169 research outputs found
On the use of specimens for gear bending fatigue design
No full textISO 6336 Standard presents different methods to design cylindrical gears against bending fatigue.. The Standard allows the use of fatigue data obtained from plain and notched specimens to design gears, but it suggests a more experienced approach based on data obtained on reference gears. In this paper, the accuracy of the different methods was verified against test data. The estimation of material notch sensitivity was improved using experimental data obtained on specimens. After calibrating the notch sensitivity factors, the specimen-based methods proved to be as accurate as the method based on reference gears
Ligand-free water-based approaches for the synthesis of metal sulfides nanostructures
No full textIn this Thesis, metal sulfides were synthesized through water-based and ligand-free synthetic routes. A simple batch approach was successfully employed for the synthesis of ZnS, CuS, PbS, MnS and Ag2S in a crystalline form at a temperature near 0 °C without employing ligands or stabilizing agents. Particles dimension, crystal structure, surface composition and susceptibility to oxidation phenomena of these materials were assessed. In the case of the batch synthesis of ZnS, a SAXS (Small Angle X-Ray Scattering) in-situ study was also performed to elucidate the dimensional evolution of the obtained NPs (nanoparticles) as function of time. Moreover, for ZnS, the behavior in water suspension and the interaction with probe molecules at the liquid/solid interface were also assessed.
Microfluidic and CHFS (Continuous Flow Hydrothermal Synthesis) approaches were employed for the synthesis of pure and doped ZnS NPs. In the case of the pure samples, the synthesis conditions were varied in order to gain insights on the growth mechanism of the NPs and to analyze the potential over the control of dimensional and structural properties of the samples. For the doped samples, the uptake of dopants was determined and their inclusion in the ZnS matrix discussed. The functional properties of selected samples were assessed. In particular, the catalytic activity for the HER (Hydrogen Evolution Reaction) was studied for pure ZnS NPs, while PL (Photoluminescence) was measured in the doped ones. Cytotoxicity assays on doped ZnS NPs obtained with the microfluidic route were also performed in view of bioimaging applications.
The effect of thermal treatment and oxidation phenomena on ZnS NPs as a function of the NPs size was also in-depth analyzed. The study addressed the variations of size, morphology, structure, composition of the nanostructures and their effect on the photocatalytic activity.
The characterization strategy relied on the complementary use of different techniques. XRD (X-Ray Diffraction) and TEM (Transmission Electron Microscopy) analyses were performed to assess mainly dimensional and structural features of the materials, while the surface composition was analyzed combining XPS (X-ray Photoelectron Spectroscopy) and FTIR (Fourier Transform Infrared Spectroscopy). The characterization of the materials was also complemented by Raman spectroscopy.
The results showed the potential of the proposed methods to control relevant features of different materials, even without the use of stabilizing agents, and allowed to assess the surface chemistry of the synthesized naked particles
Lifetime assessment of the rear axle for an off-road vehicle in a fatigue test bench by means of the Peak Stress Method
No full textIn this study the Peak Stress Method (PSM) has been applied to the fatigue assessment of the welds of an axle equipped in an off-road vehicle. In the fatigue design of welded joints, the PSM is a FE-based method to rapidly evaluate the NSIFs relevant to the opening, sliding and tearing modes by means of the linear elastic peak stresses extracted from the FE model. First, an axle, which consists of a central body and two lateral branches composed by several plates welded to a tube, has been fatigue tested under a vertical load in a test bench designed to replicate the frame-axle interface. Then, an FE model of the axle has been calibrated to simulate the behaviour observed during the fatigue test, where the reaction forces and the strains at pre-defined locations have been considered. Once the FE model has been calibrated, the PSM has been applied to the welds of the axle, taking advantage of an automatic procedure, and the crack initiation location has been estimated. Finally, the theoretical estimations have been compared with the experimental datum
Fatigue behavior of an Off-highway axle subjected to a variable amplitude strain-based load spectrum derived from field tests
No full textVerifica della resistenza a fatica di un assale Off-highway in ghisa sferoidale sottoposto a test a banco
No full textLa cooperación internacional en la gestión institucional de la Fundación Omar Dengo: 2000-2004
No full textLa presente tesis aborda el aporte de la cooperación internacional en la consolidación de la gestión institucional de la Fundación Omar Dengo, en el periodo 2000- 2004. En la investigación se detalla la cooperación internacional en esta institución en el periodo de estudio, de acuerdo con sus fuentes, modalidades y áreas. Por medio de los proyectos y programas realizados del 2000 al 2004, se evalúa con una definición propia la gestión institucional en la Fundación Omar Dengo. Se valoran los aportes de la cooperación internacional en la consolidación de la gestión institucional, mediante recopilación y análisis de datos de la cooperación internacional en el periodo mencionado y por medio de un estudio de caso del proyecto “Empresarias del nuevo milenio: Ampliando fronteras en la administración de la micro y pequeña empresa". El trabajo de investigación aquí propuesto versa sobre la comprobación de la hipótesis: Los aportes de la cooperación internacional en la Fundación Omar Dengo en el periodo 2000-2004, han sido un factor determinante para la consolidación de la gestión institucional.The following work describes the contribution of international cooperation towards the consolidation of the institutional management of the Omar Dengo Foundation during the years 2000 and through the year 2004. To fulfill this general objective, the researcher details the international cooperation in this institution during this period according to its sources, types and areas. As well, the study will discuss Omar Dengo Fondation's international cooperation during the period of 2000 to 2004, through programs and projects and through a categorization created by the author to describe the institutional management. The international cooperation's contribution in the institutional management will be examined, through the compilation and analysis of data regarding international cooperation during the period of 2000 to 2004 and through a case study of the project: “ICT Training for Women Entrepreneurs-Participation in the Knowledge Based Economy". The following work pursues the substantiation of the following hypothesis: The international cooperation's contribution to the Omar Dengo Foundation has been a key factor for the consolidation of the institutional management.Escuela de Relaciones Internacione
Experimental analysis of contact fatigue damage in case hardened gears for off-highway axles
No full textPitting is one of the main causes of failure in planetary gear sets of axles designed for agricultural
vehicles. The high torque and the low wheel speed typical of such machines result in poor
lubrication and promote the onset of contact fatigue failure by pitting, which generally occurs
earlier in the sun gear than in both the planets and the ring of wheel hub planetary drives. In
fact, sun gears are subjected to the highest contact pressure and, at the same time,
unfavourable rolling-sliding working conditions. In this paper, six case hardened sun gears
damaged by pitting during endurance tests were analysed. The aim of the analysis was to highlight
the key aspects of the morphology and the evolution of pitting damage on the case hardened
sun gears
Bending fatigue design of case hardened gears based on test specimens
No full textDifferent design methods against bending fatigue are reported in ISO 6336 standard. The standard suggests primarily the
method based on reference test gears and provides the relevant fatigue curves. Additionally, the standard suggests the
use of specimens (instead of gears) to generate the reference fatigue curves, but it also advices that specimen-based
methods can be used when gears are not available and that specimens are particularly useful for comparing fatigue
performances of gear materials relative to one another. The purpose of the present paper is to evaluate the accuracy of
the specimen-based methods mentioned in the ISO standard when applied to design gears against bending fatigue.
Experimental data were generated by means of pulsator fatigue tests on case-hardened gears used in off-highway vehicles.
Afterwards, experimental results were compared with theoretical estimations according to the approaches based on
reference test gears (as suggested by the ISO standard) and test specimens. Concerning the latter approach, the relevant
fatigue design curves were generated by testing smooth as well as notched specimens made of the same case-hardened
gear steel. It was found that the specimens-based methods are as accurate as the reference gears-based method,
provided that the material notch sensitivity factor is properly calibrated on the experimental results obtained from
specimen
In-Depth Study of ZnS Nanoparticle Surface Properties with a Combined Experimental and Theoretical Approach
No full textZnS nanoparticles (NPs) were synthesized using a simple, green, and reproducible hydrothermal method. Transmission electron micrographs show polyhedral NPs having an average diameter of 21 nm; whereas the X-ray diffraction analysis is consistent with the exclusive presence of cubic ZnS; however no oxide could be detected. A comprehensive characterization of the NPs' surface was accomplished through X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), Raman, and thermogravimetric analysis-differential scanning calorimetry, showing a fairly pure ZnS composition and a remarkable amount of adsorbed water molecules. The interaction capabilities of the surface were probed in situ by DRIFT using small molecules (CO, CO2, methanol, pyridine) as molecular probes. The same interactions were also theoretically studied with density functional calculations using a slab model based on the sphalerite ZnS (110) surface. By comparing theoretical and experimental vibrational shifts, insights on the nature of the interaction between molecular probes and surfaces were obtained. Water was found to alter both the structure as well as the reactivity of the surface, mediating the interaction of methanol with the surface, and allowing the conversion of CO2 into surface carbonates. Pyridine was instead evidenced to be able to replace water molecules because of its high adsorption energy (1 eV) which is in tune with the known pyridine-detection capabilities of ZnS. No-SH moieties or Lewis acid behavior of the exposed S atoms were observed
The Motagua Suture Zone in Guatemala. Field-trip guidebook of the I.G.C.P.-433 Workshop and 2nd Italian-Latin American Geological Meeting “In memory of Gabriel Dengo” January 2002
No full text--
- …
