Fatigue crack growth in a particulate TiB2 reinforced powder metallurgy iron-based composite

Fatigue crack growth behavior has been examined in a particulate titanium diboride (TiB2)–reinforced iron-based composite that had been produced via a mechanical alloying process. Comparison with equivalent unreinforced material indicated that fatigue crack growth resistance in the composite was superior to monolithic matrix material in the near-threshold regime. The composite exhibited relatively low crack closure levels at threshold, indicative of a high intrinsic (effective) threshold growth resistance compared to the unreinforced iron. The lower closure levels of the composite were consistent with reduced fracture surface asperity sizes, attributable to the reinforcement particles limiting the effective slip distance for stage I–type facet formation. The observed shielding behavior was rationalized in terms of recent finite-element analysis of crack closure in relation to the size of crack wake asperities and the crack-tip plastic zone. The different intrinsic fatigue thresholds of the composite and unreinforced iron were closely consistent with the influences of stiffness and yield strength on cyclic crack-tip opening displacements. Cracks in the composite were generally seen to avoid direct crack-tip–particle interaction

Fatigue of friction stir welded 2024-T351 aluminium alloy

Fatigue failure characteristics of friction stir welds in 13mm gauge 2024-T351 plate have been assessed. Failure occurred from either the weld region (nugget/flow arm) or from the material immediately surrounding the weld. Fatigue failure from the surrounding material was essentially conventional, initiating from large S-phase intermetallic particles and growing in a macroscopic mode I manner. Corresponding fatigue lives were seen to be comparable to parent plate and results previously reported for similar welds in thinner plate. Failure over the weld region was identified with discontinuities in the macroscopic flow pattern of the weld flow arm. Subsequent crack growth showed pronounced macroscopic crack deflection around the ‘onion ring’ structure of the weld nugget. The bands making up the onion rings were identified with variations in local hardness levels, consistent with a mechanical contribution to the crack deflection process

Experimental analysis of toughness in 6156 Al-alloy sheet for aerospace application

Analysis of toughness in 6156 Al-Mg-Si-Cu sheet has been performed using enhanced Kahn tear tests on samples quenched at different rates, whilst microstructures of the samples have been assessed using differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Crack initiation energies were unaffected by changing water quench temperature from 20°C to 60°C, however a significant reduction was evident on air cooling. Crack propagation resistance was reduced for both 60°C water quenched and air cooled materials. The failure morphology of the air cooled material appears consistent with classical intergranular ductile failure. Coarse voiding and shear decohesion was prevalent in the 20°C water quenched material, whilst the 60°C water quenched material showed a mixture of transgranular and intergranular fracture modes. Changes in microstructure and precipitation behaviour resulting from reduced quenching rate were identified and related to the observed fracture behaviour, particularly in terms of precipitate free zone formation and the simultaneous presence of coarse particles at grain boundaries

The influence of toughening-particles in CFRPs on low velocity impact damage resistance performance

The role of particle-toughening for increasing impact damage resistance in carbon fibre reinforced polymer (CFRP) composites was investigated. Five carbon fibre reinforced systems consisting of four particle-toughened matrices and one system containing no toughening particles were subjected to low velocity impacts ranging from 25 J to 50 J to establish the impact damage resistance of each material system. Synchrotron radiation computed tomography (SRCT) enabled a novel approach for damage assessment and quantification. Toughening mechanisms were detected in the particle-toughened systems consisting of particle–resin debonding, crack-deflection and crack-bridging. Quantification of the bridging behaviour, increase in crack path length and roughness was undertaken. Out of the three toughening mechanisms measured, particle systems exhibited a larger extent of bridging suggesting a significant contribution of this toughening mechanism compared to the system with no particle

Maltreated children in the Looked After System: a comparison of outcomes for those who go home and those who do not

This project focuses on the consequences of decisions to reunify children who had entered the looked-after system for abuse or neglect. It compares the progress and outcomes of a sample of maltreated children who either went home or remained in the looked-after system

Quantization and simulation of Born-Infeld non-linear electrodynamics on a lattice

Born-Infeld non-linear electrodynamics arises naturally as a field theory description of the dynamics of strings and branes. Most analyses of this theory have been limited to studying it as a classical field theory. We quantize this theory on a Euclidean 4-dimensional space-time lattice and determine its properties using Monte-Carlo simulations. The electromagnetic field around a static point charge is measured using Luscher-Weisz methods to overcome the sign problem associated with the introduction of this charge. The D field appears identical to that of Maxwell QED. However, the E field is enhanced by quantum fluctuations, while still showing the short distance screening observed in the classical theory. In addition, whereas for the classical theory, the screening increases without bound as the non-linearity increases, the quantum theory approaches a limiting conformal field theory.Comment: 24 pages, 10 figures. Latex with postscript figure

Permanent-magnet atom chips for the study of long, thin atom clouds

Atom-chip technology can be used to confine atoms tightly using permanently magnetised videotape along with external magnetic fields. The one-dimensional (1D) gas regime can be realised and studied by trapping the atoms in high-aspect-ratio traps in which the radial motion of the system is confined to zero-point oscillation

Reading Dario Argento\u27s \u27Inferno\u27 (Italy)

Inferno (1980) is a cult classic film written and directed by Dario Argento that both extends and resists the giallo genre. In the film, Argento continues his tradition of building a dense network of allusions that refers to his own and others’ films, as well as to canonical and ‘popular’ works of literature, politics, music, and film theory. The poetic effect of these elements, in combination with the film’s lack of continuity mechanisms, bizarrely detailed mise en scenes, gore-filled death scenes, and unpredictable and unlikely camera angles, both attracts and resists critical interpretation. The film’s penumbral location between categories of ‘high’ and ‘low’ art makes it a challenging subject of examination; in this thesis, I mean to increase our appreciation of the film’s rich level of interaction with other genres, media, and texts, as well as to experiment with my own interpretation and explication of some signs and codes operating within the film. “Part I: Situating the art and the artist” establishes the generic context of the Italian giallo and introduces the somewhat divergent cultural milieu of high and low art in which we might encounter the film. As an organizational tool or framing apparatus through which an audience “reads” a film, genre is a critical factor that mitigates popular access and acceptance. While I discuss Inferno’s relation to the Gothic and melodrama in Part IV, its participation in, and resistance to, the giallo genre is particularly relevant to our discussion of high and low art. Following the summary of Argento’s oeuvre and an overview of existing scholarship concerning the director and film, I relate a number of provocative accounts of how the director, both personally and through his films, challenges social conventions. In “Part II: Argento, Libere, De Quincey,” I reveal Fritz Leiber’s novel Our Lady of Darkness as an unacknowledged source for Argento’s film and outline how this discovery alters current critical accounts and evaluations of Inferno. Part II provides us with a foundation for understanding Inferno’s alignment with the Gothic tradition and resistance to the mystery structure, which I explore at greater length in Part IV. Inferno’s complex relationship with other texts lend richness to interpretations of the film; I illustrate this complexity by suggesting some potential links between the title of the film and other works, including Leiber’s novel. “Part III: Reading Argento and his text” ascertains some conditions for reading the film, after providing a plot synopsis for my reader. In keeping with Barthes’ promotion of the “freedom of the reader” to explore and play with texts, I provide a number of experimental and sometimes contradictory readings of specific shot sequences in the film. This exercise reveals Inferno’s nuanced texture and openness to interpretation. “Part IV: On genre” discusses how Inferno resists the rational and causal relationships underpinning the mystery, the generic tradition from which the giallo emerged in the 1960s. The film’s incorporation of key elements of the Gothic tradition leads into a discussion of the Gothic mode, in which I also refer to the psychoanalytic tradition of reading Gothic texts. In Inferno’s invocation of the Gothic, I find that the film operates by some of the same principles underlying melodrama, the theatrical antecedent to the Gothic novel. Using Brooks’ articulation of the “melodramatic mode,” I theorize how signs and codes function in Inferno. In my conclusion, “Metaphysical Knots: The terror and pleasure of unstable signs,” I use Barthes’ concept of “parsimoniously plural” texts to reconcile the different approaches I have taken in Parts I-IV. Finally, I propose that Inferno’s diegetic and extra-diegetic resistance to linearity and causality illustrates a kind of Gothic economy, a system predicated upon repetition and exchange. With this proposal, I invite my reader to consider this thesis as a treatment leading to further critical exchanges and re-visions

Surface flashover of oil-immersed dielectric materials in uniform and non-uniform fields

The applied electrical fields required to initiate surface flashover of different types of dielectric material immersed in insulating oil have been investigated, by applying impulses of increasing peak voltage until surface flashover occurred. The behavior of the materials in repeatedly over-volted gaps was also analyzed in terms of breakdown mode (some bulk sample breakdown behaviour was witnessed in this regime), time to breakdown, and breakdown voltage. Cylindrical samples of polypropylene, low-density polyethylene, ultra-high molecular weight polyethylene, and Rexolite, were held between two electrodes immersed in insulating oil, and subjected to average applied electrical fields up to 870 kV/cm. Tests were performed in both uniform- and non-uniform-fields, and with different sample topologies. In applied field measurements, polypropylene required the highest levels of average applied field to initiate flashover in all electrode configurations tested, settling at similar to 600 kV/cm in uniform fields, and similar to 325 kV/cm in non-uniform fields. In over-volted point-plane gaps, ultra-high molecular weight polyethylene exhibited the longest pre-breakdown delay times. The results will provide comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage, pulsed-power machines