Vicinity Of Contact Point Research Articles

Experimental and numerical study on the fragmentation mechanism of a single calcareous sand particle under normal compression

The rate-dependent mechanical properties of a specific geomaterial play a crucial role in engineering design and application. However, there have been very few studies involving rate-dependent mechanical properties of calcareous sand particles. This present investigation aims to study the rate-dependent breakage behavior of calcareous sand particles experimentally and numerically. Experimental tests were conducted under various loading rates. Moreover, the discrete element method was utilized in particle crushing tests to assess the breakage sub-processes. The experimental results reveal that the particle crushing strengths conform to the Weibull distribution. As the loading rates increase, the fragmentation mode changes from primary splitting and successive breaking to severe disintegration, corresponding to the three types of axial force-displacement curves, namely, the quasi-hardening, the slight quasi-softening, and the obvious quasi-softening. The simulation results show that the fractures initiate in the vicinity of contact point between the particle and loading walls, eventually penetrating through the particle along the vertical section of the sample. A higher loading rate may lead to a greater extent of particle breakage. The findings presented in this study may advance the understanding of the rate-dependent mechanical properties of calcareous sands.

High-resolution algorithms of sharp interface treatment for compressible two-phase flows

In this paper, a kind of arbitrary high order derivatives (ADER) scheme based on the generalised Riemann problem is proposed to simulate multi-material flows by a coupling ghost fluid method. The states at cell interfaces are reconstructed by interpolating polynomials which are piece-wise smooth functions. The states are treated as the equivalent of the left and right states of the Riemann problem. The contact solvers are extrapolated in the vicinity of contact points to facilitate ghost fluids. The numerical method is applied to compressible flows with sharp discontinuities, such as the collision of two fluids of different physical states and gas–liquid two-phase flows. The numerical results demonstrate that unexpected physical oscillations through the contact discontinuities can be prevented effectively and the sharp interface can be captured efficiently.

Contact analysis of three-dimensional rough surfaces under frictionless and frictional contact

A methodology for surface and sub-surface stress calculation of nominally flat on flat rough surface contact has been developed. This methodology is applicable for both large area contact (Hertzian contact) and small area of asperity contact (point load contact) with and without surface friction. A total of nine rough surfaces are generated by the computer with specified standard deviation of surface heights, σ, of 0.3, 1.0 and 3.0 nm, and correlation length, β ∗ , of 0.1, 0.5 and 0.9 μm. Under the typical applied load at the magnetic head slider-disk interface, small numbers of contact points are obtained and the deformation is purely elastic. Since these contact points are scattered and isolated, asperity contact behaves like point load contact. As β ∗ becomes larger, more adjacent points will be in contact at a certain contact spot and this is especially true at small σ. All the cases of flat on flat rough surface contact yield maximum von Mises stress on and near the surface at both frictionless and frictional contacts; no local maximum occurs in the sub-surface. In general, the friction effect in the vicinity of contact point is to increase the stress magnitude, while outside this region it also alters the stress distribution. For a surface of small β ∗ and large σ at high load of 1000 times of the nominal pressure at the head-disk interface, the contact pressure reaches the hardness at a few contact points and plastic deformation takes place in the near surface.

Multilevel Solution of the Elastohydrodynamic Lubrication of Concentrated Contacts in Spiroid Gears

This paper presents a new method for analyzing the lubrication performance of spiroid gears, which combines the elastohydrodynamic lubrication analysis with LTCA. The LTCA provides the geometry of teeth surfaces at the vicinity of contact point, normal load, lubricant entrainment velocity, etc. Multilevel techniques are used to solve the elastohydrodynamic lubrication of concentrated contacts with high ellipticity ratio under heavy load in spiroid gears. Finally, a pair of spiroid gears used in aircraft is analyzed. Some interesting new conclusions are presented.

Limits of applicability of elastic contact models of rough surfaces

Recent stochastic models for analyzing the contact of rough surfaces assume that the asperities are microhertzian, i.e. that they can be approximated as second-order surfaces in the vicinity of contact points, and that the asperities deform elastically. Using a plane strain solution from the literature for a sinusoidally corrugated half-space, the range of validity of these assumptions is shown to be related to the mean square surface slope and the macrocontact pressure. By extension to random surfaces characterized by a one-dimensional spectral density function an interval on the surface spatial frequency is found over which the asperities deform elastically but without completely flattening. A numerical example is given.