Federico Tordini

Experimental and Numerical Study of Shot Peened Thin Hard-Coated Components

A test bench was designed and assembled to carry out impact tests on samples and components. The system allows simple and rapid adjustment of the test parameters, such as the shot size and air pressure, with good repeatability of the results. Tests on steel and light alloys were carried out under both as-produced condition and on thin hard-coated samples. Significant reductions in dimple dimensions were seen after coating. FE models simulating the experiments overestimated the dimple depths, although the parameter trend was satisfactorily captured. The residual stresses from coating and shot peening determined numerically are believed to have been proven effective against fatigue.

A numerical study on the fatigue and rolling contact fatigue behaviour of PVD-coated steel and titanium spur gears

Thin hard coatings deposited with physical vapor deposition (PVD) can enhance both the fatigue and the rolling contact fatigue resistance of mechanical components. In this work a cheap and fast way to evaluate the best parameter levels of coating and bulk material is proposed. Design of Experiments (DoE) was applied to the numerical results obtained from the simulation of meshing PVD-coated spur gears. Preliminary analyses were performed to assess the fatigue behaviour of PVD-coated standard specimens for rotating bending tests. The coating elastic modulus and thickness, and the trend of the residual stresses induced by the deposition process were considered among the variables affecting the fatigue and the rolling contact fatigue behaviour. Different bulk materials, including steel and titanium alloys, were analyzed. The proposed method may help to define the optimal coating design, especially when the replacement of traditional steels with light alloys constitutes a goal that is strongly recommended.

A Numerical and Experimental Study of the RCF Behaviour of PVD-coated Spur Gears

In this work the rolling contact fatigue (RCF) behaviour of WC/C PVD-coated and uncoated case hardened transmission gears for competition motorcycles was studied both numerically and experimentally. Finite element models of the gears were processed and a theoretical-numerical procedure was applied to the numerical results to predict their RCF life. The presence of the coating and the residual stress fields induced by the surface treatments were simulated. Besides 16NiCr11, which is the actual material of the gears analyzed, the Ti-6Al-4V alloy was also considered with the numerical models. Preliminary RCF tests were carried in both dry and lubricated condition to observe the damage on the tooth flanks with and without the presence of the coating.

Fatigue Behaviour of Notched PVD-Coated Titanium Components

In this paper the fatigue behaviour of Ti-6Al-4V alloy coated with a TiN arc-deposited PVD film was studied. Rotating bending tests (R = -1) were carried out on standard “hourglass” specimens to evaluate the fatigue limit at 200000 load cycles. Conventional and notched (120° Vnotch transversal to the rotating axis at the minimum cross section area) specimens were tested, both coated and uncoated, to investigate the effect of the coating on the fatigue limit of the titanium alloy, with and without the surface notch. Fracture surfaces were observed by SEM. The coating did not improve the titanium alloy fatigue life.

Fatigue Behaviour of Notched Ti-6Al-4V in Inert Environment

This work focuses on the fatigue behaviour of notched Ti-6Al-4V titanium alloy in inert environment. V-notched flat samples were cycled under axial fatigue (R = 0.1) under inert conditions by immersion in paraffin oil. A step-loading technique was used to determine the fatigue limit at the complete fracture for a constant fatigue life of 2×105 load cycles. The results were compared with previous data obtained with tests carried out in air and 3.5 wt.% NaCl solution. Fracture surfaces were examined under stereoscopic microscope.

Study of the Effect of DCT and PVD Treatments on the Fatigue Behaviour of AISI 302 Stainless Steel

In this paper the influence of DCT (Deep Cryogenic Treatment) and a CrN arc-deposited PVD (Physical Vapor Deposition) coating on the fatigue behaviour of AISI 302 stainless steel was studied. Rotating bending tests were carried out on standard specimens to evaluate the fatigue limit at 300000 load cycles. The single and the combined effects of the two treatments were investigated by addressing untreated, PVD-coated and both PVD-coated and DC-treated specimens to the tests. All the series of specimens were also tested statically and laboratory analyses including fracture surface SEM observations and hardness measurements were performed.

Contact Fatigue Behaviour of PVD-Coated Spur Gears

In this paper the contact fatigue behaviour of gears coated with PVD (Physical Vapor Deposition) thin hard film was studied. Contact fatigue tests (R = 0) were carried out on both coated and uncoated automotive transmission spur gears. The bulk material and the coating analysed throughout the tests were, respectively, case hardened 18NiCrMo5 and CrN. The influence of the coating was both experimentally and numerically evaluated. Several FEM models were developed to assess the stress and strain distributions from tooth flank surface to in-depth layers. The influence of the surface treatments on the bulk material was taken into account with the models and the Coffin-Manson equation was used to predict the number of load cycles necessary for initial fatigue damage to occur. All the tested tooth flanks were observed using optical microscope and SEM.

A Review of the Fatigue Behaviour of Components Coated with Thin Hard Corrosion-Resistant Coatings

This paper provides a review of the state of the art on the study of the fatigue behaviour of mechanical components coated with thin hard corrosion-resistant coatings such as the physically or chemically vapour deposited ones. Some references address the experimental characterization of the fatigue resistance of coated steel and light alloys. Some coatings have been observed to prove effective against fatigue both in air and in aggressive environment. Numerical models and theoretical-numerical procedures have also been developed to shed light on the fatigue behaviour of coated components and to foresee the number of cycles until failure. As a matter of fact, the combination of good fatigue and anti-corrosion properties can significantly increase the performances of mechanical components operating in aggressive

Contact Fatigue Crack Growth in PVD-Coated Spur Gears

The aim of this work is to investigate the (rolling) contact fatigue behaviour of transmission spur gears coated with PVD (Physical Vapour deposition) thin hard films. Numerical models of coated steel and titanium spur gears were developed. The effect of the residual stress gradient induced by the coating deposition process was considered in the calculations. A theoretical-numerical procedure was arranged to foresee the crack propagation direction. Such a procedure could represent a powerful tool to predict the (rolling) contact fatigue resistance of PVD-coated gears.

Design of a fatigue ski testing bench

The aim of this paper is to show the design procedure for a fatigue ski test bench. The interest in developing an equipment to test ski characteristics has greatly raised since the introduction of carving skis. The characteristics of this kind of skis allow new trajectories and promise turn easiness and fun to everyone. These features come from a correct combination of ski shape and mechanical characteristics both of which determine load distribution under the edges. To quantify ski edge load and to characterise different skis, as well as to test their fatigue behaviour, we designed a ski test bench that allows to load an edged ski against an instrumented bed and to measure load distribution along the edge as well as the shape of the deformed edge.