Effect Of Static Friction Research Articles

Heap formation in two-dimensional granular media

Using molecular dynamics (MD) simulations, we find the formation of heaps in a system of granular particles contained in a box with oscillating bottom and fixed sidewalls. The simulation includes the effect of static friction, which is found to be crucial in maintaining a stable heap. We also find another mechanism for heap formation in systems under constant vertical shear. In both systems, heaps are formed due to a net downward shear by the sidewalls. We discuss the origin of net downward shear for the vibration induced heap.

Effects of Static Friction on the Forced Response of Frictionally Damped Turbine Blades

The effect of static friction on the design of flexible blade-to-ground vibration dampers used in gas turbine engines is investigated. It is found that for γ (ratio of dynamic and static friction coefficients) less than 1, the steady-state response is essentially harmonic when the damper slip load, S, is small. However, as S increases beyond a certain value, the steady-state response ceases to be simply harmonic and, while still periodic, is a more complex waveform. The transition slip load is found to be lower for smaller γ. The maximum possible reduction in vibratory stresses increases as γ decreases. These analytical results are compared with those from the conventional numerical time integration method. In addition, an efficient time integration algorithm is described which can be used to predict the peak displacements of the transition solution without tracing the whole waveform, a useful procedure when no harmonic steady-state solution exists. The conditions under which blade response can be adequately modeled by simulating only dynamic friction are established.

Forced Oscillations in the Servomechanism with Coulomb Friction and Static Friction

In this paper, the forced oscillations in the linear servomechanism with Coulomb friction and static friction are analysed exactly. For the forced oscillations with intermittent stopping in the system having only Coulomb friction, the natural anti-resonance phenomena exist and the multiple jumping phenomena occur in the input R/F-ono-stop period λπ/ω characteristics, etc. when viscous damping ζ is small. For large ζ, the R/F-λπ/ω characteristics, ect. are stable. The effects of static friction are that the R/F-λπ/ω characteristics are hard in contrast with the soft ones when only Coulomb friction and then the complete stopping boundaries exist. An analytic method using the frequency response of the linear part of system is possible for the forced oscillations without stopping.

Improved Ultra-Thin Sectioning of Tissue for Electron Microscopy

The use of a reservoir of liquid to collect ribbons of thin sections as they are cut enables serial sections to be obtained and provides means for detecting variations in thickness. Reducing the effects of static friction and of external vibrations makes it possible to cut long series of sections 0.2μ thick and uniform to better than five percent. Some observations which may throw some light on the mechanics of the cutting process are reported. Mounting the sections without any treatment is shown to be superior to any technique in which the embedding material is removed or replaced. It is shown that the technique provides sections in which a structural resolution of 200A is possible. The remaining artifacts introduced by the sectioning and mounting are easily recognized deformations which do not influence the interpretation.