Sergio Baragetti

Bio: Sergio Baragetti is an academic researcher from University of Bergamo. The author has contributed to research in topics: Residual stress & Fatigue limit. The author has an hindex of 18, co-authored 128 publications receiving 1043 citations. Previous affiliations of Sergio Baragetti include Instituto Politécnico Nacional & Polytechnic University of Milan.

Variables affecting the fatigue resistance of PVD-coated components

Abstract: The effect of intrinsic properties of CrN coatings on fatigue behaviour was studied in this paper. The coating layer microhardness and the residual stresses characterising the surface film were measured and the obtained results were introduced in a numerical modelling predicting fatigue life procedure of coated components. The effect of a CrN monolayer film deposited on bulk samples, produced in 2205 duplex stainless steel, H11 tool steel or 6082 aluminium alloy was investigated. The fatigue limit of coated and uncoated samples was experimentally determined while the development of FEM models, confirmed by means of experimental tests, represents a powerful tool to predict fatigue life of coated components. The effects on the fatigue strength of coating and bulk material defects like droplets and non-metallic inclusions were considered along with the residual stress gradient characterising the coating and evaluated by means of X-ray measurements. The influence of the substrate material plastic deformation on the integrity of the coating was evaluated too.

Fatigue behaviour of 2011-T6 aluminium alloy coated with PVD WC/C, PA-CVD DLC and PE-CVD SiOx coatings

Abstract: In this paper, the effect of three different thin hard coatings on the fatigue behaviour of 2011-T6 aluminium alloy was investigated. The coatings were DLC, SiOx and WC/C deposited with CVD and PVD processes. The fatigue limit at 107 load cycles was evaluated for both coated and uncoated specimens in a rotating bending machine (R=?1). The DLC and SiOx films did not significantly enhance the fatigue limit of the studied alloy, whereas a slight beneficial effect was produced by the WC/C film. Subsurface fatigue cracks nucleated in the WC/C-coated samples, as revealed by SEM micrographs of the fracture surfaces. It was therefore argued that the enhancement in the fatigue resistance of the WC/C-coated specimens could be due to residual compressive stress distributions introduced in the surface layers of the base material by the deposition process. The interface delamination was investigated with scratch tests and WC/C showed the best adhesion to the aluminium alloy.

Fatigue behavior and FEM modeling of thin-coated components

Abstract: Physical vapor deposition (PVD) surface coatings make it possible to increase the surface hardness of treated components. Despite the good wear resistance of such coatings, the fatigue behavior of the bulk material may be affected by changes in the residual stress field and microhardness. The two-fold aim of this paper is to characterize the fatigue behavior of thin-coated components and to develop a model for fatigue life prediction. The fatigue behavior characterization was carried out by means of four-point bending tests, while the microstructure of the bulk and coating materials was evaluated by means of SEM analysis, microhardness and residual stress measurements. Equipment with which to carry out the four-point bending tests was specially designed for the purpose. Numerical FEM models of the specimens used in the experimental tests were developed with the aim of giving the designer a useful tool with which to predict the fatigue behavior of thin-coated components. Experimental tests carried out on duplex stainless steel coated with CrN PVD coating (5 μm thickness) validate the numerical model.

Fatigue resistance of steel and titanium PVD coated spur gears

Abstract: The aim of this work is to investigate into the possibility of enhancing the fatigue resistance of CrN-PVD coated components. In particular, PVD coated spur gears were tested and a numerical simulation of crack propagation was carried out. The coating layer microhardness and the residual stresses characterising the surface film were measured. The results obtained were then introduced in a numerical model for predicting the fatigue life procedure of coated gears used in gearboxes for automotive applications. The number of cycles necessary to reach specified crack depths in coated and uncoated steel and titanium spur gears was numerically determined. This represents a powerful tool to predict the fatigue life of coated gears. Benefits induced by the presence of the coating were pointed out. A sensitivity analysis was also carried out: Furthermore, the effects on the fatigue crack propagation of the residual stress gradient (evaluated by means of X-ray measurements), the elastic properties of the bulk material and coating were evaluated.

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Relating Almen intensity to residual stresses induced by shot peening: a numerical approach

Abstract: Shot peening is a surface impact treatment widely used to improve the performance of metal parts and welded details subjected to fatigue loading, contact fatigue, stress corrosion and other damage mechanisms. The better performance of the peened parts is mainly due to the residual stresses resulting from the plastic deformation of the surface layers of the material caused by the impact of the shot. Shot peening intensity is usually quantified by means of the Almen-scale, which measures the residual arc height of a strip made of a specific material, and of a pre-defined size. The scale does not, in other words, apply solely to the residual stress field of a component of unspecified material and size. In this paper, a finite element to predict the residual stresses induced by shot peening in a metal part and to relate these stresses to Almen intensity is proposed; the aim is to provide the designer with a useful tool with which to choose the optimal treatment parameters with respect to the mechanical behaviour of the peened parts. Experimental measurements of residual stresses and a comparison with existing experimental data validate this approach.

Corrosion fatigue of biomedical metallic alloys: Mechanisms and mitigation

Abstract: Cyclic stresses are often related to the premature mechanical failure of metallic biomaterials. The complex interaction between fatigue and corrosion in the physiological environment has been subject of many investigations. In this context, microstructure, heat treatments, plastic deformation, surface finishing and coatings have decisive influence on the mechanisms of fatigue crack nucleation and growth. Furthermore, wear is frequently present and contributes to the process. However, despite all the effort at elucidating the mechanisms that govern corrosion fatigue of biomedical alloys, failures continue to occur. This work reviews the literature on corrosion-fatigue-related phenomena of Ti alloys, surgical stainless steels, Co-Cr-Mo and Mg alloys. The aim was to discuss the correlation between structural and surface aspects of these materials and the onset of fatigue in the highly saline environment of the human body. By understanding such correlation, mitigation of corrosion fatigue failure may be achieved in a reliable scientific-based manner. Different mitigation methods are also reviewed and discussed throughout the text. It is intended that the information condensed in this article should be a valuable tool in the development of increasingly successful designs against the corrosion fatigue of metallic implants.

A Review on Fatigue Life Prediction Methods for Metals

Abstract: Metallic materials are extensively used in engineering structures and fatigue failure is one of the most common failure modes of metal structures. Fatigue phenomena occur when a material is subjected to fluctuating stresses and strains, which lead to failure due to damage accumulation. Different methods, including the Palmgren-Miner linear damage rule- (LDR-) based, multiaxial and variable amplitude loading, stochastic-based, energy-based, and continuum damage mechanics methods, forecast fatigue life. This paper reviews fatigue life prediction techniques for metallic materials. An ideal fatigue life prediction model should include the main features of those already established methods, and its implementation in simulation systems could help engineers and scientists in different applications. In conclusion, LDR-based, multiaxial and variable amplitude loading, stochastic-based, continuum damage mechanics, and energy-based methods are easy, realistic, microstructure dependent, well timed, and damage connected, respectively, for the ideal prediction model.

On the potential applications of a 3D random finite element model for the simulation of shot peening

Abstract: Shot peening is a cold-working process that is used mainly to improve the fatigue life of metallic components. Experimental investigation of the mechanisms involved in shot peening is very expensive and complicated. Therefore, the Finite Element (FE) method has been recognized as an effective mean for characterizing the shot peening process and several types of FE models have been developed to evaluate the effects of shot peening parameters. However, in most of the existing FE models, the shot peening sequence and impact location were defined a priori. It is therefore the purpose of this study to consider the random property of the shot peening process. A novel 3D FE model with multiple randomly distributed shots was developed combining a Matlab program with the ANSYS preprocessor. The explicit solver LS-DYNA has been used to simulate the dynamic impingement process. Several potential applications of this novel model such as: the quantitative relationship of the peening intensity, coverage and roughness with respect to the number of shots have been presented. Moreover, simulations with multiple oblique impacts have been carried out in order to compare with results from normal impingements. Our work shows that such a computing strategy can help understanding and predicting the shot peening results better than conventional FE simulations.