Numerical Study On Elastic-plastic Stress-strain Field And Fracture Resistence Key Parameters Of Crack Tip

The project comes from the 13th five year national key research and development program"Key Technologies For Life Prediction And Life Extension Of Pressure Equipment In Extended Service"(2016YFC0801905),which focuses on the elastic-plastic stress-strain field in the local area of the crack tip and the key fracture resistance properties of the material.The traditional research methods of fracture mechanics include experimental research and theoretical analysis,but both have limitations.It is difficult to touch the micro area of the crack tip in the experimental method,and the stress-strain distribution in the crack tip area often determines whether the crack is extended or not,and then determines whether the specimen is safe and reliable.In this paper,the finite element method is used to study the stress-strain distribution in the crack tip region,and the size of the plastic zone at the crack tip under different constitutive conditions and different crack lengths is discussed.The research contents are as follows:(1)For the modified WOL specimen,the stress field distribution and crack opening displacement curve of crack tip region under different material constitutive laws are calculated by using the finite element method.By comparing with the theoretical value,the accuracy of the finite element setting and calculation method is proved,and the influence law of elastic-plastic parameters on the stress field distribution at the crack tip is analyzed.The V/P curve of the crack mouth opening process is obtained by using compliance method.By comparing the V/P curve obtained from finite element calculation and experiment,the influence of plastic parameters on crack mouth opening displacement is analyzed.(2)Create the finite element model of three-point bending specimen,the constitutive parameters are set as the true stress-strain of 4130X material.By extracting the elastic zone of the crack opening displacement under different crack length,fitting for the crack tip opening displacement,crack propagation resistance?-?a curve is drawn,non-sensitive fracture resistance?_0.2BL is calculated.By comparing the simulated results with the measured resistance curve and non-sensitive fracture resistance,it can be seen that the difference between the two is less than 10%.The fracture resistance of the material obtained by finite element simulation can be applied to practical engineering,and providing a foundation for the simulation of three-point bending crack propagation in the later stage of the subject.(3)The crack propagation process of three-point bending specimen under three constitutive models is simulated.The nephograms and distribution curves of?_x,Mises stress,equivalent strain,equivalent plastic strain and maximum principal stress in the crack tip region under different crack lengths are obtained.The effects of different elastic-plastic constitutive parameters on the curve shape and the mechanical behavior of the plastic zone at the crack tip are analyzed.By comparing the corresponding parameters calculated by the static load model and the crack growth model,the influence of unloading caused by crack propagation on the stress-strain distribution is obtained.