The Study Of Time-integration Crack Growth Model Considering Thickness Effect

Fatigue damage is one of the most common failure forms of metal components in engineering practice.For engineering equipment with thick plate characteristics such as tunnel boring machine,crane and pressure vessel,crack initiation and growth are often caused under heavy and shock load,the crack growth eventually causes fatigue fracture of the component,which affects the construction efficiency and even the hidden danger of safety.Plate thickness is the key factor for the crack growth life and variable amplitude load is the driving force of crack growth.Establishing the crack growth model under variable amplitude load is of great significance to the fatigue life prediction of the finite plate metal components in practical engineering.In this paper,the research on crack growth life prediction is carried out through theoretical deduction and test research.The specific work of this paper is as follows:(1)The crack opening displacement and the plastic zone of the crack tip are solved by introducing the constraint factors,the thickness effect of crack growth is described,based on the solution of crack opening stress under constant amplitude and variable amplitude load,a theoretical model of crack growth with time integration method considering thickness effect is established.In addition,based on the fatigue test results,the Q345 D low alloy steel constraint factor expression is fitted,which laid the foundation for predicting the finite plate fatigue crack growth life of Q345 D low alloy steel.(2)The fatigue crack growth test of Q345 D specimen under variable amplitude loading was carried out.At the same time,the crack growth life of the specimens was predicted by the time integration method crack growth model.The test results and the predicted life results of three different thickness specimens showed good consistency in the first 60 thousand cycles,and the maximum error in the 90 thousand cycles was 10.6%.It was proved that the time-integral method crack growth prediction model was effective for the life prediction of the growth life under variable amplitude load.In addition,the influence of crack opening angle,initial crack and critical crack on crack growth were investigated based on the time-integration method crack growth model.(3)Crack growth simulation analysis of Q345 D compact tensile specimen with different thickness under constant amplitude load of was carried out by Zencrack finite element simulation software,stress intensity factor range was solved by the simulation analysis.Based on the results of stress intensity factor range,Elber model,Newman model and Guo model were used to predict the life of compact tensile specimens.The accuracy,advantages and disadvantages of the time-integral method and the traditional fracture mechanics models for fatigue life prediction were compared and analyzed,which provided a reference for the selection of the crack growth life prediction model of actual engineering components.(4)The fatigue crack growth test of the characteristic sub-structure of the tunnel boring machine(TBM)cutter head was carried to validate the applicability of time-integral method for the fatigue crack growth life prediction of the TBM cutterhead panel,the maximum error between the theoretical prediction and the test result was 16%.At last,the time-integral method crack growth model was used to predict the crack growth life of the TBM cutter panel in a specific project.