Numerical Analysis On Micro Elastic Mechanics Behavior Of Polycrystalline Beryllium

As a low-atomic-number structure material beryllium has many superior physical and mechanical properties such as low density, high elastic modulus, good dimensional stability and superior thermal performance. Due to these superior physical and mechanical properties beryllium has a wide range of applications in the nuclear energy industry, weapon system, aerospace industry and other fields. Beryllium produced by powder metallurgical process is considered constructed by single crystals whose orientations, shapes and size are distributed randomly. Because of random grain orientation and irregular shape polycrystalline beryllium is prone to elastic mismatch within the grain or at the grain boundaries under external load. Metal beryllium has strong brittleness, and elastic mismatch in material defect in beryllium will lead brittle fracture. Therefore, we need to consider the micro grain structure such as grain geometrical shape and distribution of grain orientation. In this paper, beryllium crystalline models were established based on considering the random distribution of grain orientation and regularity of grain shape, and numerical analysis on micro elastic mismatch behavior or stiffness coefficient were carried on by using the ANSYS software. Around this problem, this paper mainly finished the following work:1. Considering the influence of grain shape on the material elastic mismatch, the ideal regular polycrystalline model including square polycrystalline or hexagonal polycrystalline model and irregular polycrystalline model based on Voronoi diagram method were established.2. For considering anisotropic mechanical properties of the single crystal, the coordinate transformation of elastic stiffness matrix containing five independent parameters of the monocrystal beryllium grain with hcp structure was carried out, and elastic property parameters of grain with any orientation were obtained. Assigning these calculated parameters to different grains randomly, then the aim of considering elastic property differences under the condition of random distributions of grain orientation were achieved.3. Finite element analysis was carried out on regular or irregular polycrystalline model to study the influence of grain shape on elastic mismatch in beryllium.4. Adopting the Voronoi polycrystalline model, the influence of beryllium grain structure including grain size, grain boundary and content or size of beryllium oxide particles on micro elastic mismatch were studied.Based on the above work, finite element analysis by ANSYS was carried out on polycrystalline model of metal beryllium. The calculations show that elastic mismatch in Voronoi polycrystalline model is more significant than the regular polycrystalline model. Mismatch stress mainly occurs at the grain boundary, and it is about10%higher than the average stress. Stress On the grain boundary into a normal distribution; As the grain size decrease, the proportion of high stress area or the material stiffness coefficient increases. With content of beryllium oxide at grain boundary increasing, the maximum stress in and stiffness coefficient of models increases gradually. Beryllia particle size has no significant impact on maximum stress or stiffness coefficient in beryllium.