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This paper aims to investigate the lubrication performance of cam/tappet contact during start up. Especially, the thermal insulation effects of coating on the lubrication performance during cold start up process and warm start up process are studied.

A numerical model for the analysis of thermal elastohydrodynamic lubrication of coated cam/tappet contact is presented. In this model, the Reynolds equation and the energy equations are discretized by the finite difference method and solved jointly.

During start up, the contact force at cam nose-to-tappet contact decreases with increasing time, while the absolute entrainment velocity has the upward trend. The minimum film thickness, maximum average temperature and friction power loss increase with increasing time, while the coefficient of friction decreases during start up. Because of the thermal insulation effect, the coating can significantly increase the degree of temperature rise. Compared with the uncoated case, the coated cam/tappet results in a lower friction power loss. Generally, the friction power loss in the cold start up process is much higher than that in the warm start up process.

By this study, the lubrication performance and the kinematics and the dynamics of the cam/tappet during start up process are investigated. Meanwhile, the thermal insulation effect of coating is also illustrated. The difference of lubrication performance between cold start up process and warm start up process is analyzed. The results and thermal elastohydrodynamic lubrication method presented in this study can be a guidance in the design of the coated cam/tappet.

During running-in, the change in the honed cylinder liner surface alters the performance and efficiency of the piston ring-pack system. The present paper, thus, aims to investigate the surface topography and wear and friction evolution of a cylinder liner surface during the running-in tests on a reciprocating ring–liner tribometer under a mixed lubrication regime. After an initial period of rapid wear termed “running-in wear”, a relatively long-term steady-state surface topography can emerge. A numerical model is developed to predict the frictional performance of a piston ring-pack system at the initial and steady-state stages.

The liner surfaces are produced by slide honing (SH) and plateau honing (PH). The bearing area parameter (Rk family), commonly used in the automotive industry, is used to quantitatively characterize the surface topography change during the running-in process. A wear volume-sensitive surface roughness parameter, Rktot, is used to show the wear evolution.

The experimental results show that a slide-honed surface leads to reduced wear, and it reduces the costly running-in period compared to the plateau-honed surface. The simulation results show that running-in is a beneficial wear process that leads to a reduced friction mean effective pressure at the steady-state.

To simulate the mixed lubrication performance of a ring–liner system with non-Gaussian roughness, a one-dimensional homogenized mixed lubrication model was established. The real surface topography instead of its statistical properties is taken into account.

This paper aims to investigate the effects of reciprocating frequency, large normal load on friction and wear behavior of hydrogenated diamond-like carbon (H-DLC) coating against Ti-6Al-4V ball under dry and lubricated conditions.

The friction and wear mechanisms are analyzed by scanning electron microscope, energy dispersive spectroscopy and Raman spectroscopy.

The results show that as reciprocating frequency increases under lubricated conditions, the friction coefficient decreases first and then increases. When the reciprocating frequency is 2.54 Hz, the value of friction coefficient reaches the minimum. The friction reduction is because of the transformation from sp³ to sp², the formation of transfer layer on Ti-6Al-4V ball and the reduction in viscous friction, whereas the increase of friction coefficient is related to wear. In dry conditions, the friction coefficient is between 0.06 and 0.1. And, the service life of H-DLC coating decreases with the increase in reciprocating frequency and normal load.

It is confirmed that adding the lubricant could prolong the service life of H-DLC coating and reduce friction and wear efficiently. And, the wear mechanisms under dry and lubricated conditions encompass abrasive wear and adhesive wear.

The results are helpful for application of diamond-like carbon coating.

The purpose of this paper is to study the real-time change of surface roughness at different small regions of piston rings during running-in process. Meanwhile, the effects of real-time change of the rough surface topography on the lubrication and friction of piston rings are investigated.

An uneven wear model has been developed to research the running-in behavior at the different small regions of piston rings. The model is verified by comparing the simulation results with the experimental results on a reciprocating friction and wear test rig.

This research shows that the wear process of piston ring surface is uneven during running-in. At most time of the operating cycle except the vicinity of top dead center and bottom dead center, the minimum oil film thickness ratio increases while the friction force and power loss decrease after the running-in period.

Through this research, the running-in behavior of piston rings is investigated in detail. The interaction between the running-in and the lubrication and friction of piston rings is understood more deeply.

Wearable health devices (WHDs) have demonstrated significant potential in assisting elderly adults with proactive health management by utilizing sensors to record and monitor various aspects of their health, including physical activity, heart rate, etc. However, limited research has systematically explored older adults’ continued usage intention toward WHD. By utilizing the extended unified theory of acceptance and use of technology (UTAUT2), this paper aims to probe the precursors of elderly adults’ continuance intention to use WHD from an enabler–inhibitor perspective.

The research model was developed based on UTAUT2 and examined utilizing the partial least squares technique (PLS). The research data were collected through in-person meetings with older people (n = 272) in four cities in China.

Results reveal that performance expectancy, effort expectancy, social influence, facilitating conditions, hedonic values and perceived complexity are the positive predictors of elderly adults’ continuance intention to use WHDs. Technology-related anxiety and usage cost negatively influence the formation of older people’s continuance intention.

This work is an original empirical investigation that draws on several theories as guiding frameworks. It adds to the existing literature on the usage of wearable technologies and offers insights into how the elderly’s intentions to continue using WHDs can be developed. This study broadens the scope of the UTAUT2 application and presents an alternative theoretical framework that can be utilized in future research on the usage behavior of wearable devices by individuals.

Lead users are essential participants in crowdsourcing innovation events; their continuance intention significantly affects the success of the crowdsourcing innovation community (CIC). Although researchers have acknowledged the influences of network externalities on users' sustained participation in general information systems, limited work has been conducted to probe these relationships in the CIC context; particularly, the predictors of lead users' continued usage intention in such context are still unclear. Hence, this paper aims to explore the precursors of lead users' continuance intention from a network externalities perspective in CIC.

This work ranked users' leading-edge status to recognize lead users in the CIC. And then, the authors proposed a research model based on the network externalities theory, which was examined utilizing the partial least squares (PLS) technique. The research data were collected from an online survey of lead users (n = 229) of a CIC hosted by a China handset manufacturer.

Results revealed that the number of peers, perceived complementarity and perceived compatibility significantly influence lead users' continuance intention through identification and perceived usefulness.

This work contributes to the crowdsourcing innovation research and provides views regarding how lead users' sustained participation can be developed in the CICs. This work also offers an alternative theoretical framework for further research on users' continued intention in open innovation activities.

This paper aims to study the effect of piston skirt design parameters on the dynamic characteristics of a piston–cylinder contact.

This paper focuses on an analysis of the piston dynamic response. The oil-film pressure and the structural deformation were approximated, respectively, by finite difference method and finite element method.

The results show that the design parameters such as clearance, offset and the axial location of piston pin have a great influence on the dynamics of the piston and hence on the piston slap phenomenon and the frictional power loss.

All the results mainly focus on the slap noise of the engine and can be used in the piston–liner development at the development of the engine.