Various textures are fabricated by a picosecond laser machine on the surfaces of circular stainless steel specimens. Vibrational and tribological effects of laser surface textures are investigated by means of a tribometer and a data acquisition and signal processing (DASP) system. Experimental results show that surface textures can reduce the coefficients of friction (COFs), enhance the wear resistance, and improve the dynamical performance of frictional surfaces. In this study, the surface with micro circular dimples in diameter of 150 μm or textured area density of 25% has the best tribological and dynamical performance. Compared with the non-textured surface, the surface with circular dimples in diameter of 150 μm and 15% textured area density has 27% reduction of COFs, 95% reduction of frictional vibrations, and 66% reduction of frictional noise. The frictional vibrations and noise in the sliding contacts can be effectively reduced by adding graphene to the lubrication oil, and the surface textures enhance the frictional noise reduction performance of lubrication.

Laser surface treatment is a very useful technology for the fabrication of functional surfaces. In this study, novel antifouling surfaces are fabricated by laser cladding of TC4 and Ni60 mixed materials in various mass ratios on the surfaces of 316L stainless steel substrates. Parametric studies are carried out to investigate the effects of the mixed powder mass ratios and laser cladding parameters on the antifouling performance of the laser clad coatings (LCCs). The antifouling mechanism of the LCCs is investigated by using the water contact angle/surface energy measurement, scanning electron microscope (SEM) surface observation, and phase composition analysis via XRD (X-ray diffractometer) testing. The experimental results show that the LCCs with Ni60/TC4 mass ratio of 3/7 has better antifouling performance in this study. The antifouling performance of the LCC decreases with the increase in laser scanning speed. Surface energy and surface topography have a significant effect on the antifouling performance of LCCs. In order to get the optimal antifouling performance of LCCs, the Ni60/TC4 mass ratio and laser cladding parameters should be optimized.

Background: Online education has been conducted widely in higher education in recent years. While online teaching brings many opportunities, it also poses numerous challenges and issues. This is especially true for college teachers, for whom teaching is considered to be a profession with a high level of burnout and anxiety. The large-scale application of online teaching methods has put teachers in an even more challenging context, which may lead to teaching anxiety affecting their mental health. In online teaching contexts, the question of what factors affect college teachers' online teaching anxiety is worth exploring to help reduce their online teaching anxiety so as to promote their work performance. In this study, therefore, we conducted a survey of college teachers to develop a model of job environment (job demands and job resources), subjective well-being, and online teaching anxiety, and to explore the influences of job environment and subjective well-being on their online teaching anxiety, as well as the mediating effects of subjective well-being between job environments and online teaching anxiety.Method: Of the 1,060 college teachers who participated, 524 were male (49.4%) and 536 were female (50.6%). An online questionnaire was sent to the teachers in January, 2022. Online teaching anxiety, subjective well-being, and job environment scales were adapted and developed. Descriptive analysis, reliability and validity analysis, and structural equation modelling were used to analyse the collected data.Results: The study model showed an adequate fit (χ² = 440.983, RMSEA = 0.070, GFI = 0.942, AGFI = 0.914, NFI = 0.949, and CFI = 0.956), confirming the relationships of job demands and online teaching anxiety (β = 0.310, p < 0.001), job resources and online teaching anxiety (β = – 0.086, p < 0.01), job demands and subjective well-being (β = – 0.411, p < 0.001), job resources and subjective well-being (β = 0.204, p < 0.001), and subjective well-being and online teaching anxiety (β = – 0.435, p < 0.001). Meanwhile, the results also proved the effects of the mediating role of subjective well-being between job demands (95% CI = [– 0.138, – 0.225]), job resources (95% CI = [– 0.119, – 0.064]), and online teaching anxiety. The model accounted for 33.8% (f² = 0.401) of online teaching anxiety.Conclusion: The results of this study indicated that it is important to reduce job demands and increase job resources to alleviate college teachers' online teaching anxiety to maintain good mental health; while maintaining a high level of college teachers' subjective well-being is also helpful for promoting their work performance. Furthermore, the indirect effects of job demands and job resources on online teaching anxiety mediated by college teachers' subjective well-being were also significant.

This study aims to minimize the noise generated by automobile cooling fans. Fan blade structures with ridged surfaces based on bio-inspired principles are 3D printed and used to replace the conventional fan blades. The effect of the bio-inspired ridge structures on the noise reduction of the cooling fan is demonstrated by orthogonal experiments in a semi-anechoic chamber. Experimental results show that with an increase in the rotational speed, the effect of the surface textures on the acoustic performance of the cooling fan becomes more significant. For example, at a fan speed of 1750 r/min, all the bio-inspired blade designs reduce noise compared with the original fan and, in particular, the sound pressure level is reduced by 3.83 dB(A) for the design with a ridge width of 4 mm and a ridge pitch of 15 mm. Through variance analysis of the measured noise, the ridge pitch distance has the most significant impact on noise reduction under low speed conditions whilst, under high speed conditions, the ridge width has the most significant influence. In addition to the experimental studies, computational fluid dynamics (CFD) simulations of the cooling fan are carried out to explain the mechanism of noise reduction for the ridged fan blades. When the fan runs, the horseshoe vortexes generated by the ridge structures disturb the flow of the boundary layer, reduce the influence of the fluid flow on the boundary layer, and delay the transition of the fan blade laminar flow to turbulence. It is also seen that there is a reduction of the intensity of the fan blade trailing edge vortices and the scale of the secondary vortices, thereby achieving the overall aim of noise reduction. This research has significance in the noise reduction design of automobile cooling fans.

This work makes use of experimental and numerical studies to investigate the reduction of braking noise and vibrations of brake disks by introducing various M-shaped grooves on the brake disk frictional surfaces. Experiments with a brake test dynamometer have been carried out to compare the braking vibrations and noise of the grooved disks with that of the un-grooved disk. The experimental results demonstrate that disks with grooves significantly reduced braking vibrations and noise at both low and high frequencies, and as the initial braking temperature and braking pressure increased, the reduction effect is further enhanced. The investigation also shows the wear rates of both the grooved disks and brake pads are also significantly reduced. Thermo-mechanical coupled finite element models of the brake pads and disks with and without grooves are developed to investigate the mechanisms of the reduction of braking noise and vibrations by the introduction of grooves on the disk frictional surfaces. The numerical results show that the number of grooves plays an important role in reducing the interface surface temperatures, enhancing heat flux, reducing thermal deformation, changing the contact pressure distribution, and stabilizing the coefficients of friction of the braking sliding contacts. The thermal effects contribute to the wear reduction of both the braking disks and pads, and the reduction of braking noise and vibrations. In addition, both the finite element modal analysis and the experimental modal testing results show that surface grooves increase the modal damping ratio of the disks, which certainly plays a role on the reduction of braking noise and vibrations. This study has significance to the surface modification of brake disks in order to reduce braking noise and vibrations, as well as the wear resistance of brake disks and pads.