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This article belongs to the Special Issue Actuators and Dampers for Vibration Control: Damping and Isolation Applications. We present the design, manufacturing, and dynamical characterization of a mechanical suspension made by a passive magnetic spring and an eddy current damper integrated into a single device. Three configurations with 2, 3, and 4 permanent magnets axially distributed with opposite polarizations are designed, simulated, manufactured, and tested. Stiffness of 2410, 2050, 2090 N/m and damping coefficient of 5.45, 10.52 and 17.25 Ns/m are measured for the 2-, 3-, and 4-magnets configurations, respectively. The magnetic suspension provides good mechanical properties combined with excellent cleanness and high reliability, which is very desirable in mechanical systems for space applications. The research leading to these results has received funding from the Spanish Ministerio de Economía y Competitividad under the Plan Estatal de I+D+I 2013-2016, grant agreement no ESP2015-72458-EXP.

The aim of this study is the detailed calculation of microwave propagation inside raw timber in cylindrical configurations. Two different approaches have been used. The first one uses an exact formulation and analytical approximations in order to explore the electromagnetic field distribution inside dry wood. The introduction of conductivity in the exact model makes it so complex that the equations are unsuitable for analytical manipulation. In order to further explore the effect of moisture in cylindrical wood structures, a full scale numerical simulation using commercial software has been performed. The results show that for microwave frequencies in the 3 GHz range and for typical wood parameters, a cylindrical log behaves as a kind of Fresnel lens. This work has important applications in microwave treatment and sensing of wood.

This article explores the influence of the appearance of micropitting in different types of additives added to a polyalphaolefinic low-viscosity base oil, namely a polyalphaolefin PAO6. Additives commonly used in mechanical transmissions by gears were used, i.e., extreme pressure, anti-wear and friction modifier. For the study, we have conducted a series of tests on a disc machine under various operating conditions. The temperature and surface roughness of the test specimens have been changed in order to study different lubricant specific film thicknesses, as the last is one of the most influential parameters on the appearance of micropitting. Tests have shown the important influence of the additives, and their concentration, in the development of micropitting and their associated effects, depending on the operating conditions of the contact. Along with the study of the effect of additives, the influence of specific film thickness on the friction coefficient, surface appearance, conditions of lubrication, and wear was also studied.

Two ways of determining Bridgman's parameters are presented to estimate the equivalent Bridgman stress–strain (BSS) curve after the onset of necking in cylindrical specimens. The accurate experimental determination of the minimum necking radius, r N , and the radius of curvature of the necking, R N , are considered to be the main problems in applying Bridgman's model to obtain the equivalent BSS curve and describe the plastic behaviour of materials. Using the combined technique of 2D digital image correlation and fringe projection, the 3D positions and displacements of the surface elements are determined for each load stage of a tensile test on steel, aluminium (Al) and copper (Cu) bars. The axial displacements are well fitted with an empirical function that allows accurate estimation of the beginning of necking and its location on the specimen. From the 3D positions, both Bridgman's parameters are estimated by adjusting a torus to the necking zone. The 3D measurements around the necking position have to be well defined to obtain the parameters in a feasible way, because the real necking profile does not fit well with the half-circle proposed by Bridgman. Nonetheless, the estimated r N parameters are noisy, affecting the BSS curve. Therefore, an alternative and simpler way for estimating r N and R N is also proposed, only requiring the measurement of total axial displacements along the loading axis of each surface element. In this way, the BSS curve obtained is smooth, although it somewhat underestimates the same curve obtained using experimentally measured 3D data.