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Kesharaju M.,Swinburne University of Technology | Nagarajah R.,Swinburne University of Technology | Nagarajah R.,Defence Materials Technology Center, Australia
Ultrasonics | Year: 2015

The motivation for this research stems from a need for providing a non-destructive testing method capable of detecting and locating any defects and microstructural variations within armour ceramic components before issuing them to the soldiers who rely on them for their survival. The development of an automated ultrasonic inspection based classification system would make possible the checking of each ceramic component and immediately alert the operator about the presence of defects. Generally, in many classification problems a choice of features or dimensionality reduction is significant and simultaneously very difficult, as a substantial computational effort is required to evaluate possible feature subsets. In this research, a combination of artificial neural networks and genetic algorithms are used to optimize the feature subset used in classification of various defects in reaction-sintered silicon carbide ceramic components. Initially wavelet based feature extraction is implemented from the region of interest. An Artificial Neural Network classifier is employed to evaluate the performance of these features. Genetic Algorithm based feature selection is performed. Principal Component Analysis is a popular technique used for feature selection and is compared with the genetic algorithm based technique in terms of classification accuracy and selection of optimal number of features. The experimental results confirm that features identified by Principal Component Analysis lead to improved performance in terms of classification percentage with 96% than Genetic algorithm with 94%. © 2015 Elsevier B.V. All rights reserved.


Yahaya M.A.,Swinburne University of Technology | Yahaya M.A.,University Technology of MARA | Ruan D.,Swinburne University of Technology | Lu G.,Nanyang Technological University | Dargusch M.S.,Defence Materials Technology Center, Australia
International Journal of Impact Engineering | Year: 2015

Aluminium honeycomb sandwich panels have potential applications as a protective mechanism that can be used to prevent failure of an important structure subjected to impact loading. Therefore it is important to fully understand the resistance of the sandwich panels subjected to impact loading conditions. The main objective of this work was to study the resistance of sandwich panels with different aluminium honeycomb cores, air sandwich panels (no core between the two face sheets) and monolithic plates of equivalent mass subjected to impact from foam projectiles. The deformation and the elastic spring-back of the honeycomb sandwich panels and the monolithic plates have been compared and discussed. The resistance of the panels and plates has been quantified by their back-face deflection with respect to the projectile impulse. Five different types of aluminium honeycombs have been used as the core material. The front-face sheet and the back-face sheet of the honeycomb sandwich panels are made of aluminium plate with 1 mm thickness. Cylindrical ALPORAS aluminium foams with a relative density between 9% and 11% are employed as the metal foam projectiles. They are fired at several hundred metres per second towards the centre of the panels and plates using a gas gun. The deflection histories of the back-face have been measured using a laser displacement sensor. From the deflection histories, the maximum deflection and the final deflection of the back-face can be distinguished. Deformation modes and failure modes of the individual component have been observed and classified into several categories. Moreover, the deflections of the honeycomb sandwich panels have been compared with deflections from air sandwich panels. It is found that the honeycomb sandwich panels outperform both the air sandwich panels and the monolithic plates within an impulse range of 2.25 kNsm-2 ∼z4.70 kNsm-2. Outside this operational range, the advantages associated with employing the honeycomb sandwich panels as a protective structure upon impact of foam projectiles diminishes. © 2014 Elsevier Ltd. All rights reserved.


Pas S.J.,Monash University | Dargusch M.S.,Defence Materials Technology Center, Australia | MacFarlane D.R.,Monash University
Physical Chemistry Chemical Physics | Year: 2011

The properties of ionic liquids give rise to applications in diverse technology areas including mechanical engineering, mining, aerospace and defence. The arbitrary physical property that defines an ionic liquid is a melting point below 100 °C, and as such, an understanding of crystallisation phenomena is extremely important. This is the first report dealing with the mechanism of crystallisation in ionic liquids. Assuming crystallisation of the ionic liquids is a thermal or mass diffusion-controlled process, the values of the isothermal Avrami exponent obtained from three different ionic liquids with three different anions and cations all indicate that growth occurs with a decreasing nucleation rate (n = 1.8-2.2). For one of the ionic liquids it was possible to avoid crystallisation by fast cooling and then observe a devitrification upon heating through the glass transition. The isothermal Avrami exponent of devitrification suggested growth with an increasing nucleating rate (n = 4.1), compared to a decreasing nucleation rate when crystallisation occurs on cooling from the melt (n = 2.0). Two non-isothermal methods were employed to determine the Avrami exponent of devitrification. Both non-isothermal Avrami exponents were in agreement with the isothermal case (n = 4.0-4.15). The applicability of JMAK theory suggests that the nucleation event in the ionic liquids selected is a random stochastic process in the volume of the material. Agreement between the isothermal and non-isothermal techniques for determining the Avrami exponent of devitrification suggests that the pre-exponential factor and the activation energy are independent of thermal history. The heating rate dependence of the glass transition enabled the calculation of the fragility index, which suggests that the ionic liquid is a "strong" glass former. This suggests that the temperature dependence of the rate constant could be close to Arrhenius, as assumed by JMAK theory. More generally, therefore, it can be concluded that there is nothing unusual about the crystallisation mechanism of the ionic liquids studied here. © the Owner Societies 2011.


Knight S.P.,RMIT University | Knight S.P.,Defence Materials Technology Center, Australia | Salagaras M.,Defence Science and Technology Organisation, Australia | Trueman A.R.,Defence Science and Technology Organisation, Australia | Trueman A.R.,Defence Materials Technology Center, Australia
Corrosion Science | Year: 2011

Atmospheric corrosion is one of the leading causes of structural damage to aircraft. Of particular importance is pitting and intergranular corrosion, which can develop into fatigue cracks, stress corrosion cracks, or exfoliation. Therefore it is of interest to the Australian Defence Force (ADF) to understand how corrosion ensues in susceptible aircraft aluminium alloys, such as AA2024-T351 and 7050-T7451. However, there are many difficulties in measuring the extent of intergranular corrosion, since it is predominantly hidden below the surface. Traditionally, cross-sectioning has been used to view and measure the depth of attack. In the present work, 2. mm diameter pin specimens were contaminated with a droplet of 3.5% NaCl and exposed to constant humidity that resulted in intergranular corrosion. X-ray computed tomography was then used to non-destructively assess the depth and volume of corrosion both as a function of time in 97% relative humidity, and as a function of relative humidity after 168. h exposure. Both corrosion depth and volume increased with time, but there was evidence for a limiting depth in AA2024. Depth and volume also increased with relative humidity of the environment, for which the time-of-wetness and oxygen concentration of the droplets were considered the important factors in driving the corrosion process. © 2010 Elsevier Ltd.


Yan M.,Defence Materials Technology Center, Australia | Yan M.,University of Queensland | Yan M.,RMIT University | Dargusch M.S.,Defence Materials Technology Center, Australia | And 4 more authors.
Acta Materialia | Year: 2014

Recent systematic experimental studies involving the benchmark Ti-6Al-4V alloy fabricated from powder have established that there exists a critical level of oxygen around 0.33 mass%, beyond which the tensile ductility of the alloy drops dramatically until reaching total brittleness. To understand the fundamental mechanisms behind this critical oxygen content, three-dimensional atom probe tomography, transmission electron microscopy and other analytical means have been used to identify and characterize the fine microstructural changes induced by the increased oxygen content beyond the critical level. Three fine microstructural features were identified in as-sintered Ti-6Al-4V when the interstitial oxygen content was increased from 0.25 mass% to 0.49 mass%. These are: (i) the formation of fine acicular α precipitates in the β phase; (ii) the formation of α2-type (Ti3Al) nanometric clusters in the α matrix; and (iii) grain boundary α-β-α-layered structures between the α grains. The impacts of these microstructural changes on the tensile ductility are discussed. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Crouch I.G.,Defence Materials Technology Center, Australia
Proceedings - 28th International Symposium on Ballistics, BALLISTICS 2014 | Year: 2014

In lightweight, ceramic-based, armour systems there are a number of established methods of improving multi-hit resistance. These can range from adopting a mosaic pattern of small ceramic tiles to the use of containment layers, like steel or polycarbonate sheeting, placed in front of the ceramic. However, these methods invariably lead to an increase in parasitic weight and are not favoured by designers of Hard Armour Plates (HAP) for lightweight Body Armour Systems (BAS). Instead, designers will adopt some form of cladding to the ceramic element before the HAP is finally constructed. But, what type of cladding is best? What effect does it have on ballistic performance? Does it actually improve multi-hit behaviour? This paper provides the answers and offers explanations about radial crack propagation emanating from the Point of Impact (POI) of a 7.62mm APM2 bullet.


Shi Z.,University of Queensland | Shi Z.,Defence Materials Technology Center, Australia | Cao F.,University of Queensland | Song G.-L.,University of Queensland | Atrens A.,University of Queensland
Corrosion Science | Year: 2014

Our recent data on Mg corrosion has been reanalysed because of the recent criticism that our previous data analysis was inadequate. Re-analysis leads to similar conclusions as previously. The apparent valence of Mg during corrosion was in each case less than 2.0, and in many cases less than 1.0. Moreover, these values were probably over-estimates. The low values were consistent with the evolving hydrogen gas acting as an insulator, so that the corrosion of parts of the specimen could occur isolated from the electrochemical measurement system. © 2014 Elsevier Ltd.


Bermingham M.J.,Defence Materials Technology Center, Australia | Bermingham M.J.,University of Queensland | Palanisamy S.,Defence Materials Technology Center, Australia | Palanisamy S.,University of Queensland | And 2 more authors.
International Journal of Machine Tools and Manufacture | Year: 2012

Thermally assisted machining is an emerging manufacturing process for improving the productivity when machining many difficult-to-cut engineering materials. Traditionally the process is reserved for very hard and high strength materials where abrasive and notching wear mechanisms cripple tool longevity. Recently there has been interest in using the process to machine titanium alloys and published reports indicate that machinability is improved, namely though a reduction in cutting forces. However, there is still ambiguity about whether the process is beneficial for tool life and the specific wear mechanisms for carbide tooling remain unknown. This work characterises the tool life and wear mechanism for two uncoated carbide tools when turning Ti-6Al-4V at high speed. While it is observed that thermally assisted machining reduces the cutting forces, it is found that the process has a deleterious effect on tool life because the dominant wear mechanism associated with diffusion is exacerbated during thermally enhanced machining. The process is compared against coolant technologies from the literature using identical tooling and cutting parameters and it is found that cooling the tool suppresses adhesion-diffusion wear and significantly prolongs tool life. © 2012 Elsevier Ltd.


Luo P.,University of Melbourne | McDonald D.T.,University of Melbourne | Palanisamy S.,Defence Materials Technology Center, Australia | Dargusch M.S.,Defence Materials Technology Center, Australia | Xia K.,University of Melbourne
Journal of Materials Processing Technology | Year: 2013

Machining chips of commercially pure Ti (ASTM grade 2) were consolidated into full density by equal channel angular pressing (ECAP) with an average grain size as low as 0.8 μm, yield strength up to 650 MPa, and ductility of ∼16%. Effect of recycling condition on the microstructure and mechanical properties were investigated in terms of ECAP temperature, number of passes and chemical composition. Using electron backscatter diffraction it is evident that continuous dynamic recrystallization (however, which is purely a phenomenological terminology) plays a significant role in grain (with misorientation ≥15°) formation, whilst benefitting from high stacking fault energy, this continuous conversion of subgrain (<15°) into grain can be essentially considered as an extended recovery with a substantial presence of low angle grain boundaries in the recycled Ti. The Hall-Petch relationship is adapted to explain the strengthening of the recycled Ti. Additionally, using scanning electron microscopy fractography, the ductility was analyzed by a modified Griffith criterion. Last, superior energy efficiency of ECAP reduces environmental impact when comparing to conventional melting/casting. ECAP develops an innovative solid-state process for improving the recycling value of waste Ti. © 2012 Elsevier B.V.


Luo P.,University of Melbourne | McDonald D.T.,University of Melbourne | Xu W.,University of Melbourne | Palanisamy S.,Defence Materials Technology Center, Australia | And 2 more authors.
Scripta Materialia | Year: 2012

Equal channel angular pressing was used to consolidate commercially pure titanium chips into fully dense bulk material with high strength (up to 650 MPa), due to an ultrafine grain size as low as 0.8 μm, and good ductility (∼16%). Electron backscattered diffraction was employed to reveal low-angle grain boundaries (LAGBs), enabling a modified Hall-Petch relationship to be analyzed in consideration of strengthening contributions from LAGBs in particular, but also interstitial solutes, high-angle grain boundaries and potential oxide dispersion. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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