L.A. Ferreira

Fatigue crack propagation behavior in railway steels

Purpose – The present paper aims to characterize the fatigue crack propagation behavior of wheel and rail steels, in particular the AVE wheel steel and an UIC60 rail steel, including several R-values and near threshold behavior. To accomplish this objective, mode I fatigue crack growth tests were performed according to the ASTM E647 standard on C(T) specimens taken from a Spanish high-speed AVE train used wheel and a UIC60 rail, tested with 0.1, 0.4 and 0.7 load ratios. Design/methodology/approach – In the present study, the two different methodologies presented in the ASTM E647 standard were used to characterize the fatigue crack propagation behavior of the two studied materials. The K-decreasing test procedure was used to characterize fatigue crack propagation near the threshold, whereas the K-increasing with constant load range method was used in the Paris law regime. Findings – It was observed that for the wheel a small influence of R-ratio was found, with greater R implying higher fatigue crack growt...

A comparative study of the tribological behaviour of TiN and ZrN PVD coatings

Abstract A comparative study of the tribological behaviour of mechanical surfaces of AISI 52100 steel non-coated and coated with TiN and ZrN PVD sputtered coatings is presented. The contact was dry or lubricated with a ISO VG 220 base mineral oil. The main objective of this work was to establish the capacity of these coatings to be used in severe situations in hydrodynamic bearings, especially in start-up, when the hydrodynamic conditions are not fully established and there is contact between the two surfaces. For these purposes a block-on-ring tribometer was used and the ISO 7148/1 standard was followed. Experimental results and a critical analysis are presented.

Thermal and non-Newtonian analysis of EHD line contacts

This work deals with the analysis of elastohydrodynamic line contacts. The analysis presented takes into account some important aspects of the problem like the rheological and thermal behaviour of the lubricant. The numerical solution of this problem might be rather complex because of the several phenomena involved. Thus a simple model was developed. The lubricant non-Newtonian behaviour, considering the “Limiting Shear Stress Model”, and the thermal exchanges between the lubricant and the contacting solids, are considered. This allows the evaluation of the tangential tractions in the lubricant film, and the lubricant and surface temperatures, with which a local apparent viscosity can be defined. This local viscosity depends on the major contact parameters like the applied load, the kinematic (rolling and sliding), the local pressure and temperature, as well as the lubricant rheology. The results presented show the influence of the operating conditions applied to the contact on the tangential pressure, friction coefficient and temperature distributions.

Journal bearings optimization for mass balancing systems used in internal combustion engines

Purpose – To provide an optimization methodology for the journal bearings of mass balancing systems, that consists in a sensibility analysis of the journal bearings design parameters in the journal bearing operating parameters, as well as the comparison and selection of the journal bearing materials and the selection of the lubrication grooves suitable.Design/methodology/approach – The methodology followed comprehends three steps. The first step is the one by one variation of the journal bearing design parameters (radial clearance, journal bearing diameter and journal bearing length) to analyse, independently, their influence on the journal bearing operating parameters (minimum film thickness, maximum pressure and power loss). The second step is the analysis and comparison of the metallic materials that can be used in the journal bearings. The third step is the selection of the lubrication groove.Findings – Applying this methodology it is shown that increasing the radial clearance the minimum film thickne...

Unmanned aerial vehicle safety assessment modelling through petri Nets

Abstract Currently we are facing an increasing trend of use of Unmanned Aerial Vehicles (UAV) in various activities both civilian and military. Although there is no legal framework for the operation of these systems, regulatory authorities require the demonstration of a safety level equivalent to manned aircraft. It is known the high vulnerability of the UAV not only to unexpected failures of their systems but also to the environment. The purpose of this paper is to present a safety assessment process modelling of a UAV by Petri Nets, that can be accepted by certifying bodies, considering the recommendations of STANAG 4671 UAV Airworthiness Requirements Specification (USAR) for analysis of fault conditions that lead to the most feared events. It is intended to show through the use of Petri Nets the frequency that the UAV enters the identified states described as most feared events; the ability of the UAV to react after being in a fault situation to the inputs of the operating crew in order to enhance trust and to facilitate the operation authorization process in UAV operations. The results obtained allowed to identify and to define critical areas and corrective actions that will lead to an acceptable level of risk for the regulatory authority.

Establishment of an initial maintenance program for UAVs based on reliability principles

Purpose The purpose of this paper is to illustrate how to develop a methodology to set up an initial maintenance program for unmanned aerial vehicles (UAVs) following the well-known Steering Maintenance Group logic method (MSG-3) and taking into account safety concerns based on items probabilities of failure. That is why it is stated that maintenance program is based on reliability principles. Design/methodology/approach The proposed methodology follows the MSG-3 framework applied to civil aircraft but where the determination of each probability of failure is achieved applying a morphological analysis. These probabilities are then affected by some factors to calculate the adjusted values to the specific conditions (design, operation and environment) under which the system is expected to operate. Findings Main findings are related to the applicability of the morphological analysis on the developing of an initial maintenance program when there is a lack of data that disable the establishment of a coherent maintenance program. Research limitations/implications Limitations are related to the absence of a legislative framework consensual in Europe for certification of UAVs and the lack of data concerning UAVs failure modes, causes and their probability of failure. Practical implications The developed work and the methodology proposed may be useful for UAVs maintenance program engineers and technicians when developing new systems. Originality/value The originality is based on the use of morphological analysis for UAVs to determine the items probabilities of failure when there is a no-data problem. Based on the referred analysis, it is possible to create an initial maintenance program for UAVs.

Time replacement optimization models for urban transportation buses with indexation to fleet reserve

Res_eng:An efficient management of physical assets in general and the urban transportation buses in particular, has as objective the optimization of its Life Cycle Cost (LCC), being the optimization of its maintenance and the determination of the right moment of its withdrawal or its renewal, essential elements for optimization of the capital investments. These aspects are related to the determination of the optimal dimension of the fleet reserve, aiming the maximization of its availability and the investment minimization. This can be reached through several algorithms that ought to be in consideration aspects like the maintenance costs, reseller cost, and inflation, among others. This is reached trough the adequate maintenance policies, being these scheduled and or on-condition predictive or any kind of planned ones. This type of decisions are determinant to maximize the LCC and, by consequence, the dimension of reserve fleet. It is through this perspective that the identification of the right moment of replacement or total renewal of an asset can be a strategic element in the competitiveness of the organizations by reducing the costs that can come from there. The validation of the management models to be implemented will be done in the road transports sector of passengers’ transportation and the models and the results have the potential to help this strategic sector in the global economy.

Electric Motors Maintenance Planning From Its Operating Variables

Abstract The maintenance planning corresponds to an approach that seeks to maximize the availability of equipment and, consequently, increase the levels of competitiveness of companies by increasing production times. This paper presents a maintenance planning based on operating variables (number of hours worked, duty cycles, number of revolutions) to maximizing the availability of operation of electrical motors. The reading of the operating variables and its sampling is done based on predetermined sampling cycles and subsequently is made the data analysis through time series algorithms aiming to launch work orders before reaching the variables limit values. This approach is supported by tools and technologies such as logical applications that enable a graphical user interface for access to relevant information about their Physical Asset HMI (Human Machine Interface), including the control and supervision by acquisition through SCADA (Supervisory Control And data acquisition) data, also including the communication protocols among different logical applications.

Maintenance of fire sprinkler systems based on the dynamic assessment of its condition

Safety is one of the major concerns of process safety engineers in most industrial facilities all over the world. To this scope, some events play an important role once the effect of their consequences can be assumed as totally undesirable. One of these events refers to the occurrence of a fire. Such event can result in catastrophic consequences for life, equipment, and continuity of activities or even leading to environmental damage. A fire protection equipment with low reliability means that this equipment are often unavailable and thus the risk of a fire increases. Maintenance of fire protection equipment is very important because this kind of systems is mostly in a dormant mode, which gives uncertainty about their operability when demanded in a real situation of fire. This article outlines the importance of tests, inspection, and maintenance operations in the context of a fire sprinkler system and proposes a methodology based on international standards and supported by test/inspection reports to correct the frequency of these actions according to the level of degradation of the components and regarding safety purposes.

Decision Making in Maintainability of High Risk Industrial Equipment

Considerations about availability and its dependence on reliability and maintainability have an increased importance when dealing with productivity or safety. This is particularly of outstanding importance if one is dealing with high risk industrial equipment, where maintainability plays an important and fundamental role in risk management when safety or huge economic values are in discussion. As availability is a function of reliability and maintainability, the objective is to improve one of these factors or both. This paper intends to show how maintainability influences availability, how to select to most important attribute for maintainability using the Analytic Hierarchy Process (AHP) and how improvements can be analysed assuming maintainability as a probability related with a restore probability density function [g(t)], and in particular using the Weibull distribution.