The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic mod...The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection(TR) method is introduced into the verification of contact models.An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity's merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.展开更多
We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted...We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.展开更多
The spatial and temporal evolution of real contact area of contact interface with loads is a challenge.It is generally believed that there is a positive linear correlation between real contact area and normal load.How...The spatial and temporal evolution of real contact area of contact interface with loads is a challenge.It is generally believed that there is a positive linear correlation between real contact area and normal load.However,with the development of measuring instruments and methods,some scholars have found that the growth rate of real contact area will slow down with the increase of normal load under certain conditions,such as large-scale interface contact with small roughness surface,which is called the nonlinear phenomenon of real contact area.At present,there is no unified conclusion on the explanation of this phenomenon.We set up an experimental apparatus based on the total reflection principle to verify this phenomenon and analyze its mechanism.An image processing method is proposed,which can be used to quantitative analysis micro contact behaviors on macro contact phenomenon.The weighted superposition method is used to identify micro contact spots,to calculate the real contact area,and the color superimposed image is used to identify micro contact behaviors.Based on this method,the spatiotemporal evolution mechanism of real contact area nonlinear phenomena is quantitatively analyzed.Furthermore,the influence of nonlinear phenomenon of real contact area on the whole loading and unloading process is analyzed experimentally.It is found that the effects of fluid between contact interface,normal load amplitude and initial contact state on contact behavior cannot be ignored in large-scale interface contact with small roughness surface.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11872033)the Beijing Natural Science Foundation,China(Grant No.3172017)
文摘The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection(TR) method is introduced into the verification of contact models.An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity's merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.
基金Project supported by the National Natural Science Foundation of China(Grant No.11872033)the Beijing Natural Science Foundation,China(Grant No.3172017)
文摘We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.
基金the National Natural Science Foundation of China(Grant No.11872033)the Beijing Natural Science Foundation,China(Grant No.3172017).
文摘The spatial and temporal evolution of real contact area of contact interface with loads is a challenge.It is generally believed that there is a positive linear correlation between real contact area and normal load.However,with the development of measuring instruments and methods,some scholars have found that the growth rate of real contact area will slow down with the increase of normal load under certain conditions,such as large-scale interface contact with small roughness surface,which is called the nonlinear phenomenon of real contact area.At present,there is no unified conclusion on the explanation of this phenomenon.We set up an experimental apparatus based on the total reflection principle to verify this phenomenon and analyze its mechanism.An image processing method is proposed,which can be used to quantitative analysis micro contact behaviors on macro contact phenomenon.The weighted superposition method is used to identify micro contact spots,to calculate the real contact area,and the color superimposed image is used to identify micro contact behaviors.Based on this method,the spatiotemporal evolution mechanism of real contact area nonlinear phenomena is quantitatively analyzed.Furthermore,the influence of nonlinear phenomenon of real contact area on the whole loading and unloading process is analyzed experimentally.It is found that the effects of fluid between contact interface,normal load amplitude and initial contact state on contact behavior cannot be ignored in large-scale interface contact with small roughness surface.
