Study On Mechanical Properties Of The Operculum In A Water Snail

Mechanical seals are widely used in petrochemical,aerospace and other fields due to their good sealing performance,long service life,and low friction power loss.With the rapid development of precision manufacturing,higher requirements have been put forward for the performance of mechanical seals.However,there has been no significant progress in research on mechanical seals in terms of friction reduction,miniaturization and lightweight.The previous study has shown that water snail can survive for months by closing the operculum to minimize water loss in dry weather,which may open up new paths for designing mechanical seal structure.This article selected the operculum of water snail as a bionic object.The macroscopic motion characteristics of the water snail and the microstructure of the operculum were observed.Besides,we proposed equivalent mathematical models to analyze the mechanisms of friction reduction and sealing.By using 3D printing technique,we fabricated the normal disk and operculum-inspired sheet and tested the sealing performance.Combining experimental results and theoretical analysis,the revised design of the stationary ring in bionic mechanical seal was proposed.Using the combination of macroscopic and microscopic methods,the mechanism of friction reduction of the operculum is revealed.The surface morphology of the operculum was observed by optical microscopy,SEM and white light interferometer.It was found that the operculum is an oval-shaped sheet with micro-grooves distributed concentrically on the surface.The average relative angular velocity between the shell and the operculum was obtained by analyzing the crawling video of the water snail.According to the micro-grooves structure of the operculum,a hydrodynamic lubrication model was established to analyze the effect of friction reduction.The calculation results proved that the theoretical friction coefficient between the operculum and the shell can reach up to 0.012,which suggests Pomacea canaliculata have the optimal geometric parameters of the operculum's micro-grooves for friction reduction.Moreover,the friction coefficient of the textured surface can be reduced to 97% compared with the smooth surface.It can be concluded that the micro-grooves structure of the operculum can generate effective hydrodynamic lubrication which administers to friction reduction.The locking behavior of the operculum was quantified by observation,and a mathematical model was established to reveal the relationship between the geometric configuration of the operculum and its sealing ability.The deformation of the edge of the operculum was measured.With the use of an optical microscope and SEM,we found the edge of the operculum consists of many layers which are parallel to the operculum.The contribution of the laminated structure to the sealing performance was demonstrated from the perspective of stiffness and contact area.The results show that the operculum's laminated microstructure has an optimum layer number and geometric parameters to provide low stiffness,which enhances sealing performance.In addition,we fabricated the normal disk and operculum-inspired model using a 3D printer and measured the leakage rate to compare the sealing effect between them.The measurement results show that under the same normal force,the water leakage rate of the bio-inspired structure is significantly reduced compared to the disk with uniform thickness.Based on the analysis of the friction reduction and sealing mechanism of the operculum,the revised design of the stationary ring in bionic mechanical seal was proposed.The stationary ring was designed as an annular sheet with ringlike microgrooves on the surface and a laminated structure at the edge,which would reduce the friction and wear,enhances sealing performance and improves service life while reducing the structural size and weight.