Two novel rolling processes of porous metal preforms prepared by spray deposition technique using conventional rolling mill

For the spray deposited preforms with the porosity up to 10–15%, densification processing is necessary to produce fully dense products. In this paper, two novel processes named as “Frame-Confined Rolling” and “Ceramic Rolling” are presented. The experimental results show that these two methods can improve the workability of the porous preforms without forming cracks on surface and edge during rolling.     

Investigation on deformation behavior of sheet metals in viscous pressure bulging based on ESPI

In order to analyze the effect of viscous medium on the deformation behavior of sheet metals in viscous pressure bulging (VPB), the entire deformation process including instability and fracture was investigated real-timely by the aid of electronic speckle pattern interferometry (ESPI). Images of speckle patterns were captured continuously to obtain fringe patterns representing the full field strain rate. Values of strain rates were calculated based on the fringe patterns. The evolution of the weak region from the initial defect to the groove until crack was also observed through the fringe patterns. The onset of diffuse and localized necking were determined qualitatively and quantitatively. Experimental results show that the deformation of sheet metals in VPB passed through five states, namely, uniform deformation, strain localization, diffuse necking, localized necking and fracture. A defect emerged in strain localization. The growth of the defect caused the diffuse necking and generated a groove. The groove expanded mainly in length direction until the localized necking occurred. Finally the specimen fractured as a result of groove deepening. The tangential adhesive stress provided by viscous medium in VPB restricted the locally larger strain of the specimen. The diffuse necking was postponed greatly. Theoretical prediction of the limit strains of sheet metals in VPB would be made based on the experimental results in further work.     

The Biotechnology of Wine Yeast

The production of wine from grapes is one of the world's oldest biotechnological processes. The alcoholic fermentation, the conversion of grape sugars to ethanol, is conducted by yeast of the genus Saccharomyces. In addition to wide-ranging roles in beverage and food processing, Saccharomyces is also a premier research model system because of its genetic tractability. Its genome has been sequenced, and an extensive array of molecular technologies has been developed for the genetic manipulation of this organism. In spite of the availability of these molecular tools, genetically engineered yeast strains are not yet in use in the commercial wine industry. Anxiety over consumer acceptance is one reason genetically modified strains are not employed, but there are other concerns as well. Wine production is unique in many respects. The wine production process is not conducted under sterile conditions, and any modified organism has the potential to become an enduring resident of the winery flora. Further, wine production is both science and art. There is concern that many of the proposed genetic modifications of yeast are designed to correct processing errors or incompetence of the winemaker rather than being useful tools to enhance the artistry of wine making. In spite of these concerns, the efficacy of genetic modification of wine yeast has been demonstrated.     

Mental strain and the problem of repeated measurements

In the past, stress and strain arising from the execution of mentally demanding tasks have been measured by means of surveys. Such methods require repeated investigation of the individual perceptions and valuations during task fulfilment to record time-dependent changes in strain levels. However, it is possible that the individual measurement procedures employed in surveys-as artefacts-may cause a change in the stress situation and subsequently in the resulting mental strain. The results of the experiments carried out to investigate this hypothesis verify that repeated measurements have a similar effect as a short break. The repeated measurements taken during progressive studies are, therefore, likely to affect the conditions of stress. A change in the level of mental strain recorded can be expected, particularly if the post-test rating is preceded by a long period of low stress before or during which an additional measurement of strain is implemented.     

Nonlocal Multilaminate Model for Strain Softening Analysis

A constitutive model formulated within the multilaminate framework is described in this paper. The basic model, incorporating deviatoric and volumetric hardening, was developed for normally consolidated or slightly overconsolidated clay. This model has been extended to account for shear softening by using a nonlocal formulation. The nonlocal plasticity is based on weighted average of plastic strains taken from neighboring material points within a certain distance which is a function of an internal length parameter. This parameter is related to the mean grain size that restricts the element size. By using a softening scaling this restriction can be eliminated and the model is therefore capable of simulating geotechnical boundary value problems. The capability of the model for simulating strain softening behavior is shown by numerical simulation of biaxial tests. Finally, the ground response curve obtained from the proposed model for excavation of a tunnel in soil is discussed.     

Influences of simple strain path changes on mechanical behaviours of pearlitic steel wire

The mechanical behaviours of the pearlitic steel wires under simple strain path changes (SSPCs) are investigated, including monotonic, cross and reversal loadings. Both the cross and reversal loadings lead to an apparent softening. Especially during the whole reversal loading, the stress is much lower than before unloading. And it is a function of the pre-strain. Additionally, it is found that the maximum strain increases significantly in reversal loading. The microstructures under different SSPCs are investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), with an aim to reveal the micro-mechanisms of the SSPC effects on the mechanical behaviours.     

Quasi-static behaviour of composite joints with protruding-head bolts

An experimental study of the quasi-static behaviour of composite bolted joints under tensile and compressive loading has been performed. The joint plates made of quasi-isotropic and 0°-dominated lay-ups were fastened by two, four, or six titanium bolts. Two specimen configurations were tested: single lap and double lap. Strain gauges were applied in order to measure strain between the bolt rows and to calculate the load transfer of the bolt rows. Bolt-movement measurements were performed using extensometers to examine bolt behaviour under static loading. The obtained experimental results showed that bolted joints with four and six bolts perform better resistance to quasi-static loading than joints with two bolts. Strain distribution between two bolts is significantly affected by the bolt presence and their behaviour under loading. The load-transfer calculations showed that different bolt rows transfer slightly different amounts of load.     

Neutron Strain measurement

The use of neutrons has extended the technique of diffraction strain measurement from an essentially two-dimensional, near-surface tool using X-rays to a true three-dimensional method. The depth scale has gone from micrometres to millimetres. This initially gave rise to subsurface measurements of type I residual macrostresses in weldments and type II residual microstresses in anisotropic and multiphase metals, and composites. Soon the possibilities of in situ applied stress measurements became apparent and today they represent a significant portion of the work being carried out. This perspective focuses on the current state of the art, the prospects and developments necessary for further progress. The transition from two- to three-dimensions raised the issues of stress free reference values, methodology for general tensor measurements, beam optics and experimental design. Workers invested great effort in resolving these issues. In addition, the development of pulsed source instruments has enabled in situ measurements of slip, fatigue, load partitioning, twinning, high T stress-strain response, thermal cycling and the shape memory effect. Most recently, the SNS instrument, VULCAN, has introduced torsion and continuous recording of data which can later be binned in the shortest statistically significant time intervals.     

Recycling of aluminium based metal matrix composite using disintegrated melt deposition technique

Abstract

In the present study, the feasibility of recycling a silicon carbide particulate reinforced aluminium composite was investigated. The composite was synthesised and recycled using an innovative disintegrated melt deposition tech nique. Microstructural characterisation studies revealed a marginal decrease in porosity, reinforcement content and size, no change in reinforcement distribution pattern, and improved interfacial integrity between matrix and reinforcement following recycling. Microhardness measurements revealed an increase in the hardness of the interfacial region in the recycled specimens. Results of physical and mechanical property characterisation revealed an increase in elastic modulus, 0·2% yield strength, ultimate tensile strength, and ductility, and a reduction in the coefficient of thermal expansion of the recycled specimens when compared with the parent composite. These properties were rationalised in terms of the microstructural characteristics associated with the disintegrated melt deposited composite specimens. Particular emphasis is placed on the study of the effect of recycling on the microstructure and properties of the composite.