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Literacy practices Victorian primary school Year 5/6 teachers use to support the development of disciplinary literacies of science
No full textThis thesis investigates Year 5/6 Victorian Australian primary teachers’ understanding of the disciplinary literacies of science and the disciplinary literacies of science practices used in their classrooms when teaching science. The literacies of a discipline provide specialised ways of understanding the knowledge of a discipline in-depth. Literacy is integral to learning science; for students to learn science, they need to move beyond the more general literacies used across disciplines and understand and use the academic literacies of science. Year 5/6, the beginning of the middle years of schooling in Victoria, is a critical time for teachers to understand the importance of teaching disciplinary literacies of science.
This research study used a Qualitative paradigm and a Constructivist Inquiry process. The research employed a Case Study design that included multiple data-gathering methods. The researcher was a non-participant observer in four Victorian primary school Year 5/6 classrooms. Data from principal and teacher interviews, student focus groups, classroom observations and documents, and teacher and student artefacts were gathered and analysed to inform the discussion of the demands facing teachers in Year 5/6 primary classrooms in relation to their understandings of, and practices in, disciplinary literacies of science. These multiple data-gathering methods enabled the development of detailed descriptions of the participants' engagement with disciplinary literacies in these settings.
This research explored how these Year 5/6 classroom teachers supported student learning of disciplinary literacies of science and built a picture of how these teachers responded to the learning and teaching of science in these classrooms. This enabled the development of detailed descriptions of the participants’ engagement with disciplinary literacies of science, their understanding of disciplinary literacies, and the practices they used in their classrooms. The study found that these teachers understood that students used general and specialised literacies to investigate and engage in science. Embedding these literacies within a constructivist, inquiry-based approach, they explicitly engaged students in using disciplinary literacies of science practices when learning science.
These research results add knowledge to the understanding that disciplinary literacies of science practices enhance teaching and learning practices in Year 5/6 primary school classrooms
Synthesis of two-dimensional indium oxide using liquid metal chemistry
No full text2D metal oxides (2D MOXs) represent an exciting class of 2D materials and have attracted considerable interest due to their distinctive properties, such as excellent optical transparency, high carrier mobility, and good environmental stability. This family of 2D material has been attracting significant attention in various fields of electronics, optoelectronics, sensing, energy storage.
Among several 2D MOXs, indium oxide (In2O3) is an important n-type semiconductor and has been intensively investigated and recognized as a promising candidate for the future of electronics and optoelectronics. However, the synthesis of large-area, uniform, and unit-cell-thick indium oxide nanosheets with minimal defects still remains a great technical challenge, limiting its use in transparent and flexible devices.
The core of this PhD thesis involves exploring a new printing technique based on liquid metal chemistry that can directly deposit lateral-large and ultrathin indium oxide nanosheets onto desired substrates. This approach provides a low-temperature, low-cost, and vacuum-free synthesis route for realizing ultrathin In2O3 which does not rely on any bulky and expensive instrument.
The author also investigates furnace-free doping methods to incorporate a small amount of impurities into the produced 2D In2O3 nanosheets. The doping process can be carried out at low temperature via either wet chemical reaction or selective migration of dopants in liquid metal alloys. The effect of anion and cation doping on the properties of 2D In2O3 was investigated for potential applications such as transistors and photodetectors. In addition, a thermal annealing process is proposed to improve the transparency and electron mobility of the synthesised 2D indium oxide, in which nanostructural changes within the oxide layers during annealing process was investigated.
In the first part of this thesis, the author developed a wet chemical method to incorporate sulfur into the structure of 2D indium oxide nanosheets. The process consists of printing indium oxide skins out of molten indium metal and a subsequent sulfur insertion conducted in a trisulfur radical anion solution. The obtained 2D indium oxysulfide (In2O3−xSx) nanosheets with a thickness of ~2 nm were utilized for fabricating back-gated field-effect transistors (FETs), revealing a notably high electron mobility of ∼20 cm2 V−1 s−1. In addition, 2D In2O3−xSx based photodetectors exhibited an excellent performance in ultraviolet (UV) region, with a photoresponsivity of ∼3.4 × 103 A W−1 greatly surpassing that of many commercial materials. More importantly, the same reaction parameters were employed to obtain 2D bismuth oxysulfide and 2D tin oxysulfide, offering a furnace-free approach for 2D oxysulfide semiconductor fabrication.
In the second stage of research, the author further explored a one-step synthesis of few-unit-cell-thick and laterally large antimony-doped indium oxide (IAO). The doping process occurs spontaneously when the oxide is grown on the surface of a molten Sb–In alloy and 2D IAO nanosheets can be easily printed onto desired substrates. With thicknesses at the atomic scale, the obtained 2D IAO sheets exhibited excellent transparency exceeding 98% across the visible and near-infrared range. Field-effect transistors based on low-doped IAO nanosheets revealed a high electron mobility of ≈40 cm2 V−1 s−1. Additionally, a notable photoresponse was observed in 2D IAO-based photodetectors under ultraviolet (UV) radiation. Photoresponsivities of low-doped and highly doped IAO at a wavelength of 285 nm were found to be 1.2 × 103 and 0.7 × 103 A W−1, respectively, identifying these materials as promising candidates for the fabrication of high-performance optoelectronics in the UV region.
Following the successful investigation of anion and cation dopants for 2D In2O3 nanosheets, the third and final stage of this PhD thesis involved studying the effect of thermal annealing on the electronic and optoelectronic properties of 2D In2O3. A simple approach has been proposed to achieve 2-nm-thick indium oxide nanosheets from liquid metal surfaces by employing a squeeze printing technique and thermal annealing at 250 °C in air. The resulting materials exhibited a high degree of transparency (>99 %) and an excellent electron mobility of ≈96 cm2 V−1 s−1, surpassing that of pristine printed 2D In2O3 and many other reported 2D semiconductors. UV-detectors based on annealed 2D In2O3 also benefited from this process step, with the photoresponsivity reaching 5.2 × 104 and 9.4 × 103 A W−1 at the wavelengths of 285 and 365 nm, respectively. These values are an order of magnitude higher than for as-synthesized 2D In2O3. Utilizing transmission electron microscopy with in situ annealing, it was demonstrated that the improvement in device performances was due to nanostructural changes within the oxide layers during annealing process. This work highlights a facile and ambient air compatible method for fabricating high-quality semiconducting oxides, which will find application in emerging transparent electronics and optoelectronics.
Overall, the author successfully demonstrated significant findings in the course of this PhD research, signifying the potential of liquid metal chemistry in the synthesis and applications of 2D materials. The author believes that the outcomes of this PhD research will not only benefit the advancement of nanotechnology, but also contribute to the development of high-performance electronic and optoelectronic devices
An intelligent agent-based framework to design warehouse management systems that assist human operators in dynamic demand environments to mitigate the impact of exceptions: a simulation
No full textThe increase in e-commerce and omni-channel commerce is having a significant impact on the supply chain sector and its warehouses. Although automation is becoming prevalent as the solution to increasing warehouse complexity, many warehouses cannot automate due to product unsuitability and/or prohibitive capital expenditure. The golden rule of material handling is smooth product flow, but there are exceptions that occur in the day-to-day work of a warehouse that can have significant effects on product flow and impact customer satisfaction. The supply chain literature on risk and event management deals with the impact of an exception or “disruptive event” on the supply chain and how it can ripple along the supply chain if not contained at its source. A major research gap is that exceptions within the warehouse and their potential for disruption are not understood.
Warehouse operations involve a sequence of material handling processes, each with various associated costs. Strategies to reduce the cost of these processes focus on optimising them along the metrics of time, quality, and productivity. The warehouse process optimisation literature includes storage assignment algorithms, pick path strategies, optimal warehouse layouts and task allocation. However, optimisation strategies mostly operate on the perfect scenario and do not account for the impact of exceptions on the successful completion of a process and the associated cost of the rework.
This research focuses on how warehouse management systems can be designed to be more robust to exceptions that can cause a disruption, augmenting the human decision maker with intelligent decision support. The purpose was to design a distributed, real-time, agent-based model for warehouse management that could detect, mitigate, and resolve exceptions while aiding the human operator with a digital mentor.
This research uses Design Science Methodology. The problem identification and motivation phase of the project was qualitative. This included:1) An exploration of common warehouse issues via exploratory interviews with warehouse practitioners. Through thematic analysis, there emerged ten main warehouse themes: automation, decision support, e-commerce, labour (people), management, manual operations, process, supply chain, systems, and warehouse exceptions. The warehouse themes provided the context within which the exception categories were grounded. The exception categories were data, operational issues, resource issues, unexpected events and the human intervention required to resolve exceptions. Further analysis of the transcripts relating to exceptions resulted in a ripple effect caused by exceptions, and three categories of resulting disruption: 1) Disruption to warehouse efficiency, 2) Disruption to warehouse productivity and 3) Disruptions to the supply chain. When the exceptions were condensed further, the following high-level underlying causes emerged: Operator attention lapses, operator cognitive limits, small problems being ignored, time-consuming and complicated resolution processes, lack of visibility, lack of critical information, lazy scheduling of priorities, some tasks are faster but less accurate when done off-system, process workarounds to fix system gaps, and a cost vs accuracy trade-off mentality.
An agent-based model for the design of warehouse management systems called HAN/DSL/MENT (HDM) was proposed. The HDM model is composed of real-time intelligent and communicating agents in a HAN (Human Agent Network). The three types of agents are entity agents, service agents and mentor agents (MENT). Entity agents are digital twins of non-human warehouse entities. Service agents provide services or perform a management role within the network. Mentor agents are differentiated from the other digital agents because they are always paired with a human operator and interact in the HAN on behalf of the human operator. Mentor agents augment the ability of the human operator to perform their job by assisting with task completion and decision support. The DSL (Decision Support Layer) which is composed of service agents, is responsible for high-level continuous trend analysis and providing appropriate algorithms and process execution priorities to meet the environmental conditions and constraints of the environment.
A simulation of the model was developed using JADEX and tested with 10 common warehouse exception condition scenarios. The evaluation of the HDM model involved simulation runs in two modes: traditional and mentor assisted. A comparison between modes was completed using parametric and non-parametric statistical analysis tests. The ten test scenarios were exception scenarios and dealt with the exception sub-categories of congestion, picking exceptions, replenishment exceptions, abandoned pallets, inventory management, and maverick operators. Mentor-assisted mode was better than traditional mode at a statistically significant level for measures within the dimensions of time, quality, and productivity.
The results of this research show that real-time intelligent software agents that work in tandem with a human operator within a human-agent system can improve the quality/accuracy of warehouse operations by improving warehouse performance measures within the categories of time, quality, and productivity. This is achieved by improvements to the visibility of warehouse exceptions, targeted troubleshooting and resolution assistance and adaptive scheduling of priorities. This allows time-critical information to be used in real-time enabling time-critical decisions and actions to be taken in proactive and reactive modes for short-term decision support. In addition, a decision support layer enables incremental changes to be made via long-term decision support driven by trends analysis. A network of real-time intelligent agents working to mitigate the occurrence of warehouse exceptions and effectively and quickly resolve them can also have a positive impact on labour productivity and motivation. Labour productivity and motivation can be enhanced by spending less time on rework (after a task fails), with implicit checks (reducing cognitive load) and with guided and targeted exception trouble shooting and resolution support.
The HDM model proposes a different approach to designing warehouse management systems. This non-centralised model consists of a human-agent network within which three components of digital agents communicate. The first component is autonomous agents connected to non-human entities and service agents. The second component is digital mentor agents assisting human operators and decision-makers. The third component is a decision support layer involved in more complex data analysis and decision support.
The HDM model is not specific to warehouses but can be applied to other complex, dynamic environment where humans and systems (computers) must interact to achieve a common goal. Warehouses can be considered one of the cases of its application
Phase equilibria study of the CaO-Al2O3-SiO2-(Na2O/B2O3) slag system to recover valuable metals from e-waste
No full textThe research presented in this thesis deals with the recovery of valuable metals from antiquated electronics known as electronic waste (e-waste) using a pyrometallurgical route. The phase equilibria and liquidus temperatures of slags comprising the major oxide components of e-waste printed circuit boards (PCBs) smelting slag was systematically studied with the addition of different fluxing materials. The effect of the flux additives on the liquidus temperature and the phase assemblages was determined. An estimation of e-waste resources in Bangladesh generated from 4 different electronic gadgets (mobile phones, TVs, desktop computers, laptop/tablets) which are most widely used across the country was also made. Finally, the deportment of targeted metals in alloy and slag phase during smelting using one of the slag systems studied is presented and discussed.
CaO-Al2O3-SiO2 based synthetic master slags were prepared with CaO/SiO2 (C/S) ratios of 0.3, 0.6 and 1.0 while keeping the Al2O3 content close to 20 wt.%. These master slags were doped separately with 3 different fluxing agents (Na2O, B2O3, Na2B4O7) at level ranging from 5-20 wt.% to prepare 36 sub-slag compositions. Master slags and different series of sub-slags were thermally equilibrated in a vertical tube furnace at different temperatures (above and below the predicted liquidus) and rapidly quenched in a water bath to retain the high temperature slag structure. The quenched slags were examined with optical microscope and Scanning Electron Microscope (SEM) to observe the equilibrium phases, and the chemical composition of the equilibrium phases was determined with the aid of an Electron Probe Microanalyzer (EPMA). The liquidus temperature of master slags and sub-slags were bracketed within ±20 °C uncertainty using an iterative approach.
Three CaO-Al2O3-SiO2 master slags and 12- Na2O doped quaternary CaO-Al2O3-SiO2-Na2O slag samples were equilibrated at various temperatures to determine the liquidus temperatures and their equilibrium phase assemblages were identified. Anorthite (CaO.Al2O3.2SiO2), pseudowollastonite (CaO.SiO2), larnite (2CaO.SiO2), and gehlenite (2CaO.Al2O3.SiO2) primary solid phases were found in equilibrium with liquid phase. In general, liquidus temperature decreased with increasing Na2O content and a gradual shift in the primary phase field was observed. The lowest liquidus temperature (1110 °C) was obtained with 16.5 wt.% Na2O in master slag with a C/S ratio of 0.6 and 15.7 wt.% Al2O3. A reduction in liquidus by 225 °C was obtained by Na2O doping with the master slag of 1335 °C liquidus temperature. However, liquidus temperature first decreased and then increased with further Na2O doping when the primary phase field moved to larnite for slag series with C/S ratio 1.0. This increase was due to the higher thermal stability of larnite.
Phase equilibria study of quaternary CaO-Al2O3-SiO2-B2O3 slag system showed the effect of B2O3 doping (5-20 wt.%) keeping the C/S ratio in the range of 0.3 to 1.0. A gradual decline of the liquidus was common for every three series of B2O3 doped slags except an increase in the liquidus for slag with C/S ratio 1.0 and 15.6 wt.% Al2O3 beyond 14.9 wt.% B2O3. B2O3 flux showed a stronger effect on reducing the liquidus of CaO-Al2O3-SiO2 master slags with progressive doping compared to the equivalent Na2O doping. The lowest liquidus temperature in this slag series was obtained as 900 °C which is 435 °C lower than that of the undoped master slag (1335 °C) with C/S ratio 0.6 and 15.8 wt.% Al2O3. Unlike Na2O doped slags, primary phases of the slags with C/S ratio 0.3 and 0.6 did not change, while for slag with C/S ratio 1.0 primary phases shifted from gehlenite to pseudowollastonite at lower level of B2O3 doping. At 14.9 and 18.8 wt.% B2O3 doping two solid phases (anorthite and pseudowollastonite) were in equilibrium with liquid. At lower temperatures tridymite (SiO2) primary phase precipitated out of the solution in slags with C/S ratio 0.3.
The combined effect of Na2O and B2O3 in the quinary CaO-Al2O3-SiO2-B2O3-Na2O slag was investigated by doping with anhydride borax (Na2B4O7) within the ternary CaO-Al2O3-SiO2 slag. Borax doping reduced the liquidus temperature of the quinary slag system of three series (C/S ratio 0.3, 0.6 and 1.0) with primary phase field shifting. However, contrary to Na2O and B2O3 doped slags, the lowest liquidus was obtained in slag series with C/S ratio 0.3. With 20 wt.% borax doping the slag liquidus dropped to 1050 ±20 °C from 1345 °C (undoped master slag) by an overall reduction of 270 °C. The primary phase remained unchanged for lower level of borax doping (up to 10 wt.%) and then shifted to pseudowollastonite for slags with C/S ratios 0.3 and 0.6. However, the shifting to pseudowollastonite from gehlenite primary phase begins at 5 wt.% borax doping and continued up to 20 wt.%. EPMA results showed limited Na and B in solid solution within the primary crystals while major portion of these remains in the liquid phase.
The general order of flux for reducing the slag liquidus temperature was found as B2O3>Na2O>Na2B4O7 although the degree of reduction slightly varies depending on the C/S ratio and the primary phase of a particular slag in equilibrium.
Based on the liquidus study smelting of real e-waste PCBs were designed to simulate a slag of CaO-Al2O3-SiO2-B2O3. Kilogram-scale smelting test was performed using an induction furnace equipped with flue gas treatment facilities and under nitrogen blanket. The char content withing the pyrolyzed PCBs helps maintain a reducing environment to protect the metals from oxidising. Smelting under these conditions shows the distribution of metals in the alloy stream and the slag stream. Almost all the valuable metals reported in the alloy phase while the more refractory ones reported to the slag phase at 1350 °C
Planning in a public-private partnership: a case study of the Melbourne Metro Project
No full textUrban transport megaprojects are important, albeit problematic, mechanisms of city formation. Initial development is often ruled by politics creating projects that run over time, over budget and fail to deliver the original scope. Yet despite these concerns, megaprojects continue as a dominant mechanism of urban change - what Flyvbjerg calls the megaproject paradox. The private sector, through public-private partnerships, is often engaged in an attempt to resolve this paradox. The delivery of these projects by the private sector challenges the concept of planning in the public interest.
Can planning in the public interest occur within a public-private partnership and, if so, through what mechanisms? This question is explored through an auto-ethnographic account of the Melbourne Metro project. It reveals the tacit knowledge associated with the practice of planning within a PPP environment. It builds upon Flyvbjerg’s use of the Aristotelian virtue of phronesis as a value-rational framework to understand the role of expert judgement in achieving planning outcomes. The methodology deploys Latourian Actor-Network Theory providing a reflective account of planning in action, making explicit the role of things, such as contracts and performance requirements, associated with outsourced project governance.
The investigation explores three matters that arose during the twelve months the author was a senior executive in the project delivery partnership. The detailed examination reveals how power was distributed and manifested through the Actor-Network and the roles played by a cast of human and non-human actors, including the Project itself. The thesis finds that no actor was free to act unilaterally to pursue their interests but must navigate points of passage with the other actors.
Planning is shown as a relational practice where the public interest emerges through a dynamic process of settling matters of concern rather than through the actions of any one actor. The planner's role is seen as one of influence empowered by judgement as to what-can-be-done within a given context. It demonstrates project development as a process of social construction rather than an exercise of instrumental rationality
The lived experiences of work integrated learning placement for low socioeconomic undergraduate students at an Australian university
No full textDespite successive Australian governments supporting a widening participation agenda to increase the diversity of the higher education student population and graduates entering the workforce, students from low socioeconomic status (SES) backgrounds, continue to face unequal graduate employment outcomes and disadvantage post-graduation. These students typically face a multitude of personal, structural, and societal constraints whilst studying at tertiary level. As this study will show, these very constraints can also impose barriers to developing their employability, including their experience of Work Integrated Learning (WIL) placements.
This study was conducted at a large urban university located in Melbourne, Australia. It focused on the experiences of undergraduate students from low SES backgrounds in WIL placements. Work Integrated Learning has been shown to be a proven strategy to enhance graduate student employability and employment outcomes. This study not only examines the challenges that these students experience in obtaining (includes finding and securing) and whilst undertaking a placement, but also, (by taking a strengths-based perspective) the enablers of WIL for this cohort. It discovers, from rich insightful interviews, the employability outcomes that these low SES students experience as a result of their WIL placements. This study then analyses these insights through the lens of a contemporary conceptual model of employability.
To elicit a deep understanding of both the context of low SES and WIL and of the meaningful experiences arising from this context, the study adopted a mixed methods approach (Creswell & Plano Clark, 2011). The first phase consisted of an online questionnaire of undergraduate low SES students across all colleges of the university. It gained broad insights into these students’ experience of WIL placement and identified the factors that had the greatest impact upon their experiences. The second phase involved semi-structured interviews being conducted with a smaller cohort of these low SES students. By illuminating the ‘voice’ of the student, this multiple-case study provides a rich and detailed exploration of the broad insights of the first phase. The results from both phases were analyzed using a Graduate Capital Model (Tomlinson, 2017), a contemporary, multi-dimensional model of employability that draws upon Bourdieu’s (1986) highly influential capitals theory. Tomlinson’s (2017) conceptualization of employability recognizes that it must be placed within a broader social and cultural context and that the ways in which students construct their employability is influenced by their backgrounds, and the capitals and opportunities available to them.
Analysis of the findings shows that the convergence of graduate capitals (Tomlinson, 2017) has a significant impact on low SES students’ WIL placement experience. Whilst a lack of capitals can pose challenges to obtaining and undertaking WIL placement, a student’s possession of different forms of capital, for example, psychological capital such as resilience, persistence, or human capital such as skills and prior experience can also act as enablers. Further, for those students who do successfully complete a WIL placement, through drawing upon their strengths, such as persistence and resilience, they overwhelmingly experience positive employability outcomes.
Work Integrated Learning placement has the potential to strengthen undergraduate low SES students’ employability capitals and to enable informed career decision making. However, the study’s results demonstrate that these students need additional support to obtain suitable WIL placements as part of their studies and to have a positive experience whilst undertaking placement. Based on the findings, a number of recommendations are presented to inform the planning and policy development of proactive and targeted strategies that enable low SES students to have the same opportunities to benefit from a WIL placement experience, and for confident transition into the professional workplace. It is anticipated that the insights generated can also be a catalyst for further systemic change within industry, whereby host organizations are encouraged to make low SES-inclusion a priority for the provision of WIL placement opportunities and a positive WIL placement experience
Exploring the potential for community-academic partnerships in social work field education to increase quality placement opportunities
No full textThe ongoing challenge of finding sufficient high-quality social work field education (SWFE) placements to meet demand has created interest in new models of field education as an alternative to the traditional apprenticeship model. The key focus of this research is to investigate the potential for community–academic partnerships (CAPs) to transform the field education landscape and address the challenge the field is facing. The RMIT partnership model, formally introduced in 2015, offers an example of a CAP and is explored in this research to identify key factors influencing effective partnerships in SWFE. The RMIT model differs from most SWFE partnerships examined in the literature in that it involves partnerships with multiple agencies that take multiple students at the same time. Whilst the literature highlights the potential for SWFE partnerships to provide more quality placements, it also identifies the limited research in this area. By investigating the RMIT–industry partnership as an example of a SWFE CAP, this research aims to contribute to further development and innovation in the field. It does so using a qualitative research approach and a critical social work frame to investigate, with 10 partner agencies and RMIT field education staff, the benefits and challenges of the RMIT partnership model and whether there are particular factors that influence partnership success and sustainability. The research demonstrates that the RMIT SWFE partnerships have successfully increased the number of quality placements available, indicating that this approach addresses the problem of insufficient quality placements to meet demand. The research identifies a range of key relational, operational and contextual factors that influence partnership success and sustainability. The empirical evidence from the research, combined with the literature, has led to the development of a model for successful and sustainable SWFE CAPs that can increase the supply of quality placements. The research informs a series of recommendations for key stakeholders – universities, host agencies and the Australian Association for Social Work, the accrediting body. This research provides empirical evidence for the field to consider in relation to partnership approaches with industry as a way of increasing the number of quality social work placements
Design of additively manufactured Ti-xFe alloys – a micro segregation (β flecks) study
No full textβ titanium alloys that feature high tensile strength and superior high cycle fatigue strength are of great interest to both academia and industry. In particular, Fe containing β titanium alloy is one of the most promising alloy systems because Fe is the most economic β stabilizer and also delivers a strong solid solution strengthening effect. However, Fe solute is highly prone to segregation during casting, which leads to the formation of β fleck defect in the subsequent thermal mechanical treatment and deteriorates the fatigue properties. This project aims to mitigate or even eliminate β flecks in a series of Ti-Fe binary alloys fabricated by Laser Directed Energy Deposition (L-DED), taking the advantages of the high cooling rate during solidification and multiple thermal cycles during the L-DED process. SEM and EDS analysis confirmed a large dendrite-segregation-induced β fleck free zone can be achieved in thin-walled Ti-Fe samples. Combining the ABAQUS temperature field simulation result, the elimination of β flecks is well rationalized. A dynamic diffusion model has been developed the dynamic diffusion model to describe the in-situ homogenization effect during the L-DED process. And it is based on the sinusoidal solution of Fick’s second law and applies the transient temperature history data which is collected from the ABAQUS temperature field simulation. This model is validated by four case studies with different bulk Fe concentrations and different laser processing conditions. The dependence of such β flecks free zone on the laser processing parameters and Fe concentration was comprehensively investigated and discussed too
Cleaning techniques and non-destructive verification of residue removal within additively manufactured implants
No full textThe human body is incredibly resilient, but not infallible. Musculoskeletal injuries can manifest that the human body is not able to repair or treat itself, and without treatment, can severely degrade quality of life; these injuries require surgical intervention in order to deliver an appropriate correction, and improve an individual’s quality of life and end outcome. Off-the-shelf implants have existed for many years, and though a variety of materials have been used in the past, titanium alloy (specifically Ti-6Al-4V) has become the most common implant material, due to a large body of clinical evidence, as well as good mechanical and biocompatible properties. These off-the-shelf implants are generally solid, and may require surgical adjustment during implantation, leading to increased surgical and recovery times.
Additive manufacturing affords a design revolution for implant creation, allowing for aspects such as: mechanical property tailoring to match the surrounding bone and implant site more closely; allowances for patient specificity to match a patient case more precisely; and allowing for the generation of porosity, lattice, and lattice gradient design, tying in with both mechanical property tailoring, as well as allowing for bone ingrowth and angiogenesis (blood vessel formation). These aspects cannot be matched by traditional subtractive manufacturing means. Laser-based powder bed fusion (LB-PBF) is one such method of additive manufacture, using metal powder as the input material. However, the metal powder input presents potential issues for implant applications; if residual powder not joined to the implant pool during the manufacturing process is allowed to run free in the body, there is a high likelihood of harm, having the potential to cause inflammation, infection, bone resorption, and ultimately, implant failure. As such, there is a need not only to clean an implant structure to remove residual powder, but also verify its removal for patient safety.
The aims of this research were to explore the following two aspects; firstly, to investigate different cleaning or residue removal techniques for powder-based AM implant structures for the goal of creating a robust and repeatable cleaning methodology; and secondly, to investigate different imaging modalities to explore viable and non-destructive methods for statistical characterisation of residual unwanted manufacturing material residue.
State of the art literature has been reviewed, detailing the use of cleaning or post-processing for removal of manufacturing material residue from LB-PBF implant structures. Testing and verification methods for ensuring powder removal are also detailed. Pitfalls and gaps are also noted, including the lack of standards and robust protocols for implant cleaning, and the need for destructive testing to ensure verification of powder removal from implant structures by regulatory bodies, which is antithetical to the freedom and flexibility that additive manufacturing affords; non-destructive testing methodologies are thus described. The lack of tools and software for non-destructive analysis was an additional gap found within the current state of the art of the field.
Three different imaging modalities were explored for their viability for image penetration of a dense lattice structure: digital microscopy, scanning electron microscopy and micro computed tomography (µCT). While the former two allowed greater surface detail, only µCT allowed for three-dimensional scanning and penetration. The ability to generate penetrative image data gave basis for the development and creation of an algorithmic methodology for the detection and categorisation of partially attached particle materials within LB-PBF structure. The algorithm was tested using three different µCT datasets of Ti-6Al-4V buckling struts manufactured at 30°, 60° and 90° build orientation angle respectively. Several histograms were generated, presenting categorical data for analysis, with a major takeaway between the datasets being the reduction of partially attached particles detected the higher the build inclination angle utilised.
Cleaning of lattice implant structures and structural components was also conducted in order to facilitate the generation of a robust post-processing protocol. The first experiment compared ultrasonic cleaning against processing via centrifugal acceleration; while there was no significant degree of difference, several concerns were noted, including feasibility of centrifugal processing on larger scale structures, and proper sample handling and preparation to present infeasible results. The second experiment used ultrasonic cleaning on a full-scale sized tibia implant. With the addition of a surfactant, a large amount of material (over 3000mg) was removed across six, one-hour cycles. The final experiment trialled a use dry-ice blasting to remove residue from lattice structures. Three different time points were chosen, and the shortest time point proved on average to remove the most manufacturing material residue, with the largest time point presenting instances of blaster and blaster input material instability. The combination of ultrasonic cleaning and dry-ice blasting in tandem presents a robust cleaning protocol to remove manufacturing material residue from LB-PBF implant structures.
Finally, µCT datasets were captured from the third experiment pre-blast and post-blast, and trialled with the particle detection algorithm in order to provide categorical information. Unfortunately, the datasets could not be processed by the algorithm in its current state; the information in full datasets was too great for the computer hardware to handle, and partial datasets while overcoming this problem had different issues present that meant they not able to be further processed for analysis. While this is a disappointing result, the particle detection algorithm in its current state represents a toolset for non-destructive testing and analysis, of which the current field presents a distinct gap and lack.
Major contributions of this research and this thesis are the development of a robust cleaning protocol for additively manufactured implants, and the generation of an algorithmic methodology for analysing µCT datasets for characterisation of attaching manufacturing material residue. The former presents a method that does not leave additional particle residue and presents a multi-faceted approach for both partially melted (sintered) and embedded material through dry-ice blasting and ultrasonication. The latter is a software algorithm that can be used to compare different post processing or cleaning states (or time points) and can be used to characterise the amount of removed material as well as remaining material from post processing or cleaning operations, which is an area that the current field has not addressed
A meta-network-based management framework for megaproject social responsibility behaviour in China
No full textPurpose: As megaprojects bear extensive and profound social responsibilities throughout the project life cycle, formulating effective measures for improving construction enterprise social responsibility is key to project success. Given the current research is relatively lack of these measures, this study aims to formulate a meta-network framework to improve the megaproject social responsibility behaviour (MSRB) for construction enterprises. Design/methodology/approach: First, this study implements literature review, expert interview and field investigation to identify the construction enterprise MSRB and its influencing factors. Second, this study evaluates the MSRB implementation level of the selected construction enterprises and proposes the above mentioned meta-network framework. Next, this meta-network is configured to reflect the impact of MSRB strategic adjustment. Last but not least, a real-world case study is carried out to validate this framework. Findings: The best MSRB performance is always witnessed from the contractor group, followed by the project client group and the site supervisor group. The outcomes of implementing certain managerial strategies indicate that (1) social responsibility cognition is a critical factor for all the groups; (2) communication mechanism and normative pressure are the critical factors for clients; (3) coercive pressure is a critical factor for supervisors and (4) cultural cognitive pressure is a critical factor for clients and contractors. Originality/value: The use of the framework in proactive assessment and management of MSRB can lead to effective strategies for construction enterprises to increase the efficiency and quality of projects