Estimation of contact stiffness at interfaces in machine structures by a beam model on an elastic foundation

The dynamic properties of machine structures are significantly influenced by an interaction at the mating surfaces of machine elements. This interaction is called contact stiffness, and the development of a simple method for contact stiffness estimation is an important tribological objective. In this paper the contact stiffness is estimated by a beam model vibrating on an elastic foundation. The effects of clamping condition and mating surface topography on the contact stiffness obtained are quantitatively and accurately represented by experimental equations.     

Formulae for the squeeze film between a rigid cylinder and a thin elastic layer with sinusoidal waviness

A set of formulae for the variation of the film thickness with time when a rigid cylinder approaching a thin elastic layer with sinusoidal waviness is derived. The shapes of the solids are assumed to be the same as the elastically deformed surfaces under dry conditions. Two geometrical configurations are investigated. First, the layer is resting without friction on a rigid substrate (unbonded layer). Second, the layer is attached firmly to a rigid substrate (bonded layer). The obtained results showed a good agreement with those reported for a smooth bonded layer.     

Normal and lateral modulation with a scanning force microscope,an analysis: implication in quantitative elastic and friction imaging

Results and an analysis are presented on elastic and friction imaging by indirect force modulation with a scanning force microscope. Two techniques are compared, normal modulation (Z-modulation, perpendicular to the surface of the sample) and lateral modulation of the contact (X-modulation in the plane of the sample, perpendicular to the axis of the cantilever). Theoretical and experimental results show that lateral modulation offers great advantages compared to normal modulation: the images are free of artifacts and can be easily quantified. This revised version was published online in August 2006 with corrections to the Cover Date.     

A finite-element analysis of the indentation of an elastic-work hardening layered half-space by an elastic sphere

An elastic–plastic contact problem in elastic-work hardening layered half-space indented by an elastic sphere was solved numerically using the finite element method. The case of a surface layer stiffer than the substrate is considered, and general solutions for the subsurface stresses and deformation fields are presented for a relatively thin elastic layer. Differences between the elastic and elastic–plastic solutions for the contact pressure distribution have been investigated for various layer thicknesses. Crack initiation and decohesion of the layer was also discussed with reference to the growth of the plastic zone.     

Effects of fiber aspect ratio evaluated by elastic analysis in discontinuous composites

An elastic stress analysis to investigate the effects of fiber aspect ratio in short fiber reinforced discontinuous composite materials has been done for different fiber volume fractions. In order to examine the elastic internal behavior, an evaluation of the load bearing capacity of discontinuous reinforcements is needed in advance. Accordingly, analytical derivation of composite mechanics has been carried out to predict fiber stresses and fiber/matrix interfacial shear stresses in discontinuous composites. The model is based on the theoretical development of conventional shear lag theory developed by Cox. However, the major shortcoming of the Cox model is due to the calculation without normal stress transfer from the end of fibers. In order to overcome the shortcoming, both of the normal and shear stress transfer mechanisms between the fiber and the matrix are accounted for with the stress concentration effects as well as material and geometrical properties. Results of predicted stresses concerning the various fiber aspect ratios are described by using the present model that is the closed form solution and compared with the Cox model and Taya model. It is found that the effect of fiber aspect ratio is significant to composite strengthening through load transfer from the matrix to the fiber, whereas the effect of fiber volume fraction is not so sensitive, relatively. It is also found that the present model has the capability to correctly predict the values of fiber stresses and fiber/matrix interfacial shear stresses.     

某型飞机前起落架焊接部位应力应变分析

起落架是飞机起飞和着陆的关键部位。某型飞机前起落架的缓冲支柱与横梁通过焊接连结,而焊接部位的性能受焊接质量影响很大,准确分析不同焊接部位的焊接质量及在各种情况下的应力应变,对于该飞机前起落架的使用和维修具有深远的意义。本文利用有限元软件,建立焊接部位实体模型,通过模拟加载,对起落架的焊接部位进行应力应变分析,找到应力最大的危险点。     

水压柱塞泵中柱塞与缸孔接触比压的分析与探讨

在考虑柱塞与缸孔之间间隙的基础上 ,利用材料力学的基本原理 ,对柱塞与缸孔的受力模型做了详尽推导 ,并运用 MATLAB工具进行求解 ,结果发现该接触比压值较传统方法的计算值大 1 0倍以上 ,同时发现该接触比压受摩擦副材料的弹性模量、摩擦副间隙大小等因素的影响。针对该接触比压的深入分析为水压柱塞泵柱塞与缸孔的粘着磨损现象提供了可信的解释     

Thermal friction problem and its development: Part 2. The role of heat phenomena in fracture of tooth wheels of cylindrical involute gears of real dimensions

The local pattern of initial of fracture of machine parts is discussed and the practical significance of determination of the zone of manifestation is highlighted. The temperature is considered the main factor in the process of improvement of the thermal friction problem governing operation of a heavily stressed contact. The results of calculation of brakes with the method of thermal dynamics of friction and wear are demonstrated.