Dynamic Young's modulus and glass transition temperature of selected tropical wood species

Abstract

Dynamic Young's modulus (E _d) of selected tropical wood species, namely Dyera polyphylla, Endospermum diadenum, Cratoxylum arborecens, Alstonia pneumatophora, Macaranga gigantea and Commersonia bartramia, used for the study was measured using the free–free flexural vibration method. Young's modulus from three point bending (E _3pb) and compression parallel to grain (E _cp) was also studied. The results show that the relationship between E _d and E _3pb for all wood species is very significant with the mean value of E _d consistently larger than or sometime equal to E _3pb. Surprisingly, the relationship between E _d and E _cp is not significant except for Alstonia pneumatophora. The dynamic mechanical thermal properties were also investigated using the dynamic mechanical thermal analyser (DMTA). The results showed that the storage modulus of the wood species at –90°C is in the range of 1·48–4·09 GPa with a glass transition temperature ranging from 50 to 70°C.     

基于漏斗模型的一体化生产计划与仿真系统IP＆S

多年来，小批量、多品种生产的企业生产计划与控制的有效性一直是人们十分重视而又难以解决的问题，本文介绍的基于漏斗模型的一体化生产计划与仿真系统ＩＰ＆Ｓ就是为适应这种需求而研究开发的支撑环境。     

Effect of presence of SiC and operating frequency on the damping behaviour of pure magnesium

Abstract

The objective of the present work was to investigate the effect of presence of SiC reinforcement and the vibration frequency on the overall damping characteristics of pure magnesium. The testing method uses a combination of the modified free – free beam method coupled with a circle fit approach. The effect of frequency on the damping property was studied by adding end masses to the specimen so as to alter the resonant frequency of the suspended beam. In the present study, the results are compared against a monolithic magnesium sample. The results revealed a higher damping capability of the composite specimen at all tested frequencies when compared to monolithic magnesium. Both monolithic and reinforced magnesium showed a progressive decrease in damping with an increase in frequency. An attempt is made to rationalise the damping behaviour of the composite in terms of the presence of a process induced plastic zone at the matrix/particulate interface and the operating frequency.     

A stress singularity approach to failure initiation in a bonded joint with varying bondline thickness

The stress singularity at the theoretical point of maximum stress in an uncracked single lap joint is analysed by a finite element method. By treating the interface corner of a bonded joint (between adherend and adhesive) as a perfectly bonded wedge and using a fracture mechanics method, considerable advantages over other continuum mechanics approaches for investigating the bondline thickness effect on joint strength are shown. This study has essentially two aims: (i) determination of the strength of the singularity by finite element analysis and comparison with the analytical prediction of Bogy for varying bondline thickness; and (ii) determination of stress intensity factors for varying bondline thickness. Good agreement is shown between the numerically-calculated strength of the singularity with the analytical value obtained from Bogy. The calculated stress intensity, after an initial decrease in the low bondline thickness range, is found to increase with increasing bondline thickness. This agrees well with the trends predicted by experiments.     

Fracture and mechanical properties of steel fibre reinforced Zn–5Al (Zamak 5) alloy

Abstract

Steel fibre reinforced Zn–5Al alloy (Zamak 5) metal matrix composite beams with different volume fractions of steel fibres were produced with varying notch to depth ratios. The fracture and mechanical properties of the specimens were investigated for their mode I fracture behaviour using three point bending tests under static loading at room temperature. Steel fibres with contents of 1, 2 and 3% of the total volume of Zn–5Al alloy were used as matrix materials. The critical stress intensity factor was determined using the initial notch depth method.     

The Measurement of Fibre Entanglement in Scoured Wool—Reply

An account is given of an experimental study conducted specifically to examine the effects of large variations in the staple strength of greasy wool on subsequent performance in combing and spinning by means of pilot-scale processing techniques. Batches were processed for two levels of mean fibre diameter (20 and 22 μm), each at four levels of staple strength (nominally 20, 30, 45, and 60 N/ktex), and there was close control over other raw-wool properties. Three comb settings were used for each batch. Yarns were spun to five counts selected to include the normal commercial range and the limiting situation. The SAWTRI mean-spindle-speed test was employed to assess spinning performance.

The resultant fibre length and its distribution for tops were found to be closely dependent on the staple strength and the comb setting. Differences in Hauteur of 11–14 mm were observed between the batches from the low- and high-staple-strength categories within each comb setting and fibre-diameter grouping. Differences in spinning performance were observed between the batches of the weakest wools and those of the other batches for which there were no marked trends in performance despite the differences in the fibre length of the tops.     

Analysis and spectroscopy of rare earth doped magnesium aluminate spinel

Abstract

Rare earth cation segregation in magnesium aluminate spinel has been imaged and analysed in an aberration corrected scanning transmission electron microscope. The SuperSTEM at Daresbury Laboratory provided evidence for monolayer segregation of europium ions along grain boundaries in spinel. EELS spectra confirmed the Eu to be within 0.5 nm of the grain boundary region. Spinel is a candidate material for hard window applications owing to its excellent transparency, intrinsic hardness, fracture toughness and resistance to thermal and chemical erosion. Rare earth cation doped spinel maintains good transparency throughout visible and near infrared wavelengths.     

24—THE BENDING BEHAVIOUR OF PLAIN-WEAVE FABRICS WOVEN FROM SPUN YARNS

The bending behaviour of square plain-weave fabrics spun and woven from nineteen different fibres, each in a range of cover factors, has been studied. It is shown how this behaviour is determined by the mechanical properties of the fibre and the frictional and geometrical restraints within and between yams in the fabric. The effects on these restraints of cover factor and of relaxation in wet finishing and in heat-setting are examined. Factors affecting cloth stiffness are summarized, and it is shown that two quantities, an elastic component and a frictional component, are required to specify the bending behaviour with reasonable completeness.