Simulation Of Micro-fracture Behavior Of Graphene Toughened Composite Ceramic Tool Materials

Graphene has excellent mechanical properties,and is usually added to the matrix as a reinforcingt phase to improve the comprehensive mechanical performance and service performance of the tools.The toughening mechanism of graphene composite ceramic tool materials are mainly crack deflection,crack branching,crack-bridging,and graphene sheet pulling out,etc.However,there are few studies on interface structure,composition and bonding strength.In this paper,the microstructure model of graphene toughened Al₂O₃composite ceramic tool material（GA）was established and the crack propagation was simulated.The main study contents are as follows:1. The microstructure and crack growth behavior of GA composite ceramic tool materials are simulated. The effects of the bonding strength of phase interface between Al₂O₃and Graphene,the volume size of graphene,and the volume content of graphene on micro-crack growth behavior of GA composite ceramic tools are analyzed.Toughening mechanisms,such as crack deflection,crack pinning,grainbridging,and graphene tensile fracture,are obtained from the simulation results.（1）The effect of the bonding strength of phase interface between Al₂O₃and Graphene on the mechanical properties of GA composite ceramic tools have been analyzed.With the improvement of bonding strength of phase interface between Al₂O₃and Graphene,the crack propagation path along graphene changed to deflect around graphene.The strong interface resisted the crack growth,and the weak interface can easily form micro-cracks to relieve the stress concentration of the main cracks.With the continuous increase of the interfacial bonding strength,the average energy release rate characterizing the fracture toughness of the tool materials showed a trend of increase first and then decrease.However,too low or too high phase interface strength will weaken the material and reduce its fracture toughness.（2）The effect of graphene’s volume size on the mechanical properties of GA composite ceramic tool was analyzed.For the influence of graphene short diameter on its mechanical properties,the average energy release rate showed a trend of increasing first and then decreasing.The shorter diameter of grapheme is helpful to toughening effect.The larger particle size of graphene at the strong interface,the easier the crack is pinned.The smaller particle size of graphene,the easier the crack is deflected,and more tortuous the crack propagation path.When the long diameter of grapheme is larger than the average grain diameter of Al₂O₃matrix at the weak interface,the cracks are easily bridged.With the constant increase of long diameter of graphene,both energy release rate and crack growth length showed a downward trend.The larger graphene will weaken the material,and reduce the fracture toughness of the tool material.（3）The effect of graphene’s volume content on the mechanical properties of GA composite ceramic tool materials wass analyzed.With the increase of the volume content of graphene,the average energy release rate showed a trend of increasing first and then decreasing.when its volume contents is 0.50vol%,the energy release rate is the highest and the fracture toughness is the best.When the volume content is 1vol%,the average energy release rate decreases greatly,so excessive graphene will weaken the material.2. The residual stress field of GA composite ceramic tool material was simulated and studied,and the crack propagation behavior was simulated and analyzed by coupling the residual stress.Through the simulation analysis,it can be seen that the residual stress in graphene is mainly compressive stress,and there is a large range of tensile stress in the corresponding Al₂O₃matrix.The compressive stress field in graphene can play a significant role in its fracture toughness improvement.（1）The effects of different grain boundary strengths under the coupled residual stress field and external load on crack growth of GA composite ceramic tool materials were simulated and studied.The value of compressive stress zone inside graphene gradually decreased from the middle to both ends.With the continuous increase of grain boundary strength,the value and range of the compressive stress zone inside graphene are also increased,while the tensile stress zone extended from the matrix part near the middle part of graphene to all matrix part around the graphene.At this time,the cracks tend to grow along the residual tensile stress zone.Compressive stress can resist crack propagation.Under external load,the average energy release rate of the tool materials keeps increasing with the increase of grain boundary strength.（2）The residual stress field in microstructure of GA composite ceramic tool materials was simulated and analyzed when the volume content of graphene was0.25vol%,0.50vol%,0.75vol%and 1vol%,respectively.The residual compressive stress showed a trend of increasing with the increase of graphene volume content.In the coupled residual stress microstructure under the action of external load,the crack growth at weak interface is mainly along graphene deflection and grain bridging.The crack growth at strong interface is mainly deflection around graphene and grain bridging.The residual tensile stress can weaken the strength of partial phase interface.Under external load,the average energy release rate of ceramic tool materials with coupled residual stress is higher than that without coupled residual stress,which indicated that more energy is needed to propagate the same level cracks.Therefore,the existence of residual stress can achieve the toughening purpose.