Xia Gao, Daijun Zhang, Xiangning Wen, Shunxin Qi, Yunlan Su and Xia Dong
This work aims to develop a new kind of semicrystalline polymer filament and optimize its printing parameters in the fused deposition modeling process. The purpose of this work…
Abstract
Purpose
This work aims to develop a new kind of semicrystalline polymer filament and optimize its printing parameters in the fused deposition modeling process. The purpose of this work also includes producing FDM parts with good ductility.
Design/methodology/approach
A new kind of semicrystalline filaments composed of long-chain polyamide (PA)1012 was prepared by controlling screw speed and pulling speed carefully. The optimal printing parameters for PA1012 filaments were explored through investigating dimensional accuracy and bonding strength of FDM parts. Furthermore, the mechanical properties of PA1012 specimens were also evaluated by varying nozzle temperatures and raster angles.
Findings
It is found that PA1012 filaments can accommodate for FDM process under suitable printing parameters. The print quality and mechanical properties of FDM parts highly depend on nozzle temperature and bed temperature. Even though higher temperatures facilitate stronger interlayer bonding, FDM parts with excellent tensile strength were obtained at a moderate nozzle temperature. Moreover, a bed temperature well above the glass transition temperature of PA1012 can eliminate shrinkage and distortion of FDM parts. As expected, FDM parts prepared with PA1012 filaments exhibit good ductility.
Originality/value
Results in this work demonstrate that the PA1012 filament allows the production of FDM parts with desired mechanical performance. This indicates the potential for overcoming the dependence on amorphous thermoplastics as a feedstock in the FDM technique. This work also provides insight into the effect of materials properties on the mechanical performance of FDM-printed parts.
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Xu Zhao, Jingyang Wang, Mengyu Wang, Xuesong Li, Xia Gao and Chunlei Huang
The purpose of this paper is to investigate the literature on the treatment of primary pupils and inspecting the role of environmental psychology, e-learning, learning style and…
Abstract
Purpose
The purpose of this paper is to investigate the literature on the treatment of primary pupils and inspecting the role of environmental psychology, e-learning, learning style and school design on the behavior of students in elementary schools.
Design/methodology/approach
A questionnaire was designed to evaluate the components of the model. Experts with significant experiences in the field of students’ behavior revised the surveys. Data were collected from 400 teachers of the elementary schools in Iran. The SMART-PLS 3.2 and SPSS 22 software package were used in the field of questionnaires’ statistical analysis.
Findings
Findings confirmed the suggested model’s validity for elementary students’ behavior assessment. The consequences of this research illustrated the effect of environmental psychology on the behavior of elementary students. In addition, the authors were concluded that intention to e-learning has a significant role in developing the action and behavior of the elementary students. Moreover, the learning style has an affirmative and considerable impact on the behavior of elementary students. Finally, school design has an affirmative and significant effect on the manner of the elementary students.
Practical implications
The consequences of this research have provided some traces about the basic perspectives, which have to be in the center of attention of administrators. For instance, school design and learning style sound to be a decisive mechanism for improving action and learning behavior. In addition, educational leaders may use the findings to evaluate their school facilities and define where developments will have the most significant impact or planners may use the results to assist architects in the design and construction of new educational services.
Originality/value
This study builds a valuable contribution by focusing on pupil environmental psychology, e-learning, learning style and school design in elementary schools by enlightening the connection between them and students’ manner.
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Lei Wang, Xinming Wang, Liang Li, Chuang Yang and Yuqin Zhu
With respect to severe working conditions such as heavy load and impact, this paper aims to investigate the friction reduction and anti-wear performance of kaolin and molybdenum…
Abstract
Purpose
With respect to severe working conditions such as heavy load and impact, this paper aims to investigate the friction reduction and anti-wear performance of kaolin and molybdenum dialkyl dithiophosphate (MoDDP) composite lubricant additives to improve the lubrication effect of a single additive.
Design/methodology/approach
A four-ball friction test was carried out to determine the optimal concentration of kaolin and organic molybdenum additives and the tribological properties of the kaolin/MoDDP composite lubricant additives. A ring block test of composite lubricant additives was designed to investigate its lubrication performance under the severe working conditions of low speed, heavy load and impact.
Findings
The results showed that the optimal addition mass fractions of kaolin and MoDDP were 4.0 and 1.5 Wt.%, respectively, when kaolin and MoDDP were used as single lubricant additives. Compared with the single additive, the 4.0 Wt.% kaolin/1.5 Wt.% MoDDP composite lubricant additive showed excellent friction reduction and anti-wear effects under heavy load and impact conditions. Physicochemical analysis of the wear surface revealed that the lamellar kaolin additive and MoDDP had excellent synergistic effects, and the friction process promoted the generation of lubricant films containing a chemically reactive layer of MoS2, MoO2, FeS2 and Fe2O3 and a physically adsorbent layer containing SiO2 and Al2O3, which play important roles in anti-wear and friction reduction.
Originality/value
The excellent friction reduction and anti-wear effects of lamellar silicate minerals and the excellent antioxidant properties and good synergistic effects of molybdenum were comprehensively used to develop the composite additives with great lubricating properties.
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Applying the internationalization process model (IPM) and the strategic fit perspective, this research aims to test the effects of firm age on Chinese firms’ outward foreign…
Abstract
Purpose
Applying the internationalization process model (IPM) and the strategic fit perspective, this research aims to test the effects of firm age on Chinese firms’ outward foreign direct investment (OFDI) in developing and developed countries.
Design/methodology/approach
Using data on some Chinese firms, this study applied the zero-inflated negative binomial model and Heckman two-stage model to do the analyses.
Findings
This research found that firm age has different effects on Chinese firms’ OFDI in developed and developing countries. State ownership and industry munificence independently and jointly can moderate these effects.
Originality/value
This study contributes to the IPM and solves the theoretical conflict about the firm age–OFDI relationship.
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Dejing Zhou, Yanming Xia, Zhiming Gao and Wenbin Hu
This study aims to investigate the influence mechanism of brazing and aging on the strengthening and corrosion behavior of novel multilayer sheets (AA4045/AA7072/AA3003M/AA4045).
Abstract
Purpose
This study aims to investigate the influence mechanism of brazing and aging on the strengthening and corrosion behavior of novel multilayer sheets (AA4045/AA7072/AA3003M/AA4045).
Design/methodology/approach
Polarization curve tests, immersion experiments and transmission electron microscopy analysis were used to study the corrosion behavior and tensile properties of the sheets before and after brazing and aging.
Findings
The strength of the sheet is weakened after brazing due to brittle eutectic phases, and recovered after aging due to enhanced precipitation strengthening in the AA7072 interlayer. The core of nonbrazed sheets cannot be protected due to the significant galvanic coupling effect between the intermetallic particles and the substrate. Brazing and aging treatments promote the redissolved of second phased and limit corrosion along the eutectic region in the clad, allowing the core to be protected.
Originality/value
AA7xxx alloy was added to conventional brazed sheets to form a novel Al alloy composite sheet with AA4xxx/AA7xxx/AA3xxx structure. The strengthening and corrosion mechanism of the sheet was proposed. The added interlayer can sacrificially protect the core from corrosion and improves strength after aging treatment.
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Hongjun Xing, Kerui Xia, Liang Ding, Haibo Gao, Guangjun Liu and Zongquan Deng
The purpose of this paper is to enable autonomous door-opening with unknown geometrical constraints. Door-opening is a common action needed for mobile manipulators to perform…
Abstract
Purpose
The purpose of this paper is to enable autonomous door-opening with unknown geometrical constraints. Door-opening is a common action needed for mobile manipulators to perform rescue operation. However, it remains difficult for them to handle it in real rescue environments. The major difficulties of rescue manipulation involve contradiction between unknown geometrical constraints and limited sensors because of extreme physical constraints.
Design/methodology/approach
A method for estimating the unknown door geometrical parameters using coordinate transformation of the end-effector with visual teleoperation assists is proposed. A trajectory planning algorithm is developed using geometrical parameters from the proposed method.
Findings
The relevant experiments are also conducted using a manipulator suited to extreme physical constraints to open a real door with a locked latch and unknown geometrical parameters, which demonstrates the validity and efficiency of the proposed approach.
Originality/value
This is a novel method for estimating the unknown door geometrical parameters with coordinate transformation of the end-effector through visual teleoperation assists.
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Zhiqi Liu, Tanghong Liu, Hongrui Gao, Houyu Gu, Yutao Xia and Bin Xu
Constructing porous wind barriers is one of the most effective approaches to increase the running safety of trains on viaducts in crosswinds. This paper aims to further improve…
Abstract
Purpose
Constructing porous wind barriers is one of the most effective approaches to increase the running safety of trains on viaducts in crosswinds. This paper aims to further improve the wind-sheltering performance of the porous wind barriers.
Design/methodology/approach
Improved delayed detached eddy simulations based on the k-ω turbulence model were carried out, and the results were validated with wind tunnel tests. The effects of the hole diameter on the flow characteristics and wind-sheltering performance were studied by comparing the wind barriers with the porosity of 21.6% and the hole diameters of 60 mm–360 mm. The flow characteristics above the windward and leeward tracks were analyzed, and the wind-sheltering performance of the wind barriers was assessed using the wind speed reduction coefficients.
Findings
The hole diameters affected the jet behind the wind barriers and the recirculation region above the tracks. Below the top of the wind barriers, the time-averaged velocity first decreased and then increased with the increase in the hole diameter. The wind barrier with the hole diameter of 120 mm had the best wind-sheltering performance for the windward track, but such barrier might lead to overprotection on the leeward track. The wind-sheltering performance of the wind barriers with the hole diameters of 240 mm and 360 mm was significantly degraded, especially above the windward track.
Originality/value
The effects of the hole diameters on the wake and wind-sheltering performance of the wind barriers were studied, by which the theoretical basis is provided for a better design of the porous wind barrier.
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Haotian Xu, Jingcheng Wang, Hongyuan Wang, Ibrahim Brahmia and Shangwei Zhao
The purpose of this paper is to investigate the design method of partial observer canonical form (POCF), which is one of the important research tools for industrial plants.
Abstract
Purpose
The purpose of this paper is to investigate the design method of partial observer canonical form (POCF), which is one of the important research tools for industrial plants.
Design/methodology/approach
Motivated by the two-steps method proposed in Xu et al. (2020), this paper extends this method to the case of Multi-Input Multi-Output (MIMO) nonlinear system. It decomposes the original system into two subsystems by observable decomposition theorem first and then transforms the observable subsystem into OCF. Furthermore, the necessary and sufficient conditions for the existing of POCF are proved.
Findings
The proposed method has a wide range of applications including completely observable nonlinear system, noncompletely observable nonlinear system, autonomous nonlinear system and forced nonlinear system. Besides, comparing to the existing results (Saadi et al., 2016), the method requires less verified conditions.
Originality/value
The new method concerning design POCF has better plants compatibility and less validation conditions.
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Jiangang Xia, Xingyuan Gao and Jianping Shen
Do principals from small, medium, and large school districts have the same level of decision making power? Do teachers from small, medium, and large school districts have the same…
Abstract
Do principals from small, medium, and large school districts have the same level of decision making power? Do teachers from small, medium, and large school districts have the same level of decision making power? This chapter tried to address these questions by analyzing 2011–2012 nationally representative School and Staffing Survey data. We found that comparing with large districts, teachers and principals at small and medium school districts perceived higher levels of decision making power in most school policy areas. We also found that although there were statistically significant differences among the three district sizes, practically significant differences existed in establishing curriculum for teachers and in establishing curriculum and deciding budget for principals. Implications of the findings were discussed.
Cheng Bo, Wang Li, Zhang Qun, Gao Xia, Xie Xiaoming and Wolfgang Kempe
Flip chip on board (FCOB) solder joint reliability under thermal shock stress was investigated. With underfill materials, the solder joint lifetime was increased from 37 to…
Abstract
Flip chip on board (FCOB) solder joint reliability under thermal shock stress was investigated. With underfill materials, the solder joint lifetime was increased from 37 to 1,300/2,480 cycles depending on the particular underfill material used. Through the use of CSAM, SEM, dye penetration tests and cross sectioning, the reliability of a FCOB assembly under thermal shock stress was evaluated. Both dye penetration and SEM fracture analysis can be used to measure quantitatively the extent of crack propagation for assemblies without underfill. A new failure mechanism, PCB cracking was also observed and discussed.