Study On The Growth Mechanism Of Microcracks In Rock Based On Molecular Dynamics Method

Rocks are primarily composed of mineral crystals.The fracture of rocks is closely related to the expansion of microcracks within mineral crystals.Macroscopic fracture or failure of rocks is often attributed to the development and coalescence of microcracks.Therefore,it is very important to explore the expansion behavior of microcracks within mineral crystals and calculate the related properties.The molecular dynamics method is widely used to explore microscopic behaviors within materials and calculate material properties.It is a suitable choice for studying microcrack expansion within mineral crystals.However,the accuracy of molecular dynamics simulation and calculation depends on the accuracy of the potential function describing the interaction between atoms.Evaluating and screening potential functions is necessary.The expansion of microcracks in brittle solids can usually be divided into dynamic expansion and subcritical crack expansion.The fracture toughness KIC is a key parameter to determine whether cracks undergo dynamic expansion.The internal surface energy y is an important parameter for calculating the speed of subcritical crack expansion.To describe the properties of microcrack expansion,we need to design a model to calculate the fracture toughness KIC and internal surface energy y of mineral crystals.We also need to pay attention to whether the behavior of microcracks within mineral crystals conforms to the theory of crack expansion in brittle solids,and infer whether it is necessary to improve the theory of crack expansion specifically.The main research results are as follows:(1)A potential function evaluation and screening system was established to obtain potential functions suitable for crack behavior research.The screening system considered the fracture morphology,curve trend,peak stress,and elastic modulus of the tensile model to evaluate the advantages and disadvantages of the BKS,Vashishta,Tersoff and MEAM potential functions.According to the evaluation results,the MEAM potential was selected for subsequent microcrack expansion studies.(2)One-dimensional models of two crack systems,[2(?)(?)0](01(?)0)and[01(?)0](2(?)(?)0),were established.It was found that the expansion paths of the two crack systems were concentrated in the<2(?)(?)0>directions,and the fracture toughness of the two crack systems was similar.(3)Two-dimensional model and three-dimensional model of the[2(?)(?)0](01(?)0)crack system were established.The twisting phenomenon in crack expansion was observed in two-dimensional model.Different from the traditional twist theory,the crack tip of this crack system had double-layer crack bonds.Part of the bonds in one layer at the front edge of the crack first broke to form a weak zone.Then part of the remaining bonds in the weak zone broke to form an actual crack.Subsequent observations in the three-dimensional model of the(01(?)0)crack system found that the front edge of the crack surface showed a stepped shape(curved front edge).The traditional theory of subcritical crack expansion velocity for straight crack fronts may need to be improved in real crack models.