This paper is concerned with the problem of bipartite containment control design for a class of nonlinear multiagent systems with time-delays in agents' states under impulsive false-data-injection ...attacks. The considered multiagent system is subject to Markovian variation in the signed communication topology. The graph among the followers is assumed to be structurally balanced for each Markovian switching mode. A memory distributed control protocol is proposed to achieve bipartite containment within the convex hull of leader agents as well as the symmetric convex hull. The bipartite containment control problem is solved by means of a Markovian switching Lyapunov function and the Razumikhin technique. In addition, the problem of bipartite leader-following consensus is also addressed for delayed nonlinear multiagent systems with one leader. Two examples are provided to show the effectiveness of the proposed control scheme, and comparison results with existing methods are given as well.
The primary goal of material management is to arrange the use of materials reasonably, which is particularly important for the construction industry. Wireless communication can transmit a lot of ...information in time in production, which can promote the management and arrangement of building materials. In order to explore the management method of prefabricated materials, this paper compares the prefabricated building materials management based on BIM with the traditional method and the management method combining BIM and wireless communication through sampling survey and sand table simulation. This paper compares the material procurement, storage and quality in the construction stage and analyzes the material management differences of different technical methods in different stages. The results show that the average inventory turnover rate of BIM-based management method is 6 times, and that of conventional method is 4 times. However, in the construction stage, the gap between the two methods is narrowed. The combination of wireless communication and BIM leads the whole process in inventory turnover rate. The turnover times of prefabricated building materials management method based on BIM Technology is reduced to 3 times, and that of conventional method is reduced to 2 times. However, the turnover times of BIM combined with wireless communication is more than 4 times. Therefore, BIM-based prefabricated building materials management can reduce the use of funds and the occupation of warehouse, and control the quality of materials better than the traditional methods. However, the combination of BIM and wireless communication can achieve better results.
High entropy alloy (HEA) is an emerging class of engineering materials that shows promising potential for high temperature applications. These multi-component alloys are mostly fabricated by arc ...melting. In this study, direct laser fabrication (DLF) is utilized to prepare AlCoCrFeNi high entropy alloy at optimized operation parameters. The phase, microstructure, mechanical and corrosion properties of as-deposited alloy as well as samples aged at temperatures of 600 °C, 800 °C, 1000 °C and 1200 °C for 168 h have been investigated. The results show that high cooling rate during deposition inhibits the formation of FCC phase, leading to a nearly single B2 solid solution structure for as-deposited sample. After ageing at 800 °C, 1000 °C and 1200 °C, the microstructures exhibit intergranular needle-like and plate-like FCC phase precipitates and wall shaped FCC phase precipitates along grain boundaries. As the FCC phase is softer than B2 phase, the formation of the FCC phase during ageing results in reduced compressive yield strength accompanied with enhanced ductility. The potential difference between Fe-Cr rich FCC phase and Al-Ni rich B2 matrix means the alloy is susceptible to galvanic corrosion, with the B2 matrix corroding preferentially.
•AlCoCrFeNi high entropy alloys prepared by direct laser fabrication (DLF) and pure elemental powder blends.•Excellent compressive properties exhibited by both as-deposited and aged AlCoCrFeNi HEAs.•Fe and Cr enriched FCC solid solution phase precipitated after ageing.•Reduced yield stress while improved ductility by the weaker FCC phase.•Al-Ni enriched B2 matrix is severely corroded as a result of galvanic coupling with Fe-Cr enriched FCC precipitate.
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•There is a demand for more highly-printable high-strength aluminium alloys for industrial laser powder bed fusion.•Research efforts are making progress in finding ways to combine ...high strength with good processability.•A growing number of industrially available alloys can now achieve a yield strength of >400 MPa.
Laser powder bed fusion (LPBF) is one of the major additive manufacturing techniques that industries have adopted to produce complex metal components. The scientific and industrial literature from the past few years reveals that there is a growing demand for the development of high-strength aluminium alloys for LPBF. However, some major challenges remain for high-strength aluminium alloys, especially in relation to printability and the control of defects. Possible strategies that have been identified to achieve high strength with printability include the adaptation of existing high-strength cast and wrought alloys to LPBF, the design of new alloys specifically for LPBF, and the development of aluminium-based composites to achieve unique combinations of properties and processability. Whilst review papers exist for aluminium alloys in general for the related work up to 2019, the purpose of this paper is to review the latest developments related to high-strength aluminium alloys for LPBF up to early 2022, including alloy and process design strategies to achieve high strength without cracking. It aims to provide fresh insights into the current state-of-the-art based on a review of extensive yield strength data for a wide spectrum of aluminium alloys and tempers that have been studied and/or commercialised for LPBF.
The addition of 1.08wt% Sc to an Al-Mg-Zr alloy produced by selective laser melting modifies the highly coarse columnar grain structure to significantly refined columnar grains separated by ...sub-micron equiaxed grains at the melt pool boundaries. The latter nucleate mainly from the Al3Sc particles in the remelting zone. An almost fully equiaxed grain structure was achieved by increasing the applied volumetric energy density from 77.1J/mm3 to 154.2J/mm3 and the platform temperature from 35°C to 200°C, due to the combined effects of potent nuclei, increased remelting zone volumes and reduced thermal gradients.
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Selective Laser Melting (SLM) has received tremendous attentions due to its high degree of flexibility for the design and fabrication of geometrically complex parts. However, the majority of the ...currently applied metals for this advanced technology are still based on the traditional weldable and/or castable alloys, and the resulting mechanical properties of SLM fabricated samples are often mediocre. This is because the conventional alloys are not designed to accommodate the dynamic metallurgical characteristics of the SLM process and the benefits offered by SLM are not fully captured. In this study, an experimentally-based novel alloy development methodology utilising wedge mould casting and laser remelting is proposed, and the processability and properties of the developed alloys can be predicted for SLM. By mimicking the high solidification rate of the SLM process, unconventionally large amounts of solute were successfully placed into solution in the aluminium (Al) matrix. A high strength Al-Mn-Sc based alloy has been successfully developed and verified by SLM processing. The developed alloy possessed an average yield strength of about 430 MPa and a ductility of 21% in the as fabricated state, compared to approximately 570 MPa and 18% after direct ageing for 5 h at 300 °C, respectively.
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•An experimental-based high strength aluminium alloy development methodology has been proposed.•High strength Al-Mn-Sc based alloys have been successfully developed specifically for SLM.•SLM fabricated Al-Mn-Sc alloy possessed a high yield strength of 570 MP a direct post-ageing treatment (300 °C for 5h).
Selective laser melting (SLM) technology is a layer-wise powder-based additive manufacturing method capable of building 3D components from their CAD models. This approach offers enormous benefits for ...generating objects with geometrical complexity. However, due to the layer-wise nature of the process, surface roughness is formed between layers, thus influenced by layer thickness and other processing parameters. In this study, systematic research has been carried out to study the influence of processing parameters on surface roughness in Hastelloy X alloy. All samples were manufactured using an EOSINT M 280 machine. Laser power, scan speed, layer thickness and sloping angle of a surface were systematically varied to understand their effects on surface roughness. The arithmetic average roughness, Ra, was measured using a surface roughness tester, and optimum conditions for achieving the lowest roughness for both up-skin surfaces and down-skin surfaces have been obtained. The formation mechanism for the roughness on these two types of surfaces has been studied. Computer simulation was also used to understand thermal profiles at those two surfaces and their resultant influence on surface roughness. The simulated result has been found to be consistent with the measured result. Contour scan and skywriting scan strategies were found to be helpful for reducing the surface roughness.
Commercially pure titanium was produced using laser engineered net shaping (LENS) and selective laser melting (SLM) processes. The SLM and LENS processing parameters as well as critical aspects ...including densification and balling effect were investigated. The resulting properties were studied and compared with those from traditional casting. Investigation of the processing parameters showed that significantly higher laser power and energy density is required in LENS compared to SLM in order to obtain near full density (99.5%). The microstructural investigations revealed an α microstructure with mixed morphologies including plate-like and widmanstätten for LENS somewhat similar to the serrated and fine acicular α obtained from casting. In contrast, the SLM samples showed only martensitic α′ phase mainly with a lath-type morphology. The difference between SLM and LENS microstructures was discussed based on interrelated aspects including energy density, solidification rate and specific point energy. Differences in their microstructures are mainly associated with differing rates of cooling and differing energy densities during SLM and LENS processing. Compression and hardness tests indicated that SLM titanium possesses better mechanical properties due to a fine grain size and martensitic phase composition, whereas LENS and cast titanium with α microstructures show similar mechanical properties.
The dynamic metallurgical characteristics of the selective laser melting (SLM) process offer fabricated materials with non-equilibrium microstructures compared to their cast and wrought counterparts. ...To date, few studies on the precipitation kinetics of SLM processed heat-treatable alloys have been reported, despite the importance of obtaining such detailed knowledge for optimizing the mechanical properties. In this study, for the first time, the precipitation behavior of an SLM fabricated Al–Mn–Sc alloy was systematically investigated over the temperature range of 300–450 °C. The combination of in-situ synchrotron-based ultra-small angle X-ray scattering (USAXS), small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) revealed the continuous evolution of Al6Mn and Al3Sc precipitates upon isothermal heating in both precipitate structure and morphology, which was confirmed by ex-situ transmission electron microscopy (TEM) studies. A pseudo-delay nucleation and growth phenomenon of the Al3Sc precipitates was observed for the SLM fabricated Al–Mn–Sc alloy. This phenomenon was attributed to the pre-formed Sc clusters in the as-fabricated condition due to the intrinsic heat treatment effect induced by the unique layer-by-layer building nature of SLM. The growth kinetics for the Al6Mn and Al3Sc precipitates were established based on the in-situ X-ray studies, with the respective activation energies determined to be (74 ± 4) kJ/mol and (63 ± 9) kJ/mol. The role of the precipitate evolution on the final mechanical properties was evaluated by tensile testing, and an observed discontinuous yielding phenomenon was effectively alleviated with increased aging temperatures.
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