Study On The Initiation And Propagation Of Nano-scale Cracks By PFC Method

The crystal phase field(PFC)method extends the concept of a phase field model by describing the topology of the microstructure of the crystalline material.Comparing with the traditional phase field(TPF)method and the molecular dynamics(MD)method to simulate the material evolution process,it have advantages in feature time scale and diffusion space scale.Comparing with many known computational simulation studies,the mechanism of nano-scale crack nucleation is still not clear enough and detailed.Therefore,the PFC method is used to simulate the nano-crack nucleation and propagation behavior of samples with different orientation angles and temperatures under uniaxial tensile strain.In addition,the PFC method has been improved on the feature time scale,and the PFC method has been modified to study the brittle micro-crack nucleation and propagation.The results show:1.The different crystal orientations have a significant effect on the initiation and propagation of the cracks.In the samples with angles of 5° and 20°,the cracks are directly cracked due to the strain concentration of the dislocations of the crack tip.The cracks mainly show a mode of the brittle expansion,and the crack edges show smooth planar features.For the samples with angles of 10°and 15°,the dislocations are first dislocated,and the dislocations slip to form vacancies.The vacancies grow to form cracks,showing a mode of the ductile expansion,and the crack edges are not smooth.2.The different temperatures have a significant effect on the initiation behavior and propagation speed of the brittle cleavage crack.As the temperature rises from-1.0 to-0.7,the nucleation mode of the brittle cleavage crack gradually changes,and no crack is formed directly at the notch,but a crack is formed after the step is formed at the notch.As the temperature increases,brittle cleavage cracks take less time to reach the same growth length.3.The modified crystal phase field(MPFC)method is more effective than the crystal phase field(PFC)method in responding to the rapid strain relaxation effect of materials.And the MPFC method not only can effectively reflect the microscopic evolution and energy change characteristics of materials,but also it is more sensitive to the response of the initiation and propagation behavior of the brittle cleavage crack of materials.This greatly reduces the time required to simulate the evolution process.In this study,the crystal phase field(PFC)method is used to study the micro-crack initiation and propagation behavior,clearly revealing the microscopic mechanism of crack nucleation and propagation.The results of the study are consistent with similar theory and experimental results.