Deformation and rupture of armour grade steel under localised blast loading

A series of 30 blast experiments were conducted on monolithic steel panels of two armour grade steels. The two steels evaluated were a high hardness armour (HHA) and a rolled homogenous armour (RHA). Tests were conducted at two standoff distances using a fixed charge diameter. The charge weight was varied to produce specific magnitudes of blast loading and to isolate the rupture threshold of each material. The results indicated that the HHA steel, generally reserved for ballistic protection, outperformed a more ductile RHA steel in terms of both its deformation resistance and rupture threshold. Optical and scanning electron microscopy was utilised for fractographic analysis of the ruptured plates. The failure of the steels in this investigation was found to be initiated by slant shear fracture with little to no localised thinning. This is in contrast to the tensile instability and ductile tearing predicted by established theories of plate rupture for mild steels under blast loading. The deformation and rupture of the candidate steels was analysed for all experimental conditions and compared to current empirical models based on a non-dimensional impulse parameter. While deformation behaviour is well predicted, the blast rupture threshold of the armour grade steels is poorly captured by current empirical modelling approaches. The identified shear fracture mode leads to lower energy absorption capabilities of the material compared to more ductile tensile failure

Perforated Plates as Passive Mitigation Systems

This paper presents the results of tests on fully-clamped circular plates subjected to blastloading directed down a tube. Four series of tests were performed. In one set of experiments,the blast wave was allowed to progress unhindered down the tube to impinge upon the plate,and in the other tests, perforated plates were placed in the path of the blast wave to hinderprogression down the tube, disrupting the blast and absorbing some of the kinetic energy.Results of the tests indicate that the perforated plates can be used as a form of passive mitigation

Towards Standardising SHPB Testing - A Round Robin Exercise

The Split Hopkinson Pressure Bar (SHPB) test, while widely utilised for high strain rate tests, has yet to be standardised. As an exploratory step towards developing a standard test method or protocol, a Round Robin test series has been conducted between four institutions: (i) Swinburne University of Technology, Australia (ii) University of São Paulo, Brazil, (iii) University of Cape Town, South African and (iv) Nanyang Technological University, Singapore. Each institution prepared specimens from a metallic material, and provided batches of specimens from their chosen material to the other institutions. The materials utilised in this round of testing were commercially pure copper and aluminium, magnesium alloy and stainless steel (316 grade). The intent of the first exercise is to establish the consistency of SHPB test results on nominally identical specimens at comparable elevated strain rates, conducted by different laboratories following notionally similar test procedures with some freedom in data processing. This paper presents and compares the results of the first batch of tests for copper, identifying variations between results from different laboratories. The variation between different laboratories’ results for copper is suffciently small that there is confidence in the potential to develop a draft standard in future

Evolving text classification rules with genetic programming

We describe a novel method for using genetic programming to create compact classification rules using combinations of N-grams (character strings). Genetic programs acquire fitness by producing rules that are effective classifiers in terms of precision and recall when evaluated against a set of training documents. We describe a set of functions and terminals and provide results from a classification task using the Reuters 21578 dataset. We also suggest that the rules may have a number of other uses beyond classification and provide a basis for text mining applications

Consequences of fish kills for long-term trophic structure in shallow lakes: implications for theory and restoration

Fish kills are a common occurrence in shallow, eutrophic lakes, but their ecological consequences, especially in the long-term, are poorly understood. We studied the decadal-scale response of two UK shallow lakes to fish kills using a palaeolimnological approach. Eutrophic and turbid Barningham Lake experienced two fish kills in the early 1950s and late 1970s with fish recovering after both events, whereas less eutrophic, macrophyte-dominated Wolterton Lake experienced one kill event in the early 1970s from which fish failed to recover. Our palaeo-data show fish-driven trophic cascade effects across all trophic levels (covering benthic and pelagic species) in both lakes regardless of pre-kill macrophyte coverage and trophic status. In turbid Barningham Lake, similar to long-term studies of biomanipulations in other eutrophic lakes, effects at the macrophyte-level are shown to be temporary after the first kill (c.20 years) and non-existent after the second kill. In plant-dominated Wolterton Lake permanent fish disappearance failed to halt a long-term pattern of macrophyte community change (e.g. loss of charophytes and over-wintering macrophyte species) symptomatic of eutrophication. Important implications for theory and restoration ecology arise from our study. Firstly, our data support ideas of slow eutrophication-driven change in shallow lakes where perturbations are not necessary prerequisites for macrophyte loss. Secondly, the study emphasises a key need for lake managers to reduce external nutrient-loading if sustainable and long-term lake restoration is to be achieved. Our research highlights the enormous potential of multi-indicator palaeolimnology and alludes to an important need to consider potential fish kill signatures when interpreting results

The response of plates under non-uniform impulsive loads

Near-field blast loads are non-uniformly distributed across the loaded face of a structural element and result in large, localised plastic deformations. Experimental characterisation of both the loading and resultant deformation is rare in the literature, and to date there have been no studies which investigate modes and mechanisms of target deformation with a detailed knowledge of the imparted load. This paper presents results from a collaboration between the University of Sheffield, UK, and the University of Cape Town, South Africa, aimed at measuring the loading imparted to, and subsequent dynamic deformation of blast loaded plates. This paper presents results from these experiments, where the presence of inward and outward travelling flexural waves are observed and discussed in relation to localised variations in the imparted load