Study On Size Effects And Numerical Simulation Of Micro-tensile

In recent years, with the rapid development of microelectronics technology and micro-electromechanical systems, micro-forming parts on the sharp increase in demand, micro-parts processing of the product in the processing and manufacturing industries is becoming more and more important. The micro-plastic-forming technology as a new kind of micro-processing methods is attaining the people's attention because of its numerous advantages. However, The small size, there has been a significant size effects, making the traditional plastic processing technology are no longer used with the micro-plastic-forming, allowed to become a new field of study.First of all, the main research of micro-plastic-forming is summarized, with emphasis on the size effects are set forth, given the definition of size effects and classification of each type of size effects theory to explain the phenomenon are summarized.Secondly, the heat treatment experiments and H62 brass foil micro-tensile test are performed to investigate the size effects phenomena, focusing on the rolling direction, grain size and sample size. The experimental results showed that:In the micro-scale, the influence of the sheet metal rolling direction on the mechanical properties had the similar trend with the traditional sizes. The grain size and feature size have a clear impact on the material stress-strain curves with a significant scale effects, as the grain size decreases, the tensile yield stress gradually increased, and the influence of the grain size on the yield strength meets the Hall-Petch relation of the grain size strengthening.Again, the cross-sectional area as a parameter which interconnects the thickness and the width, reflects the influence trend of the feature size on the yield strength of the specimen. The yield strength of the specimen decreases with decreasing cross-sectional area and shows the first size effects, when the cross-sectional area of specimen is more than 10×104μm2. And the yield strength of the specimen increases with decreasing cross-sectional area and shows the second size effects, when the cross-sectional area of specimen is less than 10×104μm2.Then, based on the study of experimental data, the paper characterized the size effects of a unified impact factor (b*D)-1/2, which is linked the grain size and the feature size of sample, two mutually independent factors, with each other. The impact factor can very well reflects the trend in yield strength of the specimen and shows that the yield strength of the specimen linearly increases with increasing value of (b*D)-1/2.Finally, the paper simulates the micro-tensile process based on the modified surface layer model making use of the finite element simulation software ABAQUS, and demonstrates that is correct through comparing the simulation results and the experiment results. The results prove that the modified surface layer model can be in a certain range as the constitutive model of simulation of micro-plastic deformation. And the process of micro deep drawing is studied by the finite element simulation.