14—EQUIVALENT TWISTS IN TYRE CORDS

This paper describes an empirical method for choosing a twist level for a new tyre cord that will ‘match’ the twist in an existing successful cord, i.e., one that will give the same twist angle. The technique is based on published cord geometry and is shown to give reliable results. No knowledge of densities or packing factors is required, and the results are independent of the number of yarns in the cord. The method offers the possibility of calculating twist angles and related properties for cords at any twist once a sufficiently reliable value of one cord constant has been determined. A table of matched twists calculated in this way is given.     

Numerical modelling for rotational moulding with non-isothermal heating

Abstract

In the rotational moulding process, the internal air temperature has been widely recognised as a tool to predict an optimum cycle time. This paper presents a new numerical approach to predict the internal air temperature in a two-dimensional (2-D) static model without requiring the consideration of the tumbling motion of polymer powder. The initial non-isothermal heating of the static model is actually formed by two changeable plastic beds (stagnant and mixing beds), which represent the actual stagnant and mixing pools inside a rotating mould respectively. In the numerical approach, the lumped-parameter system and coincident node technique are proposed to incorporate with the Galerkin Finite Element Method in order to account for the complex thermal interaction of the internal air. It helps to overcome the difficulty of multidimensional static models in predicting an accurate internal air temperature during the heating stage of rotationally powdery plastic. Importantly, the predicted temperature profiles of the internal air, oven times for different part thicknesses and process conditions accord with the available experimental results.     

Dissolution and precipitation kinetics of γ' in nickel base superalloy Udimet 520

Abstract

The influence of various solution andaging heat treatments on the dissolution and precipitation kinetics of γ' in wrought nickel base Udimet 520 superalloy was investigated, with the aim of determining optimum preforge and post-forge heat treatment schedules. Solution heat treatments at 1070, 1100, 1110, and 1120°C for 1, 2, and 4 h followed by water quenching were applied. Examination by SEM showed that in specimens solution treated at 1070°C the necklace type microstructure remained and partialagglomeration of γ' precipitates was observed even after 4 h holding. By contrast, after solutionising at 1100°C for 4 h, the γ' volume fraction decreased from 28 to 5% and when solution treated at 1140°C, abnormal grain growth was observed. The optimum solution treatment leading to an almost complete dissolution of γ' particles was determined to be 1120°C/4 h. Double aging treatments were carried out at 925°C/4 h/ AC (air cooled) followed by aging at 700 or 800°C for times ranging from 1 to 100 h. The results indicated that the precipitates have almost spherical shapes at the beginning and as the aging time is increased a partial change to a cuboidal shape is observed. This behaviour was more pronounced when aging at 800°C was employed. Microhardness measurements under both aging conditions showed that at 700°C hardness values increase about 60 HV when γ' particles grow 70 nm. On the other hand, in the samples aged at 800°C, hardness values increase with the particle size until a certain value and then drop. The precipitate growth process was followed by image analysis and the activation energy for γ' growth was evaluated to be 104 kJ mol ^-1. The results obtained are discussed in the framework of classic nucleation theory and compared with other workers' results.     

A Test for Liability to Electrostatic Charging—Reply

An investigation is described in which exhaustion exceeded 99.7 % when triphenyltin chloride was applied to wool in a hot dyebath. The associated residues were readily decomposed by persulphate, which indicated that it should be possible to mothproof wool with triphenyltin chloride without risk of contaminating the aquatic environment. Only small amounts of the triphenyltin were extracted from treated wool by human perspiration or saliva.     

Strength estimation of self-piercing rivets using lower bound limit load analysis

Abstract

This paper summarises the authors' work on strength and failure mode estimation of self-piercing rivets (SPRs) for automotive applications. First, the static cross tension strength of an SPR joint is estimated using a lower bound limit load based strength estimator. Failure mode associated with the predicted failure strength can also be identified. It is shown that the cross tension strength of an SPR joint depends on the material and gage combinations, rivet design, die design and riveting direction. The analytical rivet strength estimator is then validated by experimental rivet strength measurements and failure mode observations from nine SPR joint populations with various material and gage combinations. Next, the estimator is used to optimise rivet strength. Two illustrative examples are presented in which rivet strength is improved by changing rivet length and riveting direction from the original manufacturing parameters.     

Effect of prior austenite characteristics on mechanical properties of thermomechanically processed multiphase TRIP assisted steels

Abstract

To develop any multiphase transformation induced plasticity (TRIP) assisted steel through thermomechanical processing routes, the effects of materials and process variables are to be thoroughly identified. Accordingly, the present work was programmed to study the influence of the state of prior austenite on the subsequent transformations and the related final phase combinations. In this framework, using a low carbon TRIP assisted multiphase steel, the compression specimens were subjected to different thermomechanical processing schedules to generate different prior austenite characteristics. The results indicated that the characteristics of martensite/austenite (M/A) microcomponent in the final microstructure were dictated by the state of prior austenite. In fact, increasing prior austenite grain size led to large decrease in the amount of M/A phase and this, in turn, resulted to higher strength without sacrificing the ductility. It was also found that static recrystallisation of austenite brings about more percentage of M/A phase compared with dynamic recrystallisation.     

Fracture micromechanics of static subcritical growth and coalescence of microcracks in sintered Fe–1·5Cr–0·2Mo–0·7C steel

Abstract

Nucleation of microcracks, their growth and coalescence are analysed in powder metallurgy (PM). Fe–1·5Cr–0·2Mo–0·7C steel by fractography allied to surface replica microscopy – at several stress levels as the maximum tensile stress in three-point bend specimens was raised to 99·6% of the transverse rupture strength TRS of 1397 MPa. The fatigue limit in this material is ～240 MPa, at which stress level no microcracks were detected in static loading. Numerous microcracks, ranging in size from <5 to ～20 μm, however, were nucleated above ～800 MPa, i.e. beyond the yield strength of ～620 MPa. With increasing stress, some microcracks became dormant, whilst others grew subcritically, stress step-wise, to some 400 μm. Of particular importance are observations of the coalescence of two and three of such microcrack systems to produce a critical, propagating crack. The then estimated stress intensity factor K _a, could reach K _1C, independently estimated to be ～36 MPa m^1/2. Microcrack coalescence was associated with easy paths for crack growth, principally prior particle boundaries linking pores. Ways of making subcritical crack growth more difficult and hence improving both static and dynamic mechanical properties, are considered.     

Influence of static magnetic fields on the protective ability of phosphate coatings on aluminium alloys

Abstract

Phosphate coatings on aluminium are used to improve the corrosion resistance of aluminium before the latter is painted. Phosphate coatings deposited in phosphate solution treated with a magnetic field prior to deposition can take on new properties. A magnetic field can either improve or deteriorate the properties of the phosphate coating formed, depending on the composition of aluminium.     

2—PERMANENT-PRESS EFFECTS IN WOOL: PART V: METHODS OF STABILIZING SET

Shrink-resist wool set in the normal way can lose wanted set or acquire unwanted set during machine-washing and tumble-drying because the molecular-bond rearrangements responsible for setting can still occur during the laundering cycle. The set can be stabilized to withstand such laundering by any of the following methods:

1. the inhibition of thiol-disulphide interchange by:

   1. removing ionized thiol groups, or

   2. converting disulphide bonds to non-interchangeable links, such as —S—, —SCH₂S—;

2. the introduction of new cross-links; or

3. denaturation to form structures that are slow to rearrange during washing.

The stability of set is enhanced by a combination of the methods because these operate by different mechanisms. Prevention of thiol-disulphide interchange appears to be more important during washing, whereas the presence of cross-links appears to be more important to aid recovery during tumble-drying.     

Error Analysis and Effective Adjustment of the Walking-Ready Posture for a Biped Humanoid Robot

A walking control algorithm is generally a mixture of various controllers; it depends on the characteristics of the target system. Simply adopting one part of another researcher's algorithm does not guarantee an improvement in walking performance. However, this paper proposes an effective algorithm that can be easily adopted to other biped humanoid robots; the algorithm enhances the walking performance and stability of the robot merely by adjusting the walking-ready posture. The walking performance of biped humanoid robots is easily affected by an unsuitable walking-ready posture in terms of accuracy and repeatability. More specifically, low accuracy for the walking-ready posture may cause a large difference between an actual biped robot and its mathematical model, and the low repeatability may disturb the evaluation of the performances of balance controllers. Therefore, this paper first discusses the factors that detrimentally affect bipedal walking performance and their phenomena in the walking-ready posture. The necessary conditions for an ideal walking-ready posture are then defined based on static equilibrium and a suitable adjustment algorithm is proposed. Finally, the effectiveness of the algorithm is verified through dynamic computer simulations.