Di Wang, Xiongmian Wei, Jian Liu, Yunmian Xiao, Yongqiang Yang, Linqing Liu, Chaolin Tan, Xusheng Yang and Changjun Han
This paper aims to explore a structural optimization method to achieve the lightweight design of an aviation control stick part manufactured by laser powder bed fusion (LPBF…
Abstract
Purpose
This paper aims to explore a structural optimization method to achieve the lightweight design of an aviation control stick part manufactured by laser powder bed fusion (LPBF) additive manufacturing (AM). The utilization of LPBF for the fabrication of the part provides great freedom to its structure optimization, further reduces its weight and improves its portability.
Design/methodology/approach
The stress distribution of the model was analyzed by finite element analysis. The material distribution path of the model was optimized through topology optimization. The structure and size of the parts were designed by applying honeycomb structures for weight reduction. The lightweight designed control stick part model was printed by LPBF using AlSi10Mg.
Findings
The weight of the control stick model was reduced by 32.64% through the optimization method using honeycomb structures with various geometries. The similar stress concentrations of the control stick model indicate that weight reduction has negligible effect on its mechanical strength. The maximum stress of the lightweight designed model under loading is 230.85 MPa, which is 61.81% larger than that of the original model. The lightweight control stick part manufactured by LPBF has good printability and service performance.
Originality/value
A structural optimization method integrating topology, shape and size optimization was proposed for a lightweight AlSi10Mg control stick printed by LPBF. The effectiveness of the optimization method, the printability of the lightweight model and the service performance of LPBF-printed AlSi10Mg control stick was verified, which provided practical references for the lightweight design of AM.
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Wei Zhu, Chunze Yan, Yunsong Shi, Shifeng Wen, Changjun Han, Chao Cai, Jie Liu and Yusheng Shi
Semi-crystalline polymers such as polyamide-12 can be used for selective laser sintering (SLS) to make near-fully dense plastic parts. At present, however, the types of…
Abstract
Purpose
Semi-crystalline polymers such as polyamide-12 can be used for selective laser sintering (SLS) to make near-fully dense plastic parts. At present, however, the types of semi-crystalline polymers suitable for SLS are critically limited. Therefore, the purpose of this paper is to investigate the processibility of a new kind of semi-crystalline polypropylene (PP) with low isotacticity for SLS process.
Design/methodology/approach
The SLS processibility of the PP powder, including particle size and shape, sintering window, degree of crystallinity and degradation temperature, was evaluated. Effects of the applied laser energy density on the surface micromorphology, density, tensile strength and thermal properties of SLS-built PP specimens were studied.
Findings
The results show that the PP powder has a nearly spherical shape, smooth surfaces, an appropriate average particle size of 63.6 μm, a broad sintering window of 21 oC and low crystalline degree of 30.4 per cent comparable to that of polyamide-12, a high degradation temperature of 381.8°C and low part bed temperature of 105°C, indicating a very good SLS processibility. The density and the tensile strength first increase with increasing laser energy density until they reach the maximum values of 0.831 g/cm3 and 19.9 MPa, respectively, at the laser energy density of 0.0458 J/mm2, and then decrease when the applied laser energy density continue to increase owing to the degradation of PP powders. The complex PP components have been manufactured by SLS using the optimum parameters, which are strong enough to be directly used as functional parts.
Originality/value
This paper provides a new knowledge for this field that low-isotacticity PPs exhibit good SLS processibility, therefore increasing material types and broadening the application of SLS technology.
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Changjun Han, Chunze Yan, Shifeng Wen, Tian Xu, Shuai Li, Jie Liu, Qingsong Wei and Yusheng Shi
Selective laser melting (SLM) is an additive manufacturing process suitable for fabricating metal porous scaffolds. The unit cell topology is a significant factor that determines…
Abstract
Purpose
Selective laser melting (SLM) is an additive manufacturing process suitable for fabricating metal porous scaffolds. The unit cell topology is a significant factor that determines the mechanical property of porous scaffolds. Therefore, the purpose of this paper is to evaluate the effects of unit cell topology on the compression properties of porous Cobalt–chromium (Co-Cr) scaffolds fabricated by SLM using finite element (FE) and experimental measurement methods.
Design/methodology/approach
The Co-Cr alloy porous scaffolds constructed in four different topologies, i.e. cubic close packed (CCP), face-centered cubic (FCC), body-centered cubic (BCC) and spherical hollow cubic (SHC), were designed and fabricated via SLM process. FE simulations and compression tests were performed to evaluate the effects of unit cell topology on the compression properties of SLM-processed porous scaffolds.
Findings
The Mises stress predicted by FE simulations showed that different unit cell topologies resulted in distinct stress distributions on the bearing struts of scaffolds, whereas the unit cell size directly determined the stress value. Comparisons on the stress results for four topologies showed that the FCC unit cell has the minimum stress concentration due to its inclined bearing struts and horizontal arms. Simulations and experiments both indicated that the compression modulus and strengths of FCC, BCC, SHC, CCP scaffolds with the same cell size presented in a descending order. These distinct compression behaviors were correlated with the corresponding mechanics response on bearing struts. Two failure mechanisms, cracking and collapse, were found through the results of compression tests, and the influence of topological designs on the failure was analyzed and discussed. Finally, the cell initial response of the SLM-processed Co-Cr scaffold was tested through the in vitro cell culture experiment.
Originality/value
A focus and concern on the compression properties of SLM-processed porous scaffolds was presented from a new perspective of unit cell topology. It provides some new knowledge to the structure optimization of porous scaffolds for load-bearing bone implants.
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Yaojun Han, Changjun Jiang and Xuemei Luo
The purpose of this paper is to present a scheduling model, scheduling algorithms, and formal model and analysis techniques for concurrency transaction in grid database…
Abstract
Purpose
The purpose of this paper is to present a scheduling model, scheduling algorithms, and formal model and analysis techniques for concurrency transaction in grid database environment.
Design/methodology/approach
Classical transaction models and scheduling algorithms developed for homogeneous distributed architecture will not work in the grid architecture and should be revisited for this new and evolving architecture. The conventional model is improved by three‐level transaction scheduling model and the scheduling algorithms for concurrency transaction is improved by considering transmission time of a transaction, user's priority, and the number of database sites accessed by the transaction as a priority of the transaction. Aiming at the problems of analysis and modeling of the transaction scheduling in grid database, colored dynamic time Petri nets (CDTPN) model are proposed. Then the reachability of the transaction scheduling model is analyzed.
Findings
The three‐level transaction scheduling model not only supports the autonomy of grid but also lightens the pressure of communication. Compared with classical transaction scheduling algorithms, the algorithms not only support the correctness of the data but also improve the effectiveness of the system. The CDTPN model is convenient for modeling and analyzing dynamic performance of grid transaction. Some important results such as abort‐ratio and turnover‐time are gotten by analyzing reachability of CDTPN.
Originality/value
The three‐level transaction scheduling model and improved scheduling algorithms with more complex priority are presented in the paper. The paper gives a CDTPN model for modeling transaction scheduling in grid database. In CDTPN model, the time interval of a transition is a function of tokens in input places of the transition.
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Jie Yu, Changjun Yi and Huiyun Shen
This paper aims to study whether the adoption of an entry mode that fits the social trust level contributes to the improvement of foreign subsidiary performance.
Abstract
Purpose
This paper aims to study whether the adoption of an entry mode that fits the social trust level contributes to the improvement of foreign subsidiary performance.
Design/methodology/approach
The authors used the Probit model, linear regression, strategic fit approach and instrumental variable regression. The sample was made up of 11,095 observations of Chinese multinational enterprises' foreign subsidiaries in 54 countries from 2005 to 2020.
Findings
The results suggest that a host country with a high level of social trust results in fewer difficulties for enterprises in gaining legitimacy, thus foreign subsidiaries are more likely to select the wholly owned entry mode. The results also show that the effect is contingent on the formal institutions of host countries. The results of the mechanism test suggest that social trust influences subsidiaries' entry mode choice by reducing information asymmetry, costs and uncertainty risks. This study further finds that selecting a fit entry mode based on social trust level substantially increases foreign subsidiary performance and this effect is more significant when multinational enterprises (MNEs) are state-owned enterprises (SOEs).
Research limitations/implications
The main limitation of this paper is its only focus on foreign subsidiaries of Chinese MNEs, which may limit the generalizability of research findings.
Originality/value
This paper responds to the call for conducting more research on informal institutions. Findings highlight the critical role of informal institutions in helping foreign subsidiaries in gaining legitimacy in host countries and the essentialness of selecting a fit entry mode based on the informal institutions of host countries for the development of foreign subsidiaries.
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Xingcheng Wang, Changjun Chen and Min Zhang
This paper aims to study the effect of laser energy on the formability, microstructure and mechanical properties of AZ61D alloy to assist systematic study of laser additive…
Abstract
Purpose
This paper aims to study the effect of laser energy on the formability, microstructure and mechanical properties of AZ61D alloy to assist systematic study of laser additive manufacturing of magnesium alloys.
Design/methodology/approach
In this study, porous magnesium alloy samples were prepared by using different laser parameters. The changes of the formability and microstructure were observed by SEM, and the mechanical properties were tested. The above results were analyzed to obtain optimized laser parameters.
Findings
When the laser power is between 85 and 95 W (pulse width 3.0 ms, frequency 40 Hz), the surface morphology of the selective laser-melted (SLMed) porous samples are smooth and even. At 80 W, SLMed porous samples have a maximum relative density of 99.2 per cent. Because of the “solute capture” effect and the evaporization of magnesium, the fraction of ß-Mg17Al12 increases from 42.1 to 52.1 per cent when power rises from 80 to 105 W. The ultimate compressive strength of SLMed porous magnesium alloys is strengthened with the increase of laser power.
Originality/value
The effect of laser parameters on microstructure and mechanical properties of porous magnesium alloys prepared by SLM has not been reported.
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Since 2017, China's digital economy has accounted for more than 30% of the country's GDP. The digital economy has become the main driving force of China's economic development…
Abstract
Purpose
Since 2017, China's digital economy has accounted for more than 30% of the country's GDP. The digital economy has become the main driving force of China's economic development. Moreover, the digital economy has also changed the traditional modes of production and distribution between urban and rural areas. This paper aims to explore the influential mechanism of digital economy infrastructure (DEI) on the urban-rural income gap (URIG).
Design/methodology/approach
By analyzing the theoretical model of the URIG, this paper constructs a theoretical analysis framework and clarifies the key roles of rural land circulation (RLC) and resident population urbanization (RPU) in the relationship between DEI and the URIG.
Findings
The DEI can effectively reduce the URIG; the regression coefficient (RC) was −0.109. The reduction effect is mainly reflected in: 1) the wage income gap between urban and rural residents (RC = −0.128) and 2) the net property income gap of urban and rural residents (RC = −0.321). Also, for the spatial spillover effect, the path effect of “DEI – RLC – URIG” is almost equal to the path effect of “DEI – RPU – URIG”; for the local effect, the path effect of the former is far smaller than the latter. Moreover, when the RPU reaches the threshold of 86.29%, the DEI will expand the URIG (RC = 0.201).
Originality/value
This paper proposes a theoretical framework for the impact of DEI on the URIG, explores the mechanism of RLC and RPU in the DEI and URIG and enriches the theory of traditional research on URIG.
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Pengzhen Lu, Yu Ding, Ying Wu, Changjun He, Liu Yang and Yang Li
(1) The shear lag effect and its additional deflection contribution to composite beams based on spatial grid elements were presented. (2) A refined spatial grid element analysis…
Abstract
Purpose
(1) The shear lag effect and its additional deflection contribution to composite beams based on spatial grid elements were presented. (2) A refined spatial grid element analysis method that can simultaneously obtain the internal forces, displacements and stresses of various parts of a composite beam.
Design/methodology/approach
A refined spatial grid element analysis method.
Findings
The proposed method can directly obtain the internal forces and displacements of the joints of the composite beam roof, floor and web.
Originality/value
To comprehensively comprehend the mechanical behavior of double-girder steel plate composite girder bridge structures and facilitate refined analysis, this paper introduces a refined spatial grid element analysis model applicable to both the global and local domains.
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Changjun Yi, Yun Zhan, Jipeng Zhang and Xiaoyang Zhao
This study investigates the effect of ownership structure – ownership concentration and firm ownership – on outward foreign direct investment (OFDI) by emerging market…
Abstract
Purpose
This study investigates the effect of ownership structure – ownership concentration and firm ownership – on outward foreign direct investment (OFDI) by emerging market multinational enterprises (EMNEs), and further explores the moderating effects of international experience and migrant networks on this relationship.
Design/methodology/approach
Data of Chinese MNEs listed on Shenzhen and Shanghai stock exchanges between 2005 and 2016 are used. The empirical analysis is based on the negative binomial regression model.
Findings
The empirical results reveal a significant inverted-U relationship between ownership concentration and OFDI by EMNEs. State ownership is found to have a positive effect on OFDI by EMNEs. Both international experience and migrant networks strengthen the inverted-U relationship between ownership concentration and OFDI as well as the positive effect of state ownership on OFDI by EMNEs.
Practical implications
EMNEs need to maintain a moderate ownership concentration when conducting OFDI, and they are supposed to make full use of their own international experience and focus on migrant networks of the host country. Policy-makers in emerging economies need to better create a fair business environment for enterprises.
Originality/value
Combining agency theory and the resource-based view, this study integrates ownership structure, firm-level heterogeneous resources – international experience and country-level heterogeneous resources – migration networks into a framework to study OFDI by EMNEs, which expands the scope of research in international business.
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Badar Nadeem Ashraf and Changjun Zheng
The purpose of this paper is to examine the impact of legal protection of bank minority shareholders (noncontrolling shareholders) and bank creditors (e.g. depositors or…
Abstract
Purpose
The purpose of this paper is to examine the impact of legal protection of bank minority shareholders (noncontrolling shareholders) and bank creditors (e.g. depositors or debt-holders) on bank dividend payout policies using a panel data set of 5,918 banks from 52 countries over the period 1998-2007, after controlling for country-level deposit insurance coverage and bank- and country-level regulatory pressures.
Design/methodology/approach
Tobit panel regression models are used to examine the impact of legal protection of shareholders and creditors on bank dividend payout amounts. And, logit panel regression models are used to examine the impact of legal protection of shareholders and creditors on banks’ likelihood to pay dividends.
Findings
The authors support the outcome hypothesis by finding that banks pay higher amount of dividends and, are more likely to pay dividends in strong minority shareholder protection countries. However, the authors reject the substitute hypothesis by finding that banks pay higher dividends and are more likely to pay dividends in weak creditor rights countries, and banks do not substitute weak creditor rights with lower dividend payout amounts. Contrary, the authors support the literature which argues the importance of creditor rights for capital market development because one possible reason for low dividend payouts in strong creditor rights countries could be that the banks retain more profits for extending more loans.
Practical implications
By finding that creditor rights index has a negative relation with bank dividend policies in contrast to its positive relation with nonfinancial firms’ dividend policies, the authors support the literature which argues that managers of banks give less importance to factors such as current degree of financial leverage, the contractual constraints such as dividend restrictions in debt contracts, and the financing considerations such as the cost of raising external funds, while deciding about the dividend payments. The authors also suggest to keep financial and nonfinancial firms separate, to better understand the dividend puzzle.
Originality/value
Extant literature recognizes that legal institutions such as shareholder protection and creditor rights affect corporate firms’ dividend policies significantly but largely excludes banking sector. This paper, by examining the relations between legal protection of shareholders and creditors and bank dividend policies, fills this research gap.