18 research outputs found
Thermal analysis of laser additive manufacturing of aluminium alloys: Experiment and simulation
No full textApplication of Adaptive Element-Free Galerkin Method to Simulate Friction Stir Welding of Aluminum
No full textAnalysis of the effect of inline laser-induced ultrasonic waves on the microstructure of materials processed in laser powder bed fusion conditions
No full textInternational audienceMetallic Laser Additive Manufacturing Processes and, particularly, the Laser Powder Bed Fusion Process, demonstrate a strong and ever-growing potential in a very varied field of applications. However, standard LPBF generally produces anisotropic columnar microstructure [1], induced by solidification conditions, which is unlikely desired. Different approaches have been proposed to produce an equiaxed grain refinement through adaptations of process parameters or a modification of the composition of the alloys that cannot be generalized. Recent publications [2] proposed to extend the well-known grain refinement by ultrasonic waves in casting processes. This has been successfully demonstrated in laser cladding conditions.This study aims to explore the possibility of generating an equiaxed microstructure for LPBF using online laser-induced ultrasonic waves. This first experimental approach will be carried out on a simplified experimental setup representative of the laser fusion conditions, mainly on stainless steel material. In an initial experiment, the material is initially solicited by an external shear ultrasound transducer during the fusion process. Microstructural analysis demonstrates that this type of solicitation has a clear effect on the final microstructure. Then, new experiments including inline laser-induced ultrasonic waves is made by modulating the processing laser. The influence of process parameters (mainly process speed and laser power) and the ultrasonic signal (frequency, amplitude) is investigated. The microstructures are analyzed by EBSD and clearly evidence that the elongated grains normally generated by solidification conditions are fragmented into smaller grains for a range of frequencies.[1] G. I. Eskin & D. G. Eskin, ‘‘Ultrasonic Treatment of Light Alloy Melts’’, 2nd edn (CRC Press, Boca Raton, 2014). J. Campbel, Int. Met. Rev. 26, 71–99 (1981). M. J. Bermingham et al., J. Mater. Res. 23, 97–104 (2008). J. H. Martin et al., Nature 549, 365–369 (2017).[2] C. J. Todaro, et al., Nat. Comm., 11.1, 1-9, (2020). M. Froend et al., Mater. Sci. Eng. A 772, (2020). Zhang et al., Science, 374, 478–482 (2021).<br
Analysis of the effect of inline laser-induced ultrasonic waves on the microstructure of materials processed in laser powder bed fusion conditions
No full textInternational audienceMetallic Laser Additive Manufacturing Processes and, particularly, the Laser Powder Bed Fusion Process, demonstrate a strong and ever-growing potential in a very varied field of applications. However, standard LPBF generally produces anisotropic columnar microstructure [1], induced by solidification conditions, which is unlikely desired. Different approaches have been proposed to produce an equiaxed grain refinement through adaptations of process parameters or a modification of the composition of the alloys that cannot be generalized. Recent publications [2] proposed to extend the well-known grain refinement by ultrasonic waves in casting processes. This has been successfully demonstrated in laser cladding conditions.This study aims to explore the possibility of generating an equiaxed microstructure for LPBF using online laser-induced ultrasonic waves. This first experimental approach will be carried out on a simplified experimental setup representative of the laser fusion conditions, mainly on stainless steel material. In an initial experiment, the material is initially solicited by an external shear ultrasound transducer during the fusion process. Microstructural analysis demonstrates that this type of solicitation has a clear effect on the final microstructure. Then, new experiments including inline laser-induced ultrasonic waves is made by modulating the processing laser. The influence of process parameters (mainly process speed and laser power) and the ultrasonic signal (frequency, amplitude) is investigated. The microstructures are analyzed by EBSD and clearly evidence that the elongated grains normally generated by solidification conditions are fragmented into smaller grains for a range of frequencies.[1] G. I. Eskin & D. G. Eskin, ‘‘Ultrasonic Treatment of Light Alloy Melts’’, 2nd edn (CRC Press, Boca Raton, 2014). J. Campbel, Int. Met. Rev. 26, 71–99 (1981). M. J. Bermingham et al., J. Mater. Res. 23, 97–104 (2008). J. H. Martin et al., Nature 549, 365–369 (2017).[2] C. J. Todaro, et al., Nat. Comm., 11.1, 1-9, (2020). M. Froend et al., Mater. Sci. Eng. A 772, (2020). Zhang et al., Science, 374, 478–482 (2021).<br
Metallurgical aspects of joining commercially pure titanium to Ti-6Al-4V alloy in a T-joint configuration by laser beam welding
No full textMitigation of impacts on groundwater dependent vegetation through adaptive abstraction regimes
No full textSupporting evidence-based adaptation decision-making in Western Australia: a synthesis of climate change adaptation research
No full textThis research synthesis provides policy-makers and practitioners with an understanding of the building blocks for effective adaptation decision-making, as evidenced through the NCCARF research program. It synthesised a portfolio of adaptation research for each Australian state and territory and addressing the complex relationships between research and policy development. Each state and territory synthesis report directs users to research relevant identified priorities
Supporting evidence-based adaptation decision-making in Queensland: a synthesis of climate change adaptation research
No full textThis research synthesis provides policy-makers and practitioners with an understanding of the building blocks for effective adaptation decision-making, as evidenced through the NCCARF research program. It synthesised a portfolio of adaptation research for each Australian state and territory and addressing the complex relationships between research and policy development. Each state and territory synthesis report directs users to research relevant identified priorities.
Authored by Jennifer Cane, Laura Cacho, Nicolas Dircks, Peter Steele
Orchids as Indicators of Ecosystem Health in Urban Bushland Fragments
No full textIn this thesis I investigate the utility of orchids as indicators of ecosystem health. The study areas were urban bushland fragments on the Swan Coastal Plain, a global biodiversity hotspot. The study focuses on the abundance, reproductive success, mycorrhizal abundance and seedling biomass accumulation of a suite of native terrestrial orchids common to Perth’s urban bushland fragments. A critical factor in exploring the ecological responses of these orchids to site condition and their application as indicators of ecosystem health is the assessment of the ecosystem health of each of the study sites.
I studied the vegetation condition gradient across eleven urban bushland fragments using three known ecosystem health assessment methods. Correlations were found between the perimeter to area ratio, native vegetation cover, weed cover and canopy cover in relation to site condition gradients. Floristic complexity at sites was found to mask relationships with environmental variables that were apparent following classification into plant functional groups. Of the plant functional traits only facultative sprouter, sub-shrub, barochory and perennial trait frequencies correlated with the vegetation condition gradient, all traits showing a decline with decreasing vegetation condition.
Multivariate analysis of orchid abundances and environmental parameters revealed three orchid species that could potentially be used as indicators of ecosystem health. Diuris magnifica and Microtis media correlated strongly with poor condition sites. Pterostylis sanguinea correlated strongly with very good condition sites. However, environmental parameters, floristic composition and plant functional groups provided weak correlation to orchid species presence and abundance. Reproductive response, mycorrhizal abundance and biomass accumulation across the vegetation condition gradient were then measured to determine the extent to which orchids can be used as indicators of ecosystem health.
The effects of site condition on fruit set success were not found to be significant for any of the orchid species in this study. Widespread pollen limitation across sites revealed that fruiting success was likely to be too insensitive a measure for examining ecosystem health.
Mycorrhizal distribution across the cline of condition was found to be patchy within fragments and revealed unoccupied niches capable of supporting orchid germination. Further evidence of the use of Microtis media as an indicator of poor condition sites was found in an increased abundance of the associated mycorrhizal symbiont. The abundance of mycorrhizal symbionts for Caladenia arenicola and Elythranthera brunonis at sites of very good condition indicated their potential use as indicators.
An inverse relationship was found to exist between biomass allocation to leaf or tuber in sites of good and poor condition. In sites of poor condition, Diuris magnifica and Caladenia arenicola increased allocation of biomass to shoots presumably in order to obtain photosynthates. In sites of very good condition these two species increased their allocation of biomass to the tuber. Initial findings suggest biomass allocation in Caladenia arenicola and Diuris magnifica may be a useful tool in measuring ecosystem health.
The lack of currently undisturbed urban remnants and a poor historical record of past disturbance events in the study sites make understanding the role of past disturbances on the current condition gradient difficult. The results of this study suggest that orchid presence and abundance, orchid growth and orchid symbionts can be used as indicators of ecosystem health, although work needs to be undertaken to refine the understanding of their response to specific disturbances. This study provides a baseline for investigating the utility of orchids as indicators of ecosystem health in highly fragmented systems
Supporting evidence-based adaptation decision-making in the Australian Capital Territory: a synthesis of climate change adaptation research
No full textThis research synthesis provides policy-makers and practitioners with an understanding of the building blocks for effective adaptation decision-making, as evidenced through the NCCARF research program. It synthesised a portfolio of adaptation research for each Australian state and territory and addressing the complex relationships between research and policy development. Each state and territory synthesis report directs users to research relevant identified priorities.
Authored by Jennifer Cane, Laura Cacho, Nicolas Dircks and Peter Steele
