Analysis Of The Failure Mechanism Of Single Crystal Copper By Multi-scale

Solid materials show completely different properties and macroscopic objects in thenanometer size range. With the development of science and technology, the relationshipbetween the macroscopic properties of solid materials and their microstructure has become ahot research field. The research of the microscopic structure of solid materials can promotethe understanding of the macroscopic properties of solid materials. Micro-crack, as acommon microscopic defect seriously impairs the various properties of solid materials.Therefore, researches of micro-cracks under different criterion failure mechanisms are ofgreat importance. So far studies of the micro-crack propagation mechanism on multi-scalesof the single crystal copper have rarely been conducted. So this research is urgently needed.This thesis first adopts the molecular dynamics method and the atom-the finite elementmethod to stimulate the tensile test of the idealized single crystal copper and micron-scalesingle crystal copper. It provides the stress-strain curves on two scales of single crystalcopper, determines the yield strength and intensity limit value, and analyzes the mechanicalproperties of two scales and the mechanical properties of macro-scale. Secondly this thesisalso uses the molecular dynamics method and the atomic-finite element method to stimulatethe tensile test of the type I through crack nano-single crystal copper model and the tensiletest of micron single crystal copper, and finds that different temperature and different modelsof crack length influence the mechanical properties, the system energy, the atomicconfiguration and the mechanism of crack propagation.The research proves that as the scale increases, the yield limit and ultimate strength ofnon-defective single crystal copper decreases. The plastic materials on the nanometer andmicron scale have a short-term intensive stage, when the value reached its peak, the intensityof single crystal copper decline rapidly，And if the scale is beyond its peak, single crystalcopper will be damaged.For the single crystal copper with a crack of type I through crack, with the increasing oftemperature, the kinetic and potential energy reach a stable value and its fluctuation becomesclearer. Under lower temperature, the crack propagation is intrinsic brittle cleavage extension,the passivation of the crack tip becomes apparent, and the twin bands are not easy to appear.When the temperature is higher, the twin band easily appears near the crack tip and changesthe extension direction of the crack branch. With the increase of the initial crack length, theoriginal metal bond between the crack tip atoms gets more easily damaged, the critical stress of crack propagation is significantly reduced, and the branches of the crack along thecleavage plane mesh cross more apparently.