Numerical Simulation Of Crack Initiation And Propagation In Nano-scale Materials

The deformation and failure of materials are derived from the micro structure of materials,such as dislocation,vacancy,grain boundary and micro cracks.In order to further study the characteristics and mechanism of deformation and failure of materials,it is necessary to carry out multi-scale analysis.We should combine macro analysis with micro analysis to find the root of the problem and the mechanism of deformation in a deeper level.Due to the stress concentration at the crack tip,the crack extends along the smooth line when the crack is brittle.With the development of materials science and the continuous optimization of scientific calculation methods,the use of computer simulation to study the material properties has become a trend.The above theoretical results are consistent with the experimental results,which provide a theoretical guidance for the practical application of the material to prevent fracture failure and have an important guiding significance for the study of crack propagation mechanism and the prevention of fatigue fracture.It is convenient to study the brittle-ductile transition properties and mechanism of crack propagation by using the crystal phase field(PFC)method.The main results of this study are as follows:1.In the process of applying the tensile strain along the Y-axis,the crack exhibits a transition-passivation-extension steering characteristic,and the inter-fracture between the atomic bonds of the lattice plane where the primary and secondary atoms are located.The tensile stress caused by the tensile stress become high,a fixed atomic arrangement of the atomic bond break,result in significant cleavage fracture.2.The tensile strain continues to increase,the crack tip has a steady state passivation process.The atomic bond breaks before crack propagation.When we apply 11%of the tensile strain,the dislocation and the voids grow slowly and gradually expands followed by cracks.When we apply 13%tensile strain,the plastic zone at the front of the crack is deformed by dislocation,with dislocation movement,and the crack is expanded by toughness.The dislocation emission forms the slip step.3.The crack shows ductile mechanism.A circular notch in a certain distance next to the triangular gap.While the width of the gap is widened and the angle set in advance is zero,the crack shows brittle.The fixed angle increases,with the same parameters and the size of the gap shape changes,crack initiation and expansion become ductile to brittle transition.