Plasticity of metallic nanostructures : molecular dynamics simulations

During high speed cutting processes, metals are subject to high strains and strain rates. The dynamic nature of the deformation during high speed cutting makes it difficult to detect atomic scale deformation mechanisms experimentally. Atomic scale plasticity behaviour is often studied using various micromachining techniques such as micropillar compression testing, nanoindentation, and nanoscratching. However, strain rates in micromachining experiments are far lower than those seen during high speed cutting. Atomistic simulations can be used to study high strain rate plasticity at nanometre length scales. In this thesis, we present results from molecular dynamics simulations of plasticity in nanostructures. Results from simulations of uniaxial strain of both bcc and fcc nanopillars are presented. We find that the outcomes of these uniaxial strain simulations depend sensitively on the initial configurations of the systems. In particular, the choice of crystallographic surfaces on the faces of the pillars and the means by which strain is implemented in the simulations can affect the simulation results. We find that the twinning anti-twinning asymmetry in bcc materials causes nanopillars to deform by dislocation glide in compression and by twinning in tension. This explains the compression tension asymmetry reported experimentally in bcc micropillars. We find that deformation is mediated by glide of shockley partials in fcc pillars for compressive and tensile strains. Simulations of pure shear of nanocrystalline Fe are also presented. We find a change in deformation mechanisms for this system when at high temperatures. At low temperatures, plasticity is mediated in part by dislocation glide and twinning. However, at temperatures above 1200K the deformation is dominated by grain boundary sliding, recrystallization, and amorphization

Calculating restaurant failure rates using longitudinal census data

Failure rates in the restaurant industry are popularly perceived to be far higher than they actually are. This paper calculates failure rates in the Irish Food and Drinks Sector (IFDS), for the first time, using longitudinal census data from the Central Statistics Office (CSO) in Ireland, which follows the European statistical classification of economic activity (NACE). The results are compared with previously published literature on restaurant failure rates in the United States of America. This study also compares IFDS failure rates with other industry sectors in Ireland (construction, manufacturing). Drawing on Stinchcombe’s ’liability of newness’ theory, the informal fallacies theory ’Argumentum ad Populum’, and critical success factors (CSFs) for restaurants theory, the paper explores restaurant failure rates both in Ireland and internationally. The research finds that the average failure rates for the IFDS are 15% after one year; 37.62% after three years; and 53.06% after five years in business, which, although marginally higher than other industry sectors in Ireland, are considerably lower than popularly perceived. Comparisons with previous studies in the United States of America shows that Irish rates are significantly lower, particularly in the first few years. The methodology can be replicated to provide comparative studies between other European countries using the NACE classifications. The results may assist in ensuring that future policy decisions made by governments, financial institutions and other restaurant/ hospitality industry groups are more empirically based and better informed

In-plane Sensitive Electronic Speckle Pattern Interferometer using a Diffractive Holographic Optical Element

We describe a student project in electronic speckle pattern interferometry. The project includes holographic recording of diffraction gratings in thick, self-processing photopolymer layers made from off-the-shelf chemicals. The gratings are employed in a simple electronic speckle pattern interferometer to measure in-plane rotation

Chefs’ Perspectives of Failures in Foodservice Kitchens, part 2: A phenomenological Exploration of the Consequences and Handling of Food Production Failure

This paper explores the consequences of food production failure (FPF) and its handling in foodservice operations from the perspective of chefs. A phenomenological epistemology and qualitative methodology were followed. Fifteen semi-structured interviews with chefs working in independent restaurants and hotels were carried out using purposive sampling, and employing an emic posture. Interviews were transcribed verbatim, read repetitively, and coded. Thematic analysis yielded themes on the consequences of FPF, on operation and staff, handling failures with kitchen staff, front of the house (FOH), and management. The findings revealed that the major ramification of FPF is financial through food loss. Representing both internal and external failure costs, FPF costs were classified into four tangible types: bin cost, rework cost, lost sales cost, and recovery cost. However, the serious intangible cost of staff demoralization was also identified. Handling failure is a complex task involving different parties and the management of various emotions (anger, frustration, etc.). Furthermore, the phenomena of failure ownership, secrecy, and historic marginalization of chefs, coupled with doubts over management competency, can all obstruct learning from mistakes, the much-cherished by product of FPF, thereby negating the notion of the “learning organization.” Moreover, error management training (EMT) seems to be a potential approach to combat FPF

Chefs’ Perspectives of Failures in Foodservice Kitchens, Part 1: A phenomenological exploration of the concepts, types, and causes of food production failure

Customers visit restaurants for varying reasons ranging from utilitarian – to satisfy hunger – to hedonistic – displaying cultural capital (Bourdieu, 1984) more recently theorized as culinary capital (Naccarato & Lebesco, 2012). Restaurants are even more significant in the new ‘experience economy’ (Pine & Gilmore, 1998) where lunch or dinner are conceptualized as ‘meal experiences.’ There is widespread acceptance of the pivotal role (about 33% of tourist spend) that food now plays in the tourism product of any country (Quigley et al., 2019)

Shear melting and high temperature embrittlement:theory and application to machining titanium

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding is supplanted by amorphization in a highly localized nanoscale band, which allows massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are, lack of dislocation slip systems, low thermal conduction and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting point elements: specifically we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.Comment: Accepted for PR

Molecular dynamics simulations of compression–tension asymmetry in plasticity of Fe nanopillars

Tension-compression asymmetry is a notable feature of plasticity in bcc single crystals. Recent experiments reveal striking differences in the plasticity of bcc nanopillars for tension and compression. Here we present results from molecular dynamics simulations of nanopillars of bcc Fe in tension and compression. We find that a totally different deformation mechanism applies in each cases: dislocation glide in compression and twinning in tension. This difference explains experimentally-observed asymmetry in the nanopillar morphology