Numerical Simulation Of Dynamic Fracture Performance Of Nickel Base Superalloy And Study Of Hopkinson Bar Impact Test

Nickel based superalloys are widely used in aerospace industry due to their good mechanical and mechanical properties and good economic performance in a wide temperature range.As a precipitation hardening superalloy,GH4169 nickel base superalloy is widely used in aero engine turbine discs and turbine blades because of its excellent mechanical properties.In addition,the material has been used in the nuclear industry and oil pipeline in recent years.When the aero engine works,its internal components are subjected to a more stringent working environment,such as:high temperature,high pressure,strong impact load and so on.It is found that fracture failure is a important way of failure behavior of mechanical structure.The dynamic fracture of the components working on aero engine under impact load is the most serious way of component failure.The dynamic fracture of aero engine structural materials is caused by micro cracks in the internal parts.Therefore,it is particularly important to do experimental and numerical simulation on the dynamic toughness K_ID of the specimens with precracks made from GH4169 nickel base alloy.When the dynamic stress intensity factor curve is solved by the approximate formula method,the equivalent stiffness which is Professor Williams used is the equivalent stiffness of a beam without a crack.Eventually leads to the final calculated by the approximate formula of K_ID smaller than the values calculated by numerical simulation.In this paper,the first order natural frequency of the cracked beam is obtained by modal analysis of the precrack specimens.In the field of monitoring the initiation time of crack,a lot of research works have been carried out through simple and adaptable strain gauges.However,there is no uniform standard for strain gauge placement.In this paper,the reasonable and reliable patch position of the strain gauge is determined by the Hopkinson test bench,the high-speed camera system and the finite element simulation.In the finite simulation,the general finite element software ANSYS-LSDYNA is used,but the finite software does not have the constitutive of the GH4169 nickel based superalloy.In this paper,the stress-strain curves of materials under different strain rates are obtained by experiments,and then the Johnson-Cook constitutive equation of GH4169 is fitted.At the same time,the material will have an adiabatic temperature rise phenomenon at high strain rate.In this paper,the adiabatic correction is carried out to obtain the parameters of the modified JC constitutive equation.In addition,in order to ensure the effectiveness of the stickup position of the strain gauge in the strain gauge method,based on the high-speed camera system and strain field post-processing software GOM Correlate,the specimens were monitored dynamically during the dynamic loading process,and the direction of the main strain field near the crack tip was obtained in this paper.The experimental results are in good agreement with the finite element simulation results,which verify the rationality and effectiveness of the patch position determined by the finite element method.At the same time,the dynamic compression test is similar to that of the dynamic compression test.For the dynamic fracture experiment,the fracture specimen is symmetrical on the crack line,and the two sides should also have dynamic equilibrium before the fracture specimen is cracked.In this paper,While dynamic fracture experiments are carried out,the strain field near the crack tip is traced by the above equipment.It is found that the dynamic balance has been achieved at the left and right ends of the crack before cracking.This effectively realizes the decoupling of the stress wave effect and the strain rate effect,which ensures the effectiveness of the experimental results.In summary,a spring mass model after correction of the first order natural frequency of the sample is used and obtain the GH4169 nickel based superalloy under different loading rate under the stress intensity factor,and in this process stress wave shaping technology is used in order to the consistency of dynamic load at the loading point and the dynamic load at the test point.At the same time,the influence of the existence of the wedge on the propagation of the stress wave is considered.The dynamic load of the solving process was modified to obtain a more accurate load at the point of impact load;through experiment and numerical simulation to determine the strain gauge monitoring crack,this paper applies the reasonable position of loading rate the strain gauge,to ensure the accuracy of crack initiation time.The dynamic cracking toughness of the GH4169nickel base alloy at different loading rates was finally obtained from the above two.