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Porto, Portugal

Martins R.,University of Porto | Locatelli C.,INEGI | Seabra J.,University of Porto
Industrial Lubrication and Tribology | Year: 2011

Purpose - The purpose of this paper is to get a better understanding of roughness evolution and micropitting initiation on the tooth flank, as well as the evolution of surface topography during the test load stages in a modified DGMK short micropitting test procedure. Design/methodology/approach - A modified DGMK short micropitting test procedure was performed, using an increased number of surface observations (three times more) in order to understand the evolution of the surface during each load stage performed. Each of these surface observations consists in the evaluation of surface roughness, surface topography, visual inspection and also weigh measurements as well as lubricant analysis. Findings - This work showed that the larger modifications on surface took place in the beginning of tests, especially during load stage K3 (lowest load, considered as running-in) and on the first period of load stage K6, that is, during the first 200,000 cycles of the test. The 3D roughness parameters (St and Sv), obtained from the surface topographies, gave a more precise indication about surface roughness evolution and micropitting generation than the 2D parameters, especially in what concerns to inferring the depth of micropits and the reduction of roughness. Tooth flank topography allows to identify local changes on the surface and the appearance of first micropits. Research limitations/implications - This work was performed with gears holding a high surface roughness and with a ester-based lubricant. It was interesting to see the differences observed for surface evolution, for other base oils and also for gears with lower roughness. Practical implications - The main implication of this work is the understanding that major changes in the surface took place in the first cycles, indicating that the running-in procedure could be very important for the surface fatigue life. This work also showed that micropitting depends on local contact conditions. Depending on the roughness of the counter surface, micropitting can appear on the bottom of the deep valleys and/or do not appear on the tip of the roughness peaks. The surface topography, and implicitly 3D roughness parameters, is very useful for the observation of surface evolution. Originality/value - This paper shows in detail the evolution of the tooth surface during a micropitting test. The micropits generation and evolution and also surface wear evolution are presented. © Emerald Group Publishing Limited.

Catalanotti G.,INEGI | Catalanotti G.,University of Porto | Katunin A.,Silesian University of Technology
Computational Materials Science | Year: 2016

Modern trends in materials dedicated for aircraft applications are focused on development of highly multifunctional materials that allow not only to carry mechanical loading, but also to possess several other types of functionality, e.g. be thermal resistant, electrically conductive, etc. The material of such a type, with a possibility of conducting electrical current without loss of mechanical properties is the main topic of presented research results. The work presented here deals with the determination of the overall stochastic mechanical and electrical properties of a blend of polypyrrole (PPy) and epoxy. The material properties are obtained applying appropriate periodic boundary conditions (PBCs) to the representative volume elements (RVEs) of the material nano-structure. A strategy to model numerically the electrical percolation network in the framework of Finite Element Method (FEM) is proposed and discussed. Electrical and mechanical properties of the material are calculated as a function of the filler volume fraction. Finally, the numerical results are compared with experiments found in literature and an overall good agreement is found. © 2015 Elsevier B.V. All rights reserved.

Melro A.R.,INEGI | Camanho P.P.,University of Porto | Andrade Pires F.M.,University of Porto | Pinho S.T.,Imperial College London
International Journal of Solids and Structures | Year: 2013

Micromechanical analyses of unidirectional continuous-fibre reinforced composite materials were performed to study the mechanisms of deformation and fracture of the constituents, and their influence on the mechanical properties of the composite. Special focus was given to the matrix material behaviour as well as to the interface between constituents. The matrix was modelled using a pressure dependent, elasto-plastic thermodynamically consistent damage model. Cohesive elements were used to model the interface between matrix and fibres. Part I of this paper details the continuum model developed for a typical epoxy matrix. Part II will focus on micromechanical analyses of composite materials and the estimation of its elastic and strength properties. © 2013 Elsevier Ltd. All rights reserved.

Melro A.R.,INEGI | Camanho P.P.,University of Porto | Andrade Pires F.M.,University of Porto | Pinho S.T.,Imperial College London
International Journal of Solids and Structures | Year: 2013

This paper presents the application of a new constitutive damage model for an epoxy matrix on micromechanical analyses of polymer composite materials. Different representative volume elements (RVEs) are developed with a random distribution of fibres. Upon application of periodic boundary conditions (PBCs) on the RVEs, different loading scenarios are applied and the mechanical response of the composite studied. Focus is given to the influence of the interface between fibre and matrix, as well as to the influence of the epoxy matrix, on the strength properties of the composite, damage initiation and propagation under different loading conditions. © 2013 Elsevier Ltd.

Barbosa A.Q.,INEGI | Da Silva L.F.M.,University of Porto | Ochsner A.,Griffith University
Journal of Adhesion Science and Technology | Year: 2015

In the present study, natural microparticles of cork are used with the objective to increase the toughness of a brittle epoxy adhesive. The cork particles act as a crack stopper, leading to more energy absorption. This fact occurs because cork presents a remarkable combination of properties (low density, low cost and sustainability of the raw material). Adhesives are susceptible to the presence of moisture in the environment. There are several studies that refer that moisture can degrade the molecular structure of the adhesive, and, therefore, its mechanical properties. The main objective of this research is to investigate the effect of moisture on the degradation of an adhesive reinforced with micro cork particles, knowing that cork presents a great capability to absorb water. The water absorption and desorption characteristics have been studied, for specimens without cork and with 1% cork, 125-250 m. The moisture uptake behaviour in the adhesive was studied to obtain the coefficient of moisture diffusion. The effect of water exposure on the mechanical properties and glass transition temperature was also investigated. It was observed that the presence of water alters the mechanical properties of the adhesive (with and without cork), but these changes are not permanent. © 2015 Taylor and Francis.

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