Frictional Hertzian contact problems under cyclic loading using static reduction

In this study we investigate an axisymmetric Hertzian contact problem of a rigid sphere pressing into an elastic half-space under cyclic loading. A numerical solution is sought to obtain a steady state, which demands a large amount of computer memory and computing speed. To achieve a tractable problem, the current numerical model uses a “static reduction” technique, which employs only a contact stiffness matrix rather than the entire stiffness of the problem and is more accurate than the approach used by most finite element codes. Investigation of the tendency of contact behavior in the transient and steady states confirms that a steady state exists, showing converged energy dissipation. The dependence of dissipation on load amplitude shows a power law of load amplitude less than 3, which may explain some deviations in the experimental findings.     

渐开线斜齿轮非稳态弹流润滑数值模拟研究

建立了渐开线斜齿轮啮合的弹流润滑计算模型,将斜齿圆柱齿轮啮合的齿面接触等效为有限长线接触的弹流润滑问题.考虑斜齿轮啮合的实际因素,将斜齿轮啮合过程中的等效曲率半径和齿面载荷的变化反映到弹流润滑计算模型中,应用统一Reynolds方程方法求得轮齿在1个完整啮合周期内的瞬时弹流润滑数值解.结果表明：斜齿轮啮合线上各点处的膜厚、压力均有较大不同,各接触点处的油膜厚度受综合曲率半径的影响较大;斜齿轮传动非稳态效应相对较弱;小齿轮齿根附近和节点位置处润滑状态较差;适当增大压力角可以改善齿轮的润滑.     

Involvement of organic fluorine substitution in the crystalline packing structures of tricyclic Diels-Alder adducts derived from diarylfulvenes and N-arylimides

Fluorinated tricyclic Diels-Alder adducts derived from corresponding diarylfulvenes and N-arylmaleimides, each of different degree and positions of the fluorine substituents, and including the non-fluorinated parent compound, have been synthesized. Their X-ray crystal structures were determined in order to study the effect of fluorine substitution on the solid state organization in competition with other weak intermolecular interactions. A balanced interplay of C-H?O, C-H?F and especially C-H?π contacts is typical of the crystal packings while other potential interactions such as C-F?F, C-F?π^F, π^H?π^F and Br?Br are secondary or not to be found. Isostructurality calculations and comparison of molecular conformations have been performed in order to structurally classify the compounds depending on the number and mode of fluorination.     

Conformational and Database Study on the Intramolecular CH...π Aromatic Bond and Its Possible Influence on the Stereochemistry of Polypeptide Chains

The presence of intramolecular CH... aromatic bonds in organic molecules has been analyzed by means of CSD searches. In particular, molecules containing aromatic and methyl groups have been examined as a function of the length of the chain separating the interacting groups. The type of bonds in the chain and its geometry have also been taken into account. The maximum number of CH... interactions have been found for five-membered chains joining the aromatic and methyl moieties. In addition, this interaction seems favored when the chain contains two sp ² hybridized atoms. The interactions involving polypeptides have been carefully examined. Interest has focused on compounds containing both aromatic and methylic residues, i.e., a combination of phenylalanine (phe), tyrosine (tyr), and tryptophan (trp) with alanine (ala), valine (val), leucine (leu), and isoleucine (ile). The maximum number of CH... interactions have been found when five atoms constituted the chain, i.e., in the sequences phe–ala and ala–phe.     

Frictional moving contact over the surface between a rigid punch and piezomagnetic materials – Terfenol-D as example

A general theory of the frictional moving contact of piezomagnetic materials indented by a flat or cylindrical punch is set up. The rigid punch moves at a constant speed and the Coulomb friction law applies inside the contact region. Terfenol-D with high magnetostriction and coupling is chosen. Employing the Galilean transformation and Fourier transform, Cauchy integral equations of the second kind are obtained and solved exactly. Closed-form expressions of physical quantities on the surface in terms of elementary functions are given. Numerical analyses are conducted to reveal the effects of the friction coefficient and moving speed of the punch on various surface stresses and magnetic induction. The singularity, discontinuity and spike of the surface magnetic induction may be important factors to explain why surface damage occurs for piezomagnetic materials.     

Resolución numérica de las ecuaciones del movimiento de edificios de varias plantas con no linealidades severas

This paper presents a new algorithm for solving the equations of motion of multi-storey buildings that incorporate frictional energy dissipators as seismic protection. The behavior of the dissipators is represented by Coulomb dry friction models; they introduce severe nonlinearities in the dynamic behavior of the structure every time that the contact conditions (stick or slip) change in the dissipators. These nonlinearities complicate the resolution of the equations of motion as it usually is described by lumped masses models whose degrees of freedom are the displacements of the floors and, as the stick or slip conditions change, the degrees of freedom must be modified: for blocking conditions they are only the displacements of the storeys while under sliding conditions the displacements of the dissipators have to be also considered. In previous articles the accuracy of the proposed algorithm has been verified by comparison with experimental results; as well, the computational efficiency of the algorithm has been confirmed by comparing the required resources (in terms of computation time and of memory allocation) with those of other algorithms. The objectives of this paper are to describe in detail the numerical solution of the equations of motion and present representative examples confirming the ability of the algorithm to reproduce the dynamic behavior of buildings with friction dissipators and reporting preliminarily about the usefulness of such devices to reduce the oscillations of the structure to be protected.     

Rolling friction of a hard cylinder on a viscous plane

The resistance against rolling of a rigid cylinder on a flat viscous surface is investigated. We found that the rolling-friction coefficient reveals strongly non-linear dependence on the cylinder's velocity. For low velocity the rolling-friction coefficient rises with velocity due to increasing deformation rate of the surface. For larger velocity, however, it decreases with velocity according to decreasing contact area and deformation of the surface. Received 24 December 1998 and Received in final form 14 January 1999     

Recognition determinants in a T4 ← G4 mutant derived from a 5′-GCGTGGGCGT-3′ oligomer in a zinc finger 268–DNA complex.

The 5′-GCGTGGGCGT-3′ (T4) oligomer found in the zinc finger 268–DNA complex was mutated into the sequence 5′-GCGGGGGCGT-3′ (G4). A 3D model was constructed from the T4 sequence using an X-ray structure as a template. Molecular dynamics simulations were used to test the thermal stability of the model. A 500-ps trajectory was obtained for the fully charged complex in water using GROMOS87. The complex and the G4 sequence are found to have dynamically stationary behavior. Comparisons made with a previous T4 sequence molecular dynamics simulation show both systems have similar thermal stability. The structure of DNA appears to be maintained by its global interactions with the protein although the mutated site does not contribute with its full potential for binding. The protein structure shows some small differences compared to the T4 simulation. The simulation provided evidence for the role of a chloride ion interacting with the protein and helping in the recognition process. Received: 21 June 1999 / Accepted: 19 October 1999 / Published online: 14 March 2000     

Surface Modification and Contact Interaction of Particles

Abstract

The effects of particle surface modification by ambient media and surfactant adsorption on the cohesive forces in the immediate contacts between individual particles have been studied with the CF (cohesive force) apparatus. The values of the free energy of interaction in direct coagulation contacts between particles of various types in liquids of different polarity and in the presence of various surfactants have been measured. They cover a broad range of several orders of magnitude; these interactions define the rheological properties of concentrated thixotropic systems and their stability with respect to peptization. A similar experimental technique has been used for studying active media influences on various physico‐chemical processes of particle bridging and formation of the phase contacts responsible for the mechanical properties of related solid structures and their resistance to fracture. The effect of the adsorption induced decrease in strength and durability of such porous structures with phase contacts and compact solids is considered.