30—HEAT AND MOISTURE EXCHANGE IN WOOL BEDS: EQUILIBRIUM THEORY IN THE HYGROSCOPIC RANGE

Cassie's theory of propagation of heat and moisture changes in beds of wool fibres is re-examined by means of the method of characteristics. Substantial differences result in the predictions of the theory by treating the coefficients of the pertinent differential equations as functions of the dependent variables rather than as constants.     

31—THE EFFECT OF VARIABILITY OF FIBRE DIAMETER ON WORSTED PROCESSING. PART II. THE USE OF COMPARISON SAMPLES OF COMMERCIAL TOPS AND THEIR BLENDS

Changes in the coefficient of variation of fibre diameter (V _d ) were made by blending top qualities (a) 70s and 56s, and (b) 60s and 56s, and comparing these with a 58s. In this way, a range of values of V _d from 21.4 to 24.9% was obtained over three top samples whose mean fibre diameters and fibre lengths were closely similar. These tops were worsted-spun to determine their performance at the spinning limit and other yarn counts and to measure the yarn properties. The three samples did not give any important differences in chemical composition or in spinning limit, but did show a trend to significant differences in yarn breaking strength and elongation, the lower-V _d sample being favoured. Over this range of values of V _d at mean diameters of 25–26 μm, although there are hints of slight differences in spinning and in the product, the trend is not important. The range of V _d values for European tops of mean fibre diameter 25.3 μm appears to lie between 22 and 28%. The Australian tops investigated gave V _d values over the lower half of this range.     

INHIBITION MECHANISM OF Na2MoO4 FOR CARBON STEEL IN 55% LiBr SOLUTION

Electrochemical measurement and chemical immersion test are employed to investigate the inhibition mechanism of Na_2MoO_4 for carbon steel,which is studied in 55%LiBr+0.07mol/L LiOH solution at high temperature.Testing results indicate that the passive film on carbon steel surface is mainly composed of Fe_3O_4,and Mo is involved in the process of film forming,in a form of MoO_3 and MoO_2.The parametric analysis of the evolving potential and the blend potential of MoO_2 shows that Mo mainly exists as MoO_2 in passive film when the concentration of Na_2MoO_4 is lower than 150 mg/L.While its concentration is greater than 150mg/L,it mainly exists as MoO_3 inside the film and exists as MoO_2 outside the film.MoO_4~(2-) is deoxidized as MoO_2 on the surface of carbon steel,which may impede the corrosion of active-site and raise the blend potential of carbon steel,and then MoO_4~(2-) adsorbs onto the defects of the passive film and decompounds as MoO_3 during the process of film forming.The electric field caused by different valence of Mo in passive film may retard the dissolution of carbon steel and lead to an increase in the polarization impedance and a decrease in hydrogen evolution.As a result,heavy concentrated Na_2MoO_4 solution(greater than 150mg/L)has excellent inhibition effect on carbon steel in LiBr solution.     

15—A STUDY OF NEEDLED FABRICS. PART V: THE APPROACH TO THEORETICAL UNDERSTANDING

Needled fabrics are complicated structures, and an exact analysis of their mechanics is not yet possible. Understanding is approached through three routes. Firstly, the behaviour of a fully bonded web is used to predict the effects of orientation, and to estimate the upper limits of strength. These estimates may be reasonable if the network that actually exists at the breaking point is used in calculations. Needled fabrics can give a fairly high utilization of fibre strength. Secondly, the effects of slippage are discussed qualitatively, by analogy with the behaviour of spun yams. The influences of entanglement, fibre length, fibre fineness, and fibre friction are discussed. Thirdly, a quantitative analysis, with many approximations, of a much-simplified model is made. Despite the unsatisfactory nature of some of the assumptions, the predictions are in general accord with experimental results.     

Cathodic Protection and Stress Corrosion Cracking of Mild Steel District Heating Distribution Systems

Abstract

Inadequate design or construction of certain district heating distribution systems has led to severe corrosion problems. These systems were then cathodically protected by means of impressed current installations, and the frequency of leaks was thereby reduced. However, following this, a number of failures due to stress corrosion cracking have been discovered. This has been traced to the alkaline environment round the pipe produced by the cathodic protecion process, combined with subsequent concentration by evaporation, the potential of the pipe then being in the range known to promote caustic cracking when residual stresses are present in the pipe. The only possible solutions to the problem for existing pipelines are either to remove the cathodic protection and revert to the likelihood of general corrosion problems, or to control the applied current so that the pipeline is kept out of the potential range known to promote stress corrosion. In practice this is difficult to achieve and may result in parts of the pipeline being under-protected.     

Erosive abrasive wear behaviour of stainless steel surface produced by plasma transferred arc hardfacing

Abstract

Erosive abrasive wear is caused by high speed impact of particles entrained in a fluid system on the surfaces of components such as boilers and furnaces. Erosive abrasive wear in boilers results from the impact of hard particles such as ash or clinker entrained in flue gases and can lead to serious damage. The life of boiler and furnace components encountering erosive abrasive wear in service, which are most commonly fabricated from carbon steels, can be improved by hardfacing with a wear resistant material. The effects of wear parameters such as particle size, flux and velocity on the erosive abrasive wear behaviour of a stainless steel surface produced by the plasma transferred arc hardfacing have been investigated using an experimental design approach. The wear resistance of the stainless steel surface was found to be twice that of the carbon steel substrate.     

Geometrical range of microscopic stress distribution change due to fibre array irregularities for thermally and transversely loaded CF/epoxy composites

Abstract

A detailed numerical investigation has been carried out to investigate the effect of local fibre array irregularities on microscopic interfacial normal stress for transversely loaded unidirectional carbon fibre/epoxy composites with random fibre arrangement. Linear elastic finite element analyses were carried out for a two-dimensional image based model composed of 70 fibres. One fibre in this image based model is replaced with resin as the resin equivalent fibre, and the resulting change in microscopic interfacial normal stress distribution is investigated. Three fibres are selected for the resin equivalent fibres to clarify the individual local geometrical irregularity. Calculations were carried out for three loading conditions: case A, cooling of –155 K from the curing temperature; case B, transverse loading of 75 MPa chosen as an example of macroscopic transverse fracture strength and case C, both cooling from the curing temperature and transverse loading of 75 MPa. The effect of fibre array irregularities on the interfacial stress state is limited to the region between the resin equivalent fibre and its first neighbouring fibres. The contribution of the second neighbouring fibre is small and that of further fibres is negligible.     

The Effect of Variability of Fibre Diameter on Worsted Processing

An examination of the effect of a range of cationic surfactants on the bending properties of a woven wool fabric is reported. The changes in fabric properties caused by the surfactant differed considerably from those observed on cotton fabric. Factors affecting the fabric properties included the distribution of the surfactant on wool fibres, the nature of the surfactant, the method, time, and temperature of application, and the nature of any modification to the wool fibres.     

Adhesion Characteristics of Carbon Black Embedded Glass/Epoxy Composite

The surface of glass/epoxy composite material was embedded with carbon black which was dispersed in methyl ethyl ketone (MEK) during the curing process to enhance the adhesion strength of the glass/epoxy composite structure. The morphological effect of the carbon black on the surface of composite was observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Quantitative chemical bonding analysis with X-ray photoelectron spectroscopy (XPS) was also performed to observe chemical bonding states on the surface. The lap shear strength of the glass/epoxy composite adhesive joints where composite adherends were embedded with carbon black was investigated with respect to the type and amount of embedment. Also, the tensile properties of the carbon black embedded glass/epoxy composites were measured to observe the mechanical degradation of the composite due to the MEK. The surface free energies of carbon black embedded composites were determined from the van Oss–Chaudhury–Good equation to correlate the lap shear strength of the adhesive joints with the surface free energies of composite adherends. From the experimental results, it was found that the carbon black embedment of the composite adherend improved much the bond strength due to the increased surface roughness on nano-scale as well as increased surface free energy.