show that the average value of the creep exponent (3.7 for the indium-tin eutectic and 7.6 for indium) does not depend on the loading conditions and are in good agreement with values obtained from tensile and torsion tests (3.7 and 7.6 respectively).

A new method is proposed for the quantification of macroscopic hardness and indentation size effect. This method is based on the simultaneous treatment of several nanoindentation loading curves which are located according to the gap between their shape and the one predicted by the Bernhardt law. By applying this method on stainless steel loading curves, it is shown that hardness error can be reduced by a factor of 2 compared with usual treatment methods. It is shown that only the simultaneous treatment of all the curves enables the good prediction of pile-up in the material.

An original treatment method is proposed to accurately determine by nanoindentation, the macrohardness and the indentation size effect (ISE). This method is applied to stainless steel specimens having different rough surfaces. It uses load versus indentation depth curves and is based on two main original features. The first one concerns the correction of the zero point (i.e. depth equals to 0) to minimise the scattering between experimental curves. The latter are all described by usual hardness equations and are shifted by minimising the distance from a leading curve chosen in a random way among the experimental curves. The second feature is the simultaneous treatment of all the nanoindentation curves to compute the macrohardness and evaluate the ISE. The standard deviation for the estimated macrohardness is small, which indicates the robustness of the approach. It is shown that using a single nanoindentation curve can alter macrohardness estimation because of a bad consideration of the ISE. To prevent this misinterpretation, the curves should be treated simultaneously instead of averaging results of separately treated curves. A correlation is identified between the standard deviations of both surface roughness and correction of zero point, which highlights the effect of surface roughness on the scattering of the indentation curves.

This article presents a multi-scale theory based on wavelet decomposition to characterize the evolution of roughness in relation with a finishing process or an observed surface property. To verify this approach in production conditions, analyses were developed for the finishing process of the hardened steel by abrasive belts. These conditions are described by seven parameters considered in the Tagushi experimental design. The main objective of this work is to identify the most relevant roughness parameter and characteristic length allowing to assess the influence of finishing process, and to test the relevance of the measurement scale. Results show that wavelet approach allows finding this scale.

An extensive statistical analysis is proposed to determine the best relevant roughness parameters as a function of spatial scales that affect adhesion on surfaces. The methodology is based on a multiscale decomposition of the roughness surface and is linked with adhesion measurements. This method is applied to study cell adhesion on a very wide range of roughnesses of titanium substrates (22 surfaces, the average roughness R-a from 1 to 21 mu m) tooled by an electro-erosion process and coated with a polyelectrolyte, that leads to identical surface chemistry. It is shown that the scale length of observation should be a few times the cell size to put into evidence the influence of the surface morphology on cell adhesion. It is observed that the adhesion is the lowest when the distance between the asperities of the roughness is near the cell size.

This contribution presents results which show the possibility to develop protective coatings from perhydropolysilazane (PHPS) on low carbon steel. In order to have an effective protection, the pyrolysis conditions should be carefully controlled. Nanoindentation tests allow characterizing the mechanical resistance of the coating after different pyrolysis conditions. The pyrolysis of coated samples has also been monitored by acoustic emission; the results show that the structural conversion of the coating from polymer to ceramics can be detected by acoustic emission.

One of the objectives in the field of tribology is to solve the mechanical stress-displacement problem involved by rough contacts. In our approach, the surface chosen is a 256-256 mu m(2) 3D sinusoidal shape (amplitude 4.5 mu m, wavelength 50 mu m) with an elastoplastic constitutive behaviour. The constitutive law combines isotropic and kinematic hardening and is experimentally identified from 316L steel sheets. The FEM deformable surface is crushed then uncrushed by a rigid flat surface: stresses, contact pressure and plastic cumulated strain are computed. We investigate the results sensitivity with respect to the level of in-plane refinement. At last, we conclude on some guidelines for 3D finite elements modelling of rough surfaces.

Sheet metal blanking is widely used in various industrial applications such as automotive and electrical rotating machines. When this process is used, the designer can be faced with several problems introduced by the change of the material state in the vicinity of the cut edge. In general, blanking operations severely affect mechanical and physical properties of blanked parts. To take into account these modifications during the part design, it is important to assess the influence of the process parameters on the resulting material properties. Previous experimental and numerical investigations of blanking process have been carried out, leading to the development and the validation of a finite element model that predicts the shape of the cut edge and state of the material. The study presented in this paper makes use of nanoindentation technique to improve the validation of the previously cited model. To this end, nanoindentation tests were combined with inverse identification technique to approach some of the characteristics of material state like work hardening near its cut edges. Indentation tests were carried out in the vicinity of several parts of cut edges. Based on the corresponding load versus penetration curves, the evolution of the yielding stress resulting from the material work hardening was estimated and compared to the predictions obtained from the numerical simulation of blanking process. These comparisons show good agreement between the measurements and the predictions from finite element model.