Numerical Simulation And Experiment Of Dynamic Fracture Toughness Of Metal Materials Under High Strain Rate Load

Metal materials have many excellent mechanical properties such as high strength,high hardness,good plasticity and good impact toughness.They play a role in military and civil applications such as aerospace,weaponry,transportation and machining.Science and technology are developing rapidly.The structure of metal components is becoming more complex and precision.Metal materials are used in increasingly harsh environment.Therefore,it is inevitable to withstand the impact load during service.Especially in the aerospace field,turbine blades and turbine disks of aerospace engines usually work in high temperature and high pressure environments.They are often subjected to impact loads.The impact load causes the material to be at a high strain rate.At the high rate,The precision of metal components is damaged or failure even fracture.Structural fracture is catastrophic for mechanical components.Dynamic fracture toughness is an important criterion for evaluating the fracture properties of metal materials.It is very important to study the dynamic fracture toughness of metal materials under high strain rate.In this paper,GH4169 nickel-based alloy,which is the most widely used material in the manufacturing turbine blades and turbine disks of aero-engine,was selected as the research object.The dynamic fracture toughness of metal materials at high strain rate is studied by experimental-numerical method.Main research content:(1)Based on the improved Hopkinson pressure bar equipment to study the onedimensional stress wave shaping technique.In order to suppress the geometric dispersion of the stress wave propagating in the incident rod,smooth incident and reflected signals are obtained to ensure the consistency between the strain at the measuring point and the actual strain at the loading point.The shaper at the loading end of the incident rod.We found a shaper size that is more suitable for the experiment.(2)The impact three-point bending specimen test of GH4169 nickel-base alloy was carried out by the improved Hopkinson pressure bar.The load time history curve and the crack initiation time were obtained,which provided the necessary calculation of the dynamic fracture toughness of the material.The modeling data and boundary conditions were used.The high-speed camera was used to track the fracture process of the three-point bending specimen.The image processing software was used to analyze the strain cloud map during the fracture process,and a more accurate and reasonable patching method is obtained.(3)In order to provide the constitutive properties of the material under high strain rate for numerical simulation,the constitutive properties of the material at high strain rate includes two parts: the law of deviator deformation and the law of volume deformation.In this paper,In this paper,the separated Hopkinson pressure bar(SHPB)was used to conduct compression experiments of GH4169 nickel-based alloy at different high strain rates,the stress-strain curves at different strain rates were obtained.The MATLAB software was used to fit the Johnson-Cook constitutive model of GH4169 nickel-based alloys.The Johnson-Cook constitutive model provides the law of deviator deformation for numerical simulation.The Grüneisen equation of state of GH4169 nickel-based alloy is calculated by molecular dynamics(MD).The Grüneisen equation of state provide the law of volume deformation for numerical simulation.(4)Using ANSYS/ls-dyna software and data from three-point bending test in combination with the virtual crack closure method(VCCT)was used to calculate the dynamic fracture toughness of GH4169 nickel-base alloy.It is found that the dynamic fracture toughness of GH4169 nickel-base alloy increases gradually with the increase of loading speed,showing rate sensitivity and crack arrest.The cohesion model(CZM)is used to simulate the three-point bending experiment.The numerical simulation results are compared with the experimental results.The cohesion model can be very well simulation analysis of impact fracture experiments.The results of this study show that it is feasible to use the experimental-numerical method to calculate the dynamic fracture toughness of metal materials under high strain rate.At the same time,the dynamic fracture toughness of GH4169 nickel-based alloy can be used as a reference for the safety evaluation of the structure design using at high strain rate.