Characterizing and imaging gross and real finger contacts under dynamic loading

We describe an instrument intended to study finger contacts under tangential dynamic loading. This type of loading is relevant to the natural conditions when touch is used to discriminate and identify the properties of the surfaces of objects — it is also crucial during object manipulation. The system comprises a high performance tribometer able to accurately record in vivo the components of the interfacial forces when a finger interacts with arbitrary surfaces which is combined with a high-speed, high-definition imaging apparatus. Broadband skin excitation reproducing the dynamic contact loads previously identified can be effected while imaging the contact through a transparent window, thus closely approximating the condition when the skin interacts with a non-transparent surface during sliding. As a preliminary example of the type of phenomenon that can be identified with this apparatus, we show that traction in the range from 10 to 1000 Hz tends to decrease faster with excitation frequency for dry fingers than for moist fingers

Tribological interactions of the finger pad and tactile displays

This thesis summarise the results of an investigation of the tribological interactions of the human finger pad with different surfaces and tactile displays. In the wide range of analyses of the mechanical properties of the finger pad, an attempt has been made to explain the nature of the interactions based on critical material parameters and experimental data. The experimental data are presented together with detailed modelling of the contact mechanics of the finger pad compressed against a smooth flat surface. Based on the model and the experimental data, it was possible to account of the loading behaviour of a finger pad and derive the Young’s modulus of the fingerprint ridges. The frictional measurements of a finger pad against smooth flat surfaces are consistent with an occlusion mechanism that is governed by first order kinetics. In contrast, measurements against a rough surface demonstrated that the friction is unaffected by occlusion since Coulombic slip was exhibited. The thesis includes an investigation of critical parameters such as the contact area. It has been shown that four characteristic length scales, rather than just two as previously assumed, are required to describe the contact mechanics of the finger pad. In addition, there are two characteristic times respectively associated with the growth rates of junctions formed by the finger pad ridges and of the real area of contact. These length and time scales are important in understanding how the Archardian-Hertzian transition drives both the large increase of friction and the reduction of the areal load index during persisting finger contacts with impermeable surfaces. Established and novel models were evaluated with statistically meaningful experiments for phenomena such as lateral displacement, electrostatic forces and squeeze-film that have advanced applications

Tribometer set-up and friction coefficient in elastomers of sealing systems

El objetivo de esta tesis es, realizar la puesta a punto de un tribómetro disponible en el Departamento de Ingeniería Mecánica y Aeroespacial (DIMEAS), laboratorio del Politécnico de Torino. El tribómetro se encontró con un actuador neumático-hidráulico. Con esta configuración, con el fin de realizar la adquisición de datos, se buscaron los sensores compatibles para cada tarea, luego fueron reparados y cada uno se calibró. El tribómetro es capaz de adquirir la velocidad de deslizamiento (mm/s), la posición (mm), las fuerzas tangenciales y normal (N). Fue desarrollado un programa en Labview capaz de adquirir y guardar las respectivas señales de la forma adecuada. De la misma manera, un script en Matlab fue desarrollado para calcular el coeficiente de fricción. El modelo utilizado para calcular el coeficiente de fricción fue el más simple, pero fiable, desarrollado por Coulomb, en el que sólo toma en cuenta la fuerza normal y la fuerza tangencial. Por último, se realizaron algunas pruebas con el fin de verificar el comportamiento del tribómetro.The objective of this thesis is to, perform the setup of a tribometer available at the Department of Mechanical and Aerospace Engineering (DIMEAS), laboratory of the Polytechnic University of Turin. The tribometer was found with a pneumohydraulic actuator. With this configuration, in order to perform the data acquisition, the compatible sensors for each task were searched, then they were repaired and each one was calibrated. The tribometer is capable to acquire the sliding velocity (mm/s), position (mm), tangential and normal forces (N). A program in Labview capable to acquire and save the respective signals in the adequate way was developed. In the same way, a Matlab script was developed to calculate the friction coefficient. The model used to calculate friction coefficient was the simplest but reliable one, developed by Coulomb, in which only takes in to account the normal force and the tangential force. Finally, were done some tests in order to verify the behavior of the tribometer.Ingeniero (a) ElectrónicoPregrad

44th Aerospace Mechanisms Symposium

The Aerospace Mechanisms Symposium (AMS) provides a unique forum for those active in the design, production and use of aerospace mechanisms. A major focus is the reporting of problems and solutions associated with the development and flight certification of new mechanisms

Raman microscopic studies of PVD deposited hard ceramic coatings.

PVD hard ceramic coatings grown via the combined cathodic arc/unbalance magnetron deposition process were studied using Raman microscopy. Characteristic spectra from binary, multicomponent, multilayered and superlattice coatings were acquired to gain knowledge of the solid-state physics associated with Raman scattering from polycrystalline PVD coatings and to compile a comprehensive spectral database. Defect-induced first order scattering mechanisms were observed which gave rise to two pronounced groups of bands related to the acoustical (150-300cm[-1]) and optical (400-750cm[-1]) parts of the phonon spectrum. Evidence was gathered to support the theory that the optic modes were mainly due to the vibrations of the lighter elements and the acoustic modes due to the vibrations of the heavier elements within the lattice.A study into the deformation and disordering on the Raman spectral bands of PVD coatings was performed. TiAIN and TiZrN coatings were intentionally damaged via scratching methods. These scratches were then analysed by Raman mapping, both across and along, and a detailed spectral interpretation performed. Band broadening occurred which was related to "phonon relaxation mechanisms" as a direct result of the breaking up of coating grains resulting in a larger proportion of grain boundaries per-unit-volume. A direct correlation of the amount of damage with band width was observed. Band shifts were also found to occur which were due to the stresses caused by the scratching process. These shifts were found to be the largest at the edges of scratches. The Raman mapping of "droplets", a defect inherent to PVD deposition processes, found that higher compressive stresses and large amounts of disorder occurred for coating growth onto droplets.Strategies designed to evaluate the ability of Raman microscopy to monitor the extent of real wear on cutting tools were evaluated. The removal of a coating layer and subsequent detection of a base layer proved successful. This was then expanded to real wear situations in which tools were monitored after 3,6,12,64,120 and 130 minutes-in-cut. A PCA chemometrics model able to distinguish between component layers and oxides was developed.Raman microscopy was found to provide structural and compositional information on oxide scales formed on the surfaces of heat-treated coatings. Wear debris, generated as a consequence of sliding wear tests on various coatings, was also found to be primarily oxide products. The comparison of the oxide types within the debris to those formed on the surface of the same coating statically oxidised, facilitated a contact temperature during sliding to be estimated.Raman microscopy, owing to the piezo-spectroscopic effect, is sensitive to stress levels. The application of Raman microscopy for the determination of residual compressive stresses within PVD coatings was evaluated. TiAlN/VN superlattice coatings with engineered stresses ranging -3 to -11.3 GPa were deposited onto SS and HSS substrates. Subsequent Raman measurements found a correlation coefficient of 0.996 between Raman band position and stress (determined via XRD methods). In addition, there was also a similar correlation coefficient observed between hardness and Raman shift (cm-1). The application of mechanical stresses on a TiAlCrN coating via a stress rig was investigated and tensile and compressive shifts were observed

41st Aerospace Mechanisms Symposium

The proceedings of the 41st Aerospace Mechanisms Symposium are reported. JPL hosted the conference, which was held in Pasadena Hilton, Pasadena, California on May 16-18, 2012. Lockheed Martin Space Systems cosponsored the symposium. Technology areas covered include gimbals and positioning mechanisms, components such as hinges and motors, CubeSats, tribology, and Mars Science Laboratory mechanisms