Mechanical Properties of Laser-Deposited Ti-6Al-4V

Laser additive manufacturing is a solid-freeform-fabrication process which is being investigated for titanium-component manufacturing and repair based on its cost-reduction potential and flexibility. Laser additive manufacturing also has the potential to improve mechanical properties due to the high cooling rates involved. However, the effect of the layered manufacturing process and any lack-of-fusion porosity and texture on the magnitude and anisotropy of mechanical properties is of concern. Hence, a preliminary effort was undertaken to assess these effects for bulk Ti-6Al-4V deposits manufactured using the LENS™ process. Tension, fatigue, and crack-growth tests were performed on both stress-relieved and HIP’ed deposits in three primary directions. The results were compared to published data for conventionally processed Ti-6Al-4V castings and forgings.Mechanical Engineerin

Livestock guardian dog protection of free-range poultry from the red fox

Context: Predation of layer chickens is a major issue for free-range egg producers. Using livestock guardian dogs (LGD) to protect free-ranging poultry is a possible option for producers, although there is little published literature regarding how the dogs protect chickens. Aims: This case study was conducted at a free-range egg production farm in Western Australia, where red foxes (Vulpes vulpes) were a common predator of chickens prior to introducing Maremma LGD. We investigated LGD responses to experimental cues that might indicate fox incursion (fox urine and calls). Methods: Four dogs were GPS tracked and monitored using camera traps. Over the first week, experimental fox cues were set out around the paddock boundaries, alternating with ‘non-cue’ experimental control nights. We recorded whether the LGD altered (1) their space use, (2) activity patterns (movement speed), or (3) behaviour in response to these cues. We also recorded (4) distances between LGD from known sightings of foxes. Key results: The Maremmas appeared to work independently of each other, covering separate areas. There was no significant difference in overnight home range area by experimental fox cue treatment, but there was a significant (P < 0.001) treatment × dog interaction term for distance moved. Three dogs spent most of their time at night around the chicken shelters and generally increased distances moved on experimental fox cue nights. The fourth dog was more bonded to people and did not alter its movements. Paradoxically, dogs rested more and barked less on experimental fox cue nights; however, we recorded foxes on camera traps placed around the chicken shelters on 17 of the 23 nights of monitoring, and the high background activity level of foxes on this property compromised our experimental control (nights without experimental fox cues). The dogs did not move towards known fox sightings. Conclusions: The Maremmas in this trial closely guarded the chicken shelters rather than maintaining the entire paddock as a predator-exclusion zone. Implications: Understanding how guardian dogs behave when challenged by potential predators will help increase producers’ confidence in the efficacy of these dogs as a viable method to protect livestock from predation threat

Habitat islands in a sea of urbanisation

Cities can provide important habitat for wildlife conservation. Many species do not make much use of anthropogenic resources, but instead are largely reliant on natural habitat remaining within a matrix of urban development, and are engulfed by encroaching housing development. Understanding which factors influence their presence and activities will allow us to manage these habitat remnants for biodiversity conservation. To this aim, we carried out a field survey recording evidence of quenda (Isoodon obesulus fusciventer) foraging digs over 106 reserves managed by the City of Mandurah, the fastest growing regional city in Australia. We identified vegetation extent and condition as primary factors correlated with the presence of quenda digging activity. In addition, the extent of canopy cover and amount of woody debris are important habitat variables to quenda, while there was a negative correlation with access to the reserves by domestic dogs (Canis familiaris). Although we included a range of urbanisation measures in the analyses (including the amount of roads nearby to each reserve, the distance to roads and the distance to buildings), none were correlated with quenda digging activity. This study indicates that quenda can persist in the urban landscape despite human activities, but highlights the importance of protected bushland reserves for their conservation

Prediction of Microstructure in Laser Deposition of Titanium Alloys

Laser deposition of titanium alloys is under consideration for aerospace applications, and offers significant increases in efficiency and flexibility compared to conventional manufacturing methods. However, its ultimate success will depend on the ability to predict and control the microstructure and resulting mechanical properties of the deposit. In this study, both 2-D continuum finite element modeling and 3-D cellular automaton finite element modeling of a thinwall geometry are used to investigate the effects of deposition process variables on microstructure in laser deposited Ti-6Al-4V. Numerical results for cooling rate and thermal gradient obtained from the 2-D models are used to provide insight into grain size and morphology, while the 3-D cellular automaton models are used to provide direct predictions of deposited microstructure. The numerical model predictions are subsequently compared with observed microstructures in LENSTM deposited Ti-6Al-4V.This work was supported by the Joint AFRL/DAGSI Research Program, project number ML-WSU-01-11, as well as by a grant from Wright State University and the Ohio Board of Regents.Mechanical Engineerin

Microstructural characterisation of a nickel alloy processed via blown powder direct laser deposition (DLD)

A three dimensional structure of varying wall thickness has been manufactured from an alloy similar to 718 and subjected to metallographic characterisation. The technique is evaluated as a process capable of generating complex geometries. This can be used to add features or as a free form fabrication method. However, in order to allow for comparison to structures developed through more traditional techniques, detailed microstructural characterisation has been undertaken to attempt to understand the potential effect of variation on resultant mechanical properties.Samples were extracted from six locations with different wall thicknesses, intricate features and intersecting ligament geometry. A γ″ linearly arrayed structure within a γ matrix was consistent throughout the component. Micro-porosity was restricted to isolated, spherical pores < 1 μm in diameter. Electron back-scatter diffraction and X-ray computed microtomography quantitative microstructural analysis techniques have been utilized to assess the influence of layering upon microporosity, patternation and grain structure.A detailed comparison is also made between blown powder Direct Layer Deposition (DLD) and a similar deposition technique, shaped metal deposition (SMD). Blown powder DLD produces a smaller weld pool and results in a more consistent microstructure than SMD, with less evidence of unfavourable phases brought about by prolonged exposure to high temperatures. The improved microstructure, however, must be measured against the different process economics of the blown powder DLD technique

Shelter and a square meal: factors determining honeyeater sightings in the wheatbelt of southwest Western Australia

Honeyeaters are the major vertebrate pollinators in Australia and the most common guild of birds in southwest Western Australia. In the wheatbelt of WA, 13 of 20 honeyeater species have demonstrated significant decline over the last century; only two species have increased in abundance and/or range. We analysed nine years of Birds Australia records to determine spatial links between honeyeater sightings and datasets for presence of flowering plants, vegetation complexity and native vegetation extent for 10x10 km grid cells over the wheatbelt. Numbers of honeyeater records were positively correlated with the presence of flowering plant species known. For the wheatbelt, numbers of bird records were correlated with the extent of clearing, with higher incidence in areas that have a greater area of remnant native vegetation. The extent of native vegetation was also significantly linked with honeyeater species richness, the greatest diversity of honeyeaters being found in the northern and southeastern wheatbelt. These landscape-scale findings provide quantitative support for localised observations of the abundance of individual honeyeater species: species that have declined over time demonstrated positive correlations with native vegetation extent in the present study, those that have increased in abundance and/or range demonstrated negative correlations in the present study (perhaps reflecting their ability to use degraded habitats). Significant positive spatial correlations with the distribution of nectar-bearing flowering plant species were evident for species recorded as largely nectarivorous by other authors. Such landscape analyses offer the potential to identify regions important for the conservation and management of this avian guild

Spatial analysis of limiting resources on an island: diet and shelter use reveal sites of conservation importance for the Rottnest Island quokka

Context. For conservation of any species, we need baseline data that will guide conservation planning strategies. Identifying plant resources used by animal species for food and shelter is the first important step towards fauna conservation. The second step is to determine the extent and distribution of these resources and thus identify prime habitat or habitat that could be improved through suitable management actions. This information provides the necessary spatial targeting required to make the most of few resources and a shortage of time. Aims. Applying this model approach, we identified plant species used as food or shelter resources by the conservationally significant quokka (Setonix brachyurus) across Rottnest Island, Western Australia in the aftermath of the hottest and driest summer on record. Methods. Dietary analysis was carried out using microhistological examination of plant cuticle remains from faecal samples for 67 locations across the island. Plants acting as diurnal rest shelters (n≤73 sites) were identified through observation of individuals flushed during surveys. Identifying key resources requires both a comprehensive analysis of the current use, as well as knowledge of availability of resources to determine selectivity. We therefore compared food plants or rest sites with a comprehensive survey of floristic diversity and abundance for 210 stratified-randomly located sites across the island. Key results. We identified eight plant species that quokkas fed on preferentially and identified four plant species that were the principal shelter sites. We then used hyperspectral remote sensing data to map the distribution of these plant species to quantify their distribution and identify key habitat areas. Conclusions. Understanding resource limitation over the most physiologically challenging time of the year provides important information for quokka conservation. Quokkas prefer Malvaceae species as food plants, and use dense, abundant shrubs for shelter. Implications. Quokkas appear to have shifted their use of food plants since a previous study (50 years ago), likely reflecting modification of island vegetation due to anthropogenic influences, fire and herbivory over time. In the face of changing climate, this information will serve as an important guide towards conservation management actions on the island (e.g. future planning of revegetation and habitat protection/enhancement)

Foxes at your front door? Habitat selection and home range estimation of suburban red foxes (Vulpes vulpes)

The red fox (Vulpes vulpes) is one of the most adaptable carnivorans, thriving in cities across the globe. We used GPS-tracking of five suburban foxes across high-density residential suburbs of Perth, Western Australia to quantify (1) their habitat selection and (2) home range area. All five foxes showed statistically significant avoidance of residential locations (p < 0.001) and preference for parkland (p < 0.001), with native vegetation reserves, golf courses, and water reserves showing disproportionately greater use. Landuse category also influenced their movements, with foxes moving quickest (i.e., commuting) in proximity to roads and slowest (i.e., foraging) when they were further from roads. Three females had core home ranges (50% autocorrelated-corrected kernel density estimate; AKDEc) averaging 37 ± 20 ha or 95% AKDEc averaging 208 ± 196 ha. One male had a 95 ha core home range and 349 ha 95% AKDEc but the other male covered an area ~ 20 times this: using a 371 ha core home range and 7,368 ha 95% AKDEc. The extensive movement patterns we describe are likely to be common for urban foxes, with half of published home range estimates for urban foxes (principally based on VHF data) excluding data for ‘lost’ individuals or animals that showed ‘excursions’. It is likely that the home range estimates for these urban exploiters have therefore been grossly underestimated to date. Further application of GPS trackers that allow remote download will vastly improve our understanding of habitat preference and exploitation of resources by urban foxes