method for calculating a global dynamic factor kav in gears subjected to variable velocity and loading conditions

The present paper aims to propose a method, in ISO Standard environment, in order to calculate a single global dynamic factor KAV, replacing both KA and KV, in case of gears subjected to variable velocity and loading conditions. This procedure, based on the Miner damage rule, allows to process a given load spectrum and to calculate a value of the equivalent tangential force that includes all dynamic effects; this force value is useful for bending and pitting calculation of the service life. In this work a practical case for bending strength is presented, based on a recorded flight mission, referring to a gear box for aerospace applications. Obtained results in terms of equivalent forces and global dynamic factor values have been compared to those calculated by means of the classical ISO Standard formulae, based on the corresponding experimental data

evaluation of the fretting wear damage on crowned splined couplings

Abstract Splined couplings are widely used in many industrial fields and one of the most problematic failure mode of these components is fretting wear. Fretting wear appears because of the relative motions between teeth and it is mainly due to angular misalignments. Aim of this paper is to set up a procedure in order to identify the entity of the fretting wear damage in crowned splined couplings in real working conditions. The first Ruiz parameter has been chosen to quantify the wear damage being relatively easy to be obtained from the calculation point of view. Experimental tests have been performed by means of a dedicated test rig to validate the theoretical results, in terms of iso-Ruiz maps. The damage entity has also been quantified by measuring the angular rotation before and after each test. Obtained results confirm that, where the fretting map shows higher values of the Ruiz parameter, the fretting damage becomes more important

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

Fatigue damage in spline couplings: numerical simulations and experimental validation

Abstract Spline couplings are often over dimensioned concerning fatigue life, but they are subjected to wear phenomena. For as concerns fatigue life, standard design methods consider only a part of the spline teeth to be in contact and this brings to underestimate the components life, so a better understanding about component fatigue behavior may allow to a weight reduction and a consequent increasing of machine efficiency. On the other hand, wear damage may cause spline coupling run outs; this phenomenon is generally caused by the relative sliding between engaging teeth; the sliding may be due to kinematic conditions (angular misalignment between shafts) of teeth deflection. In order to obtain component optimization, both fatigue and wear behavior have to be taken into account. Standard spline coupling design methods do not properly consider wear damage and they evaluate fatigue life with big approximations. In this work fatigue damage are experimentally and numerically investigated while wear damage has been experimentally evaluated. Experimental results have been obtained by a dedicated test rig. Fatigue tests have been performed by means of a special device connected to a standard fatigue machine. Tests have been done by varying the most important working parameters (torque and misalignment angle). Experimental results have been compared with standard design methods to evaluate if and how they may over dimension the components. Results show that concerning the fatigue life, the actual component life is higher respect to that calculated by standard methods. Regarding wear behavior, results shows that whenever a relative motion between engaging teeth is present, wear damage appears

experimental investigation about tribological performance of grapheme nanoplatelets as additive for lubricants

Abstract Graphene has received a great interest by researchers in a wide field of applications. Referring to tribological aspects, graphene has been considered as an additive in lubricants, in order to reduce components friction and machine losses. Some papers are available in literature about graphene utilized as additive in solids or liquid lubricants. Despite the big potential of graphene in this field, its use as a lubricant or a lubricant additive on macro-meso scale remains relatively unexplored. In particular, the literature is lacking about specific applications of graphene added lubricants on mechanical systems. In this paper, the effect graphene added to a standard lubricants to create high performance compounds has been investigated. Firstly, the Coefficient of Friction (CoF) of different compositions of lubricant-graphene compounds has been experimentally evaluated. In particular, a commercial grease and two commercial oils have been chosen to be used as base lubricants. Results in terms of Coefficient of Friction values of all compounds have been compared each other. Finally, characterization results of graphene added grease have been related to that available from previous studies performed on a mechanical component (a spline coupling), commonly used in many industrial applications, lubricated by the same graphene-grease compounds. Results show that graphene added to viscous lubricants generally reduces the coefficient of friction, in both materials and components

methodology development to design a representative test specimen for wear damage in spline couplings

Abstract Aim of this paper is to develop a new methodology in order to design a representative test specimen for wear damage characterisation in spline couplings. In other words, real component and test specimen (same material) have been considered having a common target that is an isodamage condition reached after an established number of working (testing) cycles.Influence parameters chosen for this aim are, under the hypothesis of equal friction coefficient, hertzian pressure due to the load entity (torque) and the corresponding slidings. Slidings have been determined referring to two different working conditions, traditional fatigue testing with variable torque (aligned conditions) and wear testing in misaligned conditions. Specimen geometry has been firstly stated following DIN 5480 requirements, then profile micro geometries have been varied to tune the established target parameters and the corresponding FEM simulations have been carried on. Hertzian pressure values and corresponding contact areas have been verified by classical formula.A preliminary experimental activity has been done in order to verify the specimen design related to isodamage dimensioning aspects

Crack propagation behavior in planet gears

Abstract Aim of this work is to investigate crack propagation paths in planet gears for aerospace applications in order to find how gears parameters may affect the crack path and, consequently, may provide information about gears design to avoid catastrophic failures. The research activity has been carried on by means of extended finite element models (XFEM). In particular, the effect of rim thickness (expressed as backup ratio) and crack initiation point on crack paths has been considered. Obtained results have been compared with those available for standard gears, to highlight the different behavior in crack propagation

Investigation of crack propagation path in tube gears.

Abstract In this paper, the crack propagation behaviour in tube gears has been investigated. This kind of gear find application in aerospace and in particular in helicopter drivelines. For this reason, an accurate design against catastrophic failure due to particular crack propagation paths, has to be performed. In this work, the effect of tube length and rim thickness and also speed on crack propagation path has been analysed by means of extended finite elements models. In particular, to better understand the effect of speed, the changes in stress intensity factors KI and KII have been considered. Particular crack propagation shapes (wave propagation) have been found in some cases where the length ratio is particularly high

investigation of bearings overloads due to misaligned splined shafts

Abstract Bearings may be subjected to overloads due to shaft unwanted loads, caused, as an example, by tiling moments related to spline coupling misalignment. Misalignment is mainly generated by manufacturing of mounting errors (due to machining tolerances) or by the transmission working conditions. These kind of overload is critical because may reduce both bearing life and system efficiency, moreover it is quite complicated to be evaluated. In this work, the overload generated on bearings supporting a misaligned splined shafts have been investigated by means of a commercial simulation software (Romax Designer). The simulations have been performed considering a standard transmission scheme composed of two shafts connected by a spline coupling and supported by four roller bearings (two for each shaft), mounted in isostatic configuration. The effect of spline coupling teeth microgeometry has been taken into account along with the misalignment angle magnitude and the torque level. In particular, the influence of these parameters on teeth contact pressure has been evaluated, as tilting moment is mainly driven by the contact pressure distribution among engaging teeth and by the position of maximum pressure distribution along teeth in axial direction. Results obtained in this work may be useful to designers, suggesting some basic criteria to reduce the bearings overload, allowing designing more reliable and efficient machines

static and dynamic behavior of pu foams with multilayer coatings

Abstract An overview on static and dynamic behavior of functional polymeric foams is presented. In particular, a PU (Poly Urethane) open cells foam was manufactured to obtain specimens with different nanostructured coatings. An experimental campaign was performed with 7 different kind of multilayer coatings. Quasi-static compression preconditioning and compression fatigue cycles were applied and 5 parameters were measured during cycling: Hysteresis loop area, Dissipated energy per cycle, Stiffness degradation, Secant modulus, Loss factor values. The results show the effect of the contribution of nanoink layers to the static and cyclic behavior of foams