Experimental investigation of yield behaviour of metal powder compacts

Abstract

In this paper the compaction and yield response of two steel and two copper powders are examined. These were chosen to determine how the material response depends on the type of material and the morphology of the powder particles. Experiments were conducted in a computer controlled triaxial cell. Here, concentration is on the response during simulated, frictionless closed die compaction, whereby the radial stress is controlled so as to keep the radius of the sample constant. The compaction process was stopped at regular intervals and a series of probing paths were followed in stress space to construct the yield surface for the compact.

The experimentally determined yield surfaces are compared with yield surfaces predicted by empirical models and micromechanical models of the Fleck type, which assume that the compact consists of monosized spherical particles. During the early stages of compaction the form of the yield surfaces for spherical powders are consistent with Fleck's micromechanical model, but the surfaces become less elongated in the direction of loading at high densities. The yield surfaces for irregular shaped powders are significantly different from the predictions of the Fleck micromechanical model. A modified anisotropic Cam-Clay model is proposed, which is able to predict yield surfaces for the four powders at all densification levels.     

Effect of VC and (Ta,Nb)C on wear of WC–10Co based cemented carbides

Abstract

WC–Co cemented carbides, including small angular tungsten carbides particles, are used extensively to improve wear resistance. Some additives can affect mechanical and wear properties of these materials. In this study, the effect of VC and (Ta, Nb)C content on wear of WC–10Co were considered. The tests were performed at normal load of 230 N and sliding distance of 800 m up to 3200 m. Wear tests were carried out using dry sand/rubber wheel apparatus. Wear rate, standard and modified wear coefficients were calculated. The microstructures of prepared specimens were examined by optical microscopy. The morphological analysis of the worn surfaces was made by SEM. The results show that VC content has more effect than (Ta, Nb)C content on wear behaviour. Wear mechanism is different in the specimens, but removal of cobalt rich phase and fracture of carbide grains is clear in all of specimens. Abrasive wear is prevailing in all specimens.     

Classic contributions: cryogenic treatment Effects of cryogenic treatments on mechanical properties and wear behaviour of high-speed steel M2

Abstract

In this contribution, originally published in 2000, the levels of hardness, impact toughness and wear resistance of M2 high-speed steel after conventional heat treatment are compared with those imparted by additional subzero and deep cryogenic processing.     

6—THE WEAR LIFE AND ABRASION-RESISTANCE OF CARPETS MADE FROM VARIOUS FIBRES AND BLENDS

An account is given of a study of the wearing properties of woven and tufted carpets made from wool, nylon, viscose rayon, and an acrylic fibre and from various blends of these fibres. The carpets were subjected to trials on two staircases and to laboratory tests for resistance to abrasion.

It is shown that nylon resisted abrasion in use better than the other fibres studied, and the advantages of introducing nylon into a blend with one of the other fibres are demonstrated by comparison with the results obtained on carpets made entirely from the other fibres.

It is also shown that, in general, the laboratory abrasion tests confirm the ranking of the carpets in the service trials on a staircase, although the advantages of introducing nylon appear to be greater in the laboratory tests than in use.     

Thermal shock resistance of zircon/SiC composite

Abstract

In the present work, thermal shock tests of zircon/silicon carbide (30 wt-%) composite specimens were evaluated up to 1000°C and compared with pure zircon specimens at nearly the same porosity content. Results confirmed that the fracture strength of the quenched specimens was not affected with the increase in quenching temperatures by incorporating SiC particles, indicating resistance to crack propagation. On the other hand, the critical temperature difference ΔT, below which material maintains its original strength, was found higher in composite rather than pure zircon specimens. X-ray diffraction investigations showed that zircon on the surface layer of composite specimens decomposes and produces a specimen comprising core and shell.     

Estimating the strength of resistance spot welds based on sonic emission

Abstract

Audible sound signals detected during the resistance spot welding (RSW) of zinc coated steels were investigated in order to assess their suitability for estimating the strength of the weld. A new sonic emission indicator was introduced and compared to a commonly used emission count indicator. A new method of spot weld strength estimation based on the two indicators is presented. The advantage of the method is that it makes it possible to establish the stage when the electrode is worn out. The method enables the development of improved RSW process control algorithms.     

The roles of the degree of substitution and the degree of polymerization on the behaviour of cellulose ethers applied as adhesives for artwork conservation

Quite recently cellulose ethers have been introduced into the conservation field as an adhesive agent. Cellulose ethers are available in a wide range of products. Their properties are related not only to the nature of the substituent but also to the degree of polymerization (DP) and the degree of substitution (DS). Thus, the number of OH groups that are bound to C1 and C4 or to C2, C3 and C6 carbon atoms of the cellulose ether molecule affect their properties. Paper traction resistance is increased by using cellulose ethers as an adhesive to paste Tenguyo paper, a paper with a low density of fibres usually used by restorers. This increase is directly related to the molecular structure of the cellulose ethers. Therefore, the nature of substituents, the DP and the DS of cellulose ethers have to be taken into account in conservation practice. DP equals the number of anhydroglucose units in the chain and DS equals the number of hydroxyl groups replaced by the substituent in every anhydroglucose unit in the chain. As this information is not usually provided by suppliers, viscosity measurements are proposed as a means of predicting the behaviour of different products in relation to the conservation of paper artefacts, or to any other field where cellulose ethers solutions are used.     

Classic contributions: cryogenic treatment Deep cryogenic treatment of a D2 cold work tool steel

Abstract

Deep cryogenic treatment at liquid nitrogen temperatures can enhance the wear resistance of tool steels. This article, first published in 1997, reports experimental investigations that have helped to clarify the underlying mechanisms.     

Influence of heat treatments on microstructural parameters and mechanical properties of P92 steel

Abstract

The microstructural parameters (dislocation density, martensite lath width, precipitate diameters, and volume fractions) have been measured for the 9%Cr steel P92 (NF616) after different heat treatments. The austenitising temperatures were 970, 1070, and 1145°C and the tempering temperatures 715, 775, and 835°C. Increasing the austenitising temperature led to an increase in the austenite grain size and in the martensite lath width, but no significant effect on the tensile properties at 20, 600, and 650°C was observed. The creep strength was, however, reduced by tempering at 835°C due to rapid recovery of the martensitic structure with a sharp decrease in dislocation density. The lowest creep strength was found for the P92 steel subjected to a heat treatment that produced a fully ferritic microstructure; the secondary creep rate was four orders of magnitude higher than that of the steel in the usual martensitic condition.     

Evaluating fatigue performance of down gauged high strength steel suspension arm

Abstract

The use of high strength steels (HSS) in automotive components is steadily increasing as automotive designers use modern steel grades to improve structural performance, reduce vehicle weight, and enhance crash performance. Weight reduction can be achieved by substituting mild steel with a thinner gauge HSS, however it must be ensured that no deterioration in fatigue performance occurs. Fatigue studies have been carried out to determine the effects various welding processes, gauge, and material strength can have on the fatigue performance of an automotive suspensionarm.Test methodology has also been investigated and the merits of both uniaxial constant amplitude and multiaxial simulation testing have been studied. Results have shown the fatigue performance of welded components to be independent of the strength of the parent material for the steel grades studied. Also, little correlation was found between the fatigue performance of simple welded samples under uniaxial, constant amplitude loading and complex components under biaxial in service loading, road load data. This highlights the care required when estimating component in service performance from small, simplified samples. The work also highlights the need for testing components under in service conditions if optimum use of materials, design, and manufacturing methods is to be achieved.