Contact Analysis Between Rough Surfaces Of Micro-cantilever And Substrate Under Repeated Loading And Unloading

Surface contact characteristics determine the operating characteristics of many machines, especially reliability and security, of which the roles are closely related to the living environment of human, and have been a research focus of domestic and foreign scholars. While collision happens between the base end of micro-cantilever and the substrate, only a small fraction of asperities come into contact. The impact force generated will be several times larger than the static contact force, and the rest of the cantilever structure momentum will make the structure bend. The elastic energy stored will make the base end of the micro-cantilever bounce once or several times from the base of the actual point of contact, before it reaches the situation of stable contact, which will exacerbate the devastating effects of the impact, and will affect the subsequent contact dramatically.In this paper, the rough surface is characterized based on W-M fractal function. The corresponding structural parameters are determined by the actually measured roughness parameters of the engineering surface. Based on the finite element software ABAQUS, a contact model between micro-cantilever and substrate under the multiple loading and unloading is established. In this model, the micro-cantilever elastic recovery, interaction of the identical rough surface asperities, plastic deformation of the contact body and the influence of adhesion are considered. It dynamically simulates a variety of changes, such as the contact force, stress, strain, the contact area and energy dissipation during the loading and unloading. This paper also compares the effects of various loading force and loading velocities on the variables in the whole process.The results of the research show that every process of loading and unloading between the rough surfaces of the micro-cantilever and the substrate is actually a complicated process of multiple elasto-plastic contact and separation. During the course of loading and unloading, there are two or more obvious impact zones, each of which consists of multiple sub-impacts, and every time the impact force is much larger than the static contact force, and the asperities will also generate a large stress. The initial yield point is located at a certain depth beneath the surface of the highest ontact point. White the load increases, the plastic deformation of the yield point will gradually move toward the surface, and the maximum equivalent stress will also increase. The distribution curve of equivalent plastic strain along the depth is similar with the curve resulted from the experiments. The maximum equivalent plastic strain occurs at a certain depth beneath the surface or on the surface, where the origin of micro-cracks is also located. In the process of loading and unloading, the contact force and dimensionless contact area change dramatically with the change of the cyclic load, which is directly related to the elastic-plastic deformation of material. External work and plastic dissipation are increased in the process of loading and unloading, but the changes in the cycles are fluctuating, and the kinetic energy and the elastic strain energy also fluctuate within a certain range of values. The effects of different loading velocities on the variables of the system are larger than the effects of loading forces. The results of research lay a theoretical foundation for further studies on micro-mechanical switch contact characteristics and the improvement of the reliability.