Yuejian Zhou, Xiaoshan Liu, Guoqiu He, Zhiqiang Zhou, Yiping Liao, Yinfu Liu and Xiaojun Xu
This paper aims to investigate the effect of Cu content and T6 heat treatment on the mechanical properties and the tribological performance of SiCp/Al-Si-Cu-Ni-Mg hybrid…
Abstract
Purpose
This paper aims to investigate the effect of Cu content and T6 heat treatment on the mechanical properties and the tribological performance of SiCp/Al-Si-Cu-Ni-Mg hybrid composites at an elevated temperature.
Design/methodology/approach
The stir casting method was used to synthesize SiCp/Al-12Si-xCu-1Ni-1Mg (x = 2, 3, 3.5, 4, 4.5, 5 Wt.%) composites containing 20 vol% SiC. The hardness and tensile strength of the aluminum matrix composites (AMCs) at room temperature and elevated temperature were studied, and the wear mechanism was investigated using scanning electron microscopic and energy dispersive spectroscopy.
Findings
Results indicate that the hardness and tensile strength of the AMCs are affected significantly by T6 heat treatment and Cu content. The high-temperature friction and wear mechanism of AMCs is the composite wear mechanism of oxidation wear, adhesion wear, abrasive wear, peeling wear, high-temperature softening and partial melting. Among them, adhesion wear, high-temperature matrix softening and local melting are the main wear mechanisms.
Originality/value
The influence mechanism of Cu content on the hardness, tensile strength and high temperature resistance of AMCs was explained by microstructure. And the results further help to explore the application of AMCs in high temperature.
Details
Keywords
Yinfu Liu, Guoqiu He, Xiaoshan Liu, Jiaqi Pan, Zhiqiang Zhou, Yiping Liao, Qiao He and Xiaojun Xu
To improve the high-temperature wear properties of the SiCp/A359 composite, foamed iron-reinforced SiCp/A359 composite (A359–SiCp/Fe) is prepared. The purpose of this study is to…
Abstract
Purpose
To improve the high-temperature wear properties of the SiCp/A359 composite, foamed iron-reinforced SiCp/A359 composite (A359–SiCp/Fe) is prepared. The purpose of this study is to investigate the tribological behavior and mechanism of the A359–SiCp/Fe composites at different temperatures (100–500 °C) and loads (7 N, 10 N and 12 N).
Design/methodology/approach
The A359–SiCp/Fe composite was fabricated by vacuum-assisted infiltration. The dry sliding tribological behaviors of A359–SiCp/Fe composite were investigated using the ball-on-disc-type tribometer. The worn surface and wear morphology of the longitudinal section were examined using field emission scanning electron microscopy and metallographic microscope.
Findings
The critical transition temperature for severe wear in A359–SiCp/Fe composite was 50–100 °C higher than in SiCp/A359 composite. Foamed iron prevents exfoliation cracks from penetrating deeper into the matrix. The friction coefficient stability of the A359–SiCp/Fe composite was higher than the unreinforced composite at elevated temperatures. With the increase in temperature, the friction-affected layer was severely worn, and the wear mechanism transferred from abrasion and delamination to oxidation and plastic flow, respectively.
Originality/value
The preparation procedure for aluminum matrix composites reinforced with foamed metal has been less reported, and the research on the tribological behavior and mechanism of A359–SiCp/Fe composite at various temperatures is insufficient. The foamed iron structure considerably enhances the wear properties of SiCp/A359 composite in elevated temperature conditions.
Details
Keywords
Ziao Huang, Xiaoshan Liu, Guoqiu He, Zhiqiang Zhou, Bin Ge, Peiwen Le, Jiaqi Pan and Xiaojun Xu
This study aims to understand the multiaxial fretting fatigue, wear and fracture characteristics of 35CrMoA steel under the elliptical loading path.
Abstract
Purpose
This study aims to understand the multiaxial fretting fatigue, wear and fracture characteristics of 35CrMoA steel under the elliptical loading path.
Design/methodology/approach
By keeping the contact pressure and torsional shear cyclic stress amplitude unchanged; the axial cyclic stress amplitude varied from 650 MPa to 850 MPa. The fretting fatigue test was carried out on MTS809 testing machine, and the axial cyclic strain response and fatigue life of the material were analyzed. The fretting zone and fracture surface morphology were observed by scanning electron microscope. The composition of wear debris was detected by energy dispersive X-ray spectrometer.
Findings
In this study, with the increase of axial stress amplitude, 35CrMoA steel will be continuously softened, and the cyclic softening degree increases. The fretting fatigue life decreases unevenly. The fretting scars in the stick region are elongated in the axial direction. The area of fracture crack propagation zone decreases. In addition, the results indicate that wear debris in the slip region is spherical and has higher oxygen content.
Originality/value
There were few literatures about the multiaxial fretting fatigue behavior of 35CrMoA steel, and most scholars focused on the contact pressure. This paper reveals the effect of axial cyclic stress on fretting fatigue and wear of 35CrMoA steel under the elliptical loading path.
Details
Keywords
Jiaqi Pan, Xiaoshan Liu, Guoqiu He, Bin Ge, Peiwen Le, Jingquan Li and Zhiqiang Zhou
The purpose of this paper is to understand the effect of particle content, applied load and sliding speed on the tribological properties of A356-SiCP composites manufactured using…
Abstract
Purpose
The purpose of this paper is to understand the effect of particle content, applied load and sliding speed on the tribological properties of A356-SiCP composites manufactured using a newly developed vacuum stir casting technique.
Design/methodology/approach
A356 alloy reinforced with 10, 15 and 20 vol% SiC particles was prepared by vacuum stir casting. Tribological tests were carried out on block-on-ring tribometer under dry sliding conditions, room temperature. Wear mechanism was investigated by scanning electron microscope and energy dispersion spectrum.
Findings
SiCP is homogeneously dispersed in the matrix. The increase in SiCP content decrease wear rate, but it leads to an increase in coefficient of friction. The wear rate increase and friction coefficient present different variation trends with increasing load. For A356-20%SiCP composite, when the load is less than 10 MPa, wear rate and friction coefficient under sliding speed of 400 rpm are lower than those of 200 rpm. Wear mechanism transition from abrasion, oxidation, delamination, adhesion to plastic flow as load and sliding speed increasing.
Practical implications
Results of this study will help guide the use of A356-SiCP in many automotive products such as brake rotors, brake pads, brake drums and pistons.
Originality/value
There are few paper studies the effect of particle content, applied load and sliding speed on the tribological properties of A356-SiCP composites. Aluminum matrix composites with uniform distribution of reinforcing particles were successfully prepared by using the newly developed vacuum stir casting technique.
Details
Keywords
Lian Duan, Hongbo Song, Xiaoshan Huang, Weihan Lin, Yan Jiang, Xingheng Wang and Yihua Wu
The study examined the impact of feedback types through a learning management system (LMS) on employees’ training performance. The purpose of this study is to establish effective…
Abstract
Purpose
The study examined the impact of feedback types through a learning management system (LMS) on employees’ training performance. The purpose of this study is to establish effective feedback on advanced technologies for promoting corporate training.
Design/methodology/approach
A total of 148 trainees were recruited from a multinational medical company. Employees were randomly assigned to receive feedback from shallow to more constructive details on their learning performance with LMS. Data sources included are employees’ goal setting (GS) performance evaluated by the experts and their posttest scores obtained from the LMS. A series of statistical analyses were performed to investigate the impact of feedback intervention on employees’ GS and their impacts on corporate training results.
Findings
GS has a significant impact on learning outcomes. Employees who set greater specific goals attained higher scores. Furthermore, feedback with more formative evaluation and constructive developmental advice resulted in the most significant positive influence on the relationship between participants’ GS and learning outcomes.
Practical implications
Organizations can benefit from delivering appropriate feedback using LMS to enhance employees’ GS and learning efficacy in corporate training.
Originality/value
This study is one of the first to examine the moderating effect of feedback provided by LMS on GS and online learning performance in corporate training. This study contributes to GS theory for practical application and proposes a viable method for remote learning. The current study’s findings can be used to provide educational psychological insights for training and learning in industrial contexts.
Details
Keywords
Wei Wang, Junping Shi, Xiaoshan Cao and Yifeng Hu
The partition of unity of the standard meshless Galerkin method is used as basis in expressing the discontinuity of the contact surface displacement, particularly by adding…
Abstract
Purpose
The partition of unity of the standard meshless Galerkin method is used as basis in expressing the discontinuity of the contact surface displacement, particularly by adding discontinuous terms into the displacement mode, and constructing the discontinuous meshless displacement field function. In this study the contact surface equation is aimed to derive from the improved Coulomb friction contact model.
Design/methodology/approach
In this paper based on the basic idea of meshless method, an improved moving least squares approximation function (expansion method based on out of unit division) is applied to the analysis of two-dimensional contact problems.
Findings
On the basis of this equation after discrete processing, it is combined with the discrete form of the virtual work equation with added contact conditions, and eventually transformed into a standard linear complementary problem. Moreover, it is solved by using the Lemke algorithm, and a corresponding example is provided in this research.
Originality/value
The proposed method can effectively control the mutual embedding of the contact surface, and the stress distribution that is the same as the actual situation can be obtained on the contact surface.
Details
Keywords
Clement Kong Wing Chow, Michael Ka Yiu Fung and Japhet Sebastian Law
This chapter studies the technical efficiencies of Chinese airports by using a meta-frontier production function model which accounts for airports in different regions accessing…
Abstract
This chapter studies the technical efficiencies of Chinese airports by using a meta-frontier production function model which accounts for airports in different regions accessing different technologies. Our empirical results show that the technical efficiency scores of airports and provincial output in the coastal region are higher than their counterparts in the inland region. However, the technical efficiency scores of airports and provincial output in inland region are steadily increasing while the counterparts of airports and provincial output in coastal region are slowly declining. In addition, our analysis of provincial efficiency changes shows that airport productivity has a positive and statistically significant effect on the technical changes of provincial output. Our results partially confirm the success of the government policy of promoting airport construction and development in the western inland region.
Details
Keywords
Ling Zhang, Minghui Zheng and Zheyan Zhang
This paper aims to study the impact of land options on the land transfer behaviour of Chinese city governments.
Abstract
Purpose
This paper aims to study the impact of land options on the land transfer behaviour of Chinese city governments.
Design/methodology/approach
Based on the institutional environment of Hangzhou, China, the option pricing model is used to measure the option value of the trading plots. The effect of the option value on the land transfer price and the timing of transfers are estimated respectively, using the hedonic price model and the survival analysis models.
Findings
The results show that the option value has a significant explanation on land price and timing of land transfers. Under the effect of option value, the positive impact of fiscal pressure on the possibility of land transfer weakens. From the perspective of the annual option premium rate, the option premium is closely related to the real estate cycle. Option premiums are higher during booms but lower during recessions and in new urban areas.
Practical implications
By revealing the distinction of land option premiums in different places and times, this paper provides a reference for city governments seeking a balance between real estate regulation and obtaining more land revenue.
Originality/value
By introducing policy variables that reflect the degree of tightness of real estate regulation and indicators of local government financial pressure, the paper discusses the impact of options on the transfer behaviour of local governments in different situations.
Details
Keywords
Chunyan Yao, Dongdong Chen, Zhongli Zheng, Qiangsheng Wang and Kaijie Fu
The purpose of this study is to obtain an effective implant with porous structures on its surface, named porous-surfaced implant, which helps to improve the overall stability of…
Abstract
Purpose
The purpose of this study is to obtain an effective implant with porous structures on its surface, named porous-surfaced implant, which helps to improve the overall stability of the implant and promote the combination of implant and alveolar bone.
Design/methodology/approach
Porous-surfaced implants with a porosity of 16%, 21%and 32% were designed and the effect of porosity on the strength of the implant was analyzed by ABAQUS software. Porous-surfaced implants with different porosity were printed by selective laser melting and the surface morphology was observed. Animal experiments of implants with porous structures and coating were carried out in healthy beagle dogs. The experimental group was treated with hydroxyapatite coating and the control group was not treated. Bone volume (BV) and total volume (TV) of the implant surface of the experimental group and control group were calculated by Skyscan CTvol software.
Findings
With the increase of porosity of porous-surfaced implants, the neck stress of the porous-surfaced implants increased and their strength decreased. In addition, in animal vivo experiments, the ratio value of BV to TV of the porous-surfaced implants was between 55.38% and 79.86%, which was the largest when the porosity of porous-surfaced implants was 16%. The internal and surrounding bone formation content of porous-surfaced implants with hydroxyapatite coating was higher than porous-surfaced implants without coating.
Originality/value
The results of this study show that the pores on the surface of implants can be filled with the new bone and porous-surfaced implants with 16% porosity provide better space for the growth of new bone. The porous structures with hydroxyapatite coating are beneficial to the growth of new bone around implants. The results of this study are helpful to improve the overall stability of implants and to promote the combination of implant and alveolar bone.