Study On The Internal Stress And Strength Inlfuence Factors Of Polycrystalline Copper Micro Beam Component

In micro-electromechanical systems (MEMS), there are many impact factors of fatiguedamage for polycrystalline micro-beams, such as loading mode, grain size and slip systems andother interior space and so on. An important reason for the fatigue damage is the slip of internaldislocations and grain boundary, while the slip of dislocations and the boundary sliding relate tothe (shear) stress on the slip systems, also the micro-beam strength is related to the maximumstress, so this article is firstly focused on analyzing the stress of internal grain and boundary andalso comparing the easy and difficult stating angle, then the main influence factors are discussed atlast.Firstly, established by the two approaches, respectively [110] and [100] grain structure ofpolycrystalline copper that makes micro-beam model of a certain thickness, and the elasticitymodulus of different orientation grains are calculated and determined. it’s used by micromechanical methods to analyze the micro-beam in the external load, the stress-strain state and itsnumerical expression on the main crystallographic slip direction of many cell in the grain；on thisbasis，it’s determined the impact law of the internal grain crystallographic orientation angle for thepolycrystalline copper micro-beams to the driven shear stress of the slip systems in its cell, and apreliminary analysis of the geometric arrangement for micro-beams grain which impacts to themicro-beam mechanical behavior.Secondly, by establishing the geometry module of the polycrystalline and the elastic-plasticmechanics theory to calculate the stress of the inner grain and boundary for polycrystalline copperunder the external loading, and also analyze the possible happening tract of the polycrystallinecopper to slip. It is found that the analytical result is the flaw damage slip of the polycrystallinecopper has a certain relation with the grain and boundary stress. At the same time, the relationshipbetween each grain boundaries and grains strain is analyzed by micro mechanics theory, also withthe grain boundaries effect to slip and the effect of grain size to the crystal yield stress.Thirdly, micro-cantilever beam is established as the mechanical analysis model and theeffective elastic modulus of different thickness beam is calculated, based on ANSYS simulatesoftware the electrostatic force of the different thickness micro-cantilever beam is analyzed at thesame voltage (not get to the pull-in voltage) in the paper, it obtained the stress of fixed end formicro-beam and the relation between stress and thickness. At the same time, based on ANSYS, thex direction stress of fixed end with the different thickness micro-cantilever beam is analyzed at thepull-in voltage, the relationship between pull-in voltage and the thickness of beam is obtained, andthe relation between x direction stress of fixed end and thickness at the pull-in voltage is obtained. Finally, the micro-beam component damage is general fatigue fracture, while one of thedirect factors for fatigue strength is stress concentration, so the factors of micro-beam producingthe maximum stresses analyzed by using the ANSYS are like these: micro-beam length, thickness,width, distance between the two counter electrodes and so on. Thereby those factors are studied toavoid large stress concentration and raise the fatigue strength, then extend the life of micro-beamcomponents. For MEMS electrostatic drive component, its fatigue life also has direct relationshipwith the driving voltage, so it is important to analyze the impact factors of driving voltage.