Papers by Author: Federico Tordini

Abstract: In this work a preliminary data set including experimental results from fatigue tests on smooth and foreign object damaged (FOD) aluminium samples coated with WC/C deposited with PVD (physical vapour deposition) technique was considered before testing WC/C-coated spur gears for racing motorcycles under rolling contact fatigue (RCF). The fatigue behaviour of the samples was correlated with the results obtained with the RCF tests on the coated gears. A special device mounted on a universal testing machine was used to carry out the RCF tests.

Abstract: 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.

Abstract: 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.

Abstract: In this paper a review of the state of the art on the study of the fatigue and the contact/rolling contact fatigue (RCF) resistance of thin hard-coated components is provided. Physical and chemical vapor deposition (PVD and CVD) methods are used to deposit such films. A fair number of references reports experimental data highlighting the improvements achieved with coating deposition on both steels and light alloys. Numerical modelling has also been devoted to shedding light on the behaviour of coated components and reliable previsional procedures have been arranged to foresee the number of cycles until fatigue damage initiation and failure.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.