Cy Barlow

Strain gradient effects on microscopic strain field in a metal matrix composite

The purpose of this paper is to demonstrate the improved modeling accuracy of a finite-deformation strain gradient crystal plasticity formulation over its classical counterpart by conducting a joint experimental and numerical investigation of the microscopic details of the deformation of a whisker-reinforced metal-matrix composite. The lattice rotation distribution around whiskers is obtained in thin foils using a TEM technique and is then correlated with numerical predictions based on finite element analyses of a unit-cell of a single crystal matrix containing a rigid whisker. The matrix material is first characterized by a classical, scale-independent crystal plasticity theory. It is found that the classical theory predicts a lattice rotation distribution with a spatial gradient much higher than experimentally measured. A strain gradient crystal plasticity formulation is then applied to model the matrix. The strain gradient formulation accounts for both strain hardening and strain gradient hardening. The deformation thus predicted exhibits a strong dependence on the size of the whisker. For a constitutive length scale comparable to the whisker diameter, the spatial gradient of the lattice rotation is several times lower than that predicted by the classical theory, and hence correlates significantly better with the experimental results.

Deformation structures and flow stress in aluminium containing short whiskers

Abstract This study reports observations of the effect of a small content (2 vol.%) of SiC whiskers (fibres) on the deformation behaviour at low and medium strains (0.1–10%) of powder-consolidated aluminium. Direct comparisons were made between the material with and without whiskers, and showed that the addition of whiskers did not significantly affect the yield stress, but caused a significant increase in the flow stress and work-hardening rate over the whole of the strain range studied. The yield stress was related to contributions from the thermal residual stress and to dislocations introduced during cooling, and the effects of those two factors were estimated to counterbalance each other. The effect of the whiskers on the flow stress was attributed mainly to a combination of two factors, these being the presence of a mean matrix stress and dislocation strengthening. The relative contributions of these two strengthening components changed with strain. The flow stress of the material at 10% strain could be accounted for reasonably well by linear addition of the various strength contributions.

Fine scale structures from deformation of aluminium containing small alumina particles

Abstract Microstructures and mechanical properties have been studied in aluminium containing a fine dispersion of alumina particles, deformed by cold-rolling to strains between 1.4 and 3.5. The microstructure was characterised by TEM. The deformation structures evolved very rapidly, forming a nanostructured material, with fine subgrains about 0.2 μm in diameter and a fraction of high-angle boundaries which was already high at a strain of 1.4, but continued to increase with rolling strain. The yield stress and ductility of the rolled materials were measured in tension, and properties were similar for all materials. Yield stress measurements were correlated with estimates made using microstructural models. The role of small particles in forming and stabilising the deformation structure is discussed. This nanostructured cold-deformed alloy has mechanical properties which are usefully enhanced at comparatively low cost. This gives it, and similar particle-strengthened alloys, good potential for commercial exploitation.

From refining sugar to growing tomatoes: industrial ecology and business model evolution.

This article seeks to advance the understanding of the relationship between industrial ecology (IE) and business model innovation for sustainability as a means and driver of new value creation and competitive advantage by expanding the understanding of industrial symbiosis (IS) and internal symbiosis. This is explored through the case study of British Sugar, which, at the time of writing, is the UKs largest sugar producer by market share. Over the past three decades, the company has systematically sought opportunities to turn waste streams and emissions from their core production processes into useful and positive inputs to new product lines. Their core business is still sugar, but the business model has evolved to offer a broad range of additional synergistic and profitable product lines, including animal feed, electricity, tomatoes, and bioethanol. The research explores the temporal dimension of dynamic business model innovation, framing it in the context of a continuous evolutionary process rather than a discrete design activity. The case will be of interest as an additional contribution to the growing literature on IS; in offering an approach for linking the themes of IE literature and sustainable business model innovation more concretely in research and practice; and, by presenting the case as an evolutionary innovation process, the article furthers the emerging literature on business model innovation for sustainability.

Plume attenuation under high power Nd:yttritium–aluminum–garnet laser welding

During high-power continuous wave (cw) Nd:yttritium–aluminum–garnet (YAG) laser welding a vapor plume is formed containing vaporized material ejected from the keyhole. The gas used as a plume control mechanism affects the plume shape but not its temperature, which has been found to be less than 3000 K, independent of the atmosphere and plume control gases. In this study high-power (up to 8 kW) cw Nd:YAG laser welding has been performed under He, Ar, and N2 gas atmospheres, extending the power range previously studied. The plume was found to contain very small evaporated particles of diameter less than 50 nm. Rayleigh and Mie scattering theories were used to calculate the attenuation coefficient of the incident laser power by these small particles. In addition the attenuation of a 9 W Nd:YAG probe laser beam, horizontally incident across the plume generated by the high-power Nd:YAG laser, was measured at various positions with respect to the beam-material interaction point. Up to 40% attenuation of the pro...

An assessment of the current municipal solid waste management system in Lahore, Pakistan.

The current status of solid waste management in Lahore, a metropolitan city of Pakistan, is reviewed in this article using an existing approach, the UN-Habitat city profile. This involves a systematic quantitative and qualitative assessment of physical components and governance features of the current waste management system. A material flow diagram (MFD) is developed, which allows visualisation of the current waste management system with all related inputs and outputs. This study shows that in the current system, waste collection and transportation is the main focus, however the collection coverage is only about 68%. There is no controlled or even semi-controlled waste disposal facility in Lahore. There is no official recycling system in the city. It is estimated that currently ~27% of waste by weight is being recycled through the informal sector. Making use of the organic content of the waste, a composting facility is operative in the city, producing 47,230 tonnes year-1 of organic compost. Lahore does not perform very well in governance features. Inclusivity of users and providers of the waste management system is low in the city, as not all stakeholders are consulted in the decision making processes. Waste management costs US

Dislocation configurations in metal-matrix composites correlated with numerical predictions

20 per tonne of waste, where the main focus is only on waste collection, and the current user fees are much lower than the actual costs. This study recommends that recycling should be promoted by increasing public awareness and integrating the informal sector to make the current system sustainable and financially viable.

Observations of cellular transformation products in nickel-base superalloys

Abstract The development of deformation microstructures is reported in reinforced powder-consolidated aluminium. This study discusses observations of the effect of additions of SiC whiskers or particles on the microstructural evolution in the strain range 0.01–0.1. For whisker-containing materials the microstructural changes introduced by thermal cycling have also been investigated, and supplemented by measurements of the dislocation density and microhardness. In plastically deformed specimens the size, shape and microstructure of the deformation zone near the reinforcement have been characterized as a function of the imposed strain. The experimental observations have been compared to finite element model predictions of the stress and strain distribution in the uniaxially loaded composite, and good qualitative agreement has been found. This comparison also points to areas for future model development.

Framework for integration of informal waste management sector with the formal sector in Pakistan.

Transmission electron microscopy has been used to identify the products in cellularly transformed regions of alloys based on the Nimonic 80 A composition. The commercial alloy is shown to undergo a small degree of cellular transformation even after conventional heat treatments, while recrystallization is found to increase the incidence of this reaction type. Low carbon versions of this alloy demonstrate cellular precipitation over a wider range of heat treatments.It is shown that the cellular reaction may take place in these alloys under a variety of different conditions and with a range of driving forces. Reasons for this unexpected behaviour are offered, as is a suggestion as to why the cellular reaction occurs on a local scale.

Microstructure, strain fields and flow stress in deformed metal matrix composites

Historically, waste pickers around the globe have utilised urban solid waste as a principal source of livelihood. Formal waste management sectors usually perceive the informal waste collection/recycling networks as backward, unhygienic and generally incompatible with modern waste management systems. It is proposed here that through careful planning and administration, these seemingly troublesome informal networks can be integrated into formal waste management systems in developing countries, providing mutual benefits. A theoretical framework for integration based on a case study in Lahore, Pakistan, is presented. The proposed solution suggests that the municipal authority should draw up and agree on a formal work contract with the group of waste pickers already operating in the area. The proposed system is assessed using the integration radar framework to classify and analyse possible intervention points between the sectors. The integration of the informal waste workers with the formal waste management sector is not a one dimensional or single step process. An ideal solution might aim for a balanced focus on all four categories of intervention, although this may be influenced by local conditions. Not all the positive benefits will be immediately apparent, but it is expected that as the acceptance of such projects increases over time, the informal recycling economy will financially supplement the formal system in many ways.