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Study on force reduction mechanism in ultrasonic assisted grinding based on single-grain scratching

He Yuhui, Zhang Jiajia, Zhou Weihua, Tang Jinyuan, Xu Yanbin, Zhang Yutong

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 2

art. no. e80, 1--14

Ultrasonic vibration-assisted grinding (UAG) has been proven to be a promising grinding ability improvement technique due to the grinding force reduction. However, the reduction mechanism is still unclear due to the lack of knowledge on material softening and grain - work piece contact conditions in UAG. In this paper, we present a numerical and experimental study on ultrasonic vibration-assisted scratching (UAS) to understand the force reduction mechanism for UAG from a single-grain perspective. Based on crystal plasticity theory and dislocation density model, the constitutive model for ultrasonic-assisted deformation is established, in which the influence of vibration amplitude and strain rate is considered. To further study the acoustic softening effect, the ultrasonic assisted tensile test is conducted. The finite element model for UAS is developed with the kinematic analysis and the consideration of acoustic softening effect. The comparison between the simulated and experimental results indicates that the process force reduction under ultrasonic vibration can be attributed to (1) the reduction of contact area due to the path interference effect and (2) the yield stress reduction due to the acoustic softening effect. This research can deepen the understanding of the beneficial effect of ultrasonic vibration in UAG and offers new insight for studying other ultrasonic-assisted machining method.

Responses of Physiological Characteristics of Annual C4 Herbs to Precipitation and Wind Changes in Semi-Arid Sandy Grassland, Northern China

Sun Shanshan, Liu Xinping, He Yuhui, Lv Peng, Chelmeg, Zhang Lamei, Wei Shuilian

Polish Journal of Ecology

2020

Vol. 68, nr 2

121--131

The effects of changing precipitation and wind regimes on plant physiology are increasingly drawing attention of eco-physiologists. In the manipulative experiment we studied the physiological mechanisms of annual C4 herbs in the semi-arid sandy land to understand the functional significance of their traits and responses to the changing environment, grass Setaria viridis, characterized by the moderate stem water content and low leaf water content, more effectively absorbed light energy and utilized water resources than two dominant dicot plants, Salsola collina and Bassia dasyphylla. Precipitation increase and wind reduction promoted photosynthesis of the three C4 herbaceous plants, and their photosynthetic rates were higher in the end of July than that in August. Precipitation increase and the 20% reduction in wind velocity could also enhance their stomatal conductance and transpiration rate. The transpiration rate was consistent with the change in stomatal conductance, exhibiting highly positive correlation. The interactive effects of precipitation increase and wind velocity reduction made great changes in photosynthetic rate of the S. collina, lifted the photosynthetic rate and water use efficiency of the S. viridis. Our results suggest that the C4 herbs have shown some degree of stress resistance, and they are able to acclimate better to frangible environment of semi-arid sandy land. Furthermore, the changing environments heighten photosynthesis of the C4 herbs, which is pretty important to strength the arid plant stress resistance, then contributed to the ecosystem community production and dry matter accumulation.