Yanjin Lu, Yiliang Gan, Junjie Lin, Sai Guo, Songquan Wu and Jinxin Lin
The aim of the study is to obtain dense Ni-free CoCrW parts fabricated by selective laser melting (SLM) technique for dental application.
Abstract
Purpose
The aim of the study is to obtain dense Ni-free CoCrW parts fabricated by selective laser melting (SLM) technique for dental application.
Design/methodology/approach
The optimum of processing CoCrW powders was investigated by the varying laser scanning speeds between 200 and 1,500 mm/s with the other parameters fixed as constants. The investigations of density, phase, mechanical property and corrosion resistance were conducted.
Findings
It was found that a maximum relative density of 99.4 per cent was obtained with the preferable laser scanning speed of 700 mm/s; the outcome from the tensile test suggested that the 0.2 per cent yield strength of the specimen fabricated at 700 mm/s satisfied the type 5 criteria in ISO22764 for dental application, whereas the electrochemical test indicated that the specimens fabricated at 700 mm/s existed excellent corrosion resistance. The high precision dental denture could be fabricated by SLM.
Originality/value
In the study, the Ni-free CoCrW parts fabricated by SLM was investigated by the tensile and electrochemical tests. The yield strength, corrosion resistance and margin fit accuracy met requirements for dental application. It was considered that the speed of 700 mm/s with the laser powers of 95 W, the track width of 0.11 mm and the layer thickness of 25 μm are promising candidates for fabricating the CoCrW parts.
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Lin Kang, Junjie Chen, Jie Wang and Yaqi Wei
In order to meet the different quality of service (QoS) requirements of vehicle-to-infrastructure (V2I) and multiple vehicle-to-vehicle (V2V) links in vehicle networks, an…
Abstract
Purpose
In order to meet the different quality of service (QoS) requirements of vehicle-to-infrastructure (V2I) and multiple vehicle-to-vehicle (V2V) links in vehicle networks, an efficient V2V spectrum access mechanism is proposed in this paper.
Design/methodology/approach
A long-short-term-memory-based multi-agent hybrid proximal policy optimization (LSTM-H-PPO) algorithm is proposed, through which the distributed spectrum access and continuous power control of V2V link are realized.
Findings
Simulation results show that compared with the baseline algorithm, the proposed algorithm has significant advantages in terms of total system capacity, payload delivery success rate of V2V link and convergence speed.
Originality/value
The LSTM layer uses the time sequence information to estimate the accurate system state, which ensures the choice of V2V spectrum access based on local observation effective. The hybrid PPO framework shares training parameters among agents which speeds up the entire training process. The proposed algorithm adopts the mode of centralized training and distributed execution, so that the agent can achieve the optimal spectrum access based on local observation information with less signaling overhead.
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Junjie Gong, Zhixiang Li, Qingqing Lin and Kunhong Hu
This study aims to explore the synthesis and tribological performances of di-n-octyl sebacate (DOS) synthesized with spherical nano-MoS2/sericite (SMS) and carboxylated SMS (CSMS…
Abstract
Purpose
This study aims to explore the synthesis and tribological performances of di-n-octyl sebacate (DOS) synthesized with spherical nano-MoS2/sericite (SMS) and carboxylated SMS (CSMS) as catalysts.
Design/methodology/approach
SMS and CSMS were used as esterification catalysts to synthesize DOS from sebacic acid and n-octanol. The two catalysts were in situ dispersed in the synthesized DOS after the reaction to form suspensions. The tribological performances of the two suspensions after 20 days of storage were studied.
Findings
CSMS was more stably dispersed in DOS than SMS, and they reduced friction by 55.6% and 22.2% and wear by 51.3% and 56.5%, respectively. Such results were mainly caused by the COOH on CSMS, which was more conducive to improving the dispersion and friction reduction of CSMS than wear resistance. Another possible reason was the difference between the dispersion amounts of CSMS and SMS in DOS. The sericite of SMS was converted into SiO2 to enhance wear resistance, while that of CSMS only partially generated SiO2, and the rest still remained on the surface to reduce friction.
Originality/value
This work provides a more effective SMS catalytical way for DOS synthesis than the traditional inorganic acid catalytical method. SMS does not need to be separated after reaction and can be dispersed directly in DOS as a lubricant additive. Replacing SMS with CSMS can produce a more stable suspension and reduce friction significantly. This work combined the advantages of surface carboxylation modification and in situ catalytic dispersion and provided alternatives for the synthesis of DOS and the dispersion of MoS2-based lubricant additives.
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Lin Deng, Junjie Liang, Yun Zhang, Huamin Zhou and Zhigao Huang
Lattice Boltzmann method (LBM) has made great success in computational fluid dynamics, and this paper aims to establish an efficient simulation model for the polymer injection…
Abstract
Purpose
Lattice Boltzmann method (LBM) has made great success in computational fluid dynamics, and this paper aims to establish an efficient simulation model for the polymer injection molding process using the LBM. The study aims to validate the capacity of the model for accurately predicting the injection molding process, to demonstrate the superior numerical efficiency in comparison with the current model based on the finite volume method (FVM).
Design/methodology/approach
The study adopts the stable multi-relaxation-time scheme of LBM to model the non-Newtonian polymer flow during the filling process. The volume of fluid method is naturally integrated to track the movement of the melt front. Additionally, a novel fractional-step thermal LBM is used to solve the convection-diffusion equation of the temperature field evolution, which is of high Peclet number. Through various simulation cases, the accuracy and stability of the present model are validated, and the higher numerical efficiency verified in comparison with the current FVM-based model.
Findings
The paper provides an efficient alternative to the current models in the simulation of polymer injection molding. Through the test cases, the model presented in this paper accurately predicts the filling process and successfully reproduces several characteristic phenomena of injection molding. Moreover, compared with the popular FVM-based models, the present model shows superior numerical efficiency, more fit for the future trend of parallel computing.
Research limitations/implications
Limited by the authors’ hardware resources, the programs of the present model and the FVM-based model are run on parallel up to 12 threads, which is adequate for most simulations of polymer injection molding. Through the tests, the present model has demonstrated the better numerical efficiency, and it is recommended for the researcher to investigate the parallel performance on even larger-scale parallel computing, with more threads.
Originality/value
To the authors’ knowledge, it is for the first time that the lattice Boltzmann method is applied in the simulation of injection molding, and the proposed model does obviously better in numerical efficiency than the current popular FVM-based models.
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Lin Kang, Jie Wang, Junjie Chen and Di Yang
Since the performance of vehicular users and cellular users (CUE) in Vehicular networks is highly affected by the allocated resources to them. The purpose of this paper is to…
Abstract
Purpose
Since the performance of vehicular users and cellular users (CUE) in Vehicular networks is highly affected by the allocated resources to them. The purpose of this paper is to investigate the resource allocation for vehicular communications when multiple V2V links and a V2I link share spectrum with CUE in uplink communication under different Quality of Service (QoS).
Design/methodology/approach
An optimization model to maximize the V2I capacity is established based on slowly varying large-scale fading channel information. Multiple V2V links are clustered based on sparrow search algorithm (SSA) to reduce interference. Then, a weighted tripartite graph is constructed by jointly optimizing the power of CUE, V2I and V2V clusters. Finally, spectrum resources are allocated based on a weighted 3D matching algorithm.
Findings
The performance of the proposed algorithm is tested. Simulation results show that the proposed algorithm can maximize the channel capacity of V2I while ensuring the reliability of V2V and the quality of service of CUE.
Originality/value
There is a lack of research on resource allocation algorithms of CUE, V2I and multiple V2V in different QoS. To solve the problem, one new resource allocation algorithm is proposed in this paper. Firstly, multiple V2V links are clustered using SSA to reduce interference. Secondly, the power allocation of CUE, V2I and V2V is jointly optimized. Finally, the weighted 3D matching algorithm is used to allocate spectrum resources.
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Yong Cheng, Zhongxu Xiao, Haihong Zhu, Xiaoyan Zeng and Guoqing Wang
Selective laser melting (SLM) is a promising additive manufacturing technology in the field of complex parts’ fabrication. High temperature gradient and residual stress are vital…
Abstract
Purpose
Selective laser melting (SLM) is a promising additive manufacturing technology in the field of complex parts’ fabrication. High temperature gradient and residual stress are vital problems for the development of SLM technology. The purpose of this paper is to investigate the influence of substrate characteristics on the residual stress of SLMed Inconel 718 (IN718).
Design/methodology/approach
The SLMed IN718 samples were fabricated on the substrates with different characteristics, including pre-compression stress, materials and pre-heating. The residual stress at the center of the top surface was measured and compared through Vickers micro-indentation.
Findings
The results indicate that the residual stress reduces when the substrate contains pre-compression stress before the SLM process starts. Both substrate thermal expansion coefficient and thermal conductivity affect the residual stress. In addition to reducing the difference of thermal expansion coefficient between the substrate and the deposited material, the substrate with low thermal conductivity can also decrease the residual stress. Substrate pre-heating at 150°C reduces nearly 42.6 per cent residual stress because of the reduction of the temperature gradient.
Originality/value
The influence of substrate characteristics on the residual stress has been studied. The investigation results can help to control the residual stress generated in SLM processing.
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Guokui Ju, Fei Lin, Wenzhen Bi, Yongjiu Han, Wang Junjie and Xicheng Wei
The purpose of this study was to comparatively investigate interfacial intermetallic compounds (IMCs) in the Sn3.0Ag0.5Cu3.0Bi0.05Cr/Cu (SACBC/Cu) and Sn3.0Ag0.5Cu/Cu (SAC/Cu…
Abstract
Purpose
The purpose of this study was to comparatively investigate interfacial intermetallic compounds (IMCs) in the Sn3.0Ag0.5Cu3.0Bi0.05Cr/Cu (SACBC/Cu) and Sn3.0Ag0.5Cu/Cu (SAC/Cu) solder joints, and to determine any differences.
Design/methodology/approach
The samples were annealed after isothermal ageing at 150°C for 0, 168 and 500 hours, and their cross-sections were observed by scanning electron microscopy and energy dispersive spectroscopy.
Findings
The interfacial IMC morphology in two joints had significant differences. For the Cu/SAC/Cu joints, the granular and short rod-like Ag3Sn particles attached on the surface and boundary of interfacial Cu6Sn5 grains were detected, and they coarsened observably with ageing time at 150°C, and lastly embedded at the grain boundaries. However, for the Cu/SACBC/Cu joints, there were tiny filamentous Ag3Sn growing on the surface of interfacial Cu6Sn5 grains, and the Ag3Sn had a tendency to break into nanoparticles, which would be distributed evenly and cover the IMC layer, profiting from the Bi and Cr precipitates from solder matrix during ageing.
Originality/value
The paper implies that the addition of Bi and Cr could affect the IMCs of joints, thereby delaying interfacial reactions between Sn and Cu atoms and improving the service reliability. The SACBC solder is a potential alloy for electronic packaging production.
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Yogesh Patil, Ashik Kumar Patel, Gopal Dnyanba Gote, Yash G. Mittal, Avinash Kumar Mehta, Sahil Devendra Singh, K.P. Karunakaran and Milind Akarte
This study aims to improve the acceleration in the additive manufacturing (AM) process. AM tools, such as extrusion heads, jets, electric arcs, lasers and electron beams (EB)…
Abstract
Purpose
This study aims to improve the acceleration in the additive manufacturing (AM) process. AM tools, such as extrusion heads, jets, electric arcs, lasers and electron beams (EB), experience negligible forces. However, their speeds are limited by the positioning systems. In addition, a thin tool must travel several kilometers in tiny motions with several turns while realizing the AM part. Hence, acceleration is a more significant limiting factor than the velocity or precision for all except EB.
Design/methodology/approach
The sawtooth (ST) scanning strategy presented in this paper minimizes the time by combining three motion features: zigzag scan, 45º or 135º rotation for successive layers in G00 to avoid the CNC interpolation, and modifying these movements along 45º or 135º into sawtooth to halve the turns.
Findings
Sawtooth effectiveness is tested using an in-house developed Sand AM (SaAM) apparatus based on the laser–powder bed fusion AM technique. For a simple rectangle layer, the sawtooth achieved a path length reduction of 0.19%–1.49% and reduced the overall time by 3.508–4.889 times, proving that sawtooth uses increased acceleration more effectively than the other three scans. The complex layer study reduced calculated time by 69.80%–139.96% and manufacturing time by 47.35%–86.85%. Sawtooth samples also exhibited less dimensional variation (0.88%) than zigzag 45° (12.94%) along the build direction.
Research limitations/implications
Sawtooth is limited to flying optics AM process.
Originality/value
Development of scanning strategy for flying optics AM process to reduce the warpage by improving the acceleration.
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Qiqiang Cao, Jiong Zhang, Shuai Chang, Jerry Ying Hsi Fuh and Hao Wang
This study aims to further the understanding of support structures and the likely impacts on maraging steel MS1 parts fabricated by selective laser melting (SLM) at 45°, 60° and…
Abstract
Purpose
This study aims to further the understanding of support structures and the likely impacts on maraging steel MS1 parts fabricated by selective laser melting (SLM) at 45°, 60° and 75° building angles.
Design/methodology/approach
Two groups of samples, one group with support structures and the other group without support structures, were designed with the same specifications and printed under the same conditions by SLM at 45°, 60° and 75° building angles. Differences in dimensional accuracy, surface roughness, Vickers microhardness, residual stress and microstructure were compared between groups.
Findings
The results showed that with support structures, more accurate dimension and slightly higher Vickers microhardness could be obtained. Larger compressive stress dominated and was more uniformly distributed on the supporting surface. Without support structures, the dimension became more precise as the building angle increased and alternating compressive and tensile stress was unevenly distributed on the supporting surface. In addition, the surface roughness of the outer surface decreased with the increase of the built angle, regardless of the support structures. Furthermore, whether the building angle was 45°, 60° or 75°, the observed microstructures revealed that the support structures altered the orientation of the molten pool and the direction of grain growth.
Originality/value
This paper studies the influence of support structures on the workpieces printed at different building angles. Support structures affect the residual stress distribution, heat dissipation rate and microstructure of the parts, and thus affecting the printing quality. Therefore, it is necessary to balance the support strategy and printing quality to better apply or design the support structures in SLM.
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Abdulbaset Ab Klish, Moade Fawzi Shaker Shubita and Junjie Wu
Global interest in adopting the International Financial Reporting Standards (IFRS) has risen rapidly; however, the Middle Eastern and North African (MENA) countries have reacted…
Abstract
Purpose
Global interest in adopting the International Financial Reporting Standards (IFRS) has risen rapidly; however, the Middle Eastern and North African (MENA) countries have reacted differently towards the international diffusion. The purpose of this study is to examine the impact of the IFRS adoption/rejection decision on the quality of MENA region firms' financial reporting.
Design/methodology/approach
The quality of accounting is examined through five metrics models to measure earnings smoothing, managing earnings towards a target and timely loss recognition. The research sample consists of nine countries over a period of ten years (2006–2015), resulting in 3,040 firm-year observations in the main phase, and 2,580 firm-year observations in the additional analysis.
Findings
The findings reveal that the overall sample of IFRS adopters in the MENA region has benefited from the adoption of IFRS, as the results show that there is a reduction in earnings management for IFRS adopters in comparison to local standards adopters. The sub-sample analyses also reveal that firms that adopted IFRS, in both the rentier (oil-dependent states) and non-rentier states, have a higher financial reporting quality than non-IFRS adopters. However, the magnitude of the financial reporting quality was higher for IFRS adopters in rentier states.
Research limitations/implications
Similarly to previous research in this field, this study adopts a strict sample selection approach. Such an approach may limit the sample size, although the researchers have taken every possible step to ensure the use of an adequate sample size. The researchers acknowledge the strict period of ten years, despite having stated its rationale and importance of a more extended period to the quest of the paper.
Practical implications
This research provides valuable input by evaluating the current status of MENA region firms' financial reporting quality, based on their followed accounting regime. The implications of this paper result in better-informed decisions for investors as the information contents of the annual reports enhance comparisons that facilitate the further flow of investments. This research also provides significant insight into the International Accounting Standards Board (IASB). The findings of this study will assist the IASB in understanding the MENA region by measuring the consequences of the countries' decisions on the quality of firms' financial reporting.
Originality/value
The findings of this study contribute to the literature by revealing that countries with medium levels of governance quality have benefited the most from the IFRS adoption, while IFRS adopters in countries with stronger governance quality demonstrate lower financial reporting quality.