Research On Fracture Mechanics Compliance Test Method Of Metallic Materials Based On Numerical Analysis

With the development of aviation,nuclear power,high-speed railway and petroleum engineering,fatigue fracture properties of new materials attract wide attention.Compliance method as an advanced test technology recommended by kinds of fracture test standards has the advantage of simpler operation,higher automation and better accuracy.In the past,works on compliance method were carried out based on standard specimens in standards and they lacks systematical and comprehensive analysis to parameters in the compliance formulas,which causes much inconvenience to the material fracture test in scientific research and engineering applications.The thesis carried out systematical research on compliance methods and the main works are as follows:1.A series of APDL programs based on the ANSYS have been developed for the mechanical response analysis of CT(Compact Tensile) specimens, SEB(Single edged bending) specimens and chevron specimens.2.Transform formulas between COD(crack opening displacement) V_LL at load line and COD V₀ at crack mouth of CT and SEB speicimens were presented.It helps to achieve J integral test using P～V_LL curve with V₀. Numerical simulation and tests have been carried out to check the formulas and the results indicate that it has good accuracy in a small yield range.The application method of the transform formula for J_IC test by CT spcimens of A508-â…¢steel was given.3.The relations between compliance and crack length for non-standard specimens such as chevron specimens and CT(W) specimens were researched based on FEA method.Several compliance formulas were given.Numerical simulation and test performed in this thesis show that the formulas have better accuracy.Compliance formula of chevron specimens has covered compliance testing method shortage in ASTM B771-87å’ŒNACE TM0177-96.These formulas given in thesis not only offered basis for computer aided test but also improved prediction accuracy and efficiency for crack and stress intensity factor.4.Study of uncertainty factors on dimension and crack shape of standard CT and SEB specimens recommended in current standards were carred out.Much quantitative finite element analysis on uncertainty of main parameters were performed.A two-parameter model used for compliance prediction of the equivalent elastic modulus of CT and SEB specimens was presented,and the specimen thickness effects of specimens were also investigated and the correction method was given to estimate materials elastic modulus.5.Based on finite element analysis,the studies on equivalent elastic modulus E_e of a CT composite structure specimen with raw material parts and welding material part were performed.In order.to get correct prediction of crack length,investigation of influencing factors of quivalent elastic modulus E_e such as elastic modulus ratioβ,crack length a,specimen thickness B and raw material width H was given in detail.The innovation works in the thesis could provide emendation basis for compliance test method in state fracture testing standards...