93 research outputs found
High cycle fatigue and fracture behaviour of a hot isostatically pressed nickel-based superalloy
On the formation of irregular-shaped gamma prime and serrated grain boundaries in a nickel-based superalloy during continuous cooling
Recommended from our members
Three-Dimensional Finite Element Thermal Analysis in Selective Laser Melting of Al-Al2O3 Powder
The selective laser melting (SLM) of aluminium-based composites continues to be a
challenge due to the high reflectivity, high thermal conductivity and oxidation of aluminium, all
of which directly influence the thermal performance of each layer during SLM. Due to the
extremely rapid melting and cooling rate of aluminium, however, it is difficult to measure thermal
performance within practical SLM applications. A three-dimensional finite element simulation
model is thus developed in this study to simulate the transient temperature distribution and molten
pool dimensions of the premier layer during the SLM of Al-Al2O3 composite powder. In order to
produce high-quality parts with minimum defects in a highly efficient manner, the predicted
optimum volumetric energy density is found to be 40 J/mm3
, with laser power 300 W, scanning
speed 1000 mm/s, hatch spacing 150 μm and layer thickness 50 μm; the molten pool size that is
produced is 165 μm in length, 160 μm in width and 77 μm in depth, with a predicted maximum
temperature of around 3400°C. All of these factors may contribute to the creation of good
metallurgic bonding.Mechanical Engineerin
DesignGPT: Multi-Agent Collaboration in Design
Generative AI faces many challenges when entering the product design
workflow, such as interface usability and interaction patterns. Therefore,
based on design thinking and design process, we developed the DesignGPT
multi-agent collaboration framework, which uses artificial intelligence agents
to simulate the roles of different positions in the design company and allows
human designers to collaborate with them in natural language. Experimental
results show that compared with separate AI tools, DesignGPT improves the
performance of designers, highlighting the potential of applying multi-agent
systems that integrate design domain knowledge to product scheme design
On the role of melt flow into the surface structure and porosity development during selective laser melting
In this study, the development of surface structure and porosity of Ti–6Al–4V samples fabricated by selective laser melting under different laser scanning speeds and powder layer thicknesses has been studied and correlated with the melt flow behaviour through both experimental and modelling approaches. The as-fabricated samples were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The interaction between laser beam and powder particles was studied by both high speed imaging observation and computational fluid dynamics (CFD) calculation. It was found that at a high laser power and a fixed powder layer thickness (20 μm), the samples contain particularly low porosity when the laser scanning speeds are below 2700 mm/s. Further increase of scanning speed led to increase of porosity but not significantly. The porosity is even more sensitive to powder layer thickness with the use of thick powder layers (above 40 μm) leading to significant porosity. The increase of porosity with laser scanning speed and powder layer thickness is not inconsistent with the observed increase in surface roughness complicated by increasingly irregular-shaped laser scanned tracks and an increased number of discontinuity and cave-like pores on the top surfaces. The formation of pores and development of rough surfaces were found by both high speed imaging and modelling, to be strongly associated with unstable melt flow and splashing of molten material
Net-Shape Manufacturing using Hybrid Selective Laser Melting/Hot Isostatic Pressing
Purpose
The purpose of this study is to develop a manufacturing technology using hybrid selective laser melting/hot isostatic pressing (SLM/HIP) process to produce full density net-shape components more rapidly and at lower cost than processing by SLM alone.
Design/methodology/approach
Ti-6Al-4V powder was encapsulated in situ by the production of as-SLMed shell prior to the HIP process. After HIPping, the SLM shell is an integral part of the final component. Finite element (FE) modelling based on pure plasticity theory of porous metal coupled with an iterative procedure has been adopted to simulate HIPping of the encapsulated Ti-6Al-4V powder and SLMed shell. Two demonstrator parts have been modelled, designed, produced and experimentally validated. Geometrical analysis and microstructural characterisation have been carried out to demonstrate the efficiency of the process.
Findings
The FE model is in agreement with the measured data obtained and confirms that the design of the shell affects the resulting deformed parts. In addition, the scanning electron microscope (SEM) and Electron backscatter diffraction EBSD (EBSD) of the interior and exterior parts reveal a considerably different grain structure and crystallographic orientation with a good bonding between the SLMed shell and HIPped powder.
Originality/value
An approach to improve SLM productivity by combining it with HIP is developed to further innovate the advanced manufacturing field. The possibility of the hybrid SLS/HIP supported by FEA simulation as a net shape manufacturing process for fabrication of high performance parts has been demonstrated.
</jats:sec
Quantification of Myocardial Dosimetry and Glucose Metabolism Using a 17-Segment Model of the Left Ventricle in Esophageal Cancer Patients Receiving Radiotherapy
Objective Previous studies have shown that increased cardiac uptake of(18)F-fluorodeoxyglucose (FDG) on positron emission tomography (PET) may be an indicator of myocardial injury after radiotherapy (RT). The primary objective of this study was to quantify cardiac subvolume dosimetry and(18)F-FDG uptake on oncologic PET using a 17-segment model of the left ventricle (LV) and to identify dose limits related to changes in cardiac(18)F-FDG uptake after RT. Methods Twenty-four esophageal cancer (EC) patients who underwent consecutive oncologic(18)F-FDG PET/CT scans at baseline and post-RT were enrolled in this study. The radiation dose and the(18)F-FDG uptake were quantitatively analyzed based on a 17-segment model. The(18)F-FDG uptake and doses to the basal, middle and apical regions, and the changes in the(18)F-FDG uptake for different dose ranges were analyzed. Results A heterogeneous dose distribution was observed, and the basal region received a higher median mean dose (18.36 Gy) than the middle and apical regions (5.30 and 2.21 Gy, respectively). Segments 1, 2, 3, and 4 received the highest doses, all of which were greater than 10 Gy. Three patterns were observed for the myocardial(18)F-FDG uptake in relation to the radiation dose before and after RT: an increase (5 patients), a decrease (13 patients), and no change (6 patients). In a pairing analysis, the(18)F-FDG uptake after RT decreased by 28.93 and 12.12% in the low-dose segments (0-10 Gy and 10-20 Gy, respectively) and increased by 7.24% in the high-dose segments (20-30 Gy). Conclusion The RT dose varies substantially within LV segments in patients receiving thoracic EC RT. Increased(18)F-FDG uptake in the myocardium after RT was observed for doses above 20 Gy.</div
Three-dimensional finite element thermal analysis in selective laser melting of Al-Al2O3 powder
The selective laser melting (SLM) of aluminium-based composites continues to be a
challenge due to the high reflectivity, high thermal conductivity and oxidation of aluminium, all
of which directly influence the thermal performance of each layer during SLM. Due to the
extremely rapid melting and cooling rate of aluminium, however, it is difficult to measure thermal
performance within practical SLM applications. A three-dimensional finite element simulation
model is thus developed in this study to simulate the transient temperature distribution and molten
pool dimensions of the premier layer during the SLM of Al-Al2O3 composite powder. In order to
produce high-quality parts with minimum defects in a highly efficient manner, the predicted
optimum volumetric energy density is found to be 40 J/mm3
, with laser power 300 W, scanning
speed 1000 mm/s, hatch spacing 150 μm and layer thickness 50 μm; the molten pool size that is
produced is 165 μm in length, 160 μm in width and 77 μm in depth, with a predicted maximum
temperature of around 3400°C. All of these factors may contribute to the creation of good
metallurgic bondin
- …