Search results
1 – 10 of over 1000Zhijian Wang, Xuejin Shen, Xiaoyang Chen, Qiang Han and Lei Shi
The purpose of this paper is to study starvation in grease-lubricated finite line contacts and to understand film-forming mechanisms of grease-lubricated finite line contacts.
Abstract
Purpose
The purpose of this paper is to study starvation in grease-lubricated finite line contacts and to understand film-forming mechanisms of grease-lubricated finite line contacts.
Design/methodology/approach
A multiple-contact optical elastohydrodynamic (EHL) test rig is constructed to investigate the influences of lubricant properties on film thickness and lubrication conditions at different working conditions. The film thickness is calculated according to the relative light intensity principle. The degree of starvation is evaluated by the air–oil meniscus distance and the corresponding film thickness.
Findings
The experimental results show that for greases with high-viscosity base oil, the high-frequency fluctuation of film thickness is observed in low-speed operating conditions. Reducing the viscosity of the base oil and improving running speed can weaken the fluctuation of film thickness. The degree of starvation increases with increasing base oil viscosity, rolling speed and the crown drop. In addition, reducing the replenishment time by reducing the gap between the rollers also can increase the degree of starvation.
Originality/value
Starvation is often to occur in finite line contacts, such as roller bearings and gears; there are still limited finite line contact EHL test rigs, much less multiple-contact optical test rigs. Therefore, the present work is undertaken to construct the multiple-contact test rig and to evaluate the mechanism of starvation in finite line contacts.
Details
Keywords
A public–private partnership (PPP) is an agreement between the government and private investors to deliver long-term public services. The efficiency of PPP projects depends on PPP…
Abstract
Purpose
A public–private partnership (PPP) is an agreement between the government and private investors to deliver long-term public services. The efficiency of PPP projects depends on PPP contracts stipulating contractual parties' corresponding responsibilities and rights to deal with relational and performance risks. Although more complex contracts provide more remedies for mitigating ex-post transaction costs, they also result in the increased ex ante transaction costs associated with contract writing. Thus, contractual complexity is a design choice that can reduce the overall contract transaction costs.
Design/methodology/approach
Using 365 transportation PPP projects in China from 2010 to 2019, this study applies the Poisson regression model to examine the effects of payment mechanisms, ownership by investors and equity structure on contractual complexity.
Findings
PPP contracts have control and coordination functions with unique determinants. Parties in the government-pay mechanism are more likely to negotiate coordination provisions, which results in greater contractual complexity. PPP projects with state-owned enterprises (SOEs) have less contractual complexity in terms of both two functions of provisions, whereas the equity structure has no impact on contractual complexity.
Originality/value
These findings provide a nuanced understanding of how various contractual provisions are combined to perform control or coordination functions and make managerial recommendations to parties involved in PPP projects.
Details
Keywords
Samrat Ray, Elena Viktorovna Korchagina, Rohini U. Nikam and Roop Kishore Singhal
This chapter proposes a new architecture to address challenges to security and the privacy in e-healthcare under Industry 5.0. With the growing needs for high-quality medical…
Abstract
This chapter proposes a new architecture to address challenges to security and the privacy in e-healthcare under Industry 5.0. With the growing needs for high-quality medical treatment and the continuously growing costs of treating global medical problems, systems and web-based medical care are regarded as innovative solutions. In particular, the new progress in Internet of Things (IoT) has led to the development of Internet of Medical Things (IoMT). The patient history data is handled and processed remotely in real-time rather than visiting any clinic and then having that data transferred for subsequent use to third parties, such as data that gets saved in the cloud. This patient data faced security threats and it is observed as major limitations of using such systems in Industry 5.0. This chapter analyzes the security and secrecy challenges, together with the necessities, the danger involved and proposed secured blockchain-based framework which is capable of future research scope in Industry 5.0. The study has described an Eye Hospital case study that stores the eye donors’ details. With such critical scenario, this study addresses healthcare scenario with poverty-led agenda and social developmental features.
Details
Keywords
K.M. Law, Z.M. Zhang and C.S. Leung
This study examines the relationship between fashion leadership, clothing deprivation and satisfaction of Hong Kong young consumers. A survey was carried out with 309 university…
Abstract
This study examines the relationship between fashion leadership, clothing deprivation and satisfaction of Hong Kong young consumers. A survey was carried out with 309 university students and 228 working young people in Hong Kong. Factor analysis with varimax rotation was used to group various attributes into different factors related to clothing deprivation and satisfaction. Hirschman and Adcock's (1978) measure was adopted to classify subjects into various fashion groups. ANOVA followed by Scheffe's procedure was applied to detect differences in clothing deprivation and satisfaction between different fashion groups. The implications of the findings to fashion retailers are discussed.
Details
Keywords
Pengpeng Cheng and Daoling Chen
The purpose of this paper is to analyze the influence of underwear on the microenvironment of human clothing.
Abstract
Purpose
The purpose of this paper is to analyze the influence of underwear on the microenvironment of human clothing.
Design/methodology/approach
Based on the basic laws of energy and mass conservation, the paper combined the theory of heat and mass transfer to establish the simulation of the influence of underwear on human thermal reaction in microclimate and prediction model of human thermal reaction law.
Findings
The impact on the microenvironment affected by tighter underwear is less than the effect of loose underwear and computational flow dynamics (CFD) can accurately predict the thermal reaction parameters’ values of the human body.
Originality/value
It can be effectively used for the prediction of heat exchange between human body and environment in high-temperature environment and human thermophysiological parameters, and overcomes the individual differences of human experiments and the danger and repeatability of high-temperature environmental experiments.
Details
Keywords
Liang Zhang, Song-bai Xue, Li-li Gao, Yan Chen, Sheng-lin Yu, Zhong Sheng and Guang Zeng
The purpose of this paper is to investigate the effects of minor addition of the rare earth (RE) element cerium, Ce, on the microstructures and creep properties of Sn-Ag-Cu solder…
Abstract
Purpose
The purpose of this paper is to investigate the effects of minor addition of the rare earth (RE) element cerium, Ce, on the microstructures and creep properties of Sn-Ag-Cu solder alloys.
Design/methodology/approach
The pure Sn, Sn-Cu alloy, Sn-Ag alloy and Cu-Ce alloy were used as raw materials. Sn-Ag-Cu alloys with different contents of RE Ce were chosen to compare with Sn-Ag-Cu. The raw materials of Sn, Sn-Cu alloy, Sn-Ag alloy, Cu-Ce alloy were melted in a ceramic crucible, and were melted at 550°C ± 1°C for 40 minutes. To homogenize the solder alloy, mechanical stirring was performed every ten minutes using a glass rod. During the melting, KC1 + LiCI (1.3:1), were used over the surface of liquid solder to prevent oxidation. The melted solder was chill cast into a rod.
Findings
It is found that the microstructure exhibits smaller grains and the Ag3Sn/Cu6Sn5 intermetallic compound (IMC) phases are modified in matrix with the addition of Ce. In particular, the addition of 0.03 wt.% Ce to the Sn-Ag-Cu solder can refine the microstructures and decrease the thickness of the IMC layers of Sn-Ag-Cu solder alloys. Meanwhile, thermodynamic analysis showed that these phenomena could be attributed to the reduction of the driving force for Cu-Sn IMC formation due to the addition of Ce. Results calculated using the thermodynamic method are close to the above experimental data. Thus, the optimum content of Ce in Sn-Ag-Cu solder alloys should be about 0.030 percent. Additionally, the effect of Ce on the creep rupture life of Sn-Ag-Cu soldered joints was studied. It was found that the creep rupture life may be increased up to 7.5 times more than that of the original Sn-Ag-Cu alloy, when Ce accounts for 0.030 percent.
Originality/value
This paper usefully investigates the effects of the RE cerium (Ce), on the microstructures and creep properties of Sn-Ag-Cu solder alloys, optimizing the quantity of Ce in the Sn-Ag-Cu solder alloy through a thermodynamic method and by creep-rupture life testing.
Details
Keywords
Ziqiang Cui, Qi Wang, Qian Xue, Wenru Fan, Lingling Zhang, Zhang Cao, Benyuan Sun, Huaxiang Wang and Wuqiang Yang
Electrical capacitance tomography (ECT) and electrical resistance tomography (ERT) are promising techniques for multiphase flow measurement due to their high speed, low cost…
Abstract
Purpose
Electrical capacitance tomography (ECT) and electrical resistance tomography (ERT) are promising techniques for multiphase flow measurement due to their high speed, low cost, non-invasive and visualization features. There are two major difficulties in image reconstruction for ECT and ERT: the “soft-field”effect, and the ill-posedness of the inverse problem, which includes two problems: under-determined problem and the solution is not stable, i.e. is very sensitive to measurement errors and noise. This paper aims to summarize and evaluate various reconstruction algorithms which have been studied and developed in the word for many years and to provide reference for further research and application.
Design/methodology/approach
In the past 10 years, various image reconstruction algorithms have been developed to deal with these problems, including in the field of industrial multi-phase flow measurement and biological medical diagnosis.
Findings
This paper reviews existing image reconstruction algorithms and the new algorithms proposed by the authors for electrical capacitance tomography and electrical resistance tomography in multi-phase flow measurement and biological medical diagnosis.
Originality/value
The authors systematically summarize and evaluate various reconstruction algorithms which have been studied and developed in the word for many years and to provide valuable reference for practical applications.
Details
Keywords
Li‐li Gao, Song‐bai Xue and Hong Zhu
The purpose of this paper is to investigate the influence of praseodymium (Pr) additions (0, 0.05 and 0.5 wt%) on the mechanical properties and microstructure of SnAgCu solder…
Abstract
Purpose
The purpose of this paper is to investigate the influence of praseodymium (Pr) additions (0, 0.05 and 0.5 wt%) on the mechanical properties and microstructure of SnAgCu solder joint during aging process. Moreover, the authors aim to indicate that the decreased soldification undercooling of Sn3.8Ag0.7Cu solder can suppress the formation of Ag3Sn plate to some extent.
Design/methodology/approach
The shear strength evolution of SAC, SAC‐0.05Pr and SAC‐0.5Pr solder joint were studied under 150°C aging process with STR‐1000. The effect of Pr additions on the solidification behavior of SnAgCu solder was also studied by differential scanning calorimetry. To study the microstructure evolution, the cross‐sections of all specimens were observed by means of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Meanwhile, the etchant, consisting of 20%HNO3+distilled water was used for deep etching to reveal the interfacial morphology.
Findings
The shear force reduction rate of SAC solder joint during aging was restrained by 0.05%Pr addition but promoted with 0.5% Pr addition. The growth of IMC layer of SnAgCu joint in the aging process was suppressed significantly by different amounts of Pr additions. However, the beneficial effect of Pr addition due to the suppression of IMC layer growth was weakened by the micro‐cracks formed in PrSn3 compounds in SnAgCu‐0.5Pr joint. Pr additions (0.05, 0.5 wt%) decrease the solidification undercooling of SnAgCu solder, which will suppress the formation of Ag3Sn plate to some extent.
Research limitations/implications
Further studies are necessary for confirmation of the practical application, especially of the manufacturing technology of solder paste containing Pr.
Practical implications
The appropriate amount of Pr in Sn3.8Ag0.7Cu solder is about 0.05 wt%. It is found that SAC‐0.05Pr solder has an improvement in solder joint reliability in long aging processes. The results suggested the novel solder alloys can meet the requirements of high reliability application.
Originality/value
The paper demonstrates that: Pr additions promote the solidification of SAC solder; shear force reduction rate of SAC solder joint was reduced by 0.05%Pr addition; the IMC layer growth rate of SnAgCu solder joint was suppressed by Pr additions; and micro‐cracks were found in PrSn3 phases after aging.
Details
Keywords
Songtao Qu and Qingyu Shi
In the electronic assembly industry, low-temperature soldering holds great potential to be used in surface mounting technology. Tin–bismuth (Sn–Bi) eutectic alloys are lead-free…
Abstract
Purpose
In the electronic assembly industry, low-temperature soldering holds great potential to be used in surface mounting technology. Tin–bismuth (Sn–Bi) eutectic alloys are lead-free solders applied in consumer electronics because of their low melting point, high strength and low cost. This paper aims to investigate how to address the problem of hot tear crack formation during Sn–Bi low-temperature solder (LTS) in the mass production of consumer electronics.
Design/methodology/approach
This paper explored the development of hot tear cracks during Sn–Bi soldering in the fabrication of flip chip ball grid arrays. Experiments were designed to simulate various conditions encountered in Sn–Bi soldering. Quantitative analysis was conducted on the number of hot tear cracks observed in different alloy compositions and solder volumes to explore the primary cause of hot tear cracks and possible methods to suppress crack formation.
Findings
Hot tear cracks existed in Sn–Bi solders with different bismuth (Bi) contents, but increasing the solder volume reduced the number of hot tear cracks. Experiments were designed to test the degree of chip transient thermal warpage with temperature change, and, according to the results, glue was dispensed in specific areas to reduce chip warpage deformation. Finally, the results of combined process experiments pointed to an effective method of low-temperature soldering to suppress hot tear cracks.
Research limitations/implications
The study focuses on Sn–Bi solders only without other solder pastes such as SAC305 or Sn–Zn series.
Practical implications
With the growing popularity of smart electronics, especially in intelligent terminals, new energy vehicles electronics, solar photovoltaic and other field, there will be more and more demand for low- temperature, energy-saving, lead-free solders. Therefore, this study will help the industry to roll out LTS (Sn–Bi) solutions rapidly.
Social implications
In the long term, lean and green manufacturing is expected to be essential for maintaining an advanced manufacturing industry across the world. Developing new LTSs and soldering processes is the most effective, direct solution for energy conservation and emission mitigation. With the growing popularity of smart electronics, especially in intelligent terminals, new energy vehicles and solar photovoltaics, there would be an increased demand for low-temperature, energy-saving, lead-free techniques.
Originality/value
Although there are many methods that can be used to suppress hot tear cracks, there is little research on how to control the hot tear cracks caused by the low-temperature soldering of Sn–Bi in laptop applications. The authors studied the hot tear cracks that developed during the world’s first mass production of 50 million personal laptops based on low-temperature Sn–Bi alloy solder pastes. By controlling the Bi content, redesigning the solder paste printing process (e.g. through a printer’s stencil) and adding dispensing processes, the authors obtained reliable and stable experimental data and conclusions.
Details
Keywords
Muhammad Aamir, Majid Tolouei-Rad, Israr Ud Din, Khaled Giasin and Ana Vafadar
Tin-Silver-Copper is widely accepted as the best alternative to replace Tin-Lead solders in microelectronics packaging due to their acceptable properties. However, to overcome…
Abstract
Purpose
Tin-Silver-Copper is widely accepted as the best alternative to replace Tin-Lead solders in microelectronics packaging due to their acceptable properties. However, to overcome some of the shortcomings related to its microstructure and in turn, its mechanical properties at high temperature, the addition of different elements into Tin-Silver-Copper is important for investigations. The purpose of this paper is to analyse the effect of lanthanum doping on the microstructure, microhardness and tensile properties of Tin-Silver-Copper as a function of thermal aging time for 60, 120 and 180 h at a high temperature of 150°C and at high strain rates of 25, 35 and 45/s.
Design/methodology/approach
The microstructure of un-doped and Lanthanum-doped Tin-Silver-Copper after different thermal aging time is examined using scanning electron microscopy followed by digital image analyses using ImageJ. Brinell hardness is used to find out the microhardness properties. The tensile tests are performed using the universal testing machine. All the investigations are done after the above selected thermal aging time at high temperature. The tensile tests of the thermally aged specimens are further investigated at high strain rates of 25, 35 and 45/s.
Findings
According to the microstructural examination, Tin-Silver-Copper with 0.4 Wt.% Lanthanum is found to be more sensitive at high temperature as the aging time increases which resulted in coarse microstructure due to the non-uniform distribution of intermetallic compounds. Similarly, lower values of microhardness, yield strength and ultimate tensile strength come in favours of 0.4 Wt.% Lanthanum added Tin-Silver-Copper. Furthermore, when the thermally aged tensile specimen is tested at high strains, two trends in tensile curves of both the solder alloys are noted. The trends showed that yield strength and ultimate tensile strength increase as the strain rate increase and decrease when there is an increase in thermal aging.
Originality/value
The addition of higher supplement (0.4 Wt.%) of Lanthanum into Tin-Silver-Copper showed a lower hardness value, yield strength, ultimate tensile strength, ductility, toughness and fatigue in comparison to un-doped Tin-Silver-Copper at high temperature and at high strain rates. Finally, simplified material property models with minimum error are developed which will help when the actual test data are not available.
Details