1,721,001 research outputs found
The influence of rounded edges on indentation by a flat punch
No full textThe contact problem and stress state for indentation by a flat punch with rounded edges is studied. For the contact problem itself analytical solutions are obtained for both surface pressure and interior stress fields. Cases of normal indentation and frictional contact, the latter in both sliding or partial slip conditions, are all treated. The transition from the Hertzian configuration to the contact between a nominally flat pad and contacting flat surface is discussed, and it is found that the strength of the contact decays surprisingly slowly. Regarding the von Mises yield parameter, there is range of configurations for which the strength is actually higher than the Hertzian one, and the strength decays only when the corner radii are very small. The present solution is therefore a realistic alternative to the classical rigid-flat punch idealization, and has particular application to fretting fatigue tests
Frictionally excited thermoelastic instability in multi-disk clutches and brakes
Full text linkThe propensity toward thermoelastic instability (TEI) in multi-disk clutches and brakes is investigated by introducing a new bidimensional analytical model, where metal and friction disks are replaced by two-dimensional layers of finite thickness. This new model permits to estimate the effect of the thickness ratio a1/a2, between friction and metal disks, on the critical speed, critical wave parameter and migration speed of the sliding system. It is found that as the thickness ratio a1/a2 decreases the critical speed reduces significantly taking up values about 80 percent smaller than that predicted by previous two-dimensional models for commonly used ratios (0.1<a1/a2<1), whilst the critical wave parameter slightly increases. Therefore, not only the susceptibility towards TEI can be reduced by changing the material properties of the friction lining but also by adjusting suitably the thickness ratio of the disks. The two-dimensional model is also employed to determine the critical speed in a real multi-disk clutch, and the results are compared with a three-dimensional finite element code. It is shown that the critical speed estimated by the present two-dimensional plane strain model is in good agreement with that determined by the FE code for sufficiently large radial thickness of the disks, whilst the two-dimensional plane stress solution has to be used for relatively small radial thickness ratios. Also, it is found that the critical number of hot spots is independent of the radial thickness ratio and it is correctly predicted by the two-dimensional mode
The design of hydrodynamically lubricated journal bearings against crack propagation
No full textFollowing a recently published paper, the likelihood of radial crack propagation from the surface of a hydraulically lubricated journal bearing is studied, under the hypothesis of the previous paper, i.e. assuming a half-Sommerfeld pressure distribution in an infinitely elongated bearing. Simple results are obtained and the effect of the lubricant is estimated. A complete set of stress intensity factors is given
Contact problems for a wedge with rounded apex
No full textElastic contact between a shallow elastic wedge, whose apex is blunted by a finite radius, and an elastically similar half-plane is studied. A closed-form contact law is found, and the interior stress field is then deduced using a Muskhelishvili's solution in series form, for frictionless and sliding conditions, This geometry removes one of the principal objections to classical solutions to the wedge indentation problem-the unrealistic infinite stress concentration implied by an atomically sharp apex-and in the latter part of the paper the strength of the contact is evaluated explicitly. Further, cases of partial slip associated with the application, of tangential load less than needed to cause sliding are considered
Tangible Digital Master for Product Lifecycle Management in Augmented Reality
No full textWe present a novel approach, called tangible
digital master (TaDiMa), based on a flexible access to
Product LifecycleManagement (PLM) database using a tangible/
graphical user interface and augmented reality.
We developed and tested a technical drawing template with
automatically embedded markers for augmentation. We
embedded the Mozilla FireFox engine into our annotation
system for the integration of web 2.0 applications in the AR
environment. We also extended the concept of web feed to
PLM for notification of technical contents.We implemented
a dynamic labelling management with view-driven filtering
and placement. We also present a tangible management for
layers visualization and users access by marked tokens. We
validated the TaDiMa approach in a selection of possible scenarios
for different PLM applications. The main benefit of
the TaDiMa system is the easy and low-cost integration in
the product lifecycle process
Frictionally-excited thermoelastic contact of rough surfaces
No full textFrictional sliding contact between two elastically similar half-planes, one of which has a sinuisoidally wavy surface, is studied in the full-contact regime. The steady-state regime is evaluated, within the limits imposed by the well-known phenomenon of thermo-elastic instability (TEI). TEI gives a critical speed whose value deqends on the wavelength of the perturbation, and above which the perturbation itself grows arbitrarily with time. It is found that the TEI critical speed, V-cr, is clearly identified by the steady-state solution only in the special and limiting case when the flat half-plane is non-conductor; in that case, V-cr is the speed for which the steady-state predicts infinite amplification. In all other cases, V-cr (appropriate to the wavelength of the profile) does not correspond to infinite amplification, nor to the maximum one, V-M. In the limiting case of thermoelastically similar materials, not only the system is unconditionally stable (V-cr = infinity) for fH(1) < 0.5, where f is the friction coefficient and H-1 a certain thermoelastic constant, but the regime at the maximum amplification is also always stable, and arbitrarily large amplification is obtained for fH(1) tending to infinity. However, it is found that in most practical cases of braking systems, V-cr much less than V-M, and so the limiting conditions are reached at V-cr. At this speed, the amplification is typically not extremely high. (C) 2000 Elsevier Science Ltd. All rights reserved
The influence of rounded edges on indentation by a flat punch
Full text linkThe contact problem and stress state for indentation by a flat punch with rounded edges is studied. For the contact problem itself analytical solutions are obtained for both surface pressure and interior stress fields. Cases of normal indentation and frictional contact, the latter in both sliding or partial slip conditions, are all treated.The transition from the Hertzian configuration to the contact between a nominally flat pad and contacting flat surface is discussed, and it is found that the strength of the contact decays surprisingly slowly. Regarding the von Mises yield parameter, there is a range of configurations for which the strength is actually higher than the Hertzian one, and the strength decays only when the corner radii are very small. The present solution is therefore a realistic alternative to the classical rigid-flat punch idealization, and has particular application to fretting fatigue tests
The design of hydrodynamically lubricated journal bearings against crack propagation
No full textFollowing a recently published paper, the likelihood of radial crack propagation from the surface of a hydraulically lubricated journal bearing is studied, under the hypothesis of the previous paper, i.e. assuming a half-Sommerfeld pressure distribution in an infinitely elongated bearing. Simple results are obtained and the effect of the lubricant is estimated. A complete set of stress intensity factors is given
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