Prediction Method for the Surface Damage in Splined Couplings

The primary purpose of my PhD thesis was to develop design criteria and to verify procedures about fretting wear, that are applicable to crowned spline couplings of a power transmission system of the aeroengines. Fretting is a very complex phenomenon being influenced by many factors, the most important being the presence or absence of lubrication, the load distribution (contact pressure) and the sliding between the bodies. Therefore, the study of fretting needs a deep knowledge of these three main aspects. The first aspect of the problem was based on models and experimental tests considering specify specimens (crowned spline couplings) and imposed movements, so as to uniquely identify the working conditions (load and sliding), in order to facilitate the comparison between the experimental tests and the analytical models. The analytical models have been validated with numerical simulations and by comparison with experimental data, that have been obtained by means of a dedicated test bench that has been designed and built. Thanks to the test rig was possible to determinate the real contact pressure of two engaging teeth; in fact, it is one of the most important parameters affecting the fretting phenomenon, but it is very difficult to evaluate in a quantitative way, especially when considering components with complex geometries. The second phase of this thesis was the development of a predictive model for crowned splined couplings. This model is based on the Ruiz first parameter. The aim of my thesis is to demonstrate how this parameter may be correctly applied to a complex component as the crowned spline coupling, taking into account experimental and FEM validation

Fretting damage parameters in splined couplings

This work focuses on the analysis of the debris found in the lubrication oil produced by the wear abrasion during wear tests conducted on crowned splined couplings. During each test the presence and the dimensions of the debris in the oil have been monitored. Tests have been performed by means of a dedicated splined couplings test rig and they have been performed by imposing an angular misalignment on the axes of the components. Results shows that when these components work in misaligned conditions, the relative motion between engaging teeth brings to the rise of a wear phenomenon called fretting wea

Identification of contact regimes in mechanical components for the evaluation of fretting damage

In this work the regimes of contact in misaligned crowned splined couplings have been analyzed. Experimental tests have been performed in order to identify if fretting damage on the components appears as fretting wear or fretting fatigue. A significant difference was identified on the surface of specimen by analyzing two different tests; the first test emphasized a fatigue damage and in the second test a wear phenomena has been achieved. Also a good correlation has been obtained by analyzing the fretting map obtained by using the Mindlin's theory and experimental result

Advanced Life Assessment Methods for Gas Turbine Engine Components

In combustion systems for aircraft applications, liners represent an interesting challenge from the engineering point of view regarding the state of stress, including high temperatures (up to 1500°C) varying over time, high thermal gradients, creep related phenomena, mechanical fatigue and vibrations. As a matter of fact, under the imposed thermo-mechanical loading conditions, some sections of the liner can creep; the consequent residual stresses at low temperatures can cause plastic deformations. For these reasons, during engine operations, the material behaviour can be hardly non-linear and the simulation results to be time expensive. Aim of this paper is to select and implement some advanced material life assessment methods to gas turbine engine components such as combustor liners. Uniaxial damage models for Low Cycle Fatigue (LCF), based on Coffin-Manson, Neu-Sehitoglu and Chaboche works, have been implemented in Matlab®. In particular, experimental LCF and TMF results for full size specimens are compared to calibrate these models and to assess TMF life of specimens. Results obtained in different testing conditions have been used for validation. In particular, each model needs specific parameter calibrations to characterize the investigated materials; these parameters and their relation with temperature variation have been experimentally obtained by testing standard specimens

Evaluating the role of seagrass in Cenozoic CO2 variations

Marine seagrass angiosperms play an important role in carbon sequestration, removing carbon dioxide from the atmosphere and binding it as organic matter. Carbon is stored in the plants themselves, but also in the sediments both in inorganic and organic forms. The inorganic component is represented by carbonates produced by calcareous organisms living as epiphytes on seagrass leaves and rhizomes. In this paper, we find that the rate of seagrass epiphyte production (leaves and rhizomes) averages 400 g m−2 yr−1 , as result of seagrass sampling at seven localities along the Mediterranean coasts, and related laboratory analysis. Seagrasses have appeared in the Late Cretaceous becoming a place of remarkable carbonate production and C sequestration during the whole Cenozoic era. Here, we explore the potential contribution of seagrass as C sink on the atmospheric CO2 decrease by measuring changes in seagrass extent, which is directly associated with variations in the global coastal length associated with plate tectonics. We claim that global seagrass distribution significantly affected the atmospheric composition, particularly at the Eocene-Oligocene boundary, when the CO2 concentration fell to 400 ppm, i.e., the approximate value of current atmospheric CO2