Phase Field Crystal Method To Study Crack Extension And Dislocation Emission Behavior Of Microvoids

In metallic materials,the dislocation emission behavior plays an important role in the process of void growth and crack extension,and has been a hot topic of interest in material fracture research.Although many works have been investigated the mechanism of crack extension and crack-emitting dislocations at the atomic scale,revealing the mechanism of crack-emitting wedge gap under the action of applied stress or strain at the atomic level is still lacking.The newly proposed phase field crystal model can reveal the dynamic evolution behavior of material microstructures on the diffusion time scale and atomic space resolution scale,and it has achieved remarkable research results in grain boundary premelting,grain boundary dislocation motion,and crystal epitaxial growth,but there are few reports on this aspect of crack emission dislocations at voids studied by the phase field crystal model.Therefore,in this paper,the phase field crystal model is used to study the crack extension and dislocation emission behavior of microvoids,and the simulation experiments and analysis of the cases of single and multiple voids are carried out,respectively.The innovative work of this paper is mainly reflected in the use of advanced phase field crystal model to conduct simulation experiments,and establish an energy model for the emission of gap dislocations at the crack tip,revealing the mechanism of crack propagation and dislocation emission behavior from the perspective of energy.The study achieved the following important results and conclusions:(1)Under the action of applied strain,the crack will be closed in the middle of the crack during the crack propagation process,and the crack tip will be separated from the main crack.The blunted crack tip grows a sharp crack tip by forming a step structure through dislocations,and emits dislocations through the crack tip,which changes from a sharp crack tip to a blunt crack tip.The presence of dislocations leads to a ductile-brittle transition,which is consistent with experimental observations and results obtained from molecular dynamics simulations.(2)The energy change of the system before and after the crack-emission dislocation is analyzed from the perspective of energy,and the established energy model matches well with the simulation experimental results of the phase field crystal model,revealing the microscopic mechanism and physical essence of the crack-emission dislocation at the void.(3)Different grain orientation angles affect the sprouting and expansion mode of the crack at the void.The crack sprouting at the void at 0~°is a blunt crack,mainly in a ductile expansion mode;the crack sprouting at the void at 10~°is a sharp crack,mainly in a brittle expansion mode,and a ductility-brittle transition occurs during the crack expansion process by emitting dislocations.(4)Under uniaxial tensile strain,crack sprouting and extension of multiple voids also occur,and dislocation emission also occurs during crack extension.Compared with the case of a single void,the crack emission dislocation is more complicated in the case of multiple voids.(5)Under strain conditions,multiple voids sprout cracks and emit dislocations,and due to the interaction between voids,multiple sets of grain boundary dislocation pairs are formed around the voids,resulting in several nanograins in the region between the multiple voids.The above main results and conclusions can provide some guidance for the study of three-dimensional crack dislocation emission and for the fracture failure behavior.It is helpful to understand the evolution process and causes of crack extension and dislocation emission from the atomic scale.It is helpful to explore the energy release characteristics of the atomic evolution process of crack-emitting dislocations to reveal the microscopic mechanism of crack-emitting dislocations.It is helpful to observe and study the interaction process between defects(voids,cracks,dislocations)from the atomic scale to reveal the potential microscopic mechanism.From the energy perspective,the energy model of crack-emitting wedge-shaped gap dislocation complex is established,and a new mechanism of crack-emitting wedge-shaped gap dislocation complex is proposed,which provides certain reference value for experimental research and has certain scientific guidance significance.