Ion energy-induced nanoclustering structure in a-C:H film for achieving robust superlubricity in vacuum

Hydrogenated amorphous carbon (a-C:H) films are capable of providing excellent superlubricating properties, which have great potential serving as self-lubricating protective layer for mechanical systems in extreme working conditions. However, it is still a huge challenge to develop a-C:H films capable of achieving robust superlubricity state in vacuum. The main obstacle derives from the lack of knowledge on the influencing mechanism of deposition parameters on the films bonding structure and its relation to their self-lubrication performance. Aiming at finding the optimized deposition energy and revealing its influencing mechanism on superlubricity, a series of highly-hydrogenated a-C:H films were synthesized with appropriate ion energy, and systematic tribological experiments and structural characterization were conducted. The results highlight the pivotal role of ion energy on film composition, nanoclustering structure, and bonding state, which determine mechanical properties of highly-hydrogenated a-C:H films and surface passivation ability and hence their superlubricity performance in vacuum. The optimized superlubricity performance with the lowest friction coefficient of 0.006 coupled with the lowest wear rate emerges when the carbon ion energy is just beyond the penetration threshold of subplantation. The combined growth process of surface chemisorption and subsurface implantation is the key for a-C:H films to acquire stiff nanoclustering network and high volume of hydrogen incorporation, which enables a robust near-frictionless sliding surface. These findings can provide a guidance towards a more effective manipulation of self-lubricating a-C:H films for space application.

Analytical calculation models for mesh stiffness and backlash of spur gears under temperature effects

The temperature has a great contribution to the mesh stiffness and backlash of the gear pair. Presence of thermal deformation caused by temperature will complicate the gear teeth interaction. In this paper, the thermal time-varying stiffness model and thermal time-varying backlash model are proposed with the consideration of tooth profile error and total thermo-elastic deformation consists of the teeth deformation, teeth contact deformation, and gear body-induced deformation. The key parameters of thermo-elastic coupling deformation affected by temperature are calculated. Based on the proposed models, the influencing mechanism of temperature on the tooth profile error, mesh stiffness, total deformation, and backlash are revealed. The effects of shaft radius and torque load on the thermal stiffness and thermal backlash are studied. The proposed thermal stiffness and backlash calculation model are proven to be more comprehensive and the correctness is validated.

Entrepreneurs’ Felt Responsibility for Constructive Change and Entrepreneurial Performance: A Moderated Mediation Model of Technology Action and Market Orientation

Drawing on self-determination theory, we examine the mechanism through which entrepreneurs’ felt responsibility for constructive change affects entrepreneurial performance and how market orientation affects the influencing mechanism. A questionnaire survey was conducted with 424 entrepreneurs in China. The results show that entrepreneurs’ felt responsibility for constructive change is positively related to technology action and entrepreneurial performance, and technology action mediates the relationship between entrepreneurs’ felt responsibility for constructive change and entrepreneurial performance. In addition, market orientation moderates the relationship between technology action and entrepreneurial performance such that the relationship is stronger when the market orientation is higher. Our findings suggest that when entrepreneur feel responsible for constructive change, they tend to take technology actions to achieve their goals and improve the long-term development of ventures. It is also important for entrepreneurs to hold a market orientation, which helps them be aware of changes in customer needs rather than blindly focusing on the use of the latest technologies. Our study is pioneering in exploring entrepreneurs’ felt responsibility for constructive change in the entrepreneurial context, advancing the research on entrepreneurship psychology.

The Influencing Mechanism of Social Effort-Reward Imbalance on Life Satisfaction among Aging Workforces in the United States: A Longitudinal Study

Improving life satisfaction is consistent with the United Nations (UN) sustainable development goals. Although there are many studies examining life satisfaction, research on the influencing mechanisms remains a hot topic and scholars hope to explore more aspects that improve life satisfaction. The purpose was to explore how the relationship between social effort-reward imbalance and life satisfaction are mediated by positive and negative affect. We collected longitudinal data from 909 respondents participating in the 2008 and 2012 wave of the Health and Retirement Study (HRS). We used the first-order difference method and structural equation modeling (SEM) analysis to evaluate the validity of the proposed hypotheses. Our results demonstrated that social effort-reward imbalance was positively related to negative affect, and negatively related to positive affect. Positive affect was positively related to life satisfaction, while negative affect was negatively related to life satisfaction. The findings also indicated that positive and negative affect completely mediated the relationship between social effort-reward imbalance and life satisfaction. This study has made a contribution to the research on the influencing mechanism of life satisfaction from the aspects of theory and practice. Longitudinal data ensured that the conclusions were more reliable so that the study could provide useful suggestions for improving life satisfaction.

Effect of forming process on mechanical and interfacial properties for thermoplastic composite I-stiffened structures

The forming process is the core factor to control the quality of thermoplastic composite components. In this paper, the common I-stiffened structures in the aerospace field were taken as the research object, and the forming process scheme was designed. Based on the prefabrication of C-shaped parts, the I-stiffened structures were prepared by the compression molding process. The influence law of molding temperature on the quality of the prefabricated C-shaped parts was explored. The time dependence of the PEEK melt viscosity was tested to provide the basis for the optimization of forming process parameters of I-stiffened structures. The influencing mechanism of thermoplastic composites repeatedly forming to the bonding strength of remelting interface was studied. The results show that repeated forming would lead to polymer aging and result in low bonding strength at the remelting interface of the I-stiffened structures. Optimizing the forming process could effectively reduce the aging of materials and improve the bonding strength of the remelting interface and overall mechanical properties of components. The research provides technical guidance for the manufacturing of complex thermoplastic composite components, especially the influence mechanism of the forming process on the bonding strength of remelting interface.

Optimization of Resistance Spot Welding with Inserted Strips via FEM and Response Surface Methodology

Resistance spot welding (RSW) with inserted strips, a recent variant of traditional RSW, was usually adopted in joining thin gage steels to lower the temperature developed at the electrode surface and to extend electrode life. In order to understand the influencing mechanism how the inserted strips affect the heat transfer behavior and to optimize the selection of suitable strips, an approach integrated with FEM and response surface methodology (RSM) was employed. FEM results showed that the inserted strips would not only lead to earlier initiation of weld and bigger weld size in both diameter and thickness but also lower the electrode surface temperature. Based on FEM, uniform design and RSM were further employed to build a regression model between the strip properties (i.e., electrical/thermal conductivity, thickness) and the responses (i.e., electrode tip temperature, weld diameter, and temperature at strip/sheet interface). A graphical optimization was conducted to identify a preferable strip, and a Cu55Ni45 strip with a thickness of 0.12 mm was recommended for a 0.4 mm steel sheet.

A deeper exploration of the relation between sulfonation degree and retanning performance of aromatic syntans

It is well-known that the sulfonation degree (DS) of aromatic syntan is an important factor affecting its retanning performances. But the quantitative relation between DS and syntan property and the influencing mechanism of DS on syntan property are not clarified. In this work, five phenolic formaldehyde syntans (PFSs) with the same polymerization degree but varying DS were prepared to investigate the effect of DS on the properties of syntan and crust leather. It was found that the absolute value of zeta potential and the particle size of PFS decreased with increasing DS in aqueous solution. Molecular dynamic simulation results proved that the DS of PFS was a major contributor to electrostatic interaction and hydrogen bonding in the PFS–water system and greatly affected the aggregation and dispersion of PFS in aqueous solution. The PFS with a low DS was prone to aggregate to large particles in aqueous solution because of low intermolecular electrostatic repulsion and less hydrogen bonds and therefore can be used to increase the thickness and tightness of leather. The PFS with a high DS presented a small particle size with more anionic groups in aqueous solution, thereby sharply decreasing the positive charge of leather surface and facilitating the penetration of the post-tanning agents into the leather. These results might be scientifically valid for rational molecular design of syntans and more productive use of syntans in leather making. Graphical Abstract