32—A USEFUL METHOD FOR CALCULATING COEFFICIENTS OF FRICTION OF WOOL FIBRES FROM CAPSTAN MEASUREMENTS

An account is given of an investigation in which a variant of the capstan method was used to study the dependence of the frictional properties of wool fibres on the tension in the fibres when they slid at a very low speed over a rod of horn immersed in water (to which a wetting agent had been added). Some ofthe fibres had been given a mild shrinkproofing treatment with KMnO₄ in saturated salt solution. The curves relating the tensions T ₁ and T ₀ in the two ends of a sliding fibre, with T ₁ > T ₀, were found to be accurately linear in the range from T ₀=O up to T ₁=05 gf. For with-scale sliding, they all passed very close to the origin, but nevertheless the coefficient of with-scale friction,μ_w(={1/π}ln{T ₁/T ₀}), was markedly dependent on the tension owing to the high sensitivity of the logarithm to ‘zero error’ in the range of T ₁/T ₀ appropriate to with-scale sliding. For against-scale sliding, the intercept was larger and more variable, so that μ_a also depended markedly on the tension. It is suggested that the most satisfactory parameters to use for characterization of the friction are the coefficients of friction calculated from the slopes of the curves of T ₁ against T ₀, without regard to the intercepts.

It is shown that these new parameters reveal satisfactorily a previously determined difference between the shrinkproofed and the untreated fibres, namely, that the with-scale coefficient is significantly larger for the shrinkproofed fibres.

The measured coefficients for untreated fibres depend on the state of polish of the horn surface. For treated fibres, repolishing the horn greatly increases the variance of the measurements. The best conditions to use for particular applications are dicussed.     

Analysis of rolling load generated by pair crossed rolling mill

Abstract

Although a pair crossed rolling mill has a very high control capability of strip crown, a frictional force always occurs in the strip width direction between the strip and the work rolls. An analysis of rolling load was carried out, considering the shear deformation of strip cross-section caused by the frictional force. From the examination of the calculated results for a large-scale mill for production, the following conclusions were obtained: (a) the cross angle hardly influences the rolling force and torque, (b) the thrust force on the roll induced by the frictional force decreases as a result of shear deformation, (c) the thrust factor, i.e. the thrust force divided by the rolling force, is little influenced by the strip deformation resistance and the friction coefficient between the work rolls and the strip during hot rolling, (d) the thrust force applied to the rolls during hot rolling is 3–6% of the rolling force for the cross angle of 1° and this is not an obstacle related to the design of rolling mills.     

Study on TIG welding of dissimilar Mg alloy and Cu with Fe as interlayer

Abstract

Dissimilar Mg alloy and Cu lap joints were prepared by tungsten inert gas (TIG) welding with Fe as an interlayer, without producing intermetallic compounds MgCu₂ and Mg₂Cu. Copper and Fe were joined together in the form of remelt deposit welding and Mg alloy and Fe plate were joined together in the form of brazing. During tensile testing, the joints between Fe plate and Mg alloy fractured, and Mg alloy and Fe plate were joined together by interatomic force. Metallic oxides produced in the interface between Mg and Fe resulted in reduction in the mechanical properties of the welded joints.     

Fibre reinforced cellular microstructure of cork wood

Abstract

Scanning electron microscopy was used to observe the microstructures of a cork wood. It showed that the wood consists of countless rectangular and honeycomb wood cells. The wall of each wood cell connects with adjacent wood cells at the middle of the cell wall. More careful observation showed that the walls of the wood cells are a kind of fibre reinforced biocomposite consisting of crystalline cellulose fibre layers and hydrocarbonated polymer matrix. The crystalline cellulose fibres in different fibre layers possess different directions, which compose a kind of fibre helicoidal microstructure. In the microstructure, the helicoidal angle is very large. The maximum pullout force of the fibre helicoidal microstructure, which is closely related to the fracture toughness of the wood, was theoretically and experimentally investigated and compared with that of the fibre parallel microstructure. It showed that the maximum pullout force of the fibre helicoidal microstructure is markedly greater than that of the fibre parallel microstructure and that the larger the helicoidal angle, the more the maximum pullout force will increase compared with that of the parallel microstructure.     

Adhesion measurement of thin films to a porous low dielectric constant film using a modified tape test

In the microelectronics industry, a simple tape test (ASTM 3359) is typically used to qualitatively study the adhesion of dielectric films. In this work, a novel approach to conduct the tape test is proposed. This new method eliminates the inconsistency in the results encountered in the traditional tape test, and, at the same time, it provides both qualitative and quantitative results. This approach employs a spring-loaded mechanism and eliminates the subjective interpretation of the results of the traditional tape test. It also provides quantitative measures of the peel rate and force, factors that are relevant in the characterization of the interfacial strength of thin films. We illustrate the use of this new, modified tape test (MTT) in the study of the adhesion of multi-layered thin film structures. This study is of significance to the understanding of the damascene interconnect process integration. Thus, the adhesion of various films (e.g. oxide, insulator and metallic films) on the spun-on porous carbon-doped silicon dioxide low dielectric constant (k) material is examined. Also, the effects of surface treatments (ion implantation and N₂ plasma) and curing temperature of the porous low-k films on the adhesion of the overlying oxide films are also described. An explanation of the adhesion strength with respect to the thickness of the cap layer (overlayer) is presented as well.     

Application of a Genetic Algorithm Associated With Adhesive Joint Analysis to the IC Chip Pick-up Process

In the condition investigated here, a concentrated force is applied to both IC chip and blue tape bonded by an adhesive under pin–pin boundary conditions. The experimental results show that even though IC chips of 0.1 mm thickness are subjected to a concentrated force of 4.8 N, they cannot be fully separated from the blue tape and fail easily during the pick-up process. However, when IC chips of 0.34 mm thickness are subjected to a concentrated force of only 3.5 N, they can be fully separated from the blue tape without breakage. These two experimental findings are then explored analytically by applying the C++ program of the genetic algorithm associated with adhesively bonded joint analysis to the IC chip pick-up process. In accordance with the experimental results, the results for the 0.1 mm thick IC chips reveal no solutions for the material properties or adhesive thickness to satisfy the conditions of the IC chip successful pick-up process, although those for the 0.34 mm thick IC chips show solutions for the values of both the elastic modulus and the adhesive layer's thickness. As regards the easy failure of IC chips with 0.1 mm thickness, if the blue tape's mechanical properties are appropriately chosen and then used in this process and its elastic modulus is greater than one-tenth that of the IC chips, the probability of the IC chips being fully separated from the blue tape can be expected to increase.     

Effect of chain length of self-assembled monolayers on adhesion force measurement by AFM

It has been confirmed experimentally that the adhesion force measured between an atomic force microscope (AFM) tip and the self-assembled monolayers (SAMs) has a direct correlation with the chain length of SAMs, and that the adhesion force decreases with the increase of the chain length. In this paper, a theoretical model is put forward to calculate the adhesion force between the AFM tip and the SAMs by integrating the Lennard–Jones potential. The theoretical results are in good agreement with the existing experimental results.     

MUSTA‐type upwind fluxes for non‐linear elasticity

The present paper is devoted to the construction and comparative study of upwind methods as applied to the system of one‐dimensional non‐linear elasticity equations with particular attention to robustness and accurate resolution of delicate features such as linearly degenerate fields. Copyright © 2007 John Wiley & Sons, Ltd.